COMPARISON OF THE EFFECT OF INHALED SELECTIVE AND NONSELECTIVE ADRENERGIC AGONISTS ON CARDIORESPIRATORY PARAMETERS IN CHRONIC STABLE ASTHMA

Increased hypoxia has been found after beta(2) adrenoceptor agonists ( but not adrenaline) in asthmatics. Combined with hypokalaemia and symp athomimetic stimulation, this may predispose to cardiac arrhythmias. W e have compared the effects of nebulized adrenaline and a selective be ta(2) agonist (salbutamol) on the arterial oxygen saturation (SaO(2)), minute ventilation (VE), forced expiratory volume in 1 s (FEV(1)), pl asma potassium and the electrocardiogram (ECG) in patients with chroni c 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 SaO(2) after both adrenaline (mean % fall (SEM) 3.3 (0.2)) and salbutamol (4. 0 (0.7)) associated with an increase in FEV(1), with no change in VE. Therefore, the fall in SaO(2) must have been caused by increased venti lation-perfusion imbalance. There was an increased heart rate after bo th adrenaline and salbutamol and ventricular ectopic beats and a short run of parasystole were recorded on the ECG in one patient after adre naline and in two patients after salbutamol. No change was found in pl asma potassium levels. We conclude that both adrenaline and a selectiv e beta(2) agonist salbutamol can cause a fall in SaO(2) and ventricula r ectopy in some asthmatic patients.