Explore the effect of head of bed (HOB) angle on tidal volumes (Vt) delivered to patients on pressure support ventilation (PSV). Given the importance attached to compliance with the Institute of Healthcare Improvement's (IHI) ventilator care bundle mandating HOB at 30–45 degrees for the prevention of ventilator associated pneumonia (VAP), we decided to study the effect of HOB on Vt in patients being weaned using PSV.
34 stable patients being weaned on PSV were randomly and sequentially ventilated at HOB angles of 0,15,30,45, and 60 degrees at constant pressure. After allowing a two-minute period of equilibration, the resultant inspiratory Vt was measured 5 times and then averaged. The frequencies and percentages of the highest (best) and lowest (worse) HOB angles were judged by resultant Vt.
20 of the 34 patients (58.8%) achieved the best Vt at 30–45 degrees, however there were 3 patients (8.8%) that had their worse Vt at the recommended HOB angle. 14 patients (41.2%) achieved their best Vt in at a different angle, 2 patients at 60 degrees and 12 at 0 and 15 degrees.
HOB angle between 30–45 degrees resulted in the best Vt 58.8 % of the time; and worst Vt 8.8% of the time. Thus if HOB angle is adjusted per IHI's recommendations for VAP reduction, this will potentially result in suboptimal conditions for weaning 41.2% of the time. Thus while these angles may reduce the incidence of VAP they may also prolong weaning and time on mechanical ventilation by increasing the work of breathing in a significant number of patients.
Implementation of the IHI ventilator bundle is standard of care as it reportedly reduces the incidence of VAP. A key element of this bundle is elevation of the HOB to 30–45°. While HOB angles of 30–45° may lower the VAP rate, they maybe counterproductive if such angles are associated with impaired ventilator mechanics in individual patients. Study of HOB on time of weaning is warranted.
Laura Barber, No Financial Disclosure Information; No Product/Research Disclosure Information