Acute Respiratory Distress Syndrome (ARDS) is a devastating cause of acute respiratory failure in veterinary patients. It occurs when a severe lung or systemic insult triggers widespread inflammation, leading to non-cardiogenic pulmonary edema, impaired oxygen exchange, and reduced lung compliance.
In 2025, the ARDSVet Consensus Definitions (Balakrishnan et al., J Vet Emerg Crit Care) modernized how clinicians diagnose and classify ARDS in small animals, introducing standardized criteria for both intubated and non-intubated patients.
What Is ARDS in Dogs and Cats?
ARDS represents the end stage of severe lung inflammation, regardless of the initiating cause. In dogs and cats, this syndrome may follow:
- Aspiration of gastric contents
- Pneumonia or sepsis
- Smoke inhalation or near-drowning
- Pancreatitis or trauma
Unlike cardiogenic pulmonary edema, ARDS develops independently of heart disease and reflects inflammatory injury to the alveolar-capillary barrier.
Pathophysiology of ARDS: When Inflammation Floods the Lungs
The hallmark of ARDS is increased permeability of the pulmonary microvasculature, resulting in fluid, protein, and inflammatory cell leakage into alveoli.
Stages of ARDS Development
- Exudative Phase (first 1–7 days):
- Alveolar flooding with protein-rich fluid and neutrophils
- Surfactant dysfunction and atelectasis
- Profound hypoxemia and respiratory distress
- Proliferative Phase (7–21 days):
- Fibroblast proliferation, partial epithelial repair
- Persistent inflammation and reduced compliance
- Fibrotic Phase (>21 days):
- Interstitial fibrosis and irreversible lung stiffening
Systemically, hypoxemia and inflammation can precipitate multi-organ dysfunction, making ARDS a critical emergency.
Updated ARDSVet Diagnostic Criteria
The ARDSVet framework establishes clear diagnostic criteria that align with human ARDS definitions but are adapted to veterinary settings.
A diagnosis of ARDSVet requires all of the following:
- Known or suspected acute risk factor
(e.g., sepsis, aspiration, pancreatitis, trauma, inhalation injury). - Acute onset of new or worsening respiratory distress within 1 week of the insult.
- Evidence of non-cardiogenic pulmonary edema, confirmed by thoracic imaging and exclusion of left-sided heart failure or fluid overload.
- Diffuse pulmonary infiltrates on thoracic radiographs, CT, or ultrasound.
- Hypoxemia, measured by arterial blood gas (PaO₂/FiO₂) or pulse oximetric (SpO₂/FiO₂) ratios.
Optional: Bronchoalveolar lavage or airway cytology showing neutrophilic, high-protein inflammation.
Severity Stratification: IMV-ARDS vs. Non-Intubated ARDS
1. IMV-ARDS (Invasive Mechanical Ventilation)
Applies to intubated patients ventilated with PEEP ≥ 5 cm H₂O.
| Severity | Criteria |
|---|---|
| Mild/Moderate | PaO₂/FiO₂ > 100 to ≤ 300 OR SpO₂/FiO₂ > 150 to ≤ 315 (with SpO₂ ≤ 97%) |
| Severe | PaO₂/FiO₂ ≤ 100 OR SpO₂/FiO₂ ≤ 150 (with SpO₂ ≤ 97%) |
2. Non-Intubated ARDS
For patients on supplemental oxygen or high-flow nasal oxygen (HFNO) without invasive ventilation.
| Severity | Criteria |
|---|---|
| Mild/Moderate | PaO₂/FiO₂ > 100 to ≤ 300 OR SpO₂/FiO₂ > 150 to ≤ 315 (with SpO₂ ≤ 97%) |
| Severe | PaO₂/FiO₂ ≤ 100 OR SpO₂/FiO₂ ≤ 150 (with SpO₂ ≤ 97%) |
Altitude correction: Multiply ratio by (barometric pressure / 760) if altitude > 1,000 m.
These categories allow consistent diagnosis across both ventilated and non-intubated patients, improving clinical and research communication.
How to Recognize ARDS in Practice
- History: recent severe systemic or pulmonary insult
- Clinical signs: tachypnea, dyspnea, cyanosis, and crackles
- Imaging: diffuse bilateral infiltrates (alveolar or interstitial)
- Oxygenation: worsening SpO₂ or PaO₂ despite oxygen therapy
- Exclusion of heart disease: echocardiography or point-of-care ultrasound
Early recognition is critical; ARDS can progress rapidly from moderate hypoxemia to severe respiratory failure.
Treatment and Clinical Management
Because ARDS results from inflammatory lung injury rather than infection alone, management is largely supportive and directed at stabilizing oxygenation while treating the initiating cause.
1. Treat the Underlying Cause
Address sepsis, aspiration pneumonia, or pancreatitis aggressively.
2. Optimize Oxygenation
- Begin with supplemental oxygen or HFNO.
- Escalate to mechanical ventilation if oxygenation remains inadequate.
- Use lung-protective strategies: low tidal volumes, adequate PEEP, and permissive hypercapnia.
3. Manage Fluids Carefully
Avoid excessive IV fluids once perfusion is restored to prevent worsening pulmonary edema.
4. Supportive & Adjunctive Measures
- Broad-spectrum antimicrobials when indicated
- Analgesia and sedation
- Nutritional support
- Consider advanced ventilation modes (e.g., APRV) in referral settings
Prognosis
Despite advances in care, mortality remains high, particularly for mechanically ventilated patients. Early detection, prompt management of the underlying cause, and timely referral to an ICU-equipped facility remain key to improving outcomes.
Conclusion
The 2025 ARDSVet Consensus Definitions represent a significant leap forward in recognizing and categorizing acute respiratory distress syndrome in dogs and cats. Standardized diagnostic criteria enable clearer communication, more consistent research, and ultimately better patient care. As veterinary critical care continues to evolve, early identification, advanced oxygenation strategies, and multidisciplinary teamwork remain the cornerstones of ARDS management.
