In first aid, ICP stands for intracranial pressure. Generally it is noted in context with increasing intracranial pressure as a result of a traumatic brain injury (TBI). Increasing ICP is a serious life threat that can occur up to 24 hours from the time of the head injury and is generally signaled by intense vomiting, seizing, unequal pupils, and intense pain.
In such a case, the casualty has sustained a severe enough head injury that the brain has begun to swell, increasing the pressure inside the cranium due to the increasing volume of blood in the area. The increased pressure over time will force the brain down through the spine, resulting in death. Moreover, since some most basic and important brain functions are at the brain stem, these may be first to be damaged. A person suffering from increasing ICP needs hospital and/or ALS care immediately and will likely require brain surgery.