Importance of pulmonary aspiration

Five large studies from 1970 to 2000 documented the overall frequency of perioperative pulmonary aspiration to be approximately 1:3000; the mortality rate is 5% in patients who have a witnessed aspiration. Fortunately, not all patients who aspirate develop respiratory sequelae. The frequency of pulmonary complications and fatality as a consequence of aspiration are shown in Table 241-1.

Based on the information in Table 241-1, if similar mortality rates were to be found within the United States in general, approximately 200 deaths from perioperative pulmonary aspiration would be expected each year. In our largest institutions (i.e., those that perform as many as 50,000 general anesthetics annually), only 1 death from pulmonary aspiration would occur every 18 months. By applying the numbers (1 death per 75,000 general anesthetics) to individual practice settings, an idea of the anticipated frequency of this event can be derived.

Serious morbidity and considerable costs are associated with aspiration of gastric contents that results in an aspiration pneumonitis, acute lung injury, or acute respiratory distress syndrome. Approximately 25% of patients who perioperatively aspirate gastric contents require intensive care support. About 10% of these patients need mechanical ventilation support for more than 24 h, and, as mentioned previously, half of them will die.

Pulmonary aspiration in children

The rate of perioperative pulmonary aspiration in children is similar to that in adults, but children rarely die from aspiration. Their outcomes after aspiration tend to be better, and their recoveries seem to be quicker. The children at highest risk for aspiration and serious morbidity are those who are younger than 1 year and who have gastrointestinal ileus.

Use of medications and preoperative fasting

Medications used to decrease gastric contents, acidity, or both clearly work. However, no data suggest that the use of these medications decreases the risk of pulmonary aspiration. Many anesthesia organizations have developed guidelines to decrease the risk of perioperative aspiration, and all guidelines make similar recommendations. The recommendations of the American Society of Anesthesiologists for medications and fasting are given in Tables 241-2 and 241-3, respectively. Routine use of these medications is NOT recommended, and yet many anesthesia providers feel compelled to administer these medications to their patients, despite an adverse risk-benefit ratio. Evidence is lacking, but the only patients who might benefit are those in whom the anticipated risk of pulmonary aspiration is high.

Occurrence of aspiration in the perioperative period

Although aspiration may occur at any time (including immediately before anesthesia induction), it is most common during tracheal intubation and extubation, though a small percentage of those patients who aspirate do so during the intraoperative period. A common factor found in patients who aspirate when a tracheal tube is being used is inadequate muscle relaxation. Laryngoscopy in an inadequately paralyzed patient may cause the patient to gag and vomit. The same sequence occurs during extubation in a patient who is either weak or not alert and nonresponsive. There is insufficient information on the effectiveness of laryngeal mask airways to prevent aspiration, but there are case reports of aspiration with their use in both high-risk and low-risk patients. Patients who have had a previous esophagectomy will regurgitate gastric contents into their pharynx when supine and anesthetized; a tracheal tube is probably a better choice than a laryngeal mask airway to secure the airway for general anesthesia in these patients.

Management of perioperative pulmonary aspiration

Patients who aspirate require supportive care. Careful suctioning of aspirated material is useful to decrease the volume remaining in the lungs, but lavage with saline should not be performed because it may increase the spread of aspirate and has not been associated with improved outcomes. If particulate material is present, bronchoscopy should be performed to remove material that might obstruct bronchi. Prophylactic use of antibiotics or steroids has been ineffective in decreasing the frequency of pneumonia and of lung inflammation and has not been associated with improved outcomes. Respiratory care is provided as needed.

The severity of pulmonary aspiration and its consequences vary widely. Scant amounts of aspirated gastric contents may have little impact on the lungs, whereas large volumes of aspirate with a low pH (< 3) may immediately impair oxygenation and lead to the development of severe acute respiratory distress syndrome. Patients who aspirate small volumes perioperatively and who are asymptomatic during the first 2 postoperative hours are unlikely to develop respiratory sequelae. Therefore, it is reasonable to discharge asymptomatic patients to regular postoperative nursing units or even home with little risk of delayed development of respiratory symptoms.

Conclusion

Pulmonary aspiration is an infrequent perioperative event, occurring at a rate of approximately 1 per 3000 children and adult patients undergoing general anesthesia. This rate varies dramatically among patients, with those who are sicker and undergoing emergency procedures, especially if they have recently eaten or have an ileus or small bowel obstruction, are at greatest risk for regurgitation of gastric contents and have the highest rate of aspiration. Approximately 25% of patients who aspirate gastric contents during the perioperative period develop significant respiratory complications. The overall mortality rate from pulmonary aspiration is 5%, and death occurs primarily in adults; children rarely die after perioperative aspiration. The routine use of preoperative medications to reduce the risk of pulmonary aspiration is NOT warranted. Preoperative fasting guidelines suggest shortening fasting periods, especially for clear liquids.