POSTPARTUM PATIENTS HAVE SLIGHTLY PROLONGED NEUROMUSCULAR BLOCK AFTERMIVACURIUM

Postpartum patients have decreased plasma cholinesterase activity, whi ch may slow the metabolism of mivacurium. We compared the duration of a mivacurium neuromuscular block in 11 women undergoing postpartum tub al ligation 36-99 h after delivery with that in 11 control women under going gynecological surgery. Anesthesia was induced with propofol and fentanyl and maintained with propofol and nitrous oxide. Neuromuscular block was monitored by electromyography, and the ulnar nerve was stim ulated transcutaneously using a train-of-four pattern. Patients receiv ed a bolus dose of mivacurium 0.15 mg/kg. The median (range) duration of neuromuscular block until 25% recovery of the first twitch response was longer in the postpartum group, 19.4 (15.6-25.2) min, compared wi th the control group, 16.3 (11.0-23.4) min (P = 0.04). The median (ran ge) plasma cholinesterase activity was decreased in the postpartum gro up, 4.0 (0.1-5.5) kU/L, compared with the control group, 7.1 (6.2-10.0 ) kU/L (P < 0.001). The duration of neuromuscular block was inversely correlated with cholinesterase activity (Kendall rank correlation tau = -0.43, P = 0.005). The slight prolongation of neuromuscular block sh ould not be significant clinically. Implications: Postpartum patients have decreased amounts of the plasma cholinesterase enzyme. This would slow the metabolism of the muscle relaxant mivacurium. However, the d uration of muscle paralysis is only prolonged by approximately 3 min, which would not normally cause any significant problems.