Skin Vasomotor Reflex as an Objective Indicator to Assess the Level of Regional Anesthesia

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Abstract
We examined whether the absence of a skin vasomotor reflex (SVmR), which represents a sympathetic vasoconstrictive response to various stimuli, is an objective indicator of a somatosensory blockade.Skin blood flow was measured by using a laser Doppler flowmeter on the index finger tip. The somatosensory blockade level was determined in 15 patients under subarachnoid anesthesia. A cold stimulus, an ice cube applied to the skin, was repeated sequentially at each dermatome from L3 cephalad. The uppermost dermatome with negative response (the SVmR cold level) was determined, and the SVmR pain level was determined similarly using an electrical impulse (20-mA, 50-Hz, 0.25-ms square wave). The SVmR cold level and the SVmR pain level showed significant correlation with the conventionally assessed cold level (r = 0.83) and the pinprick level (r = 0.96). We conclude that the SVmR is useful to objectively estimate the level of somatosensory block induced by regional anesthesia. Implications: We evaluated the absence of decrease in skin blood flow after various stimuli as an indicator of somatosensory blockade. In patients under subarachnoid anesthesia, the uppermost level with negative response showed significant correlation with the conventionally assessed blockade level. This method is useful for objective assessment of regional anesthesia level. (Anesth Analg 1998;86:336-40)