Description of the condition
Acute bronchiolitis is one of the most frequent causes of emergency department visits and hospitalisation in infants (Deshpande 2003; Handforth 2000). Bronchiolitis (inflammation of the small airways in the lung) is predominantly a viral disease and usually affects infants and children younger than three years of age. It is mostly caused by respiratory syncytial virus (RSV) (CDC 2010). About 2% to 3% of all infants require hospitalisation due to bronchiolitis in the USA (Meissner 2009). Bronchiolitis occurs more frequently in males infants who are not breast fed, and who live in crowded conditions (Meates-Dennis 2005).
Bronchiolitis typically presents with viral symptoms (sneezing, rhinorrhoea and fever) which gradually progress to paroxysmal cough, wheezing, respiratory distress and irritability. Chest findings are non-specific and include wheezing, with or without fine crackles. Although not required for diagnosis, chest X-ray may reveal hyperinflated lungs with patchy atelectasis. About 10% to 15% of patients hospitalised with bronchiolitis respond poorly to treatment and require intensive care management. Further, nearly half of these develop respiratory failure and need mechanical ventilation (Navas 1992). Although uncommon, bronchiolitis may cause mortality which ranges from 0.5% to 2% (Kabir 2003; Levy 1997). The mortality rate is higher in low-income countries.
The management of bronchiolitis mainly includes supportive measures like adequate fluid intake, antipyretics and humidified oxygen supplementation if hypoxia is present (Davison 2004). Nebulised adrenaline (Hartling 2011a; Hartling 2011b) and hypertonic nebulised saline (Zhang 2011) have been found to be beneficial in acute bronchiolitis. Other therapeutic options, such as corticosteroid therapies (Fernandes 2010), antibiotics (Spurling 2011), bronchodilators (Gadomski 2010), heliox inhalation therapy (Liet 2010), chest physiotherapy (Roqué i Figuls 2012), nebulised recombinant human deoxyribonuclease (Merkus 2001; Nasr 2001), ribavirin (Ventre 2007) and steam inhalation (Umoren 2011), have been tried with no definitive benefit in bronchiolitis.
Description of the intervention
Continuous positive airway pressure (CPAP) is the application of positive pressure to the airways of the spontaneously breathing patient throughout the respiratory cycle (Duncan 1986). It keeps the airways open. CPAP may be applied to infants using nasal prongs (NCPAP), nasopharyngeal tube (NP-CPAP) or infant nasal mask (NM-CPAP). It is administered with a commercially available circuit used in conjunction with a continuous flow source, or a ventilator. CPAP devices may include the function of providing a heated and humidified flow to the patient. The use of CPAP has been associated with some adverse effects which may include local and systemic effects, for example, nasal mucosal damage, nasal excoriation, scarring, pressure necrosis and septal distortion (Lee 2002; Robertson 1996), aspiration secondary to gastric insufflation (Kiciman 1998), pneumothorax (de Bie 2002) and a decrease in cardiac output due to impaired pulmonary blood flow.
How the intervention might work
In bronchiolitis the peripheral airways are most severely affected by inflammation. In infants with acute bronchiolitis expiratory resistance is found to be greater than inspiratory resistance suggesting dynamic narrowing of the airways on expiration (Wohl 1969). Acute bronchiolitis is associated with increased thoracic gas volume (air trapping) and total pulmonary resistance, and decreased dynamic compliance (Phelan 1968). Initially infants compensate for the increased physiological dead space by increasing respiratory rate resulting in increased minute volume. Gradually they becomes exhausted and minute volume falls with increase in partial pressure of carbon dioxide (PCO2) and hypoxaemia. From here, the infant may improve with oxygen supplementation or may progress to respiratory failure.
When CPAP is applied it increases the functional residual capacity of lungs which results in enlargement of the diameter of almost all airways including the peripheral airways. The widening of the peripheral airways allows deflation of over-distended lungs in bronchiolitis. The increase in airway pressure also prevents the collapse of poorly supported peripheral small airways during expiration. CPAP has been used in bronchiolitis and benefits have been noted in observational studies (Beasley 1981; Soong 1993). One of the advantages is that it may prevent the need for mechanical ventilation in infants with acute bronchiolitis.
Why it is important to do this review
Acute bronchiolitis is a common clinical condition in paediatrics, yet no specific treatment is available except for supportive therapy. CPAP is often used for its management on an empiric basis (i.e. based on personal experience without good evidence from literature). We aim to assess the role of CPAP for this condition and a systematic review is best suited for the purpose.