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

ObjectiveTo measure muscle blood flow (Qtis) and oxygen consumption (VO2tis) in septic and non-septic critically ill patients by near-infrared spectroscopy (NIRS).SettingSurgical intensive care unit of a university hospital.Patients and participantsFour patients with septic shock, eight post-surgical critically ill patients and ten healthy volunteers.Measurements and resultsOxyhaemoglobin (HbO2) and deoxyhaemoglobin (HbH) variations after venous occlusion were measured by NIRS in the brachioradialis muscle. We calculated Qtis by the rate of HbO2 and HbH increase in the first 30 s of venous occlusion divided by haemoglobin blood concentration. VO2tis 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 = HbO2/(HbO2+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. VO2tis 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.ConclusionIn septic-shock patients the increase in VO2tis was associated with an equivalent increase in Qtis. Therefore, tissue O2 supply does not seem to be a limiting factor for muscle O2 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.