The feline lungs—two triangular shaped, elastic organs located opposite one another on each side of the heart—occupy most of the space in a cat’s chest cavity. They are virtually identical in structure to their human counterparts, they function in the same manner, and they fulfill the same fundamental purposes—removing carbon dioxide from the bloodstream and keeping the blood constantly supplied with life-sustaining oxygen. Also like human lungs, these vital organs are susceptible to pneumonia, an affliction that can put a cat’s life at risk if not diagnosed and treated at the earliest stage of its development. Fortunately, says Daniel Fletcher, DVM, an assistant professor of emergency and critical care at Cornell University’s College of Veterinary Medicine, feline pneumonia is extremely rare.

The lungs perform their vital functions by means of processes referred to as ventilation and perfusion. Ventilation is the rhythmic inhalation of oxygen-rich air from the environment. Perfusion is the process by which blood flows to the lungs where life-supporting oxygen is removed from the inhaled air and delivered into the cat’s circulating blood. In this process, the oxygen is exchanged for carbon dioxide, which is produced in the animal’s cells and is expelled from the body via exhaled air. Pneumonia may occur when this process is disrupted.

The two major types of the disease are aspiration pneumonia and infectious pneumonia. Aspiration pneumonia, explains Dr. Fletcher, occurs when a cat has inhaled foreign matter into its lungs—a tiny piece of plastic, for example, or a seed pod. “Such objects are bound to irritate the sensitive tissues lining the lungs,” he notes. “Or a cat may vomit and, in the process, inhale some of its stomach contents, which tend to be very acidic and will also irritate the tissues.” Moreover, he adds, the vomited material may contain bacteria from the small intestine, which can cause a secondary infection in the lung tissues.

The other type of the disorder, infectious pneumonia, can result from exposure to such agents as bacteria, viruses, protozoa, or fungi inhaled from the environment or from other cats. This type of pneumonia can also stem from an existing bacterial infection elsewhere in the body. “Blood vessels branch down into tiny capillaries in the lungs,” says Dr. Fletcher, “and this allows infectious agents that are moving through the bloodstream to eventually infect the lung tissue.”

The clinical signs for both types of pneumonia are the same, he says: increased respiratory rate, rapid heartbeat, green or yellow nasal discharge, and fever. “Progression of these signs depends on the severity of the pneumonia,” he notes. “Some cats may show the signs for a few days and then clear them without veterinary care. But if you have an infection in the lungs and a huge amount of blood is being pushed out with every heartbeat, the cat will be at high risk for what we call systemic inflammatory response syndrome, a process in which local inflammation in the lungs will spread throughout the body. The inflammatory mediators go out and start to affect other organs—the kidney, gastrointestinal tract, the heart, the brain. The animal can go into what we call multiple organ dysfunction syndrome, which can lead to death.

“So if you’re seeing any signs that are respiratory in nature, you have to get the cat to a veterinarian as soon as possible. If the cat has pneumonia and treatment is delayed, the prognosis is not good.”

Initial treatment for both aspiration and infectious pneumonia will entail “aggressive, broad-spectrum, antibiotic therapy,” says Dr. Fletcher. That therapy will continue until the cat is strong enough to tolerate more aggressive diagnostic measures aimed toward identifying the specific bacterial agent causing the infection. For pneumonia caused by agents other than bacteria, therapies such as antifungal or antiviral drugs might be required. In most cases, supportive care including intravenous fluids, nebulization to keep the airways moist, and oxygen supplementation will also be required.

“Some cats,” he says, “will be well enough to go home after two or three days, but most will have to spend four or five days in the hospital. At home, they’ll have to be given oral antimicrobials for several weeks, sometimes for several months. It all depends on how advanced and how widespread the pneumonia was when they entered the hospital.”

Two weeks or so following a cat’s discharge from the hospital, says Dr. Fletcher, “it will have to come back for additional chest x-rays, and we’ll continue treatment with antibiotics until the x-rays are normal.”