Burn Size Predicts Hypermetabolic Response that Drives Mortality Risk

GALVESTON, Tex., Aug. 23 -- Burn-associated morbidity and mortality in children are driven by an increased hypermetabolic and inflammatory reaction and impaired cardiac function related to burn size.

As the surface area of the burn increased, so did the number of operations, incidence of infection and sepsis, and mortality, Marc G. Jeschke, M.D., Ph.D., of Shriners Hospitals for Children here, and colleagues, reported online in Critical Care.

Patients with 80% or greater total body surface area involvement had the highest resting energy expenditure, followed by patients with 60-79% body surface burns, they said.

Urine cortisol concentration increased with burn size and was associated with significant myocardial depression and change in liver size, the researchers found. Cytokine expression also differed according to burn size.

"Based on our findings, we suggest that a burn injury involving more than 80% of the total body surface causes marked and prolonged inflammation, marked increases in hypermetabolism, catabolism, cardiac dysfunction and subsequently higher incidences of infection, sepsis, and death," the authors concluded.

"Treatment should focus on several aspects of the pathophysiologic events postburn, such as treatment of the inflammatory response, insulin resistance, hypermetabolism, catabolism, and cardiac dysfunction," they added.

Many studies have shown that as burn size increases, so does mortality risk. Burn size also has been posited as the major determinant of hypermetabolism. However, the principal contributor to the increased mortality risk -- inflammation, hypermetabolism, or other pathophysiologic factors -- had not been determined.

Dr. Jeschke and colleagues reviewed data on 189 pediatric burn patients admitted to their hospital's burn unit over nine years and who required at least one surgical intervention. Patients were resuscitated by means of a locally developed formula, and all patients underwent total burn wound excision within 48 hours of admission.

Skin grafting, followed by additional surgery, continued until all open wound areas were covered with autologous skin material.

All patients received the same nutritional support in accordance with a standardized protocol.

Resting energy expenditure was measured within one week of admission, at two to four weeks, at discharge, and at six months postburn. A measurement of resting energy expenditure at discharge from the hospital was used to determine the degree of hypermetabolism when burn wounds were 95% healed.

Blood or urine specimens were used to measure serum and urine hormone, protein, and cytokine levels. Measurements were taken at admission, preoperatively, and then every five days postop for four weeks. A commercial assay was used to measure expression of 17 inflammatory mediators. Cortisol was measured by standard laboratory techniques.

Patients also underwent serial ultrasound evaluations to assess changes in the liver and heart.

The study population comprised 43 patients with involvement of < 40% of total body surface area, 79 with 40-59% involvement, 46 with 60-79%, and 21 burns of 80% or more.

Predicted resting energy expenditure for children with burns < 40% was increased only slightly and returned to the normal range at six months.

Those with burns of 40-59% and 60-79% had significantly greater predicted energy expenditure compared with children with < 40% (P

Cardiac output, predicted cardiac output, and stroke volume were all significantly decreased in patients with burns >80 (P60%, reaching a maximum of 150%. In contrast, patients with burns < 40% surface area had a rapid decrease in liver size.