I have been doing a monthly fluid and electrolyte conference for the residents at St. John. Today we did a case of hypernatremia initially due to hypercalcemia and then due to nephrogenic diabetes insipidus.
Dysnatremia chapters (chapters 6-9) of Fluids
Chapter 9: Polyuria/Polydipsia
Things have been coming in pairs: electrolyte free water and hypernatremia
First we had the highest creatinine followed by the lowest creatinine.
Internal Medicine Board Review: Fluids, Electrolytes and Acid Base
The chief resident at Providence asked me to do a board review class for the third-years. They have small sessions weekly (?) in the physician lounge. This afternoon we went over fluids, electrolytes and acid-base. We did the first 14 questions. Seems like it went pretty well.
Lecture at Providence Hospital on Electrolytes
I am trying to do a monthly lecture for the Providence internal medicine residents on electrolytes. I gave my second one last Friday. It was an interesting case we had of hypernatremia on the consult service last summer.
I did this lecture in Keynote and I am blown away by how good it presents through SlideShare. Really impressive.
iPhone Medical Applications
I have four medical applications on my iPhone, of which I use two. Here is a quick review.
To show how the iPhone equipped physician approaches clinical problems I will use the DB’s Medical Rants most recent acid-base problem. He presents a case with the following information:
49-year-old man, previously in good health, presents after a few weeks of progressive weakness and dizziness. He admits to polyuria. Your job is to extensively discuss his lab tests.
The first step in my mind is to fully interpret the ABG. To do this we will use the application ABG.
ABG
This simply named program is an ABG calculator that runs through the standard algorithms for detecting multiple primary acid-base abnormalities. Can’t remember Winter’s Formula. As long as you don’t have boards coming up you can just plug’n chug and turn DB’s ABG into the following:
This does two of the calculations that DB describes at length:
- Winter’s formula (16 * 1.5 + 8 ±2) shows that the predicted pCO2 is 30-34. The patient’s CO2 is 33 so the patient has isolated and appropriately compensated pCO2 of 33. ABG displays this information in the second line when it describes the acid-base disorder as “Compensated metabolic acidosis.” It does not describe a second primary condition such as respiratory acidosis or alkalosis.
- Gap-Gap or delat-delta. The patient has a dramatically elevated anion gap at 27 (15 over the upper limit of normal of 12) but his bicarb of 16 is only 8 below normal. The difference between the delta gap and the delta anion gap is 7 (15-8) when this is added to the normal bicarbonate you get 31; so the patient had a pre-existing metabolic alkalosis with a bicarbonate of 31. ABG displays this information as the corrected bicarbonate.
The next step is adjusting his sodium for the hyperglycemia. To do this we will use Mediquations though Medical Calc works just as well.
Though DB did not explore free water defecits in his discussion of the case this is a clinically relevent point. You can use Mediquation to calculate the water deficit.
Polyuria, polydipsia
The set up
urine lytes:
Step one
174-145 / 145 = 0.2 (the sodium is 20% above 145)
I used 60% for estimated total body water. The patient looks like a young boy. Rose suggests lowering the estimated % body water by 10% so 50% would be okay also. In the elderly and obese this number can go below 50%.
Step two
12/(174-12) = 0.08 x total body water = 2.0 liters or just over 80 mL/hour
Step three
The urine has 39% electrolyte content of plasma, another way of thinking about this is that 39% of the urine volume is isotonic and the remainder (61%) is pure water. The 61% is what we are interested in; multiply the urne output by 61% this is the volume of water we need to give the patient to account for his ongoing renal losses.