Head-of-bed elevation improves end-expiratory lung volumes in mechanically ventilated subjects: a prospective observational study

Abstract

Background: Head-of-bed elevation (HOBE) has been shown to assist in reducing respiratory complications associated with mechanical ventilation; however, there is minimal research describing changes in end-expiratory lung volume. This study aims to investigate changes in end-expiratory lung volume in a supine position and 2 levels of HOBE.

Methods: Twenty postoperative cardiac surgery subjects were examined using electrical impedance tomography. End-expiratory lung impedance (EELI) was recorded as a surrogate measurement of end-expiratory lung volume in a supine position and at 20° and then 30°.

Results: Significant increases in end-expiratory lung volume were seen at both 20° and 30° HOBE in all lung regions, except the anterior, with the largest changes from baseline (supine) seen at 30°. From baseline to 30° HOBE, global EELI increased by 1,327 impedance units (95% CI 1,080-1,573, P < .001). EELI increased by 1,007 units (95% CI 880-1,134, P < .001) in the left lung region and by 320 impedance units (95% CI 188-451, P < .001) in the right lung. Posterior increases of 1,544 impedance units (95% CI 1,405-1,682, P < .001) were also seen. EELI decreased anteriorly, with the largest decreases occurring at 30° (-335 impedance units, 95% CI -486 to -183, P < .001).

Conclusions: HOBE significantly increases global and regional end-expiratory lung volume; therefore, unless contraindicated, all mechanically ventilated patients should be positioned with HOBE.

Keywords: electrical impedance tomography; end-expiratory lung volume; lung volume; mechanical ventilation; positioning; surgery.