Slide 1
Burns
Pathophysiology TypesDegreePerCentage 62019
Pathophysiology Burns are tissue injuries resulting from direct
contact with flames, hot liquids, gases, or surfaces; chemicals;
electricity; or radiation. Most commonly, the skin is injured,
which compromises its function as a barrier to injury and infection
and as a regulator of body temperature, fluid loss, and
sensation.However it can damage airway and lungs with life
threatening consequenses.Airway injuries Respiratory system injury
Amount of tissue destruction depends on time of exposure and
temperature. It takes 6 hours for skin maintained at 44c to suffer
irreversible changes, but surface temp of 70c for 1 second is all
needed to produce epidermal destruction.
At temperatures greater than44 C(111F), proteins begin losing
their three-dimensional shape and start breaking down. This results
in cell damage. The direct health effects of a burn are usually
secondary to those caused by the disruption in the normal
functioning of the skin. The skin has a number of important
functions including: prevention of water loss through evaporation,
temperature control, and sensation. Disruption of cell membranes
causes cells to lose potassium to the spaces outside the cell and
to take up water and sodium. This results in tissueedema.Damage to
the cells may also result in the release of pro-inflammatory
mediators.Water loss leads to blood becoming more concentrated.
Burned skin activates a web of inflammatory cascades.The release of
neuropeptides and activation of complement are initiated by the
stimulation of pain fibres and alteration of proteins by heat. On a
cellular level, complement causes degranulation of mast cells and
coats the protein altered by the burn.This atttracts neutrophils,
which also degranulate,with release of large quantities of free
radical and proteases.These can further damage the tissue.Mast cell
also release primary cytokines such as tumor necrosis factor alpha
.These act as chemotactic agents to inflammatory cells and
subsequent release of many secondary cytokines.These inflamatory
factors alter the permeability of blood vessels. The increased
permeability is such that large protein molecules escapes with
ease.
The damaged collagen and these extravasted protein increase the
oncotic pressure within the burned tissue, further increasing the
flow of water from intravascular space to extravascular space.The
flow occurs over first 36 hours after injury but does not include
RBC.The volume of fluid lost is dircetly proportional to area of
burn.In small burn these reaction is localized but when it
approaches 10-15% of total body surface area, loss of intravascular
fluid can cause a level of circulatory shock. If it is more than
25% of TBSA, then inflammation occurs even in the blood vessels
remote to the burn, causing greater fluid loss.
Degreeof burnsFirst-degree burns are limited to the epidermis.
The skin is painful and red. There are no blisters. These burns
should heal spontaneously in 3 to 4 days.
Second-degree burns, which are subdivided into superficial and
deep partial- thickness burns, are limited to the dermal layers of
the skin. Superficial partial-thickness burns involve the papillary
dermis. They appear red, warm, edematous, and blistered, often with
denuded, moist, mottled red or pink epithelium. The injured tissue
is very painful, especially when exposed to air. Such burns
frequently arise from brief contact with hot surfaces, liquids,
flames, or chemicals. superficial partial thickness
Deep partial-thickness burns involve the reticular dermis and
thus can damage some dermal appendages (e.g., nerves, sweat glands,
or hair follicles). Hence, such burns can be less sensitive, or
hairs may be easily plucked out of areas with deep
partial-thickness burns. Nonetheless, the only definitive method of
differentiating superficial and deep partial-thickness burns is by
length of time to heal. Superficial burns heal in less than 2 weeks
without residual scarring; deep ones require at least 3 weeks and
usually lead to hypertrophic scarring. Furthermore, any
partial-thickness burn can convert to full-thickness injury over
time, especially if early fluid resuscitation is inadequate.
Full-thickness (third- or fourth-degree) burns involve all
layers of the skin and some subcutaneous tissue. In third-degree
burns, all the skin appendages, including hair follicles and sweat
and sebaceous glands, and sensory fibers for touch, pain,
temperature, and pressure are destroyed. This results in an
initially painless, insensate dry surface that may appear either
white and leathery or charred and cracked, with exposure of
underlying fat. Fourth-degree burns also involve fascia, muscle,
and bone. They often result from prolonged contact with thermal
sources or high electrical current. All full-thickness burns are
managed surgically, and immediate burn expertise should be
sought
TypesMajor burnModerate burnMinor burnSize-Partial
Thickness>25% adults>20% children15-25% adults 10-20%
children
