Effects of fluid resuscitation, burn eschar excision, and blockade of afferent pain responses on bacterial translocation and acid-base balance after murine burn injury

We tested effects of fluid resuscitation, early burn excision/grafting, and blockade of afferent stimuli from the burn wound on bacterial translocation and acid-base balance after murine burn injury. Burn excisions were performed with patients either 15 minutes or 2 hours after burn injury under anesthesia, and excised wounds were immediately closed with murine allograft skin. Twenty-four hours after 25% total body surface area (TBSA) burn injury and 48 hours after 32% TBSA injury, mesenteric lymph nodes were cultured. Incidences of bacterial translocation in 25% and 32% TBSA burns were 31.6% and 68.4% of animals, respectively. Burned animals were in severe shock, and metabolic acidosis reached a nadir 12 hours after burn injury, with base deficit — 27.8 ± 0.6 mEq/L; 5% to 10% of animals died acutely after burn injury. After excision/grafting of burned mice at 2 hours after burn injury, the incidence of bacterial translocation was unchanged (35.7% with 25% TBSA burn, 73.3% with 32% TBSA burn), and mortality did not change. When 32% TBSA excisions were performed exactly 10 minutes after burn injury, four of the 13 mice died within several hours, and five (55.5%) of the nine survivors translocated. Rates of bacterial translocation in mice receiving anesthesia or excision/grafting without burn injury were 15.0% and 20%, respectively (p = NS compared with normal mice). Subcutaneous implantation of normal or burned skin into normal animals neither elicited shock nor increased the incidence of bacterial translocation. Increasing amounts of fluid resuscitation in the 25% TBSA burn model provided only delayed improvement of acid-base balance; increased amounts of fluid did not decrease bacterial translocation. In the 32% TBSA burn model no effect on bacterial translocation was observed after different resuscitation volumes were administered. Blocking the acute afferent response before burn by infiltrating the dorsum with the local anesthetic bupivacaine hydrochloride, followed by excising/grafting within 2 hours of burn injury, did not decrease acid-base alterations or bacterial translocation. Immediate responses to burn injury other than mediators/toxins released from the burn wound and pain-mediated central responses may promote acute shock and bacterial translocation.