Poor mask fit and mouth leak are associated with nasal symptoms and poor sleep quality in patients receiving domiciliary non-invasive ventilation (NIV) through a nasal mask. Normal subjects receiving continuous positive airways pressure demonstrate increased nasal resistance following periods of mouth leak. This study explores the effect of mouth leak during pressure-targeted nasal NIV, and whether this results in increased nasal resistance and consequently a reduction in effective ventilatory support.

A randomised crossover study of 16 normal subjects was performed on separate days. Comparison was made of the effect of 5min of mouth leak during daytime nasal NIV with and without heated humidification. Expired tidal volume (V_T), nasal resistance (R_N), and patient comfort were measured.

Mean change (Δ) in V_T and R_N were significantly less following mouth leak with heated humidification compared to the without (ΔV_T −36±65ml vs. −88±50ml, p<0.001; ΔR_N +0.9±0.4 vs. +2.0±0.7cmH₂Ols⁻¹, p<0.001). Baseline comfort was worse without humidification (5.3±0.4 vs. 6.2±0.4, p<0.01), and only deteriorated following mouth leak without humidification.

In normal subjects, heated humidification during nasal NIV attenuates the adverse effects of mouth leak on effective tidal volume, nasal resistance and improves overall comfort. Heated humidification should be considered as part of an approach to patients who are troubled with nasal symptoms, once leak has been minimised.