Effects of epinephrine and vasopressin on cerebral microcirculatory flows during CPR and after resuscitation

Objectives: Both epinephrine and vasopressin increase aortic and carotid arterial pressure when administered during cardiopulmonary resuscitation. However, we recently demonstrated that epinephrine reduces cerebral cortical microcirculatory blood flow. Accordingly, we compared the effects of nonadrenergic vasopressin with those of epinephrine on cerebral cortical microvascular flow together with cortical tissue Po-2 and PCo2 as indicators of cortical tissue ischemia. Design: Randomized, prospective animal study. Setting: University-affiliated research laboratory. Subjects: Domestic pigs. Measurements and Main Results: The tracheae of ten domestic male pigs, weighing 40 +/- 2 kg, were noninvasively intubated, and the animals were mechanically ventilated. A frontoparietal bilateral craniotomy was created. Microcirculatory blood flow was quantitated with orthogonal polarization spectral imaging. Blood flow velocity in pial and cortical penetrating vessels measuring < 20 mu m was graded from 0 (no flow) to 3 (normal). Cerebral cortical tissue carbon dioxide and oxygen tensions (P(b)co(2) and P(b)o(2)) were measured concurrently using miniature optical sensors. Ventricular fibrillation, induced with an alternating current delivered to the right ventricular endocardium, was untreated for 3 mins. Animals were then randomized to receive central venous injections of equipressor doses of epinephrine (30 mu g/kg) or vasopressin (0.4 units/kg) at 1 min after the start of cardiopulmonary resuscitation. After 4 mins of cardiopulmonary resuscitation, defibrillation was attempted. Spontaneous circulation was restored in each animal. However, postresuscitation microvascular flows and P(b)o(2) were greater and P(b)co(2) less after vasopressin when compared with epinephrine. We observed that a significantly greater number of cortical microvessels were perfused after vasopressin. Conclusions: Cortical microcirculatory blood flow was markedly reduced after epinephrine, resulting in a greater severity of brain ischemia after the restoration of spontaneous circulation in contrast to the more benign effects of vasopressin.