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 and lower respiratory tract, the portions of the respiratory system from the trachea 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. 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.
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 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, 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 to empty the stomach. 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.
