Spinal anesthesia with bupivacaine, typically used for elective and emergency cesarean section, is associated with a significant incidence of hypotension resulting from sympathetic blockade. A variety of dosing regimens have been used to administer spinal anesthesia for cesarean section. The objective of this study was to compare the incidence of hypotension following two different fixed dosing regimens.

This was a randomized double-blind clinical trial with a two-sided design, 5% significance level and 80% power. After approval of the hospital ethics review committee, 60 patients were divided randomly into two groups. In one group, the local anesthetic dose was adjusted according to height and weight, and in the other, the dose was adjusted according to height only.

Sixty women with a singleton pregnancy were included. Of the factors that could affect dose and blood pressure, including age, weight, height, and dose, only height differed between the groups. Mean heart rate was similar between the groups. Hypotension was significantly more frequent with dosage based on height alone than with two-factor dose calculation (56.7% vs. 26.7%; P = 0.018).

Adjusting the dose of isobaric bupivacaine to a patient's height and weight provides adequate anesthesia for elective cesarean section and is associated with a decreased incidence and severity of maternal hypotension and less use of ephedrine.