Accuracy of fetal pulse oximetry.
BACKGROUND
The goal of this investigation was to evaluate the agreement of fetal pulse oximetry to saturation readings from hemoximetry at low oxygen saturation.


METHODS
Fetal oxygen saturation measurements obtained by pulse oximetry were compared with those obtained by hemoximetry in fetal scalp blood samplings. The prospective observational trial included fetuses with non-reassuring fetal heart rate tracings suggestive of hypoxia and requiring fetal scalp blood samplings. Arterial oxygen saturation was determined by a blinded pulse oximeter (N400, FS14; Nellcor Puritan Bennett, Pleasanton, CA, USA) and continuously stored on a notebook computer. Saturation from fetal scalp blood samples was measured by hemoximetry (Bayer Diagnostics 865; ABL 625, Radiometer). Data analysis focussed on the absolute and relative difference between hemoximetry and pulse oximetry of fetuses, showing the most distinct difference in neonatal outcome. Normal outcome was defined as spontaneous delivery and umbilical artery pH >or= 7.20 + Apgar 5 >or= 7 (n = 42). In contrast, a group of neonates with combined respiratory and metabolic acidemia at birth was defined by pH <or= 7.16 and an additional base excess <or= -9.4 mmol/l in the umbilical artery (n = 18).


RESULTS
The correlation coefficient between hemoximetry and pulse oximetry measurements was r = 0.72; p = 0.002 in the acidemic group. The median of absolute differences in saturation was + 5.2% (95%CI 2.5-10.3) saturation. The absolute differences ranged from -21% to + 36% saturation. The median of relative differences amounted to 23% (95%CI 15.1-55.0). The relative differences ranged from -30% to + 217%. Observing the saturation distribution in the two groups (hemoximetry and pulse oximetry, respectively) presented a median hemoximetry pulse oximetry of 38% (42%) in the normal and 26% (39%) in the acidemic group. In this small group of cases, the correlation coefficient between pH and saturation from pulse oximetry in fetal scalp blood from the samplings was r = 0.19.


CONCLUSIONS
Fetal pulse oximetry tends to overestimate arterial oxygen saturation compared with hemoximeter values.
Luttkus
Andreas K
AK
Clinic of Obstetrics, Charité, Campus Virchow-Klinikum, Medical School of Humboldt-Universität Berlin, Germany. Andreas.Luttkus@Charite.DE
Lübke
Marion
M
Büscher
Ulrich
U
Porath
Martina
M
Dudenhausen
Joachim W
JW
D000328:Adult; D001784:Blood Gas Analysis; D005260:Female; D005312:Fetal Blood / Q000378:metabolism*; D005323:Fetal Monitoring / Q000379:methods / Q000592:standards*; D006801:Humans; D007231:Infant, Newborn; D010092:Oximetry / Q000592:standards*; D011237:Predictive Value of Tests; D011247:Pregnancy; D011256:Pregnancy Outcome; D011446:Prospective Studies