Effect of d-tubocurarine pretreatment on succinylcholine twitch augmentation and neuromuscular blockade.

Subparalyzing doses of d-tubocurarine (dTC) given before succinylcholine decrease the duration of neuromuscular blockade. In animal preparations, they also abolish succinylcholine-induced twitch augmentation, defined as a greater-than-maximal contraction in response to a single stimulus. To determine quantitatively the effect of dTC on succinylcholine potency and on twitch augmentation in humans, 60 adult patients, ASA physical status I or II, were assigned randomly to receive either 0.05 mg/kg of dTC or saline 2 min before induction of anesthesia with fentanyl and thiopental. Train-of-four stimulation was applied every 12 s to the ulnar nerve and the force of contraction of the adductor pollicis muscle was measured. One minute after induction of anesthesia, 0.15, 0.20, 0.25, 0.35, or 0.50 mg/kg of succinylcholine was given. The height of the first twitch (T1) reached 121% +/- 6% (mean +/- SEM) of control without dTC, and was virtually abolished by dTC pretreatment (105% +/- 1%, P less than 0.01). Twitch augmentation was more noticeable with lower doses of succinylcholine, and was not observed in the response to the fourth stimulus of the train of four (T4). The potency of succinylcholine was decreased by approximately one-half in the dTC-pretreated groups. The ED50 was 0.27 +/- 0.04 mg/kg without dTC and 0.50 +/- 0.06 mg/kg with dTC (P less than 0.002). The corresponding values for ED90 were 0.51 +/- 0.07 and 1.02 +/- 0.12 mg/kg, respectively (P less than 0.02). The ED95 values were 0.63 +/- 0.09 and 1.28 +/- 0.15 mg/kg, respectively (P less than 0.02). The slopes of the regression lines did not deviate significantly from parallelism.(ABSTRACT TRUNCATED AT 250 WORDS)