Pulmonary aspiration

Pulmonary aspiration is the entry of material such as pharyngeal secretions, food or drink, or stomach contents from the oropharynx or gastrointestinal tract, into the larynx (voice box) and lower respiratory tract, the portions of the respiratory system from the trachea (windpipe) to the lungs. A person may inhale the material, or it may be delivered into the tracheobronchial tree during positive pressure ventilation. When pulmonary aspiration occurs during eating and drinking, the aspirated material is often colloquially referred to as "going down the wrong pipe".

Consequences of pulmonary aspiration range from no injury at all, to chemical pneumonitis or pneumonia, to death within minutes from asphyxiation. These consequences depend on the volume, chemical composition, particle size, and presence of infectious agents in the aspirated material, and on the underlying health status of the person.

In healthy people, aspiration of small quantities of material is common and rarely results in disease or injury. People with significant underlying disease or injury are at greater risk for developing respiratory complications following pulmonary aspiration, especially hospitalized patients, because of certain factors such as depressed level of consciousness and impaired airway defenses (gag reflex and respiratory tract antimicrobial defense system). The lumen of the right main bronchus is more vertical and slightly wider than that of the left, so aspirated material is more likely to end up in this bronchus or one of its subsequent bifurcations.

About 3.6 million cases of pulmonary aspiration or foreign body in the airway occurred in 2013.

Particle-related
Pulmonary aspiration of particulate matter may result in acute airway obstruction which may rapidly lead to death from arterial hypoxemia.

Acid-related
Pulmonary aspiration of acidic material (such as stomach acid) may produce an immediate primary injury caused by the chemical reaction of acid with lung parenchyma, and a later secondary injury as a result of the subsequent inflammatory response.

Bacterial
Pulmonary aspiration may be followed by bacterial pneumonia. Community-acquired aspiration pneumonia is usually caused by anaerobic bacteria, whereas hospital-acquired aspiration pneumonia is more often caused by mixed flora, including both aerobic and anaerobic bacteria.

Death
Pulmonary aspiration resulting in pneumonia, in some patients, particularly those with physical limitations, can be fatal.

Risk factors
Risk factors for pulmonary aspiration include conditions which depress the level of consciousness (such as traumatic brain injury, alcohol intoxication, drug overdose, and general anesthesia). A decreased gag reflex, upper esophageal sphincter and lower esophageal sphincter tone, gastroesophageal reflux, full stomach, as well as obesity, stroke, and pregnancy can all increase the risk of aspiration in the semiconscious. Tracheal intubation or presence of a gastric tube (for example, a feeding tube) may also increase the risk.

Prevention
The lungs are normally protected against aspiration by a series of protective reflexes such as coughing and swallowing. Significant aspiration can only occur if the protective reflexes are absent or severely diminished (in neurological disease, coma, drug overdose, sedation or general anesthesia). In intensive care, sitting patients up reduces the risk of pulmonary aspiration and ventilator-associated pneumonia.

Measures to prevent aspiration depend on the situation and the patient. In patients at imminent risk of aspiration, tracheal intubation by a trained health professional provides the best protection. A simpler intervention that can be implemented is to lay the patient on their side in the recovery position (as taught in first aid and CPR classes), so that any vomitus produced by the patient will drain out their mouth instead of back down their pharynx. Some anesthetists will use sodium citrate to neutralize the stomach's low pH and metoclopramide or domperidone (pro-kinetic agents) to empty the stomach. In veterinary settings, emetics may be used to empty the stomach prior to sedation. Due to growing issues with patients not complying with fasting recommendations before surgery, some hospitals will now also routinely administer emetics prior to anesthesia. Newer operating rooms are often equipped with dedicated vomitoria for this purpose.

People with chronic neurological disorders, for example, after a stroke, are less likely to aspirate thickened fluids on an instrumental swallowing assessment. However, this does not necessarily translate into reduced risk of pneumonia in real life eating and drinking. Also, pharyngeal residue is more common with very thickened fluids: this may subsequently be aspirated and lead to a more severe pneumonia.

The location of abscesses caused by aspiration depends on the position one is in. If one is sitting or standing up, the aspirate ends up in the posterior basal segment of the right lower lobe. If one is on one's back, it goes to the superior segment of the right lower lobe. If one is lying on the right side, it goes to the posterior segment of the right upper lobe, or the posterior basal segment of the right upper lobe. If one is lying on the left, it goes to the lingula.

