Skin blood flow changes in anaesthetized humans: comparison between skin thermal clearance and finger pulse amplitude measurement.

The effect of general anaesthesia on skin blood flow in the left hand, measured by a new non-invasive probe using the thermal clearance method was examined. A mercury silastic gauge was placed around the third left finger and the plethysmographic wave amplitude was recorded to measure changes in finger pulse amplitude. Heart rate (HR), mean arterial blood pressure (MABP) and skin temperature were also recorded. General anaesthesia was induced by droperidol and phenoperidine injection and propanidid infusion in eight female patients. Skin thermal clearance, plethysmographic wave amplitude, HR, MABP and skin temperature were 0.40 +/- 0.02 w X m-1 degree C-1, 9 +/- 1 mm, 98 +/- 5 beats X min-1, 12.50 +/- 0.93 kPa and 33.3 +/- 3.4 degrees C respectively. The minimal value of MABP was 9.58 +/- 1.06 kPa, whereas skin thermal clearance, plethysmographic wave amplitude, HR and skin temperature increased to 0.45 +/- 0.02 w X m-1 degree C-1, 29 +/- 3 mm, 110 +/- 4 beats X min-1 and 34.4 +/- 0.4 degrees C. Changes in skin thermal clearance correlated well with plethysmographic wave amplitude. Statistically significant changes in these two parameters occurred before significant change in HR, MABP or skin temperature. The results show that the new non-invasive probe using the thermal clearance method appears to be a useful device for measuring cutaneous microcirculation in anaesthetized humans, and responds more quickly than change in skin temperature, which is a delayed effect of skin blood flow change. Our results also show that the intensity of cutaneous vasodilatation induced by general anaesthesia did not relate to the vascular tone before anaesthesia.