EFFECTS OF EPIDURAL TEST DOSE VOLUME ON SKIN PERFUSION, TEMPERATURE, AND REFLEX VASOCONSTRICTION

Background and Objectives. The authors sought to define the effects of differing volumes of epidural test dose on skin perfusion, skin tempe rature, and reflex vasoconstriction to a maximal inspiration (inspirat ory gasp vasoconstrictive response, IGVR). Methods. With informed cons ent and Institutional Review Board approval, the authors studied 40 pa tients undergoing epidural anesthesia. Skin perfusion was monitored in glabrous skin on the foot using laser Doppler. Inspiratory gasp vasoc onstrictive response and temperature measurements were obtained at 1-m inute intervals. After a baseline period, 5 patients received 60 mg in travenous lidocaine HCl; 5 received 5 mt normal saline, via epidural c atheter; and 30 patients received 50 mg lidocaine HCl and 20 mcg epine phrine in 2.5, 5.0, or 7.5 mt normal saline (10 patients each). Inspir atory gasp vasoconstrictive response was defined as the percent change in perfusion from baseline produced by an inspiratory gasp. Perfusion was normalized by expressing each patient's value as a percentage of the respective baseline value. Results. Significant increases in perfu sion, of up to 169% of baseline, were seen 12 minutes after the test d ose. Inspiratory gasp vasoconstrictive response showed significant cha nges from baseline in all test groups. The temperature change was insi gnificant. Control groups did not show perfusion or IGVR changes. Conc lusions, Skin perfusion and IGVR changed significantly after epidural test dose; the minimal effect of volume appears to be 5 mt of lidocain e-epinephrine solution; the presence of IGVR or perfusion changes, or both, are positive predictors of successful placement of the catheter into the epidural space; and temperature changes as observed here were not reliable predictors of proper placement of epidural catheters.