Management
See also: Choking § Treatment, Basic Life Support, Advanced Cardiovascular Life Support

Treatment of foreign body aspiration is determined by the age of the patient and the severity of obstruction of the airway involved.

Basic management
An airway obstruction can be partial or complete. In partial obstruction, the patient can usually clear the foreign body with coughing. In complete obstruction, acute intervention is required to remove the foreign body.

If foreign body aspiration is suspected, finger sweeping in the mouth is not recommended due to the increased risk of displacing the foreign object further into the airway.

For choking children less than 1 year of age, the child should be placed face down over the rescuer's arm. Back blows should be delivered with the heel of the hand, then the patient should be turned face-up and chest thrusts should be administered. The rescuer should alternate five back blows followed by five chest thrusts until the object is cleared. The Heimlich maneuver should be used in choking patients older than 1 year of age to dislodge a foreign body. If the patient becomes unresponsive during physical intervention, cardiopulmonary resuscitation (CPR) should be started.

Advanced management
In the event that the basic measures do not remove the foreign body, and adequate ventilation cannot be restored, need for treatment by trained personnel becomes necessary. Laryngoscopy should be performed in unresponsive patients if non-invasive airway clearance techniques are unsuccessful. Laryngoscopy involves placing a device in the mouth to visualize the back of the airway. If the foreign body can be seen, it can be removed with forceps. An endotracheal tube should then be placed in order to prevent airway compromise from resulting inflammation after the procedure. If the foreign body cannot be visualized, intubation, tracheotomy, or needle cricothyrotomy can be done to restore an airway for patients who have become unresponsive due to airway compromise.

If non-invasive measures do not dislodge the foreign body, and the patient can maintain adequate ventilation, rigid bronchoscopy under general anesthesia should be performed. Supplemental oxygen, cardiac monitoring, and a pulse oximeter should be applied to the patient. Efforts should be made to keep the patient calm and avoid agitating the patient to prevent further airway compromise. Flexible rather than rigid bronchoscopy might be used when the diagnosis or object location are unclear. When flexible bronchoscope is used, rigid bronchoscope is typically on standby and readily available as this is the preferred approach for removal. Rigid bronchoscopy allows good airway control, ready bleeding management, better visualization, and ability to manipulate the aspirated object with a variety of forceps. Flexible bronchoscopy may be used for extraction when distal access is needed and the operator is experienced in this technique. Potential advantages include avoidance of general anesthesia as well as the ability to reach subsegmental bronchi which are smaller in diameter and further down the respiratory tract than the main bronchi. The main disadvantage of using a flexible scope is the risk of further dislodging the object and causing airway compromise. Bronchoscopy is successful in removing the foreign body in approximately 95% of cases with a complication rate of only 1%.

After the foreign body is removed, patients should receive nebulized beta-adrenergic medication and chest physiotherapy to further protect the airway. Steroidal anti-inflammatories and antibiotics are not routinely administered except in certain scenarios. These include situations such as when the foreign body is difficult or impossible to extract, when there is a documented respiratory tract infection, and when swelling within the airway occurs after removal of the object. Glucocorticoids may be administered when the foreign body is surrounded by inflamed tissue and extraction is difficult or impossible. In such cases, extraction may be delayed for a short course of glucocorticoids so that the inflammation may be reduced before subsequent attempts. These patients should remain under observation in the hospital until successful extraction as this practice can result in dislodgement of the foreign body. Antibiotics are appropriate when an infection has developed but should not delay extraction. In fact, removal of the object may improve infection control by removing the infectious source as well as using cultures taken during the bronchoscopy to guide antibiotic choice. When airway edema or swelling occur, the patient may have stridor. In these cases, glucocorticoids, aerosolized epinephrine, or helium oxygen therapy may be considered as part of the management plan.

Patients who are clinically stable with no need for supplemental oxygen after extraction may be discharged from the hospital the same day as the procedure. Routine imaging such as a follow-up chest x-ray are not needed unless symptoms persist or worsen, or if the patient had imaging abnormalities previously to verify return to normal. Most children are discharged within 24 hours of the procedure.