Increased
hypoxia has been found after beta 2
adrenoceptor agonists (but not
adrenaline) in asthmatics. Combined with hypokalaemia and
sympathomimetic stimulation, this may predispose to
cardiac arrhythmias. We have compared the effects of nebulized
adrenaline and a selective beta 2 agonist (
salbutamol) on the arterial oxygen saturation (SaO2), minute ventilation (VE), forced expiratory volume in 1 s (FEV1), plasma
potassium and the electrocardiogram (ECG) in patients with chronic stable
asthma. Six patients were studied according to a randomized, placebo-controlled, double-blind cross-over protocol.
Adrenaline (5 mg),
salbutamol (5 mg) and placebo were administered during 4 min tidal breathing using a
nebulizer driven by air. There was a fall in SaO2 after both
adrenaline (mean % fall (SEM) 3.3 (0.2)) and
salbutamol (4.0 (0.7)) associated with an increase in FEV1, with no change in VE. Therefore, the fall in SaO2 must have been caused by increased ventilation-perfusion imbalance. There was an increased heart rate after both
adrenaline and
salbutamol and
ventricular ectopic beats and a short run of
parasystole were recorded on the ECG in one patient after
adrenaline and in two patients after
salbutamol. No change was found in plasma
potassium levels. We conclude that both
adrenaline and a selective beta 2 agonist
salbutamol can cause a fall in SaO2 and ventricular ectopy in some asthmatic patients.