Endobronchial adrenaline: Should it be reconsidered? Dose response and haemodynamic effect in dogs
Tracheal drug administration is a route for drug delivery during cardiopulmonary resuscitation when intravenous access is not immediately available. However, tracheal adrenaline (epinephrine) injection has been recently shown to be associated with detrimental decrease in blood pressure. This was attributed to exaggerated early beta2 mediated effects unopposed by alpha-adrenergic vasoconstriction. We hypothesized that endobronchial adrenaline administration is associated with better drug absorption, which may abolish the deleterious drop of blood pressure associated with tracheal drug administration. To determine haemodynamic variables after endobronchial adrenaline administration in a non-arrest canine model. Prospective, randomized, laboratory study. Adrenaline (0.02, 0.05, 0.1 mg/kg) diluted with normal saline was injected into the bronchial tree of five anaesthetized dogs. Injection of 10-ml saline served as control. Heart rate, blood pressure and arterial blood gases were monitored for 60 min after drug instillation. The protocol was repeated after 1 week. Adrenaline at a dose of 0.02 mg/kg produced only a minor initial decrease in diastolic (from 90 +/- 5 to 78 +/- 3 mmHg, P=0.05), and mean blood pressure (from 107 +/- 4 to 100 +/- 3 mmHg, P=0.05), in all dogs. This effect lasted less then 30 s following the drug administration. In contrast, higher adrenaline doses (0.05 and 0.1 mg/kg) produced an immediate increase in diastolic (from 90 +/- 5 to 120 +/- 7 mmHg; and from 90 +/- 5 to 170 +/- 6 mmHg, respectively), and mean blood pressure (from 107 +/- 4 to 155 +/- 10 mmHg; and from 107 +/- 4 to 219 +/- 6 mmHg, respectively). All adrenaline doses resulted in an immediate increase in systolic blood pressure and pulse. Endobronchial administration of saline (control) affected none of the haemodynamic variables. In a non-arrest model, endobronchial adrenaline administration, as opposed to the effect of tracheal adrenaline, produced only a minor decrease in diastolic and mean blood pressure. We suggest that endobronchial adrenaline administration should be investigated further in a CPR low-flow model when maintaining adequate diastolic pressure may be crucial for survival.