Most people have heard the term pneumonia and know it is a serious lung infection. In fact, "pneumonia" is not a very specific term and essentially means inflammation of any origin in the deep lung tissues, down where oxygen is normally absorbed and waste gases are normally removed.

    Pneumonia has the potential to be life-threatening regardless of its cause, and there can be many possible causes. Usually, there is an infectious disease at the root (virus, bacteria, fungus, even a worm) but not necessarily. Pneumonia can be caused by inhaling vomited or regurgitated food (aspiration pneumonia or pneumonitis), inhaling smoke or chemicals, or it could be immune-mediated with no infection at all (eosinophilic infiltration). Bronchitis is a separate condition from pneumonia and involves inflamed airways of the lung rather than inflammation in the deep lung tissue itself, but pneumonia and bronchitis commonly go together to create what is called bronchopneumonia.

Profile view of the chest of an adolescent puppy who contracted pneumonia shortly after shelter adoption. Air-filled healthy lung is mostly black with a fine lacy overlay of lung tissue. The sections that appear whited out represent pus and fluid secretion within the lung. Notice the dark "tree branch" appearance over the white area of lung tissue. This is called an air bronchogram and represents air inside an airway highlighted by the fluid-filled abnormal lung around it. Normally the branching of an airway is not visible as it is adjacent to air-filled lung and blends in. Image courtesy MarVistaVet

Pneumonia is commonly classified by its original cause:

• Fungal pneumonia - caused by a fungus, typically Coccidioides immitis, Cryptococcus neoformans, or other fungi.
• Viral pneumonia - usually the result of canine distemper virus infection, canine influenza virus, or a complicated feline upper respiratory infection.
• Parasitic pneumonia - directly from lungworms or from migration of other worms through the lung.
• Bacterial pneumonia - often secondary to severe kennel cough, particularly in young puppies that have been shipped long distances; aspiration as from megaesophagus; or secondary to either cause.
• Allergic pneumonia - the result of extreme infiltration of the lung by inflammatory cells in the absence of infection.

In most cases of pneumonia, there is a bacterial component. This means that no matter what started the pneumonia, bacteria have joined in, adding their own pus, fever, and potential for disaster; in most cases, managing the bacteria is vital. This article centers on the management of bacterial component of pneumonia.

When to Suspect Pneumonia

The diagnosis of pneumonia hinges on the chest radiograph (x-ray) but knowing when to take chest radiographs can be tricky. The veterinarian must put together findings from the history, physical examination, and possibly response to initial therapies to decide if radiographs should be checked.

• Coughing puppies from the pet store or shelter may have a simple kennel cough (minor bronchitis) but they are at a high risk for distemper infection.
  
  
• Coughing dogs or cats with a fever, listlessness, or appetite loss should definitely be radiographed for pneumonia; though many patients with pneumonia will not have fevers and some will still be deceptively active.
  
  
• Coughing dogs with a history of megaesophagus or with a history of symptoms typical of megaesophagus should be radiographed for pneumonia. Megaesophagus involves a floppy, dilated esophagus with a very high risk for regurgitating and aspirating food.
  
  
• Kittens with severe upper respiratory infections who do not respond to the usual management should be radiographed for pneumonia.

Aerial view or VD chest film showing the collapsed/consolidated lung when this dog first started treatment. Image courtesy of MarVistaVet

Coughing is the hallmark symptom, though certainly not all coughing pets or even most of them have pneumonia, and many pets with pneumonia - especially cats - hardly cough at all. Bacterial pneumonia does not just happen; it is virtually always caused by something else, so some kind of diagnostics will likely be needed to determine what led to the bacterial pneumonia if it is not readily apparent.

It has cleared substantially after a few days of treatment. Image courtesy MarVistaVet

Treatment

The pneumonia patient may be in one of three states:

• Stable: in other words, eating well and active despite a nasty cough and/or abnormal chest radiographs. These patients can often be treated at home.
• Unstable: poor appetite, inactive, in need of hospitalization.
• Critical: unable to get enough oxygen into their systems. These patients require oxygen therapy and possibly 24-hour care.

The goal is to get the patient stable enough for home treatment as several weeks are needed to fully clear pneumonia. When the patient is eating well, he may be discharged with antibiotic pills, a regimen of physical therapy, and a schedule for re-check radiographs (usually weekly).

The hospitalized patient has the following needs:

Intravenous Fluid Therapy
Coughing may be annoying but it is therapeutic and, when it comes to pneumonia, we want to encourage it, not suppress it. Coughing brings up the pus, mucus, and inflammatory cell products that make our patients sick. If the secretions of the lung are allowed to dry up, the patient will never be able to cough them up. For this reason, IV fluids must be maintained to keep our patient hydrated and keep the respiratory secretions wet.

