Everyone knows that if you give a liter of saline, all of it remains in the extracellular compartment.
But what if you give a patient just the salt from the saline and none of the water? How much does the solute contribute to the increase in the extracellular volume? How does 154 mmols of NaCl affect the size of the extracellular and intracellular compartments?
Assume the patient is a 70 kg lean young male with a serum osmolality of 280 mOsm/kgH2O. Ignore any renal losses during the process.
For full credit fill out the following:
Total body water: Size of the extracellular compartment: Size of the intracellular compartment:
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Step one calculate the total number of osmoles the patient has:
70 kg lean young male means 60% total body water or 42 liters 42 liters times 280 mOsm/Kg = 11,760 osmoles in the body
Giving 308 mosm of solute will increase that to 12,068. There is no additional water so dividing that by 42 liters gives us a new osmolality of 287 mOsm/Kg water.
Remember that even though the solute is trapped in the extracellular compartment, the osmolality is the same across all body compartments since water can flow from compartment to compartment.
Now we need to find out how much the extracellular compartment expands in osmoles.
Before the addition of solute the extracellular compartment should be one third of total body water, so 14 liters times osmoality of 280 is 3920 mOsmoles. Add 308 and then divide that by the new osmolality to give you the new volume:
That increased volume of course comes from the intracellular compartment, so it goes down by 0.7 liters. You can also get there by taking the original volume of 28 liters multiplying by 280 mOsm to get 7840 miliosmoles and divide that by the new osmolality of 287:
So the addition of 308 miliosmoles from the bag of saline will increase the extracellular compartment by 0.7 liters. Only 0.3 liters less than the increase you would get with a liter of 0.9 NS.
It’s all about the salt.
Total body water: 42 liters Size of the extracellular compartment: 14.7 liters Size of the intracellular compartment: 27.3 liters
So I checked in at DreamRCT and noticed that my DreamRCT is no longer in the top five.
I’m a big boy and can take this (very minor) form of rejection but I do want to plead my case for a moment. You can read the entire description of my DreamRCT here. One of the dirty little secrets of nephrology is the almost total lack of prospective data on hyponatremia. There are a number of RCTs with regards to tolvaptan, conivaptan and other approved, and soon to be approved, vaptans. But after those there is an evidence desert populated by only a few mirages made up of case reports and retrospective analysis. From this scant data we have built a comprehensive and detailed model of how sodium acts in the body and the importance of osmoregulation. But thats like theoretical physics without a supercollider. We need to test the model with real data.
Think about the fact that hyponatremia is the most common electrolyte disorder. We order metabolic profiles on every patient, every day, but when it comes to interpreting those results we might as well be reading hieroglyphics.
RCTs are difficult and expensive but there are particular areas where we should require them prior to treatment. One of these corners is when we treat people with no symptoms and we are effectively treating a number. High cholesterol, high blood pressure, and low sodiums are three such areas, however hypertension and hypercholesterolemia have both gone through the right of passage called a randomized controlled trial. I am confident that my patients with asymptomatic hypertension benefit from treatment. My patients with coronary disease and hypercholesterolemia will live longer and better with treatment with a high potency statin. On the other hand, patients with sodiums of 129 and no apparent symptoms are supposed to be at higher risk of falls, have a higher mortality from heart and liver failure. Does treating them reduce these risks?
¯_(ツ)_/¯
We can do better. Hyponatremia is the most common electrolyte disorder found in patients, we owe it to them to have real, prospective, data to answer these questions.
Go to UKidney to vote for my trial: No hyponatremia modification in asymptomatic hyponatremia. Thanks.
DreamRCT is a creative writing project for nephrologists. The assignment is to scour the landscape of nephrology knowledge for a corner that is dominated by dogma and retrospective evidence. Once the target is identified, the writer needs to summarize the gaps, and think up a creative way to shine science’s greatest flashlight on the subject, a randomized controlled trial.
We have recruited 16 people to submit DreamRCTs which were published today on MedPage Today. Thanks Ivan, Kristina and Elbert. It is a amazing collection of creativity; there are trials on kidney stones, electrolytes, dialysis, proteinuria and lupus. Please go check them out; read them and see which are great and which should be relegated to The Journal of Craptology.
After reading the DreamRCTs move on over to Jordan Weinstein’s excellent UKidney where it is time to channel your inner Mark Cuban and play Shark Tank with the DreamRCTs.
Which trial should be funded which shouldn’t. How much should each trial be awarded. You will get $100,000 to distribute among the trials. Think KickStarter meets NIH. You will not be alone in this endeavor. We have recruited an expert panel of clinical researchers to score the trials. At the conclusion of the contest we will look at how the experts spent their cash and how the crowd did. We will also award a small prize to the funder whose distribution best matches the expert panel.
DreamRCT only works if we get a critical mass of people to participate. Please check out the trials at MedPage Today and then go to UKidney to vote with your (completely virtual, don’t ask me for a refund) dollars. Announce the project at morning report, assign your fellows to vote and then submit discuss and submit your own DreamRCT, because in the end DreamRCT is not just a game but a shorthand expression for what we need to do to fix nephrology and heal our patients.
