Epinephrine absorption following endotracheal administration: effects of hypoxia-induced low pulmonary blood flow.

To investigate the effects of hypoxia-induced decreased pulmonary blood flow on the trans-pulmonary absorption of epinephrine, we measured pulmonary blood flow and arterial plasma tritium counts per minute following endotracheal [3H]epinephrine administration in six chronically instrumented newborn lambs. The lambs were ventilated alternately with room air and with an hypoxic gas mixture sufficient to decrease pulmonary blood flow to approximately 50% of baseline values. Using this model, we found that hypoxia-induced low pulmonary blood flow did not lead to lower concentrations of epinephrine following endotracheal administration, but rather higher concentrations (P < 0.03). In all six lambs, counts per minute of tritium were higher following administration during low pulmonary blood flow. There was a negative correlation between pulmonary blood flow and arterial plasma tritium counts per minute (r = -0.64, P < 0.03). We conclude that trans-pulmonary absorption of epinephrine is not decreased during times of hypoxia-induced low pulmonary blood flow. These data lend support to the clinical practice of intratracheal epinephrine administration during neonatal resuscitation.