A 44-year-old woman is brought to hospital having been found disorientated and confused in her neighbour’s driveway.
Describe and interpret her venous blood gas:
Additional laboratory values:
Urea (plasma) = 4.5 mmol/L
Measured serum osmolality = 227 mmol/kg
Measured urine osmolality = 183 mmol/kg
Urine sodium (spot) = 11 mmol/L
Click below to expand solutions:
7.590 = severe alkalaemia
HCO3 48.6 → primary metabolic alkalosis
Expected pCO2 = 0.7 x HCO3 + 20 (± 5)
= 0.7 x 48.6 + 20 ± 5
≈ 49 – 59
Measured pCO2 is 50.4, therefore there is maximal respiratory compensation.
Anion gap = Na – (Cl + HCO3)
= 104 – (48 + 48.6)
= 7.4 = low
Calculated serum osmolalty = (2 x Na) + urea + glucose (+ ethanol)
= (2 x 104) + 4.5 + 6.6
Osmolar gap = measured osmolality – calculated osmolality
= 227 – 219.1
= 7.9 mmol/kg (normal < 10)
Sodium, potassium, chloride, and calcium all severely low. Glucose is normal. Lactate is mildly elevated. Creatinine 19. Hb 101
Description: This venous blood gas reveals a severe metabolic alkalosis with maximal respiratory compensation. There is profound hyponatraemia, hypokalaemia, hypochloraemia, and hypocalcaemia. The serum lactate is mildly elevated. The patient is normoglycaemic and mild-moderately anaemic.
Interpretation: In the absence of any additional information, this clinical picture would be most consistent with either severe volume contraction +/- gastric alkalosis (vomiting or nasogastric drainage), or diuretic abuse (typically loop and thiazide diuretics).
Additional information: The patient suffered from chronic alcoholism and had been vomiting for proceeding week of so. The patient was admitted to the High-Dependency Unit for volume correction and judicious electrolyte replacement. During her admission the patient developed haematemesis and melaena necessitating emergency oesophagogastroduodenoscopy which revealed evidence of ulcerative oesophagitis. A oral proton pump inhibitor was commenced and the patient was discharged several days later having made a complete recovery.