Increasing percent burn is correlated with increasing inflammation in an adult rodent model

Burn injury has been associated with systemic/compartmental inflammatory responses and myocardial dysfunction. We hypothesized that burn size correlates with the extent of cardiac inflammatory response/contractile dysfunction. Adult male Sprague-Dawley rats were divided to receive anesthesia, a 3-degree burn covering 20%, 30%, 40%, or 60% total body surface area (TBSA) plus fluid resuscitation (lactated Ringer, 4 mL/kg per percent burn); sham burn animals were included as controls. There were seven rats in each group. Rats were euthanized Twenty-four h postburn, and TNF-α, IL-1β, and IL-6 were measured in the plasma and in supernatant from isolated cardiac myocytes by enzyme-linked immunosorbent assay. In addition, left ventricular function (Langendorff) was studied in vitro, and troponin levels were measured by enzyme-linked immunosorbent assay. There were progressive, statistically significant increases in plasma and myocyte inflammatory cytokine levels, as well as plasma troponin with increasing burn size. Similarly, left ventricular pressure (in millimeters of mercury) and ±dP/dt_max (in millimeters of mercury per second) progressively fell with increasing burn size. However, myocardial contractile depression induced by 60% TBSA burn was similar to that produced by 40% TBSA burn. These data suggest that the degree of inflammatory response, cardiac tissue injury, and myocardial contractile depression were correlated directly with the percent TBSA burn. However, unlike inflammation and cardiac tissue damage, myocardial contractile depression reached a plateau, with maximal myocardial contraction and relaxation defects observed at 40% TBSA burn, which were not further aggravated by a larger (60%) burn.