Lab case 293 interpretation

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Question 1:

PH = 7.27 that is mild acidaemia

HCO3 = 16 mmol/L, this is low (<24), so we have metabolic acidosis.

Once we get metabolic acidosis then we need to calculate the anion gap and check for compensation using winter’s formula.

Anion gap = Na – (HCO3 +Cl ) = 140 – (16 + 116) = 8 So, we have normal anion gap metabolic acidosis.

Compensation (Winter’s formula), that is expected PCO2 = 1.5 x HCO3 + 8   (+/- 2), using this formula, the expected PCO2 = 30 – 34. So, we don’t have additional respiratory process.

According to that we have pure normal anion gap metabolic acidosis.

Other findings:

The most significant other abnormal finding is K level of 2.2, that is severe hypokalaemia (<2.5)

Cl = 116, that is hyperchloraemia.

Potassium level usually rise by 0.6 mmol for every 0.1 reduction in PH below 7.35. Accordingly, the real level of K in this case is even lower than 2.2 (Around 1.7 mmol/L).

Question 2:

We use the USED CARP mnemonic for the causes of NAGMA.

  • Ureteroenterostomies  (No previous surgical history)
  • Small bowel fistula (No previous surgical history)
  • Excess chloride ( This patient was not given any IV fluids)
  • Diarrhoea (Excluded from the history)
  • Carbonic anhydrase inhibitors / acetazolamide. (Excluded from the history)
  • RTA ( Possible)
  • Addisson’s disease (Doesn’t fit, usually those patients have high K and low Na levels)
  • Pancreatic fistula. (No previous surgical history).

The only thing that was not excluded was RTA. On further history taking, this patient was using large amount for Ibuprofen for her back pain and that was the cause for her gastritis.

RTA associated with ibuprofen has been described in the literature. The mechanism of ibuprofen-induced RTA is poorly understood. However,  it is thought to be due to inhibition of carbonic anhydrase enzyme.

 Question 3:

Treatment:

  • Treat underlying disorder or stop the offending agent. In this case, stop Ibuprofen.
  • NaHCO3 and K+ replacement.
  • Consider thiazide diuretics (some patients respond to it.  It  increases proximal HCO3 reabsorption).
  • Remember to replace Mg+ whenever we are replacing K+.