Lab case 435 interpretation

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PH = 7.507, that is alkalaemia

pCO2 = 28 mmHg. So, we have respiratory alkalosis.

Next we will check the compensation. For acute respiratory alkalosis, we expect HCO3 to drop by 2 mmol/L  for every 10 pCO2 below 40 mmHg.

pCO2 is 28, (That is 12 below 40). Accordingly, expected HCO3 should be:

24 – (0.2×12 )= 21.6.  This patient’s HCO3 is 22. That is very close. So we have well compensated respiratory alkalosis. (IS IT????).

It is a good practice to calculate the Anion Gap for every patient. Anion gap is calculated as: AG = Na – (Cl + HCO3) = 137 – (102 + 22) = 13  ( Normal AG with out K is 12).

Although AG is very close to normal. It is recommended that you always consider the patient is having HAGMA with the slightest increase in AG above 12 as HAGMA is more dangerous than NAGMA.

Other abnormal findings:

Na = 137 mmol/L that is within the low side of the normal range

K = 3.2, that is mild hypokalaemia

Cl = 12 mmol/L that is within the high side of the normal range.

Usually the changes in Na and Cl go in the same direction. We should have concerns when Na level is low and Cl level is high as this is usually a sign of potential seriousness of the condition.

Causes of Hyperchloraemia:  ***

1- Chloride administration ( IV fluids rich in chloride or TPN)

2- Water loss (True water loss or relative to chloride). That can be either renal or extra renal)

  •  Renal causes include: Diabetic insipidus, Diuretics use, Osmotic diuresis or postobstructive diuresis.
  •  Extra renal causes include: Fever, Hypermetabolic state, Diarrhoea, Burns or exercise and severe dehydration.

3- Increase in tubular chloride reabsorption (RTA, Renal failure, Acetazolamide use Ureteral diversion procedure and post hypocapnia).

The other abnormal finding is Creatinine of 120 umol/L. This level in a 60-year-old man will give us eGFR of 56. If this is a chronic condition then this means that this patient has mild chronic kidney disease (CKD). Stage 3 CKD.

Next, we need to look at the causes of respiratory alkalosis. For that we use the mnemonic CHAMPS.

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

This patient had urosepsis.

Special thanks to Dr Amanda Montgomery for providing the details for this case

 

 

 

*** Causes of hyperchloremia.  | Download Table (researchgate.net)