PROLONGED NEUROMUSCULAR BLOCKADE AND DIFF ERENT REVERSAL EFFECTS FOLLOWING SUCCESSIVE EXPOSURE TO COMBINED VECURONIUM AND SUCCINYLCHOLINE IN A PATIENT WITH ATYPICAL PLASMA CHOLINESTERASE

An 81-year-old patient had prolonged competitive neuromuscular blockad e with train-of-four ratios of 0.1 and 0.5, respectively, after two su ccessive anaesthesia procedures (enflurane-N20/02; vecuronium-succinyl choline-sequence) for transurethral prostate resection. Although antag onism with neostigmine was promptly successful after the first, 65-min period of anaesthesia (1.5 mg vecuronium for precurarization, 100 mg succinylcholine for intubation, 3 mg vecuronium), repetitive and chron ologically staggered administration of neostigmine after the second, 3 0-min period of anaesthesia (1 mg vecuronium for precurarization, 100 mg succinylcholine for intubation) had hardly any effect, so that the patient had to be ventilated mechanically for a total of 4.5 h. Labora tory analysis revealed homozygous, atypical, plasma cholinesterase (79 0 U/1; dibucaine number 23; genotype E1(a)E1a). This retrospectively c onfirmed a succinylcholine-induced phase II block in both instances, a s had already been suspected following the second anaesthetic procedur e. The degree of block transformation, and thus the available time, ar e decisive in explaining the diverse effects of antagonism here. it mu st be assumed that a complete phase II block developed after the first succinylcholine exposure owing to the longer duration of anaesthesia; the purely competitive component (train-of-four ratio 0.1) was easily antagonized by neostigmine. At the time of the attempted antagonism a fter the second, shorter period of anaesthesia, however, block transfo rmation was still incomplete (train-of-four ratio 0.5). The administra tion of neostigmine therefore rather intensified the depolarization se gment of the mixed block, so that repeated attempts at antagonism then inhibited any further block transformation.