Simultaneous measurement of hepatic tissue pH, venous oxygen saturation and hemoglobin by near infrared spectroscopy

The purpose of this study was to investigate the feasibility of using near infrared (NIR) spectroscopy of the liver to simultaneously assess oxygen co ntent in combination with tissue pH, an indicator of anaerobic metabolism. Six anesthetized swine were subjected to 45 min of hemorrhagic shock follow ed by resuscitation with blood and crystalloid. Calibration models between NIR spectra and reference measurements of tissue pH, hepatic venous oxygen saturation (SvO2), and blood hemoglobin concentration (Hb) were developed u sing partial least-squares regression. Model accuracy was assessed using cr oss validation. The average correlation (R-2) between NIR and reference mea surements was 0.87, 0.68, and 0.93, respectively for pH, Hb, and SvO2. Esti mated accuracy, the root mean squared deviation between spectral, and refer ence measurements was 0.03 pH units, 0.3 g/dL, and 6%. NIR determination of hepatic oxygen content and tissue pH during shock and resuscitation demons trated that there can be a variance between hepatic venous oxygenation and regional tissue acidosis. NIR spectroscopy provides a technique to explore the implications of post-shock depression of tissue pH and evaluate new met hods of resuscitation.