Shunting (right to left shunt, PE) (Elevated A-a gradient)
Hypoventilation (normal A-a gradient)
Altitude, low inspired FiO2 (normal A-a gradient)
Illness script for PCP Pneumonia: Usually HIV +, chronic non-productive cough (due to high viscosity of sputum), often normal lung exam and chest film, may see ground glass opacities in the bilateral lower lung fields, hypoxia worse with exertion
Start steroids in addition to Bactrim for FiO2 < 70 or A-a gradient > 35, treatment of PCP fungal death causes a profound inflammatory reaction which is why steroids decrease mortality, treatment course is for 21 days
Prophylaxis for PCP in HIV for CD4 < 200, 95% effective in preventing PCP
