Dynamics of skin blood flow in human sepsis

Abstract

The study was undertaken to determine if sepsis alters the pattern of vasomotion and reactive hyperaemia in the skin. This was a prospective, observational study. The study was performed in the medical and surgical intensive care units of a tertiary referral hospital. 11 patients with sepsis (using Bone's criteria [1]), were compared with 19 patients recovering from coronary artery bypass grafting who were used as non-septic controls. Nineteen normal volunteers were also studied. Skin blood flow was measured on the forearm using laser Doppler flowmetry at rest and after 2 min arterial occlusion with a tourniquet. The resting blood signal was analyzed by calculating the mean skin blood flow, the power of the skin blood flow signal (variance) and the power spectrum. The rate of recovery after arterial occlusion was determined by calculating the peak increase in skin blood flow and the time constant of the decay of skin hyperaemia back to baseline flow. Patients with sepsis had a mean skin blood flow of 6.24 (3.48) ml min-1 per 100 g tissue compared with 4.35 (1.41) ml min-1 per 100 g tissue for the patients after coronary artery bypass grafting (p < 0.05). The septic patients also showed a marked increase in the fraction of total power in the 0.1-0.15 Hz frequency band (0.19 (0.17) versus 0.068 (0.033), p < 0.05), a decreased peak hyperaemic response (40 (23)% increase in flow above baseline after cuff release versus 147 (19)%) and a prolonged time constant for recovery from hyperaemia (22.8 (12.7) versus 11.7 (8.5) seconds, p < 0.05). These results imply an increased local rather than central control of skin blood flow. The laser Doppler flowmeter allows local rather than global haemodynamics to be studied. Abnormalities of skin blood flow control are found in sepsis, and this technique may prove useful to monitor the effects of treatment, especially if the use of laser Doppler flowmetry can be extended to other organs at risk of damage during sepsis such as gastro-intestinal mucosa.