Why does the level of carbon dioxide decrease when a child becomes dehydrated? — CARLA HIGBEE, FNP-C, Long Beach, Calif.

Dehydration can have many causes. The most common cause in infants and children is vomiting and/or diarrhea. As fluid volume is depleted, electrolyte concentration must be maintained in the intracellular fluid. Hydrogen (H+) ion regulation is necessary for acid/base balance. Dehydration most often results in metabolic acidosis. Initially, this is uncompensated, and the increasing H+ ion concentration stimulates respiratory compensation. The buffering effect of bicarbonate plus H+ leads to formation of water and carbon dioxide. The carbon dioxide is blown off at a high respiratory rate, and plasma Pco2 decreases (Ganong WF. Review of Medical Physiology. Stamford, Conn.: Lange Basic Science; 2003: 671-673). — Julee B. Waldrop, DNP (145-2)

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