Head-of-Bed Elevation Improves End-Expiratory Lung Volumes in Mechanically Ventilated Subjects: A Prospective Observational Study

Amy J Spooner, Amanda Corley, Nicola A Sharpe, Adrian G Barnett, Lawrence R Caruana, Naomi E Hammond and John F Fraser. Respiratory Care October 2014, 59 (10) 1583-1589

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 degrees and then 30 degrees. RESULTS: Significant increases in end-expiratory lung volume were seen at both 20 degrees and 30 degrees HOBE in all lung regions, except the anterior, with the largest changes from baseline (supine) seen at 30 degrees. From baseline to 30 degrees 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.