Succinylcholine neuromuscular blockade in subjects heterozygous for abnormal plasma cholinesterase.

The relationship between plasma cholinesterase genotype and duration and type of succinylcholine neuromuscular blockade was studied in 43 anesthetized patients heterozygous for abnormal plasma cholinesterase using train-of-four nerve stimulation. Twenty-eight patients were heterozygous for the usual and the atypical gene (E1uE1a), eight were heterozygous for the usual and the silent gene (E1uE1s), three were heterozygous for the usual and the fluoride-resistant gene (E1uE1f), three were heterozygous for the fluoride-resistant and the atypical gene (E1fE1a), and one was heterozygous for the fluoride-resistant and the silent gene (E1fE1s). Mean time to 90 per cent recovery of twitch height in patients with genotypes E1uE1a, E1uE1s, and E1uE1f (14.6, 12.4, and 12.0 min, respectively) was significantly prolonged compared to patients with normal cholinesterase genotype (9.3 min). No significant difference was found between the three groups of patients with one abnormal gene (E1uE1a, E1uE1s, and E1uE1f). In 13 (46 per cent) of the 28 patients with genotype E1uE1a the twitch height did not return to control for more than 15 min after the administration of succinylcholine and in three patients (10.7 per cent) for more than 20 min after succinylcholine. The four patients with abnormal genes on both chromosomes (E1fE1a and E1fE1s) all showed significantly prolonged paralysis following the administration of succinylcholine (mean time to 90 per cent twitch recovery was 30 min). Patients heterozygous for the usual and one of the abnormal genes (E1uE1a, E1uE1s, and E1uE1f) had typically depolarizing blocks following the administration of succinylcholine, 1 mg/kg. Patients with abnormal genes on both chromosomes (E1fE1a and E1fE1s), however, all showed desensitization type of neuromuscular blockade (phase II block).