Which one of the following is most likely to result in contraction alkalosis?
The term "contraction alkalosis" refers to the development of metabolic alkalosis (excess plasma HCO3-) when there is a loss of extracellular fluid volume (hypovolemia). Hypovolemia evokes numerous homeostatic reflexes that act to normalize extracellular fluid volume, including stimulation of the renin-angiotensin-aldosterone system. In the kidney, elevated levels of angiotensin II and aldosterone increase Na reabsorption through processes that are ultimately coupled to hydrogen secretion. Consequently, volume regulation results in a net increase in plasma HCO3-. Correction is obtained when the lost volume is replenished through intake of water and sodium. Loop diuretics such as furosemide act primarily on the thick segment of the medullary and coical ascending limbs of Henle's loop. They inhibit the coupled transpo of Na+ and Cl- that results in the production of large volumes of relatively iso osmotic urine. Excessive use of these drugs can result in hypovolemia and contraction alkalosis. Antacid and infant formula can result in metabolic alkalosis but not as a result of hypovolemia. In patients with renal insufficiency, antacids containing calcium carbonate can increase the plasma HCO3- concentration. Infant formulas that contain sodium but very little chloride enhance Na+ reabsorption in the renal tubule and, like volume contraction, this results in an increase in urinary H+ secretion. Administration of laxatives or acetazolamide promotes metabolic acidosis. Laxatives result in the loss of intestinal fluids that are relatively alkaline and contain large amounts of HCO3-. Acetazolamide inhibits the enzyme carbonic anhydrase. As a result, acetazolamide reduces the reabsorption of HCO3- in the renal tubule. Acetazolamide is often used in combination with loop diuretics to correct the alkalosis caused by these compounds. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 35. Gas Transpo & pH. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds),Ganong's Review of Medical Physiology, 24e.
Laxatives
Infant formula
Loop diuretics
Acetazolamide