Case of the Month

Case of the Month #5, Answer

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Our winner is the illustrious ablumenberg!

For the initial presentation, see here.

In brief, we have a gorilla of an acid-base question with pertinent history including a history of diabetes and alcohol abuse. This one’s a little long, so put on your focus hat.

VBG: pH 7.3, PO2 102, PCO2 30, HCO3 14, lactate 3

BMP:  Na 145, K 5.2, Cl 103, HCO3 15, BUN 10, Cr 0.5, gluc 301

Serum Osm: 298

The correct interpretation is as follows

1. pH 7.3 = acidosis

2. HCO3 low at 14 with PCO2 at 30 = metabolic acidosis with respiratory compensation.

3. Per all three rules below, the metabolic acidosis is appropriately compensated with respiratory alkalosis

 1. Winter’s formula: PCO2 = 1.5 (HCO3) + 8 +/- 2 = 30.5 +/- 2

2. Rule of 15: PCO2 = HCO3 +15 = 30

3. Rule that the PCO2 in compensated metabolic acidosis should be the last 2 digits of the pH. Hence pH 7.30 and PCO2 30. 

4.To narrow our differential, let’s calculate the Anion Gap.

AG = Na – (Cl-HCO3). Here, it’s 27 with normal being less than 12.

5. The differential for anion gap metabolic acidosis is long.

Methanol, Metformin

Uremia

Diabetic (or any other
Ketoacidosis)

Paraldehyde, Phenformin,
Propylene

Iron, Isoniazid

Lactate

Ethylene Glycol

Salicylates, Sulfur
(inorganic)

Theopylline, Toluene

Cyanide, Carbon Monoxide 

6.  What about the osmolar gap?

OG = Serum Osm – 2*Na + glucose/18 + BUN/2.8 + ETOH/4.6  Here it’s 32 (nml is -7ish to 10ish, depending on what you read). Classically from toxic alcohols, an osmolar gap can also be seen in DKA, alcoholic ketoacidosis, lactic acidosis, renal failure, shock.

7. As we are edge-of-our seats curious about a potential concomitant  acid/base process going on let’s check out the Delta/Delta… Here we go!

The concept
The basic concept is that, in a metabolic acidosis, for every extra “1” unit of acid, you should see a drop in “1” unit of bicarb.  As a normal bicarb is 24 and a normal AG is 12, we get the following formulas, both of which are mathematically equivalent.
The formulas

1. (AG-12)/(24-HCO3). If the value is < 1, you have more bicarb than you should, implying that you have a concomitant metabolic alkalosis. If the value is >2, you have LESS HCO3 than you should and have a concomitant non-gap metabolic acidosis.

– Here it equals 1.7, which is borderline between a pure metabolic acidosis and a concomitant metabolic alkalosis.

2. Corrected HCO3 = measured HCO3 + (anion gap – 12)

If Corrected HCO3 < 24, then a concomitant non-anion gap exists

If Corrected HCO3 > 24 then a concomitant metabolic alkalosis exists.

-Here, Corr HCO3 = 30.

8. So his actual acid base disorder is? 

An anion gap metabolic acidosis with a moderate osmolar gap and a mild concomittant metabolic alkalosis.

9. So his diagnosis is? 

Like in many things in life, the joy  is in the journey, not the destination…aka it can’t really be narrowed down to one diagnosis. Ha! Top on my differential was alcoholic ketoacidosis, dka, or toxic alcohols with a concomitant contraction alkalosis.

10. What are you going to do about it?

Along with a full work-up, I would definitely give thiamine, glucose, IV fluids, insulin, and may start fomepizole.

 

 

By Dr. Andrew Grock with special thanks to Dr. Rich Sinert!

 

 

References

Dr. Sinert

Golfrank’s Toxicologic Emergencies

Harrison’s

uptodate.com

 

 

 

The views expressed on this blog are the author's own and do not reflect the views of their employer. Please read our full disclaimer here. Any references to clinical cases refer to patients treated at a virtual hospital, Janus General Hospital.
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andygrock

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1 comment for “Case of the Month #5, Answer”

  1. Raul
    November 14, 2014 at 4:52 pm

    Since you were discussing compensation and how to calculate it I thought I would send out this link (http://www.anaesthesiamcq.com/AcidBaseBook/ab9_3.php) which has a bunch of rules on the subject. Hope it helps!

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