The integrity of the normal endothelial barrier is responsible for two of the three major safety factors preventing pulmonary edema. This is why edema due to increased pressure is usually not as severe as edema due to increased permeability. Management ought to follow sound physiologic principles. These principles are to lower microvascular hydrostatic pressure and to provide adequate supportive therapy. Positive end-expiratory pressure may improve arterial oxygen transport, but there is no evidence that it improves the balance of pulmonary fluid in edema. Raising the microvascular protein osmotic pressure may be beneficial in edema due to increased pressure but has no demonstrated rationale in edema due to increased permeability.