Lab case 366 interpretation

Question 1:

PH = 7.23, that is moderate acidaemia.

pCO2 = 62 mmHg, S we have respiratory acidosis, this can be acute or chronic.


Next, we calculate the compensation, for acute respiratory acidosis, we expect HCO3 to increase by 1 for every 10 pCO2 above 40. Accordingly, if the case was acute then the expected HCO3 should be: 24 + 22 x 0.1 = 26.2. (That very close to the value we have for this patient).

Now we will calculate the compensation for chronic respiratory acidosis, for that expected HCO3 will be 24 + 22 x 0.4. (For chronic respiratory acidosis we expect HCO3 to increase be 4 for every 10 pCO2 above 40). That is equal to 32.8, that is higher than the value we have here. 25.

The best way to differentiate between acute and chronic respiratory acidosis is by taking good history. This patient presented with hypoglycemia (Glucose = 2 after treatment), he is not short of breath. (Very uncommon for acute respiratory acidosis). Also, if the case was well compensated acute respiratory acidosis we should expect PH to be close to 7.35.  (High Chloride level also gives us a clue).

Accordingly, most probably the patient is suffering from chronic respiratory acidosis. And because the HCO3 is less than expected for chronic respiratory acidosis, then we have additional metabolic acidosis.

Because we have metabolic acidosis, then we need to calculate the anion gap. That is Na – (Cl + HCO3) = 141 – (109+25) = 7 so we have additional NAGMA.

Other abnormal findings:

The most significant abnormal finding is serum glucose of 2 mmol/L. This should be looked at and corrected before starting to interpret the blood gas results.

Cl = 109 mmol/L, that is hyperchloremia.

Lactate is slightly elevated.

Cr = 161 umol/L, for an 87 year old man that will give gine GFR of 33.

The final conclusion:

This patient has combined chronic respiratory acidosis and hyperchloraemic normal anion gap metabolic acidosis and stage 3B kidney disease complicated by hypoglycemia.

Now, we will look at the causes of NAGMA, for that we use the mnemonic USED CARP

  • U = Ureteroenterostomy
  • S = Small bowel fistula
  • E = Extra chloride
  • D = Diarrhea
  • C = Carbonic anhydrase inhibitors
  • A = Adrenal insufficiency/ Addison’s disease
  • R = Renal tubular acidosis
  • P = Pancreatic fistula.

From the list above, the list above, RTA is the only possible explanation.  (RTA causes hyperchloremia metabolic acidosis).

Question 2:

The most important step is to urgently correct the glucose level and monitor the level to make sure it doesn’t happen again. Since this patient is conscious, we can correct hypoglycemia by giving the patient rapidly absorbable sugar orally, (Glucogel or juice).

This patient developed hypoglycemia because the deterioration of kidney functions led to increase half-life of insulin. This patient needs his insulin doses adjusted.

Also, we need to look at the causes of kidney functions deterioration.