Second Impact Syndrome

What is Second Impact Syndrome (SIS) ?

Second impact syndrome (SIS) is a rare fatal condition that develops as a result of two separate events. Initially, the athlete sustains a concussion/traumatic brain injury, which causes them to suffer from concussion signs and symptoms such as fatigue, headache, nausea, disorientation, as well as sensory, motor and mental disturbances. The second event occurs when the athlete returns to play before the concussive symptoms have resolved and receives a second blow to the head. This second impact does not need to be forceful in order to be fatal. It may be a minor blow to the chest in which enough accelerating forces on the brain are created to cause major damage. These forces result in massive swelling of the brain (cerebral edema), which can lead to the death of the athlete within two to five minutes after the injury has been sustained.

What happens on Second Impact ?

When exploring SIS and the first hit versus the second hit, the first hit (and resulting concussion) is considered less severe than the second because of an internal regulatory system known as auto-regulation. This system reduces the stress placed on the brain by limiting the amount of blood flow in an attempt to prevent swelling. As a result, several by-products, such as lactic acid, cannot be cleared and begin to accumulate, leading to an altered metabolism of the brain.

Researchers believe that once the brain loses its ability to auto-regulate, it becomes more vulnerable and therefore more susceptible to traumatic brain injuries and SIS. If an athlete were to sustain a second injury before the brain has properly healed, the auto-regulatory mechanism would not function properly, there would be no alteration in the amount of blood flow to the brain, and it would result in massive swelling of the brain tissue.

The brain is contained within a rigid, compact skull. Most tissues in the body have give, and swelling is therefore not a big issue; however, there is no give to the solid bone that surrounds the brain, and the body cannot compensate for the increase in swelling. As a result, pressure placed on the brain increases. After the second impact, the athlete remains conscious but appears to be stunned; however, sometimes within seconds or minutes, the athlete will suddenly collapse, their pupils will become dilated and they will eventually stop breathing, resulting in death.

Can you prevent Second Impact Syndrome?

Second impact syndrome, though fatal, is extremely preventable. Any athlete who continues to show concussion signs and symptoms must be prohibited from returning to play. Parents, teachers, coaches and health care providers must be educated and trained to look for these signs and symptoms.
Further research about the cause and detection of SIS is needed in order for society to become better educated about this condition, and stricter return to play guidelines need to be enforced. Ultimately, the life of an athlete can be saved if the signs are recognized and the athlete is prohibited from returning to play.

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