Physiologic Responses to Trauma, Burns, and Inflammation
Core concepts
The injured patient mounts a stereotypic stress response: sympathetic activation with catecholamine surge, hypothalamic-pituitary-adrenal axis activation with cortisol release, and a cytokine cascade (TNF, IL-1, IL-6) producing fever, catabolism, and capillary leak. The ebb phase (hypoperfusion, low metabolic rate) transitions to the flow phase (hypermetabolism, hyperglycemia, negative nitrogen balance, sodium and water retention). Burn injury adds massive evaporative losses, hypermetabolic demand, and a systemic inflammatory response proportional to burn size; resuscitation formulas (e.g., weight- and burn-size-based crystalloid) are starting points, not endpoints, and urine output guides titration.
Trauma physiology includes the lethal triad (hypothermia, acidosis, coagulopathy), now often framed as a lethal diamond with hypocalcemia, and the rationale for damage-control resuscitation: permissive hypotension in uncontrolled hemorrhage, balanced blood products, calcium repletion, and rapid hemorrhage control. Candidates must understand why aggressive crystalloid worsens outcomes (dilutional coagulopathy, edema, abdominal compartment syndrome).
Traps
Questions test the difference between the ebb and flow phases, the misconception that burn formulas are rigid prescriptions, and the error of normalizing blood pressure before hemorrhage control. Another trap is missing that hypocalcemia from citrate and shock impairs clotting.
Worked rule of thumb
In a hypotensive trauma patient with suspected active bleeding, prioritize blood products and operative or angiographic control over large crystalloid boluses; permissive hypotension is acceptable until hemorrhage is controlled, except in traumatic brain injury where cerebral perfusion pressure must be protected. Rule: stop the leak first, then restore volume and temperature.
Exam strategy
Map each intervention to the phase of injury response and ask whether it addresses the mechanism (hemorrhage, leak, catabolism) or merely the number.