QUESTION: What is the effect of the Mapleson C circuit compared with the Laerdal circuit in removing secretions and improving ventilation and gas exchange during manual hyperinflation? DESIGN: Prospective, randomised, cross-over trial. PARTICIPANTS: Twenty patients from a tertiary-level intensive care unit who were being mechanically ventilated. INTERVENTION: Manual hyperinflation in side-lying with both the Mapleson C or Laerdal circuit on the one day, one circuit in the morning and one in the afternoon, with a washout period of at least three hours between them. OUTCOME MEASURES: Secretion clearance was measured as sputum weight, ventilation was measured as respiratory compliance and tidal volume, while gas exchange was measured as oxygenation and CO2 removal. RESULTS: The Mapleson C circuit cleared 0.89 g (95% CI 0.80 to 1.15) more secretions than the Laerdal circuit (p < 0.02). There was no difference between the Mapleson C and the Laerdal circuits on respiratory compliance (p = 0.81), tidal volume (p = 0.45), oxygenation (p = 0.28), or CO2 removal (p = 0.17). CONCLUSION: Although more secretions were cleared using the Mapleson C compared with the Laerdal circuit in this study, this had no consequence in terms of oxygenation and compliance only trended to improve. As the study was underpowered the clinical significance of these findings is not clear.

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