Effect of injection rate on hypotension associated with spinal anesthesia for cesarean section

Maternal hypotension is a common problem during cesarean section under spinal anesthesia. We evaluated in a prospective observational study the influence of injection speed on maternal hypotension. Hyperbaric bupivacaine 10 mg, sufentanil 2 microg and morphine 200 microg (total volume 4 mL) were injected either quickly (<15 s) or slowly (=120 s) in 50 women scheduled for elective cesarean section. Hypotension (systolic arterial pressure (SAP) <100 mmHg or <70% of baseline) was promptly treated with 5 mg ephedrine boluses. Slow injection significantly reduced the incidence of hypotension (68% in the 120 s group and 92% in the other, P =0.03). In addition, onset of hypotension was delayed, had a shorter duration and required less ephedrine for hypotension in the 120 s group (11.6 mg vs. 19.6 mg, P =0.019). Anesthesia was satisfactory for all women. We conclude that a 2 mL/min injection rate may be a simple and effective way to reduce the incidence and severity of hypotension during cesarean section under spinal anesthesia.