Diagnosis of Ventilator- Associated Pneumonia in Children: A Comparative Study of Bronchoscopic and Non-Bronchoscopic Methods

Introduction Ventilator associated pneumonia (VAP) is defined as nosocomial pneumonia developing in a patient 48 hours after the initiation of mechanical ventilatory support (by endotracheal tube (ETT) or tracheostomy tube) (1). Despite major advances in the techniques for the management of ventilator dependent patients, VAP continues to complicate the course of 8-28% of the patients receiving mechanical ventilation (MV) (1-3). Rates of pneumonia are considerably higher among patients hospitalized in intensive care units (ICUs) compared with those in the hospital wards. The risk of pneumonia is increased 3 to 10 folds for the intubated patient receiving mechanical ventilation (1, 2, 4-6). The mortality with VAP is considerably high, varying from 24 to 50% and can reach as high as 76% in some specific settings or when lung infection is caused by high risk pathogens (1).

For many years, VAP was diagnosed by clinical criteria such as fever, leukocytosis and purulent tracheobronchial secretions supported by the radiological evidence of new or persistent pulmonary infiltrates (7). However these criteria are non-specific (8). Studies have shown that clinical criteria have imperfect diagnostic reliability in ventilated patients, and therefore, additional procedures such as cultures of the lower respiratory tract are required for the accurate diagnosis and treatment of VAP (9, 10). However, clinical criteria do remain crucial for defining those patients who may require respiratory sampling (1).

Given the invasive nature and high incidence of complications with techniques such as lung biopsy and percutaneous needle aspiration, these have now been replaced by safer methods such as endotracheal aspiration (ETA), bronchoscopic bronchoalveolar lavage (BAL), protected sampling brushing (PSB) and non-bronchoscopic methods such as blind BAL and blind bronchial aspirates (BBA) as approaches for the definitive diagnosis of VAP (8, 12). The ETA is the most widely used sampling technique in ventilated patients (13). This technique is known to have a high sensitivity but also has a high false positive rate and correlates poorly to actual pathogen due to respiratory tract colonization (14). Invasive bronchoscopic sampling techniques like bronchoscopic BAL and PSB are currently considered as the reliable sampling techniques in adult ICU to recover organism from the lower respiratory tract (15) and have high sensitivity and specificity (16). The usefulness of these techniques in routine clinical practice is, however, hampered by the potential risks of bronchoscopy, the unavailability of equipment and trained personnel on a 24-hour basis in many critical care facilities and the associated cost.

The microscopic identification of organisms causing pneumonia requires a simple, safe, effective and inexpensive method with good sensitivity and specificity with results at least equal to bronchoscopic BAL. Non-bronchoscopic bronchoalveolar lavage and BBS have been reported to have good efficacy in the microbiological diagnosis of VAP (17- 19). Though these techniques have not been standardized in children, they appear promising (20).

The methods of diagnosing VAP are debatable and there is no accepted 'gold standard'. No study has shown the superiority of a specific method. The methods proposed have different sensitivities and specificities (11). So, additional validation studies are needed. Other indications of the need for further studies of the non-bronchoscopically directed techniques are the absence of standardized diagnostic thresholds for quantitative cultures, and to develop cheaper, reliable and easy to use diagnostic method involving inexpensive easily available equipment.