Ventilator‑associated pneumonia (VAP) is a hospital‑acquired infection. Although there is no consensus definition, it is often defined as pneumonia that occurs in patients who have had intubation with an endotracheal or tracheostomy tube to help or control respiratory function continuously for at least 48 hours before the onset of the pneumonia (American Thoracic Society and Infectious Diseases Society of America, 2005). The presence of a tracheal tube interferes with the normal protective reflexes of the upper airway, such as coughing. This can result in impaired clearance of micro‑organisms and rapid colonisation of the oropharyngeal secretions with aerobic Gram‑negative bacteria. These contaminated secretions gather above the cuff of the tracheal tube and slowly leak down into the airway, leading to the unintentional entry of very small amounts of contaminated material into the respiratory tract (micro‑aspiration). This is the main cause of VAP (Hunter 2012). There are no standard criteria to diagnose VAP; a diagnosis is generally based on clinical signs and symptoms, chest X‑rays and microbiological confirmation (American Thoracic Society and Infectious Diseases Society of America, 2005).
Around 83,500 intubations were carried out in England in 2013–14 (Health and Social Care Information Centre, 2015). Because of a lack of standardised diagnostic criteria, it is difficult to quantify the exact incidence of VAP. However, VAP is a common complication of mechanical ventilation and the most common infection in ICU (Bouza et al. 2006, Zuschneid et al. 2007, Hunter 2012). Between 10% and 20% of patients who have mechanical ventilation for longer than 48 hours will develop VAP. Critically ill patients who develop VAP appear to be twice as likely to die compared with similar patients without VAP (Safdar et al. 2005).
Risk factors for the development of VAP include prolonged mechanical ventilation, older age, lying face‑up and comorbidities (Bauer et al. 2000). The risk for patients is highest during early ICU stay when it is estimated to be 3% per day during days 1–5 of ventilation, 2% per day during days 5–10 of ventilation and 1% per day thereafter (Masterton, 2008).
Various strategies have been developed to reduce the risk of ICU patients developing VAP, including specialised endotracheal tubes. These tubes include features for continuous subglottic drainage and adequate pressure of the endotracheal‑tube cuff to prevent leakage of colonised subglottic secretions into the lower airway (Kollef, 1999; Dodek et al. 2004).