Aspiration Risk

Etiology

Risk Factors

1. Cognitive Neurologic impairment: This can be due to stroke, seizure, intoxication, developmental delay, or any other cognitive impairment
2. Focal Neurologic impairment: This is related to a history of stroke, cranial nerve injury, and pharyngeal muscle injury.
3. Pulmonary disease: This includes patients who require mechanical ventilation for any reason, patients with a poor cough, or poor forced expiratory volume.
4. Supraglottic disease: This includes patients with anatomic irregularities in the oropharynx, poor dental hygiene, or disease states which cause esophageal dysmotility and impaired swallowing.
5. Other causes: Position changes can lead to aspiration even in healthy patients. Fifty percent of healthy individuals have silent aspiration during sleep identified by radio markers. Frequent, high-volume vomiting is another potential risk factor. Also, proton pump inhibition which changes the gastric pH, and subsequently the gastric flora, allowing overgrowth of potentially harmful microorganisms.[3][4] Analgesia of the pharynx and/or larynx, patients undergoing any oral, esophageal, or airway procedure, and trauma patients.
6. Mechanical. When patients have an NG tube, tracheostomy, upper endoscopy, bronchoscopy, or a gastrostomy feeding tube, they are at a risk for aspiration.

Epidemiology

Aspiration can affect any age group, but the youngest and oldest are at the highest risk because of a higher incidence of risk factors. It equally affects both genders.

The exact number of individuals who develop aspiration pneumonia is not known but they are not minuscule. Hospitalized patients develop aspiration pneumonitis as a result of a drug overdose, stroke, and other CNS pathology.

Pathophysiology

Healthy people in the community can tolerate small aspiration events without significant sequelae. However, micro-aspiration has been implicated in the pathogenesis of ventilator-associated pneumonia (VAP). Several factors may contribute to this. Ventilated patients have significant disease states that may predispose them to a superimposed infection. It should be noted that the endotracheal tube cuff, or tracheostomy tube cuff, does not protect from micro-aspiration, even when properly inflated. The use of endotracheal tubes with aspiration ports proximal to the cuff and connected to continuous suction has successfully decreased the risk of VAP but has not completely stopped its occurrence. It is prudent to use this for patients that are not expected to be weaned from the ventilator early.

Another important consideration is the widespread use of proton pump inhibitors in the intensive care unit (ICU) population. The use of these agents for peptic ulcer prophylaxis is ubiquitous and changes the gastric pH to a less acidic environment. This change in gastric pH leads to a change in the gastric flora, which favors pathogenic organisms over the normal colonizers. Micro-aspiration increases the likelihood of pathogenic organisms getting entry into the bronchial tree.[5]

Chemical pneumonitis occurs when a significant amount of gastric content is aspirated. This fluid devoid of bacteria can cause severe respiratory distress within 60 minutes. The acidic fluid results in severe damage to the upper and lower airways.

When patients develop aspiration pneumonia, the predominant organisms are anaerobes but one may also find gram-positive and gram-negative pathogens. Today, MRSA is widely reported to be the cause of aspiration pneumonia in the community.

Toxicokinetics

Aspiration of gastric acid into the bronchial tree can lead to chemical pneumonitis. Depending on the volume of aspirated material, it may be unilateral or bilateral. Often, because the right main-stem bronchus is less acutely angled at the carina, it affects the right lower lobe. However, based on the patient's position at the time of aspiration, any lobe may be affected, or all of them given a sufficiently large volume. In chemical aspiration, the injury to the bronchial mucosa is instantaneous. If witnessed, and the equipment is available, bronchoalveolar lavage may be performed to clear the airways and prevent obstruction. However, the tissue reaction to the acid naturally causes increased permeability of the mucosa and neutralization of the acid. The pH of the aspirate is also important, with the highest risk when aspirates are below 2.5 pH.

History and Physical

The pertinent physical findings include tachypnea, coughing, low oxygen saturation, rhonchi, rales, and the absence of breath sounds if an obstruction occurs. In obtunded patients, aspiration may be an ongoing process rather than a single event. History is important as both inpatients and outpatients may have had a witnessed aspiration or developed acute shortness of breath.

Evaluation

Get a chest x-ray to determine the extent of the aspiration. With sufficiently large aspirations, it may become necessary to perform bronchoscopy and bronchoalveolar lavage to clear as much macroscopic material as possible. Perform a swallow evaluation and barium swallow study on any patient at risk for aspiration by a speech therapist. The patient should be made NPO until evaluated. In young children and some adults, this is done under fluoroscopy. Dietary alterations, such as thickened liquids or pureed diets, can help patients with functional swallowing disorders.[6]

The blood gas can provide details about oxygenation and pH status. In addition, lactate levels can be used as a marker of shock.

