Pulmonary aspiration

Editor-in-Chief: Santosh Patel M.D., FRCA [mailto:santosh.patel@pat.nhs.uk]

Overview
In medicine, aspiration is the entry of secretions or foreign material into the trachea and lungs. The patient may either inhale the material, or it may be blown into the lungs during positive pressure ventilation or CPR. As the right main bronchus is more vertical and of slightly wider lumen than the left, aspirated material is more likely to end up in this branch or one of its subsequent bifurcations.

Risk factors
As a rule of thumb, any condition which compromises a patient's level of consciousness and/or gag reflex is a risk factor for pulmonary aspiration.

Causes of unconsciousness where aspiration may occur include trauma (especially head injuries), poisoning (including drug/alcohol overdose), general anaesthetics, and diseases or metabolic conditions. Gastroesophageal reflux, a full stomach, pregnancy, and obesity all increase the risk of aspiration in the semiconscious.

Normally fasting for six hours before elective surgery is enough to empty the stomach. Severe injuries can slow the movement of digesta from the stomach and through the duodenum.

Acute alcohol poisoning is a relatively common cause of severe pulmonary aspiration as the alcohol renders the victim unconscious and can induce vomiting. Patients with neurological conditions may also aspirate food or drink.

During labour, early respiratory movements by the baby facilitate filling of alveolar ducts and alveolar lumens with elements of amniotic fluid: amniotic cells, squamous and squamous cells from fetal skin, lanugo, meconium. Reduced inflammatory infiltrate (neutrophils) and capillary congestion is present. Photos at: 1

Causes

 * Alcohol or sedative use
 * Altered sensorium
 * Convulsions
 * Dental, pharyngeal, or airway procedures
 * General anesthesia
 * Impaired cough reflex
 * Impaired swallow reflex
 * Loss of consciousness
 * Maxillofacial trauma
 * Mental retardation
 * Poor dentition

Consequences
If enough material enters the lungs, the patient may simply drown. However, small volumes of gastric acid contents can fatally damage the delicate lung tissue. Even small volumes of aspirated food may lead to bronchopneumonia infection. Chronic aspiration may lead to bronchiectasis and may cause some cases of asthma.

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 (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, endotracheal 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 rescue 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.

People with chronic neurological disorders, for example, after a stroke, are less likely to aspirate thickened fluids.

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 superior segment of the right middle lobe, or the posterior basal segment of the right upper lobe. If one is lying on the left, it goes to the lingula.