Effects of a Continuous Epinephrine Infusion on Regional Blood Flow in Awake Newborn Piglets

Abstract

Objective: To determine the effects of a continuous epinephrine infusion on renal and mesenteric blood flow in both healthy newborn piglets and animals subjected to hemorrhagic shock. Methods: Superior mesenteric artery (SMA) and left renal artery ultrasonic flow probes were implanted into 16 1- to 3-day-old piglets. Two days later, the effects of epinephrine on SMA and renal blood flow, mean arterial pressure (MAP) and central venous pressure were measured in conscious, non-sedated normovolemic piglets. Epinephrine doses of 0.2, 0.4, 0.8, 1.6 and 3.2 µg/kg·min were used in random order. Piglets were subsequently hemorrhaged (20 ml/kg) to mild hypotension and again received epinephrine infusion in the same doses. Results: Doses of epinephrine less than 3.2 µg/kg·min had no significant effects on renal or mesenteric arterial flow. At 3.2 µg/kg·min of epinephrine during normovolemia, there was a significant decrease in SMA blood flow (34% [SD 42], p < 0.05) and increase in SMA vascular resistance (147% [SD 114], p < 0.05). Similar results were shown during hypovolemia, SMA flow decreased by 32% (SD 33), and SMA vascular resistance increased by 220.3% (SD 177). At 3.2 µg/kg·min renal artery flow decreased by 43% (SD 21) during normovolemia and a similar decrease occurred during hypovolemia, 37% (SD 31). Renal vascular resistance increased by about 200% at this dose (normovolemia 211% [SD 185], hypovolemia 186% [SD 150], p < 0.01). Low-to-moderate dose epinephrine caused no significant change in SMA or renal blood flow. During hypovolemia low dose epinephrine infusion was associated with a trend to increased SMA blood flow. Conclusion: Low-dose epinephrine does not cause vasoconstriction in the renal or mesenteric circulations during normovolemia or hypovolemia. High doses of epinephrine above 1.6 µg/kg·min may cause renal or mesenteric ischemia, in either the normovolemic or hypovolemic neonate.