Advertisement

Prediction of spinal anesthesia-induced hypotension during elective cesarean section: a systematic review of prospective observational studies

  • C. Yu
    Affiliations
    Department of Anesthesiology and Key Laboratory of Birth Defects and Related Diseases of Women and Children Sichuan University, Ministry of Education, West China Second University Hospital, Sichuan University, Chengdu, China
    Search for articles by this author
  • J. Gu
    Affiliations
    Department of Anesthesiology and Key Laboratory of Birth Defects and Related Diseases of Women and Children Sichuan University, Ministry of Education, West China Second University Hospital, Sichuan University, Chengdu, China
    Search for articles by this author
  • Z. Liao
    Affiliations
    Department of Anesthesiology and Key Laboratory of Birth Defects and Related Diseases of Women and Children Sichuan University, Ministry of Education, West China Second University Hospital, Sichuan University, Chengdu, China
    Search for articles by this author
  • S. Feng
    Correspondence
    Correspondence to: S. Feng, Department of Anesthesiology and Key Laboratory of Birth Defects and Related Diseases of Women and Children (Sichuan University), Ministry of Education, West China Second University Hospital, Sichuan University, No. 20, Section 3, South Renmin Road, Chengdu 610041, Sichuan Province, China.
    Affiliations
    Department of Anesthesiology and Key Laboratory of Birth Defects and Related Diseases of Women and Children Sichuan University, Ministry of Education, West China Second University Hospital, Sichuan University, Chengdu, China
    Search for articles by this author
Open AccessPublished:April 30, 2021DOI:https://doi.org/10.1016/j.ijoa.2021.103175

      Highlights

      • A systematic review of predictors of spinal anesthesia-induced hypotension.
      • Blood volume/fluid responsiveness may predict spinal anesthesia-induced hypotension.
      • Supine stress tests may optimize the predictive value of static state predictors.
      • Autonomic nervous system and peripheral perfusion index were not reliable.
      • Maternal demographics and baseline hemodynamic parameters were not useful.

      Abstract

      Background

      Spinal anesthesia is the standard for elective cesarean section but spinal anesthesia-induced hypotension remains an important problem. Accurate prediction of hypotension could enhance clinical decision-making, alter management, and facilitate early intervention. We performed a systematic review of predictors of spinal anesthesia-induced hypotension and their predictive value during cesarean section.

      Methods

      PubMed, Embase, Cochrane Library, Google Scholar and Web of Science databases were searched for prospective observational studies assessing the diagnostic accuracy of predictors of spinal anesthesia-induced hypotension in elective cesarean section. The quality of studies was assessed and predictors were grouped in domains based on the type of predictor.

      Results

      Thirty-eight studies (n=3086 patients) were included. In most studies, patients received 500–1000 mL crystalloid preload or 500–2000 mL crystalloid coload. Vasopressors for post-spinal hypotension were boluses of ephedrine 5–15 mg and/or phenylephrine 25–100 µg in most studies. The hypotension rate varied from 29% to 80% based on the definition. For analysis, >30 predictors were classified into seven domains: demographic characteristics, baseline hemodynamic variables, baseline sympathovagal balance, postural stress testing, peripheral perfusion indices, blood volume and fluid responsiveness indices, and genetic polymorphism.

      Conclusions

      Environmental and individual factors increased outcome variability, which restricted the value of the autonomic nervous system and peripheral perfusion indices for prediction of spinal anesthesia-induced hypotension. Supine stress tests may reflect parturients’ cardiovascular tolerance during hemodynamic fluctuations and may optimize the predictive value of static state predictors. Future research for predicting spinal anesthesia-induced hypotension should focus on composite and dynamic parameters during the supine stress tests.

      Keywords

      Introduction

      Spinal anesthesia is the standard method of anesthesia for elective cesarean section globally.
      • Eltzschig H.K.
      • Lieberman E.S.
      • Camann W.R.
      Regional anesthesia and analgesia for labor and delivery.
      Spinal anesthesia-induced hypotension remains a common and clinically important problem, occurring in up to 70% of cases.
      • Klöhr S.
      • Roth R.
      • Hofmann T.
      • Rossaint R.
      • Heesen M.
      Definitions of hypotension after spinal anaesthesia for caesarean section: literature search and application to parturients.
      • Kinsella S.M.
      • Carvalho B.
      • Dyer R.A.
      • et al.
      International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia.
      Hypotension causes problems for both the mother and fetus, including maternal nausea, vomiting, dizziness, rarely loss of consciousness, cardiac arrest, death; and fetal compromise.
      • Kinsella S.M.
      • Carvalho B.
      • Dyer R.A.
      • et al.
      International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia.
      • Lim G.
      • Facco F.L.
      • Nathan N.
      • Waters J.H.
      • Wong C.A.
      • Eltzschig H.K.
      A Review of the impact of obstetric anesthesia on maternal and neonatal outcomes.
      Although various measures, such as intravenous fluid administration, prophylactic vasopressor administration, and patient positioning, are used to mitigate hypotension, it may not be avoided completely, with the incidence as high as 30% despite these measures.
      • Zieleskiewicz L.
      • Noel A.
      • Duclos G.
      • et al.
      Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
      • Hasanin A.
      • Amin S.
      • Refaat S.
      • et al.
      Norepinephrine versus phenylephrine infusion for prophylaxis against post-spinal anaesthesia hypotension during elective caesarean delivery: a randomised controlled trial.
      When vasopressors are used prophylactically, reactive hypertension occurs in up to 30% of women.
      • Xiao F.
      • Shen B.
      • Xu W.P.
      • Feng Y.
      • Kee W.D.
      • Chen X.Z.
      Dose–response study of 4 weight-based phenylephrine infusion regimens for preventing hypotension during cesarean delivery under combined spinal-epidural anesthesia.
      Hypotension occurs in ≥40% of patients after fluid loading, and adverse effects such as volume overload, anaphylaxis, and coagulopathy, although rare, must be considered.
      • Loubert C.
      Fluid and vasopressor management for Cesarean delivery under spinal anesthesia: continuing professional development.
      Accurate prediction of spinal anesthesia-induced hypotension could enhance clinical decision-making, alter therapeutic management, and lead to appropriate early interventions. This study performed a systematic review with the aim of summarizing the possible predictors of spinal anesthesia-induced hypotension and their predictive value during cesarean section.

      Methods

      Search strategy

      This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement (PRISMA; Supplementary Material 1). Scientific databases, including PubMed, Embase, Cochrane Library, were searched for relevant publications using the following Medical Subject Headings and search terms: “cesarean section/delivery,” “hypotension,” “spinal anesthesia or intrathecal anesthesia or combined spinal-epidural anesthesia,” and “predict/prediction/predictor/correlation” (for a detailed search strategy see Supplementary Material 2). The initial search was conducted on August 15, 2020, restricted to English publications, and updated on December 19, 2020. Google Scholar and Web of Science database searches were additionally performed following the same strategy on December 19, 2020. All databases were searched since inception. Two investigators (FSM and YC) independently screened the databases using the described search strategy.

      Study inclusion

      The titles and abstracts of all articles retrieved were reviewed independently by FSM and YC, and disagreements were resolved by consensus. Full-text articles from potentially relevant abstracts were retrieved and assessed for eligibility. The bibliographies of all relevant articles were manually reviewed to identify additional articles. Studies were included if they fulfilled the following criteria: (1) prospective observational design, investigating parameters to predict spinal anesthesia-induced hypotension; (2) parturients of American Society of Anesthesiologists (ASA) Physical Status I-II undergoing elective cesarean section with spinal anesthesia or combined spinal-epidural anesthesia; (3) measurement of parameters before induction of spinal anesthesia; and (4) predictive data (sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), odds ratio (OR), risk ratio (RR), area-under-the-receiver operating characteristic curve (AUROC), or correlation coefficient (r)) had been reported or could be calculated from the information provided. If raw data were not published but the study was otherwise eligible for inclusion, the authors were contacted to obtain additional information. Exclusion criteria were (1) parturients of ASA ≥III; (2) non-elective cesarean section; (3) epidural or general anesthesia; and (4) no available predictive data.

      Data extraction

      Two investigators (FSM and YC) independently abstracted data from all selected studies, with disagreement resolved by consensus. The following data were extracted from each study: (1) study characteristics (author, year, mode of anesthesia, intravenous fluid loading, and vasopressor use), (2) characteristics of trial participants (number of patients, definition of hypotension, hypotension rate), (3) parameters used to predict spinal anesthesia-induced hypotension, and (4) tested variables (cut-off threshold, sensitivity, specificity, PPV, NPV, OR, relative RR, AUROC, r).