Antibiotic Therapy
Antibiotics are given to kill the bacteria, but which antibiotics should be chosen? We need something that will penetrate into the pus and mucus, which many antibiotics cannot do. Often a four-quadrant approach is used that covers bacteria classified as Gram-negative and Gram-positive as well as those classified as aerobic and anaerobic. This typically involves two (or more) antibiotics used in combination to synergize one another and covers almost every possible bacterial organism.

Alternatively, the lungs may be cultured through a procedure called a tracheal wash. This process involves light sedation, which the patient must be stable enough to withstand. Sample fluid from deep in the lung is retrieved for culture. A culture identifies the organism and provides a list of antibiotics that can kill it. If possible, it is best to obtain a culture as a surprising number of resistant bacteria are in the environment and we not only want to confirm our antibiotic choice is appropriate but we do not want to needlessly develop resistant bacteria. Culture can sometimes be falsely negative (especially if antibiotics have already been started), or may only show common, non-pathological bacteria.

If the patient is sick enough for hospitalization, antibiotics are typically given as injections so as to maximize absorption into the body.

Nebulization

This is a nebulizer. Many models are available and they are even priced low enough for home use.

Nebulization is similar to vaporization and involves equipment called a nebulizer. The nebulizer creates a mist of fine fluid droplets that can be combined with antibiotics or airway dilators. Unlike vaporized droplets, though, these droplets are small enough to penetrate down into the lung. (Vaporizers make larger droplets, which mostly penetrate to the sinuses only. They are used to moisten upper airway secretions while nebulizers moisten lower airway secretions.) Nebulized saline or water may carry antibiotics with it, providing an additional source of moisture and antibiotics for the sick lung thus deeply treating the infection.

Caption: A nebulizer is used to treat aspiration pneumonia. Photo courtesy of Dr. Kathy Morris-Stilwell.

Physical Therapy
A technique called coupage helps mobilize respiratory secretions, and your veterinarian can demonstrate how to properly do this for your pet.  Coupage involves a person’s hand being cupped and gently tapping repeatedly over different areas of the patient’s chest wall quickly. It is important not to pat too hard to avoid injuring your pet, and best to use one hand with small breeds.

Watch a video demonstration of coupage.

Light exercise is also helpful in mobilizing the respiratory secretions. The patient should not be over-exerted as lung capacity is not normal but use your judgment as to what level of exercise is tolerated.

Oxygen Therapy
In most cases, oxygen therapy is not necessary but when a pneumonia patient simply cannot move enough air, there is no substitute for oxygen. Room air is 20% oxygen. An oxygen cage typically is set to deliver 40% oxygen, and oxygen-delivery hoods, nasal oxygen, and high-flow oxygen are also popular. Your veterinarian will determine which method is best for your pet. Pets who cannot maintain oxygenation with these methods sometimes need to be mechanically ventilated with a machine.

Home Care

Once a good appetite is evident, the patient may be discharged for home care. The following tips are recommended as long as the patient is coughing:

• Do not allow prolonged exposure to extreme cold or wet weather. Keep your pet primarily indoors.
• Consider using a vaporizer (or better yet, buy your own nebulizer, many models are available and are even priced low enough for home use) for 10 to 15-minute intervals a couple of times daily. If you do not have a vaporizer, leave the pet in the bathroom with the shower on to create a misty vapor. If the bathroom does not get sufficiently misty, a small pet can be confined to a carrier and the vaporizer can be directed into this smaller space. As discussed, nebulization is superior but vaporization is the next best thing.
• Perform coupage at least four times daily and allow light exercise to promote the cough.
• Do not try to suppress the cough with over-the-counter cough suppressants. We want the infected material in the chest to be coughed up.
• Use the antibiotics as directed. Advice regarding antibiotic regimens has recently changed, so a short or long course may be prescribed based on your pet's needs and the cause of pneumonia. 
• Fungal infectious may require several weeks of antifungal medications, as well as other medications to control inflammation. 
• Water intake is vital in treating pneumonia at home - encourage your pet to take in as much water as they can, and discuss methods of increasing water intake (such as adding broth or water to food) with your veterinarian.
• Know when you should return for re-check radiographs.

Pneumonia is a serious infection and several weeks are needed to clear it. Prognosis ultimately depends on what the underlying cause was but the good news is that most patients are not sick enough to require oxygen therapy and the majority of these ultimately recover with proper treatment.