Effect of spinal versus epidural anaesthesia with 0.5% bupivacaine on lower limb blood flow

Changes in the haemodynamics of the lower extremities, big toe temperature, blood pressure and heart rate were studied in 20 patients undergoing spinal or epidural anaesthesia for transurethral surgery. Calf blood flow was determined by strain gauge plethysmography (SGP) and Doppler ultrasound. Bupivacaine 0.5% was injected at the L3-L4 interspace, the dose being 3-4 ml (mean 3.6) in the spinal and 17-20 ml (mean 18.6) in the epidural group. The number of sensory blocked segments 30 min after anaesthesia was 12.7 +/- 0.7 (mean +/- s.e.mean) and 14.4 +/- 0.7, respectively. Only minor decreases in blood pressure were noted following the blocks. Heart rate remained virtually unchanged. The increase in skin temperature was more pronounced (P less than 0.01) following epidural (mean 8 degrees C) than spinal anaesthesia (mean 4 degrees C). In addition, the arterial blood flow was significantly higher (P less than 0.05) following epidural than spinal block (means 3.5 and 2.2 ml/100 ml/min, respectively). The venous capacity and maximum venous outflow remained practically unchanged in both groups. Obviously, epidural anaesthesia with bupivacaine causes a more intensive sympathetic block than does spinal anaesthesia. As probably no venous pooling occurred, when examined by SGP and Doppler ultrasound, neither of the blocks is likely to contribute to the initiation of deep vein thrombosis.