      Statistics

      Extracted data from all included studies were entered into a spreadsheet. The quality of studies was assessed independently by two investigators (FSM and YC) using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2)
      • Whiting P.F.
      • Rutjes A.W.S.
      • Westwood M.E.
      • et al.
      QUADAS-2: A revised tool for the quality assessment of diagnostic accuracy studies.
      (Review Manager 5.3, clicktime.com, Inc., San Francisco, USA), and disagreements were resolved by consensus. The predictors identified were grouped into domains based on the type of predictor and analyzed qualitatively.

      Results

      Study flow

      Initially, we identified 1046 studies of which 981 were excluded after title and abstract review. A full-text review of the 65 potentially eligible articles was performed, resulting in the exclusion of another 27 articles. Consequently, 38 studies were included in our analysis, including one randomized controlled trial with prospective data in one group (Fig. 1).
      • Hanss R.
      • Bein B.
      • Francksen H.
      • et al.
      Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
      Figure thumbnail gr1
      Fig. 1Flow chart of study selection and inclusion

      Study characteristics

      The characteristics of each individual study are presented in Table 1 and Supplementary Table 1. The quality of the studies is presented in Fig. 2. All studies were published between 1996 and 2020 (total n=3086). Patients in most studies received a 500 1000 mL crystalloid preload
      • Riffard C.
      • Viêt T.Q.
      • Desgranges F.P.
      • et al.
      The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
      • Meirowitz N.
      • Katz A.
      • Danzer B.
      • Siegenfeld R.
      Can the passive leg raise test predict spinal hypotension during cesarean delivery? An observational pilot study.
      or 500–2000 mL crystalloid coload.
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      • Daher M.
      • Saito R.B.
      • Barra G.B.
      • Govêia C.S.
      • Magalhães E.
      • Neves F.A.
      The effect of beta-2 adrenergic receptor haplotype variations on the haemodynamic response following spinal anaesthesia for caesarean delivery.
      Other studies used 500 mL colloid preload
      • Hanss R.
      • Bein B.
      • Francksen H.
      • et al.
      Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
      • Toyama S.
      • Kakumoto M.
      • Morioka M.
      • et al.
      Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery.
      or coload
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      as fluid infusion strategy. Vasopressors used to treat spinal anesthesia-induced hypotension were bolus doses of ephedrine 5–15 mg and/or phenylephrine 25–100 µg in most studies.
      • Kozanhan B.
      • Bardak O.
      • Sami Tutar M.
      • Ozler S.
      • Yildiz M.
      • Solak I.
      The influence of body roundness index on sensorial block level of spinal anaesthesia for elective caesarean section: an observational study.
      • Xu Z.
      • Xu T.
      • Zhao P.
      • Ma R.
      • Zhang M.
      • Zheng J.
      Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
      • Kim H.
      • An J.
      • Kim E.
      • et al.
      A pilot study on the role of autonomic function testing in predicting hypotension in patients undergoing cesarean section under spinal anesthesia.
      • Kim H.J.
      • Choi Y.S.
      • Kim S.H.
      • Lee W.
      • Kwon J.Y.
      • Kim D.H.
      Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
      Only one study reported the use of prophylactic phenylephrine and ephedrine infusions.
      • Zieleskiewicz L.
      • Noel A.
      • Duclos G.
      • et al.
      Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
      Other vasopressors were cafedrin-1-HCl/theodrenaline-HCl,
      • Hanss R.
      • Bein B.
      • Francksen H.
      • et al.
      Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
      mephentermine,
      • Kundra P.
      • Arunsekar G.
      • Vasudevan A.
      • Vinayagam S.
      • Habeebullah S.
      • Ramesh A.
      Effect of postural changes on inferior vena cava dimensions and its infuence on haemodynamics during caesarean section under spinal anaesthesia.
      and nor-epinephrine.
      • Arslan M.
      • Öksüz G.
      • Bilal B.
      • et al.
      Can perfusion index or pleth variability index predict spinal anesthesia-induced hypotension during caesarean section?.
      The hypotension rate varied from 29% to 80% based on the various definitions in each study.
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      • Manouchehrian N.
      • Torabi F.
      • Shayan A.
      • Otogara M.
      Investigation of effect of blood pressure and heart rate changes in different positions (lying and sitting) on hypotension incidence rate after spinal anesthesia in patients undergoing caesarean section.
      More than 30 predictors were classified into seven domains based on the type of predictor.
      Table 1Characteristics of the studies included
      StudyNumber of patientsFluid loadingVasopressorHypotension definitionIncidence of hypotensionIIIIIIIVVVIVII
      Kinsella SM. 1996
      • Kinsella S.M.
      • Norris M.C.
      Advance prediction of hypotension at cesarean delivery under spinal anesthesia.
      27Crystalloid coloadEphedrine/phenylephrine, treatmentSBP <70% of baseline51.9%*
      Frölich MA. 2002
      • Frölich M.A.
      • Caton D.
      Baseline heart rate may predict hypotension after spinal anesthesia in prehydrated obstetrical patients.
      40Crystalloid preloadEphedrine, treatmentMAP decrease >30%60%**
      Chamchad D. 2004
      • Chamchad D.
      • Arkoosh V.A.
      • Horrow J.C.
      • et al.
      Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
      22Crystalloid preloadEphedrine, treatmentSBP ≤ 75% of baseline50%***
      Hanss R. 2006
      • Hanss R.
      • Bein B.
      • Francksen H.
      • et al.
      Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
      40Colloid preloadcafedrin-1 HCl / theodrenaline HCl, treatmentmoderate (SBP <100 mmHg)

