Body position change and its effect on hemodynamic and metabolic status

Objective The study’s objective was to examine the effect of body position on oxygen consumption (Vo2) and hemodynamics. Although gravity-dependent hemodynamic and pulmonary consequences are well documented, less is known about the effect of body positions on VO2 and hemodynamics, which is of importance in critical care. Design This was a quasi-experimental study. Setting The setting was a physiology laboratory controlled for noise and temperature (21°C). Subjects Healthy, nonsmoking subjects were studied (n = 32; 18 women and 14 men aged 20 ± 0.84 years [mean ± SD]). Outcome measures After each subject was in each position of interest for 10 minutes, heart rate (HR), blood pressure (BP), rate pressure product (RPP) (an index of myocardial Vo2 = HR × systolic BP), Vo2 · min · m2, and arterial saturation (Spo2) were recorded for 10 minutes and averaged. All testing was conducted at midday. Interventions Five body positions used in the intensive care unit were standardized and included the following: sitting in a firm chair with feet supported (sitting), horizontal supine flat position (H-S), head-down (30°) supine flat position (HD-S), and right- and left-side lying (90°) positions (RSL and LSL, respectively). Results Generally, HR, BP, RPP, and Vo2 were highest in the sitting position compared with the lying positions (P < .05) and lowest in the LSL position (P < .05). The H-S and HD-S positions tended to affect these variables comparably with the exception of HR, which was lowest in the H-S position and significantly lower in the HD-S positions (P < .05). Both systolic and diastolic BP were comparable in the sitting, H-S, and HD-S positions, and significantly lower in the RSL and LSL positions (P < .001). Similar to mean Vo2, the mean RPP tended to be reduced across positions in the following sequence: sitting, HD-S, H-S, RSL, and LSL. Spo2 did not change across body positions. Conclusions These results yield further insight into how the adverse and beneficial effects of body positioning as a therapeutic intervention may be mediated through gravitational stress and myocardial mechanics. Such an understanding is crucial when prescribing body positioning to enhance oxygenation in the patient in the intensive care unit and to minimize its adverse effects.