Snapshot A 46-year-old woman is admitted to the ICU with severe pancreatitis. During the first 24 hours of admission, she develops severe hypoxemia that requires ventilatory support with high concentrations of inspired oxygen develop. On exam the patient has rhonchi and crackles bilaterally. An arterial blood gas collected at 60% FiO2 reveals pH 7.42, PCO2 35 mmHg, and PO2 108 mmHg. Introduction ARDS is a form of hypoxemic respiratory failure due to inflammatory injury to alveolar capillary barrier Etiology acute endothelial damage resulting from aspiration infection / sepsis pancreatitis multiple blood transfusions lung injury major trauma / burns near-drowning drug overdose Histology ARDS is represented by three phases Phase Timeline Exudative Initially Hyaline membrane comprised of fibrin forms Proliferative 3 days Alveolar exudate resolves/organizes Fibrotic 3-4 weeks Alveolar ducts and spaces undergo fibrosis Presentation Symptoms can manifest within 1 week of known clinical insult dyspnea / shortness of breath fever Physical exam tachypnea / intercostal retractions bilateral rales/crackles and rhonchi mottled, cyanotic skin Evaluation Timing within 1 week of clinical insult or new/worsening symptoms Chest imaging diffuse bilateral opacities not explained by effusions, lobar/lung collapse, or nodules Origin of edema not fully explained by cardiac failure or fluid overload rule out cardiogenic pulmonary edema via objective factors (e.g., BNP, echocardiogram) explore other etiologies of ARDS via bronchoalveolar lavage or flexible bronchoscopy if clinical history is inadequate Severity of hypoxemia mild: PaO2 / FiO2 ratio 200 to 300 mm Hg with peak end-expiratory pressure (PEEP) or continuous positive airway pressure (CPAP) > 5 cm H2O moderate: PaO2 / FiO2 ratio 100 to 200 mm Hg with PEEP > 5 cm H2O severe: PaO2 / FiO2 ratio less than 100 mm Hg with PEEP > 5 cm H2O Treatment Non-operative treat the underlying pathology/disease conservative fluid management with diuresis ensure adequate nutrition, ideally enteral stress ulcer and DVT prophylaxis prevention and management of nosocomial infections Operative/Interventional mechanical ventilation low tidal volume: goal of 4-6 cc/kg ideal body weight to maintain plateau pressure of <30 cm H2O high plateau pressure can cause volutrauma on alveoli oxygenation: goal of PaO2 55-80 mm Hg or SaO2 88-95% can be attained by adjusting peak end-expiratory pressure (PEEP) pH goal of 7.3 to 7.45 inspiratory:expiratory ratio goal of 1:1 to 1:3 permissive hypercapnea high PEEP Prognosis, Prevention, and Complications Prognosis high mortality rate (50% overall) is associated with ARDS even in setting of ICU Prevention closely monitor PEEP in patients at-risk of ARDS serial X-rays in concerning patients can assist in early identification and intervention Complications pneumothorax secondary to ventilator with high PEEP