Combination of Non-invasive Positive Pressure Ventilation with Airway Clearance Techniques

Table 1 shows the summary of three studies evaluating the short-term effectiveness of the combination of either FET or ACTB or directed cough with NIPPV.^20–22 A randomised cross-over design was used in these studies. In one study the number of directed cough manoeuvres was repeated the same number of times incorporating different treatments: these were PEPm, CPAP, bi-level ventilation and directed cough, which was used also as single ACT (control treatment).²² Various radioaerosol studies showed that coughing and FET improve tracheobronchial clearance and may influence sputum weight. For this reason, the standardisation of the number of cough and FET manoeuvres is an important methodological aspect in short-term studies that compare ACTs that include coughing and huffing.⁵ Holland et al. and Placidi et al. included patients with CF and severe lung disease who were admitted to hospital for treatment of a pulmonary exacerbation.^21,22

As shown in Table 1, patients were asked to report their subjective impressions, such as fatigue or breathlessness, induced by the ACT.^20–22 They felt less tired and dyspnoeic after the treatment, which combined one ACT with NIPPV compared with the standard treatment.^20–22 NIPPV has been shown to decrease inspiratory muscle work and improve respiratory muscle performance: it may explain the improvement in subjective scores recorded in those studies.²⁷ Fauroux et al. and Holland et al. found a statistically significant decrease in maximum inspiratory pressure during a standard ACT session.^20,21 Inspiratory muscle strength improved after an NIPPV session of similar length in both studies.^20,21 Similar results were found for maximum expiratory pressure.^20,21 These findings are also relevant for the effectiveness of ACTs. In fact, if inspiratory and expiratory muscle strength is preserved, repeated expulsive efforts and deep inspirations with breath holding at total lung capacity can be performed comfortably and effectively during an ACT session.⁶ When NIPPV is administered to patients with severe lung disease, tidal volume increases and respiratory rate decreases: the resulting improvement in alveolar ventilation could explain the increase in oxygen saturation observed during ACT combined with NIPPV.^20,21,27 The use of positive expiratory pressure during NIPPV may have a role in the prevention of airway closure and collapse during forced expirations required for airway clearance in patients with bronchiectasis and severe lung disease.^6,7

In concordance with previous short-term studies of airway clearance techniques, Table 1 shows that standard ACTs had no effect on lung function parameters.^5,20–22 The findings of the study by Placidi et al. suggested that sputum weight mainly represented mucus clearance by directed cough.²² Spirometric testing and sputum weight could be considered a safety evaluation of NIPPV as an adjunct to standard ACTs. This applies especially in light of concerns regarding impaction of secretions in the airways as a result of positive pressure.²⁸ The studies reported in Table 1 found no significant change in both spirometry and sputum weight using NIPPV combined with ACTs compared with standard ACTs.^20–22 Placidi et al. showed that sputum clearance and spirometry were not impaired by the short-term administration of either CPAP or bi-level ventilation combined with directed cough.²² To our knowledge, it is the first report on CPAP used to clear bronchial secretions in CF.²²

Conclusions

The limitation of sputum weight and spirometry for assessing the short-term effectiveness of ACTs should make us cautious in choosing one technique over another. More sensitive measurements should be used to assess the short-term effects of removal of mucus plugs from airways. High-resolution chest computed tomography, radioaerosol studies and lung function methods for testing regional distribution of ventilation should be performed with this aim. Moreover, clinically valuable information can be gained from long-term studies that assess the efficacy and safety of ACTs considering decline in lung function and morbidity as outcome measures.

According to the benefits of NIPPV on respiratory work and gas exchange and to the results shown in Table 1 of comparable spirometry and amount of sputum cleared using the different treatments, we could consider the short-term administration of NIPPV combined with an ACT as a possible airway clearance regimen. This choice could be of potential clinical relevance and justifiable when patients felt tired and uncomfortable and when significant falls in oxygen saturation were recorded using standard ACTs in patients with severe lung disease, especially during pulmonary exacerbations. Further studies are necessary to evaluate the physiological effects of NIPPV in the context of ACTs in both stable clinical conditions and during pulmonary exacerbations of CF. Moreover, the effect of nocturnal and long-term NIPPV on sputum clearance should be addressed in future studies.