Noninvasive estimation of the arterial partial pressure of oxygen in NICU infants

Le résumé fourni par la source

The O2-hemoglobin dissociation curve can be used to calculate the arterial partial pressure of oxygen (PaO2) from the peripheral saturation (SpO2) in adults as an alternative to blood gas analysis. Our objective was to evaluate whether this calculation could be performed in infants born prematurely. We obtained blood gas measurements from three infant cohorts, two from the University of Iowa Hospitals and Clinics (UIHC) neonatal intensive care unit (NICU) and one from Harvard Medical school. We plotted PaO2 against SaO2, measured by co-oximetry, and compared the resultant curve to published curves for adults and neonates. The UIHC curve was leftward shifted compared to published curves for newborns and adults, and the newborn and adult curves overestimated PaO2 in the UIHC neonates. We tested the additional hypothesis that this was because of the large proportion of premature infants in our cohort, but gestational age was not a predictor of the shift. Next, we quantified the degree to which pH, PCO2, and gestational age contributed to sources of error in using this curve to estimate PaO2 from SpO2. Because pH, PCO2, and gestational age are known to shift the O2-hemogloin dissociation curve. We found that deviations in pH and CO2 from the physiological ideal contribute a limited source of error, respectively, to the calculation of PaO2 using our cohort’s curve. This suggests that data from published cohorts may not be universally useful for the calculation of PaO2 in neonates. We validated the UIHC curve in additional patients with well characterized clinical phenotypes. We found promising accuracy (PO2 within 5 mmHg of the gold standard blood gas analyses) in simulations that quantified the additive contribution of pH, CO2, and gestational age to the error in calculated PaO2 in neonates. In future studies we will perform prospective analysis on patient data to limit potential variation in SpO2 measures and further refine our technique.

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