Smoke inhalation causes direct damage to the upper airways, which include: the nose, sinuses, oropharynx (back of the mouth), trachea (the windpipe), bronchi, and bronchioles (lower airways) and the lung tissue. Additional damage caused by smoke inhalation include the following: Heat from the fire (thermal injury) can burn the airways so that they become dry, irritated and lose their ability to remove particles away from the lower airways. Burns to the airways predispose the patient to infection with bacteria.
Particulate matter within smoke is deposited in both the upper and lower airways and increases irritation and the risk of infection.
Gases within fires can cause chemical burns in the upper and lower airways, constriction and spasm of the airways, and poisoning, such as cyanide or carbon monoxide poisoning. Carbon monoxide poisoning is a main component of smoke inhalation injury.
The combined effects of smoke, heat and gases lead to difficulty breathing, respiratory distress and sometimes death of the patient. Respiratory symptoms may develop immediately after exposure to heat and smoke or may take up to 48 hours before they appear. Pulmonary edema (accumulation of fluid within the lungs) can take 6 to 72 hours to develop. If the patient survives the initial injury, pneumonia can follow (2 to 3 days after initial injury) before complete recovery.
Smoke inhalation injury is usually not confused with other diseases because of the circumstances under which it occurs, for example, the pet is removed from a burning building. Other findings can support a diagnosis of smoke inhalation such as the smell of smoke on the pet's fur and singed or burned hair and whiskers. However, if it is not clear that smoke inhalation is the cause of the pet's respiratory difficulty, the following should be considered:
Pulmonary edema. The accumulation of fluid within the lungs an can result from congestive heart failure, biting through an electric cord or an obstruction in the upper airways.
Pneumonia. This infection within the lungs can lead to difficulty breathing.
Pleural effusion. An accumulation of fluid within the chest cavity around the lungs makes it difficult for the lungs to expand when the pet takes a breath. The effusion may be blood, pus, chyle (fluid from the lymphatic system) or may result from diseases such as congestive heart failure or hypoproteinemia (low protein levels in the blood).