THE EFFECTS OF MATERNAL POSITION AND CARDIAC-OUTPUT ON INTRAPULMONARYSHUNT IN NORMAL 3RD-TRIMESTER PREGNANCY

Objective: To assess the effect of pregnancy, maternal position, and c ardiac output on intrapulmonary shunting (Qs/Qt) in normotensive nulli parous women near term. Methods: Ten normotensive nulliparas between 3 6 and 38 weeks' gestation underwent pulmonary artery catheterization ( via the subclavian route) and radial artery canalization. Baseline ass essments were made with subjects in the left lateral recumbent positio n after a 30-minute stabilization period. Measurements were obtained s equentially in the left lateral, right lateral, supine, knee-chest, si tting, and standing positions. Each position change was followed by a 10-minute pre-measurement stabilization period. Cardiac output was mea sured via the thermodilution technique. Blood samples were obtained si multaneously from the pulmonary and radial arteries and analyzed in du plicate for oxygen content with a blood gas analyzer. Qs/Qt was calcul ated using the classic shunt equation. Statistical analysis was perfor med by analysis of variance of repeated measures of Qs/Qt and maternal position. The relationship of Qs/Qt to maternal cardiac output was ev aluated by the correlation coefficient. Significance was defined as P <.05. Results: Directly measured Qs/Qt averaged 15.3% in left lateral, 15.2% in right lateral, 13.9% in supine, 12.8% in knee-chest, 13.8% i n sitting, and 13.0% in standing positions. There was no statistically significant correlation between Qs/Qt and cardiac output (R(2) = 0.11 , not significant). Conclusion: This is the first report of directly m easured Qs/Qt in normal pregnant women in the third trimester. Qs/Qt v alues reported in pregnancy are higher than those reported in nonpregn ant individuals.