Question 20.2

Last updated 25/07/2019 - 23:46
 Topic: Acid-Base Disorders
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A 23-year-old female was found unconscious at home and subsequently admitted to the ICU. At admission she had the following results:

Test

Value

Normal Adult Range

Sodium*

122 mmol/L

135 – 145

Potassium

3.8 mmol/L

3.2 – 4.5

Chloride*

91 mmol/L

100 – 110

Bicarbonate*

14 mmol/L

24 – 32

Glucose

4.0 mmol/L

3.0 – 6.0

Urea

6.8 mmol/L

2.7 – 8.0

Creatinine*

122 μmol/L

65 – 115

Measured Osmolality*

295 mosmol/Kg

275 – 290

Give the likely diagnosis and the rationale for your answer.

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College Answer

Methanol (or some other alcohol) toxicity.

High anion gap acidosis, increased osmolar gap.

Discussion

Let us dissect these results systematically.

  1. The A-a gradient cannot be calculated.
  2. There is no pH supplied
  3. The PaCO2 is not given.
  4. The SBE is not available, but the bicarbonate is 14mmol/L, suggesting a metabolic acidosis.
  5. The respiratory compensation cannot be assessed.
  6. The anion gap is raised:
    (122) - (91  + 14) = 17, or 20.8 when calculated with potassium
    The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (17 - 12) / (24 - 14) = 0.5
    This suggests that there is a mixed high anion gap and normal anion gap metabolic acidosis here.
     
  7. The osmolar gap is increased: 295 - (2 × 122 + 6.8 + 4.0) = 40.2

This young lady is suffering from a high anion gap metabolic acidosis with a high osmolar gap. Clearly, she swilled some sort of osmoles at home, of which only some are responsible for the acidosis. What sort of poisoning is this? Salicylate toxicity and ketoacidosis do not tend to cause such a high osmolar gap, nor does lactic acidosis (until you are nearly dead). Toxic alcohols are the answer implied by the young age of the victim, which suggests a certain sort of ageist cynicism among the examiners.

References

Kraut, Jeffrey A., and Ira Kurtz. "Toxic alcohol ingestions: clinical features, diagnosis, and management." Clinical Journal of the American Society of Nephrology 3.1 (2008): 208-225.

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