Chemical stability of bupivacaine, lidocaine and epinephrine in pH-adjusted solutions.

Epinephrine and sodium bicarbonate may be added to local anaesthetic solutions in order to reduce the onset time and enhance the quality of epidural anaesthesia for Caesarean section. Such mixtures are sometimes prepared several hours in advance for subsequent use in emergency Caesarean section through a pre-existing epidural catheter. To evaluate this practice, we studied the chemical stability in solution over 24 h of nine epidural mixtures consisting of different combinations of bupivacaine, lidocaine, epinephrine and sodium bicarbonate. In mixtures alkalinised with sodium bicarbonate, epinephrine concentrations decreased significantly over 24 h (p<0.0001), whereas those in nonalkalinised mixtures did not change with time. Bupivacaine and lidocaine concentrations in all mixtures did not decrease over time regardless of alkalinisation. We do not recommend adding epinephrine to alkalinised epidural solutions that are to be stored for a prolonged period before clinical use.