Let’s start with some initial basic labs:
Would you describe this patient’s arterial blood pH as acidemic or alkalemic?
Alkalemic
The normal range for arterial blood pH is 7.35 – 7.45. A pH greater than 7.45 would be alkalemic. Try again!
Acidemic
That’s right! The normal range for arterial blood pH is 7.35 – 7.45. This pH less than 7.35 is acidemic.
What is the primary process that led to the pH change?
Respiratory
A respiratory acidosis would be the consequence of a high PCO2. In this case the PCO2 is lower than normal (40 mmHg), meaning it is not the primary process driving the acidemia. Try again!
Metabolic
That’s correct! The bicarbonate level is lower than normal (24 mEq/L), identifying a metabolic acidosis.
Is there appropriate compensation?
Yes
Correct! Based on Winter’s Formula, the expected PCO2 is 18-22 mmHg.
No
Try again! We should use Winter’s Formula here to determine what the PCO2 should be…
Is there an Anion Gap?
Yes
Correct! The anion gap is 19 (133 – [106 + 8]).
No
Try again! Remember, the anion gap is [Na] – ([Cl] + [CO2]).
Is there another process going on?
Yes
Yes! The anion gap is 19 and the bicarbonate is 8. Therefore the delta gap (change in Anion Gap / change in bicarbonate) is much less than 1.0. There is a concomitant non-anion gap metabolic acidosis.
No
Try again! Remember to look at the delta gap, or the change in (Anion Gap / change in bicarbonate).
Let’s also take a look at the urinalysis:
At this point, what is at the top of your differential diagnosis (pick 3)?
Diabetic ketoacidosis
Lactic acidosis
Starvation ketoacidosis
Pyelonephritis
“Pre-renal” acute kidney injury
Toxic alcohol ingestion
Pregnancy
Renal tubular acidosis
Alcoholic ketoacidosis
Pyroglutamic metabolic acidosis
Choose the highest yield diagnostic tests to perform next (more than one may be correct)!
Urine β-HCG
Always a good choice in a woman presenting with nausea. This patient’s β-HCG is negative.
Methanol and ethylene glycol levels
There might be some higher yield tests here…pick again!
Serum osmolality
Great! In patient with the acid-base disorders above, it’s a good idea to look for an osmolal gap (actual osm – calculated osm > 15). The serum osmolality here is 285 mosm/kg. Calculate this patient’s osmolality here.
Urine culture
Based on this patient’s urinalysis, this test is not the best choice.
Serum β-hydroxybutyrate
Good choice! This is an important test in a patient with an anion gap metabolic acidosis and a history of diabetes. This patient’s serum β-hydroxybutyrate is elevated at 6.07 mmol/L.
Salicylate and 5-oxoproline levels
These are reasonable tests to consider, though this patient does not have the typical signs of salicylate toxicity (look for a respiratory alkalosis). Risk factors for a 5-oxoproloine (or pyroglutamic) metabolic acidosis include elderly women, sepsis, penicillin use, liver impairment (gluthiaione depletion), decreased kidney clearance of 5-oxoproline, pregnancy acetaminophen use, and malnutrition.
Time to start treatment! What would you like to give this patient? (Choose one)
IV insulin and IV dextrose
Excellent choice! This patient should improve with IV insulin, and she should also receive IV dextrose to maintain serum glucose levels
IV insulin alone
While IV insulin is a good choice, this patient is at risk of hypoglycemia with insulin alone…Try again!
IV sodium bicarbonate
While this may help raise her bicarbonate and improve her pH, this will not treat the underlying problem…Try again!
Fomepizole
This might be a good choice for certain toxic alcohol ingestions, which seem unlikely here…Try again!
What is your leading diagnosis?
Diabetic ketoacidosis
Lactic acidosis
Starvation ketoacidosis
Pyelonephritis
“Pre-renal” acute kidney injury
Toxic alcohol ingestion
Pregnancy
Renal tubular acidosis
Alcoholic ketoacidosis
Pyroglutamic metabolic acidosis
Click here to close out this case!
Case 51 Index
Case 51 Introduction
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