THE RELATIONSHIP BETWEEN OXYGEN-SATURATION AND PH IN UMBILICAL BLOOD - IMPLICATIONS FOR INTRAPARTUM FETAL OXYGEN-SATURATION MONITORING

OBJECTIVE: Our purpose was to evaluate the relationship between umbili cal arterial blood oxygen saturation determined by hemoximetry (Sao(2) ) and umbilical arterial blood pH and base excess determined by blood gas analysis to establish a ''critical threshold'' for fetal preductal arterial oxygen saturation determined by reflectance pulse oximetry ( Spo(2)). STUDY DESIGN: Umbilical artery and vein blood specimens were obtained at delivery. Blood gas analysis and hemoximetry were performe d. Polynomial regression analysis and receiver-operator characteristic curves were calculated for umbilical arterial blood Sao(2) and theore tic preductal arterial blood Sao(2) Versus umbilical arterial blood pH and base excess. RESULTS: A total of 1101 paired umbilical artery and vein specimens were obtained. When the umbilical arterial blood Sao(2 ) was greater than or equal to 30%, umbilical arterial blood pH was gr eater than or equal to 7.13 in 99.0% (388/392) of cases and <7.13 in 1 .0% (4/392) of cases. When umbilical arterial blood Sao(2) was <30%, u mbilical arterial blood pH was greater than or equal to 7.13 in 91.4% (648/709) of cases and <7.13 in 8.6% (61/709) of cases. CONCLUSIONS: F rom these analyses, it appears that an Spo(2) cutoff value of 30% woul d be reasonable in clinical trials of intrapartum fetal pulse oximetry .