Plasma free hemoglobin: a novel diagnostic test for assessment of the depth of burn injury.

BACKGROUND Accurate determination of the depth of burn injury is difficult, even for experienced surgeons. The authors hypothesized that the level of plasma free hemoglobin following burn injury is correlated to the depth of burn injury, and they evaluated this hypothesis in a murine model. METHODS Full-thickness and partial-thickness burn injuries of varying sizes were inflicted on 38 and 36 male Wistar rats, respectively. Blood specimens were taken at 0, 15, 30, 45, and 60 minutes after burn injury, and the levels of plasma free hemoglobin were determined spectrophotometrically. RESULTS Full-thickness burns cause two times more hemolysis than partial-thickness burns (p < 0.05). A linear correlation was demonstrated between plasma free hemoglobin levels and total body surface area burned in both the full-thickness (r = 0.91, p < 0.001) and partial-thickness burn groups (r = 0.94, p < 0.001). The correlation between the quantity of hemolysis and the total body surface area burned was strongest at 15 minutes after the onset of burn injury. The levels of free hemoglobin peaked rapidly between 15 and 30 minutes after thermal injury and declined thereafter. CONCLUSIONS The authors' data suggest that the level of plasma free hemoglobin after burn injury is related to the size and depth of burn injury. This test can potentially be a valuable diagnostic adjunct in the assessment of burns.