Influence of Epinephrine and Medetomidine on Systemic Absorption of Lidocaine Applied Epidurally in Anesthetized Swine

Epinephrine and alpha 2 agonist drugs are often used with epidural anesthesia to minimize local anesthetic systemic absorption, as well as to prolong the duration of the block. The aim of the current study was to determine by which extent epinephrine and medetomidine influenced lidocaine systemic absorption rate following epidural application. This was achieved by monitoring the serum lidocaine concentration in a porcine model. During general anesthesia, the first group received epidurally plane lidocaine, the second received lidocaine containing epinephrine (1 : 80.000), and the third lidocaine with medetomidine (15 μg/kg). Venous blood samples were taken before and 5, 10, 20, 30, 45, 60 and 90 minutes following epidural administration of the anesthetic. The effects of epinephrine and medetomidine were comparable. They both failed to cause a significant decrease in serum lidocaine concentration (p>0.05). In these settings we were unable to demonstrate a greater capacity of these two adrenergic agonists for reducing lidocaine systemic uptake and, accordingly, its systemic toxicity potential.