Muscle perfusion and oxygen consumption by near-infrared spectroscopy in septic-shock and non-septic-shock patients

Objective. To measure muscle blood flow (Qtis) and oxygen consumption (VO(2)tis) in septic and non-septic critically ill patients by near-infrared spectroscopy (NIRS). Setting. Surgical intensive care unit of a university hospital. Patients and participants. Four patients with septic shock, eight post-surgical critically ill patients and ten healthy volunteers. Measurements and results. Oxyhaemoglobin (HbO(2)) and deoxyhaemoglobin (HbH) variations after venous occlusion were measured by NIRS in the brachioradialis muscle. We calculated Qtis by the rate of HbO(2) and HbH increase in the first 30 s of venous occlusion divided by haemoglobin blood concentration. VO(2)tis was calculated by subtraction of the arterial HbH from the initial increase of HbH after venous occlusion extrapolated to 1 min. Tissue oxygenation index [TOI = HbO(2)/(HbO(2)+HbH)] was also measured before venous occlusion. Two measurements in patients with septic shock, and one measurement in non-septic-shock patients and healthy subjects, were obtained. Of the measurements, 35% were repeated because of low-quality NIRS signal. VO(2)tis and Qtis were two times larger (P<0.05) in patients with septic shock than in patients without and in healthy subjects. The TOI was very similar among the three groups. Conclusion. In septic-shock patients the increase in VO(2)tis was associated with an equivalent increase in Qtis. Therefore, tissue O-2 supply does not seem to be a limiting factor for muscle O-2 consumption. NIRS combined with venous occlusion allows a rapid, non-invasive and simultaneous assessment of regional perfusion and oxygen consumption. In case of microcirculatory shunt occurrence, the TOI should be cautiously used to assess tissue oxygenation state.