NAVLE Respiratory

Canine Pneumonia Study Guide

📅 March 28, 2026 ⏱ 25 min read

Pneumonia is inflammation of the pulmonary parenchyma (small airways, interstitium, and alveoli) that results in respiratory disturbance and is a common clinical diagnosis in dogs.

Overview and Clinical Importance

Pneumonia is inflammation of the pulmonary parenchyma (small airways, interstitium, and alveoli) that results in respiratory disturbance and is a common clinical diagnosis in dogs. Pneumonia can be caused by aspiration of gastric contents, bacteria, viruses, fungi, parasites, or protozoa. Understanding the different types, diagnostic approaches, and treatment modalities is essential for the NAVLE, as pneumonia-related questions frequently appear in the exam.

The prognosis for bacterial and aspiration pneumonia is generally good with appropriate treatment, with reported survival rates of 77% to 88%. However, fungal pneumonias require prolonged treatment courses and have more variable outcomes depending on the extent of disease.

Type	Common Pathogens	Key Features
Bacterial	Bordetella bronchiseptica, E. coli, Pasteurella spp., Streptococcus spp., Staphylococcus spp., Mycoplasma spp.	Often secondary to viral infection; cranioventral distribution; common in young dogs in shelters/boarding
Viral	Canine distemper virus, Canine influenza virus, Parainfluenza virus, Adenovirus types 1 and 2	Predisposes to secondary bacterial infection; bronchointerstitial to alveolar pattern; often self-limiting
Aspiration	Secondary bacterial infection with enteric organisms, Pasteurella, anaerobes	Associated with megaesophagus, vomiting, anesthesia; right middle lobe commonly affected
Fungal	Blastomyces dermatitidis, Histoplasma capsulatum, Coccidioides immitis	Geographic distribution; chronic course; miliary or nodular pattern; hilar lymphadenopathy
Parasitic	Filaroides spp., Aelurostrongylus spp., Paragonimus spp., Angiostrongylus vasorum	Eosinophilic inflammation; patchy bronchointerstitial pattern; diagnosed via Baermann or BAL

Classification of Canine Pneumonia

Pneumonia in dogs is classified by etiology. Understanding the different types is critical for appropriate diagnosis and treatment.

High-YieldFor NAVLE, remember that bacterial pneumonia is more common in dogs than cats, and viral infection followed by bacterial invasion is common in young dogs, while aspiration pneumonia is more common in older dogs with predisposing conditions.

Respiratory Signs	Systemic Signs
Cough: Moist, productive Tachypnea: Increased respiratory rate Dyspnea: Labored breathing Nasal discharge: Mucopurulent Exercise intolerance: Reduced activity	Fever: Often present, but not always Lethargy: Depression, weakness Anorexia: Decreased appetite Weight loss: Chronic cases Cyanosis: Blue mucous membranes in severe cases

Clinical Signs and Physical Examination

Clinical signs of pneumonia can be acute or chronic and do not always reflect the severity of the underlying respiratory condition. Recognition of these signs is essential for early diagnosis.

Common Clinical Signs

Auscultation Findings

Crackles (rales): Indicate fluid in alveoli - suggestive of pneumonia, edema
Wheezes: Narrowed airways - more typical of bronchitis
Increased bronchovesicular sounds: Consolidated lung tissue
Decreased lung sounds: Pleural effusion, severe consolidation

Esophageal Disease	Neurologic/Anatomic	Iatrogenic
Megaesophagus Esophageal stricture Myasthenia gravis Esophagitis Hiatal hernia	Laryngeal paralysis Cleft palate Brachycephalic syndrome Seizure disorders Altered consciousness	Post-anesthesia (0.17%) Force feeding Improper liquid medication Barium administration Tube feeding complications

Aspiration Pneumonia

Aspiration pneumonia results from inhalation of gastric acid, oropharyngeal secretions, food material, or foreign bodies. It remains a common cause of bacterial pneumonia in dogs, with up to 25% mortality rate requiring aggressive therapy.

Risk Factors

NAVLE TipMegaesophagus is the TOP predisposing factor for aspiration pneumonia. When you see a regurgitating dog with respiratory signs, always consider aspiration pneumonia secondary to megaesophagus. The prognosis is poor to guarded, and aspiration pneumonia is the most common cause of death in dogs with megaesophagus.

