To repeat the problem:
26-year-old man comes in for flank pain. He has a history of renal stones. It is August in Alabama, he has been working outside. He does state that he has been drinking and urinating.
| Na | 139 | Cl | 92 | BUN | 28 | glu | 128 |
| K | 4.5 | CO2 | 22 | creat | 2.5 | Ca++ | 10.6 |
These lab tests led to his admission. What can you glean from these labs? Postulate on the cause of these numbers.
The comments were spot on – increased anion gap acidosis (gap 25) and metabolic alkalosis (delta gap of approximately 13 with a normal bicarb)
The patient was markedly volume contracted. We explained his anion gap from his phosphate level of 9.6. After volume expansion his phosphate returned to normal, as did his increased gap. His calcium also returned to normal.
The resident did not get an ABG; I agree that it would have added some information, but in this situation I believe we can understand what happened without it.
Teaching points:
1. Always look at the anion gap.
2. When the patient has an increased anion gap, estimate the delta gap.
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Good case.
Well, I will make another of my broken record pleas for a blood gas -this case is an excellent example of how much more it adds to our understanding of physiology, something that will be valuable in future cases (where are all the"we have to have students take one million hours of basic sciences to have a firm grasp of chemistry" people when the cases actually occur to push for more information?). I doubt our residents would have gotten an ABG – this shows that our interests in the actual biochemistry and physiology of disease isn't all it's cracked up to be. I'm sure Dr. Centor would agree that the actual acid base numbers in cases like this would not only enhance our understanding, they might occasionally change our thinking.
Also kudos for saying the patient is volume contracted and not dehydrated- most house officers and attendings today would mistakenly say dehydrated – another error being perpetuated that illustrates a lack of understanding about basic physiology and chemistry
One of the first things I do when I admit a patient is to evaluate the anion gap and calculate the delta gap is one is present. I've saved many lives doing so. It is a basic responsibility of internists.
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