      severe (SBP <80 mmHg).
      57.5%*
      Dahlgren G 2007
      • Dahlgren G.
      • Granath F.
      • Wessel H.
      • Irestedt L.
      Prediction of hypotension during spinal anesthesia for cesarean section and its relation to the effect of crystalloid or colloid preload.
      25Crystalloid preloadEphedrine, treatmentSBP <100 mmHg or decrease ≥20% from baseline with maternal discomfort52.0%*
      Ledowski T. 2010
      • Ledowski T.
      • Paech M.J.
      • Browning R.
      • Preuss J.
      • Schug S.A.
      An observational study of skin conductance monitoring as a means of predicting hypotension from spinal anaesthesia for caesarean delivery.
      40Crystalloid coloadEphedrine/phenylephrine, treatmentMild/moderate/severe/very severe reduction of SBP 0–9%/10–20%/>20%/>30%, respectively from baseline5%/52.5%/30%/12.5%***
      Jeon YT. 2010
      • Jeon Y.T.
      • Hwang J.W.
      • Kim M.H.
      • et al.
      Positional blood pressure change and the risk of hypotension during spinal anesthesia for cesarean delivery: An observational study.
      66Crystalloid coloadEphedrine, treatmentMAP <70% of baseline41%***
      Ghabach MB. 2011
      • Ghabach M.B.
      • El-Khatib M.F.
      • Zreik T.G.
      • et al.
      Effect of weight gain during pregnancy on heart rate variability and hypotension during caesarean section under spinal anaesthesia.
      66Crystalloid preloadEphedrine, treatmentSBP decrease ≥25% or SBP <80 mmHg48.5%*
      Daher M. 2012
      • Daher M.
      • Saito R.B.
      • Barra G.B.
      • Govêia C.S.
      • Magalhães E.
      • Neves F.A.
      The effect of beta-2 adrenergic receptor haplotype variations on the haemodynamic response following spinal anaesthesia for caesarean delivery.
      143Crystalloid coloadEphedrine, treatmentDecrease of 20 mmHg in SBP or 20% in the MAP71.3%*
      Orbach-Zinger S. 2012
      • Orbach-Zinger S.
      • Ginosar Y.
      • Elliston J.
      • et al.
      Influence of preoperative anxiety on hypotension after spinal anaesthesia in women undergoing Caesarean delivery.
      93Crystalloid preload and coloadEphedrine/phenylephrine, treatmentThe effect of low, medium, and high anxiety groups on the maximum percentage change in SAP (%△SAP) was assessed-/*
      Ursulet L. 2012
      • Ursulet L.
      • Cros J.
      • De Jonckheere J.
      • Senges P.
      • Vincelot A.
      • Nathan N.
      Bedside analysis of hear t rate variability by Analgesia Nociception Index (ANI) predicts hypotension after spinal anesthesia for elective Caesarean delivery.
      28UnclearUnclearDecrease in SBP >20% or SBP <100 mmHg35.7%*
      Meirowitz N. 2012
      • Meirowitz N.
      • Katz A.
      • Danzer B.
      • Siegenfeld R.
      Can the passive leg raise test predict spinal hypotension during cesarean delivery? An observational pilot study.
      40Crystalloid preloadEphedrine/phenylephrine, treatmentMAP <70% of baseline65%*
      Toyama S.2013
      • Toyama S.
      • Kakumoto M.
      • Morioka M.
      • et al.
      Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery.
      35Colloid preloadPhenylephrine, treatmentDecrease in SBP >25% from baseline60.0%***
      Sun S. 2014
      • Sun S.
      • Huang S.Q.
      Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section.
      82Colloid coloadPhenylephrine, treatmentSBP <80% of baseline51.2%***
      Kundra P. 2015
      • Kundra P.
      • Arunsekar G.
      • Vasudevan A.
      • Vinayagam S.
      • Habeebullah S.
      • Ramesh A.
      Effect of postural changes on inferior vena cava dimensions and its infuence on haemodynamics during caesarean section under spinal anaesthesia.
      32Crystalloid preloadMephenteramine, treatmentDecrease in SBP >20%76.0%*
      Yokose M. 2015
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      81Colloid coloadEphedrine, treatmentSBP <80 mmHg63.0%****
      Sun S. 2015
      • Sun S.
      • Liu N.H.
      • Huang S.Q.
      Role of cerebral oxygenation for prediction of hypotension after spinal anesthesia for caesarean section.
      41Colloid coloadPhenylephrine, treatmentSBP <80%78.0%**
      Kuok CH. 2016
      • Kuok C.H.
      • Huang C.H.
      • Tsai P.S.
      • et al.
      Preoperative measurement of maternal abdominal circumference relates the initial sensory block level of spinal anesthesia for cesarean section: an observational study.
      40Crystalloid preloadEphedrine, treatmentSBP <100 mmHg or MAP decrease >30%62.5%*
      Sakata K. 2016
      • Sakata K.
      • Yoshimura N.
      • Tanabe K.
      • Kito K.
      • Nagase K.
      • Iida H.
      Prediction of hypotension during spinal anesthesia for elective cesarean section by altered heart rate variability induced by postural change.
      45Crystalloid coloadEphedrine/phenylephrine, treatmentDecrease in SBP ≥20%78%**
      Manouchehrian N 2016
      • Manouchehrian N.
      • Torabi F.
      • Shayan A.
      • Otogara M.
      Investigation of effect of blood pressure and heart rate changes in different positions (lying and sitting) on hypotension incidence rate after spinal anesthesia in patients undergoing caesarean section.
      63Crystalloid preloadEphedrine, treatmentSBP <100 mmHg29%*
      Bishop DG. 2017
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      102Crystalloid coloadEphedrine/phenylephrine, treatmentSBP <90 mmHg (until 15 min after delivery)47.1%***
      Bolea J. 2017
      • Bolea J.
      • Lázaro J.
      • Gil E.
      • et al.
      Pulse rate and transit time analysis to predict hypotension events after spinal anesthesia during programmed cesarean labor.
      51Crystalloid preloadUnclearSBP decrease >20% from baseline64.7%*
      Duggappa DR. 2017
      • Duggappa D.R.
      • Lokesh M.P.
      • Dixit A.
      • Paul R.
      • Rao R.R.
      • Prabha P.
      Perfusion index as a predictor of hypotension following spinal anaesthesia in lower segment caesarean section.
      120Crystalloid preloadEphedrine, treatmentMAP ≤ 65 mmHg42.5%*
      Prashanth A. 2017
      • Prashanth A.
      • Chakravarthy M.
      • George A.
      • Mayur R.
      • Hosur R.
      • Pargaonkar S.
      Sympatho-vagal balance, as quantified by ANSindex, predicts post spinal hypotension and vasopressor requirement in parturients undergoing lower segmental cesarean section: a single blinded prospective observational study.
      108Crystalloid preloadEphedrine, treatmentMAP >20 % decrease78.7%*
      Xu ZF. 2017
      • Xu Z.
      • Xu T.
      • Zhao P.
      • Ma R.
      • Zhang M.
      • Zheng J.
      Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
      94Crystalloid preloadEphedrine/phenylephrine, treatmentSBP <80 mmHg or hypotension symptoms44.7%****
      Fakherpour A. 2018
      • Fakherpour A.
      • Ghaem H.
      • Fattahi Z.
      • Zaree S.
      Maternal and anaesthesia related risk factors and incidence of spinal anaesthesia induced hypotension in elective caesarean section: a multinomial logistic regression.
      511Crystalloid preloadEphedrine, treatmentMild /moderate/ severe: reduction 10–20%/ 20–30%/ >30% of baseline SBP20%/35% /40%**
      Kuwata S. 2018
      • Kuwata S.
      • Suehiro K.
      • Juri T.
      • et al.
      Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
      50Crystalloid preload and colloid coloadEphedrine, treatmentSBP <90 mmHg or 80% of the baseline64%****
      Riffard C. 2018
      • Riffard C.
      • Viêt T.Q.
      • Desgranges F.P.
      • et al.
      The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
      200Crystalloid preloadEphedrine, treatmentDecrease in SBP >20%70.0%**
      Zieleskiewicz L. 2018
      • Zieleskiewicz L.
      • Noel A.
      • Duclos G.
      • et al.
      Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
      40Crystalloid coloadEphedrine/phenylephrine, prophylaxisDecrease in MAP >20%43%**
      Arslan M. 2019
      • Arslan M.
      • Öksüz G.
      • Bilal B.
      • et al.
      Can perfusion index or pleth variability index predict spinal anesthesia-induced hypotension during caesarean section?.
      87Crystalloid coloadNorepinephrine, treatmentSBP <80 mmHg or hypotension symptoms60%**
      Günüşen, İ. 2019
      • Günüşen İ.
      • Sargin A.
      • Akdemir A.
      • Ergenoğlu A.M.
      The effects of uterine size with or without abdominal obesity on spinal block level and vasopressor requirement in elective cesarean section: a prospective observational study.
      125Crystalloid preloadEphedrine, treatmentSBP <90 mmHg or decrease ≥20% from baseline52%*
      Kim H. 2019
      • Kim H.
      • An J.
      • Kim E.
      • et al.
      A pilot study on the role of autonomic function testing in predicting hypotension in patients undergoing cesarean section under spinal anesthesia.
      32Crystalloid coloadPhenylephrine, treatmentSBP decrease ≥20% from baseline68.7%*
      Parthasarathy P. 2019
      • Parthasarathy P.
      • Aithal R.R.
      • Rao R.R.
      • Raghuram S.
      • Ramesh R.
      • Nazneen A.
      Correlation of symphysiofundal height and abdominal girth with the incidence of hypotension in cesarean section under spinal anesthesia using bupivacaine with fentanyl as adjuvant: a clinical study.
      90Crystalloid preloadEphedrine, treatment˃ 20% decrease in SBP from the baseline42%*
      Singh Y. 2019
      • Singh Y.
      • Anand R.K.
      • Gupta S.
      • et al.
      Role of IVC collapsibility index to predict post spinal hypotension in pregnant women undergoing caesarean section. An observational trial.
      40Crystalloid coloadEphedrine, treatmentReduction in MAP >20% and/or MAP <65 mmHg57.5%*
      Kozanhan B. 2020
      • Kozanhan B.
      • Bardak O.
      • Sami Tutar M.
      • Ozler S.
      • Yildiz M.
      • Solak I.
      The influence of body roundness index on sensorial block level of spinal anaesthesia for elective caesarean section: an observational study.
      175Crystalloid preloadEphedrine, treatmentSBP <90 mmHg or decrease in SBP >30%55.2%*
      Jendoubi A. 2020
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      100Crystalloid coloadEphedrine, treatmentSBP decrease ≥20% from baseline or <100 mmHg80%*
      Yeh PH. 2020
      • Yeh P.H.
      • Chang Y.J.
      • Tsai S.E.
      Observation of hemodynamic parameters using a non-invasive cardiac output monitor system to identify predictive indicators for post-spinal anesthesia hypotension in parturients undergoing cesarean section.
      77Crystalloid preloadEphedrine, TreatmentSBP decrease >20% from baseline51.9%**
      Kim, HJ. 2020
      • Kim H.J.
      • Choi Y.S.
      • Kim S.H.
      • Lee W.
      • Kwon J.Y.
      • Kim D.H.
      Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
      35Crystalloid coloadEphedrine/phenylephrine, treatmentSBP <80 mmHg or <75% of baseline or if symptoms consistent with hypotension60%**
      *The study had predictors belonging to the domain.
      Figure thumbnail gr2
      Fig. 2Quality assessment of included diagnostic accuracy studies using QUADAS-2
      • Whiting P.F.
      • Rutjes A.W.S.
      • Westwood M.E.
      • et al.
      QUADAS-2: A revised tool for the quality assessment of diagnostic accuracy studies.

