Pneumonia is either an acute or chronic inflammation of the lungs and bronchi. Bronchi are the main airways of the lungs. This inflammation causes difficulty breathing as well as a decrease in oxygenation of the blood. The resulting decrease in blood oxygenation can cause damage to body organs if left uncorrected. 

The two the two main sources of pneumonia are aspiration (inhalation of vomit, food, fluid or inhalant toxins) and infectious agents (viruses, bacteria or fungus).

Pneumonia is classified into 2 categories; aspiration pneumonia and infectious pneumonia. Aspiration pneumonia occurs when an animal inhales something like food, water or vomit into its lungs. These substances irritate the lining of the lungs causing inflammation, sometimes they also contain bacteria causing a secondary infection. Infectious pneumonia is caused when bacteria, viruses, fungi or other organisms are inhaled from the environment into the lungs. These organisms cause an immune response in the body causing inflammation and mobilization of white blood cells to the lungs. Because of inflammation and the accumulation of white blood cells, the alveoli (tiny air sacs in the lungs which allow for gas exchange) fill with fluid and pus. This causes a barrier between inhaled oxygen red blood cells. This results in a lack of oxygen to the blood and there for the rest of the body.

 The typical signs of pneumonia are depression and lethargy, inappetance, fever, a deep often productive cough, difficulty breathing (which may be made more noticeable by puffing of the cheeks or next extension), a blue tint to the gums of the mouth as well as exercise intolerance. 

Diagnosis  of pneumonia involves a thorough history, a complete physical exam as well as a variety of diagnostics. During a physical examination the veterinarian will listen to the lungs on both sides of the chest, look at the gums, take a temperature and check a blood oxygenation level. This is done by attaching a small clip to the lip or the ear, this testing is called pulse oximetry (often referred to as SpO2). Pulse oximetry uses a beam of light passed through the blood circulating in the lip or ear to measure the amount of oxygen present. This tool measures the changes of light absorption in oxygenated or deoxygenated blood. Blood may be drawn to perform a complete blood count and a serum chemistry, x-rays of the chest will likely be performed as well. Animals with pneumonia will usually have an elevated white blood cell count, this is a normal physiological response to infection. In some cases the veterinarian may recommend a tracheal wash or a bronchoalveolar lavage (a method used to obtain a sample from deep within the lungs) this sample may need to be sent to an outside reference lab for microscopic examination and culture for bacteria.

Treatment of pneumonia focuses on resolving the underlying cause of infection as well as supportive care of the patient. Most patients will require intravenous fluid therapy, injectable antibiotics and humidified breathing treatments to help loosen and move any debris that has consolidated in the lungs. Some patients require oxygen support and medications to help open up the passages in the lungs to ease their breathing. Depending on the size of the patient they may be placed in a closed cage with increased oxygen concentration. Large dogs may have a small tube placed in one nostril to provide oxygen support, these are called nasal cannulas and are very well tolerated by most patients. Once a patient is able to breathe room air without increased respiratory effort they may be sent home with a variety of medications as well as instructions to perform nebulization at home.

Patients recovering from pneumonia should be re-examined by a veterinarian regularly while they are undergoing at home treatment. X-rays of the chest should be repeated at regular intervals to assess how well the treatment is working.