Pattern	Radiographic Appearance	Clinical Significance
Alveolar	Fluffy, ill-defined opacities; air bronchograms; lobar sign; silhouette effect	Air replaced by fluid/cells; indicates bacterial pneumonia, edema, hemorrhage
Interstitial	Hazy opacity; vessels visible but margins indistinct (trees in fog)	Early/resolving pneumonia; viral infection; pulmonary fibrosis
Bronchial	Donuts (end-on bronchi) and tramlines (bronchial walls); peribronchial cuffing	Chronic bronchitis; CIRDC; parasitic disease
Nodular/Miliary	Multiple discrete soft tissue nodules; may coalesce	Fungal pneumonia; metastatic neoplasia; granulomatous disease

Radiographic Diagnosis

Thoracic radiography is essential for diagnosing pneumonia. Three-view thoracic radiographs (right lateral, left lateral, and VD/DV) are recommended to visualize all lung fields.

Radiographic Patterns in Pneumonia

Distribution Patterns

Cranioventral distribution: Most characteristic of bronchopneumonia and aspiration pneumonia. The right cranial, right middle, and left cranial lung lobes are most commonly affected. The right middle lung lobe is anatomically predisposed due to the straighter angle of the right principal bronchus (165.8 degrees versus 142.7 degrees on the left).

Caudodorsal distribution: More typical of non-cardiogenic pulmonary edema, foreign body pneumonia, or hematogenous spread.

High-YieldAir bronchograms are the CLASSIC sign of alveolar lung pattern - air-filled bronchi visible against fluid-dense lung. For NAVLE, remember: cranioventral alveolar pattern with air bronchograms = bacterial pneumonia or aspiration pneumonia until proven otherwise.

Technique	Advantages	Disadvantages
Transtracheal wash (TTW)	No anesthesia required; good for upper airway sampling	May not sample affected lung lobe; patient restraint needed
Endotracheal wash	Samples lower airways; can be done during anesthesia	Requires anesthesia; oropharyngeal contamination possible
Bronchoalveolar lavage (BAL)	Targeted sampling; best cytology yield; gold standard	Requires bronchoscopy and anesthesia; risk of hypoxemia

Diagnostic Approach

Minimum Database

CBC: Leukocytosis with left shift (neutrophilia); stress leukogram; anemia in chronic cases
Chemistry panel: Usually unremarkable; assess overall health status
Three-view thoracic radiographs: Essential for pattern recognition and distribution
Pulse oximetry/arterial blood gas: Assess oxygenation (SpO2 less than 94% or PaO2 less than 80 mmHg indicates hypoxemia)

Airway Sampling

Airway sampling with culture is most indicated for patients with suspected infectious pneumonia, those requiring hospitalization, and patients at risk for multidrug-resistant organisms.

Clinical Scenario	First-Line	Alternative	Duration
Mild infectious pneumonia	Doxycycline 5 mg/kg PO q12h or 10 mg/kg PO q24h	Amoxicillin-clavulanate 14 mg/kg PO q12h	7-10 days minimum; 1 week past clinical resolution
Severe/hospitalized	Ampicillin-sulbactam 30 mg/kg IV q8h + Enrofloxacin 10-15 mg/kg IV q24h	Amoxicillin-clavulanate + Fluoroquinolone	Traditionally 3-6 weeks; evidence suggests 10-21 days may be adequate
Aspiration pneumonia	Ampicillin-sulbactam + Enrofloxacin (anaerobic coverage important)	Clindamycin + Fluoroquinolone	4-6 weeks typically
Bordetella/Mycoplasma suspected	Doxycycline (penetrates airways well)	Azithromycin 10 mg/kg PO q24h	7-14 days

Antimicrobial Therapy

Antimicrobial selection should ideally be based on culture and sensitivity testing. However, empiric therapy is often initiated while awaiting results.

Empiric Antibiotic Selection

Exam Focus: Doxycycline is the FIRST-LINE empiric choice for infectious bronchopneumonia because both Bordetella bronchiseptica and Mycoplasma species are generally susceptible. Beta-lactam antibiotics (amoxicillin, cephalexin) are NOT recommended for Bordetella due to poor penetration into the larger airways where Bordetella colonizes.

