Pulmonary aspiration during surgery is the entry of foreign material, typically stomach contents, into the lungs. While uncommon in modern surgical practice, it is a serious complication that anesthesiologists work diligently to prevent. Consequences can range from mild irritation to severe lung injury and respiratory failure, directly impacting a patient’s recovery. The body’s natural defenses are temporarily suspended during the procedure, creating a window of vulnerability that requires careful management.
How Aspiration Happens Under Anesthesia
General anesthesia temporarily overrides the body’s natural protective reflexes that guard the airway, suppressing the cough and gag reflexes with anesthetic agents. This loss of protective function means that material from the stomach can enter the trachea and lungs without immediately provoking a clearing action.
Anesthetic medications can cause the lower esophageal sphincter, the muscular ring between the esophagus and the stomach, to relax. This relaxation allows stomach contents to flow backward into the esophagus and throat, a process called regurgitation. When protective reflexes are absent, this regurgitated material—including stomach acid, bile, and partially digested food—can be inhaled into the lungs.
The risk is particularly high during the induction phase, as the patient is losing consciousness, and during emergence, as the effects of the anesthesia wear off. Factors such as a full stomach, medical conditions that slow digestion, or emergency surgery can increase the volume and acidity of the material available for aspiration. Positive pressure ventilation applied via a face mask before securing the airway can also inadvertently push air into the stomach, increasing pressure and the likelihood of regurgitation.
Acute Injury and Subsequent Complications
The moment gastric contents enter the lungs, the immediate reaction is a severe chemical injury known as aspiration pneumonitis. This is a direct burn to the delicate lung tissue, or parenchyma, caused by the highly acidic nature of stomach acid, which typically has a pH below 2.5. Even a relatively small volume, such as 0.4 milliliters per kilogram of body weight, can cause significant damage if the pH is low enough.
This chemical burn triggers an intense inflammatory response independent of any bacterial infection, leading to acute respiratory distress and hypoxia. Symptoms often appear within minutes to a few hours and include sudden coughing, wheezing, shortness of breath, and a rapid heart rate. If the aspirated material contains solid particles, it can also cause immediate mechanical blockage of the airways, leading to a sudden drop in oxygen saturation.
Aspiration pneumonitis can progress to Acute Respiratory Distress Syndrome (ARDS), a form of life-threatening lung failure. If the patient survives the initial chemical injury, the damaged lung tissue becomes vulnerable to infection. Aspiration pneumonia, a bacterial infection, may develop hours to days later as bacteria colonize the inflamed lungs, compounding the initial injury and requiring targeted antibiotic treatment.
Critical Preoperative Safety Protocols
The primary strategy to prevent aspiration is adhering to Nulla Per Os (NPO) guidelines, which strictly manage what the patient consumes before surgery. These guidelines specify the minimum time a patient must fast from food and drink to ensure the stomach is empty, minimizing the volume of contents available for aspiration. Current American Society of Anesthesiologists (ASA) guidelines recommend fasting from non-human milk or a light meal for at least six hours before the procedure.
Patients are allowed to consume clear liquids, such as water or black coffee, up to two hours before an elective surgery, as these empty from the stomach quickly. These guidelines are tailored for healthy individuals, but patients with conditions that delay gastric emptying, such as diabetes, obesity, or certain medications, may require longer fasting periods.
For patients identified as having an elevated risk of aspiration, the anesthesia team may use Rapid Sequence Induction (RSI). This method involves administering fast-acting sedative and muscle-relaxing medications to quickly secure the airway with a cuffed endotracheal tube. The goal of RSI is to minimize the time the airway remains unprotected, the period when aspiration is most likely to occur.
Treatment and Long Term Outlook
Immediate recognition and intervention are paramount if aspiration occurs during surgery, beginning with prompt suctioning of the airway to remove the material. Once stabilized, treatment for aspiration pneumonitis is largely supportive, focusing on maintaining adequate oxygen levels. This often involves supplemental oxygen or, in severe cases, mechanical ventilation to help the lungs recover from inflammatory damage.
Antibiotics are generally not prescribed immediately for chemical pneumonitis because it is an inflammation, not an infection. They are reserved for cases where symptoms persist beyond 48 hours or if a subsequent bacterial aspiration pneumonia is suspected or confirmed. The patient will be closely monitored, often in an intensive care unit, for signs of worsening respiratory function or secondary infection.
The prognosis following aspiration varies based on the volume and acidity of the aspirated material and the patient’s underlying health. Most patients who experience a mild to moderate event recover fully within 24 to 48 hours with supportive care. However, severe cases, particularly those that lead to ARDS or complicated aspiration pneumonia, can result in extended hospital stays and may leave some patients with long-term respiratory issues or reduced lung function.