      Domain I. Demographic characteristics

      Eighteen studies with 1805 patients reported the use of maternal demographic characteristics to predict hypotension (Supplementary Table 2). Among them, only three reported a weak relationship between maternal weight and body mass index (BMI) with spinal anesthesia-induced hypotension.
      • Xu Z.
      • Xu T.
      • Zhao P.
      • Ma R.
      • Zhang M.
      • Zheng J.
      Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
      • Jeon Y.T.
      • Hwang J.W.
      • Kim M.H.
      • et al.
      Positional blood pressure change and the risk of hypotension during spinal anesthesia for cesarean delivery: An observational study.
      • Yeh P.H.
      • Chang Y.J.
      • Tsai S.E.
      Observation of hemodynamic parameters using a non-invasive cardiac output monitor system to identify predictive indicators for post-spinal anesthesia hypotension in parturients undergoing cesarean section.
      Many more studies found no predictive value of BMI, maternal weight, height, or body roundness index.
      • Zieleskiewicz L.
      • Noel A.
      • Duclos G.
      • et al.
      Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
      • Riffard C.
      • Viêt T.Q.
      • Desgranges F.P.
      • et al.
      The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      • Toyama S.
      • Kakumoto M.
      • Morioka M.
      • et al.
      Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery.
      • Kozanhan B.
      • Bardak O.
      • Sami Tutar M.
      • Ozler S.
      • Yildiz M.
      • Solak I.
      The influence of body roundness index on sensorial block level of spinal anaesthesia for elective caesarean section: an observational study.
      • Kim H.J.
      • Choi Y.S.
      • Kim S.H.
      • Lee W.
      • Kwon J.Y.
      • Kim D.H.
      Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
      • Chamchad D.
      • Arkoosh V.A.
      • Horrow J.C.
      • et al.
      Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
      • Kuwata S.
      • Suehiro K.
      • Juri T.
      • et al.
      Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
      • Sun S.
      • Liu N.H.
      • Huang S.Q.
      Role of cerebral oxygenation for prediction of hypotension after spinal anesthesia for caesarean section.
      Ghabach et al.
      • Ghabach M.B.
      • El-Khatib M.F.
      • Zreik T.G.
      • et al.
      Effect of weight gain during pregnancy on heart rate variability and hypotension during caesarean section under spinal anaesthesia.
      reported that maternal weight gain during pregnancy was valuable in predicting spinal anesthesia-induced hypotension, however the sensitivity was low (53.1%). Fakherpour et al.
      • Fakherpour A.
      • Ghaem H.
      • Fattahi Z.
      • Zaree S.
      Maternal and anaesthesia related risk factors and incidence of spinal anaesthesia induced hypotension in elective caesarean section: a multinomial logistic regression.
      found that gravidity ≥4 and history of hypotension were associated with spinal anesthesia-induced hypotension. Parthasarathy et al.
      • Parthasarathy P.
      • Aithal R.R.
      • Rao R.R.
      • Raghuram S.
      • Ramesh R.
      • Nazneen A.
      Correlation of symphysiofundal height and abdominal girth with the incidence of hypotension in cesarean section under spinal anesthesia using bupivacaine with fentanyl as adjuvant: a clinical study.
      found that the distance between the symphysis pubis and the fundus and abdominal girth could effectively predict spinal anesthesia-induced hypotension, however, this correlation was not confirmed by Kuok et al.
      • Kuok C.H.
      • Huang C.H.
      • Tsai P.S.
      • et al.
      Preoperative measurement of maternal abdominal circumference relates the initial sensory block level of spinal anesthesia for cesarean section: an observational study.
      and Günüşen et al.
      • Günüşen İ.
      • Sargin A.
      • Akdemir A.
      • Ergenoğlu A.M.
      The effects of uterine size with or without abdominal obesity on spinal block level and vasopressor requirement in elective cesarean section: a prospective observational study.

      Domain II. Baseline hemodynamic parameters

      Fifteen studies with 1032 patients assessed the baseline maternal heart rate for prediction of spinal anesthesia-induced hypotension (Supplementary Table 3). Chamchad et al.,
      • Chamchad D.
      • Arkoosh V.A.
      • Horrow J.C.
      • et al.
      Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
      Frölich et al.,
      • Frölich M.A.
      • Caton D.
      Baseline heart rate may predict hypotension after spinal anesthesia in prehydrated obstetrical patients.
      and Yokose et al.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      found a significantly increased incidence of hypotension in individuals with a higher baseline heart rate. Jeon
      • Jeon Y.T.
      • Hwang J.W.
      • Kim M.H.
      • et al.
      Positional blood pressure change and the risk of hypotension during spinal anesthesia for cesarean delivery: An observational study.
      reported the correlation coefficient (r) between baseline maternal heart rate and spinal anesthesia-induced hypotension was 0.35. Eleven other studies did not confirm this relationship.
      • Zieleskiewicz L.
      • Noel A.
      • Duclos G.
      • et al.
      Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
      • Riffard C.
      • Viêt T.Q.
      • Desgranges F.P.
      • et al.
      The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      • Toyama S.
      • Kakumoto M.
      • Morioka M.
      • et al.
      Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery.
      • Xu Z.
      • Xu T.
      • Zhao P.
      • Ma R.
      • Zhang M.
      • Zheng J.
      Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
      • Kim H.J.
      • Choi Y.S.
      • Kim S.H.
      • Lee W.
      • Kwon J.Y.
      • Kim D.H.
      Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
      • Kuwata S.
      • Suehiro K.
      • Juri T.
      • et al.
      Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
      • Sakata K.
      • Yoshimura N.
      • Tanabe K.
      • Kito K.
      • Nagase K.
      • Iida H.
      Prediction of hypotension during spinal anesthesia for elective cesarean section by altered heart rate variability induced by postural change.
      • Ledowski T.
      • Paech M.J.
      • Browning R.
      • Preuss J.
      • Schug S.A.
      An observational study of skin conductance monitoring as a means of predicting hypotension from spinal anaesthesia for caesarean delivery.
      • Sun S.
      • Huang S.Q.
      Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section.
      Baseline maternal blood pressure was also assessed in 11 studies with 1281 patients. Fakherpour et al.
      • Fakherpour A.
      • Ghaem H.
      • Fattahi Z.
      • Zaree S.
      Maternal and anaesthesia related risk factors and incidence of spinal anaesthesia induced hypotension in elective caesarean section: a multinomial logistic regression.
      reported a strong relationship between baseline systolic blood pressure (SBP) and spinal anesthesia-induced hypotension (relative RR 6.53). Two studies by Chamchad et al.
      • Chamchad D.
      • Arkoosh V.A.
      • Horrow J.C.
      • et al.
      Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
      and Riffard et al.
      • Riffard C.
      • Viêt T.Q.
      • Desgranges F.P.
      • et al.
      The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
      found limited predictive value of SBP, with a low sensitivity of approximately 50%. Eight other studies did not confirm this relationship.
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      • Xu Z.
      • Xu T.
      • Zhao P.
      • Ma R.
      • Zhang M.
      • Zheng J.
      Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
      • Kim H.J.
      • Choi Y.S.
      • Kim S.H.
      • Lee W.
      • Kwon J.Y.
      • Kim D.H.
      Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
      • Kuwata S.
      • Suehiro K.
      • Juri T.
      • et al.
      Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
      • Sakata K.
      • Yoshimura N.
      • Tanabe K.
      • Kito K.
      • Nagase K.
      • Iida H.
      Prediction of hypotension during spinal anesthesia for elective cesarean section by altered heart rate variability induced by postural change.
      • Ledowski T.
      • Paech M.J.
      • Browning R.
      • Preuss J.
      • Schug S.A.
      An observational study of skin conductance monitoring as a means of predicting hypotension from spinal anaesthesia for caesarean delivery.
      • Sun S.
      • Huang S.Q.
      Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section.

