• George Ntoumenopoulos, Harriet Shannon, and Eleanor Main.
• Physiotherapy Department, Guy's and St Thomas' National Health Service Foundation Trust, London, UK. georgentou@yahoo.com
• Resp Care. 2011 Dec 1;56(12):1887-92.

BackgroundIntubation and mechanical ventilation can impair mucociliary clearance and cause secretion retention, airway occlusion, atelectasis, and pneumonia. Animal and laboratory work has demonstrated that mechanical ventilator settings can generate a flow bias (inspiratory or expiratory) that may result in mucus movement either away from the ventilator (deeper into the lungs) or toward the ventilator (toward the mouth), respectively. An absolute difference of 17 L/min, and a relative difference of ≥ 10%, between the expiratory and inspiratory flow have been reported as thresholds for mucus movement.MethodsWe measured baseline peak inspiratory and expiratory flows during quiet mechanical ventilation in a convenience sample of 20 intubated and ventilated adult patients.ResultsNineteen patients had an inspiratory flow bias of ≥ 10%. Eight patients had an absolute mean inspiratory flow bias of ≥ 17 L/min.ConclusionsCommonly used mechanical ventilator settings generate an inspiratory flow bias that may promote secretion retention.

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