Understanding that serum Na abnormalities almost always imply a problem with water is something that has been hammered into us since pre-clinical med school years. And whenever a nephrology attending asks you what is going on with a patient with hypernatremia, you can always answer “Not enough water!” and be 100% correct.
However, when it comes to the free water deficit, many renal fellows still pull out their smartphone apps and med students still pull out their pocket notecards. This video will hopefully demystify this equation, reinforce your understanding of water repletion, and provide a clinical shortcut for you to quickly estimate a patient’s water deficit within seconds. Hopefully you find it helpful!