Second Impact Syndrome

Second impact syndrome (SIS) occurs when an athlete who has sustained an initial head injury, most often a concussion, sustains a second head injury before the symptoms associated with the first have fully cleared. While most commonly reported in football, the SIS can occur during any sport that can produce head blows. Any athlete still complaining of post-concussion symptoms after a head injury must not be allowed to return to play.

An athlete who sustains an initial concussion may develop cerebral edema, accounting for loss of consciousness, memory impairment, disorientation and headache. The brain's auto regulatory mechanisms compensate for this mechanical and physiologic stress and protect against massive swelling. This is thought to be accompanied by acutely limiting cerebral blood flow. After the initial phase, a state of altered cerebral metabolism occurs and may last a number of days. This makes the brain more vulnerable and susceptible to death after a second sub-lethal impact of even less intensity. Fischer and Vaca concluded that when an athlete sustains a "second impact," the brain loses its' ability to auto regulate intracranial and cerebral pressures. Death has been reported to occur in a matter of two to five minutes, usually without time to stabilize or transport an athlete from the playing field to the ED.