- The primary physiological response immediately following a traumatic injury is a catecholamine surge.
- This occurs as the body rapidly activates the sympathetic nervous system to prepare for the "fight or flight" response, leading to increased heart rate, blood pressure, and energy mobilization.
- This surge happens within seconds to minutes and is critical for maintaining perfusion and oxygen delivery to vital organs.
- Other responses like inflammation and coagulation occur slightly later.

Reference: Schwartz’s Principles of Surgery, 11th Edition, Chapter 2, Page 34