The importance of burn wound size in determining the optimal calorie:nitrogen ratio

Calorie requirements in hypermetabolic burned patients have been established based on burn size and patient weight. However, the requirement for nitrogen (N), especially with variable open wound sizes, is not clear. Thirty-six adult burned patients were fed with diets containing two different calorie to N (kcal:N) ratios--150:1 (group 1) and 100:1 (group 2)--and N balance was studied with wounds of different sizes. Calorie requirements were calculated with the Curreri formula (25 cal X weight (kg) + 40 Cal X % body surface area [BSA] burned). Daily N balance was calculated from total N intake less total N output (estimated by adding 4 gm to the measured 24-hour urea N production). The data were selected on 233 patient-days when actual calorie intakes were 100% to 150% of the calculated requirement. For a wound size of 1% to 10% BSA, group 1 patients had an N balance of +2.33 gm/day and group 2, +5.54 gm/day. For a wound size of 11% to 30% BSA, N balance was +0.13 and +3.49 gm/day, respectively. For a wound size of 31% to 60% BSA, N balance was -3.38 and +3.88 gm/day, respectively. The traditional 150:1 kcal:N ratio may be adequate for patients with open wounds of less than 10% BSA. Patients with greater than 10% BSA open wounds require a dietary regimen containing a nonprotein kcal: N ratio of 100:1 in order to achieve positive N balance.