Influence of the burn wound on local and systemic responses to injury

Abstract

Total resting leg blood flow, measured by venous occlusion plethysmography; leg oxygen consumption; substrate turnover; and leg surface temperature were determined in 21 nonseptic burn patients and four normals. The patients studied during the second to third week postinjury sustained total body surface injuries averaging 45% (range 12-86%) and leg injuries of 35% total leg surface (0-82.5%). To integrate the peripheral metabolic and circulatory events with the systemic responses to injury, total body oxygen consumption, cardiac output, rectal and mean skin temperatures were also measured. Leg blood flow and leg surface temperature generally increased with total burn size but did not correlate with cardiac output, total body oxygen consumption, or body temperature. However, leg blood flow was closely related to the extent of the leg burn (r(2) = 0.73). To evaluate the metabolic determinants of the wound blood flow, patients were matched for burn size (40.5% total body surface in one group vs. 42%), resulting in similar systemic responses to injury (cardiac index 7.8 +/- 0.7 L/min m(2) vs. 7.5 +/- 0.8, VO(2) 204 +/- 12 ml/min m(2) vs. 241 +/- 22, rectal temperature 38.5 +/- 0.3 degrees vs. 38.3 +/- 0.3 degrees , NS). One group (n = 7) had extensive leg burns (58% of the leg surface), the other (n = 9) minimal leg injuries (9.5%). Leg oxygen consumption was similar in the two groups (0.24 +/- 0.01 ml/100 ml leg min vs. 0.19 +/- 0.04, NS), although leg blood flow was markedly increased in the injured extremities (8.0 +/- 0.5 ml/100 ml leg min vs. 4.2 +/- 0.4, p < 0.001). Glucose uptake and lactate production were enhanced in the burned extremities (glucose 0.34 +/- 0.08 mg/100 ml leg mmn vs. 0.04 +/- 0.03, p < 0.01, lactate 0.30 +/- 0.08 mg/100 ml leg min vs. 0.06 +/- 0.06, p < 0.05) and related in a general manner with size of the leg burn. Increased peripheral blood flow following injury is directed to the wound and unrelated to aerobic metabolic demands of the extremity. The selectively perfused wound consumes glucose and produces lactate. The increased systemic cardiovascular and metabolic responses to thermal injury are essential for the enhanced circulatory and anaerobic demands of the healing wound.