Peripheral Muscle Near-Infrared Spectroscopy (NIRS) Variables are Altered Early in Septic Shock

Noninvasive evaluation of muscle perfusion using near-infrared spectroscopy (NIRS) coupled with a vascular occlusion test (VOT) may provide an early and simple marker of altered perfusion and microcirculatory function in sepsis.The aim of the study was to compare the time-course of NIRS-derived variables with systemic measures of perfusion in an experimental model of peritonitis.Peritonitis was induced in eight anesthetized, mechanically ventilated, adult sheep (24-34 kg), by injecting autologous feces into the peritoneal cavity. Animals were followed until death or for a maximum of 30 h. Muscle tissue oxygen saturation (StO2) was determined using NIRS on the right posterior leg and arterial VOTs were performed by intermittent intra-aortic balloon inflation. Microdialysis was used to measure muscle lactate and pyruvate levels.Muscle StO2 was significantly lower than baseline values from 8 h after sepsis induction, but with considerable intersubject variability. The NIRS VOT ascending (Asc) slope decreased to values 2 mmol/L in most of the animals only 24 and 28 h after sepsis induction, respectively. Muscle NIRS StO2 correlated strongly with femoral venous oxygen saturation (r = 0.820) and moderately with SvO2 (r = 0.436).The muscle NIRS Asc slope after a VOT is altered earlier than global markers of tissue hypoperfusion during sepsis. This simple noninvasive test can detect early changes in peripheral perfusion in sepsis.