Describe and interpret this blood gas:
History: 35-year-old woman presenting with acute dyspnoea. She has been taking an over-the-counter analgesic for a sore throat.
|pH 7.17||Na 136 mmol/L|
|pCO2 20 mmHg||K 1.7 mmol/L|
|HCO3 7 mmol/L||Cl 114 mmol/L|
|Lactate 1.1 mmol/L||Glucose 6.2 mmol/L|
What is the pH?
7.17 = severe acidaemia
What is the primary process?
HCO3 7 = primary metabolic acidosis
Is there compensation?
Expected pCO2 = 1.5 x HCO3 + 8 ± 2
= 1.5 x 7 + 8 ± 2
= 16.5 – 20.5
Measured pCO2 is 20, therefore there is maximal respiratory compensation.
Are there other clues to diagnosis?
Anion gap = Na – (Cl + HCO3)
= 136 – (114 + 7)
Therefore there is a normal anion gap.
Potassium is severely low. Chloride is elevated. Sodium, lactate and glucose are within the normal range.
Description: This VBG demonstrates a severe, non-anion gap metabolic acidosis with full respiratory compensation. There is profound hypokalaemia and elevated chloride. Sodium, lactate and glucose are within normal limits.
Interpretation: In this clinical setting, this VBG would be consistent with a renal tubular acidosis with hypokalaemia and hyperchloraemia. Such a picture could be seen with misuse of ibuprofen (OTC analgesic), or solvent abuse (toluene). Autoimmune conditions causing RTA such as Sjogren’s syndrome, renal abnormalities and hypercalciuric conditions should also be considered. Diarrhoea and adrenal insufficiency are possible differentials. Management is with potassium replacement +/- bicarbonate replacement and removal or control of the underlying cause.
Additional information: History of polysubstance misuse and chronic diarrhoea. VBG normalised over 24 hours with potassium and bicarbonate replacement.