Postural influence on maternal capillary oxygen and carbon dioxide tension

Abstract

Summary: The effect of posture on maternal capillary blood Po2 and Pco2 was studied in pregnant and non-pregnant women. There was a significant decrease of Po2 (mean 13-0 mm. Hg) and significant decrease of Pco2 (mean 2*4 mm. Hg) when pregnant women sat up, but these changes did not occur in the non-pregnant. These findings may be relevant to debate on the optimum posture for labour.

Closing Volume and Pregnancy

“…More women had airway closure above FRC in the sitting than in the supine position but the difference is probably due to the wide scatter of results in a relatively small number of patients. Studies of arterial oxygenation during pregnancy show a fall in arterial oxygen tension when the patient is moved from the sitting to the supine position (Ang et al, 1969). The measurements of lung volumes by spirometry are in agreement with other authors (Thompson and Cohen, 1938;Cugell et al, 1953).…”

“…Despite the hypocapnia they tend to be lower than in non-pregnant women of the same age (Stenger et al, 1964). The cause of this fall in arterial oxygenation is unknown but has been attributed to cardiovascular and respiratory disturbances (Ang et al, 1969). A fall in FRC in other situations-for example, after surgery (Craig et al, 1971;Alexander et al, 1972)-results in impaired distribution of pulmonary ventilation.…”

Comparison of helium dilution and plethysmographic lung volumes in pregnant women

“…Even in erect subjects, an increased airway closure (FRC and RV differences >150 mL at week 36) must induce hypoxaemia due to shunt, because the slight physiological hyperventilation of pregnancy would not undo the venous admixture in very poorly-ventilated or closed compartments [32,33]. Other possible mechanisms to explain the difference between the two techniques are a change in transpulmonary pressure gradient [34], or changes in the pressure-volume characteristics of the lung [35].…”

Mechanical Ventilation in Critically Ill Obstetric Patient

“…• The minute ventilation increases by 40 % due to progesterone mediated increased sensitivity of respiratory center to carbon dioxide [ 3 ].…”