From the Guidelines
The bimodal injury course of Traumatic Brain Injury (TBI) is characterized by a primary injury caused by the initial physical impact, and a secondary injury that develops hours to days later due to a cascade of biochemical and cellular events. The primary injury, which occurs at the moment of impact, includes direct mechanical damage such as contusions, lacerations, hemorrhage, and axonal shearing, and is irreversible 1. This initial damage is determined by the physics of the traumatic event.
Key Aspects of TBI Injury Course
- The secondary injury phase involves a complex interplay of inflammation, excitotoxicity, oxidative stress, mitochondrial dysfunction, and apoptosis, leading to progressive neuronal damage, cerebral edema, increased intracranial pressure, and potential ischemia 1.
- Understanding the distinction between primary and secondary injuries is crucial for optimizing TBI management, as primary injuries can only be prevented through safety measures, while secondary injuries can potentially be mitigated through proper medical management.
- Proper medical management includes maintaining adequate cerebral perfusion, controlling intracranial pressure, preventing hypoxia and hypotension, and providing neuroprotective treatments, such as targeted temperature control (TTC) to prevent further brain injury and improve neurological outcome 1.
Clinical Implications
- The secondary injury phase represents a window of opportunity for therapeutic intervention, and healthcare providers should prioritize interventions that address the underlying pathophysiological mechanisms of secondary injury.
- The use of TTC, which aims to control body or brain temperature, can modulate important physiological parameters such as cerebral metabolism and intracranial pressure, and may improve long-term outcomes in patients with TBI 1.
From the Research
Bimodal Injury Course of TBI
The bimodal injury course of Traumatic Brain Injury (TBI) refers to the two distinct phases of injury that occur after a TBI.
- The primary injury occurs at the time of the initial trauma, resulting in immediate damage to the brain tissue 2.
- The secondary injury occurs in the hours and days following the primary injury, resulting from a complex series of pathophysiological changes that can exacerbate the initial damage 2.
Pathophysiological Changes
The pathophysiological changes that occur after a TBI can be characterized into three distinct phases: early, intermediate, and late phases.
- The early phase is characterized by energy depletion and cell death secondary to excitotoxicity 2.
- The intermediate phase is characterized by neuroinflammation 2.
- The late phase is characterized by increased susceptibility to seizures and epilepsy 2.
Treatment and Management
Current treatments of TBI are aimed at ameliorating secondary insults arising from the injury, and have been tailored to these distinct pathological stages with some overlap 2.
- Hyperosmolar therapy, which includes mannitol or hypertonic saline, is frequently administered to reduce intracranial pressure (ICP) 3, 4, 5.
- The choice between mannitol and hypertonic saline is still a topic of debate, with some studies suggesting that hypertonic saline may be more effective in reducing ICP and improving outcomes 3, 4.