Effects of supine versus sitting bedrest upon blood gas tensions, cardiac output, venous admixture and ventilation-perfusion ratio in man after upper abdominal surgery.

The effects of body position (sitting versus supine) on respiratory and haemodynamic patterns were evaluated in nine patients who have undergone upper abdominal surgery. Posture showed no significant influence upon arterial blood gas tensions, while in the sitting position mean central venous oxygen tension lowers and arterial-venous oxygen content difference rises. In seated patients cardiac output was notably reduced. Pulmonary gas exchange analysis, according to Riley's method, showed that the sitting position allows a higher alveolar ventilation-pulmonary capillaries perfusion ratio, as well as a lower degree of venous admixture.