SKIN VASOMOTOR REFLEX AS AN OBJECTIVE INDICATOR TO ASSESS THE LEVEL OF REGIONAL ANESTHESIA

We examined whether the absence of a skin vasomotor reflex (SVmR), whi ch represents a sympathetic vasoconstrictive response to various stimu li, is an objective indicator of a somatosensory blockade, Skin blood flow was measured by using a laser Doppler flowmeter on the index fing er tip. The somatosensory blockade level was determined in 15 patients under subarachnoid anesthesia. A cold stimulus, an ice cube applied t o the skin, was repeated sequentially at each dermatome from L3 cephal ad. The uppermost dermatome with negative response (the SVmR cold leve l) was determined, and the SVmR pain level was determined similarly us ing an electrical impulse (20-mA, 50-Hz, 0.25-ms square wave). The SVm R sold level and the SVmR pain level showed significant correlation wi th the conventionally assessed cold level (r = 0.83) and the pinprick level (r = 0.96). Mie conclude that the SVmR is useful to objectively estimate the level of somatosensory block induced by regional anesthes ia. Implications: We evaluated the absence of decrease in skin blood f low after various stimuli as an indicator of somatosensory blockade. I n patients under subarachnoid anesthesia, the uppermost level with neg ative response showed significant correlation with the conventionally assessed blockade level. This method is useful for objective assessmen t of regional anesthesia level.