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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • May develop after inhalation of foreign material and bacteria into the lower respiratory tract
  • Causes include dysphagia, obstructive esophageal disorders, GI reflux, and accidental inhalation of foreign material (nasogastric intubation)

Signalment!!navigator!!

Foals appear more prone to GI reflux and subsequent aspiration pneumonia.

Signs!!navigator!!

Historical Findings

  • Dysphagia, ptyalism, or discharge of food, water, or milk from the nostrils
  • Recent history of drenching or nasogastric intubation

Physical Examination Findings

  • Clinical signs—fever, depression, anorexia, cough, nasal discharge (may be serohemorrhagic), tachypnea, and dyspnea
  • Foul-smelling breath or nasal discharge suggests strongly anaerobic infection
  • Abnormal lung sounds (auscultation)

Causes and Risk Factors!!navigator!!

Dysphagia

  • Neurologic diseases affecting cranial nerves IX and X—guttural pouch diseases, botulism, lead toxicity, and viral encephalitis
  • Primary myopathies of pharyngeal and laryngeal muscles—white muscle disease and hyperkalemic periodic paralysis
  • Pharyngeal obstruction—strangles, pharyngeal abscess, neoplasia, foreign body, dorsal displacement of soft palate
  • Congenital—cleft palate and hypoplasia of the soft palate
  • Iatrogenic causes—pharyngeal and laryngeal surgery

Esophageal Disorders

  • Esophageal obstruction
  • Esophageal diverticulum
  • Esophageal fistula
  • Megaesophagus

GI Reflux

Gastric outflow obstruction (foals).

Accidental Inhalation of a Foreign Body

Administration of fluids by drenching or nasogastric tube.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Acute bronchopneumonia
  • Pleuropneumonia
  • Interstitial pneumonia
  • Respiratory distress syndrome

CBC/Biochemistry/Urinalysis!!navigator!!

  • Hyperfibrinogenemia, hyperglobulinemia, and anemia are common with chronic pneumonia
  • Elevated white blood cell count with neutrophilia may be observed

Other Laboratory Tests!!navigator!!

  • Increased blood and tissue concentrations of lead (lead toxicity)
  • Decreased whole-blood selenium concentration and glutathione peroxidase activity with increased serum creatine kinase and aspartate aminotransferase (white muscle disease)
  • Hyperkalemic periodic paralysis—genetic testing or finding hyperkalemia during clinical episodes

Imaging!!navigator!!

  • Thoracic radiography commonly reveals ventral patchy opacity obscuring the cardiac silhouette
  • Contrast radiography may help to identify esophageal diseases
  • Thoracic ultrasonography may detect pleural effusion

Other Diagnostic Procedures!!navigator!!

  • Tracheobronchial aspiration and/or thoracocentesis for cytology, Gram stain, and culture (both aerobic and anaerobic)
  • Endoscopy of the respiratory and upper GI tracts may help to identify the primary cause

Pathologic Findings!!navigator!!

  • Lung consolidation (ventral part)
  • Acute cases—hemorrhagic and edematous areas
  • Chronic cases—lungs with necrotic and purulent materials
  • Pleural space—fibrinous exudate and adhesions

Treatment ⬆ ⬇

TREATMENT

  • Restore airway patency, drain pleural effusion, etc.
  • Nasal oxygen (6–10 L/min) if PaO2 <60 mmHg
  • Thoracocentesis or indwelling chest tubes can achieve drainage; a one-way valve prevents pneumothorax
  • Treat primary disease
  • Stall rest
  • Dysphagic horses may be fed with a nasogastric tube
  • Fluid therapy as needed

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Systemic administration of broad-spectrum antimicrobials. Preferred combinations include sodium or potassium penicillin (22 000–40 000 IU/kg IV every 6 h), aminoglycoside (gentamicin (6.6–8.8 mg/kg IV every 24 h) or amikacin (15–20 mg/kg IV or IM every 24 h) for foals), and metronidazole (15–25 mg/kg IV or PO every 6–8 h)
  • Other antimicrobial options include procaine penicillin G (22 000 IU/kg IM every 12 h), trimethoprim–sulfamethoxazole (30 mg/kg PO every 12 h), ceftiofur (1–5 mg/kg IV or IM every 12 h), or chloramphenicol (20–50 mg/kg PO every 6–8 h for adults and foals >1 week)
  • NSAIDs—flunixin meglumine (1.1 mg/kg PO or IV every 12–24 h) or phenylbutazone (2.2–4.4 mg/kg PO or IV every 12 h)

Contraindications/Possible Interactions!!navigator!!

Use aminoglycosides and NSAIDs with caution in horses with renal dysfunction and/or dehydration.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Follow progress of pulmonary lesions by radiography/ultrasonography.

Prevention/Avoidance!!navigator!!

Prevent or avoid exposure to primary causes.

Possible Complications!!navigator!!

  • Pleuritis, lung abscess
  • Thrombophlebitis
  • Laminitis
  • Disseminated intravascular coagulation
  • Septicemia

Expected Course and Prognosis!!navigator!!

  • Prolonged treatment is often needed
  • Prognosis is guarded

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Abbreviations!!navigator!!

  • GI = gastrointestinal
  • NSAID = nonsteroidal anti-inflammatory drug
  • PaO2 = partial pressure of oxygen in arterial blood

Suggested Reading ⬆ ⬇

Ainsworth DM, Hackett R. Bacterial pneumonia. In: Reed SM, Bayly WM, Sellon DC, eds. Equine Internal Medicine, 3e. St. Louis, MO: WB Saunders, 2010:325–328.

Author(s) ⬆

Author: Daniel Jean

Consulting Editors: Daniel Jean and Mathilde Leclère

Acknowledgment: The editors acknowledge the prior contribution of Laurent Couëtil.