There seems to be an association between the use of "normal" saline and acute kidney injury (when compared with other IV fluids).
Why would that be?
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We need to first understand 2 things:
💥What is the difference between saline and other "balanced" crystalloid IV fluids?
💥What is the evidence that saline is associated with kidney injury?
💥How is saline different from other "balanced" crystalloid IV fluids?
💡Saline has⬆️levels of Na/Cl
💡Bc of this difference in composition, when used in large volumes saline⬆️serum Cl levels and causes a hyperchloremic metabolic acidosis
bit.ly/358PJah
![](https://pbs.twimg.com/media/ENIISgWVAAAsBuY.png)
💥What is the evidence that saline is associated with renal injury?
There are several studies suggesting this association. Here's one 👇
bit.ly/2ZG8wbZ
![](https://pbs.twimg.com/media/ENIIS3BUEAUfmOD.jpg)
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Because there is significantly more chloride in saline than other IV fluids, let's zoom in and see how that might affect the kidney 👇
Infusing high chloride-containing fluids into dogs decreased renal perfusion and glomerular filtration rate (GFR).
bit.ly/36ei7cy
![](https://pbs.twimg.com/media/ENIITWxU4AQlnIT.png)
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💥Why would high serum chloride levels decrease renal blood flow and GFR?
The answer involves the macula densa.
To review:
💡Macula densa cells sense Na/Cl levels in the distal convoluted tubule (DCT)
💡In response to increased Na/Cl levels in the DCT the macula densa decreases renal blood flow and GFR by inducing renal afferent arteriole vasoconstriction
bit.ly/2Qdwzf7
![](https://pbs.twimg.com/media/ENIITwXUwAIkfBI.png)
Look how close the macula densa and renal afferent arteriole are to each other 👇
ncbi.nlm.nih.gov/pmc/articles/P…
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When exposed to high levels of Cl (and Na) the macula densa cells literally swell.
ncbi.nlm.nih.gov/pubmed/12060602
![](https://pbs.twimg.com/media/ENIIUcDVUAEq2We.png)
Along with swelling the macula densa cells release ATP, signalling nearby afferent arterioles to constrict,⬇️renal blood flow and GFR.
This process is called tubuloglomerular feedback, allowing the kidney to regulate its own perfusion
bit.ly/2ZGbzRs
![](https://pbs.twimg.com/media/ENIIUwTUUAU61TW.png)
ATP release from the macula densa cells is actually stimulated directly by Cl 👇
ncbi.nlm.nih.gov/pmc/articles/P…
![](https://pbs.twimg.com/media/ENIIVIVUUAI458y.png)
Let's summarize:
💡"Normal" saline has⬆️levels of Cl compared w/ other IV crystalloid fluids
💡Increased serum Cl levels⬇️renal blood flow and GFR
💡This occurs because of ATP release from macula densa cells, which causes renal afferent arteriolar vasoconstriction