The Rule of Nine, also known as Wallace’s Rule of Nine, is a tool used in trauma and emergency medicine to assess the total body surface area (TBSA) involved in burn patients

Dealing with an emergency scenario involving the possibility of severe burns results in a certain speed of assessment.

It is therefore important for the rescuer to be equipped with some basic knowledge that will enable him/her to correctly frame the burn victim.

Measuring the initial surface area of the burn is important for estimating fluid resuscitation requirements since patients with severe burns will experience massive fluid loss due to the removal of the skin barrier.

This tool is only used for second- and third-degree burns (also referred to as partial-thickness and full-thickness burns) and assists the provider in the rapid assessment to determine severity and fluid requirements.

Modifications to the Rule of Nine can be made according to body mass index (BMI) and age

The Rule of Nine has proven to be the algorithm most frequently recited by physicians and nurses to estimate burn surface area in numerous studies.[1][2][3]

The Rule of Nine’s estimation of burnt body surface area is based on assigning percentages to different areas of the body.

The entire head is estimated at 9% (4.5% for front and back).

The entire torso is estimated at 36% and can be further divided into 18% for the front and 18% for the back.

The front part of the trunk can be further subdivided into thorax (9%) and abdomen (9%).

The upper extremities total 18% and then 9% for each upper extremity. Each upper extremity can be further subdivided into anterior (4.5%) and posterior (4.5%).

The lower limbs are estimated at 36%, 18% for each lower limb.

Again this can be further subdivided into 9% for the anterior aspect and 9% for the posterior aspect.

The groin is estimated at 1%.[4][5]

Function of the Rule of Nine

The Rule of Nine functions as a tool for assessing the second- and third-degree total body surface area (TBSA) in burn patients.

Once the TBSA is determined and the patient is stabilised, fluid resuscitation can often begin with the use of a formula.

The Parkland formula is often used.

It is calculated as 4 ml intravenous (IV) fluid per kilogram of ideal body weight per TBSA percentage (expressed as a decimal) over 24 hours.

Due to reports of excessive resuscitation, other formulas have been proposed such as the modified Brooke formula, which reduces IV fluid to 2 ml instead of 4 ml.

After establishing the total volume of resuscitation with intravenous fluids for the first 24 hours, the first half of the volume is administered in the first 8 hours and the other half is administered in the next 16 hours (this is converted to an hourly rate by dividing half of the total volume of 8 and 16).

The 24-hour volume time starts at the time of the burn.

If the patient presents 2 hours after the burn and fluid resuscitation has not been started, the first half of the volume should be administered in 6 hours with the remaining half of the fluids being administered as per protocol.

Fluid resuscitation is very important in the initial management of second- and third-degree burns comprising more than 20 per cent of TBSA as complications of renal failure, myoglobinuria, haemoglobinuria and multi-organ failure may occur if not treated aggressively early.

Mortality has been shown to be higher in patients with TBSA burns greater than 20% who do not receive appropriate fluid resuscitation immediately after injury.[6][7][8]

There is concern among clinicians about the accuracy of the Rule of Nine for obese and paediatric populations

The Rule of Nine can best be used in patients weighing more than 10 kilograms and less than 80 kilograms if defined by BMI as less than obese.

For infants and obese patients, special attention should be paid to the following:

Obese patients

Patients defined as obese by BMI have disproportionately large trunks compared to their non-obese counterparts.

Obese patients have closer to 50% TBSA of the trunk, 15% TBSA for each leg, 7% TBSA for each arm and 6% TBSA for the head.

Android-shaped patients, defined as a preferential distribution of trunk and upper body adipose tissue (abdomen, chest, shoulders and neck), have a trunk that is closer to 53% TBSA.

Patients with gynoid shape, defined as preferential distribution of adipose tissue in the lower body (lower abdomen, pelvis and thighs), have a trunk that is closer to 48% TBSA.

As the degree of obesity increases, the degree of underestimation of TBSA involvement of the trunk and legs increases when adhering to the Rule of Nine.

Infants

Infants have proportionally larger heads that alter the surface contribution of other major body segments.

A ‘Rule of Eight’ is best for infants weighing less than 10 kg.

This rule imposes approximately 32% TBSA for the patient’s trunk, 20% TBSA for the head, 16% TBSA for each leg and 8% TBSA for each arm.

Despite the efficiency of the Rule of Nine and its penetration into surgical and emergency medicine specialities, studies show that at 25% TBSA, 30% TBSA and 35% TBSA, the percentage of TBSA is overestimated by 20% compared to computer-based applications.

An overestimation of the TBSA burned can lead to excessive resuscitation with intravenous fluids, giving the possibility of volume overload and pulmonary oedema with increased cardiac demand.

Patients with pre-existing comorbidities are at risk of acute cardiac and respiratory decompensation and should be monitored in the intensive care unit (ICU) during the aggressive phase of fluid resuscitation, preferably in a burn centre.[9][10]

The Rule of Nine is a quick and easy tool used for the initial management of resuscitation in burn patients

Studies have found that after examining the fully undressed patient, the percentage of TBSA can be determined by the Rule of Nine within minutes.

Several studies found in a review of the literature stated that the patient’s palm, excluding the fingers, accounted for approximately 0.5 per cent TBSA and that verification was detected with computer-based applications.

The inclusion of the fingers in the palm accounted for approximately 0.8% TBSA.

The use of the palm, which is the basis on which the Rule of Nine was established, is considered more appropriate for smaller second- and third-degree burns.

It has been noted that the more training a specialist has, the lower the overestimation, especially on minor burns.

Other problems

Due to the inherent nature of error in human burn assessment even in rule setting, computer-based applications available for smartphones are produced to minimise over- and underestimation of TBSA rates.

The applications use standardised sizes of small, medium and obese male and female models.

Applications are also moving towards measurements of newborns.

These computer applications are experiencing variability in the reporting of TBSA rates of up to 60 per cent overestimation of the burned surface up to 70 per cent underestimation.

Intravenous fluid resuscitation guided by the Rule of Nine is only valid for patients with a TBSA percentage above 20% and these patients should be transported to the nearest trauma centre.

With the exception of special areas, such as the face, genitals and hands, which must be seen by a specialist, transfer to major trauma centres is only necessary for more than 20% TBSA burns.

The American Burn Association (ABA) has also defined criteria for which patients should be transferred to a burn centre.

Once fluid resuscitation has begun, it is important to identify whether appropriate perfusion, hydration and renal function are present.

Resuscitation derived from the Rule of Nine and intravenous fluid formula (Parkland, Brooke modified, among others) should be carefully monitored and adjusted as these initial values are guidelines.

The management of severe burns is a fluid process that requires constant monitoring and adjustments.

Lack of attention to detail can lead to increased morbidity and mortality as these patients are critically ill.

The Rule of Nine, also known as Wallace’s Rule of Nine, is a tool used by healthcare professionals to assess the total body surface area (TBSA) involved in burn patients.

The measurement of the initial burn surface area by the healthcare team is important for estimating fluid resuscitation requirements because patients with severe burns have massive fluid losses due to the removal of the skin barrier.

The activity updates healthcare teams on the use of the Rule of Nine in burn victims that will produce better outcomes for patients. [Level V].

Bibliographic references

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