AMIDE LOCAL-ANESTHETICS REDUCE ALBUMIN EXTRAVASATION IN BURN INJURIES

Burn injury was induced in anesthetized rats by exposing the abdominal skin to a temperature of 55° C by means of a hot aluminum rod. Temperature was registered of a Grass® polygraph. Skin exposure was interrupted when hot rod temperature had decreased to 45° C. A full-thickness burn trauma of the skin was induced as judged from histologic sections. The burned skin was dissected and extravasation of Evans blue (EB) bound plasma albumin was quantified by a spectrophotometric technique and visualized by fluorescence microscopy. In the first set of experiments, one group of rats (n = 15) was topically treated with a lidocaine-prilocaine cream 5% (25 mg of each in 1 g; EMLA®) for 1.5 h starting 15 min after inducing the burn injury. In one control group (n = 14) the thermal injury was treated with placebo cream. A second control group (n = 15) was topically treated with placebo cream without being exposed to thermal trauma. Results showed a significant inhibition of EB-albumin extravasation in the skin of burned rats treated with lidocaine-prilocaine cream compared with placebo-treated burned skin (P<0.001). EB-albumin contents in the skin of burned rats treated with lidocaine-prilocaine cream did not differ significantly from unburned skin (P>0.05). In the second set of experiments continuous iv lidocaine infusions at a rate of 5 (n = 10), 10 (n = 12), 20 (n = 10), or 30 (n = 10) μg·kg-1·min-1 was given. The infusions were started 15 min after the burn injury and lasted for 1.5 h. A corresponding infusion of isotonic saline was given to burned control animals (n = 10) and to animals not exposed to thermal trauma (n = 10). A maximum inhibition of albumin extravasation from the burned area was induced by iv lidocaine at an infusion rate of 10 μg·kg-1·min-1 compared with burned controls treated with isotonic saline infusions (P<0.01). At infusion rates below or above this, the effect of lidocaine on albumin extravasation was significantly reduced. Results show that topical or systemic administration of local anesthetics increases vascular patency and reduces albumin extravasation at the site of experimental burn injury. Furthermore, the effect of systemic lidocaine administration on burn-induced albumin extravasation appears to be biphasic. Future trials are required to determine the clinical relevance of these results in burned patients.