Blog | Monday, May 21, 2012

Dangerous electrolytes, part 2


Reviewing the patient thus far:
The patient, a 40-something year old woman, has a long history of alcohol abuse. Recently she has had minimal oral intake with much vomiting. BP 100/60, pulse 120
120, 67, 32, 99
1.9, 21, 0.7, 8.9

pH=7.6
pCO2=26
pO2=100
HCO3=21

Your job is to identify all the abnormalities in this panel, and suggest the sequence of events most likely to result in these numbers. What other information do you want?

Three respondents did a great job describing the acid-base disorder.
1) The anion gap equals 32, thereby by definition the patient has an increased anion gap metabolic acidosis.
2) The delta gap equals 21, thereby the revealed bicarbonate is 42, supporting an underlying metabolic alkalosis.
3) These two metabolic problems fit the story perfectly. The patient had both positive ketones and a mildly elevated lactic acid level. We expected a metabolic alkalosis with persistent vomiting. The hypokalemia fits the clinical picture perfectly.
4) Using the Winter's equation, one also finds a respiratory alkalosis. Clinically, we felt that the respiratory alkalosis resulted from the hypotension and alcohol withdrawal.
5) All the acid-base abnormalities resolved over the next few days.

Now the electrolytes are really the point of this presentation. The patient has hyponatremia, likely secondary to volume contraction. Her serum osm = 259 with urine osm = 411.

She had hypokalemia secondary to vomiting. We confirmed that vomiting was the cause with urine electrolytes. Urine Na less than 10, Cl less than 10, K = 45

We also checked Mg, normal at 2.5 and PO4, which was very low at 0.7.

What are the risks of the severe hypophosphatemia, and how would that abnormality impact your treatment plan? Also speculate why her initial PO4 was so low.

db is the nickname for Robert M. Centor, MD, FACP. db stands both for Dr. Bob and da boss. He is an academic general internist at the University of Alabama School of Medicine, and is the Associate Dean for the Huntsville Regional Medical Campus of UASOM. He also serves as a frequent ward attending at the Birmingham VA Hospital. This post originally appeared at his blog, db's Medical Rants.