Low dose hyperbaric bupivacaine for unilateral spinal anaesthesia

Purpose: To evaluate the effects of hyperbaric bupivacaine concentration in producing unilateral spinal anaesthesia. Methods: With Ethical Committee approval and written consent, 60 patients undergoing lower limb surgery were placed in the lateral position with the side to be operated on dependent. After dural puncture (25-gauge Whitacre spinal needle), the needle hole was turned toward the dependent side and patients were randomly assigned to receive 8 mg of either 0.5% (Group_0.5% n = 30) or 1% (Group₁%, n = 30) hyperbaric bupivacaine. The lateral position was maintained for 15 min, while a blinded observer recorded loss of pinprick sensation and degree of motor block on both sides until two segment regression of sensory level on the dependent side. Results: At the end of the 15 min lateral position spinal anaesthesia was more frequently unilateral in Group_0.5% (80%) than in Group₁% (53%)(P <0.05). However, 30 min after patients were turned supine, unilateral spinal anaesthesia decreased to 60% of cases in Group_0.5% and 40% of cases in Group₁% (P = NS). The maximum sensory level on the dependent side [T₁₀ (L₁ -T₂) in Group_0.5% and T₈ (T₁₂ - T₃) in Group₁%], time to reach it [20 (5 - 30) min in Group_0.5% and 25 (10 - 35) min in Group₁%], and time to two segment regression of sensory level [80 (30 - 135) min in Group_0.5% and 75 (20 - 135) min in Group₁%] were similar in both groups. Conclusion: Highly concentrated solutions of hyperbaric bupivacaine are not advantageous in obtaining a unilateral spinal anaesthesia, when a small anaesthetic dose is injected slowly through a Whitacre spinal needle.