Equis ISSN 2398-2977

Lung: pneumonia - aspiration

Synonym(s): Aspiration pneumonia

Contributor(s): Graham Munroe, Nicola Menzies-Gow

Introduction

  • Cause: any disease leading to pharyngeal or esophageal dysphagia may lead to aspiration of food, water and saliva into the trachea and the rest of the respiratory tract, eg esophageal obstruction or choke. Neurological disorders may affect the control of swallowing and lead to pharyngeal paralysis or paresis, eg guttural pouch disease (mycosis), grass sickness, equine protozoal myeloencephalitis. Iatrogenic aspiration of material may occur with incorrect passage of a nasogastric tube into the trachea and the administration of mineral oil, milk (in foals), or other mixtures. A well known complication of laryngeal prosthesis surgery for recurrent laryngeal neuropathy.
  • Signs: sudden death. Clinical signs of any primary problem leading to dysphagia and aspiration of food and saliva. Food material may be present at the nostrils. Fever, tachypnea and dyspnea, nasal discharge, coughing, inappetence, depression, exercise intolerance, weight loss and malodorous breath in anaerobic infections.
  • Diagnosis: clinical history and signs, auscultation of the respiratory tract, endoscopy of the respiratory tract with collection of tracheobronchial samples, blood samples for hematology and biochemistry, thoracic radiography, ultrasonography of the chest.
  • Treatment: measures to specifically address the cause of the aspiration and prevent its further occurrence. Broad spectrum antimicrobial administration until culture and sensitivity testing reveals any specific medications. NSAIDs to control lung inflammation. Other treatment modalities that have been suggested include nebulized mucolytics, bronchodilators and expectorants. Stress- and dust-free environment, with good ventilation and a high quality, appetizing diet.
  • Prognosis: guarded to poor. Very variable depending on the severity of the pneumonia, the inciting cause, the ability to resolve the original inciting cause of aspiration, the volume and nature of the aspirated material, the type of bacteria introduced, and the rapidity of treatment. All have an influence on the final outcome.

Pathogenesis

Etiology

  • Any disease leading to pharyngeal or esophageal dysphagia may lead to the aspiration of food, water and/or saliva into the trachea and the rest of the respiratory tract. The most common of these conditions is esophageal obstruction   Esophagus: impaction  or choke.
  • Other esophageal disorders that could also lead to regurgitation include strictures   Esophagus: stricture  , megaesophagus    Esophagus: megaesophagus  , esophagitis and congenital disorders such as persistent right aortic arch and esophageal stenosis.
  • Neurological disorders may affect the control of swallowing and lead to pharyngeal paralysis or paresis. Guttural pouch disease, especially mycosis   Guttural pouch: mycosis  , grass sickness   Grass sickness  , tetanus   Tetanus  , rabies   Rabies  , equine protozoal myeloencephalitis   CNS: Equine protozoal myeloencephalitis (EPM)  , botulism   Botulism  , Streptococcus equi infection   Strangles (Streptococcus equi infection)  and bacterial meningitis can fit into this category.
  • Cleft palate can lead to aspiration of milk into the trachea.
  • Foreign bodies or a mass in the pharynx (subepiglottic or pharyngeal cysts or tumors of esophagus can cause dysphagia.
  • Abnormalities of the movement of the soft palate (dorsal displacement   Soft palate: dorsal displacement  or rostral displacement of the palatopharyngeal arch   Pharynx: 4th branchial arch defects  may lead to aspiration of foreign material, but usually at a low level. Severe inflammation of the pharynx, esophagus and stomach may also lead to dysphagia and regurgitation.
  • Various poisonings may lead to dysphagia, including plants   Poisonous plants: overview  (oleander   Oleander (Nerium oleander)  ), lead   Toxicity: lead  , arsenic and some snake bites   Toxicity: snakebite  .
  • Iatrogenic aspiration of material may occur with incorrect passage of a nasogastric tube   Gastrointestinal: nasogastric intubation   into the trachea and the administration of mineral oil , milk (in foals) or other mixtures. Drenching horses can also lead to the aspiration of the administered chemicals. Saliva and food material can be aspirated into the trachea during general anesthesia.
  • A well known complication of laryngeal prosthesis surgery    Larynx: laryngoplasty  for recurrent laryngeal neuropathy   Larynx: hemiplegia   is aspiration of food and saliva into the trachea.

Predisposing factors

General
  • Horses are very tolerant of the entry of foreign material into their trachea without the induction of a severe coughing response compared with other species. The lack of a significant protective response may be a factor in predisposing the horse to aspiration pneumonia.

Pathophysiology

  • The severity of the injury to the pulmonary tissue following aspiration depends on the amount and composition of the aspirated material.
  • If large quantities of fluids are aspirated the animal may die acutely.
  • If gastric contents are aspirated then the damage is sever with pulmonary edema and hemorrhagic pneumonia.
  • Aspiration of mineral oil leads to a chronic and progressive granulomatous pneumonia which is difficult to treat.
  • In general, aspiration of material into the lungs leads to bacterial contamination of the lower respiratory tract which overwhelms the normal respiratory defense mechanisms resulting in pulmonary infection, lung consolidation and in some cases pleuropneumonia   Lung: pleuropneumonia - bacterial (pleuritis)   and/or lung abscess   Lung: abscess  formation.
  • The bacteria involved are mixed and anaerobic infections are quite common, including:
  • The cranioventral parts of the lung are at most risk because of the structure and orientation of the bronchi and other conducting airways.

Timecourse

  • In early cases, clinical signs may not be obvious, being limited to fever and depression.
  • As the pneumonia progresses, the clinical signs become more apparent.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Reuss S M & Giguère S (2015) Update on bacterial pneumonia and pleuropneumonia in the adult horseVet Clin North Am Equine Pract 31 (1), 105-120 PubMed.
  • Shaw S D, Norman T E, Arnlod C E & Coleman M C (2015) Clinical characteristics of horses and foals diagnosed with cleft palate in a referral populatoin: 28 cases (1988-2011). Can Vet J 56 (7), 756-560 PubMed.
  • Barakzai S Z, Fraser B S & Dixon P M (2014) Congenital defects of the soft palate in 15 mature horsesEquine Vet J 46 (2), 185-188 PubMed.
  • Holcombe S J, Hurcombe S D, Barr B S & Schott H C 2nd (2012) Dysphagia associated with presumed pharyngeal dysfunction in 16 neonatal foalsEquine Vet J Suppl (41), 105-108 PubMed.
  • Chiavaccini L & Hassel D M (2010) Clinical features and prognostic variables in 109 horses with esophageal obstruction (1992-2009). J Vet Intern Med 24 (5), 1147-1152 PubMed. 

Other sources of information

  • Reed S M, Balyly W M & Sellon D C (2009) Eds. Equine Internal Medicine. 3rd edn. Saunders.
  • Marr T (2007) Miscellaneous Pulmonary  Disorders. In: Equine Respiratory Medicine and Surgery. Eds: McGorum BC et al. Saunders Elsevier, USA. pp. 611-612.


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