Physiological measurement
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Physiological measurement · May 2015
Variability in estimating shunt from single pulse oximetry measurements.
Virtual shunt describes the overall loss of O2 content between the alveolar gas and arterial blood. Clinicians indirectly estimate the magnitude of the virtual shunt by monitoring peripheral blood oxygen saturation (SpO2) using non-invasive pulse oximetry. An inherent limitation of this method is the variable precision of pulse oximeters and the non-linear relationship between virtual shunt and SpO2 which is rarely depicted. ⋯ Although a variable bias (1.2-2.1%) in SpO2 between the pulse oximeter brands was observed, the tested pulse oximeters were both within tolerance specified by the manufacturers and matched the probability distributions from the model. The theoretical and experimental findings show that the estimation of virtual shunt is challenging with a single SpO2 measurement using pulse oximeters with tolerances of 2%. Clinical decisions must be based on an appreciation of these limitations.