For each of the varieties of acid–base disturbance A–E, select the best option for a possible cause from the following list

A. Option 1 Sudden laryngeal obstruction. The obstruction leads to a rapid rise in PCO2 before the kidneys can compensate by generating bicarbonate thus raising the blood bicarbonate level.

B. Option 5 Severe diarrhoea. Severe diarrhoea results in loss of bicarbonate in the stools and thus to a fall in the blood bicarbonate level.

C. Option 2 Severe chronic respiratory disease. The raised PCO2 in chronic respiratory dis-ease may be compensated for by renal generation of bicarbonate to raise the blood bicar-bonate level.

D. Option 4 Mountain climbing. The respiratory drive caused by the action of low Po2 on arterial chemoreceptors washes out CO2. This lowers the PCO2 to cause an alkalosis. Eventually the kidneys compensate by eliminating more bicarbonate.

E. Option 3 Chronic renal failure. The fall in blood bicarbonate used in buffering the acid residues of protein digestion in chronic renal failure is compensated for by an increased respiratory drive that results in a fall in PCO2.