lab case 445 interpretation

Ph = 7.51, that is mild alkalaemia.

HCO3 = 47.5 mmol/L. So, we have metabolic alkalosis.

Next we need to calculate the respiratory compensation. For metabolic alkalosis we use the following formula:

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

Accordingly, expected pCO2 is: 0.7 x 47.5 + 20 = 53.25 (range between 48.25 to 58.25). This patient’s pCO2 is 59.5. that is very close to the maximum accepted range.. So this patient might have additional very mild respiratory acidosis (The sample was venous and the pCO2 value is usually higher than the arterial value by 8 mmHg).

Next we will check the Anion Gap for this patient. Anion Gap is calculated as:

AG = Na – (Cl + HCO3) = 3.5… No additional HAGMA.

So Far this patient has Metabolic alkalosis with possible additional mild respiratory acidosis.

Other abnormal findings:

K = 3.1 mmol/L, that is mild hypokalaemia.

Cl = 93 mmol/L, that is mild hypochloraemia

Glucose = 19.3, that is hyperglycemia.

Na level usually measured lower than the serum level in the presence of hyperglycemia. That is due to movement of water from intracellular to extracellular compartments because of the osmotic difference.

To calculate the corrected Na level we use the following formula:

Corrected Na = Measured Na – (Glucose – 5)/3 = 148.8 (So we have mild hypernatraemia).

Final conclusion: This patient has metabolic alkalosis with Mild hypernatraemia, mild hypokalaemia and hypochloraemia with hyperglycaeemia and possible mild respiratory acidosis.

Next we need to look at the causes:

For the differential diagnosis of metabolic alkalosis we use the mnemonic CLEVER PD.

• C – contraction (dehydration) – Possible
•  L – liquorice (diuretic), laxative abuse – excluded by taking history
•  E – endocrine (Conn’s, Cushing’s) – Possible (High Na and high glucose level).
•  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 – unlikely, normal bloods previously
•  P – post hypercapnia – Possible
•  D – diuretics  – excluded by taking history.

Patient was not on steroids and she has history of Diabetes.. Doctors were happy to exclude that.

Post hypercapnia is possible if the patient has chronic respiratory acidosis and then developed respiratory alkalosis (tachypnoea) due to the pain…However, her HCO3 was normal on previous blood tests…This condition was excluded on these bases.

Dehydration was considered to be the cause…

This patient had lots of medical problems and she was unfit for surgery… Comfort care was prescribed for this patient.