A6 Physical trauma

Topic

Physical trauma occurs when the body suddenly receives an amount of mechanical energy exceeding what its tissues can tolerate. The energy transferred depends on the object's mass and, especially, its velocity: the greater both are, the greater the potential damage. The duration of the impact also matters. The same amount of energy transferred over a very brief interval generates much greater forces than when distributed over a longer period; consequently, high-speed impacts can cause particularly severe injuries.

When this force acts upon a bone, a fracture occurs if the mechanical stress exceeds the bone's strength. This limit depends on bone microstructure and pre-existing microcracks; the more extensive these alterations, the less force is required to fracture the bone. In osteoporosis, the deterioration of the internal structure significantly reduces strength, making it possible for forces that a healthy bone would tolerate to cause a fracture.

Trauma can also rupture blood vessels and cause hemorrhage. The rate of blood loss is highly sensitive to the size of the vascular injury: small increases in the diameter of the damaged section can significantly increase the volume of blood lost. Therefore, the severity depends largely on the size of the injured vessel and the proportion of total blood volume lost. Initially, the body compensates through peripheral vasoconstriction and an increased heart rate, maintaining blood pressure despite the loss of volume. When the hemorrhage approaches a very large fraction of the blood volume, these mechanisms are no longer sufficient, and blood pressure begins to drop.

Head trauma presents an additional problem because the skull constitutes a rigid space with a virtually fixed volume. According to the Monro-Kellie doctrine, blood, cerebrospinal fluid, and brain tissue must share this volume. If a hematoma develops, the body can initially compensate by displacing cerebrospinal fluid out of the skull, thereby limiting the rise in pressure. However, this capacity is finite. Once this capacity is exhausted, even small additional increases in volume can cause a sharp rise in intracranial pressure.

Increased intracranial pressure also reduces the effective pressure driving blood to the brain. Consequently, a hematoma causes damage not only by occupying space but also by progressively compromising cerebral perfusion as intracranial pressure approaches the level required to maintain cerebral blood flow.

In cases of severe trauma, hemorrhage can trigger a vicious cycle known as the "lethal triad" of trauma. Blood loss and exposure promote hypothermia; a drop in temperature reduces the activity of coagulation enzymes, making it harder to stop the bleeding. At the same time, poor perfusion fosters the accumulation of acid in the body. Thus, hemorrhage, hypothermia, and acidosis reinforce one another: bleeding worsens temperature and perfusion, while these alterations impair coagulation and allow the bleeding to continue.

Treatment for severe trauma aims to rapidly break this cycle using a damage-control strategy. The initial priority is to stop the source of bleeding through rapid procedures, deferring more complex repairs until the patient is stabilized. Blood replacement involves a balanced combination of blood components, while active rewarming attempts to correct hypothermia and restore effective coagulation. This approach allows for simultaneous intervention against several components of the lethal triad.

Overall, the severity of the trauma depends on the energy and duration of the impact, the resilience of the affected tissues, and the secondary consequences that develop after the injury. The mechanical threshold determines whether a bone fractures; the size of the injured vessel dictates the extent of the hemorrhage; the rigid volume of the skull turns small increases in contents into potentially critical spikes in pressure; and the interplay between hemorrhage, hypothermia, and acidosis can transform an initial injury into a state of progressive deterioration. The treatment aims to control these alterations before their feedback mechanisms overwhelm the body's capacity to compensate for them.

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