Disease	Geographic Region	Diagnosis	Treatment
Blastomycosis	Ohio, Missouri, Mississippi, Tennessee River valleys; Great Lakes; Southeast US	Urine antigen test (highly sensitive); cytology showing broad-based budding yeast	Itraconazole 5 mg/kg PO q24h for 4-6 months minimum
Histoplasmosis	Mississippi, Ohio, Missouri River valleys	Urine antigen test; cytology showing small intracellular organisms with halo	Itraconazole 10 mg/kg PO q24h; may require IV amphotericin B
Coccidioidomycosis	Southwestern US (Arizona, California deserts)	Serology (tube precipitin, complement fixation); spherules on cytology	Fluconazole or itraconazole; often lifelong for disseminated

Supportive Care and Physiotherapy

Antibiotic therapy alone is insufficient for most pneumonia patients. Resolution depends on clearance of secretions from the airway via the cough reflex and mucociliary escalator.

Oxygen Therapy

Required for patients with moderate to marked hypoxemia (SpO2 less than 94% or PaO2 less than 80 mmHg on room air). Administer oxygen at 40-60% concentration via oxygen cage, nasal catheter, or mask.

Nebulization

The goal of nebulization is to hydrate the lower airway (specifically the ciliary escalator) with small droplets of water which are inhaled into the respiratory tract. Use sterile saline for 15-20 minutes, 2-4 times daily. Alternative home technique: Run a hot shower in a closed bathroom to create steam; keep dog in the steam-filled room for 10-15 minutes.

Coupage

Coupage is chest percussion that helps expel pulmonary and bronchial secretions by stimulating the cough reflex. Perform immediately after nebulization.

Technique: Cup hands (air between palm and chest wall) and rhythmically pat both lateral thoracic walls
Direction: Work dorsal to ventral, caudal to cranial
Frequency: Several times daily, especially in recumbent patients
Contraindication: Do NOT perform in patients with regurgitation (increases aspiration risk)
Post-coupage: Encourage activity to promote coughing and expectoration

High-YieldCUPPED hands are CRITICAL for effective coupage - flat hands are useless. The impact should create a drumbeat-like sound. Always perform coupage AFTER nebulization to help mobilize loosened secretions.

Pneumonia Type	Survival Rate	Key Prognostic Factors
Bacterial pneumonia	77-94% discharge rate	Response to therapy; underlying disease control; nutritional status
Aspiration pneumonia	75-82% survival	Early diagnosis; management of underlying cause; prevention of recurrence
Blastomycosis	50-75% recovery	Number of body systems involved; severity of lung disease; CNS/eye involvement (poor)
Megaesophagus with AP	Poor to guarded	AP most common cause of death; 7.69x increased mortality risk

Fungal Pneumonia

Fungal pulmonary infections occur more commonly in dogs than cats. They are characterized by chronic course, geographic distribution, and systemic involvement.

NAVLE TipFor NAVLE, remember geographic associations: BLASTOMYCOSIS = Great Lakes/Ohio-Mississippi River valleys (young male hunting dogs at highest risk). COCCIDIOIDOMYCOSIS = Desert Southwest. Recovery rates for blastomycosis are 50-75% with proper treatment. The critical period is the first 24-72 hours when fungi begin to die, causing severe pulmonary inflammation.

Memory Aids and Clinical Pearls

Pneumonia Pattern Recognition

"CAVE" for Aspiration Distribution = Cranial, Anterior (ventral), Ventral = Right cranial, Right Middle, Left cranial lobes

"RMM" = Right Middle Most affected (anatomically predisposed to aspiration)

"ABC" of Alveolar Pattern = Air bronchograms, Border effacement (lobar sign), Consolidation

Antibiotic Selection Memory

"DOXY for DOGs with kennel cough" = Doxycycline is first-line for infectious bronchopneumonia (Bordetella, Mycoplasma)

Fungal Geographic Memory

"BLASTO = Lakes and Rivers" (Great Lakes, Ohio/Mississippi) | "COCCI = Desert" (Arizona, California)

Prognosis and Monitoring

Monitoring During Treatment

Clinical signs: Respiratory rate, effort, cough character, appetite, activity
Pulse oximetry: Monitor SpO2 for trends (target greater than 94%)
Radiographs: Every 3-4 days during hospitalization; radiographic improvement lags behind clinical improvement
Inflammatory markers: C-reactive protein (CRP) can guide antibiotic duration
Re-evaluation: 10-14 days after starting treatment to assess response

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