Coma and brain death are two of the worst words you can hear in a hospital. Both words suggest critical illness and very poor prognosis. Coma is actually better than brain death because brain death is no going back from it while one may recover from a coma. Simply because these are dire situations, it is very important to have a clear idea about what’s what if in case you ever come across these conditions.
Coma is medically known as unconsciousness for more than six hours duration. During a coma, the person is unresponsive to all stimuli, cannot be awoken and does not perform any active spontaneous movements. There is a scoring system to assess the level of consciousness called the “Glasgow Coma Scale”; GCS, in short. In a comatose patient, the GCS score ranges from 3 to 15. GCS score is 15 in a conscious and rational individual and 3 to 8 in a comatose patient. It is very important to note that the patient has some electrical brain activity. There are two main areas in the brain which are associated with wakefulness. They are the cerebral cortex and reticular activating system. The cerebral cortex is a dense organization of neurons which are responsible for complex thinking and higher brain functions. The reticular activating system is a primitive brain structure associated with reticular formation, comprised of ascending and descending tracts. Injury to any of these areas results in a coma. However, injury is not the only cause. Coma may be a healing mechanism where all the energy is channeled towards healing the immediate injuries. The cause governs the onset and the severity of the coma. Coma due to low blood sugar may be preceded by agitation, obtundation and stupor. Coma due to bleeding into the brain matter may be instantaneous. Intoxication (drugs, poisons), stroke, hypoxia, herniation of the brain or brainstem and hypothermia are a few well known causes of coma.
Once an unresponsive patient comes to the emergency room the first steps are to ensure the airway, breathing and circulation is adequate. Temperature (rectal), pulse (central and peripheral), blood pressure, cardiovascular system, breathing pattern, saturation, breathing sounds, stereotypic posture, cranial nerves, pupils and special reflexes will be assessed. Temperature will give a clue towards hypothermia. Pulse rate, rhythm, volume, and peripheral pulses give and idea about circulation and vascular integrity. Blood pressure is key and sometimes pressure in both arms needs to be measured. Cardiovascular system examination will give clues towards any structural of functional abnormalities of heart and vessels (carotid bruits in stroke). Breathing pattern is very important because specific patterns give clues towards the cause of the coma. Cheyne-stokes rhythm may be due to cortical/ brain stem damage. Apneustic breathing may be due to pontine lesions. Ataxic breathing is due to medullary lesions. Saturation will suggest hypoxia/hypercapnia. Decorticate posturing is due to a lesion above the red nucleus and decerebrate posturing is due to a lesion below the red nucleus. Light reflex assesses the optic and oculomotor nerves. Corneal reflex assesses the fifth nerve and the seventh nerves. Gag reflex is to test ninth and tenth nerves. Pinpoint pupils may be due to intoxication or pontine lesions. Dilated fixed pupils may be due to anoxia. Oculocephalic reflex tests the integrity of the brain stem as well as the 3, 4 and 6th cranial nerves. Computer tomography will give the location of the lesion as well as confirm any bleeding.
Medical treatment includes maintenance of airway, breathing and circulation, IV fluids, balanced nutrition, physical therapy to prevent contractures, infections, and bedsores.
Brain death is a phenomenon where the brain activity is irreversibly stopped. There is no electrical brain activity. The heart may go on at a slow pace due to internal pacemaker, but there is no respiration in brain death. Because there are no signals coming from the brain to maintain vital functions, only life support machines can keep these functions going.
What is the difference between Coma and Brain Death?
• Coma is a reduced level of consciousness due to injury to specific brain areas or some metabolic cause. Brain death is due to total brain necrosis.
• Coma may be reversible, but brain death is not.
• In coma, there is some brain activity to maintain vital function while it is not so in brain death.
• Brain death is taken as legal death is many countries but coma is not taken as such.