Describe and interpret this venous blood gas:
History: 24-year-old man transferred from another institution post-cardiac arrest secondary to torsade de pointes.
|pH 7.47||Na 129 mmol/L|
|pCO2 50 mmHg||K 2.8 mmol/L|
|HCO3 36 mmol/L||Cl 90 mmol/L|
|Lactate 1.3 mmol/L||Glucose 5.3 mmol/L|
What is the pH?
7.47 = alkalaemia
What is the primary process?
HCO3 36 = primary metabolic alkalosis
Is there compensation?
Expected pCO2 = 0.7 x HCO3 + 20
= 0.7 x 36 + 20
= 45.2 mmHg (+/-5)
Actual pCO2 is 50, therefore fully compensated.
Are there other clues to diagnosis?
Lactate is borderline high at 1.3. Sodium, potassium and chloride are low. Glucose is within the normal range.
Description: This VBG shows a fully compensated metabolic alkalaemia associated with hypochloraemia, hyponatraemia and hypokalaemia.
Interpretation: In this clinical setting, hypokalaemia is likely to be associated with QT prolongation and torsades, however magnesium and calcium should also be measured and replaced as well. Hypochloraemic alkalosis could be secondary to upper GI loss through vomiting, from use of diuretics or volume depletion. Primary hyperaldosteronism could be considered however this is usually associated with mild hypernatraemia, therefore Na 129 would argue against this diagnosis. Further investigation of hyponatraemia with serum osmolality, urinary sodium and osmolality could be performed to further define the aetiology. Management includes electrolyte replacement, intravenous rehydration and supportive care.
Additional information: Strong ion difference (Na – Cl) = 39 is consistent with high strong ion difference alkalosis.
Diagnosis: Cannabis hyperemesis syndrome, cardiac arrhythmia thought to be due to hypokalaemia secondary to vomiting.