Abstract: Objective To investigate the muscle relaxation by a loading dose followed repeat of rocuronium in elderly patients with ASA Ⅱ-Ⅲ including longevity old patients ≥90 years, middle old patients 75-89 years and young old patients 60-74 years and in middle-aged patients 45-59 years with ASA Ⅱ. Methods Longevity old patients (n=20), middle old patients (n=20) and young old patients (n=20) were investigated with middle-aged patients (n=20) as control. Anesthesia was induced with intravenous midazolam 0.02 mg/kg, sufentanyl 0.4 μg/kg and propofol 1.5-2.0 mg/kg. Intubation was done after the first twitch (T₁) disappeared following train of four stimuli after a loading dose of rocuronium 0.5 mg/kg intravenously within 10 seconds. Anesthesia was maintained with propofol at a rate of 5-12 mg/(kg·h) by infusion pump with intravenous bolus of sufentanyl. The first twitch (T_c) as control was measured before rocuronium was administered. Muscle relaxation was maintained with increment of rocuronium 0.1 mg/kg when T₁ returned to 25% of T_c. Results ①There was significant difference in onset time, no response time and time of 25% recovery of T₁/T_c after induction dose of rocuronium between elderly patients and middle-aged patients (P<0.05). Onset time was shorter in elderly patients than in middle-aged patients (P<0.05) which related with age, and shortest in longevity old patients. No response time and time of 25% reco-very of T₁/T_c were longer in elderly patients than in middle-aged patients (P<0.05), and longest in longevity old patients. ②No response time and time of 25% recovery of T₁/T_c increased with increasing in numbers of incremental doses. The duration was longer in elderly patients than in middle-aged patients which related with age. ③Neostigmine shortened the time of 75% recovery of T₁/T_c in all of the patients significantly (P<0.05). Duration of 75% recovery of T₁/T_c was longer in elderly patients than in middle-aged patients which related with age. Conclusions Onset time of rocuronium was shorter in elderly patients including longevity old patients, middle old patients and young old patients than in middle-aged patients. No response time and time of 25% recovery of T₁/T_c were longer in elderly patients than in middle-aged patients. The duration increased with increasing numbers of incremental doses.

Key words: Rocuronium, Elderly, Neuromuscular blockade, Dose-response relationship