Effect of Body Position on PaO₂ and PaCO₂during Pregnancy

Abstract

Background: The body position may have an effect on gas exchange though the magnitude of this effect has not been studied thoroughly during the three trimesters of pregnancy. Objectives: This study analyzes the effect of body position change on arterial oxygen tension (PaO₂) and arterial carbon dioxide tension (PaCO₂) in healthy pregnant women. Methods: We examined 21 lung healthy pregnant women at the end of the first, second and third trimester of pregnancy. Blood was drawn from the radial artery first in the sitting and subsequently in the supine position. Peak expiratory flow rate was determined as well. Results: No statistically significant difference was detected between the mean values of PaO₂ in the supine and in the sitting position at the end of the first trimester. On the contrary, at the end of the second trimester the mean value of PaO₂ in the supine position was 92.39 ± 1.95 mm Hg, while in the sitting position the mean PaO₂ was 96.56 ± 1.83 mm Hg (p < 0.001). At the end of the third trimester the mean PaO₂ in the supine position was 90.48 ± 2.91 mm Hg while in the sitting position the mean PaO₂ was 97.48 ± 1.46 mm Hg (p < 0.001). Conclusions: According to our data we conclude that the statistically significant difference in PaO₂ in the sitting and supine positions clearly shows that the position needs to be considered both when attempting to establish reference values and when evaluating gas tensions at the end of pregnancy.

Effect of maternal position on fetal behavioural state and heart rate variability in healthy late gestation pregnancy

“…In addition to the consideration of blood flow changes with maternal position, body position may affect oxygenation. Changes in maternal P aO 2 have been found when a subject in late pregnancy is changed from a supine to a sitting position (Spiropoulos et al 2004), although fetal parameters were not assessed in that study.…”

“…Changes in maternal have been found when a subject in late pregnancy is changed from a supine to a sitting position (Spiropoulos et al . ), although fetal parameters were not assessed in that study.…”

A Study of Fvc, Pefr and Mep in Different Trimesters of Pregnancy

“…Exclusion Criteria : Subjects with acute respiratory infection in the previous three months, chronic respiratory infection including asthma, history or clinical signs of cardiovascular diseases, diabetes mellitus, hypertension , tobacco consumption in any form , alcohol intake, endocrine disorders, obesity & moderate to severe anemia were excluded from the studies. 15,16 . Moreover, progressively reduced value of PEFR in three trimesters of pregnancy may be attributed to the mechanical effects of enlarged gravid uterus reducing vertical dimension by limiting movement of diaphragm 17 .…”

Effects of maternal central hemodynamics on fetal heart rate patterns

“…However, the systolic‐to‐diastolic blood flow ratio is not altered by maternal body position (6). In the supine position, the lung function is also worsened in late pregnant women, causing a lower oxygen tension of the blood (7). Furthermore, compression of the inferior vena cava may also be involved in the decreased placental blood supply, since lowered venous return (preload) results in less oxygenated blood and stroke volume (SV).…”