      Domain III. Baseline sympathovagal balance indices

      Eight studies with 426 patients assessed the predictive value of maternal heart rate variability (HRV) (Supplementary Table 4). A variety of techniques are available for assessment, including three main methods: fast Fourier transformation (LF/HF),
      • Hanss R.
      • Bein B.
      • Francksen H.
      • et al.
      Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
      wavelet transformation,
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      and point correlation dimension (PD2).
      • Chamchad D.
      • Arkoosh V.A.
      • Horrow J.C.
      • et al.
      Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
      Chamchad et al.
      • Chamchad D.
      • Arkoosh V.A.
      • Horrow J.C.
      • et al.
      Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
      initially proposed HRV as a predictive tool for spinal anesthesia-induced hypotension in 22 patients using point correlation dimension (PD2), reporting 100% accuracy. Fast Fourier transformation (LF/HF), a classic method of HRV analysis, was assessed in five studies. The LF/HF ratio was suggested as a predictor of hypotension by Hanss et al. (n=40)
      • Hanss R.
      • Bein B.
      • Francksen H.
      • et al.
      Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
      and Bishop et al. (n=102)
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      ; the predictive value of LF/HF was moderate (AUROC 0.64).
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      However, three further studies determined that the baseline LF/HF was not predictive of hypotension.
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      • Sakata K.
      • Yoshimura N.
      • Tanabe K.
      • Kito K.
      • Nagase K.
      • Iida H.
      Prediction of hypotension during spinal anesthesia for elective cesarean section by altered heart rate variability induced by postural change.
      Sakata et al.
      • Sakata K.
      • Yoshimura N.
      • Tanabe K.
      • Kito K.
      • Nagase K.
      • Iida H.
      Prediction of hypotension during spinal anesthesia for elective cesarean section by altered heart rate variability induced by postural change.
      and Ursulet et al.
      • Ursulet L.
      • Cros J.
      • De Jonckheere J.
      • Senges P.
      • Vincelot A.
      • Nathan N.
      Bedside analysis of hear t rate variability by Analgesia Nociception Index (ANI) predicts hypotension after spinal anesthesia for elective Caesarean delivery.
      suggested that dynamic heart rate variations associated with different patient positions improved the predictive value compared with a static state.
      Sympathovagal balance was analyzed in 416 patients in five studies using other techniques. Skin conductance monitoring is a noninvasive technology providing information about sympathetic tone by measuring sweat gland filling. Ledowski et al.
      • Ledowski T.
      • Paech M.J.
      • Browning R.
      • Preuss J.
      • Schug S.A.
      An observational study of skin conductance monitoring as a means of predicting hypotension from spinal anaesthesia for caesarean delivery.
      found no predictive value of skin conductance or anxiety score. The analysis of pulse rate variability (PRV) provides the assessment of autonomic nervous system (ANS) regulation of the heart as well as peripheral vascular regulation information. Bolea et al.
      • Bolea J.
      • Lázaro J.
      • Gil E.
      • et al.
      Pulse rate and transit time analysis to predict hypotension events after spinal anesthesia during programmed cesarean labor.
      found a moderate predictive value for pulse rate variability. Furthermore, Riffard et al.
      • Riffard C.
      • Viêt T.Q.
      • Desgranges F.P.
      • et al.
      The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
      suggested that the pupil autonomic innervation may reflect the balance of sympathetic and parasympathetic systems and verified its predictive value for the onset of spinal anesthesia-induced hypotension. Kim et al.
      • Kim H.
      • An J.
      • Kim E.
      • et al.
      A pilot study on the role of autonomic function testing in predicting hypotension in patients undergoing cesarean section under spinal anesthesia.
      used the deep breathing and hand grip tests (which may reflect parasympathetic and sympathetic functions) to predict spinal anesthesia-induced hypotension, finding an AUROC of approximately 0.6.

      Domain IV. Postural stress testing

      Four studies
      • Manouchehrian N.
      • Torabi F.
      • Shayan A.
      • Otogara M.
      Investigation of effect of blood pressure and heart rate changes in different positions (lying and sitting) on hypotension incidence rate after spinal anesthesia in patients undergoing caesarean section.
      • Jeon Y.T.
      • Hwang J.W.
      • Kim M.H.
      • et al.
      Positional blood pressure change and the risk of hypotension during spinal anesthesia for cesarean delivery: An observational study.
      • Dahlgren G.
      • Granath F.
      • Wessel H.
      • Irestedt L.
      Prediction of hypotension during spinal anesthesia for cesarean section and its relation to the effect of crystalloid or colloid preload.
      • Kinsella S.M.
      • Norris M.C.
      Advance prediction of hypotension at cesarean delivery under spinal anesthesia.
      with 181 patients confirmed that the supine stress test (SST) predicted severe systolic hypotension with a sensitivity of 55% to 80% and a specificity of 80% to 90%. In contrast, Frölich et al.
      • Jendoubi A.
      • Khalloufi A.
      • Nasri O.
      • Abbes A.
      • Ghedira S.
      • Houissa M.
      Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
      found that HR and BP variations during the orthostatic change were not good predictors of spinal anesthesia-induced hypotension (Supplementary Table 5).

      Domain V. Peripheral perfusion indices

      The perfusion index (PI) was investigated in seven studies with 549 patients, while one study with 41 patients assessed cerebral oxygen saturation (ScO2). Duggappa et al.
      • Duggappa D.R.
      • Lokesh M.P.
      • Dixit A.
      • Paul R.
      • Rao R.R.
      • Prabha P.
      Perfusion index as a predictor of hypotension following spinal anaesthesia in lower segment caesarean section.
      and Toyama et al.
      • Toyama S.
      • Kakumoto M.
      • Morioka M.
      • et al.
      Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery.
      showed the PI, as a predictor of spinal anesthesia-induced hypotension, had an AUROC >0.8. Xu et al.
      • Xu Z.
      • Xu T.
      • Zhao P.
      • Ma R.
      • Zhang M.
      • Zheng J.
      Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
      tested toe PI as a predictor of hypotension and the AUROC was >0.75. In the other four studies, the predictive value of the PI was weak
      • Kuwata S.
      • Suehiro K.
      • Juri T.
      • et al.
      Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
      or completely lacking.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      • Arslan M.
      • Öksüz G.
      • Bilal B.
      • et al.
      Can perfusion index or pleth variability index predict spinal anesthesia-induced hypotension during caesarean section?.
      • Sun S.
      • Huang S.Q.
      Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section.
      Cerebral oxygen saturation (ScO2) was associated with blood perfusion in cerebral tissue; however, Sun et al.
      • Sun S.
      • Liu N.H.
      • Huang S.Q.
      Role of cerebral oxygenation for prediction of hypotension after spinal anesthesia for caesarean section.
      found it had no predictive value (Supplementary Table 6).

      Domain VI. Blood volume and fluid responsiveness indices

      Individuals who are hypovolemic before the initiation of spinal anesthesia may be at increased risk for spinal anesthesia-induced hypotension. Maternal blood volume and fluid responsiveness were evaluated in 11 studies with 658 patients (Supplementary Table 7). Kundra et al.
      • Kundra P.
      • Arunsekar G.
      • Vasudevan A.
      • Vinayagam S.
      • Habeebullah S.
      • Ramesh A.
      Effect of postural changes on inferior vena cava dimensions and its infuence on haemodynamics during caesarean section under spinal anaesthesia.
      and Singh et al.
      • Singh Y.
      • Anand R.K.
      • Gupta S.
      • et al.
      Role of IVC collapsibility index to predict post spinal hypotension in pregnant women undergoing caesarean section. An observational trial.
      evaluated inferior vena cava collapsibility index (IVCCI) as a predictor of spinal anesthesia-induced hypotension; the AUROC was <0.5.
      The pleth variability index (PVI) has predicted fluid responsiveness in mechanically ventilated patients with a high degree of sensitivity and specificity. However, the predictive value of PVI in two studies was moderate (AUROC 0.6 and 0.75) (Supplementary Table 7),
      • Kuwata S.
      • Suehiro K.
      • Juri T.
      • et al.
      Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
      • Sun S.
      • Huang S.Q.
      Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section.
      and in three additional studies the PVI was not predictive of spinal anesthesia-induced hypotension.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      • Xu Z.
      • Xu T.
      • Zhao P.
      • Ma R.
      • Zhang M.
      • Zheng J.
      Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
      • Arslan M.
      • Öksüz G.
      • Bilal B.
      • et al.
      Can perfusion index or pleth variability index predict spinal anesthesia-induced hypotension during caesarean section?.
      Baseline cardiac output index, stroke volume (SV)
      • Yeh P.H.
      • Chang Y.J.
      • Tsai S.E.
      Observation of hemodynamic parameters using a non-invasive cardiac output monitor system to identify predictive indicators for post-spinal anesthesia hypotension in parturients undergoing cesarean section.
      and cardiac output change during passive leg raise (PLR) test
      • Meirowitz N.
      • Katz A.
      • Danzer B.
      • Siegenfeld R.
      Can the passive leg raise test predict spinal hypotension during cesarean delivery? An observational pilot study.
      were also not good predictors.
      Measurement of subaortic variation in the velocity–time integral (VTI) with PLR allows the prediction of fluid responsiveness. Zieleskiewicz et al.
      • Zieleskiewicz L.
      • Noel A.
      • Duclos G.
      • et al.
      Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
      used VTI variation in different patient positions to predict spinal anesthesia-induced hypotension; the AUROC was approximately 0.8. Kim et al.
      • Kim H.J.
      • Choi Y.S.
      • Kim S.H.
      • Lee W.
      • Kwon J.Y.
      • Kim D.H.
      Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
      found that carotid artery-corrected blood flow time accurately predicted spinal anesthesia-induced hypotension (AUROC >0.9).

      Domain VII. Genetic polymorphism

      Daher et al.
      • Daher M.
      • Saito R.B.
      • Barra G.B.
      • Govêia C.S.
      • Magalhães E.
      • Neves F.A.
      The effect of beta-2 adrenergic receptor haplotype variations on the haemodynamic response following spinal anaesthesia for caesarean delivery.
      reported the relationship between beta-2 adrenergic receptor (ADRB2) genetic polymorphism and blood pressure during spinal anesthesia-induced hypotension. Two copies of the ArgGln haplotype were associated with a lower risk for hypotension (52.2% vs 75.0%; OR 0.36, 95% confidence interval 0.15 to 0.91; P=0.042).

