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 umbilical arterial blood oxygen saturation determined by hemoximetry (Sao2) 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 (Spo2).


METHODS
Umbilical artery and vein blood specimens were obtained at delivery. Blood gas analysis and hemoximetry were performed. Polynomial regression analysis and receiver-operator characteristic curves were calculated for umbilical arterial blood Sao2 and theoretic preductal arterial blood Sao2 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 Sao2 was > or = 30%, umbilical arterial blood pH was > or = 7.13 in 99.0% (388/392) of cases and < 7.13 in 1.0% (4/392) of cases. When umbilical arterial blood Sao2 was < 30%, umbilical arterial blood pH was > or = 7.13 in 91.4% (648/709) of cases and < 7.13 in 8.6% (61/709) of cases.


CONCLUSIONS
From these analyses, it appears that an Spo2 cutoff value of 30% would be reasonable in clinical trials of intrapartum fetal pulse oximetry.
Dildy
G A
GA
Department of Obstetrics and Gynecology, University of Missouri School of Medicine, Saint Luke's Hospital of Kansas City, Missouri, USA.
Thorp
J A
JA
Yeast
J D
JD
Clark
S L
SL
D000137:Acid-Base Imbalance / Q000175:diagnosis; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D005323:Fetal Monitoring; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007231:Infant, Newborn; D010092:Oximetry; D010100:Oxygen / Q000097:blood*; D011247:Pregnancy; D011296:Prenatal Diagnosis; D014469:Umbilical Arteries; D014471:Umbilical Veins
D010100:Oxygen