Lab case 436 interpretation


PH = 7.391, that is within the normal range, slightly to the acidic side.

pCO2 = 57 mmHg, that is high. So we have respiratory acidosis.

It is not clear from the history if the condition is acute or chronic. Accordingly we are going to check for both.

For acute respiratory acidosis we expect HCO3 to increase by 1 for every 10 pCO2 above 40 mmHg. Accordingly, HCO3 should be 25.7 mmol/L if the case was pure acute respiratory acidosis.

For chronic respiratory acidosis we expect HCO3 to increase by 4 for every 10 pCO2 above 40 mmHg. Accordingly HCO3 should be 30.8 mmol/L if the case was pure chronic respiratory acidosis.

HCO3 for this patient is 34 mmol/L. Higher than both values. So we have additional metabolic alkalosis.

It is a good practice to calculate the anion gap in every blood gases. Anion Gap is calculated as: AG = Na – (Cl + HCO3) = 15. So we have additional HAGMA.

This patient has Respiratory Acidosis (Acute or Chronic), Metabolic alkalosis and HAGMA.

Other abnormal finding:

K = 2.4 mmol/L, that is moderate to severe hypokalaemia

Cl = 90 mmol/L, that is hypochloraemia.

This patient has Hypokalaemic, hypochloraemic metabolic alkalosis. This is the classic features for upper GI vomiting… However, This patient was not vomiting.

Glucose = 12.1 mmol/L, this patient was diabetic

Lactate = 2.6 mmol/L that is mild hyperlactataemia.

This patients had bad lungs (CCF, obstructive sleep apnoea, COPD) all these can lead to respiratory acidosis.

For the causes of Metabolic alkalosis we use the mnemonic CLEVER PD.

  • C – contraction (dehydration) – Possible, especially with lactate that is elevated.
  •  L – liquorice (diuretic), laxative abuse – excluded by taking history
  •  E – endocrine (Conn’s, Cushing’s) – Possible with low K and Na to the high side.
  •  V – vomiting, GI loss (villous adenoma) – excluded by taking history
  •  E – excess alkali (antacids) – excluded by taking history
  •  R – renal (Bartter’s), severe K depletion – excluded by checking previous blod results that showed normal K and Na.
  •  P – post hypercapnia – No
  •  D – diuretics  –Possible, this patient is on Frusemide.

This patient had congestive heart failure and she was on Frusemide, condition got corrected by electrolytes replacements and adding spironolactone to her medication.