Just saw 2 ICU hyperNa cases, so here's a #medsky #nephsky🧵 on why...
🤨 Out: Solute-free H2O clearance
😎 In: Electrolyte-free H2O clearance
🫘 1st was recovering from AKI -->⬆️ filtered urea load as the BUN ⬇️
🥩 2nd was receiving very high protein tube feeds -->⬆️ filtered urea load with stable BUN
🤨 Out: Solute-free H2O clearance
😎 In: Electrolyte-free H2O clearance
🫘 1st was recovering from AKI -->⬆️ filtered urea load as the BUN ⬇️
🥩 2nd was receiving very high protein tube feeds -->⬆️ filtered urea load with stable BUN
Comments
This suggests that the urine was more concentrated than the blood, and therefore excess free water excretion was not the cause of hypernatremia.
👉But when the rate of urea filtration is high, it acts as an effective osmole in the renal tubule, pulling water into the urine.
🥇Therefore in cases of a urea diuresis, electrolyte-free water clearance beats the solute-free water clearance.
Also see https://bsky.app/profile/pulmcrit.bsky.social/post/3lb3eduu2fc2g