The Rule of Nines, also known as the Wallace Rule of Nines, is a tool used by trauma and emergency medicine providers to assess the total body surface area (TBSA) involved in burn patients. Measurement of the initial burn surface area is important in estimating fluid resuscitation requirements since patients with severe burns will have massive fluid losses due to the removal of the skin barrier. This tool is only utilized for second-degree and third-degree burns (also referred to as partial thickness and full thickness burns) and aids the provider in quick assessment to determine the severity and intravenous fluid needs. Alterations to the Rule of Nines may be made based on body mass index (BMI) and age. The Rule of Nines has been shown to be the most frequently recited algorithm by physicians and nurses for estimating burn surface area in numerous studies.
The Rule of Nines estimation of body surface area burned is based on assigning percentages to different body areas. The entire head is estimated as 9% (4.5% for anterior and posterior). The entire trunk is estimated at 36% and can be further broken down into 18% for anterior compnents and 18% for the back. The anterior aspect of the trunk can further be divided into chest (9%) and abdomen (9%). The upper extremities total 18% and thus 9% for each upper extremity. Each upper extremity can further be divided into anterior (4.5%) and posterior (4.5%). The lower extremities are estimated at 36%, 18% for each lower extremity. Again this can be further divided into 9% for the anterior and 9% for the posterior aspect. The groin is estimated at 1%.