Calibration of a reflectance pulse oximeter in fetal lambs for arterial oxygen saturations below 70%.

ABSTRACT

OBJECTIVE: To calibrate a reflectance pulse oximeter developed at the Division of Perinatal Physiology, University Hospital of Zurich, for monitoring of oxygen saturations below 70%. METHODS: Oxygen saturation measured noninvasively with the reflectance pulse oximeter in fetal sheep was compared with oxygen saturation of arterial blood samples measured by a conventional two-wavelength oximeter. Oxygen saturation was varied by stepwise reduction of the inspired oxygen concentration of the ewe. RESULTS: A total of 58 data pairs was obtained from five fetuses, with a range of 10.9-73.5% for the reference method and 6.8-69.2% for the pulse oximetry oxygen saturation values. There was good correlation between the results obtained by the two methods (r2 = .89, P < .0001), with a 95% confidence interval of +/- 12.5%. The pulse oximeter showed a precision of 6.2% oxygen saturation. CONCLUSION: The Zurich reflectance pulse oximeter offers valid measurements of oxygen saturation levels down to 10% oxygen saturation, and is therefore suitable for monitoring the fetus during delivery.