Abstract: A total of 28 studies (involving 788 children and adults) were included in the review; 18 studies involving 296 participants were cross-over in design. Data were not published in sufficient detail in most of these studies to perform any meta-analysis. In 22 of the 28 studies the PEP technique was performed using a mask, in three of the studies a mouthpiece was used with nose clips and in three studies it was unclear whether a mask or mouthpiece was used. These studies compared PEP to ACBT, autogenic drainage (AD), oral oscillating PEP devices, high-frequency chest wall oscillation (HFCWO) and BiPaP and exercise. Forced expiratory volume in one second was the review's primary outcome and the most frequently reported outcome in the studies (24 studies, 716 participants). Single interventions or series of treatments that continued for up to three months demonstrated little or no difference in effect between PEP and other methods of airway clearance on this outcome (low- to moderate-quality evidence). However, long-term studies had equivocal or conflicting results regarding the effect on this outcome (low- to moderate-quality evidence). A second primary outcome was the number of respiratory exacerbations. There was a lower exacerbation rate in participants using PEP compared to other techniques when used with a mask for at least one year (five studies, 232 participants; moderate- to high-quality evidence). In one of the included studies which used PEP with a mouthpiece, it was reported (personal communication) that there was no difference in the number of respiratory exacerbations (66 participants, low-quality evidence). Participant preference was reported in 10 studies; and in all studies with an intervention period of at least one month, this was in favour of PEP. The results for the remaining outcome measures (including our third primary outcome of mucus clearance) were not examined or reported in sufficient detail to provide any high-quality evidence; only very low- to moderate-quality evidence was available for other outcomes. There was limited evidence reported on adverse events; these were measured in five studies, two of which found no events. In a study where infants performing either PEP or PDPV experienced some gastro-oesophageal reflux , this was more severe in the PDPV group (26 infants, low-quality evidence). In PEP versus oscillating PEP, adverse events were only reported in the flutter group (five participants complained of dizziness, which improved after further instructions on device use was provided) (22 participants, low-quality evidence). In PEP versus HFCWO, from one long-term high-quality study (107 participants) there was little or no difference in terms of number of adverse events; however, those in the PEP group had fewer adverse events related to the lower airways when compared to HFCWO (high-certainty evidence). Many studies had a risk of bias as they did not report how the randomisation sequence was either generated or concealed. Most studies reported the number of dropouts and also reported on all planned outcome measures. The evidence provided by this review is of variable quality, but suggests that all techniques and devices described may have a place in the clinical treatment of people with CF. Following meta-analyses of the effects of PEP versus other airway clearance techniques on lung function and patient preference, this Cochrane Review demonstrated that there was high-quality evidence that showed a significant reduction in pulmonary exacerbations when PEP using a mask was compared with HFCWO. It is important to note that airway clearance techniques should be individualised throughout life according to developmental stages, patient preferences, pulmonary symptoms and lung function. This also applies as conditions vary between baseline function and pulmonary exacerbations.

Plain-language summary: The review includes 28 studies with 788 people (from infants to adults) with CF with mild to severe lung disease. The studies compared PEP to other methods of chest physiotherapy; the length of treatment ranged from a single session to two years of treatment. Generally, the efficacy of PEP is similar to other methods of chest physiotherapy such as postural drainage with percussion, active cycle of breathing techniques, autogenic drainage, oscillatory PEP devices such as the flutter and acapella, thoracic oscillating devices such as the 'Vest', and bilevel positive airway pressure (BiPaP) (typically used for ventilatory support, but by changing the inspiratory and expiratory pressures on the device and combining it with huffing, BiPaP has been used for airway clearance). We found no difference between PEP and other forms of chest physiotherapy in lung function, the amount of mucus cleared from the airways or its related effects on the health of people with CF. However, the rate of flare ups of respiratory symptoms decreased in people using PEP compared to other forms of physiotherapy such as a vibrating PEP device or a vibrating vest. There was some evidence that people with CF may prefer PEP to other chest physiotherapy methods. There was no evidence of PEP causing harm, except in one study where infants performing either PEP or percussion in various positions which use gravity to help drain secretions, experienced some gastro-oesophageal reflux (regurgitation of food) in head-down positions; this was more severe in the group using postural drainage with percussion. In all the other trials PEP was performed in a sitting position. In 10 of the 28 studies studied single PEP treatment sessions. The results from these studies are very limited as they could not report on the number of respiratory infections and lung function did not change with just one treatment. Two one-year studies compared PEP to postural drainage and percussion; in the study with children, PEP improved their lung function, while in the adult study, lung function declined slightly with both PEP and postural drainage and percussion. Also, the method of performing PEP was different in the two age groups. Although PEP seems to have an advantage in reducing flare ups (based on the combined results of a few studies), different physiotherapy techniques and devices may be more or less effective at varying times and in different individuals during baseline function and chest flare ups. Each person should talk to their clinician to help choose which method of airway clearance is best for them and which they will adhere to, so as to provide the best quality of life and long-term outcomes. Some studies were of low quality. These studies highlight the difficulty in comparing studies using PEP compared to other forms of chest physiotherapy. Factors such as age and severity of lung disease in the participants may affect the results as well as the method of performing each treatment. Overall, the evidence provided by this review for whether PEP reduces flare ups compared to other forms of chest physiotherapy was moderate to high quality, but evidence for other outcomes was of very low to moderate quality, as results were limited.