Lab case 413 interpretation

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Question 1:

PH = 7.13, that is moderate acidaemia.

HCO3 = 9.4 mmol/L, Accordingly, it is metabolic acidosis.

Next, we need to calculate the respiratory compensation and the anion gap.

Respiratory compensation is calculated to exclude the presence of additional respiratory process. For that, we use Winter’s Formula. That is:

Expected CO2 = 1.5 x HCO3 + 8 (+/- 2). = 22.1 (Acceptable range between 20.1 to 24.1). This patients pCO2 is slightly higher than the acceptable range ( 26 mmHg), that means she has additional mild respiratory acidosis.

We calculate the Anion Gap to know which type of metabolic acidosis this patient has.

Anion Gap (AG) is calculated as: AG = Na – (Cl + HCO3) = 24.6. Accordingly this patient has High Anion Gap Metabolic Acidosis (HAGMA) as normal AG is 12.

Since we have HAGMA, then we need to calculate Delta Ratio to exclude the presence of additional metabolic process.

We calculate Delta ratio using the following formula:

Delta Ratio = (AG – 12) / (24 – HCO3) = 0.86. This means that this patient’s metabolic abnormality is purely HAGMA. (Delta Ratio between 0.8 and 2 = Pure HAGMA).

So far we concluded that this patient has HAGMA with mild respiratory acidosis.

Now we will look for other abnormalities that will help us narrow down the differential diagnosis.

K = 3.3, that is very mild hypokalaemia. However, K level is usually affected by PH level. To correct that we calculate the correct K. K level usually increase by 0.6 for every 0.1 PH below 7.4. Accordingly, Corrected K should be: 3.3 – (0.23 x 0.6/0.1) = 1.92 mmol.L. This is severe hypokalaemia.

The most obvious abnormality is Ketone of 8 mmol/L. (Accepted normal level is 0.4 mmol/L).

Next we look at the possible causes, for the causes of HAGMA we use the mnemonic CAT MUDPILES:

  • C = cyanide, carbon monoxide
  • A = alcoholic ketoacidosis and starvation Ketoacidosis.
  • T = toluene
  • M = methanol, metformin
  • U = uraemia
  • D = diabetic ketoacidosis
  • P = phenformin, pyroglutamic acid, paraldehyde, propylene glycol, paracetamol
  • I = iron, isoniazid
  • L = lactate
  • E = ethanol, ethylene glycol
  • S = salicylates

Looking at the causes above, alcoholic ketoacidosis, starvation ketoacidosis and diabetic ketoacidosis are the potential causes.

Alcohol level was normal, we left with startvation and diabetic Ketoacidosis. Although, the sugar level was normal, this patient has normal functioning kidneys,,, that she might have normoglycemic diabetic ketoacidosis.

Question 2:

Initially this patient was treated as starvation ketoacidosis as sugar level was not high and she doesn’t have non-gestational diabetes. She was started on Dextrose infusion with KCl infusion. Repeat blood gases after one hour didn’t show any improvement.

Then, the patient was started on Insulin that led to dramatic improvement of the ketones level and the acidosis.

This patient was insulin deficient.

Gestation diabetes is a disease of insulin deficiency then when the patient gain weight during pregnancy insulin resistance develops leading to gestational diabetes.