Canine Bronchopneumonia
World Small Animal Veterinary Association World Congress Proceedings, 2014
Ninette Keller, BVSc, BVSc (Hons), MMedVet (Med) (Pret), Grad Cert Ed (JCU)
Veterinary Specialist Services, Gold Coast, QLD, Australia

Introduction

The coughing and/or dyspnoeic patient can be a challenge for all of us. The first step is to try to determine whether you are dealing with a dyspnoeic patient secondary to heart failure (lung oedema) or whether the underlying disease is primarily lung related. The same breeds that are predisposed to myxomatous mitral valve degeneration are also prone to chronic bronchitis which makes it tricky. Not every dyspnoeic patient with a heart murmur has lung oedema.

Some tips that may help with the differentiation on clinical examination include:

1.  Most cases in congestive heart failure will be tachycardic (compensatory mechanism). If they have a sinus arrhythmia, they are unlikely in heart failure.

2.  If they are coughing but are eupnoeic, then it is more likely primarily lung disease (bronchitis, neoplasia, etc.).

3.  Chronic cough without progression is usually indicative of bronchitis or other lung disease.

4.  If they are tachypnoeic or dyspnoeic with a tachycardia, arrhythmia and/or murmur, then the differentiation can only be made with further diagnostics (radiographs and echocardiograms).

This paper will mainly focus on canine bronchopneumonia which is just one subset of lung disease causing dyspnoea. Bronchopneumonia is the acute inflammation of the walls of the lungs, bronchi and the bronchioles, whereas pneumonia is the inflammation of the lungs and not the bronchioles, but these terms are often used interchangeably. Bronchopneumonia usually implies bacterial infection but is not limited to it.

Diagnostics

History is usually an acute onset of expiratory dyspnoea or tachypnoea. Some (not all) patients may also have a concomitant productive cough. Other patients may present pyrexic, but a lack of fever does not exclude bronchopneumonia. Many patients will not exhibit pyrexia or even a leukocytosis.

Differential diagnoses for dyspnoea that needs to be excluded include:

1.  Respiratory (e.g., laryngeal, tracheal, bronchial, pleural)

2.  Cardiovascular - congestive heart disease

3.  Anaemia

4.  Neuromuscular (e.g., tick paralysis, polyradiculoneuritis, snake envenomation, puffer fish)

5.  Metabolic diseases (e.g., uraemia)

6.  Other (e.g., pain, fever)

On physical examination, it is important and can be very helpful to focus on the respiratory pattern. An expiratory dyspnoea is usually evident with audible crackles on the affected sides. Some patients may also display expectoration (coughing and retching with phlegm produced). Keeping the differential list above in mind - also evaluate mucous membrane colour, abdominal palpation, neurological examination if indicated. Be careful not to stress a dyspnoeic patient too much during physical examination.

Complete blood count and serum chemistry may be normal and are usually not very helpful or specific in patients with bronchopneumonia. Patients with bronchopneumonia may have a left shift neutrophilia, but a lack of leucocytosis does not exclude bronchopneumonia.

Thoracic radiographs are paramount in a dyspnoeic patient. Please be careful with the amount of stress induced by taking radiographs. If the patient is stable, then three views should be taken (left and right lateral and either a ventrodorsal or dorsoventral view). Bronchopneumonia usually causes an interstitial (mild) to alveolar pattern (severe). It can be focal or diffuse. Other differentials to consider with this type of lung pattern include: bronchitis, foreign body, parasitic, aspiration pneumonia, oedema (cardiogenic or noncardiogenic), fungal or viral pneumonia.

If cardiogenic oedema cannot be excluded on history, physical examination or radiographs, then the next step may include an echocardiogram. If this is not available, then a treatment trial of a diuretic can be tried. Usually there should be some improvement within a few hours after treatment. Please note that ongoing treatment of a diuretic may worsen bronchopneumonia.

A blood gas may be helpful to determine extent of lung involvement, but is unlikely to add further to the diagnostic workup. Heartworm test should be considered if the patient is in a heartworm area and not on preventative treatment.

Bronchoscopy and bronchoalveolar lavage is the next step in the workup and often the most useful in definitively diagnosing bronchopneumonia. Treatment for bronchopneumonia is often long term and can be extensive; therefore, collecting samples for cytology, culture and antibiogram can be extremely helpful. Bronchoscopy can also diagnose other concomitant problems (i.e., bronchial or tracheal collapse).

