Area

The severity of the injury is usually approximated to the burn surface area (BSA) as a
percentage of the total body surface area, though this does not take into account the
burn depth or any pulmonary injuries. In crude terms, the larger the burn, the more
severe the injury, and the greater the degree of inflammatory response to fluid shift
from the intravascular compartment to the tissues—hence the burn surface area is
used to assess the risk of developing hypovolaemic shock.
• The body is divided into regions of 9% total body surface area (head and neck,
upper limbs) or 18% (lower limbs, front of trunk and back of trunk) and 1%
(perineum).
• Wallace’s rule of nines is easy to remember, but is only an approximation (it tends
to overestimate the size of the burn). It is unsuitable for children (different body
proportions), except when modified.
• Patient’s palm area (the palmar surface of both the anatomical palm and the closed
fingers) is taken as 1% of the total body surface area. This is good for patchy
burns, but is only an approximation (the area is nearer 0.8% of the body area).
This method is not suited for burns larger than 10% of the total body surface area.

• Burns charts, e.g. the Lund and Browder chart, take account of different body proportions
with age and provide a permanent visual record of the area and the depth
of the burn.
Erythema (associated with first-degree burns) is not included in the assessment as it
represents intra-epidermal damage with little irreversible damage or pathological
insult, and heals without scarring.