Background Elevating the head of bed (HOB) 30°-45° has been widely supported as a means of ventilator associated pneumonia (VAP) prevention.However,it was poorly adhered in clinical practice.This observational study aimed to investigate the factors impeding this simple practice at the bedside.Methods This prospective study was conducted in 33 Chinese academic hospital intensive care units (ICUs).HOB angle was measured four times daily at 5-7 hour intervals.The predefined HOB elevation goal was an angle ＞30°.Results The overall rate of achieving the HOB goal was 27.8％ of the 8647 measurements in 314 patients during 2842 ventilation days.The HOB goal of ＞3 times/d was consistently achieved only in 15.9％ of the cases.Almost 60％ of patients had at least one 24 hours period during which the HOB goal was never documented.This low rate of protocol compliance was not associated with acute physiology and chronic health evaluation (APACHE) Ⅱ score or dependence on vasopressors.In a survey,nurse workload was identified as the most important factor for non-compliance with the HOB goal.In addition,the rates of compliance were significantly different (P ＜0.001) between physicians self-reporting that they either did or did not know the Institutes of Healthcare Improvement (IHI) ventilator bundle.Conclusions Low adherence to a HOB angle of ＞30° was found in this nationwide survey.Nursing workload and lack of knowledge on VAP prevention were important barriers to changing this practice.