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Aspiration-related respiratory disorders in dogs | VETgirl Veterinary Continuing Education Podcasts

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In today’s VETgirl online veterinary CE podcast, we review aspiration-related respiratory disorders in dogs. Much of our veterinary medical information gathered over time has first stemmed from information available in human medicine. So, Nafe et al wanted to review canine aspiration-related respiratory disorders that are already classified conditions in human medicine. In a publication called Aspiration-related respiratory disorders in dogs, the authors provide us a literature review on aspiration-related respiratory disorders in dogs, and describe the similarities between canine and human conditions. By drawing comparisons between known human conditions and canine conditions, we may be able to more effectively treat these veterinary conditions or mitigate damage caused to the respiratory tract.

Aspiration-related disorders can be grouped into those affecting the upper airways (e.g., oropharynx, nasopharynx, larynx, and proximal trachea) and those affecting the lower airways (e.g., intrathoracic trachea, mainstem bronchi, and pulmonary parenchyma). The authors propose the following classification of aspiration-related respiratory disorders in dogs:

  • Aspiration-related upper airway disorders
  • Aspiration-related large airway obstruction
  • Aspiration-related bronchiectasis
  • Aspiration-related small airway disease
  • Aspiration pneumonitis and pneumonia
  • Aspiration-related lipid pneumonia
  • Aspiration-related interstitial lung disease.

So, in this VETgirl podcast, we’ll review some of the common conditions resulting in aspiration-related respiratory disease. First, gastroesophageal reflux (GER or GERD). This is a common condition in both the human and veterinary fields. In this condition, reflux of both acidic and non-acidic gastric contents leads to inflammation of the esophagus and upper airways. Inflammation to the oropharynx, nasopharynx, and larynx in humans can cause voice change, cough, stertor and can even result in upper airway obstruction. Humans suffering from GERD describe heartburn, nausea, belching, cough, and dysphagia. Diagnosis in humans is made by pairing these clinical signs with evidence of laryngeal or oropharyngeal inflammation. Esophageal pH monitoring may not be helpful as some cases present with non-acidic reflux, but even non-acidic gastric contents is still damaging to the tissues and results in clinical signs associated with GERD. Coughing can either be the cause of reflux, or the result of reflux. Studies have shown that exposure to gastric contents can produce laryngeal irritation and cough in dogs. The authors propose that the clinical sign of chronic coughing in dogs should trigger the clinician to consider GERD as a possible cause and perhaps a proton pump inhibitor trial could be attempted.

Aspiration-related large airway obstruction is, thankfully, an uncommon condition in dogs, but requires immediate recognition and treatment for good outcome. Dogs with dysphagia or laryngeal dysfunction are at an increased risk of accidentally inhaling objects and liquids. Things dogs might inhale could include food, plant matter, and pieces of toys or materials they are chewing on. Often times the object is not radiographically apparent, so lack of radiographic evidence should not deter the clinician from the suspicion of foreign material inhalation. Radiolucent objects may still produce radiographically apparent atelectasis and/or air trapping or regional inflation of the affected lung lobe. CT has 100% sensitivity for showing you that there is a problem, but it’s only 66.7% specific in being able to tell you that the problem is an inhaled object. At least a CT can trigger the clinician to recommend endoscopic investigation of the affected airway segment, which can be both diagnostic and curative (endoscopic retrieval). Clinicians should take caution that sometimes the object inhaled may show up on radiographs as a soft tissue structure that can mimic the appearance of tracheal collapse. Look for clear demarcations around the soft tissue structures involved in the presumed collapse segment to identify the outline of the inhaled object. Depending on the location, inhaled tracheal obstructions may reachable with alligator forceps under endoscopic guidance.

Bronchiectasis is more often thought of as a congenital or acquired pathology of the bronchi in which the elastic and muscular components of the bronchi walls breakdown and results in chronic inflammation with secondary infections in the airways. Occasionally, inhaled liquids or material can be a cause for bronchiectasis. CT is the preferred diagnostic for identification. Bronchoscopy is tricky and successful identification of bronchiectasis via endoscopy depends heavily on the skill of the clinician performing the bronchoscopy. Sometimes the object (i.e. kibble) can be identified via bronchoscopy, or more often cultures collected via bronchoscopy can help paint the picture of a bacterial dysbiosis that is the result of aspirated material or liquids. Friable objects cannot be retrieved via bronchoscopy due to the risk of the material breaking apart during retrieval and then lodging in other airways. In these cases, surgical removal of the affected lung lobe may be warranted.

