Continuous Monitoring of Fetal Oxygen Saturation by Pulse OximetrY ANDREAS LUTTKUS, MD, THOMAS W, FENGLER, MD, WOLFGANG FRIEDMANN, MD, ÄND IOACHIMW. DUDENHÄUSEN, MD Objectioesz To compare spectrophotometric saturation val- ues of fetal blood sampling to the saturation readings by pirlse oximetry. Methodst During a clinical trial, fetal oxygen saturation was monitored during labor by a fetal oxisensor and a fetal pulse oximeter. Fifty-one fetal scalp blood samples wele assessed because of abnormal fetal heart rate (FHR) patterns' The pulse oximeter displayed only signal quality readings' The investigator had to perform adjustments if signal qual- ity fell below 50%. After delivery, the saturation at the moment of fetal blood analysis could be read from a printout and compared to the saturation values of scalp blood sam- pling. Resultst The share of usable signal time was 51% overall, but only 40'Ä in the 20-minute period during fetal blood sampling, Comparison with the reference method resulted in a median deviation of 5% (tenth percentile -10%; 90th percentile 18%) for pulse oximetry. The correlation coeffi- cient between saturation values by pulse oximetry and fetal scalp blood sampling was 0'67. The correlation coefficient with the partial Pressrue of orygen and oxygen saturation by pulse oximetqr was 0.51, whereas it was 0.88 between partial pressure and saturation from the spectrophotometric analy- sis of the scalp sample Conclusiotrsz Fetal pülse oximetry corresponds satisfacto' rily to results from fetal blood analysis. Low invasiveness and continuous monitoring are the advantages of this method. At present, .the available sensor Senerates only a limited amount of signal time. However, in combination with FHR monitoring, pulse oximetry promises greatly im- proved.detection of fetal hypoxia. (Obstet Gynecol 7995;85: )ofi-)oo Although pulse oximetry is used routinely in children and adults, its use in labor and delivery has been limited to experimental studies.'2 The design of the From the Departmart of Obstetics, Utiuersity Hospital Rudolf V ir chow, B erlin, G ermany. 'We are indebted to llrgm Paduly for his adtsice on statistical etsaluation and to Nellcor Itc., Pleasanton, Califonria, for supporting equipment used in tlrc studY, . VOL.85, NO.2, FEBRUARY 1995 fetal monitor now makes clinical use possible' During the development of fetal pulse oximeky, animal exPer- iments served to calibrate the saturation values mea- sured by pulse oximetry with -saturation in blood sam- ples taken at the same time.3'a No investigation has ionfirmed the saturation values measured by pulse oximetry in human fetuses. The objective of this study was to evaiuate fetal pulse oximetry and correlate it with speckophotometry as a reference method. We compared the saturation values measured during clinically indicated fetal scalp blood analysis to continuous pulse oximetry readings' In addition to correlating oxygen saturation assessed by both methods, we also correlated it with the oxygen pressure (PO). Materials and Methods The study, carried out from February until October 1993, was approved by the ethics committee of the University Hospital Rudolf Virchow, Berlin, Germany' We used the Nellcor N 400 fetal oxygen saturation monitor and the Nellcor FS 10 fetal oxisensor (wave- length X = 660/890 nm) (Nellcor Inc., Pleasanton, CA)' The oxisensor was positioned between the uterine waii and fetal cheek after rupture of membranes, but not attached to the fetal scalp. This form of application is not traumatic and of low invasiveness' Contact between the fetal head and the sensor had to be adjusted by the investigator according to signal quality readings' The signal quality should not fall below 50%. Saturätion values by pulse oximetry were not visible to the investigator, so any keatment was based on clinical data or fetal heart rate (FHR) monitoring' If indicated, fetal blood samples were collected' Interven- tions, such as the administration of fenoterol or oxyto- ciry or decisions about operative delivery were made without knowledge of the oxygen saturation by pulse oximetry. 0029-7844/95/99.50 1 T I I 'i {l 'I I l