Aspiration: Understanding the Risks and Optimizing Management

Assessment of Patient Risk

Assessment of the risk for aspiration should be a part of the routine preoperative evaluation. Because most patients are presumed to be at low risk, the history and clinical evaluation related to risk for aspiration is often limited. For those patients with known risk factors for aspiration, a more thorough evaluation is required to assess the likelihood of risk, including preoperative silent aspiration, and to guide anesthesia and perioperative management. Patients at highest risk for aspiration include those with known swallowing and esophageal mobility disorders, those with epiglottic and vocal cord abnormalities, and patients with reduced cough reflex. ^, Elderly patients, those who require emergency surgery associated with recent trauma, and those who have recently eaten, particularly solid foods, have a higher risk for aspirating. Other risk factors include delayed gastric emptying as is associated with diabetes mellitus, pregnancy, and obesity. Clinical management strategies also affect the risk for aspiration, including intraoperative positioning (supine, Trendelenburg, or lithotomy) and administration of positive pressure ventilation before securing the airway. Because the clinical manifestations of aspiration are variable, the actual risk and incidence of aspiration may be significantly underestimated. Some adults and children experience silent aspiration sometimes during normal sleep, further complicating the understanding of the true risk for aspiration in any patient population. ^, As a result, it is essential to consider the risk for aspiration as part of the preoperative clinical assessment for all patients and, when clinically indicated, to plan for management throughout the perioperative period (See the section on Evidence: Risk Factors for Aspiration).

Management Strategies to Minimize Risk of Aspiration

A number of approaches have been recommended to reduce the risk for aspiration and the physiologic consequences of aspiration should it occur. The primary method for reducing the likelihood of aspiration is to ensure that the patient has an empty stomach before inducing anesthesia. Preoperative fasting is the recommended approach for reducing the quantity of gastric contents, although it is not failproof. Gastric secretions are also not eliminated by fasting. Because gastric emptying time varies considerably and is affected by underlying medical conditions, pain, and some medications, defining the exact duration of fasting that is required is challenging. Nonetheless, a number of recommendations have been proposed and guidelines have been developed to guide management. Current practice guidelines define the most appropriate duration of fasting for adults and children. They recommend a minimum fasting period of 2 hours after ingesting clear liquids (except alcohol). Adult patients should be advised to refrain from ingesting solid foods for at least 6 hours before surgery, although a longer period of time may be required if the patient has ingested a high-fat diet. For children, breast milk can be ingested up to 4 hours and infant formulas can be ingested up to 6 hours before elective surgical procedures. Although these guidelines are helpful, after fasting for the recommended time periods or longer, some patients still have significant gastric volumes and remain at high risk. Although there is variability in gastric volume after fasting of any duration, some investigators have suggested that shorter periods of time between feedings and induction of anesthesia may be appropriate, particularly if only clear liquids were taken or there is objective assessment of intragastric volumes using ultrasound or other techniques to confirm that the stomach is empty. As a result, although preoperative fasting guidelines are helpful, each anesthesiologist must still be cognizant of the potential risk for aspiration even when a patient has been fasting for an extended period of time.

Other management strategies are also recommended to either reduce the risk for aspiration or limit the consequences should an aspiration event occur. To reduce the volume and acidity of gastric secretions, a number of pharmacologic agents such as gastrointestinal stimulants, gastric acid secretion blockers, and antacids are commonly used by many clinicians. Although of theoretic value, there is, unfortunately, limited data to support their routine use. As a result, the routine use of any of these agents is not recommended, except in patients with a high likelihood of delayed gastric emptying, such as obese, pregnant, diabetic, or trauma patients. For this select group of patients at higher risk for aspiration, antacids and metoclopramide should be considered to reduce gastric volume and increase gastric pH. If antacids are to be used, nonparticulate agents (e.g., sodium citrate) should be administered. The routine use of other agents, such as antiemetics or anticholinergics, has not been demonstrated to reduce the risk for pulmonary aspiration, although they may be of value in select patients at high risk for aspiration or in patients with known gastroesophageal reflux, including some elderly patients. Similarly, antiemetics should be considered for patients with a history of significant nausea and vomiting, although they should not be routinely administered to most patients.

Anesthetic Induction Strategies in Patients at Risk

The optimal approach to minimizing the risk for aspiration during airway management or at other times during a patient’s perioperative care is not known. For patients at known increased risk for aspiration, including those with a full stomach or delayed gastric emptying (e.g., patients with diabetes, obesity, ascites, strictures or bowel obstruction, trauma), the airway must be secured with extreme caution and steps taken to reduce the likelihood of either passive regurgitation or active vomiting and its consequences. Before inducing anesthesia, administration of a nonparticulate antacid (sodium citrate) to neutralize the gastric pH and metoclopramide to improve gastric emptying may be provided. When clinically feasible, the patient should be positioned with their head elevated. The approach to securing the airway should be based on the patient’s clinical condition and the skills of the intubating provider. For most patients at risk for aspiration, either awake fiberoptic intubation or a rapid sequence induction (RSI) is used to secure the airway quickly, particularly for those patients with a full stomach. As part of the RSI, preoxygenation using a tight-fitting mask while the patient is spontaneously breathing is provided before administration of any drugs. Thereafter anesthetic agents and muscle relaxants are administered. Although succinylcholine can increase intragastric pressure, either depolarizing or nondepolarizing muscle relaxants have been successfully used during RSI. Positive pressure ventilation is generally avoided to minimize the risk for gastric distension before securing the airway unless oxygenation deteriorates, or the intubation attempt is lengthy.

