Thoracic sympatholysis with epidural blockade assessed by quantitative measurement of cutaneous blood flow.

Abstract

Quantifying sympathetic activity is difficult. Direct measurement is possible and superior to indirect techniques, but nerves to internal organs are not accessible in humans. Recently, we validated a quantitative technique for measurement of cutaneous blood flow using heat as an indicator. The aim of the study was to investigate whether sympatholysis during thoracic epidural blockade (TEA) may be documented by changes in regional cutaneous blood flow. A secondary aim was to assess whether, during TEA, local heating itself enhances regional blood flow. Six patients scheduled for elective coronary artery bypass grafting (CABG) were studied. An epidural catheter was inserted at the T2-3 interspace. Measurements were performed with an electrode, which can measure the local temperature of the skin. The probe is covered with a thermostatically controlled cap to avoid a thermic gradient to air. As a result of the cap, a change in temperature of the central disc depends almost solely on the blood flow in the underlying tissue. Regional cutaneous blood flow rates were measured before and after epidural anesthesia with and without local heating. All patients had a sensory blockade covering at least T1-5. Cutaneous blood flow increased in all six patients after blockade (13.6 ml/min/100 g, range 10.6-14.6 vs. 18.4 ml/min/100 g, range 13.9-24.5; P<0.05). Local heating did not further enhance blood flow. High TEA is associated with a uniform increase in thoracic cutaneous blood flow, and is suggestive of regional sympatholysis. Quantitative measurements of skin blood flow appear promising for documenting regional sympatholysis during TEA.