Ammonia Toxicity Workup

Updated: May 04, 2019
  • Author: Steven Issley, MD, FRCPC; Chief Editor: Sage W Wiener, MD  more...
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Workup

Approach Considerations

Serum ammonia lconcentrations are of little value in patients with ammonia exposure because they do not correlate with clinical toxicity. However, patients with compromised hepatic function may show increased serum ammonia concentrations because of less efficient metabolism.

Laboratory studies and procedures in patients with ammonia exposure include the following:

  • In intentional exposures – Serum acetaminophen concentration
  • Complete blood count (CBC)
  • Electrolytes, blood urea nitrogen (BUN), and creatinine
  • Serum lactic acid
  • in cases of significant respiratory distress  –  Serial arterial blood gases (ABGs), to assess for metabolic acidosis, respiratory alkalosis, increased alveolar-arterial gradient
  • In patients with eye injury  – Slit-lamp examination with fluorescein staining, tonometry to determine if intraocular pressure is elevated, conjunctival pH measurement

Depending on the clinical presentation, other tests and procedures may include the following:

  • Chest radiography
  • Abdominal series – To rule out perforation following ingestion
  • Cardiac monitoring
  • Pulse oximetry
  • Pulmonary capillary wedge pressure (PCWP) monitoring – In cases of severe acute lung injury (ALI) or acute respiratory distress syndrome (ARDS)
  • Pulmonary function tests (PFTs)
  • Ventilation/perfusion (V/Q) scan
  • Bronchoscopy – In severe acute inhalation injury
  • Endoscopy – In significant ingestion exposures
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Pulmonary Testing

Once the acute emergency is controlled, PFTs are useful to gauge the severity of injury and to monitor progress and recovery. PFTs may show obstructive lung disease (in both acute and chronic cases) or restrictive lung disease (in chronic cases).

A V/Q scan may be useful to gauge the severity or progression of disease, but the results are unlikely to change acute management. Ventilation deficits generally are more pronounced in the larger airways. The ventilation scan also may show abnormal air trapping in the setting of lower airway obstruction.

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Bronchoscopy

Perform bronchoscopy to assess respiratory tract damage following acute inhalation injury (in severe cases), or in cases of ingestion with aspiration.  Bronchoscopic findings may include the following:

  • Airway edema, obstruction, and necrosis
  • Epithelial sloughing
  • Laryngitis and tracheitis
  • Diffuse alveolar damage
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Endoscopy

Consider endoscopy for significant ingestion exposures (large volume and/or industrial concentrations). Indications are somewhat controversial; obtain toxicology and GI consultations if needed. Perform endoscopy on symptomatic patients and patients with intentional exposure within 24-48 hours following ingestion. The risk of perforation increases if endoscopy is performed more than 72 hours post ingestion.

Findings on endoscopy may include the following:

  • Laryngeal and epiglottic edema
  • Friable erythematous esophagus
  • Corrosive injury
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