VF: Epinephrine mechanism

Epinephrine in a concentration of 0.02 mg/kg (approximately 1.0 mg in adults) is given for cardiovascular collapse, asystole, ventricular fibrillation, electromechanical dissociation, or anaphylactic shock. The larger dose range is recommended in these critical situations to maintain myocardial and cerebral perfusion through peripheral vasoconstriction. This vascoconstriction increases aortic diastolic blood pressure, which promotes coronary blood flow. According to Miller, this “may be the single most important determinant of survival.” However, during VF epinephrine also reduces the VF threshold and cellular refractory period, thereby stabilizing fibrillation.In non-VF or asystolic situation, doses less than 10 mcg/min increases HR, contractility and decreases the refractory period. Doses above 10 mcg/min will cause peripheral vasoconstriction and renal vasoconstriction. Rarely, epinephrine may cause reflex bradycardia due to the marked elevation in BP from the peripheral vasoconstriction.