Lab case 362 interpretation

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Question 1:

PH = 7.299 that is mild acidaemia

pCO2 = 80 mmHg, So we have metabolic acidosis. Next we need to calculate the compensation.

The information provided in the stem is not enough to figure if the shortness of breath is acute or chronic. We are going to calculate the compensation for both (acute and chronic).

For Acute respiratory acidosis we expect the HCO3 to increase by 1 for every 10 pCO2 above 40. Accordingly, expected HCO3 should be (24 + 40 x 0.1) = 28.

For chronic respiratory acidosis, we expect HCO3 to increase by 4 for every 10 pCO2 above 40. Accordingly, expected HCO3 should be (24 + 40 x 0.4) = 40. That is very close to the value we have… Most likely this patient has chronic respiratory acidosis.

It is good practice to always calculate the anion gap, for this patient:

AG = 143 – (97 + 38.5) = 75, that is with in normal range, no additional HAGMA.

The rest of the results are within normal ranges.

Final conclusion: Chronic respiratory acidosis.

Question 2:

Chronic respiratory acidosis usually doesn’t present with respiratory symptoms.  The signs and symptoms of chronic respiratory acidosis are neurological.

Signs of chronic respiratory acidosis include:

  • Memory loss
  • Sleep disturbances
  • Daytime sleeping
  • Personality changes

Symptoms of chronic respiratory acidosis include:

  • Tremor
  • Gait disturbances
  • Blunted reflexes
  • Myoclonic Jerks
  • Asterixis
  • Papilledema

Increased CO2 leads to vasodilatation and increase ICP.

Patients with acute respiratory acidosis usually present with headache, confusion, drowsiness, tremor, myoclonic jerks, asterixis,,,

Normal individuals don’t develop altered consciousness until pCO2 level is greater than 75. While patients with chronic hypercapnia may not experience alteration of conscious level until pCO2 level is more than 90.

There is a theory that CO2 leads to increase GABA level and Glutamine level and that is the cause of reduced consciousness with hypercapnia.

 Question 3:

For the treatment of this patient, we need to look for a reversible causes and fix them. Chronic respiratory acidosis usually indicates deteriorating lung functions (Chronic lungs condition that is getting worse).