Chronic, recurrent aspiration disorders can result in aspiration-related small airway disease (DAB). Clinical history, documentation of aspiration on radiographs, CT, and histology are all tools to help identify this condition. In humans, GER is the most common disease associated with development of DAB. In dogs, videofluoroscopic swallow assessment may reveal megaesophagus, and CT may reveal bronchiolocentric lesions. Treatment of this condition in dogs weighs heavily on treating the underlying condition responsible for the silent or witnessed recurrent aspiration events.

Aspiration pneumonia is probably the most widely recognized result of aspiration disorders in dogs. In veterinary medicine, it is difficult to differentiate aspiration pneumonitis, which occurs from aspiration of large volumes and represents sterile inflammation, and aspiration pneumonia, which has a bacterial component. Clinical signs alone cannot differentiate the two conditions in dogs as both will cause pyrexia and respiratory distress. Aspiration pneumonitis typically occurs within hours of the aspiration event, whereas the aspiration event in aspiration pneumonia may go unrecognized. This is not a reliable feature for differentiating the two conditions. Pneumonitis also causes disruption of the lungs normal mucociliary clearance making the tissues primed for a bacterial infection, so pneumonitis in dogs can easily progress to a pneumonia. If the inhaled agent is identified – such as inhaling salt water- the clinician can presume the dog is suffering from pneumonitis. Why this matters is when to decide on antimicrobial therapy. Clinicians must use their best judgment on whether to start antimicrobial therapy as we all must take responsibility for the continued development of antimicrobial resistance in our veterinary patients.

Aspiration-related lipid pneumonia, more commonly just called lipid pneumonia, is a rare condition identified in dogs. The inhalation of lipid containing materials results in a patchy consolidation on thoracic radiographs. Diagnosis is made based on history, radiographic findings, and/or cytologic or histologic findings that show macrophages containing consumed lipids and extracellular fat globules in the airway sample. In the few cases I have diagnosed in both dogs and cats, the cause of lipid pneumonia was presumably related to the owner administering a lipid-based medication to an uncooperative pet. This article fails to discuss treatment for this condition, and perhaps that is because there isn’t really anything that can be done to effectively treat this type of aspiration.

Lastly, chronic aspiration in humans can result in interstitial lung disease such as pulmonary fibrosis. This is not a widely identified condition in veterinary patients at this time. However, clinicians with patients that are showing progressive decline in lung function over time despite treatment may want to keep the possibility of an acquired pulmonary fibrosis in their knowledge bank for treatment purposes.

So, what can we take away from this VETgirl podcast? Identification of the cause of aspiration is key to effective treatment. Get a good history from your clients, prod them with leading questions to help identify whether the patient could have chewed up the trash, or inhaled shrubbery debris while hunting, or aspirated while at their camp two weeks ago. Always warn clients that radiographs can be misleading and can miss the disease but they are still a necessary screening tool, and perhaps CT or endoscopy may be warranted under the supervision of a veterinary specialist. Ultimately, the prognosis for aspiration-related respiratory disorders is typically good (Kogan, Tart), with a specific prognosis for aspiration pneumonia being approximately 77% with aggressive supportive care and treatment.

Abbreviations:
DAB: aspiration-related small airway disease
GERD: gastroesophageal reflux

References:
Nafe LA, Grobman ME, Masseau I, et al. Aspiration-related respiratory disorders in dogs. J Am Vet Med Assoc 2018;253(3):292-300.

DA Kogan, LR Johnson, KE Jandrey, RE Pollard. Clinical, clinicopathologic, and radiographic findings in dogs with aspiration pneumonia: 88 cases (2004-2006). J Am Vet Med Assoc 2008;233(11):1742-1747.

DA Kogan, LR Johnson, BK Sturges, et al. Etiology and clinical outcome in dogs with aspiration pneumonia: 88 cases (2004–2006). J Am Vet Med Assoc 2008;233(11):1748-1755.

KM Tart, DM Babski, JA Lee. Potential risks, prognostic indicators, and diagnostic and treatment modalities affecting survival in dogs with presumptive pulmonary aspiration pneumonia: 125 cases (2005-2008). J Vet Emerg Crit Care 2010;20(3):319-329.

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