Ventilatory effects of subarachnoid fentanyl in the elderly

Twenty-eight elderly patients scheduled for urological surgery were randomly assigned to receive, in a double-blind study, subarachnoid hyperbaric bupivacaine 15 mg with 50 micrograms (group A, n = 7), 25 micrograms (group B, n = 7), or 12.5 micrograms (group C, n = 7) of fentanyl or 1 ml of saline (group D, n = 7) in a total volume of 4 ml. The pattern of breathing and the ventilatory response to CO2 were studied before and 90, 150 and 480 min after the subarachnoid injection. In group A, mild pruritus and sedation occurred in five patients, while nausea, vomiting and periodic breathing occurred in two. In group B, mild pruritus and sedation were observed in four patients, while nausea and vomiting occurred in two. No significant differences in minute ventilation, respiratory drive and respiratory timing were observed between the groups. Patients receiving fentanyl 50 micrograms showed a percentual change from baseline values as function of time (slope VE/PE'CO2) significantly below baseline at 90 and 150 min (p less than 0.05). However, the baseline values in this group reverted after 480 min. No side effects were observed in groups C or D. It is concluded that subarachnoid fentanyl 50 micrograms can cause an early respiratory depression and its use as a postoperative analgesic should be avoided in the elderly.