Succinylcholine pharmacodynamics in peripartum patients.

Serum cholinesterase activity decreases 30% during pregnancy and remains depressed during the postpartum period. However, succinylcholine recovery is not prolonged in term-pregnant patients. This contrasts with results obtained in other patients with decreased serum cholinesterase activity. To better understand this paradox, the authors compared serum cholinesterase activity and recovery from succinylcholine, 1 mg/kg, in nonpregnant (with and without oral contraceptive use), in term-pregnant, and in postpartum patients. Serum cholinesterase activity was lower in both term-pregnant (3.66 +/- 0.39 U/ml, means +/- SE) and postpartum (2.84 +/- 0.35 U/ml) patients than in nonpregnant patients not taking oral contraceptives (5.01 +/- 0.33 U/ml, P less than 0.05). Cholinesterase activity in postpartum patients also was significantly lower than in nonpregnant patients taking oral contraceptives (4.81 +/- 0.63, P less than 0.05). In contrast, the time to 25% twitch-height recovery did not differ between term-pregnant (470 +/- 56 s) and nonpregnant patients taking (499 +/- 29 s) or not taking (501 +/- 21 s) oral contraceptives, but was significantly increased in postpartum patients (685 +/- 22 s, P less than 0.001). The similar duration of action of succinylcholine in term-pregnant patients (with decreased serum cholinesterase activities) and nonpregnant patients may be related to the increased volume of distribution of succinylcholine at term.