Abstract 2839: Alpha1 Actions of Epinephrine Reduce Cerebral Perfusion During Cardiopulmonary Resuscitation
Introduction. Epinephrine is the primary drug for CPR. The rationale is to restore threshold levels of myocardial blood flows through its alpha1 (α1) and alpha2 (α2)-adrenergic actions.
Hypothesis. We hypothesized that epinephrine decreases cerebral cortical microvascular flow (MBF) through its α1 effects.
Methods. Four groups of 5 pigs weighing 40 ± 3 kg were investigated. A bilateral craniotomy was created. MBF was measured with Orthogonal Polarization Spectral imaging. Cerebral cortical carbon dioxide and oxygen tensions (PbCO2 and PbO2) were concurrently measured utilizing miniature optical sensors. Blood flow velocity in pial and penetrating vessels < 20 μm was graded from 0 (no flow) to 3 (normal). Ventricular fibrillation (VF) was induced and untreated for 3 min. At one min after the start of CPR, animals were randomized to receive central venous injections of (1) placebo, (2) epinephrine, (3) epinephrine with both α1- and beta (ß)-adrenergic effects blocked by previous administration of prazosin and propranolol, and (4) epinephrine with both α2- and ß-adrenergic effects blocked by previous administration of yohimbine and propranolol. After 4 min of CPR including precordial compression and ventilation with oxygen, defibrillation was attempted.
Results. Aortic pressure was increased after administration of epinephrine, however, this was associated with decreases in MBF and PbO2 and increases in PbCO2. Reductions in MBF, decreases in PbO2 and increases in PbCO2 were significantly less when epinephrine was combined with α1-adrenergic blockade with prazosin and non-specific ß blockade with propranolol. After selective α2 blockade with yohimbine together with propranolol the adverse effects of epinephrine on PbO2, PbCO2 and microvascular flow persisted (Table⇓).
Conclusions. Epinephrine reduces cerebral blood flow through its α1 actions. It may therefore increase the severity of cerebral ischemia during CPR.