A 52-year-old man presented after having been found unconscious in the street. On examination, he had a Glasgow coma score of 5, a pulse of 110 beats per minute and a blood pressure of 95/65 mmHg. His respiratory rate was 35 breaths per minute and there were no focal neurological signs.
Investigations:
arterial blood gases, breathing 40% oxygen:
PO2 11.5 kPa
PCO2 3.9 kPa (4.7–6.0)
pH 7.24 (7.35–7.45)
H+ 58 nmol/L (35– 45)
serum bicarbonate 12 mmol/L (21– 29)
What acid–base disturbance is most likely to be present?
Question 84 A: metabolic acidosis
B: mixed metabolic acidosis and metabolic alkalosis
C: mixed metabolic acidosis and respiratory acidosis
D: mixed respiratory alkalosis and metabolic acidosis
E: respiratory acidosis
Correct answer: A Explanation There is an elevated H+ therefore this is acidosis. The low bicarbonate and low PCO2 both support a metabolic acidosis (i.e. not a respiratory acidosis due to CO2 retention). There is no indication of mixed causes for acidosis.