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)
Acute respiratory acidosis with metabolic alkalosis
Clinical scenario – acute respiratory failure in COAD (Acute on chronic respiratory failure)
Let us dissect these results systematically.
- Oxygenation cannot be assessed
- There is acidaemia
- The PaCO2 is high, and looks to be the cause of the acidosis
- The SBE is not available, but the bicarbonate is high, suggesting a metabolic alkalosis
- 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.
- The anion gap is (145) - (101 + 34) = 10, or 14 when calculated with potassiu, i.e. totally normal.
- The delta ratio is therefore irrelevant.