• Marcia S Volpe, Alexander B Adams, Marcelo B P Amato, and John J Marini.
• Respiratory Intensive Care Unit, University of São Paulo School of Medicine, Brazil.
• Resp Care. 2008 Oct 1;53(10):1287-94.

BackgroundRetention of airway secretions is a common and serious problem in ventilated patients. Treating or avoiding secretion retention with mucus thinning, patient-positioning, airway suctioning, or chest or airway vibration or percussion may provide short-term benefit.MethodsIn a series of laboratory experiments with a test-lung system we examined the role of ventilator settings and lung-impedance on secretion retention and expulsion. Known quantities of a synthetic dye-stained mucus simulant with clinically relevant properties were injected into a transparent tube the diameter of an adult trachea and exposed to various mechanical-ventilation conditions. Mucus-simulant movement was measured with a photodensitometric technique and examined with image-analysis software. We tested 2 mucus-simulant viscosities and various peak flows, inspiratory/expiratory flow ratios, intrinsic positive end-expiratory pressures, ventilation waveforms, and impedance values.ResultsVentilator settings that produced flow bias had a major effect on mucus movement. Expiratory flow bias associated with intrinsic positive end-expiratory pressure generated by elevated minute ventilation moved mucus toward the airway opening, whereas intrinsic positive end-expiratory pressure generated by increased airway resistance moved the mucus toward the lungs. Inter-lung transfer of mucus simulant occurred rapidly across the "carinal divider" between interconnected test lungs set to radically different compliances; the mucus moved out of the low-compliance lung and into the high-compliance lung.ConclusionsThe movement of mucus simulant was influenced by the ventilation pattern and lung impedance. Flow bias obtained with ventilator settings may clear or embed mucus during mechanical ventilation.

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