A coma is a prolonged state of unconsciousness. During a coma, a person is unresponsive to his or her environment. The person is alive and looks like he or she is sleeping. However, unlike in a deep sleep, the person cannot be awakened by any stimulation, including pain.
Comas are caused by an injury to the brain. Brain injury can be due to increased pressure, bleeding, loss of oxygen, or buildup of toxins. The injury can be temporary and reversible. It also can be permanent.
More than 50% of comas are related to head trauma or disturbances in the brain’s circulatory system. Problems that can lead to coma include:
Trauma: Head injuries can cause the brain to swell and/or bleed. When the brain swells as a result of trauma, the fluid pushes up against the skull. The swelling may eventually cause the brain to push down on the brain stem, which can damage the RAS (Reticular Activating System) – a part of the brain that’s responsible for arousal and awareness.
Swelling: Swelling of brain tissue can occur even without distress. Sometimes a lack of oxygen, electrolyte imbalance, or hormones can cause swelling.
Bleeding: Bleeding in the layers of the brain may cause coma due to swelling and compression on the injured side of the brain. This compression causes the brain to shift, causing damage to the brainstem and the RAS (mentioned above). High blood pressure, cerebral aneurysms, and tumors are non-traumatic causes of bleeding in the brain.