Oxygen consumption and ventilation during normal labor.

Oxygen consumption (VO2) and minute ventilation (VE) were measured breath-by-breath for 10 min periods in the third trimester of pregnancy in 16 healthy women. These measurements were repeated during the first stage of labor in eight of the women. The 10-min mean VO2 was 3.56 ml/kg/min (+/- 0.82 SD) at term and 4.28 ml/kg/min (+/- 0.93) during labor, for an average increase of 23 percent (+/- 28 percent, p = 0.04) from third trimester to labor. The mean VE was 0.15 L/kg/min (+/- 0.03) at term and increased significantly (p = 0.05) to 0.24 L/kg/min (+/- 0.11) during labor for an average increase in VE of 65 percent (+/- 78 percent). Peak VO2 and VE occurred during contractions with five-breath average peak VO2 being 86 percent (+/- 53%) above the 10-min mean value at term and VE increasing 167 percent (+/- 154 percent) from third trimester to peak values during labor. These data may be useful in identifying patients at risk for developing respiratory insufficiency during labor. We propose an algorithm for approaching the obstetric patient with respiratory disease.