Frequency of hypotension during conventional or asymmetric hyperbaric spinal block

Background and Objectives. The purpose of this randomized, double-blind stu dy was to evaluate if use of an asymmetric spinal block affects the inciden ce of hypotension during spinal anesthesia. Methods. With Ethical Committee approval and patient consent, 120 patients undergoing lower limb surgery w ere placed in the lateral position with the side to be operated on dependen t, and received 8 mg 0.5% hyperbaric bupivacaine through a 25-gauge Whitacr e spinal needle. Patients were randomized to one of two groups: (a) local a nesthetic was injected with barbotage through a cranially directed needle o rifice, then patients were immediately turned to supine (conventional, n = 60); (b) local anesthetic was injected without barbotage with the needle or ifice turned toward the dependent side, then the lateral position was maint ained for 15 minutes (unilateral, n = 60). A blind observer recorded noninv asive hemodynamic variables, as well as loss of cold and pinprick sensation and motor block on both sides. Results. In the unilateral group, 31 patien ts (52%) showed a unilateral loss of cold sensation and 48 patients (80%) h ad no motor block on the nondependent side for the duration of the study, w hereas 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 min utes and 60 +/- 18 minutes) than in the unilateral group (22 +/- 8 minutes and 67 +/- 19 minutes) (P < .05 and P < .05, respectively). The incidence o f hypotension (SAP decrease >30% from baseline) was higher in the conventio nal (22.4%) than unilateral group (5%) (P < .01). The maximum percentage ch anges from baseline values of systolic arterial blood pressure and heart ra te were greater in conventional group (-28% +/- 16% and -19% +/- 10%) than in unilateral group (-8% +/- 16% and -12% +/- 18%) (P < .0001 and P <.01, r espectively). Conclusions. Achieving an asymmetric distribution of spinal b lock by injecting a small dose of 0.5% hyperbaric bupivacaine through a Whi tacre spinal needle into patients placed in the lateral position for 15 min reduces the incidence of hypotension during spinal anesthesia.