Effects of fenoterol and ipratropium on respiratory resistance of asthmatics after tracheal intubation

We have studied the effects of a beta-agonist, fenoterol, and a cholinergic antagonist, ipratropium, on post-intubation total respiratory system resistance (Rrs) in asthmatics who developed increased Rrs after tracheal intubation. Sixteen stable asthmatics in whom Rrs increased after intubation were allocated randomly to receive either 10 puffs of fenoterol (group F) or 10 puffs of iptatropium (group IB) via a metered dose inhaler 5 min after intubation. Anaesthesia was induced and maintained with propofol i.v. Rrs was recorded before treatment and again 5, 15 and 30 min after treatment. Rrs decreased significantly from pretreatment values by mean 53 (SD 8)%, 53 (7)% and 58 (6)% at 5, 15 and 30 min, respectively, in group F, but declined by only 12 (6)%, 15 (4)% and 17 (5)% in group IB. At all times after treatment, patients in the fenoterol group had significantly lower Rrs values than those in the ipratropium group. We conclude that increased Rrs after tracheal intubation in asthmatics can be reduced effectively by treatment with fenoterol. A secondary finding of our study was that even after induction of anaesthesia with propofol, patients with a history of asthma may develop high Rrs.