      Discussion

      Blood pressure depends on blood volume, cardiac output, and vascular resistance, which are modulated by the cardiovascular, ANS, and endocrine systems.
      • Moertl M.G.
      • Ulrich D.
      • Pickel K.I.
      • et al.
      Changes in haemodynamic and autonomous nervous system parameters measured non-invasively throughout normal pregnancy.
      In theory, factors reflecting these three aspects could predict spinal anesthesia-induced hypotension. Many parameters for predicting hypotension during cesarean section with spinal anesthesia have been assessed. According to our review, accurate blood volume and fluid response assessments may predict spinal anesthesia-induced hypotension. Supine stress tests reflect cardiovascular tolerance during hemodynamic fluctuations and may optimize the predictive value of static state predictors. Environmental and individual factors increased outcome variability, thereby restricting the value of the ANS and peripheral PI for the prediction of spinal anesthesia-induced hypotension. Further study with larger sample sizes is necessary to confirm these findings.
      Hypovolemia, resulting from decreased systemic vascular resistance after spinal anesthesia, is one possible reason for spinal anesthesia-induced hypotension. Pre-operative blood volume assessment was investigated in several studies as a predictor for spinal anesthesia-induced hypotension. Pleth variability index and IVCCI were the most studied, however findings were inconsistent. The PVI is a well-known predictor of fluid responsiveness in mechanically ventilated patients.
      • Cannesson M.
      • Desebbe O.
      • Rosamel P.
      • et al.
      Pleth variability index to monitor the respiratory variations in the pulse oximeter plethysmographic waveform amplitude and predict fluid responsiveness in the operating theatre.
      However, in spontaneously breathing patients, fluid responsiveness assessment becomes problematic as the tidal volume and frequency of breathing vary among patients, and cardiopulmonary interactions are more complicated in such patients than in those on mechanical ventilation.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      Respiratory variation in inferior vena cava diameter has limited ability to predict fluid responsiveness in other settings, particularly in spontaneously ventilated patients.
      • Long E.
      • Oakley E.
      • Duke T.
      • Babl F.E.
      Does respiratory variation in inferior vena cava diameter predict fluid responsiveness: a systematic review and meta-analysis.
      Furthermore, blood volume is not the only factor influencing blood pressure; this may explain why blood volume assessment for prediction of spinal anesthesia-induced hypotension is of limited value. Velocity time integral variation in different patient positions
      • Zieleskiewicz L.
      • Noel A.
      • Duclos G.
      • et al.
      Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
      and corrected blood flow time
      • Kim H.J.
      • Choi Y.S.
      • Kim S.H.
      • Lee W.
      • Kwon J.Y.
      • Kim D.H.
      Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
      have been used effectively to predict spinal anesthesia-induced hypotension. These two predictors were not only valuable for blood volume assessment but also may reflect myocardial contractility and carotid artery-corrected blood flow time may also reflect afterload. Thus, we believe that composite parameters reflecting preload, myocardial contractility and afterload are likely to be more useful for predicting spinal anesthesia-induced hypotension.
      The SST may reflect different cardiovascular tolerances of individuals with aortocaval compression through changes in heart rate, blood pressure, or maternal discomfort. Kinsella et al.
      • Kinsella S.M.
      • Norris M.C.
      Advance prediction of hypotension at cesarean delivery under spinal anesthesia.
      and Dahlgren et al.
      • Dahlgren G.
      • Granath F.
      • Wessel H.
      • Irestedt L.
      Prediction of hypotension during spinal anesthesia for cesarean section and its relation to the effect of crystalloid or colloid preload.
      demonstrated that women with reduced tolerance for the supine position were more likely to experience hypotension and had higher vasopressor requirements. However, Frölich et al.
      • Frölich M.A.
      • Caton D.
      Baseline heart rate may predict hypotension after spinal anesthesia in prehydrated obstetrical patients.
      found that heart rate and blood pressure changes between the lateral supine and upright positions were not predictive of hypotension, suggesting that the SST may be more suitable for pregnant individuals with different cardiovascular tolerance assessments of aortocaval compression. The combination of SSTs with other predictors, such as heart rate variability, may improve the predictive value of HRV assessment in the static state.
      • Sakata K.
      • Yoshimura N.
      • Tanabe K.
      • Kito K.
      • Nagase K.
      • Iida H.
      Prediction of hypotension during spinal anesthesia for elective cesarean section by altered heart rate variability induced by postural change.
      • Ursulet L.
      • Cros J.
      • De Jonckheere J.
      • Senges P.
      • Vincelot A.
      • Nathan N.
      Bedside analysis of hear t rate variability by Analgesia Nociception Index (ANI) predicts hypotension after spinal anesthesia for elective Caesarean delivery.
      The ANS plays a central role in the adaptation and short-term control of the cardiovascular system to meet various hemodynamic requirements.
      • Fu Q.
      • Levine B.D.
      Autonomic circulatory control during pregnancy in humans.
      Pre-operative ANS assessment, for example, by assessing HRV, may provide useful information regarding the risk for hypotension following induction of spinal anesthesia. However, sympathovagal balance is influenced by many factors, such as blood volume, anxiety,
      • Orbach-Zinger S.
      • Ginosar Y.
      • Elliston J.
      • et al.
      Influence of preoperative anxiety on hypotension after spinal anaesthesia in women undergoing Caesarean delivery.
      and environmental temperature.
      • Hanss R.
      • Bein B.
      • Francksen H.
      • et al.
      Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      A favorable environment for HRV assessment is quiet and temperature-controlled; furthermore, ensuring that the patient is calm is very important. In addition, the ANS may undergo rapid changes, so HRV assessment should be performed immediately prior to the induction of neuraxial anesthesia. Even with accurate assessment of ANS activity, the baroreceptor sensitivity of each patient may differentially affect cardiovascular adaptations.
      • Moertl M.G.
      • Ulrich D.
      • Pickel K.I.
      • et al.
      Changes in haemodynamic and autonomous nervous system parameters measured non-invasively throughout normal pregnancy.
      • Prashanth A.
      • Chakravarthy M.
      • George A.
      • Mayur R.
      • Hosur R.
      • Pargaonkar S.
      Sympatho-vagal balance, as quantified by ANSindex, predicts post spinal hypotension and vasopressor requirement in parturients undergoing lower segmental cesarean section: a single blinded prospective observational study.
      Furthermore, some predictors, such as skin conductance, detect peripheral ANS instead of central ANS activity and may be inaccurate or exhibit a time lag. Under ideal environmental and mental conditions, the baseline heart rate may also reflect cardiovascular sympathetic activity and a higher baseline heart rate indicate a higher risk of spinal anesthesia-induced hypotension.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      • Chamchad D.
      • Arkoosh V.A.
      • Horrow J.C.
      • et al.
      Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
      The PI assesses peripheral perfusion dynamics due to changes in peripheral vascular tone. Even with a stable blood volume, the PI is commonly affected by other factors such as movement, temperature, psychological stress and anxiety, which induce sympathetic activation. It is difficult to control for these factors in awake patients, which may explain the inconsistent outcomes found.
      • Yokose M.
      • Mihara T.
      • Sugawara Y.
      • Goto T.
      The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
      Maternal demographics and baseline hemodynamic parameters to predict hypotension in this setting have been investigated but only a few demonstrated predictive value.
      • Riffard C.
      • Viêt T.Q.
      • Desgranges F.P.
      • et al.
      The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
      • Bishop D.G.
      • Cairns C.
      • Grobbelaar M.
      • Rodseth R.N.
      Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
      • Kozanhan B.
      • Bardak O.
      • Sami Tutar M.
      • Ozler S.
      • Yildiz M.
      • Solak I.
      The influence of body roundness index on sensorial block level of spinal anaesthesia for elective caesarean section: an observational study.
      We speculate that these parameters are not direct determinants of blood pressure, restricting their predictive efficacy. Although polymorphisms within the ADRB2 gene were associated with increased risk,
      • Daher M.
      • Saito R.B.
      • Barra G.B.
      • Govêia C.S.
      • Magalhães E.
      • Neves F.A.
      The effect of beta-2 adrenergic receptor haplotype variations on the haemodynamic response following spinal anaesthesia for caesarean delivery.
      genotype screening is not a routine procedure. Some studies addressed the predictive value of parameters measured after spinal anesthesia, for example, sensory block level,
      • Jeon Y.T.
      • Hwang J.W.
      • Kim M.H.
      • et al.
      Positional blood pressure change and the risk of hypotension during spinal anesthesia for cesarean delivery: An observational study.
      • Sun S.
      • Huang S.Q.
      Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section.
      decrease in ScO2 after spinal anesthesia,
      • Sun S.
      • Liu N.H.
      • Huang S.Q.
      Role of cerebral oxygenation for prediction of hypotension after spinal anesthesia for caesarean section.
      and PI or PVI changes after spinal anesthesia.
      • Kuwata S.
      • Suehiro K.
      • Juri T.
      • et al.
      Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
      These predictors were excluded from this systematic review because they do not help in the decision-making process for a prophylactic strategy against spinal anesthesia-induced hypotension.
      Several limitations should be considered when assessing the clinical relevance of our results. Quantitative analysis was not performed because of obvious heterogeneity among studies. First, the doses of spinal drug(s), fluid loading and vasopressor use were very different among studies. Second, the definition of spinal anesthesia-induced hypotension and assessment of its predictors varied among studies. All these diverse study characteristics may influence the predictive value of the different parameters. Moreover, the predictive value of VTI variation or corrected blood flow time were only studied once and further investigation is needed. Finally, we did not include studies in which predictive data were not reported, those published in languages other than English, or studies which were unpublished, which may have increased the risk of reporting bias. However, to the best of our knowledge, this systematic review is the most comprehensive qualitative analysis of spinal anesthesia-induced hypotension predictors to date. Thus, this resource provides investigators in this area with a status report. Composite parameters reflecting preload, myocardial contractility and afterload may predict spinal anesthesia-induced hypotension, while the SST may be valuable for pregnant women with different cardiovascular tolerance assessments of aortocaval compression. To further examine these factors, future research should focus on composite and dynamic parameters during the SST.
      In summary, an accurate evaluation of blood volume and fluid responsiveness assessment may predict post-spinal hypotension. Furthermore, the SST may reflect the individual’s cardiovascular tolerance during hemodynamic fluctuations and may optimize the predictive value of static state predictors. Environmental and individual factors increased outcome variability, thereby restricting the value of the ANS and peripheral PI for prediction of spinal anesthesia-induced hypotension.

