Burn shock is a severe, life-threatening complication that develops rapidly following major thermal injuries. It is a form of hypovolemic shock, characterized by a dangerously low volume of circulating blood. This condition is distinct from simple blood loss due to the unique physiological response to the burn itself, causing a massive shift of fluid out of the bloodstream. This fluid loss ultimately impairs the body’s ability to deliver oxygen and nutrients to vital organs, requiring timely recognition and aggressive management to prevent multi-organ failure.
Understanding Burn Shock: Definition and Thresholds
Burn shock is defined as a state of circulatory collapse resulting from the profound fluid imbalance that occurs after an extensive burn injury. This condition is a direct consequence of the body’s reaction to thermal trauma and subsequent systemic inflammation. It is associated with second-degree (partial thickness) or third-degree (full thickness) burns covering a significant portion of the body’s surface area.
The threshold for developing burn shock is determined by the Total Body Surface Area (TBSA) affected by the burn. In adults, fluid resuscitation is initiated for burns exceeding 15% to 20% TBSA, where the systemic response becomes overwhelming enough to cause shock. Children and elderly patients are more susceptible, often requiring intervention for burns greater than 10% TBSA. Understanding the TBSA calculation is a fundamental step in initial burn care, as the goal is to prevent this state from fully developing.
The Role of Capillary Leak in Systemic Failure
The pathology of burn shock centers on a widespread breakdown of the vascular barrier, known as the capillary leak phenomenon. When a large area is burned, the injury triggers a massive systemic inflammatory response. This reaction involves the immediate release of inflammatory mediators, such as histamine, prostaglandins, and cytokines, both at the injury site and throughout the circulation.
These chemical messengers act on the lining of blood vessels, causing endothelial cells to separate and junctions to widen. This dramatic increase in capillary permeability allows plasma, the fluid component of blood, to rapidly leak out of the intravascular space into surrounding interstitial tissues. Crucially, this fluid loss includes large plasma proteins, which drastically reduces the oncotic pressure inside the blood vessels. The resulting imbalance between hydrostatic and oncotic pressures favors fluid movement out of the circulation, leading to severe edema and profound hypovolemia. This rapid loss of circulating volume is the direct cause of the circulatory impairment characteristic of burn shock.
Recognizing the Critical Signs and Monitoring
The patient’s physical presentation provides observable indicators that burn shock is developing. As circulating blood volume diminishes, the cardiovascular system attempts to compensate by increasing heart rate, resulting in tachycardia. This compensation is often insufficient, leading to hypotension (a drop in blood pressure) as the heart struggles to pump an adequate volume.
Reduced blood flow to the brain can manifest as neurological changes, such as confusion, disorientation, or unconsciousness. The most reliable sign of poor organ perfusion is a sharp reduction in urine output, known as oliguria. When kidneys do not receive sufficient blood flow, they conserve fluid, leading to output significantly below the normal rate. Monitoring the hourly urine output is a standard practice, providing a real-time assessment of whether vital organs are adequately supplied with blood.
Immediate Medical Intervention and Resuscitation
Treatment for burn shock must be swift, focusing on restoring lost intravascular volume through aggressive fluid resuscitation. Emergency medical protocols prioritize establishing intravenous (IV) access to begin delivering large volumes of fluid immediately. Crystalloid solutions, such as Lactated Ringer’s, are the preferred fluid choice for this initial phase.
Medical teams use specific formulas to calculate the estimated fluid volume required over the first 24 hours to prevent or reverse the shock state. The most recognized is the Parkland formula, which uses the patient’s weight and the calculated Total Body Surface Area (TBSA) of the burn to determine the total fluid amount. Half of this volume is administered during the first eight hours following the injury, with the remaining half delivered over the subsequent 16 hours. Resuscitation success is continuously measured by monitoring the patient’s response, aiming to achieve a target urine output, typically 0.5 milliliters per kilogram of body weight per hour for adults, ensuring adequate tissue perfusion.