Effect of positioning on SvO2 in the critically ill patient with a low ejection fraction

Abstract

Background: Critically ill patients with a low ejection fraction may be vulnerable to decreased mixed venous oxygen saturation (SvO2) resulting from position change.

Objectives: The objectives of this study were to describe the effects of changes in positioning on SvO2 in critically ill patients with a low ejection fraction (< or = 30%) and to describe the contribution of variables of oxygen delivery (DO2) and oxygen consumption (VO2) to the variance in SvO2.

Method: An experimental two-group repeated-measures design was used to study 42 critically ill patients with an ejection fraction of less than or equal to 30% (M= 19.5%). Patients were assigned randomly to one of two position sequences: supine, right lateral, left lateral; or supine, left lateral, right lateral. Data on SvO2 were collected at baseline, each minute after position change for 5 minutes, and at 15 and 25 minutes.

Results: Repeated-measures multivariate analysis of variance showed a difference in SvO2 among the three positions across time (p< .0001), with the greatest differences occurring within the first 4 minutes and in the left lateral position. Stepwise multiple regression showed that VO2 accounted for a greater proportion of the variance in SvO2 with position change than did DO2 (54% [p = .001] vs. 31% [p= .001]).

Conclusions: Changes in SVO2 occur with positioning in critically ill patients with a low ejection fraction. These changes are transient and are the result of changes in VO2 rather than changes in DO2.