HYPOXEMIA

Alveolar-Arterial Gradient = P_AO_2 - P_aO_2 P_AO_2 = F_IO_2 (P_B - P_H2O) - (P_aCO_2 / 0.8) In Calgary, P_B = 660mmHg, Sea level P_B = 760mmHg Hypoxemia → Low PO_2, Low O_2, Cyanosis High AA Gradient Right-to-Left Shunt Parenchymal Severe Pneumonia Atelectasis Intracardiac Ventricular Septal Defect Atrial Septal Defect Ventilation/Perfusion Mismatch Airway Disease (Asthma, COPD) Vascular (PE*) Parenchymal Disease (+/- Diffusion Defect) Congestive Heart Failure Diffusion Limitation Interstitial lung disease Pulmonary Arterial Hypertension Pulmonary Arteriovenous Malformation Normal AA Gradient Low Inspired PO_2 High Altitude Hypoventilation (Increased PCO_2) Central Drugs* Coma Hypothyroidism Obesity Hypoventilation Syndrome Peripheral Neuromuscular Weakness Pleural Abnormalities Chest Wall Abnormalities * Denotes acutely life-threatening causes