Background and Objectives Hyperbaric local anesthetic pools in the thoracic spinal curvature in supine patients. The authors hypothesized that patients receiving 12 or 15 mg of hyperbaric bupivacaine would achieve similar levels of sensory block but the spinal anesthetic would be denser and longer lasting in patients receiving the 15 mg dose.

Methods Twenty eight healthy term parturients scheduled for elective cesarean delivery randomly received 12 or 15 mg hyperbaric 0.75% bupivacaine in 8.25% dextrose. Patients were in the right lateral position during drug injection and were then positioned supine with left uterine displacement on a horizontal operating table. A blinded anesthesiologist assessed the dermatome level of sensory analgesia to pinprick every 2 minutes for 20 minutes, then every 15 minutes until the sensory level regressed to T10.

Results The mean level of sensory anesthesia was 2.2 spinal segments higher in patients receiving 15 mg versus 12 mg hyperbaric bupivacaine (24.8 ± 3.7 versus 22.6 ± 1.4 spinal segments; P = .031). Regression to T10 occurred more quickly in the 12 mg than in the 15 mg group (140.0 ± 16.5 versus 162.1 ± 33.8 minutes, P = .046). Patient height did not correlate with the maximum number of spinal segments blocked in either group. All patients had adequate surgical anesthesia.

Conclusions Parturients receiving 15 mg of hyperbaric bupivacaine developed a higher mean level and longer duration of sensory analgesia than those receiving 12 mg.