Head-of-bed elevation improves end-expiratory lung volumes in mechanically ventilated subjects: a prospective observational study.
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.
Critical Care Research Group, Adult Intensive Care Services, The Prince Charles Hospital and University of Queensland, Chermside, Brisbane, Australia amy.spooner@health.qld.gov.au.
Amy J
AJ
Spooner
Critical Care Research Group, Adult Intensive Care Services, The Prince Charles Hospital and University of Queensland, Chermside, Brisbane, Australia.
Amanda
A
Corley
Critical Care Research Group, Adult Intensive Care Services, The Prince Charles Hospital and University of Queensland, Chermside, Brisbane, Australia.
Nicola A
NA
Sharpe
Institute of Health and Biomedical Innovation and School of Public Health and Social Work, Queensland University of Technology, Kelvin Grove, Brisbane, Australia.
Adrian G
AG
Barnett
Critical Care Research Group, Adult Intensive Care Services, The Prince Charles Hospital and University of Queensland, Chermside, Brisbane, Australia.
Lawrence R
LR
Caruana
Critical Care Research Group, Adult Intensive Care Services, The Prince Charles Hospital and University of Queensland, Chermside, Brisbane, Australia.
Naomi E
NE
Hammond
Critical Care Research Group, Adult Intensive Care Services, The Prince Charles Hospital and University of Queensland, Chermside, Brisbane, Australia.
John F
JF
Fraser
D001513:Beds; D006348:Cardiac Surgical Procedures; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011182:Postoperative Care; D011446:Prospective Studies; D012121:Respiration, Artificial; D016683:Supine Position / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology*
electrical impedance tomography; end-expiratory lung volume; lung volume; mechanical ventilation; positioning; surgery