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Physical trauma is the sudden and supraphysiological transfer of mechanical energy to the body. The kinetic energy E = ½mv² is the fundamental physical parameter: the higher the impact speed or the greater the mass, the greater the potential for damage. The impact duration t is equally critical: the same energy absorbed in 1 ms (high-speed impact) produces forces 100× greater than in 100 ms (low-speed fall).

Bone fracture occurs when the mechanical stress exceeds _fracture, which depends on the microstructural integrity of the bone (size of pre-existing microcracks a_crack) and its material properties (E_bone, _s). Griffith fracture mechanics explains why osteoporotic bone fractures with lower energy: thinned trabeculae create stress concentrators (higher effective a_crack) that reduce _fracture by 3050%.

Hemorrhage is the most immediate vascular consequence of trauma. The loss rate follows Hagen-Poiseuille: Q r, so the section of the broken glass exponentially determines the gravity. The ATLS classification of hemorrhage (I: < 15%, II: 1530%, III: 3040%, IV: > 40% blood volume) guides replacement. The initial compensatory response (reflex vasoconstriction, tachycardia) maintains blood pressure up to losses of 30%.

The Monro-Kellie doctrine states that intracranial volume is fixed (rigid skull): blood + CSF + parenchyma = constant. An epidural or subdural hematoma of only 2550 mL can raise ICP to > 20 mmHg, compromising cerebral perfusion (CPP = MAP - ICP; normal CPP > 60 mmHg). Intracranial C_IC compliance is high in early stages (CSF is displaced) and drops sharply when compensatory mechanisms are exhausted.

The lethal triad of severe trauma (hypothermia + acidosis + coagulopathy) is a vicious circle: hypothermia (T < 34°C) reduces the enzymatic activity of coagulation factors (Q10 2, so at 32°C clotting times double), which aggravates bleeding; bleeding causes hypothermia and acidosis. Damage control (rapid surgery to control bleeding, balanced replacement with plasma/platelets/RBC in a 1:1:1 ratio, active rewarming) interrupts this cycle.

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