Estimating the size of burns can be difficult to do well. The percentage of total surface area affected is an important figure as it has bearing on whether or not the patient should be referred to a specialist Burns Centre for management. It is also used to decide if patients require intravenous fluids and in formulae to calculate the requirements for fluid resuscitation. It is relatively difficult to measure the surface area of an irregularly shaped three dimensional object at any time and pretty much impossible in an acute situation with an unwell patient. It may also be difficult to differentiate simple erythema from partial thickness burns in the immediate presentation.
There are four main methods of estimating the percentage of a patients body surface area that is involved in a burn: Lund and Browder charts form a fairly detailed diagram with percentage surface areas of different parts of the body, dependent on age, that can be combined for a total figure(1); the Rule of Nines chart splits the body into 11 areas of 9% and the perineum makes up the final 1%(3); serial halving invoves dividing the surface area of the patient into areas of 50% and deciding if the burn covers more or less than this area. This process is continued for a further two times if necessary to get an approximate value of the percentage surface area affected; for smaller areas the palmar surface of the patient’s hand is taken to represent 1% of their total body surface area and used to aid estimation.
There have also been a couple of studies using computers to calculate the surface area affected from an image of the patient. Although there are several papers comparing different groups of physicians estimates for percentage areas of burns there were only a few papers, found in this search, directly comparing the different methods used.
Due to the impracticality of having several physicians independently assess a real patient with burns, various alternatives were used. Various gold standards were used, the best of which involved measuring the surface area of the burn, although event these studies used formulae to calculate the overall surface area rather than measuring it directly.
The literature suggested that there was significantly less variation in the estimates made using the Lund and Browder chart from the schematic burns than using the Rule of Nines technique, although the variation remained substantial. There also appeared to be less variation and greater accuracy in documenting the size of the burns graphically than in converting this to a percentage surface area.
The ‘rule of nines’ technique appears to be quicker to use and does not require a special chart as long as the physician can recall the attributed surface areas percentages. Serial halving provides a very approximate result which can be used quickly in the field to establish whether or not intravenous access is required with reasonable consistency. Once a burn has been mapped to a two-dimensional diagram then a computer or planimeter can accurately calculate the percentage surface area affected. Interestingly, when this technique is used to measures the surface areas of the different regions on a blank Lund and Browder chart, they do not correspond with the values that they are purported to represent. This intrinsic error means that there is a limit to how accurately the chart could ever be interpreted. It is not difficult to imagine a computer program than could provide a manipulatable three-dimensional figure on screen that could be drawn onto and provide an estimate of percentage burn size based on the height, weight and age of the patient. This may improve the accuracy and consistency of estimates but would require access to the computer and software and may still leave problems of documentation in the medical notes and communication with other hospitals.
The question that leads on from this discussion is whether more accurate assessment of burn size would actually result in an clinical benefit for patients or whether an rough estimate and then titration of treatment according to response is as good.
Clinical Bottom Line:
The Lund and Browder chart allows more consistent estimates of percentage surface area from drawings of burns than the Rule of Nines. No evidence was found of a benefit of one form of estimation over another in clinical practice.