Lab case 402 interpretation


Ph = 7.56, that is alkalaemia

Both HCO3 and pCO2 are low. So, most likely we have combined metabolic and respiratory alkalosis. We will start with the metabolic alkalosis as it is easier to run the calculations for the blood gases on the metabolic side.

To calculate the respiratory compensation for metabolic acidosis we use the following formula:

Expected pCO2 = 0.7 x HCO3 + 20 (+/-5). Accordingly, expected pCO2 for this patient should be 0.7 x 18 + 20 = 32.6 (range 27.6 to 37.6). This patient’s pCO2 is 19, less than the lowest value in the range. This confirms that this patient had additional respiratory alkalosis at that time.

Next, we will calculate the anion gap to make sure. that this patient didn’t have additional HAGMA at the time.

This is calculated as Na – (Cl + HCO3) = 19 (>12). This patient had HAGMA as well.

This patient had a triple metabolic abnormalities, combined Metabolic and respiratory alkalosis plus HAGMA.

Other abnormalities we can find among these blood gases results:

  • Glucose = 14 mol/L, that is hyperglycemia
  • Lactate = 4.2 mmcl/L, that is hyperlactataemia.
  • Ketones = 1.2, that is slightly elevated

Next we need to look at the differential causes of these abnormalities.

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

  • C – contraction (dehydration)
  • L – liquorice (diuretic), laxative abuse
  • E – endocrine (Conn’s, Cushing’s)
  • V – vomiting, GI loss (villous adenoma)
  • E – excess alkali (antacids)
  • R – renal (Bartter’s)
  • P – post hypercapnia
  • D – diuretics.

From the list above, the patient presented with vomiting. This will be a contributing cause. The patient might be dehydrated. (Vomiting and Contraction are the possible causes).

For the causes of respiratory alkalosis we use the mnemonic CHAMPS.

  • C = CNS diseases
  • H = Hypoxia
  • A = Anxiety
  • M = Mechanical ventilation/ over ventilation
  • P = Progesterone
  • S = Salicylates / sepsis

From the list above, anxiety is the cause of this patient’s respiratory alkalosis.

Lastly, for the causes of metabolic acidosis we use the mnemonic CAT MUDPILES.

  • C = cyanide, carbon monoxide
  • A = alcoholic ketoacidosis and starvation Ketoacidosis.
  • T = toluene
  • M = methanol, metformin
  • U = uraemia
  • D = diabetic ketoacidosis
  • P = phenformin, pyroglutamic acid, paraldehyde, propylene glycol, paracetamol
  • I = iron, isoniazid
  • L = lactate
  • E = ethanol, ethylene glycol
  • S = salicylates

From the list above, hyperlactataemia (High lactate = 4.2) is the potential cause.