Short-term appraisal of the effects and safety of manual versus ventilator hyperinflation in an animal model of severe pneumonia

BACKGROUND: In patients on mechanical ventilation, lung hyperinflation is often performed to reverse atelectasis and clear retained mucus. We evaluated the effects of manual hyperinflation and ventilator hyperinflation on mucus clearance, gas exchange, pulmonary mechanics, and hemodynamics. METHODS: Six mechanically ventilated pigs with severe Pseudomonas aeruginosa pneumonia randomly received either 12 manual hyperinflation breaths over a period of 2 min (through a gradual manual compression of a resuscitation bag within 4 s to achieve 40 cm H2O of airway pressure), or 12 ventilator hyperinflation over 2 min to achieve the same ventilatory end points as in manual hyperinflation. Mucus clearance rate was measured through fluoroscopic tracking of tracheal markers. Prior to each maneuver and 15 min thereafter, we assessed arterial and mixed gas exchange, pulmonary mechanics, and hemodynamics. RESULTS: Both manual hyperinflation and ventilator hyperinflation significantly decreased inspiratory flow by approximately 16 L/min (P <.001) and increased peak expiratory flow by roughly 44 L/min (P <.001). The median (interquartile range) mucus clearance rate was 1.31 (0.84–2.30) prior to the interventions, and 0.70 (0.00–2.58) and 0.65 (0.45–1.47) during manual hyperinflation and ventilator hyperinflation, respectively (P =.09). Hyperinflations, whether delivered manually or through the ventilator, did not significantly modify pulmonary or hemodynamic parameters. CONCLUSIONS: In an animal model of severe P. aeruginosa pneumonia, neither manual hyperinflation nor ventilator hyperinflation improved mucus clearance. If confirmed in comprehensive clinical experimentations, these findings should promote reappraisal of indications for both manual hyperinflation and ventilator hyperin-flation as a therapeutic technique for mucus clearance and atelectasis reversal.