3RD-TRIMESTER ARTERIAL BLOOD-GAS AND ACID-BASE VALUES IN NORMAL-PREGNANCY AT MODERATE ALTITUDE

Objective: To report arterial blood gas and acid base values of normal nulliparous patients at moderate altitude for commonly used maternal positions. Methods: Ten normotensive nulliparous women between 36 and 38 weeks' gestation volunteered to undergo radial and pulmonary artery cannulation as part of a larger study. Following instrumentation, bas eline assessments were made in the left lateral recumbent position aft er a 30-minute stabilization period. Sequential measurements were then obtained in the left lateral, right lateral, supine, knee-chest, sitt ing, and standing positions. Blood samples were analyzed in duplicate for oxygen content on a blood gas analyzer. Statistical analysis was p erformed by analysis of variance of repeated measures with significanc e defined at P less than or equal to.05. Results: There was no signifi cant difference in arterial blood gas or acid base values between any positions in this antepartum population of term healthy women. The com posite mean values were as follows: pH 7.46, arterial carbon dioxide p ressure (PaCO2) 26.6 mmHg, arterial oxygen pressure 88.3 mmHg, bicarbo nate 18.2 mEq/L, saturated arterial hemoglobin level 0.96. Conclusion: Arterial blood gas and acid base values are not altered by maternal p osition in the late third trimester of pregnancy. The PaO2 in these wo men studied at moderate altitude was lower than previously reported fo r healthy pregnant women studied at sea level. Appropriate interpretat ion of arterial blood specimens of pregnant women should take into acc ount both the pregnancy and altitude at which the women reside.