Cricoid pressure has also been advocated as part of the RSI to reduce the risk for regurgitation and aspiration. Until recently, cricoid pressure represented the standard of care during induction of anesthesia and tracheal intubation patients at risk for aspiration. Despite years of experience, limited data document the value of cricoid pressure. ^, As a result, current practice does not require the application of cricoid pressure, although some clinicians continue to advocate for its use as part of the RSI management (see Areas of Uncertainty section).

A cuffed endotracheal tube is generally used for all adult patients, whether at high risk for aspiration or not. The cuffed endotracheal tube protects against aspiration of larger particulate matter. Nevertheless, although the cuff of the endotracheal tube provides some protection from aspiration, the presence of a cuff alone may not prevent aspiration of liquids around the cuff, particularly if the patient is in the supine (or head down) position, has increased gastric pressure, or has increased volume of secretions. Endotracheal tubes with low-volume, low-pressure cuffs may reduce the risk for aspiration. Other studies have suggested that endotracheal tubes with subglottic suction ports may allow for better suctioning of secretions above the cuff of the endotracheal tube and thus may minimize the risk for aspiration when the patient is intubated. ^, Although placement of a cuffed endotracheal tube remains the most common way to secure the airway and prevent aspiration, placement of selected types of laryngeal mask airways have been shown to protect adult and pediatric patients from large-volume aspiration, although no studies have confirmed that these airways are as effective as cuffed endotracheal tubes at reducing the risk for aspiration. ^,

Management Strategies After Documented Aspiration

When a patient has aspirated, the primary therapeutic interventions are supportive. No specific therapies directed toward the aspiration itself are generally required unless there is clinical evidence to suggest the airway obstruction is caused by particulate or foreign body aspiration. The primary intervention is to optimize gas exchange, both oxygenation and CO ₂ removal. Supplemental oxygen should be provided to maintain adequate oxygenation. If the patient is not intubated, high-flow oxygen should be administered to achieve a safe oxygen saturation. If the patient is already intubated or is hypoventilating, some level of ventilatory support may be required, including pressure support ventilation or mandatory ventilatory support.

For management of the aspiration, routine bronchopulmonary hygiene, including suctioning of pulmonary secretions, and other supportive measures are the only additional approaches that have been demonstrated to be effective. Use of other therapies immediately after a witnessed or suspected aspiration have not been demonstrated to improve the clinical situation or outcome, although a number of other interventions may be appropriate for specific indications. For example, if the aspiration is witnessed, careful assessment of the oropharynx should be performed. If necessary, the removal of debris from the oropharynx should be done with the use of a Yankauer suction catheter. If the debris is causing complete or partial upper airway obstruction, removal of the material, whether solid food or other material, should be done immediately, most often using bronchoscopy. If regurgitation or vomiting continues, the patient should be placed in the head down lateral decubitus position to minimize the risk for further aspiration into the airway. Placement of a nasogastric tube, if not already in place, may be required to remove additional gastric contents and prevent ongoing aspiration, although leaving a nasogastric tube in place may increase the risk for reflux. Bronchodilator therapy with beta-agonists is indicated if bronchospasm is triggered by the aspiration. The bronchodilatory therapy will not only improve the wheezing but also might improve mucociliary function and facilitate clearance of secretions in the postoperative period.

For some patients with large-volume aspiration or those known to have aspirated particulate material or material with a low pH, additional interventions may be required. Bronchoalveolar lavage is not indicated in these situations because it can cause the aspirate to move more distally into the smaller airways rather than facilitate clearance of the aspirate. Lavage does not reduce the likelihood of pneumonitis. Bronchoscopy is indicated only when a foreign body is identified in the larger airways. If the patient develops further complications after aspiration, including systemic inflammation and sepsis, additional therapeutic interventions may be necessary, including vasopressors and appropriate fluid resuscitation for optimization of intravascular volume.

For most patients who aspirate, antibiotic therapy is not required and should be withheld. Rarely is infection an associated clinical problem immediately after aspiration. Unless there is documented evidence of infection, the early administration of antibiotics may be counterproductive, increasing the likelihood of antibiotic-resistant infection. Antibiotics should be administered based on documented clinical infection with a positive sputum Gram stain, positive cultures, or a focal persistent infiltrate associated with fever and an elevated white blood cell count. Nevertheless, early administration of antibiotics may be appropriate in some select clinical situations. For example, if a patient has known bowel obstruction or the aspirated material is feculent, antibiotic therapy that provides adequate gram-negative bacterial coverage should be initiated. Later in the patient’s postoperative course, if a pulmonary infiltrate persists and cultures obtained by bronchoalveolar lavage become positive, antibiotic coverage directed toward the offending organism should be initiated.

Incidence of Clinically Significant Aspiration

Although aspiration is of concern to every anesthesiologist, the incidence of aspiration in patients receiving anesthesia is difficult to define. It has been found to occur in 1 per 2000 to 3000 adult patients undergoing elective surgery and in 1 per 1200 to 2600 anesthetic procedures in children. ^, During emergency procedures, the incidence may be three to four times higher than it is during elective procedures. ^, One of the difficulties in evaluating information obtained from published studies of the risk for aspiration is that the diagnosis is difficult to make and the frequency varies considerably by patient population and approaches to airway management. In some cases, the aspiration may be silent and unrecognized. Diagnosing silent aspiration is also challenging because the clinical manifestations are variable. Even patients with witnessed aspiration may not demonstrate any sequelae. As a result, the diagnosis may be missed because it is based primarily on the complications that result from the aspiration rather than on observation of aspiration itself.