Low-dose bupivacaine: a comparison of hypobaric and near isobaric solutions for arthroscopic surgery of the knee

The results of studies on the effect of volume, concentration or total dose of local anaesthetic on che spread of spinal anaesthesia are inconclusive. Most support the assumption that the total dosage is more important than t he volume. We compared low-dose bupivacaine (6 mg) in 0.5% and 0.18% soluti ons as sole anaesthetic to achieve predominantly unilateral spinal anaesthe sia for knee arthroscopy. Sixty patients were randomly allocated to two gro ups to receive either 1.2 ml 0.5% bupivacaine (6 mg) (n = 30) or 3.4 ml 0.1 8% hypobaric bupivacaine (6.1 mg) (n = 30). Drugs were administered at the L3-4 interspace with the patient in the lateral position. Patients remained in this position for 30 min before being turned supine for the operation. Spinal block was assessed by pinprick and modified Bromage scale and compar ed between dir operated and nonoperated sides. No significant changes were found in the spread or duration of sensory or motor block (p > 0.05). The h aemodynamic changes were also similar between the groups. The same pinprick level of analgesia. degree of motor block and duration of spinal anaesthes ia was obtained with bupivacaine (6 mg) in low (1.2 ml) or high (3.1 ml) vo lumes.