Oxygen desaturation in women in labor.

Oxygen saturation and end-tidal CO2 tension were monitored in 15 healthy women during labor. Oxygen saturation was determined with a pulse oximeter and end-tidal CO2 with a CO2 monitor. Fetal heart rate, uterine contractions and maternal blood pressure were also monitored. End-tidal CO2 tension was followed to determine if falls in oxygen saturation during labor were related to hyperventilation. Ten of the 15 patients exhibited periods of oxygen saturation of less than 90%. End-tidal CO2 was consistently low, usually less than 30 mm Hg. Most, but not all (7 of 10), of the patients who showed desaturation had received narcotics. There were often periods of apnea and/or shallow respirations between contractions. These aberrations and hyperventilation-induced hypocarbia were probably the cause of the oxygen desaturation. No changes in fetal heart rate or low Apgar scores were noted.