What is the chemical mediator in a scald burn?

Chemical Mediators in Thermal Burns

Histamine is the primary chemical mediator in a spilled hot water burn (scald burn).

Pathophysiology of Thermal Burns

Thermal burns from hot water (scald burns) trigger an immediate inflammatory cascade characterized by several key events:

1. Initial mediator release: When tissue is exposed to heat, mast cells degranulate and release histamine as the earliest chemical mediator 1, 2

2. Vascular response sequence:

   • Histamine causes the earliest stage of vasodilation and increased microvascular permeability 2
   • This leads to rapid edema formation at the burn site
   • The inflammatory response progresses with subsequent release of other mediators

3. Secondary mediator cascade:

   • Following histamine release, additional mediators are activated:
     • Bradykinins
     • Prostaglandins
     • Thromboxanes
     • Leukotrienes 3, 2

Evidence for Histamine as Primary Mediator

The evidence strongly supports histamine as the primary chemical mediator in scald burns:

• Histamine is responsible for the "earliest stage of vasodilation and increased venous permeability" following thermal injury 2
• The European Respiratory Journal guidelines specifically identify histamine as being released first in the inflammatory cascade triggered by thermal injury 1
• In burn shock pathophysiology, histamine is listed first among the kinins released into the bloodstream as a result of burns 3

Role of Other Mediators

While histamine is the primary initial mediator, other chemical mediators play important roles in the burn response:

• Bradykinins: Released after histamine and contribute to ongoing pain and inflammation 3, 4
• Prostaglandins: Formed through arachidonic acid metabolism and potentiate the plasma exudation produced by histamine 5, 2
• Thromboxanes: Contribute to the inflammatory cascade but are not the initial mediators 3
• Serotonin: Released alongside histamine but plays a secondary role 3

Clinical Implications

Understanding histamine as the primary mediator in scald burns has important clinical implications:

• Cooling therapy: Immediate cooling of burns helps limit the histamine-mediated inflammatory response 1
• Pain management: The histamine-initiated cascade contributes significantly to burn pain, requiring multimodal analgesia 6
• Fluid resuscitation: The histamine-triggered increase in vascular permeability necessitates appropriate fluid management in severe burns 6

Common Pitfalls

• Focusing only on later mediators: While prostaglandins and bradykinins are important in the ongoing inflammatory response, histamine is the initial mediator that triggers the cascade
• Overlooking the temporal sequence: The burn response involves a sequence of mediator release, with histamine being the earliest
• Confusing primary vs. potentiating mediators: Prostaglandins primarily potentiate the effects of histamine rather than initiating the response 5

Therefore, among the options presented (Serotonin, Bradykinins, Thromboxane, Prostaglandins), histamine is the primary chemical mediator in a spilled hot water burn.