      Funding

      This work was supported by a grant from the Science and Technology Department of Sichuan Province, China (No. 2018SZ0211 ).

      Conflicts of interest

      Author Zhimin Liao received research support from the Science and Technology Department of Sichuan Province, China (No. 2018SZ0211).

      References

        • Eltzschig H.K.
        • Lieberman E.S.
        • Camann W.R.
        Regional anesthesia and analgesia for labor and delivery.
        N Engl J Med. 2003; 348: 319-332https://doi.org/10.1056/NEJMra021276
        • Klöhr S.
        • Roth R.
        • Hofmann T.
        • Rossaint R.
        • Heesen M.
        Definitions of hypotension after spinal anaesthesia for caesarean section: literature search and application to parturients.
        Acta Anaesthesiol Scand. 2010; 54: 909-921https://doi.org/10.1111/j.1399-6576.2010.02239.x
        • Kinsella S.M.
        • Carvalho B.
        • Dyer R.A.
        • et al.
        International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia.
        Anaesthesia. 2018; 73: 71-92https://doi.org/10.1111/anae.14080
        • Lim G.
        • Facco F.L.
        • Nathan N.
        • Waters J.H.
        • Wong C.A.
        • Eltzschig H.K.
        A Review of the impact of obstetric anesthesia on maternal and neonatal outcomes.
        Anesthesiology. 2018; 129: 192-215https://doi.org/10.1097/ALN.0000000000002182
        • Zieleskiewicz L.
        • Noel A.
        • Duclos G.
        • et al.
        Can point-of-care ultrasound predict spinal hypotension during caesarean section? A prospective observational study.
        Anaesthesia. 2018; 73: 15-22https://doi.org/10.1111/anae.14063
        • Hasanin A.
        • Amin S.
        • Refaat S.
        • et al.
        Norepinephrine versus phenylephrine infusion for prophylaxis against post-spinal anaesthesia hypotension during elective caesarean delivery: a randomised controlled trial.
        Anaesth Crit Care Pain Med. 2019; 38: 601-607https://doi.org/10.1016/j.accpm.2019.03.005
        • Xiao F.
        • Shen B.
        • Xu W.P.
        • Feng Y.
        • Kee W.D.
        • Chen X.Z.
        Dose–response study of 4 weight-based phenylephrine infusion regimens for preventing hypotension during cesarean delivery under combined spinal-epidural anesthesia.
        Anesth Analg. 2020; 130: 187-193https://doi.org/10.1213/ANE.0000000000004092
        • Loubert C.
        Fluid and vasopressor management for Cesarean delivery under spinal anesthesia: continuing professional development.
        Can J Anesth. 2012; 59: 604-619https://doi.org/10.7326/0003-4819-155-8-201110180-00009
        • Whiting P.F.
        • Rutjes A.W.S.
        • Westwood M.E.
        • et al.
        QUADAS-2: A revised tool for the quality assessment of diagnostic accuracy studies.
        Ann Intern Med. 2011; 155: 529-536https://doi.org/10.7326/0003-4819-155-8-201110180-00009
        • Hanss R.
        • Bein B.
        • Francksen H.
        • et al.
        Heart rate variability–guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery.
        Anesthesiology. 2006; 104: 635-643https://doi.org/10.1097/00000542-200604000-00005
        • Riffard C.
        • Viêt T.Q.
        • Desgranges F.P.
        • et al.
        The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.
        Anaesth Crit Care Pain Med. 2018; 37: 233-238https://doi.org/10.1016/j.accpm.2016.10.004
        • Meirowitz N.
        • Katz A.
        • Danzer B.
        • Siegenfeld R.
        Can the passive leg raise test predict spinal hypotension during cesarean delivery? An observational pilot study.
        Int J Obstet Anesth. 2012; 21: 324-328https://doi.org/10.1016/j.ijoa.2012.08.004
        • Jendoubi A.
        • Khalloufi A.
        • Nasri O.
        • Abbes A.
        • Ghedira S.
        • Houissa M.
        Analgesia nociception index as a tool to predict hypotension after spinal anaesthesia for elective caesarean section.
        J Obstet Gynaecol. 2020; 9: 1-7https://doi.org/10.1080/01443615.2020.1718624
        • Bishop D.G.
        • Cairns C.
        • Grobbelaar M.
        • Rodseth R.N.
        Heart rate variability as a predictor of hypotension following spinal for elective caesarean section: a prospective observational study.
        Anaesthesia. 2017; 72: 603-608https://doi.org/10.1111/anae.13813
        • Daher M.
        • Saito R.B.
        • Barra G.B.
        • Govêia C.S.
        • Magalhães E.
        • Neves F.A.
        The effect of beta-2 adrenergic receptor haplotype variations on the haemodynamic response following spinal anaesthesia for caesarean delivery.
        Anaesthesia. 2012; 67: 1251-1259https://doi.org/10.1111/j.1365-2044.2012.07296.x
        • Toyama S.
        • Kakumoto M.
        • Morioka M.
        • et al.
        Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery.
        Br J Anaesth. 2013; 111: 235-241https://doi.org/10.1093/bja/aet058
        • Yokose M.
        • Mihara T.
        • Sugawara Y.
        • Goto T.
        The predictive ability of non-invasive haemodynamic parameters for hypotension during caesarean section: a prospective observational study.
        Anaesthesia. 2015; 70: 555-562https://doi.org/10.1111/anae.12992
        • Kozanhan B.
        • Bardak O.
        • Sami Tutar M.
        • Ozler S.
        • Yildiz M.
        • Solak I.
        The influence of body roundness index on sensorial block level of spinal anaesthesia for elective caesarean section: an observational study.
        J Obstet Gynaecol. 2020; 40: 772-778https://doi.org/10.1080/01443615.2019.1647523
        • Xu Z.
        • Xu T.
        • Zhao P.
        • Ma R.
        • Zhang M.
        • Zheng J.
        Differential roles of the right and left toe perfusion index in predicting the incidence of postspinal hypotension during cesarean selivery.
        Anesth Analg. 2017; 125: 1560-1566https://doi.org/10.1213/ANE.0000000000002393
        • Kim H.
        • An J.
        • Kim E.
        • et al.
        A pilot study on the role of autonomic function testing in predicting hypotension in patients undergoing cesarean section under spinal anesthesia.
        Anesth Pain Med. 2019; 14: 259-265https://doi.org/10.17085/apm.2019.14.3.259
        • Kim H.J.
        • Choi Y.S.
        • Kim S.H.
        • Lee W.
        • Kwon J.Y.
        • Kim D.H.
        Predictability of preoperative carotid artery-corrected flow time for hypotension after spinal anaesthesia in patients undergoing caesarean section: a prospective observational study.
        Eur J Anaesthesiol. 2020; 37: 1-8https://doi.org/10.1097/EJA.0000000000001376
        • Kundra P.
        • Arunsekar G.
        • Vasudevan A.
        • Vinayagam S.
        • Habeebullah S.
        • Ramesh A.
        Effect of postural changes on inferior vena cava dimensions and its infuence on haemodynamics during caesarean section under spinal anaesthesia.
        J Obstet Gynaecol. 2015; 35: 667-671https://doi.org/10.3109/01443615.2014.991291
        • Arslan M.
        • Öksüz G.
        • Bilal B.
        • et al.
        Can perfusion index or pleth variability index predict spinal anesthesia-induced hypotension during caesarean section?.
        Anestezi Dergisi. 2019; 27: 251-257https://doi.org/10.5222/jarss.2019.69775
        • Manouchehrian N.
        • Torabi F.
        • Shayan A.
        • Otogara M.
        Investigation of effect of blood pressure and heart rate changes in different positions (lying and sitting) on hypotension incidence rate after spinal anesthesia in patients undergoing caesarean section.
        Int J Med Res Health Sci. 2016; 5: 407-412
        • Jeon Y.T.
        • Hwang J.W.
        • Kim M.H.
        • et al.
        Positional blood pressure change and the risk of hypotension during spinal anesthesia for cesarean delivery: An observational study.
