• Aspiration is defined as the inhalation of gastric, oropharyngeal, or other foreign contents into the larynx and lower respiratory tract. It can be divided into 2 broad categories:
  • Aspiration pneumonitis: Inhalation of sterile acidic gastric contents resulting in chemical injury to the lung; also known as Mendelson syndrome
  • Aspiration pneumonia: An infectious, pathologic process caused by inhalation of secretions that have been colonized by microorganisms
• Although aspiration is rare during anesthesia, it is an important cause of anesthesia-related mortality and ventilator-associated pneumonia (VAP) in the ICU setting.

• Extremes of age
• Full stomach at the time of anesthesia
• Pregnancy
• Critical illness
• Emergency surgeries
• Gastroesophageal reflux disease
• Diabetic gastroparesis
• Obesity
• Difficult airway
• Acidic gastric content pH <2.5
• Gastric volume >0.4 mL/kg
• Loss of airway reflexes
  • Drug/alcohol overdose
  • Unconscious patient from general anesthesia, deep sedation, trauma
• Neurologic dysphagia

• There are several structures and reflexes that protect against aspiration.
  • Upper esophageal sphincter (UES)
    • The cricopharyngeus muscle acts as the constrictor muscle of the pharynx and divides the upper esophagus from the hypopharynx.
    • Decreased tone is seen with sodium thiopental, succinylcholine, midazolam, and halothane.
    • Increased tone is seen with the use of ketamine.
  • Lower esophageal sphincter (LES)
    • Located at the border between the stomach and the esophagus
    • Composed of the right crux of the diaphragm and the acute angle of the left margin of the esophagus with the gastric fundus; it forms a sling around the lower esophagus.
    • Decreased tone is seen with opioids, inhalation agents, and sodium thiopental.
    • Increased tone is seen with antiemetics (metoclopramide), cholinergic drugs, and succinylcholine.
  • Airway reflexes
    • Laryngospasm: Hypoxia results from the closure of the false and true vocal cords; however, this prevents aspiration of foreign contents.
    • Coughing: forceful expiratory flow can aid with removal of foreign contents.
    • Expiration: Describes a forceful expiratory effort without preceding inspiration
    • Spasmodic panting: Episodes of shallow breathing result in rapid vocal cord opening and closing and reduce the aspiration of foreign material.
• Consequences of aspiration
  • Large particles will cause airway obstruction. Areas of lung that are not being ventilated are still perfused leading to ventilation/perfusion (V/Q) mismatching, shunting, hypoxemia, and death.
  • In aspiration pneumonitis, acid-related effects of gastric contents will cause inflammatory reactions and direct lung tissue injury, airway constriction, and edema. Release of cytokines and chemokines attract inflammatory mediators, neutrophils, and macrophages. Altered lung defenses may lead to bacterial infection.
  • In aspiration pneumonia, the aspiration of oropharyngeal secretions and contaminated gastric contents will elicit an acute inflammatory lung response to bacteria and bacterial products. The pathogens that are frequently associated with aspiration pneumonia are Gram-positive cocci, Gram-negative rods, and (rarely) anaerobes.

Pregnancy Considerations

• Adequate preoperative fasting to control gastric content and volume:

  Ingested material	Minimum fasting period
  Clear liquid	2 hours
  Breast milk	4 hours
  Infant formula	6 hours
  Non-human milk	6 hours
  Light meal	6 hours

• Decrease gastric acidity:
  • Sodium citrate is a nonparticulate antacid that functions to raise gastric pH as well as increase gastric motility.
  • H₂ antagonists inhibit secretion of acid, thereby reducing acidity of stomach contents and gastric volume.
• Decrease gastric volume:
  • Metoclopramide is an antidopaminergic and cholinergic which speeds gastric emptying and increases LES tone.
  • Nasogastric tube insertion and suctioning prior to or after induction for gastric decompression
  • In situ nasogastric tubes should be suctioned prior to induction. Of note, it can form a mechanical barrier to LES protection against aspiration.
• Application of cricoid pressure/Sellick maneuver:
  • Described by Sellick in 1961 as a way to prevent aspiration during the rapid sequence induction phase of anesthesia
  • The upward and backward directed pressure on the cricoid cartilage compresses the esophagus against the vertebral bodies, thus occluding the esophagus. The recommended pressure is 30–40 Newtons (difficult to ascertain while performing the technique).
  • Theoretically, this will prevent passage of gastric content into the pharynx and subsequent aspiration into the tracheobronchial tree.
  • Minimizes gastric insufflation and aspiration in unconscious patients; however, it may also prevent effective mask ventilation by reducing airway patency. It may cause discomfort to the patient if applied too early.
• Early endotracheal intubation with a cuffed endotracheal tube will decrease but not eliminate the risk of gastric aspiration.
  • Excessive cuff pressure may compromise the microcirculation of tracheal mucosa leading to necrosis. Insufficient cuff pressure may impair ventilation and allow leakage of supraglottic material into the tracheobronchial tree.
  • A better seal can be achieved by using the ultra thin cuff (low pressure, high volume). This prevents the formation of folds that can lead to longitudinal channels for supraglottic material to enter the tracheobronchial tree.

Pregnancy Considerations

• Pulmonary thromboembolism
• Pulmonary air embolism
• Pulmonary tuberculosis
• ARDS
• Drug reaction
• Asthma
• Bronchospasm
• Laryngospasm
• Myocardial infarction

• In 4,459 total anesthesia-related claims:
  • Aspiration was the primary or secondary cause of morbidity in 158 (3.5%) of all claims.
  • Aspiration was the primary source of adverse events in 1.75% of these patients.
  • The majority of aspiration events (42%) occurred during the induction of anesthesia.
  • Obstetrical related aspiration accounted for 21% of all claims.

• Ventilator-Associated Pneumonia
• Asthma
• Venous Air Embolism

• 482.9 Bacterial pneumonia, unspecified
• 507.0 Pneumonitis due to solids and liquids

• J15.9 Unspecified bacterial pneumonia
• J69.0 Pneumonitis due to inhalation of food and vomit

Kanishka Monis , MD

Poovendran Saththasivam , MD