EFFECTS OF GRADED DOSES OF EPINEPHRINE DURING ASPHYXIA-INDUCED BRADYCARDIA IN NEWBORN LAMBS

To study the hemodynamic effects of graded doses of epinephrine (EPI) in a newborn animal model of hemodynamically significant bradycardia, we performed the following study. Ten newborn lambs were chronically i nstrumented with catheters and flow transducers so that systemic, pulm onary arterial, left atrial and right atrial pressures as well as hear t rate, cardiac output and left carotid artery flow could be monitored . During each of five asphyxia induced bradycardia episodes, with card iac output depressed to approximately 30% of baseline, lambs were give n either 0, 1, 10, 50, or 100 mug of EPI in a randomized sequence. Aft er 30 s, the lambs were resuscitated with room air ventilation while h emodynamic parameters were monitored. During asphyxia and prior to EPI administration, all hemodynamic parameters were similar. In addition, for the first 30 s following EPI administration, hemodynamic paramete rs continued to deteriorate in a manner that was not influenced by the dose of EPI administered. During the resuscitation period with resump tion of ventilation, systemic blood pressure and coronary perfusion pr essure rose higher following 50 and 100 mug/kg of EPI than after the s maller doses. Heart rate was highest following the 100 mug/kg dose. St roke volume and cardiac output, however, appeared to be blunted by the 100 mug/kg dose of EPI with no differences in carotid flow noted by d ose of EPI administered. It appears that doses of EPI greater than 10 mug/kg, the dose currently recommended by the American Heart Associati on, may be beneficial as an adjunct in treatment of hemodynamically si gnificant bradycardia. However, doses as high as 100 mug/kg may blunt cardiac output and stroke volume and should be used with caution.