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In a healthy pet, oxygen in the lungs travels from air sacs to the interstitium (the fluid-filled space between tissues or vessels) and into blood vessels.

Red blood cells in the blood vessels transport oxygen to tissues in the body. When fluid leaks into the interstitial spaces (a normal process by which nutrients are delivered out of the bloodstream), lymphatic vessels (the lymphatic system is a part of the body’s immune system) act as a vacuum to absorb excess fluid. This prevents an accumulation of fluid in the interstitial spaces. If this process is overloaded (because of disease that results in too much fluid entering the interstitial spaces in the lungs), pulmonary edema results. Gas exchange becomes less efficient, making it difficult to oxygenate blood and remove carbon dioxide.

Pulmonary edema creates hypoxia (hypoxemia), which is a deficiency of oxygen in the blood and, therefore, a deficiency of oxygen reaching the tissues that depend on it.  Common signs include breathlessness with exertion or at rest. If left untreated the condition can be fatal.

Pulmonary edema occurs as a result of other diseases. It can be categorized based on the underlying cause: cardiogenic  (due to heart disease, also called congestive heart failure, or CHF) or non-cardiogenic (not due to heart disease).

Non-cardiogenic pulmonary edema (NCPE) is driven by direct damage to the blood vessels in the lungs because of inflammation, sepsis, or trauma. The cause of pulmonary edema needs to be found to determine the most appropriate treatments.

Diagnosis

Diagnostics are recommended anytime your pet is in respiratory distress to rule out pulmonary edema. Shortness of breath is particularly common and often worsens when the pet is lying down. You may also notice that your pet is trying to breathe rapidly or with difficulty. A lack of energy is also common but not specific to pulmonary edema.

Your pet’s history and the physical examination can provide important clues as to the cause of pulmonary edema. Most small-breed dogs with cardiogenic edema will have a loud heart murmur identified by the veterinarian. It can be more difficult with larger breeds, but many large breed dogs will have obvious arrhythmia (abnormal heart rhythms). A history of extreme anxiety and stress, or evidence of stress such as chewing on an electrical cord, can help the veterinarian raise the suspicion of non-cardiogenic pulmonary edema. However, in many cases, no obvious event can be identified.

Your veterinarian will likely obtain X-rays (radiographs) of the chest to confirm the presence of fluid in the interstitial spaces of the lungs. The veterinarian can use a combination of several anatomical indicators to distinguish cardiogenic or non-cardiogenic pulmonary edema. If chest X-rays don’t identify a cause of the pulmonary edema, additional diagnostic imaging, including ultrasonography and computed tomography (CT), might be offered or performed. A diagnosis of non-cardiogenic pulmonary edema is often a combination of several diagnostic indicators, largely reached when the X-rays show evidence of excess lung fluid along with the absence of obvious severe heart disease. It can be a difficult diagnosis to reach in some cases. 

Treatment

Treatment of non-cardiogenic pulmonary edema differs from congestive heart failure (CHF). Oxygen supplementation can be offered to counteract poor respiration. Often, this involves putting your pet into an oxygen chamber, but in very severe cases, it can involve anesthesia with mechanical ventilation. Fluid therapy is often considered to maintain hydration, but must be monitored to prevent further fluid accumulation in the lungs. Unlike CHF treatment (which mostly involves diuretics), non-cardiogenic edema does not respond to diuretics. Successful treatment of the primary illness will help resolve the secondary pulmonary edema. Along with treatments, your pet should be given time to rest in a stress-free environment to prevent further respiratory distress.

Prognosis

The prognosis and recovery are determined on a case-by-case basis. With an early diagnosis, proper supportive care and treatment, the prognosis significantly improves. If your pet is experiencing any sign of respiratory distress, seek veterinary medical care immediately.