Understanding TBI

Traumatic brain injury (TBI) refers to damage to the brain caused by an external physical force such as a car accident, a gunshot wound to the head, or a fall. A TBI is not caused by something internal such as a stroke or tumor, and does not include damage to the brain due to prolonged lack of oxygen (anoxic brain injuries). It is possible to have a TBI and never lose consciousness. For example, someone with a penetrating gunshot wound to the head may not lose consciousness.

Commonly accepted criteria established by the TBI Model Systems (TBIMS) to identify the presence and severity of TBI include:

Damage to brain tissue caused by an external force and at least one of the following:

• A documented loss of consciousness
• The person cannot recall the actual traumatic event (amnesia)
• The person has a skull fracture, post-traumatic seizure, or an abnormal brain scan due to the trauma

A TBI can range from mild to severe in effect. The TBI Model System program focuses on those with moderate to severe TBI that requires participation in rehabilitation. Much of the information provided below focuses on those with moderate-severe TBI.

Statistics from Centers for Disease Control and Prevention for 2007 to 2013 indicate that the leading cause of brain injury is falls (47%). This is followed by being hit by or against an object (15%) and car crashes (14%). Many of these injuries are mild. If you focus only on moderate to severe TBI (those that may require admission to a neurointensive care unit), falls are the most common cause of TBI, followed by car crashes and assaults.

 Types of injuries

The brain is about 3-4 pounds of extremely delicate soft tissue floating in fluid within the skull. Under the skull there are three layers of membrane that cover and protect the brain. The brain tissue is soft and therefore can be compressed (squeezed), pulled, and stretched. When there is sudden speeding up and slowing down, such as in a car crash or fall, the brain can move around violently inside the skull, resulting in injury. 

 Closed versus open head injury

Closed means the skull and brain contents have not been penetrated (broken into or through), whereas open means the skull and other protective layers are penetrated and exposed to air. A common example of an open head injury is a gunshot wound to the head. A common closed head injury is one that occurs as the result of a motor vehicle crash.In a closed head injury, damage occurs because of a blow to the person's head or having the head stop suddenly after moving at high speed. This causes the brain to move forward and back or from side to side, such that it collides with the bony skull around it. This jarring movement bruises brain tissue. When brain injury occurs at high speed, the brain rotates inside the skull. This type of rotational movement damages axons (part of the nerve cell), and blood vessels by stetching and tearing them. After a closed head injury, damage can occur in specific brain areas (localized injury) or throughout the brain (diffuse axonal injury).Damage following open head injury tends to be localized and therefore damage tends to be limited to a specific area of the brain. However, such injuries can be as severe as closed head injuries, depending on the destructive path of the bullet or other invasive object within the brain.    

 Measuring the severity of TBI

"Severity of injury" refers to the degree or extent of brain tissue damage. The degree of damage is estimated by measuring the duration of loss of consciousness, the depth of coma and level of amnesia (memory loss), and through brain scans.

The Glasgow Coma Scale (GCS) is used to measure the depth of coma. The GCS rates three aspects of functioning: eye opening, movement and verbal response. Individuals in deep coma score very low on all these aspects of functioning, while those less severely injured or recovering from coma score higher. A GCS score of 3 indicates the deepest level of coma, describing a person who is totally unresponsive. A score of 9 or more indicates that the person is no longer in coma, but is not fully alert. The highest score (15) refers to a person who is fully conscious.

A person's first GCS score is often done at the roadside by the emergency response personnel. In many instances, moderately to severely injured people are intubated (a tube is placed down the throat and into the air passage into the lungs) at the scene of the injury to ensure the person gets enough oxygen. To do the intubation the person must be sedated (given medication that makes the person go to sleep). So, by the time the person arrives at the hospital he/she has already received sedating medications and has a breathing tube in place. Under these conditions it is impossible for a person to talk, so the doctors cannot assess the verbal part of the GCS. People in this situation often receive a "T" after the GCS score, indicating that they were intubated when the examination took place, so you might see a score of 5T, for instance.

The GCS is done at intervals in the neurointensive care unit to document a person's recovery.

The duration of a confusional state following injury, often referred to as post-traumatic amnesia (PTA), is another good estimate for severity of a brain injury. Anytime a person has a major blow to the head he or she will not remember the injury and related events for sometime afterward. People with these injuries might not recall having spoken to someone just a couple of hours ago and may repeat things they have already said. This is the period of post-traumatic amnesia. The longer the duration of confusion/amnesia, the more severe the brain damage.