Overview
This lesson covers the diagnosis and management strategies for Acute Respiratory Distress Syndrome (ARDS), reviewing key diagnostic criteria, workup, and a wide range of evidence-based treatment approaches tailored for critically ill patients.
Diagnosis of ARDS
- ARDS is primarily diagnosed using the Berlin criteria: acute onset (<1 week), bilateral pulmonary infiltrates, exclusion of cardiogenic pulmonary edema, and PF ratio <300 with ≥5 cm H2O PEEP/CPAP.
- Initial evaluation includes clinical history and exam, focusing on deteriorating respiratory status and potential triggers (e.g., pneumonia, sepsis, shock).
- Common causes include pneumonia and sepsis, with other etiologies like trauma, inhalation injury, and pancreatitis also considered.
- Chest X-ray is key, identifying bilateral infiltrates and excluding heart failure if the heart and great vessel sizes are normal.
- CT scans help differentiate causes and assess the extent or source of infection, especially when diagnosis is unclear.
- Pulmonary artery occlusive pressure (<18 mmHg) or echocardiography/ultrasound can exclude cardiogenic edema.
- Laboratory workup includes ABG for PF ratio, lactic acid, infection screening, CBC, CRP, and procalcitonin.
- Bronchoscopy is rarely indicated, except for suspected alveolar hemorrhage.
- Pseudo-ARDS (e.g., atelectasis) can mimic ARDS but rapidly improves with adequate airway pressure.
Management Goals and General Strategies
- Management targets: reduce shunt fraction, increase oxygen delivery, decrease oxygen consumption, and prevent further lung injury.
- Treat the underlying cause as the primary intervention for ARDS resolution.
Fluid and Supportive Management
- Aim for euvolemia; consider diuretics or renal replacement therapies in fluid-overloaded or oliguric patients.
- Use corticosteroids selectively, guided by underlying etiology due to mixed evidence.
Ventilatory Support and Lung Protection
- Start with non-invasive support (high-flow nasal cannula, CPAP/BiPAP) for mild cases; proceed to early intubation for moderate/severe ARDS or instability.
- Lung-protective mechanical ventilation uses low tidal volumes (4–8 ml/kg ideal body weight, aiming for 6 ml/kg) and adequate PEEP (≥5 cm H2O).
- Increase PEEP as FiO2 requirement rises, noting risk of hypotension and decreased cardiac output at high levels.
- Monitor and maintain plateau pressures ≤30 cm H2O to minimize barotrauma.
- Allow permissive hypercapnia, maintaining pH >7.20–7.25; increase rate/volume only if pH <7.15.
- Prefer inspiratory-to-expiratory ratios keeping inspiratory time less than expiratory time.
Adjunctive Strategies and Escalation
- Optimize ventilator synchrony via adjustments, sedation (e.g., propofol and fentanyl), or neuromuscular blockade if necessary.
- Early prone positioning is recommended for PF ratio <150, and may benefit non-intubated patients as well.
- Consider APRV (Airway Pressure Release Ventilation) for refractory hypoxemia, monitoring for acidosis due to CO2 retention.
- Use neuromuscular blockade for ventilator synchrony, barotrauma prevention, and reduced metabolic demand.
- Inhaled vasodilators (nitric oxide, EPO) may be used to improve oxygenation and reduce right ventricular afterload.
- ECMO is considered for severe cases (PF ratio <150) when conventional strategies fail.
Additional Considerations
- Prioritize enteral nutrition for critically ill ARDS patients to maintain skin integrity and reduce VAP risk.
- Damage control strategies for refractory cases: temperature control (afebrile target), inotropes for cardiac output, higher hemoglobin threshold (8.0 g/dL), and drainage of pleural effusions.
- COVID-19 ARDS may present differently but general management principles remain applicable.
Recommendations / Advice
- Focus on early identification and tailored management of ARDS based on severity and patient comorbidities.
- Engage multidisciplinary teams, particularly respiratory therapists, for ventilator management and patient optimization.
- Regularly review and adjust strategies as patient status evolves.