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The purpose of this randomized, double-blind study was to evaluate if use of an asymmetric spinal block affects the incidence of hypotension during spinal anesthesia.With Ethical Committee approval and patient consent, 120 patients undergoing lower limb surgery were placed in the lateral position with the side to be operated on dependent, and received 8 mg 0.5% hyperbaric bupivacaine through a 25-gauge Whitacre spinal needle. Patients were randomized to one of two groups: (a) local anesthetic was injected with barbotage through a cranially directed needle orifice, then patients were immediately turned to supine (conventional, n = 60); (b) local anesthetic was injected without barbotage with the needle orifice turned toward the dependent side, then the lateral position was maintained for 15 minutes (unilateral, n = 60). A blind observer recorded noninvasive hemodynamic variables, as well as loss of cold and pinprick sensation and motor block on both sides.In the unilateral group, 31 patients (52%) showed a unilateral loss of cold sensation and 48 patients (80%) had no motor block on the nondependent side for the duration of the study, whereas all conventional patients had bilateral distribution of spinal block (P.0001). The onset time and two-segment regression of sensory block on the dependent side were more rapid in the conventional group (18 +/- 7 minutes and 60 +/- 18 minutes) than in the unilateral group (22 +/- 8 minutes and 67 +/- 19 minutes) (P.05 and P.05, respectively). The incidence of hypotension (SAP decrease30% from baseline) was higher in the conventional (22.4%) than unilateral group (5%) (P.01). The maximum percentage changes from baseline values of systolic arterial blood pressure and heart rate were greater in conventional group (-28% +/- 16% and -19% +/- 10%) than in unilateral group (-8% +/- 16% and -12% +/- 18%) (P.0001 and P.01, respectively).Achieving an asymmetric distribution of spinal block by injecting a small dose of 0.5% hyperbaric bupivacaine through a Whitacre spinal needle into patients placed in the lateral position for 15 min reduces the incidence of hypotension during spinal anesthesia.