We compared hemodynamic effects of two methods of administering epinephrine endotracheally in two different preparations: 1.) A 100μg/kg solution was instilled directly into the endotracheal tube; and 2.) 75μg/spray, 1 spray/kg in a surfactant-based aerosol preparation. New Zealand White rabbits(n=18) weighing 2.41 +/- 0.27 kg were anesthetized with Ketamine (55mg/kg), Xylazine (5mg/kg) and Acepromazine (0.01 mg/kg), IM, tracheostomized, and internal carotids cannulated. Blood pressure and heart rate were continuously monitored. Normal model: both epinephrine preparations were given endotracheally without any other medications either by direct instillation(n=5) with a lcc saline flush, or by aerosol (n=5). Heart rate, systolic blood pressure, diastolic blood pressure and pulse pressure were recorded pre-treatment, with treatment, then 30 sec., 1,5,10 and 20 min. thereafter.Shock model: rabbits were paralyzed with Vecuronium (0.1mg/kg) and observed until systolic blood pressure decreased to 40-45 mmHg. They were then ambu-bagged for 30 sec. and epinephrine given by direct instillation (n=4) or by aerosol (n=4). Hemodynamic parameters were recorded as above. Analysis of variance was performed on the data. Normal model: there was no significant difference between the two groups in any parameter at any time. There were significant changes over time within each groups. Shock model: there was no significant difference between the two groups except in pulse pressure at 10 minutes after treatment. (However, in both models there was a slight, but insignificant, drop in blood pressure at 30 seconds using the instilled preparation. This may be explained by a vagal response induced by the saline flush.)

Conclusions: Epinephrine administered endotracheally when intravenous access is not available is a well recognized and accepted medical practice. Currently, instillation of the IV form through the endotracheal tube is recommended. This method is cumbersome and requires computation based on the patient's body weight, aspiration of the medication with a syringe and flushing the tube with saline. There is no significant difference in hemodynamic response between the methods of administration. The MDI form is easier to administer and may have additional clinical benefits in improving airway function when spontaneous respirations are restored. Since the dose/kg was less, the response could be significantly greater if the dose is increased. Further studies using higher doses are suggested.