Question

In reviewing each system, discuss characteristics of the acute phase of burn injury.

Answer 1

Characteristics of the acute phase of burn injury.

The acute phase of burn injury is defined as a period extending from the onset of burns with shock to the time taken for wound epithelialization.

Major burns cause massive tissue destruction and result in activation of a cytokine-mediated inflammatory response that show pathophysiologic effects at sites local and distant from the burn. The systemic effects occur in two distinct phases, a burn shock phase and a hypermetabolic phase.

• Generalized edema occurs when the injury exceeds 25–30% total body surface area.
• After major burn injury continued loss of plasma into burned tissue can occur up to the first 48 h or even longer.
• Loss of intravascular fluid into burned areas and formation of edema can quickly result in burn shock with impaired tissue and organ perfusion. Burn shock occurs not only because of depletion of intravascular volume, but also due to elevated systemic vascular resistance and depressed cardiac output. The depressed cardiac output continues for 24–36 h.
• The hypermetabolic and hyperdynamic phase which develops 48 to 72 h after injury is characterized by increased oxygen consumption, carbon dioxide production and protein wasting.
• The onset of sepsis further increases the cardiac output and decreases systemic vascular resistance.

The early phase of burn injury is characterized by,

· The decreased cardiac output and decreased blood flow to all organs. The decreased cardiac output is due to loss of intravascular volume, direct myocardial depression, increased pulmonary and systemic vascular resistance and hemoconcentration, and it can lead to metabolic acidosis and venous desaturation.

· Decreased urine flow results from decreased glomerular filtration and elevated aldosterone and antidiuretic hormone levels.

· Oxygenation and ventilation problems can occur due to inhalation injury and distant effects of burn on airways and lung.

· Compartment Syndrome can occur in abdomen, extremities or orbits without local or circumferential burns.

· Mental status can be altered because of hypoxia, inhaled toxins and/or drugs.

After 48–72 h, the hypermetabolic-hyperdynamic phase starts, characterized by

· Increased oxygen consumption, carbon dioxide production and cardiac output with enhanced blood flow to all organs including skin, kidney and liver and decreased systemic vascular resistance.

· Increased venous oxygen saturation is related to peripheral arteriovenous shunting.

· Lungs and airways may continue to be affected because of inhalation injury and acute respiratory distress syndrome.

· Pulmonary edema can occur due to distant effects of major burn and to reabsorption of edema fluid. The altered mental status may be related to burn itself and concomitant drug therapy.

· Release of catabolic hormones and insulin resistance shows muscle protein catabolism and hyperglycemia.

· The presence of an inhalation injury significantly increases the morbidity and mortality associated with burn injuries.