Augmentation of calf blood flow by epinephrine infusion during lumbar epidural anesthesia.

Lower rates of deep vein thrombosis after hip surgery performed under epidural anesthesia were noted in patients who received intravenous epinephrine infusion. To determine whether this effect could be mediated by enhanced lower extremity blood flow, 12 patients were studied immediately preoperatively. Calf blood flow increased from 3.7 +/- 1.6 to 5.0 +/- 2.2 mL.100 mL-1.min-1 with an intravenous epinephrine infusion (1.9 +/- 0.5 microgram/min). After epidural anesthesia calf blood flow increased to 6.3 +/- 3.3 mL.100 mL-1.min-1 with epinephrine infusion (2.7 +/- 1.0 micrograms/min) but was reduced to 2.6 +/- 1.5 mL.100 mL-1.min-1 when norepinephrine (0.8 +/- 0.7 microgram/min) was infused. Calf vascular resistance decreased from 27.7 +/- 13.5 to 7.9 +/- 4.6 mmHg.mL-1.100 mL-1.min-1 after epidural anesthesia with epinephrine (2.7 +/- 1.0 micrograms/min) but was unchanged when norepinephrine (0.8 +/- 0.7 microgram/min) was infused. The augmentation of lower extremity blood flow when epinephrine is used in conjunction with epidural anesthesia may in part explain the low frequency of deep vein thrombosis with conduction anesthesia.