A wide gap second derivative NIR spectroscopic method for measuring tissue hemoglobin oxygen saturation.
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Animals↗
Biomedical subjects
Dean E Myers
Publications and source records attributed to Dean E Myers.
Use of near-infrared spectroscopy in early determination of irreversible hemorrhagic shock.
BACKGROUND: In field situations, patient triage may require early determination of patients progressing to irreversible shock. We investigated the utility of near-infrared spectroscopy (NIRS) in early detection of irreversible hemorrhagic shock. METHODS: Twenty instrumented pigs were treated with a protocol involving 35% blood volume hemorrhage, 90 minutes of shock, and stepwise resuscitation with lactated Ringer's. Hemodynamics and NIRS measurements of skeletal muscle (leg), stomach, and liver tissue oxyhemoglobin saturation (StO2) were measured at baseline, every 30 minutes during shock, and after each resuscitative step. Measurements were compared between animals that expired during resuscitation (unresuscitatable) and animals that survived all resuscitative steps (resuscitatable). RESULTS: Neither global oxygen delivery, oxygen consumption, nor lactate distinguished resuscitatable from unresuscitatable animals. Invasive measurements of SvO2 did distinguish resuscitatable from unresuscitatable animals. After the first fluid bolus, both stomach and leg StO2 differed significantly between resuscitatable and unresuscitatable animals. Regression analysis revealed skeletal muscle (leg) StO2 obtained after the first resuscitative step was a significant mortality predictor despite resuscitation (r2=0.45) (p = 0.005). CONCLUSIONS: Non-invasive NIRS monitoring of leg and stomach StO2 differentiates resuscitatable from unresuscitatable animals after the initial resuscitative bolus. Use of this non-invasive tool may guide appropriate use of resuscitative fluids and has possible point-of-care applications.
Animals↗
Noninvasive method for measuring local hemoglobin oxygen saturation in tissue using wide gap second derivative near-infrared spectroscopy.
A simple continuous wave near-infrared algorithm for estimating local hemoglobin oxygen saturation in tissue (%StO2) is described using single depth attenuation measurements at 680, 720, 760, and 800 nm. Second derivative spectroscopy was used to reduce light scattering effects, chromophores with constant absorption, baseline/instrumentation drift, and movement artifacts. Unlike previous second derivative methods which focused primarily on measuring deoxyhemoglobin concentration; a wide 40 nm wavelength gap used for calculating second derivative attenuation significantly improved sensitivity to oxyhemoglobin absorption. Scaled second derivative attenuation at 720 nm was correlated to in vitro hemoglobin oxygen saturation to generate a %StO2 calibration curve. The calibration curve was insensitive to total hemoglobin, optical path length, and optical scattering. Measurement error due to normal levels of carboxyhemoglobin, methemoglobin, and water absorption were less than 10 %StO2 units. Severe methemoglobinemia or edema combined with low blood volume could cause StO2 errors to exceed 10 StO2 units. Both a broadband and commercial four-wavelength spectrometer (InSpectra) measured %StO2. The InSpectra tissue spectrometer readily detected limb ischemia on 26 human volunteers for hand, forearm, and leg muscles. A strong linear correlation, r2>0.93, between StO2 and microvascular %SO2 was observed for isolated animal hind limb, kidney, and heart.
Adult↗