Acid base teaching – Case 5

An elderly man was admitted as an emergency after collapsing in the street, was deeply comatose. A clinical examination showed that he had a ruptured aortic aneurysm leading to shock and circulatory failure.

Her results were:

[H+] = 90 nmol/L   pH = 7.05
PaCO2 = 7.5 kPa
[HCO3] = 15 mmol/L

Question 1

What is his acid base disturbance in this case? (Choose one of these and then click to see if you are correct)

FALSE – Compensated metabolic acidaemia is expected but due to his comatose state hypoventilation takes place resulting in respiratory acidaemia.

TRUE – Circulatory failure result in metabolic acidaemia and hypoventilation results in respiratory acidaemia.

FALSE -Yes, he has got a metabolic acidaemia but you would expect a compensatory respiratory alkalaemia which is not present in this case because of his comatose state resulting in hypoventilation.

FALSE – You are partially correct but this is a mixed acid base disturbance.


Circulatory failure and shock (following a ruptured aortic aneurysm, in this case) result in metabolic (= lactic) acidaemia. He is hypoventilating as a consequence of his comatose state, causing the respiratory acidaemia. These sorts of results are commonly seen in patients with cardiorespiratory arrest.