Postoperative arterial blood gas measurement in obese patients: effect of position on gas exchange.

The effect of position change on blood gas exchange was studied in 22 markedly obese, otherwise healthy, women both preoperatively and postoperatively. There was a statistically significant decrease in arterial oxygen tension and a simultaneous reduction both in the arterial carbon dioxide tension and the base excess with the assumption of the supine versus the semirecumbent position on postoperative days one and two. However, no positional difference was demonstrable in any variable by the third postoperative day. This study indicates that in obese patients during the first 48 hours after abdominal surgery, assumption and maintenance of the semirecumbent posture is a valuable therapeutic adjunct to improve arterial oxygenation.