Levels of electrolytes, BUN, and creatinine can be used to assess renal function and fluid status. The CBC may reveal leucocytosis, anemia, and thrombocytosis.

The value of sputum culture and gram stain is limited because of contamination. Blood cultures are often not positive and not useful for initial management.

The chest x-ray is important as it can provide information on the patient's position when aspiration occurs. The right lower lobe is the most common site for aspiration because of its vertical orientation. Individuals who aspirate while upright may have bilateral lower lobe infiltrates. Those lying in the left lateral decubitus position may have left-sided infiltrates. The upper lobe is classically involved when the patient aspirates in the prone position. This is often seen in alcoholics. Some patients may develop a parapneumonic effusion, which can be aspirated for culture and gram stain.

CT scan is not routine but may be required if the patient is not improving and there is suspicion of empyema or a cavitary lesion with necrosis.

Bronchoscopy is usually indicated in chemical pneumonitis when food or foreign material has been aspirated. The technique can also help retrieve samples for culture and can detect any bronchial obstruction.

Treatment / Management

It is important to determine the type of aspiration that has occurred. If a chemical pneumonitis is suspected, supportive therapy should be initiated. Depending on the overall health status of the patient, intubation may or may not be necessary and should be guided by the clinical picture. It should be noted that chemical pneumonitis may progress very rapidly and commonly leads to acute respiratory distress syndrome. As noted earlier, most cases are not purely chemical or bacterial, so prophylactic antibiotics should be instituted until definitive evidence exists that there is no infectious component.[7][8][9]

If large particles of food or other oral or gastric content enter the bronchial tree, it may require bronchoscopy to alleviate the obstruction of the airways. Any obstruction should be removed as quickly as possible to allow the normal physiologic mechanisms to mobilize secretions and infectious particles.

If the aspiration leads to bacterial pneumonia, appropriate cultures should be obtained and broad-spectrum antibiotics instituted. Once culture sensitivities are available, more directed antibiotic therapy can be used.

Patients at high risk for aspiration should have precautions put in place to reduce the risk. These precautions are dependent on the predisposing risk factors for any individual. Patients unable to contribute to their oral hygiene should have an oral cleansing program provided. This can be accomplished using chlorhexidine oral swabs twice daily, especially in chronically intubated patients. In the intubated patient, it is important to place the patient in a semi-recumbent position (head up 45 degrees) rather than supine, as long as it is not contraindicated. If ventilatory support is expected to be longer than 48 to 72 hours, an endotracheal tube with subglottic suction capability should be placed, and either continuous or intermittent suction should be utilized.

Hemodynamic compromise is common in aspiration pneumonia and patients may require ICU monitoring and inotropic support.

Debilitated and neurologically impaired patients should be fed in an upright position, and a swallow evaluation should be done by a speech therapist or nutritionist to determine the proper consistency of food and liquids. For those unable to tolerate oral intake, a percutaneous endoscopic gastrostomy tube (PEG tube) or jejunostomy tube (J-tube) should be considered if recovery is expected to be protracted.

Differential Diagnosis

• Pneumonia (bacterial or viral)
• Pulmonary embolism
• Acute respiratory distress syndrome (ARDS)
• Heart failure
• Lung cancer
• Tuberculosis
• Gastroesophageal reflux disease (GERD)

Pertinent Studies and Ongoing Trials

At the time of publication, there are two active studies found on ClinicalTrials.gov. These are:

• Gastric Ultrasound for Estimation of the Aspiration Risk Study - the University of Florida, Gainesville, Florida
• Continuous Supraglottic pH Monitoring in Prolonged Intubated Intensive Care Patients and High-Risk Aspiration Intraoperative Patients: Vanderbilt University Medical Center Nashville, Tennessee, United States

These two studies will help the clinician narrow the differential diagnosis when a new clinical finding of hypoxemia, tachypnea, or change in lung auscultation occurs.

Prognosis

The prognosis of aspiration is highly variable and dependent on a number of factors. Patients in good health before the event, small-volume aspiration, and better pulmonary reserve tend to have a more favorable outcome. Patients with poor host defenses, recurrent aspiration events, large-volume acid aspiration, and underlying pulmonary disease may poorly tolerate the insult. The majority of inpatient management should be focused on prevention when possible. The mortality rate for aspiration pneumonia varies from 10-50%. Any delay in diagnosis or treatment usually leads to high mortality.

Complications

• Lung abscess
• Empyema
• Bronchopleural fistula
• ARDS