CALIBRATION OF A REFLECTANCE PULSE OXIMETER IN FETAL LAMBS FOR ARTERIAL OXYGEN SATURATIONS BELOW 70-PERCENT

OBJECTIVE: To calibrate a reflectance pulse oximeter developed at the Division of Perinatal Physiology, University Hospital of Zurich, Jar m onitoring of oxygen saturations below 70%. METHODS: Oxygen saturation measured noninvasively with the reflectance pulse oximeter in fetal sh eep was compared with oxygen saturation of arterial blood samples meas ured by a conventional two-wavelength oximeter. Oxygen saturation was varied by stepwise reduction of the inspired oxygen concentration of t he ewe. RESULTS: A total of 58 data pairs was obtained from five fetus es, 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 tvas good corre lation between the results obtained by the two methods (r(2) = .89, P < .0001), with a 95% confidence interval of +/- 12.5%. The pulse oxime ter showed a precision of 6.2% oxygen saturation. CONCLUSION: The Zuri ch reflectance pulse oximeter offers valid measurements of oxygen satu ration levels down to 10% oxygen saturation, and is therefore suitable for monitoring the fetus during delivery. Copyright (C) 1998 by the S ociety for Gynecologic Investigation.