The Rule of Nines is a standardized method used in emergency medicine to quickly estimate the total body surface area (TBSA) affected by second-degree and third-degree burns in adult patients. This rapid assessment tool is frequently employed by first responders and emergency department staff. The resulting TBSA percentage informs initial patient management decisions by assigning specific percentage values to major anatomical regions.
The Adult Calculation Method
The system divides the adult body into eleven distinct regions, each representing 9% of the total body surface area, or a multiple of nine. The entire head and neck region accounts for 9% of the TBSA. Each complete upper extremity is also assigned a value of 9%.
The trunk is divided into four sections, with the entire front torso representing 18% and the entire back torso representing another 18%. The entire trunk area accounts for 36% of the total body surface. Similarly, each complete lower extremity is designated 18% of the TBSA.
The remaining 1% of the body surface area is allocated to the perineum. Healthcare professionals calculate the total burn size by adding the percentages of only the burned areas. The full 9% or 18% value is used only if the entire region is affected; otherwise, the total percentage for that region is divided accordingly.
The Necessity of Accurate Assessment
Calculating the Total Body Surface Area (TBSA) affected by a burn is essential for patient stability. The TBSA percentage is the primary variable used to determine the necessary volume of intravenous fluids. This calculation is the basis for fluid resuscitation protocols, such as the Parkland formula, which guides the administration of crystalloid solutions to counteract fluid loss.
Inaccurate TBSA estimates can lead to complications, including over-resuscitation, which causes fluid aggregation and pulmonary edema, or under-resuscitation, which results in shock. The TBSA assessment plays a role in triage decisions, helping personnel determine the severity of the injury. Burns exceeding TBSA thresholds, typically above 20% in adults, require immediate transfer to a specialized burn center.
Adjusting the Rule for Children
The standard Rule of Nines is not accurate for infants and small children because their body proportions differ significantly from adults. A child’s head is proportionally much larger, while their legs are proportionally smaller. Using adult values would overestimate the burn size on the head and underestimate the burn size on the lower limbs.
A modified approach is necessary for pediatric patients to account for changing body geometry. The head and neck of a newborn may account for 18% of the TBSA, double the adult value. Each lower limb in an infant may be assigned a reduced value of around 13.5% or 14%.
The percentages are adjusted based on the child’s age. The head’s percentage decreases by 1% and each leg’s percentage increases by 0.5% each year after the age of one. While the Rule of Nines is a quick field tool for adults, more precise methods like the Lund-Browder chart are preferred in pediatric settings for accurate, age-adjusted TBSA calculation.