116	J. Knighton

8.3.2Local Damage

Local damage varies, depending upon:

(a) Temperature of the burning agent

(b)Duration of contact time

(c)Type of tissue involved Zones of tissue damage:

• Inner zone of coagulation (full-thickness injury) – irreversible cell death, skin grafting needed for permanent coverage

• Middle zone of stasis (deep, partial-thickness injury) – some skin-reproducing cells present in the dermal appendages with circulation partially intact, healing generally within 14–21 days

• Outer zone of hyperaemia (superficial, partial-thickness injury) – minimal cell involvement and spontaneous healing within 7–10 days

8.3.3Fluid and Electrolyte Shifts

The immediate post-burn period is marked by dramatic circulation changes, producing what is known as “burn shock” (Fig. 8.2).

•As the capillary walls begin leaking, water, sodium and plasma proteins (primarily albumin) move into the interstitial spaces in a phenomenon known as “second spacing”.

•When the fluid begins to accumulate in areas where there is normally minimal to no fluid, the term “third spacing” is used. This fluid is found in exudate and blisters.

•There is also insensible fluid loss through evaporation from large, open body surfaces. A non-burned individual loses about 30–50 mL/h. A severely burned patient may lose anywhere from 200 to 400 mL/h.

•Circulation is also impaired in the burn patient due to haemolysis of red blood cells.

•Following successful completion of the fluid resuscitation phase, capillary membrane permeability is restored. Fluids gradually shift back from the interstitial space to the intravascular space, and the patient is no longer grossly oedematous and diuresis is ongoing.

8.4Cardiovascular, Gastrointestinal and Renal System Manifestations

During the hypovolemic shock phase, only vital areas of circulation are maintained.

•Cardiac monitoring is essential, particularly if the patient has a pre-burn history of cardiac problems.

•Electrical burn patients, who arrest at the scene or who experience cardiac arrhythmias post-injury, warrant particular vigilance.