Continuous noninvasive hemoglobin monitoring: the standard of care and future impact.

While the authors present analysis of trends, observations reflect more static, than dynamic hematological conditions, and they suggest that CNHM “…may be a feasible alternative to invasive hemoglobin monitoring”. However, they do not present decision-making or outcomes results, per se, and wisely, stop short of implying CNHM should replace discrete in vitro diagnostic hemoglobin testing when the article ends with the somewhat circuitous caveat, “A laboratory hemoglobin determination could be limited to situations where a blood transfusion is considered”. Oxygen saturation measured noninvasively by traditional pulse oximetry using red (~660 nm) and infrared (~905 nm) light emitting diodes (LEDs) differentiates oxy- versus deoxyhemoglobin, respectively (2). The ratio of red versus infrared light is correlated with a calibration curve empirically derived from clinical studies to calculate oxygen saturation over a limited range (2, 3), while pulse rate is determined from the plethysmogram. Newer devices incorporate robust treatment of the red/infrared ratio, multiple wavelengths, advanced algorithms, and proprietary sensor calibrations integrated (3). These principles extend to pulse co-oximetry, where up to twelve wavelengths and sophisticated signal reduction enable measurement of carboxyhemoglobin, methemoglobin, total hemoglobin,