Snapshot A 46-year-old woman is admitted to the ICU with severe pancreatitis. During the first 24 hours of admission, 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 Defined asacute diffuse, inflammatory lung injury leading to increased vascular permeability, increased lung weight and loss of aerated lung tissue hyperactivation of coagulation and/or inflammation damages both type I and II pneumocytes ↓ type II pneumocytes results in ↓ surfactant production ↓ surfactant production results in low lung compliance and subsequent atelectasis repair often results in interstitial fibrosis Causes infection pneumonia sepsis typically gram-negative sepsis aspiration acute pancreatitis trauma with shock amniotic fluid embolism (rare) uremia Presentation Symptoms dyspnea Physical exam tachypnea bilateral rales and decreased breath sounds Evaluation Arterial blood gas severe hypoxemia on pulse oximetry and ABG may not be responsive to 100% O2 atelectasis results in intrapulmonary shunting Radiology diffuse, bilateral alveolar infiltrates on CXR ground glass opacities and consolidations on chest CT often with dependent lung predominence Histology diffuse alveolar damage protein-rich leakage (exudate) forming an intra-alveolar hyaline membrane Severity graded on PaO2 / FiO2 ratio and required PEEP (see below) Treatment Respiratory support & treat underlying cause Mechanical ventilation with low tidal volume (4-6 mL/kg ideal body weight) High FiO2 PEEP (positive end-expiratory pressure) prevents airway collapse at end-expiration recruits collapsed alveoli increases FRC and decreases shunting improves oxygenation