        Anesth Analg. 2010; 111: 712-715https://doi.org/10.1213/ANE.0b013e3181e8137b
        • Yeh P.H.
        • Chang Y.J.
        • Tsai S.E.
        Observation of hemodynamic parameters using a non-invasive cardiac output monitor system to identify predictive indicators for post-spinal anesthesia hypotension in parturients undergoing cesarean section.
        Exp Ther Med. 2020; 20: 168https://doi.org/10.3892/etm.2020.9298
        • Chamchad D.
        • Arkoosh V.A.
        • Horrow J.C.
        • et al.
        Using heart rate variability to stratify risk of obstetric patients undergoing spinal anesthesia.
        Anesth Analg. 2004; 99: 1818-1821https://doi.org/10.1213/01.ANE.0000140953.40059.E6
        • Kuwata S.
        • Suehiro K.
        • Juri T.
        • et al.
        Pleth variability index can predict spinal anaesthesia-induced hypotension in patients undergoing caesarean delivery.
        Acta Anaesthesiol Scand. 2018; 62: 75-84https://doi.org/10.1111/aas.13012
        • Sun S.
        • Liu N.H.
        • Huang S.Q.
        Role of cerebral oxygenation for prediction of hypotension after spinal anesthesia for caesarean section.
        J Clin Monit Comput. 2015; 30: 417-421https://doi.org/10.1007/s10877-015-9733-4
        • Ghabach M.B.
        • El-Khatib M.F.
        • Zreik T.G.
        • et al.
        Effect of weight gain during pregnancy on heart rate variability and hypotension during caesarean section under spinal anaesthesia.
        Anaesthesia. 2011; 66: 1106-1111https://doi.org/10.1111/j.1365-2044.2011.06873.x
        • Fakherpour A.
        • Ghaem H.
        • Fattahi Z.
        • Zaree S.
        Maternal and anaesthesia related risk factors and incidence of spinal anaesthesia induced hypotension in elective caesarean section: a multinomial logistic regression.
        Indian J Anaesth. 2018; 62: 36-46https://doi.org/10.4103/ija.IJA_416_17
        • Parthasarathy P.
        • Aithal R.R.
        • Rao R.R.
        • Raghuram S.
        • Ramesh R.
        • Nazneen A.
        Correlation of symphysiofundal height and abdominal girth with the incidence of hypotension in cesarean section under spinal anesthesia using bupivacaine with fentanyl as adjuvant: a clinical study.
        Anesth Essays Res. 2019; 13: 214-218https://doi.org/10.4103/aer.AER_36_19
        • Kuok C.H.
        • Huang C.H.
        • Tsai P.S.
        • et al.
        Preoperative measurement of maternal abdominal circumference relates the initial sensory block level of spinal anesthesia for cesarean section: an observational study.
        Taiwan J Obstet Gynecol. 2016; 55: 810-814https://doi.org/10.1016/j.tjog.2015.04.009
        • Günüşen İ.
        • Sargin A.
        • Akdemir A.
        • Ergenoğlu A.M.
        The effects of uterine size with or without abdominal obesity on spinal block level and vasopressor requirement in elective cesarean section: a prospective observational study.
        Turk J Med Sci. 2019; 49: 50-57https://doi.org/10.3906/sag-1804-167
        • Frölich M.A.
        • Caton D.
        Baseline heart rate may predict hypotension after spinal anesthesia in prehydrated obstetrical patients.
        Can J Anesth. 2002; 49: 185-189https://doi.org/10.1007/BF03020493
        • Sakata K.
        • Yoshimura N.
        • Tanabe K.
        • Kito K.
        • Nagase K.
        • Iida H.
        Prediction of hypotension during spinal anesthesia for elective cesarean section by altered heart rate variability induced by postural change.
        Int J Obstet Anesth. 2016; 29: 34-38https://doi.org/10.1016/j.ijoa.2016.09.004
        • Ledowski T.
        • Paech M.J.
        • Browning R.
        • Preuss J.
        • Schug S.A.
        An observational study of skin conductance monitoring as a means of predicting hypotension from spinal anaesthesia for caesarean delivery.
        Int J Obstet Anesth. 2010; 19: 282-286https://doi.org/10.1016/j.ijoa.2010.01.001
        • Sun S.
        • Huang S.Q.
        Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section.
        Int J Obstet Anesth. 2014; 23: 324-329https://doi.org/10.1016/j.ijoa.2014.05.011
        • Ursulet L.
        • Cros J.
        • De Jonckheere J.
        • Senges P.
        • Vincelot A.
        • Nathan N.
        Bedside analysis of hear t rate variability by Analgesia Nociception Index (ANI) predicts hypotension after spinal anesthesia for elective Caesarean delivery.
        Eur J Anaesthesiol. 2012; 29: 5
        • Bolea J.
        • Lázaro J.
        • Gil E.
        • et al.
        Pulse rate and transit time analysis to predict hypotension events after spinal anesthesia during programmed cesarean labor.
        Ann Biomed Eng. 2017; 45: 2253-2263https://doi.org/10.1007/s10439-017-1864-y
        • Dahlgren G.
        • Granath F.
        • Wessel H.
        • Irestedt L.
        Prediction of hypotension during spinal anesthesia for cesarean section and its relation to the effect of crystalloid or colloid preload.
        Int J Obstet Anesth. 2007; 16: 128-134https://doi.org/10.1016/j.ijoa.2006.10.006
        • Kinsella S.M.
        • Norris M.C.
        Advance prediction of hypotension at cesarean delivery under spinal anesthesia.
        Int J Obstet Anesth. 1996; 5: 3-7https://doi.org/10.1016/s0959-289x(96)80067-7
        • Duggappa D.R.
        • Lokesh M.P.
        • Dixit A.
        • Paul R.
        • Rao R.R.
        • Prabha P.
        Perfusion index as a predictor of hypotension following spinal anaesthesia in lower segment caesarean section.
        Indian J Anaesth. 2017; 61: 649-654https://doi.org/10.4103/ija.IJA_429_16
        • Singh Y.
        • Anand R.K.
        • Gupta S.
        • et al.
        Role of IVC collapsibility index to predict post spinal hypotension in pregnant women undergoing caesarean section. An observational trial.
        Saudi J Anaesth. 2019; 13: 312-317https://doi.org/10.4103/sja.SJA_27_19
        • Moertl M.G.
        • Ulrich D.
        • Pickel K.I.
        • et al.
        Changes in haemodynamic and autonomous nervous system parameters measured non-invasively throughout normal pregnancy.
        Eur J Obstet Gynecol Reprod Biol. 2009; 144: S179-183https://doi.org/10.1016/j.ejogrb.2009.02.037
        • Cannesson M.
        • Desebbe O.
        • Rosamel P.
        • et al.
        Pleth variability index to monitor the respiratory variations in the pulse oximeter plethysmographic waveform amplitude and predict fluid responsiveness in the operating theatre.
        Br J Anaesth. 2008; 101: 200-206https://doi.org/10.1093/bja/aen133
        • Long E.
        • Oakley E.
        • Duke T.
        • Babl F.E.
        Does respiratory variation in inferior vena cava diameter predict fluid responsiveness: a systematic review and meta-analysis.
        Shock. 2017; 47: s550-559https://doi.org/10.1097/SHK.0000000000000801
        • Fu Q.
        • Levine B.D.
        Autonomic circulatory control during pregnancy in humans.
        Semin Reprod Med. 2009; 27: 330-337https://doi.org/10.1055/s-0029-1225261
        • Orbach-Zinger S.
        • Ginosar Y.
        • Elliston J.
        • et al.
        Influence of preoperative anxiety on hypotension after spinal anaesthesia in women undergoing Caesarean delivery.
        Br J Anaesth. 2012; 109: 943-949https://doi.org/10.1093/bja/aes313
        • Prashanth A.
        • Chakravarthy M.
        • George A.
        • Mayur R.
        • Hosur R.
        • Pargaonkar S.
        Sympatho-vagal balance, as quantified by ANSindex, predicts post spinal hypotension and vasopressor requirement in parturients undergoing lower segmental cesarean section: a single blinded prospective observational study.
        J Clin Monit Comput. 2017; 31: 805-811https://doi.org/10.1007/s10877-016-9906-9