Changes of epidural blood flow after epidural administration of epinephrine in young rats

Summary Purpose For caudal epidural analgesia, the needle is inserted at a site where vessels are abundant. To avoid complications related to intravascular administration of the local anesthetic, epinephrine is usually added, but there is no evidence about the safety of epidural administration of epinephrine in pediatric patients. The objective of this study was to assess the changes in epidural blood flow after epidural injection of epinephrine in young rats. Methods With approval of the local ethics committee, four young Sprague–Dawley rats weighing 110–120 g were investigated. The rats were anesthetized with isoflurane via a mask. After there was no escape reaction to pain, an arterial catheter, epidural blood flow monitor (Laser Doppler blood flow ALF 21; ADVANCE Corp.), and caudal epidural catheter were inserted while the rats remained under general anesthesia. Exactly, 10 μl of 1 : 1000 epinephrine was then infused, followed by measurement of the blood pressure and epidural blood flow. After the recovery of the blood pressure and epidural blood flow to baseline, 10 μl of saline was infused through the epidural catheter. The blood pressure and epidural blood flow were then measured again. Results One rat was excluded because epinephrine was inadvertently injected into the epidural vessels. Therefore, three rats were investigated in this experiment. Blood flow in the epidural space showed no change after the injection of saline. When epinephrine was administered into the epidural space, epidural blood flow decreased immediately and low flow persisted for 6–15 min. The reduction of blood flow was not very great, being only 8–14%, so there was no risk of spinal ischemia which would require 60–80% reduction. Conclusion Administration of epinephrine into the epidural space was safe in young rats. While reduction of epidural blood flow was observed, there was no spinal ischemia.