Short term stability of pH-adjusted lidocaine-adrenaline epidural solution used for emergency caesarean section

Abstract 

Background

Lidocaine-bicarbonate-adrenaline mixtures are commonly used for epidural bolus doses for emergency caesarean section. Previous research has shown that adrenaline degrades completely 24h after mixing. Anecdotal enquiries suggest that anaesthetists who use such mixtures commonly prepare the solution ahead of use, despite a lack of data about its stability between 0 and 24h. The aim of this study was to monitor the degradation of adrenaline in the above mixture over 20h.

Methods

2mL of sodium bicarbonate 8.4% was added to 20mL of 2% lidocaine; 2mL of this mixture was discarded and 0.1mL of adrenaline 1:1000 added. The mixtures were stored in plastic syringes at 24°C unprotected from light (n=3) or in the dark (n=3). Non-alkalinised controls were also prepared. Adrenaline and lidocaine were assayed by high performance liquid chromatography at 0, 2, 4, 6 and 20h.

Results

In the bicarbonated mixture exposed to light, chemical degradation of adrenaline was fast at room temperature, only 73.0±3.6% of adrenaline remaining after 6h. In the dark, the stability of adrenaline improved and 95.8±3.6% remained after 6h. Negligible degradation occurred in the absence of bicarbonate in either condition. Lidocaine concentrations remained unchanged regardless of the storage conditions.

Conclusions

This study suggests that preparation of pH-adjusted lidocaine-adrenaline mixtures in advance and prolonged storage in the light is inadvisable.

Keywords: Analgesia, epidural, Drug stability, Adrenaline, lidocaine, Sodium bicarbonate