Changes in blood flow and vascular resistance in the arm and leg during spinal anaesthesia and vasopressor therapy...

The effects of subarachnoid block with hyperbaric bupivacaine 0.5% on forearm and calf blood flow and vascular resistance were examined using venous occlusion plethysmography in 10 fit patients. Following blockade there was an increase in mean (SD) calf blood flow from 2.0 (0.4) to 2.6 (1.2) ml.100 ml-1.min-1 (p = 0.057), a decrease in mean (SD) calf vascular resistance from 55 (15) to 38 (14) R units (p < 0.01), a decrease in mean (SD) forearm blood flow from 3.1 (1.2) to 1.8 (0.9) ml.100 ml-1.min-1 (p < 0.01) and an increase in mean forearm vascular resistance from 38 (16) to 62 (24) R units (p < 0.01). Methoxamine 2 mg was administered intravenously when the mean arterial blood pressure decreased by 15%. There was a resultant marked increase in mean (SD) forearm blood flow from 1.8 (0.9) to 3.0 (0.8) ml.100 ml-1.min-1 (p < 0.001) but a decrease in mean (SD) calf blood flow from 2.6 (1.2) to 2.1 (1.4) ml.100 ml-1.min-1 (p = 0.11). Correspondingly, the mean (SD) forearm vascular resistance decreased from 62 (24) to 46 (17) R units (p < 0.01) with an increase in mean (SD) calf vascular resistance from 38 (14) to 56 (22) R units (p < 0.01). These findings indicate that whereas methoxamine produces the anticipated constrictor response in the calf vessels it causes a simultaneous reduction in vascular resistance in the forearm.