Tracheal epinephrine or norepinephrine preceded by beta blockade in a dog model. Can beta blockade bestow any benefits?

Tracheal epinephrine (adrenaline) has been associated with two major deletorious side effects: increased heart rate (HR) and an initial decrease of blood pressure (BP). This prospective randomized animal study compared the haemodynamic responses to tracheally administered epinephrine or norepinephrine (nor adrenaline) alone versus each after pretreatment with propranolol for ameliorating those two untoward effects associated with epinephrine administration. Five anaesthetized mongrel dogs underwent 25 experiments of tracheal epinephrine or norepinephrine (0.02 mg/kg diluted with normal saline to 5 ml total volume) with or without an I/V non-selective beta-blocker (propranolol 0.1 mg/kg) pretreatment, and served as their own controls. Tracheal epinephrine alone produced a rise in both diastolic and mean arterial BP and an increase of HR. Tracheal norepinephrine alone produced the largest increase of diastolic and mean BP but this change was associated with a significant tachycardia (from 37 to 72/m, P<0.001). While both epinephrine or norepinephrine after pretreatment with propranolol produced a significant increase in both diastolic (from 106 to 166 mmHg and from 118 to 169 mmHg, respectively) (P<0.01) and mean BP (from 122 to 183 mmHg and from 133 to 188 mmHg, respectively) (P<0.01), only propranolol-pretreated tracheal epinephrine yielded a significant decrease in HR (from 52 to 33/m, P=0.002). Pretreatment with a beta-blocker protected against the deleterious tachycardia associated with epinephrine or norepinephrine and, by doing so, may improve the myocardial oxygen supply-and-demand balance. At the same time, the pretreatment augmented the relatively mild diastolic BP increase associated with the beta-adrenergic effect of epinephrine.