Lab case 433 interpretation

Question 1:

PH = 7.409, that is with in normal range

pCO2 = 54 mmHG, that is suggestive of respiratory acidosis.

HCO3 = 33.3, that is suggestive of metabolic alkalosis.

Since the PH is normal, most probably we have combined acidosis and alkalosis. We will start with the metabolic process “The calculations will be easier if we start with the metabolic process. Although history taking is the most important process to differentiate acute from chronic process”.

For the compensation of metabolic alkalosis, we use the following equation:

Expected pCO2 = 0.7 x HCO3 + 20 (+/- 5).

Accordingly, expected pCO2 for this patient should be: 0.7 x 33 + 20 = 43. pCO2 that we have here is higher than that (54) so the patient has associated respiratory acidosis.

Other abnormal findings:

Hb = 86 g/L. This patient is anaemic.

Cl = 91 mmol/L , that is low. So we have hypochloraemia.

Glucose = 11.5 mmol/L, hyperglycemia

Creatinine = 139, that is elevated. For 80 years old man, that will give him GFR of 41.

Final conclusion: Combined hyperchloremic metabolic alkalosis and respiratory acidosis with anaemia, hyperglycemia and stage 3B (moderate) CKD.

Question 2:

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), severe K depletion
•  P – post hypercapnia
•  D – diuretics,

For this patient the cause of metabolic alkalosis was the diuretics he takes for CCF. Frusemide and Thiazides interfere with reabsorption of Na and Cl. This will lead to more Cl loss compared to HCO3.

Patients on diuretics develop alkalosis when they are volume depleted. (Volume depletion lead to stimulation of aldosterone)

In those patients K level is usually elevated then the level starts to drop when they become volume depleted.