A comparison of mivacurium infusion requirements between young and elderly adult patients.

Forty-one patients of ASA classes I or II, undergoing elective surgery, were divided into two groups: young, 18-41 years (mean 31), and elderly, 64-79 years (mean 71). The integrated evoked compound electromyogram of the adductor pollicis muscle elicited by stimulation of the ulnar nerve was used to monitor the neuromuscular block of the non-depolarizing muscle relaxant mivacurium. An initial dose of mivacurium 0.15 mg kg-1 allowed six excellent, nine good, three adequate and three poor intubations in the young group, and nine excellent, eight good, three adequate and no poor intubations in the elderly group. Patients recovered until 1-2 stimuli of the train-of-four were visible, and an infusion of mivacurium was started (0.5 mg kg-1 h-1). At 3 min intervals the rate was adjusted by +/- 0.05 mg kg-1 h-1 (+/- 10% initial rate), as indicated during anaesthesia which was provided by nitrous oxide in oxygen, infusion of propofol, and fentanyl supplements. In the first 30 min, the young group had their mivacurium requirement increased to 111.4% (0.56 mg kg-1 h-1), which was reached in the first 15 min, after which it gradually decreased to 92.9% (0.46 mg kg-1 h-1). The elderly group's requirements decreased from the start, to 78.5% (0.39 mg kg-1 h-1). The difference between the two groups was significant (P < 0.05). After the first 30 min, both groups requirements decreased, with time, but with no statistically significant differences.