Ultrasound-guided fine-needle aspirations can be considered for consolidated lung lesions that are near the periphery and accessible transthoracic. The patient should be carefully monitored post needle aspirations for a pneumothorax.

PCR panels are now more routinely available to diagnose viral and some of the more common bacterial causes of bronchopneumonia. The respiratory PCR panel usually includes: Bordetella bronchiseptica, canine respiratory coronavirus, canine adenovirus type 2, canine distemper virus, canine parainfluenza virus, canine herpesvirus type 1, canine influenza virus as well as H1N1 influenza virus. Samples could be from the BAL fluid or a pharyngeal swab.

A computed tomography (CT) scan is usually not indicated in bronchopneumonia, but may be considered in cases with solid lesions (either focal or diffuse) on radiographs. A CT scan will not always give a definitive diagnosis and may need to be followed by bronchoalveolar lavage or lung aspirates.

Treatment and Management

If the patient is cyanotic or has low oxygen saturation, then supply excess oxygen by placing them in an oxygen cage or supplying nasal oxygen or flow-by. Be careful with masks, as this may lead to excess stress.

Maintaining normal hydration is extremely important in bronchopneumonia patients, as dehydration will result in more viscous secretions which will tend to be retained, leading to further ventilation-perfusion mismatch. It is for this reason that diuretics are contraindicated. Prevent overhydration, as this may lead to pulmonary oedema which will further compromise respiratory function.

Antibiotic therapy should be started as soon as possible. As culture results will take a few days, a good broad-spectrum antibiotic should be considered. Bacteria most commonly cultured in primary bronchopneumonia are Bordetella bronchiseptica and Streptococcus zooepidemicus. Bordetella is highly contagious. Secondary pneumonias, e.g., due to aspiration, include both gram-negative bacteria (E. coli, Klebsiella, Pasteurella and Pseudomonas) as well as gram-positive bacteria (Staphylococcus and Streptococcus). Mycoplasma and Mycobacterium tuberculosis and bovis can also play a role. In one study, over 60% of cases with pneumonia had more than one bacteria species as part of the infection, hence the importance of culture and antibiograms.

Bronchopneumonia can develop secondary to parainfluenza virus or canine adenovirus type-2. Antivirals are not commonly used. Usually the treatment is aimed as secondary bacterial infections and the virus to take its course.

Another part of treatment includes removal of the exudates from the lung. This can be achieved by nebulisation and coupage and encouraging the patient to cough. If the patient is oxygen dependant, then frequent turning may help. In patients off oxygen, a short brisk walk 3–4 times a day will also be effective in stimulating coughing. If nebulisation is not available, then leaving the patient in the bathroom when the owners are running a hot bath or shower will help to moisten the lower airways and decrease the viscosity of the mucoid secretions. Mucolytics may also be considered (bromhexine). Antitussive therapies are contraindicated in these patients.

Bronchodilator therapy is controversial. Aminophylline may decrease the immune response in the lungs and aggravate the VQ mismatch.

Improvement should be seen within two to three days after treatment has started. If the patient is not improving, then consider if an incorrect diagnosis was made or incorrect therapy (antibiotic choice if culture is not yet available). Antibiotics should be given for at least 4 weeks and then 14 days post complete resolution of clinical signs on thoracic radiographs. Thoracic radiographs should be repeated every 7–10 days during therapy. This will assist in detecting any complications including consolidation, atelectasis or abscess formation.

A repeat workup including bronchoalveolar lavage should be considered if there is no adequate response after 14–21 days.

References

1.  Turnwald G, Hoover J. The initial assessment: identifying abnormal breathing patterns. Vet Med. 1994;89(2):108.

2.  Hawkins E. Bronchoalveolar lavage in the evaluation of pulmonary disease in the dog and cat. J Vet Intern Med. 1990;4(5):267.

3.  Daly JM, Macrae S, et al. Equine influenza: a review of an unpredictable virus. Vet J. 2011;189:7–14.

4.  Erles K, Brownlie J. Canine respiratory coronavirus: an emerging pathogen in the canine infectious respiratory disease complex. Vet Clin North Am Small Anim Pract. 2008;38:815.

5.  Priestnall S, Erles K. Streptococcus zooepidemicus: an emerging canine pathogen. Vet J. 2011;188:142–148.

  

Speaker Information
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Ninette Keller, BVSc, BVSc (Hons), MMedVet (Med) (Pret), Grad Cert Ed (JCU)
Veterinary Specialist Services
Gold Coast, QLD, Australia


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