1. Plasma concentrations of noradrenaline and adrenaline were measured in 11 anaesthetized patients during normocapnia, hypocapnia and hypercapnia. Hypocapnia was produced by deliberate hyperventilation and hypercapnia by adding carbon dioxide to the inspired gas mixture.
2. With a median (range) arterial partial pressure of carbon dioxide of 4.7 (4.2–5.2) kPa, the median (range) plasma concentration of noradrenaline was 0.41 (0.12–0.94) nmol/l and of adrenaline was 0.15 (0.05–0.31) nmol/l.
3. With an arterial partial pressure of carbon dioxide of 2.6 (2.2–3.3) kPa, there was no change in the plasma concentration of noradrenaline [0.37 (0.12–0.86) nmol/l] or that of adrenaline [0.16 (0.05–0.32) nmol/l].
4. However, with an arterial partial pressure of carbon dioxide of 10.4 (7.6–13.2) kPa, there were significant increases in the plasma concentrations of both noradrenaline [1.13 (0.79–2.05) nmol/l, P < 0.01] and adrenaline [0.67 (0.20–2.92) nmol/l, P < 0.05].
5. This is the first demonstration in man that respiratory acidosis causes an increase in plasma concentrations of catecholamines.