ONSET AND DURATION OF ACTION OF VECURONIUM IN THE ELDERLY - COMPARISON WITH ADULTS

The onset and duration of action of vecuronium were studied in young adult (n = 30; mean age 34 +/- 11.1 (s.d.) yr), middle-aged (n = 20; mean age 60 +/- 5.8 yr) and elderly patients (n = 30; mean age 80 +/- 4.6 yr) anaesthetised with thiopentone, nitrous oxide in oxygen and halothane. Neuromuscular block was monitored by applying the train-of-four (TOF) stimulation at 2 Hz to the ulnar nerve every 12 s. Half the patients in each group received 0.08 and the other half 0.12 mg kg-1 of the relaxant. The time to return of T1 (first response in the TOF sequence) to 25% of control was 28 +/- 5.2 (s.d.), 34 +/- 7.1 and 39 +/- 10.2 min following 0.08 mg kg-1 dose (P < 0.05 between the elderly and young adults) and 45 +/- 9.2, 48 +/- 6.2 and 69 +/- 19.2 min following 0.12 mg kg-1 dose, respectively, in the three age groups (P < 0.05 between the elderly and the other two groups). The recovery indices (time for 25-75% recovery of T1) after the 0.08 mg kg-1 was 9.6 +/- 3.4, 13.6 +/- 5.1 and 17.4 +/- 6.1 min, respectively (P < 0.05 between the elderly and young adults). There was no significant difference in any of the parameters between the young adults and the middle-aged. The onset of block at each dose was not significantly different between the three age groups; however, the time to maximum effect was significantly shorter with the higher dose in the young and the middle-aged, but not in the elderly. Regression analysis of the data between age and the duration of action and recovery index suggested a significant prolongation (P < 0.05) of these parameters in the elderly.