Effect of lateral positions on tissue oxygenation in the critically ill.

Objective: The purpose of this study was to assess the effect of lateral positions on tissue oxygenation in critically ill patients.

Design: The study design was prospective and quasi-experimental, and we used a convenience sample with random assignment.

Setting: The study took place in the intensive care unit and the cardiac intensive care unit of a 450-bed medical center in the northwestern United States.

Patients: The sample included 12 adult patients with indwelling pulmonary artery and radial arterial catheters who were receiving mechanical ventilation and who met the criteria of "critical illness" by having impaired arterial oxygenation (PaO2 < or = 70 mm Hg) and/or cardiac index < or = 2.0 L/min/m2.

Outcome Measures: The outcome measures were dependent variables reflecting oxygen delivery including heart rate, cardiac output, arterial oxygen content (CaO2) and oxygen consumption, and the adequacy of tissue oxygenation (serum lactate).

Intervention: Each patient was passively turned to each of the three positions (right and left 45 degrees lateral and supine) according to a computer-generated, randomized positioning sequence. Dependent variables were measured 15 minutes after each position change. No changes in ventilator settings or vasoactive drugs occurred during data collection.

Results: Analysis of variance for repeated measures was used in the data analysis. Post hoc analysis determined an effect size of 0.558 and power of 0.80 at an alpha level of.05. No statistically significant differences caused by position were found in mean CaO2, cardiac output, heart rate, respiratory rate, PaO2, SaO2, or lactate level. Pearson correlation analysis found no significant relationships between the primary variables reflecting oxygen delivery (cardiac output and CaO2) and serum lactate levels.

Conclusions: These findings suggest that lateral positioning of critically ill patients who are hypoxemic or have low cardiac output does not further endanger tissue oxygenation. Evaluation of individual patient responses to position changes in the clinical setting is encouraged until further studies using more heterogenous populations can provide more definitive guidance.