Aspiration-induced lung injury

Abstract

Objective: Aspiration of oropharyngeal or gastric contents into the lower respiratory tract is a common event in critically ill patients and can lead to pneumonia or pneumonitis. Aspiration pneumonia is the leading cause of pneumonia in the intensive care unit and is one of the leading risk factors for acute lung injury and acute respiratory distress syndromes. Despite its frequency, it remains largely a disease of exclusion characterized by ill-defined infiltrates on the chest radiograph and hypoxia. An accurate ability to diagnose aspiration is paramount because different modalities of therapy, if applied early and selectively, could change the course of the disease. This article reviews definitions, diagnosis, epidemiology, pathophysiology, including animal models of aspiration-induced lung injury, and evidence-based clinical management. Additionally, a review of current and potential biomarkers that have been tested clinically in humans is provided.

Data sources: Data were obtained from a PubMed search of the medical literature. PubMed "related articles" search strategies were used.

Summary and conclusions: Aspiration in the intensive care unit is a clinically relevant problem requiring expertise and awareness. A definitive diagnosis of aspiration pneumonitis or pneumonia is challenging to make. Advances in specific biomarker profiles and prediction models may enhance the diagnosis and prognosis of clinical aspiration syndromes. Evidence-based management is supportive, including mechanical ventilation, bronchoscopy for particulate aspiration, consideration of empiric antibiotics for pneumonia treatment, and lower respiratory tract sampling to define pathogenic bacteria that are causative.

Figure 1. Relative severity of acute pulmonary injury in rats instilled with different gastric aspirates

The severity of lung injury in rats was measured as a function of time after tracheal instillation of ACID, SNAP, CASP, or normal saline (NS). Lung injury was assessed by ELISA measurements of albumin levels in bronchoalveolar lavage (BAL) (Panel A), and by the ratio of the arterial partial pressure of oxygen (PaO₂) to the fraction of inspired oxygen (FiO₂) (Panel B). Rats breathed 98% O₂ for a 15 min period prior to measurements of arterial oxygenation in order to emphasize the relative severity of intrapulmonary shunting. Data are Mean ± SEM for n= 9–2. Statistical symbols are: p<0.0001 compared to NS (+), ACID (*) and SNAP (#). Adapted from (5).

Figure 2. Proposed Algorithm for suspected or witnessed aspiration event

An algorithm, based on the available evidence to date, is presented. For practical purposes and based on current practice patterns, it is difficult to differentiate aspiration pneumonitis from aspiration pneumonia. The indication to perform endotracheal intubation and mechanical ventilation is not different from other clinical scenarios. Additionally the institution of the type of antibiotics should be based on local ecology of the ICU and should follow the practice guidelines (74).