EFFECT OF POSITIONING ON S(V)OVER-BARO(2) IN THE CRITICALLY ILL PATIENT WITH A LOW EJECTION FRACTION

Background: Critically ill patients with a low ejection fraction may b e vulnerable to decreased mixed Venous oxygen saturation (S(v)over-bar O(2)) resulting from position change. Objectives: The objectives of th is study were to describe the effects of changes in positioning on S(v )over-barO(2) in critically ill patients with a low ejection fraction (less-than-or-equal-to 30%) and to describe the contribution of variab les of oxygen delivery (DO2) and oxygen consumption (VO2) to the Varia nce in S(v)over-barO(2). Method: An experimental two-group repeated-me asures design was used to study 42 critically ill patients with an eje ction fraction of less than or equal to 30% (M= 19.5%). Patients were assigned randomly to one of two position sequences: supine, right late ral, left lateral; or supine, left lateral, right lateral. Data on S ( v) over bar O-2 were collected at baseline, each minute after position change for 5 minutes, and at 15 and 25 minutes. Results: Repeated-mea sures multivariate analysis of variance showed a difference in S(v)ove r-barO(2) among the three positions across time (p less-than .0001), w ith 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 S(v)over-ba rO(2) with position change than did DO2 (54% [p =.001] vs. 31% [p = .0 01]). Conclusions: Changes in S(v)over-barO(2) 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 change s in DO2.