Near-infrared spectroscopy measurement of regional tissue oxyhemoglobin saturation during hemorrhagic shock

Adequate resuscitation of patients from shock states depends on restoration of oxygen delivery (DO2) to tissues. Direct measurement of systemic DO2 du ring shock states requires invasive techniques such as pulmonary artery cat heterization. These experiments were performed to examine the ability of ne ar-infrared spectroscopy (NIRS), to measure regional tissue oxygenation in a large-animal model of hemorrhagic shock, and to compare these measures to global measures of oxygen delivery. Splenectomized female pigs (n=11) were anesthetized, instrumented, and monitored. NIRS probes were placed on the leg, in the stomach via nasogastric tube, and on the liver during laparotom y. Hemorrhagic shock was induced by phlebotomy of 28% of blood volume. Afte r I hour, resuscitation was with shed blood and crystalloid until cardiac o utput plateaued. Measurements of physiologic parameters, blood gases, lacta te, intramucosal pH, and NIRS values for regional tissue hemoglobin oxygen saturation (StO(2)), and cytochrome a, a3 redox state were recorded at inte rvals throughout the experiment. Tissue oxygenation as measured by oxyhemog lobin saturation and cytochrome a,a3 redox (NIRS) correlated with measures of systemic DO2 throughout the experiment. The liver probe demonstrated blu nted changes in tissue oxygenation suggesting relatively protected circulat ion. Intramucosal pH did not correlate well with DO2. Regional tissue oxyge nation as measured by NIRS shows excellent correlation with global oxygen d elivery. NIRS may allow estimation of systemic oxygen delivery using rapid non-invasive techniques.