Aspiration of oral and gastro-esophageal contents is a common cause of direct lung injury in trauma and critically ill patients.  The resulting injury can lead to a variety of pulmonary syndromes, most notably the inflammatory process of aspiration pneumonitis or the infectious process of aspiration pneumonia.  Approximately one-third of these patients will go on to develop a more serious and protracted pulmonary inflammatory response known as acute lung injury (ALI) or worse, acute respiratory distress syndrome (ARDS).  The economic burden of ALI/ARDS in the United States is substantial, estimated at $3.5-6.0 billion annually.  Moreover, despite major recent advances in critical care medicine and in the management of trauma patients, overall mortality from ARDS remains unacceptably high at 30-40%. 

Though common, most aspiration events are unwitnessed or silent, which makes diagnosis difficult in the early phase of injury.  Recognition of risk factors for aspiration is therefore imperative.  Risk factors include:

• Anatomic abnormalities of the upper gastrointestinal tract such as gastro-esophageal reflux, gastroparesis, bowel obstruction, and ileus
• Elderly and nursing home patients who have a high incidence of reflux disease, dysphagia, and poor oral hygiene
• Dysphagia from neurologic disorders including stroke, seizures, and head/spinal cord injuries
• Decreased level of consciousness associated with trauma, intoxication, or sedation from general anesthesia
• Nasogastric tube placement and feeding
• Endotracheal tube intubation
• Obesity

 Unfortunately, modification of many aspiration-associated risk factors is not possible. Therefore, prevention is the key.  Preventative measures include the followings:

• Minimizing the time patients are supine by maintaining head-of-bed elevation at 30-45° or using reverse Trendelenburg positioning if spinal flexion is contraindicated
• Rapid sequence intubation for trauma patients
• Maintaining endotracheal tube pressures > 20 cm H­­₂0 and avoiding excessive tube manipulation to decrease microaspiration events
• Nasogastric or gastrostomy tube decompression
• Minimizing, or completely discontinuing sedating medications as clinically appropriate
• Frequent and thorough oral care to decrease bacterial loads
• In some patients, formal swallow evaluation prior to initiating or advancing oral feeding, especially after recent extubation

In the case of witnessed or suspected aspiration, particulate matter and excessive secretions should be suctioned from the upper airway.  Additional therapies with nebulized bronchodilators and humidified oxygen along with close observation may prevent the onset of ALI.  Intubation is not required if there is no respiratory distress.  Prophylaxis with antibiotics is not recommended unless there are signs and symptoms of an acute infectious process occurring at least 48 hours after a witnessed event, or if aspiration has occurred in a patient with a bowel obstruction where the aspirate is likely to be colonized with enteric organisms. There is no data supporting early fiberoptic bronchoscopy after aspiration of gastric contents.

Once aspiration has occurred leading to acute respiratory failure, the patients should be intubated and placed on mechanical ventilator support.  Therapeutic measures of benefit are limited to low tidal-volume ventilation and conservative fluid management.  Targeted medical therapies to reduce inflammation have not demonstrated any reduction in mortality to date.  Antibiotics should be started if bacterial culture shows > 10⁴ cfu /ml in bronchoalveolar lavage (BAL) specimen.  Ongoing basic science and clinical research are crucial for understanding the pathophysiology of aspiration-induced lung injury and developing novel therapeutic strategies.

Additional Information:

Acute Respiratory Distress Syndrome – Medscape Reference

http://emedicine.medscape.com/article/165139-overview

Aspiration Pneumonia – Medscape Reference

http://emedicine.medscape.com/article/296198-overview

Reference:

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Authors: Peter Smit, MD, MS, W. Alan Guo, MD, PhD, FACS