Anaesthesia, Coma and Disorders of Consciousness

From the first public ether operation in 1846 to modern intensive care: how anaesthesia switches consciousness off, and how doctors distinguish coma, vegetative state, minimally conscious state, locked-in syndrome and brain death.

The birth of anaesthesia

On 16 October 1846, at Massachusetts General Hospital in Boston, the dentist William T. G. Morton gave ether to a patient, Gilbert Abbott, while the surgeon John Collins Warren removed a tumour from his neck. The patient felt no pain. The demonstration, in a room now called the Ether Dome, launched modern surgery. Chloroform followed in 1847.

How anaesthetics work

General anaesthesia combines unconsciousness, amnesia, pain relief and immobility. Many anaesthetics (such as propofol and the gas sevoflurane) enhance GABA-A receptors; others, like ketamine, block NMDA receptors. How these molecular actions switch off consciousness is still being worked out. Leading ideas involve disrupting communication between brain regions — especially between the thalamus and cortex and between frontal and posterior cortex — so that information can no longer be integrated. Under propofol, the EEG shows characteristic slow waves and frontal alpha rhythms. Brain-monitoring helps anaesthetists avoid giving too much or too little; rare "accidental awareness" during anaesthesia occurs in a small fraction of cases.

A spectrum after brain injury

Coma: eyes closed, unrousable, no sleep-wake cycles; usually lasts days to weeks. Vegetative state, now often called unresponsive wakefulness syndrome: the eyes open and sleep-wake cycles return, but there's no sign of awareness. Minimally conscious state: inconsistent but definite signs of awareness — following a command, tracking a mirror with the eyes. Locked-in syndrome is not a disorder of consciousness: the person is fully aware but paralysed, often able to move only the eyes. Brain death is the irreversible loss of all brain function, including the brainstem, and is legally recognised as death in many countries.

Hidden awareness

In 2006 Adrian Owen and colleagues asked a young woman diagnosed as vegetative to imagine playing tennis or walking through her house during fMRI. Her brain activity matched that of healthy volunteers — motor areas for tennis, navigation areas for walking — showing she understood and followed instructions. Later work used the same imagery to answer yes/no questions. A large 2024 international study found that roughly a quarter of unresponsive patients showed such covert consciousness on fMRI or EEG tasks. This has major implications for diagnosis, care and ethics.