This year I worked with Saiyed Muddasser on an article looking at cold dialysate for cardio protection. Take a look at the summary and then go to the eJC site and make a comment.
One night that I was on call, I received an interesting patient from the ED.
The patient was confused but walked into the ER and was able to give at least a partial history. They did some initial chemistries and called me with the following results:
This is the kind of lab that grabs your attention.
With that glucose the first thought should be, “Is this DKA?”
Yes.
Beta-hydroxybutyrate: 6 mmol/L
I try to account for the anion gap. So I look at all the anions I measure and see how well they explain the gap. And if I can’t account for the majority of the gap I have difficulty sleeping. This patient’s gap was 51, 12 is normal which leaves 39 to account for. Only 6 can be accounted for with beta-hydroxybutyrate.
“Is there a lactic acidosis?”
Yes.
Lactate:16
That still leaves 17 mmol/L of unexplained anions.
Propylene glycol is normally due to the solvents used to dissolve IV drips. So usually we see problems in patients who have been in the ICU for awhile.
Propylene glycol is also found in antifreeze and hydraulic fluids.
The molecular weight is 76, so the 8.1 mg/dl represents only about 1 mmol/L, however it may explain the severe lactic acidosis and by stimulating the production of D-lactate it may explain even more of the gap.
Dialysis removes the parent compound and metabolites. Whether patients need to receive fomepizole is less clear. Kraut and Kurtz suggest fomepizole would be beneficial, while others feel less strongly.
Fomepizole not needed in PG toxicity. IMO, propofol, PG, & paracetamol (APAP) should replace phenformin in MUDPILES. https://t.co/B3PTX2cjOc
PBFluids has been quiet. Took awhile to just clear the cobwebs to get this post up.
One of the things that has kept me busy has been a project with a company called MedMastery. Franz Wiesbauer was a fan of my fluids book and reached out to me. We worked together to create a curriculum covering body water, diuretics, IV Fluids, sodium and potassium. The full course is about 1,000 slides. But the genius of MedMastery is how they edit and craft the course so it is broken up into an odd fifty 6-minute morsels. It is medical school for Generation Keurig.
MedMastery has opened up a few of the K-cups for promotion.
Art Levinson is the current Chairman of Apple. He was brought on to the board in 2000 during Job’s second act and was present for the introduction of the iPod, iTunes and iPhone.
Art Levinson is always introduced as the former CEO of Genentech but I didn’t know his story until I read the Herceptin story in Emperor of All Maladies. Turns out Levinson was trained by Nobel Michael Bishop of oncogene fame. In the late 80’s Levinson was leading a group pursuing treatment for breast cancer by doggedly tracking a gene called HER-2. Genentech’s executives turned away from cancer research after some high profile failures in the 80’s. This should have been the end of genentech’s role in HER-2 except for the leadership of Levinson. He dodged the bureaucracy, pursued resources and lead a small team to continue work on HER-2. The group produced Herceptin, one of the most important breakthroughs in chemotherapy in the molecular era in, a jaw-dropping, 3 years. Laureate
Reading that story I can see why Jobs would want him on the Apple board.
As we were gearing up for NephMadness Mealnie Hoenig mentioned that she loved working with the Nephmadness crew because they were “her people.” This resonated with me and has become my latest way of looking at the word. This particularly resonated with me when my college roommate introduced me to Public Broadcast Service.
Gene Kranz
There best song is “Go” which samples Gene Kranz dialog with his flight controllers during the Apollo 11 lunar lander landing. I love this because though I have heard the story of the Apollo mission a 100 times I had never thought of it from the perspective of the flight controllers.
This struck me as a great example of my people. While I never could imagine myself as Neil Armstrong, I could imagine me, and my ilk, being a flight controller in Houston. Which one would I be? flight SURGEON, of course.
Summary of the different flight controllers can be found here.
Transcript from the song:
Narrator (NASA Spokesman?) This is Apollo Control 102 hours into the flight of Apollo 11. It has grown quite quiet here at Mission Control A few moments ago Flight Director Gene Krantz requested that everyone sitdown and get prepared for the events that were coming and he closed with the remark “Good luck to all of you.” [Ed. not quite One small step for man; one giant leap for Mankind] 12 minutes now until ignition for powered descent. Everything still looking very good at this point Gene Krantz Okay all flight controllers, “Go” “No go” for powered descent.
CAPCOM we are go for powered descent [CAPCOM, capsule communicator, was an astronaut in Houston responsible for communicating with the mission astronauts. At the time of the landing it was Charlie Duke] We are off to a good start. Play it cool. Okay all flight controllers, I’m going around the horn RETRO? Go! FIDO? Go! GUIDANCE? Go! CONTROL? Go! Deltcom? Go! GNC? Go! EECOM? Go! SURGEON? Go!
Armstrong: Houston…ah…Tranquility base here. The Eagle has Landed.
Kranz: Okay keep the chatter down in this room. [The greatest moment in the history NASA and Kranz is focused on keeping his team on task]
CAPCOM: T1 standby for T1
Kranz: Stay or no Stay all flight controllers [Apparently it was possible to land on the moon but have something go wrong requiring an immediate return to orbit, so this was a check to see if they could proceed to the lunar surface mission]
