Clinical usefulness of pulse oximetry in the fetus with non-reassuring heart rate pattern?

The objective of this study was the evaluation of intrapartum pulse oximetr y as an indicator of fetal distress and the condition of the newborn during clinical routine surveillance in an University Perinatal Center. Between 1 998 and 1999 pulse oximetry (SpO(2)) was used additionally to routine fetal monitoring by electronic fetal heart rate tracing (CTG) and fetal blood sa mpling (FBA) in 128 cases with nonreassuring heart rate pattern. Cut off va lues were FIGO Score < 8 for the heart rate pattern and for fetal blood sam pling during labor results of < 7.25 (preacidosis). The condition of the ne wborn was defined by the APGAR score with the cut off < 7 at 1 minute, whil e the biochemical status was evaluated by means of arterial blood sampling of the umbilical artery directly after birth using a pH of < 7.20 to verify acidosis. Predictive values of critically low SpO(2) values (< 30%) for at least 10 minutes as well as corresponding sensitivities and specificities were calculated together with 95% confidence intervals to identify fetal di stress or a depressed condition of the newborns. Of 128 fetuses included in this study 66 (52%) were born spontaneously, 23 (18%) were born by operative vaginal delivery and 39 (31%) by means of cesa rean section. The high rate of cesarean section was due to cephalopelvic di sproportion in 29 cases. Fetal outcome was evaluated with a clinical score: mean APGAR score value 8.5 SD +/- 1. The mean value of the pH in the umbil ical artery was 7.23 +/- 0.04. During a SpO(2) monitoring period of 18,381 minutes we analyzed a contact time of 63%. Comparing SpO values of < 30% wi th preacidosis in the fetal blood sampling, we found a positive predictive value of merely 0.17 (95% CI: 0.00-0.64). Of 9 preacidotic cases during del ivery only 1 was indicated by a saturation value below 30% (sensitivity 0.1 1, 95% CI: 0.00-0.48), The specificity and negative predictive value were c alculated as 0.83 (95% CI: 0.65-0.94) and 0.76 (95 % CI: 0.58-0.89) respect ively. Of eleven cases with acidosis in the blood of the umbilical cord art ery, pH < 7.20, only 2 were indicated by a SpO(2) values below 30%. Which i s equivalent to a sensitivity of 0.18 (95% CI: 0.03-0.52). Results of a rec eiver operator curve analysis showed no substantial deviation from the diag onal. The area under the curve was 0.62. the 95% CI (0.47-0.76) indicating no significant discrimination. Three of 49 fetuses with SpO(2) recording du ring the last 10 minutes were born in clinical depressed status (APGAR< 7). None was indicated by a SpO(2) value below 30%. Conclusion: Fetal distress and impaired condition of the newborn are not id entified or predicted during routine application of SpO(2) monitoring in th e fetus during labor with adequate safely.