Pneumonia: what you need to know
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The most common cause of pneumonia in small animals is a bacterial infection. Other causes include viruses (rare), fungi, aspiration, parasites, ventilator-induced, chemical, or smoke inhalation. Pneumonia starts with an infection or infiltration of the alveoli, roughly 300 million tiny air sacs within the lungs where the exchange of oxygen and carbon dioxide takes place. After an infection or infiltration into the alveoli, the pulmonary membrane becomes inflamed and highly porous. This allows for fluid and red and white blood cells to pass into the alveoli. The fluid will continue to build up causing a spreading of the infection. Eventually it can worsen so that an entire area becomes "consolidated", whereby an entire or partial lobe or lung is affected. This results in hypoxia and hypercapnia in the patient. Ultimately the hypoxia leads to cardiac, respiratory, and central nervous system failure.
Epidemiology
Pets that are immunocompromised (e.g. diabetes, renal disease) and those with functional disorders (e.g. laryngeal paralysis, megaesophagus) are at greater risk for developing pneumonia. As in humans, pediatric and geriatric individuals are also at greater risk. Brachycephalic breeds are at a greater risk for developing aspiration pneumonia and often have chronic airway disease, which sets them up for pneumonia due to the excessive respiratory secretions. These alter the defence mechanisms and increase the risk of bacteria colonizing and causing infection.
Signs
Owners often mistake laboured breathing as “panting” or shallow breathing as “sniffing.” Any change in an animal’s breathing is an emergency. Typical signs include lethargy, anorexia, coughing, increased respiratory effort, panting in a cat, and exercise intolerance. In severe cases, pets may present collapsed, cyanotic, with severe respiratory effort and orthopnea.
Diagnostics
Radiographs are essential if pneumonia is suspected. Typically alveolar changes or an alveolar pattern is noted in bacterial pneumonia. Other findings may include bronchial or interstitial patterns or consolidation of lobes. In cases of aspiration pneumonia, infiltrative patterns in the right cranial or in the middle and left cranial lung lobes are often noted.
Obtaining a sample and submitting it for culture and sensitivity will allow for a definitive diagnosis of bacterial pneumonia. Studies have shown that when antimicrobial therapy is chosen there is a higher chance of survival. There are a myriad of ways to obtain a sample, but one of the most common is the transtracheal wash.
Nursing care
If the pet is in severe respiratory distress, or if any panting is noted in a cat, the pet must receive oxygen immediately. Animals should be allowed to assume any position that provides them the most relief. Sedation should be considered in patients that are very stressed; sedating a patient will calm them and decrease the incidence of hyperventilation.
Patients with most types of pneumonia will require IV fluids and antibiotics. While most veterinarians will start broad-spectrum antibiotics, it is best to obtain a culture and sensitivity test first. That being said, it is rarely recommended to withhold antibiotics while waiting for the sample result. If obtaining a sample puts the patient at too much risk, then antibiotics should be started.
Providing appropriate nutrition is an important part of nursing care and is often overlooked in veterinary medicine. Malnutrition can alter pulmonary defence mechanisms resulting in worsening of the pneumonia. An important role of the veterinary technician is to ensure the patient receives appropriate nutrition and hydration, and it is important to record the amount and type of food ingested.
Ensuring that pneumonia patients are nebulized is important as it provides moisture to the lower airways, which increases hydration of the mucociliary system. This allows for the viscosity of the secretions to be decreased and cleared from the airways. Vaporizers and humidifiers should not be used as they will not create small enough particles to infiltrate to the lower airways. The animal should be placed into a small sealed cage and provided with ventilation for 20-30 minutes about 3-4 times a day. Because steam can accumulate in the cage and as a result the patient will expel more breath than normal, there is a potential for hyperthermia to develop. These patients must be monitored and not left in sealed cages for too long.
Coupage is a form of physiotherapy and a complement to nebulization as it helps to expel fluid from the patient’s lungs. Firm rhythmic cupping hand movements help to mobilize the airway secretions. Coupage should be performed for 5-10 minutes after each nebulization. If the pet does not tolerate coupaging, taking it for a short walk after nebulization with mild exercise will also help to clear the secretions.
Carrying the pet to and from the walking area will help in pets that have exercise intolerance. Excessive use of choke and slip leads should be avoided as they press down on the airway and cause a worsening of the dyspnea. Body harnesses are often more appropriate.
Monitoring
In a clinical setting there are four parameters that can be monitored: respiratory rate/effort, mucous membrane colour, blood oxygen saturation, and blood gas.
Respiratory rate and effort are relatively easy parameters to monitor. It is important to look at the rate as well as the effort; often prolonged expiration may be observed, indicating lower airway disease. Auscultation of the chest should occur if increased respiratory effort or rate are noted. Detection of wheezes, crackles, harshness, or increased sounds will indicate respiratory distress and a need for supplemental oxygen.
Along with respiratory rate and effort, mucous membrane colour is one of the easiest parameters to monitor and should be part of every physical exam. Though not completely accurate, any presence of cyanosis indicates a life-threatening oxygenation issue that needs to be addressed immediately.
Pulse oximetry is less invasive; measuring the oxygen saturation of hemoglobin is a very insensitive measure of oxygenation. Normally animals should have a range from 98-100% on room air.
A blood gas reading can be obtained to get either the partial pressure of oxygen in venous blood (PvO2) or the partial pressure of oxygen in arterial blood (PaO2). PvO2 is not very reliable and ideally should not be used. PaO2 is still considered the gold standard when monitoring for overall oxygenation of a patient. While PaO2 is the gold standard, an arterial blood sample must be obtained, but this may not be possible in some patients.
Discharging the pneumonia patient
Pets are often discharged with mild to moderate coughing and slight to moderate increase in respiratory effort. Owners need to know to watch for problems in their pet, so they should be told how much coughing to expect and what their pet’s normal breathing sounds like. Pets often go home with 4-6 weeks of antibiotics and require several rechecks, including radiographs to ensure the pneumonia is clearing.
This article is based on a presentation given at the 2012 Veterinary Emergency and Critical Care Society Conference in San Antonio, TX.CVT
