Burn-depth teaching: The toast analogy and colour changes

Abstract

Burn depth is a difficult topic to teach for several reasons. Depth is dynamic, and can change over time. This change in depth over time is called burn-depth conversion. Several factors affect this conversion, adding to the complexity of depth assessment. As the dermis is white, a piece of white bread will be used in this analogy. Just as white bread is soft, floppy and moist with some stretch before going into the toaster, so is the skin soft, stretchable and moist in the dermis. Once the white bread begins toasting, the following colour changes occur: light yellow, light brown, dark brown and then black. The white dermis of the skin goes through similar colour changes when burned. Toasted white bread also loses more of its moistness and elasticity as it is increasingly toasted. The same happens in the skin. It loses its elasticity and moistness, and so a full-thickness burn (eschar) has to be cut open (-otomy; escharotomy) to accommodate stretch from swelling, or to allow mobility of joints or functional structures, or the chest wall. To understand the colour changes in the dermis, the vascular plexus in the superficial dermis must be considered. The blood colour is red in the superficial dermis, and mixed with the white of the dermis, it will appear pink. Capillary refill time will be rapid in superficial partial-thickness areas, and this is considered an important clinical test to increase the accuracy of depth assessment. As the burn goes deeper than the vascular plexus, the normal whiter/paler colour of the dermis will appear. Changes will then be reflected by the toast analogy: yellow, then brown, then black. As burn depth is difficult for students to learn and grasp, the toast analogy may help in the teaching of the topic. Understanding the dynamic nature of burn depth is important, as is understanding the importance of, and being able to use, the diagnostic clinical tests for burn depth, such as the capillary refill test, to increase the accuracy of the assessment.