OBJECTIVE: To examine the effect of a change in body position (right or left lateral) and timing of backrub (immediate or delayed) on mixed venous oxygen saturation in surgical ICU patients. METHODS: A repeated-measures design was used to study 57 critically ill men. Mixed venous oxygen saturation was recorded at 1-minute intervals for 5 minutes in each of three periods: baseline, after turning, and after backrub. Subjects were randomly assigned to body position and timing of backrub. Subjects in the immediate-backrub group were turned and given a 1-minute backrub. Mixed venous oxygen saturation was measured at 1-minute intervals for 5 minutes at two points: after the backrub and then with the patient lying on his side. For subjects in the delayed-backrub group, saturation was measured at 1-minute intervals for 5 minutes at two different points: after the subject was turned to his side and after the backrub. RESULTS: Both position and timing of backrub had significant effects on mixed venous oxygen saturation across conditions over time. Subjects positioned on their left side had a significantly greater decrease in saturation when the backrub was started. At the end of the backrub, saturation was significantly lower in subjects lying on their left side than in subjects lying on their right side. The pattern of change differed according to the timing of the backrub, and return to baseline levels of saturation after intervention differed according to body position. CONCLUSIONS: Two consecutive interventions (change in body position and backrub) cause a greater decrease in mixed venous oxygen saturation than the two interventions separated by a 5-minute equilibration period. Turning to the left side decreases oxygen saturation more than turning to the ride side does. Oxygen saturation returns to clinically acceptable ranges within 5 minutes of an intervention. In patients with stable hemodynamic conditions, the standard practice of turning the patient and immediately giving a backrub is recommended. However, it is prudent to closely monitor individual patterns of mixed venous oxygen saturation, particularly in patients with unstable hemodynamic conditions.