Lab case 395 Interpretation

Question 1:

PH = 7.29 That is moderate acidaemia

PCO2 = 60 mmHg, that is high (>40). So, we have respiratory acidosis.

Next, we need to look at HCO3 to determine if it is acute or chronic respiratory acidosis.

Respiratory acidosis can be acute or chronic.

In acute respiratory acidosis, PaCO2 level is more than 40 mmHg with pH < 7.35. In chronic respiratory acidosis, PaCO2 level is more than 40, with a normal or near-normal pH secondary to renal compensation (elevated serum bicarbonate levels, usually >30). Accordingly, most probably we have chronic respiratory acidosis.

The expected compensation for chronic respiratory acidosis is: HCO3 will increase by 4 for every 10 increases in PCO2 above 40.

Accordingly, expected HCO3 should be: 24 + 0.4 x 20 = 32 this is very close to 31.

So, we have chronic respiratory acidosis.

The presence of high Hb level also support Chronic respiratory acidosis. This is due to chronic hypoxia. Which is what we have in this case.

Expected PO2 = inspired O2 x 4 = 160.

(We can use Winter’s formula to measure magnitude of a respiratory acidosis. That is by measuring the difference between actual PCO2 and expected PCO2. Expected PCO2 in this case is 54.5 – Accordingly we might have some element of acute on chronic respiratory acidosis).

Question 2:

Management of this patient should be directed to treat the underlying disease. Usually with bronchodilators and steroids. Antibiotics if bacterial infection was identified to be a cause.

Non-invasive ventilation should be used with caution. Rapid correction of hypercapnia by using noninvasive positive-pressure ventilation or invasive mechanical ventilation can result in metabolic alkalosis. Accordingly, these techniques should be used with caution. (Mainly in severe acute cases).