Effects of epidural test dose volume on skin perfusion, temperature, and reflex vasoconstriction

Background and Objectives. The authors sought to define the effects o f differing volumesof epidural test dose on skin perfusion, skin temperature, and reflex vasoconstriction to a maximal inspiration (inspiratory gasp vasoconstrictive response, IGVR). Methods. With informed consent and Institutional Review Board approval, the authors studied40 patients undergoing epidural anesthesia. Skin perfusion was monitored in glabrousskin on the foot using laser Doppler. Inspiratory gasp vasoconstrictive response andtemperature measurements were obtained at 1-minute intervals. After a baseline period,5 patients received 60 mg intravenous lidocaine HC1; 5 received 5 mL normalsaline, via epidural catheter; and 30 patients received 50 mg lidocaine HC1 and 20meg epinephrine in 2.5, 5.0, or 7.5 mL normal saline (10 patients each). Inspiratorygasp vasoconstrictive response was defined as the percent change in perfusion frombaseline produced by an inspiratory gasp. Perfusion was normalized by expressingeach patient's value as a percentage o f the respective baseline value. Results. Significantincreases in perfusion, o f up to 169% o f baseline, were seen 12 minutes after thetest dose. Inspiratory gasp vasoconstrictive response showed significant changes frombaseline in all test groups. The temperature change was insignificant. Control groupsdid not show perfusion or IGVR changes. Conclusions. Skin perfusion and IGVRchanged significantly after epidural test dose; the minimal effect o f volume appearsto be 5 mL o f lidocaine-epinephrine solution; the presence o f IGVR or perfusionchanges, or both, are positive predictors o f successful placement o f the catheter intothe epidural space; and temperature changes as observed here were not reliable predictorsof proper placement o f epidural catheters. Reg Anesth 1994: 19: 52-58. Key words: anesthetic technique, epidural, anesthetics, local, lidocaine, inspiratorygasp vasoconstrictive response (IGVR), measurement technique, laser Doppler flovvmetry.