Acute beta-adrenoreceptor blockade and induced hypotension.

Thirty patients scheduled for major middle ear surgery and induced hypotension, with a trimetaphan/sodium nitroprusside infusion, were randomly allocated to receive a single oral dose of beta-adrenoreceptor antagonist 2 hours before surgery. In group 1 ten patients received metoprolol 50 mg, in group 2 ten patients received metoprolol 25 mg and in group 3 ten patients received oxprenolol 20 mg. There were ten controls for each group. The nitroprusside infusion rate was significantly reduced in groups 1 and 3. However, there was an unacceptably high incidence of profound bradycardia after induction of anaesthesia in those patients who had received beta-adrenoreceptor antagonists pre-operatively and this technique is not recommended for routine use.