Near-infrared and nuclear magnetic resonance spectroscopic assessment of tissue energetics in an isolated, perfused canine hind limb model of dysoxia

This controlled laboratory study examined the efficacy of near-infrared spectroscopy (NIRS) and ³¹P-nuclear magnetic resonance (NMR) spectroscopy in measuring regional tissue oxygenation in a isolated, perfused hind limb model of tissue dysoxia. Isolated hind limb perfusion was carried out in 20 mongrel dogs and oxygen delivery was varied by manipulating either hemoglobin concentration, oxygen saturation, or flow. Hind limbs from anesthetized mongrel dogs (n = 20) were separated and isolated perfusion performed. NIRS probes for recording relative O₂ saturation of tissue hemoglobin (HbO₂) and cytochrome a,a₃ and NMR probes for measuring ³¹P-high energy phosphates were placed over the limb. Measurements of physiologic parameters, blood gases, lactate, NIRS values for HbO₂ and cytochrome a,a₃ redox state, and ³¹P-phosphate levels were recorded at set intervals throughout the experiment. Measures of tissue oxygen consumption (VO₂) correlated with tissue oxygenation as measured by HbO₂ and cytochrome a,a₃ redox state (NIRS), as well as by ³¹P-high energy phosphate levels (NMR) throughout the experiment. Delivery-dependent tissue oxygenation was detected at a higher DO₂ by NIRS than by VO₂ or NMR. Tissue oxygenation as measured by NIRS and NMR shows excellent correlation with oxygen delivery in an isolated, perfused model of shock. NIRS may allow early detection of tissue dysoxia using rapid non-invasive techniques.