Perioperative Hemodynamic Events following Intrathecal Fentanyl versus Buprenorphine as Adjuvants to Hyperbaric Bupivacaine in Infraumbilical Surgery: A Prospective Observational Study

BACKGROUND: Hemodynamic instability is a recognized consequence of spinal anesthesia, but comparative evidence on intrathecal fentanyl and buprenorphine under routine clinical conditions remains limited. OBJECTIVE: To compare the incidence of hypotension and bradycardia and to explore the timing of these events with intrathecal fentanyl 25 μg versus buprenorphine 60 μg as adjuvants to hyperbaric bupivacaine in elective infraumbilical surgery. METHODS: This prospective observational study included 192 American Society of Anesthesiologists Physical Status I-II adults (96 per group). The attending anesthesiologist selected the adjuvant; there was no random allocation. Hypotension was defined as a reduction of 20% or more in mean arterial pressure from baseline. Crude comparisons were supplemented by modified Poisson regression for hypotension incidence and Cox regression for time to first hypotension, adjusted for recorded baseline covariates. RESULTS: Hypotension occurred in 59/96 (61.5%) fentanyl recipients and 50/96 (52.1%) buprenorphine recipients (crude relative risk [RR]: 1.18, 95% confidence interval [CI]: 0.92-1.51; P = 0.244). Median hypotension-free time was 27.5 versus 45.0 min, respectively, but the survival distributions were not statistically significantly different (log-rank P = 0.155). Fentanyl was not independently associated with hypotension incidence (adjusted RR: 1.18, 95% CI: 0.92-1.49; P = 0.188) or time to hypotension (adjusted HR: 1.41, 95% CI: 0.95-2.11; P = 0.091). Bradycardia and desaturation did not differ significantly. CONCLUSION: No statistically significant between-group difference in the incidence or time to hypotension was demonstrated. The numerically shorter median hypotension-free time with fentanyl remained nonsignificant after adjustment and should be considered hypothesis-generating. These findings neither establish equivalence nor support a fentanyl-specific monitoring schedule.