September 21, 2021

I, Science

The science magazine of Imperial College

Awake in a coma – a nightmare which becomes reality for some. We investigate some of the technologies used by doctors to predict patient consciousness and survival following brain injury.

Geoffrey lay in a hospital bed; unable to move or speak, and yet was able to understand everything being said around him. Even on hearing his fate being discussed, he was unable to respond. It seems the stuff of nightmares, but it may be a reality for many comatose patients.

Geoffrey Lean is a journalist who has written about his experience. He fell into a coma for one month after a routine operation went disastrously wrong. Geoffrey recalls being very aware of his surroundings; conversations around him, the news broadcasts, and could repeat anecdotes about things said to his apparently deaf ears. Research over the last few years has demonstrated that many comatose patients may experience something similar which raises questions about how much we actually understand about the brain when patients are in a coma or vegetative state.


The brain is the ultimate communication tool. In the form of chemical messages, nerve impulses and hormones, the brain is responsible for sending and receiving millions of signals every second, making us move, think, eat and sleep. The normal functioning of the brain can be impaired or lost by traumatic injury such as a blow to the head, or acquired injury at a cellular level.

A coma is a consequence of brain swelling and is one of the signs of brain trauma patients can experience. Patients in comatose states are unable to show signs of response to stimuli such as pain or sound, such as when a close relative calls their name. Without communication with the patient, it can be difficult for doctors to determine the extent of their coma and brain trauma.

To assess the coma level of patients, doctors use two different scales: The Glasgow Coma Scale and the Los Amigos Scale. These scales both focus on the patient’s responses to certain stimuli, responses can include eye opening, motor responses and verbal responses, as it is common for coma patients to make sounds.

While many patients recover from a comatose state, it is no indication that they will be left without further brain damage. MRI and CAT/CT scans are used to measure the anatomy of the brain and can identify structure deviations such as tumours, haemorrhages and blood clots. Obvious defects such as these can sometimes provide an indication of whether the patient is likely to make a full recovery.

Methods such as Positron Emission Tomography (PET) are used to measure the activity in the brain by using the emission of positrons following a small injection of radioactive isotope. The result is a 2D map which can potentially diagnose areas affected by strokes, cardiovascular disease and changes in activity.

Other frequently used techniques include Electroenchephalography (EEG) which works by measuring the fluctuations in voltage that result from ionic current flows between neurons in the brain. It can be used to diagnose patients with seizures, tumours, head injuries, degenerative diseases and even brain death.

These methods can tell us a lot about the functionality of the brain but cannot always determine the outcome for patients, nor provide clues to patients such as Geoffrey’s levels of awareness while in a coma.

One technique that stands out is the London Hospital Survival predictor, devised in 1972, used for predicting whether patients in comas resulting from heart attacks would recover. A box with a single dial, if the needle swings one way, it points to one word, ‘survive’, and the other to ‘IBD’ (irreversible brain damage leading to death). The software was taught which EEG features indicated a more or less favourable outcome, using data from patients who had either died or completely recovered.

The device was never actually used to determine whether life support should be withdrawn and staff were aware of its potential for misinterpretation. However from Geoffrey’s story alone, it is frighteningly clear how much is still unknown about the awareness of comatose patients and those with other brain trauma symptoms.


Lizzie Norris is studying for a PhD in Advanced Characterisation of Materials

Image: MRI head scan, CGinspiration