Monday, July 30, 2012

Canine Pneumonia

By Beth Guerra, DVM  

Pneumonia is an infection in the lower airways that causes inflammation in the lungs. Organisms can be bacterial, viral or fungal in nature. The infection is established when these organisms are inhaled, aspirated (from gastrointestinal contents), or spread through the blood from other body systems. The usual defense system of the body traps infectious organisms in the mucus lining the respiratory tract and moves them upward where they can be expelled by coughing. Failure of this mechanism allows bacteria or fungi to colonize the airways. Once the infection is established, secondary inflammation can develop, impairing normal oxygen exchange.

Bacterial pneumonia is frequently seen at our facility. The two most dominant types of organisms are Bordatella bronchiseptica and E. coli. In young or incompletely vaccinated dogs, we often see Bordatella pneumonia, otherwise known as kennel cough pneumonia, which is a contagious disease. The E. coli organism is the most common inhabitant of the upper GI tract and infection results from aspiration of stomach contents.

Aspiration pneumonia is by far the most common type of pneumonia we encounter in our ICU. Patients at risk for aspiration include sedate or recumbent animals, or those recovering from anesthesia. Pets that have vomiting, regurgitation or reflux, or altered esophageal motility are also at high risk for aspiration. Another condition, known as laryngeal paralysis, can also precipitate an aspiration event.

Often the only symptom in these dogs is acute lethargy and inappetance. There may be weight loss, fever, or a moist or productive cough. Diagnosis is made by thoracic x-rays, but bloodwork often reveals an elevated white blood cell count, and can also help to rule out other predisposing conditions. To further support a diagnosis, samples of the lower airway bacteria are collected by endotracheal or transtracheal wash, where sterile saline is introduced in small amounts into the lower airway in an attempt to retrieve bacterial organisms for culture. This will help direct antibiotic therapy.

Dogs with pneumonia can range from fairly stable patients that are eating and active to patients that are severely ill and dependent on oxygen. In the former, treatment with oral antibiotics for an extended period may be all that is required. In the latter, hospitalization is recommended to provide more aggressive supportive care. Systemic hydration is important to help loosen secretions and also because the patient is usually not eating or drinking. Intravenous antibiotics are usually given for a minimum of 48 hours. Oxygen therapy, via nasal cannula or chamber, is needed in those patients with low oxygen saturation. Nebulization with saline, followed by coupage, or gentle percussion to the chest cavity, can help the patient cough up secretions.

Several years ago, we examined the records of the animals we had treated for pneumonia over a two-year period. We treated 94 cases and were able to send home 82%. In animals who were less than two years old, 95% went home. Most of the cases that we could not save were found to have an underlying condition such as a megaesophagus, laryngeal paralysis, other neurologic disease, or concurrent diabetes. 

The treatment for pneumonia often includes four to six weeks of antibiotic therapy. Follow-up chest x-rays are very helpful in tracking the progression of the disease. Once a patient is eating and stable without oxygen, convalescence can continue at home with rechecks as needed. 


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