Lab case 373 interpretation

PH = 7.55, that is moderate alkalaemia.

PCO2 = 30 mmHg (Less than 40) so we have respiratory alkalosis.

Next, we look at the compensatory processes. For acute respiratory alkalosis we expect HCO3 to drop by 2 for every 10 pCO2 less than 40. According to that expected HCO3 should be 24 – (10 x 0.2) = 22.

HCO3 value for this patient is 27, higher than the expected for pure respiratory alkalosis. That means we have additional metabolic alkalosis.

Anion gap for this patient = 141 – (93 + 27) = 21. So, we have additional HAGMA.

Other abnormal results

Cl = 91 mmol/L, that is mild hypochloraemia. This is most likely due to vomiting and loss of HCl.

Lactate = 3.3 mmol/L, that is mild to moderate hyperlactataemia. Most probably due to reduced tissue perfusion secondary to dehydration. This conclusion can be supported by slightly elevated creatinine level (103 umol/L).

Final conclusion, this patient has triple metabolic condition, that is respiratory alkalosis with metabolic alkalosis and HAGMA.

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

For the causes of acute respiratory alkalosis, we use the mnemonic CHAMPS

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

In this case, anxiety and pain are the potential causes.

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

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

In this case, contraction alkalosis and vomiting are the potential causes.

For the causes of HAGMA, 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

We need more information in figure out the causes (Urea level, Ketones levels and more information from history). However, lactate level of 3.3 is a contributing cause.