Inspect the following biochemical data:

Parameter Patient Value Normal Adult Range
Sodium 145 mmol/L 135 – 145
Potassium 4.0 mmol/L 3.2 – 4.5
Chloride 101 mmol/L 100 – 110
Bicarbonate 34 mmol/L* 22 – 26
pH 7.20* 7.35 – 7.45
pCO2 90 mmHg* (11.7 kPa)* 35 – 45 (4.6 – 5.9)

Describe the abnormalities and give an example of an associated clinical scenario. (20% marks)

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College Answer

Acute respiratory acidosis with metabolic alkalosis
Clinical scenario – acute respiratory failure in COAD (Acute on chronic respiratory failure)

Discussion

Let us dissect these results systematically.

  1. Oxygenation cannot be assessed
  2. There is acidaemia
  3. The PaCO2 is high, and looks to be the cause of the acidosis
  4. The SBE is not available, but the bicarbonate is high, suggesting a metabolic alkalosis
  5. The increase in bicarbonate is excessive compared with the increase expected from the hypercapnia on its own: the expected HCO3 = (5 × 1) + 24 = 29 mmol/L, and so there is also a metabolic alkalosis according to the Boston rules. The Copenhagen rules cannot be applied in this case, as they require an SBE.
  6. The anion gap is (145) - (101 + 34) = 10, or 14 when calculated with potassiu, i.e. totally normal.
  7. The delta ratio is therefore irrelevant.