A defasciculating dose of d-tubocurarine causes resistance to succinylcholine

Forty-four patients, ASA physical status I or II, undergoing thiamylal, fentanyl, N2O/O₂ anaesthesia were studied to determine the dose-response to succinylcholine (Sch) without prior defasciculation (24 pt -Group I), or three minutes following d-tubocurarine (dTC), 0.043 mg · kg^-1 (20 pt -Group 2). The individual log dose-logit response curve for each patient was determined using a cumulative dose plus infusion technique and integrated EMG monitoring of the first dorsal interosseous muscle. The mean (±SEM) ED₅₀, ED₉₀ and ED₉₅ values for Sch in Group I were 0.13 ±0.01, 0.19 ±0.01 and 0.22 ±0.01 mg · kg^-1, and in Group 2 were 0.16 ±0.01, 0.25 ±0.01 and 0.29 ±0.02 mg · kg^-1, respectively. The mean ED values in Group 2 were significantly greater than the equivalent values in Group 1 (P < 0.05). Compared with values in Group I, ED values in Group 2 represented mean increases of 23, 32, and 32 per cent, respectively. These pharmacodynamic data indicate that the dose of Sch needs to be increased by 32 per cent following a defasciculating dose of dTC 3 mg · 70 kg^-1 (0.043 mg · kg^-1).