ACCURACY AND UTILITY OF A NEW REFLECTANCE PULSE OXIMETER FOR FETAL MONITORING DURING LABOR

Objective. To evaluate the accuracy of a new pulse oximeter in estimat ing the oxyhemoglobin (O(2)Hb) concentration in fetal arterial blood ( SaO(2)) with either a high concentration of hemoglobin F (HbF) or a lo w concentration of O(2)Hb during labor. Patients and Methods. Fetal fo rehead arterial oxygenation was determined in 44 fetuses by reflectanc e pulse oximeter (SpO(2)) during labor and was compared with SaO(2) de termined immediately after birth. Because HbF has little or no known e ffect on pulse oximetry, but does affect the laboratory multiwavelengt h ''CO-oximeter'' type reading, the SaO(2) was corrected by HbF concen tration. SpO(2) and SaO(2) were simultaneously measured in five hypoxi c adult volunteers achieved by inhaling 11% oxygen. Results. A gradual decline in HbF concentration was seen during weeks 37 to 40 of gestat ion. HbF concentration varied near term, ranging between 53 and 88% of the fetal hemoglobin concentration (mean +/- SD = 74.6 +/- 6.3%). Thi s alteration produced a lower % O(2)Hb percent by 4% at the most. The corrected SaO(2) in cord blood correlated with fetal SpO(2) (y = 0.974 , x - 7.279, r = 0.90). In five adults, SpO(2) reflected well SaO? wit h a mean +/- SD of bias of -1.1 +/- 2.9%. Conclusions. SpO(2) determin ed by a new reflectance pulse oximeter at the end of labor correlated with an immediate post-natal cord arterial blood sample before the fir st breath, with a mean and SD of bias of 8.5 +/- 6.2%. Reflectance pul se oximetry is a useful tool for continuous noninvasive monitoring of the fetal oxygen status during labor.