Hypoxia can lead to redistribution of systemic blood and abrupt increases in pulmonary blood volume. Furosemide and chlorothiazide not only promote diuresis and dehydration, but also increase renal blood flow and reduce left ventricular filling pressure. Thus, blood in the lungs is transported to the periphery, improving pulmonary congestion. In addition, oral acetazolamide can play a significant role in the treatment of HAPE because it can increase urine output in patients with HAPE or fluid retention. Acetazolamide is a carbonic anhydrase inhibitor that inhibits carbonic anhydrase activity in the brain, kidney, and blood. In the kidney, acetazolamide reduces the formation of hydrogen and bicarbonate ions and Pulmonary Medicine 5 inhibits sodium bicarbonate reabsorption to increase urine output and, thus, reduce sodium and water retention. In the brain, acetazolamide inhibits brain choroid plexus carbonic anhydrase activity to reduce cerebrospinal fluid production rate and hence reduce intracranial pressure.