Saturday, February 16, 2019

Water balance, respiration and ventilator

Q: Water via oxidation in the human body is? (select one)

A) fluid gain
B) fluid loss

Answer: A

Water generated via oxidation of carbohydrates and fatty acid in the body is a gain of about 300 mL. But this loss is balanced via the respiratory tract where water and CO2 are eliminated in parallel because the partial pressures of water vapor and CO2 are almost equal in alveolar air. 

This concept is important for understanding as this physiologic process get disrupted in a patient who are tachypenic (more loss) or on a ventilator, inspiring humidified air which decreases alveolar water losses.




Shafiee MA, Bohn D, Hoorn EJ, Halperin ML. How to select optimal maintenance intravenous fluid therapy. QJM 2003; 96:601.

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