A patient with severe brain injury lies in a hospital bed, on life support. He shows no outward sign of consciousness, and the level of brain damage this person suffered, and subsequently his prognosis, is unknown. He is diagnosed as being in an “Unresponsive Wakefulness State” (UWS), the politically correct term that has replaced the more familiar but unpalatable “vegetative state”.
Ultimately, this patient’s life hangs on the decision to prolong or end his life-support. Whilst already an emotionally and ethically difficult situation for the family, the possibility that this patient might in fact be conscious and unable to reveal his awareness to the outside world makes the effort to reliably detect consciousness a vital mission for the clinician in charge. But it is gruellingly difficult because there is a long way to go with detecting consciousness accurately: alarmingly, in one study, researchers found that up to 41% of patients who were initially deemed to be in UWS were in fact conscious (1).
Dr Caroline Schnakers of the University of California, Los Angeles, has spent the last 14 years of her career studying consciousness in adult patients with severe brain injury. In a guest talk at the University of Nottingham Psychology Department in December 2014, she presented some key concepts to strategically pick away at this daunting challenge: how can various observable states of consciousness be defined, what tests are used and how useful are these in determining signs of awareness, and can patients in the minimally conscious state feel pain?
Part 1: Scales and States of Consciousness
It is important to distinguish the various states of consciousness which are observed to exist along a continuum of awareness and arousal (see fig. 1). Awareness refers to cognitively perceiving one’s environment, having conscious thoughts and feeling, whilst arousal is the observable physiological response to stimuli. Arousal could therefore include autonomic responses to changes in the environment, say temperature.
Coma is defined as the minimum state of both arousal and awareness, and is placed at one end of the continuum. The patient shows no cognitive awareness or purposeful movement. In the “Unresponsive Wakefulness State” (UWS), the patient shows some arousal, with return of some autonomic processes such as the sleep-wake cycle; the eyes may even open and close in synchrony with these states, but awareness is minimal and there is no ability to communicate with the patient. Climbing towards consciousness gets us to the “Minimally Conscious State” (MCS), where there is significant fluctuation in the level of arousal and awareness presented. This is what makes it very difficult to distinguish from the UWS; the patient may inconsistently respond to communication attempts and instructions, at times being able to reply with simple words or gestures, and at other times showing no awareness at all.
Efficient detection of awareness in MCS patients has profound impact on their prognosis; the earlier the diagnosis, the better the prognosis and patients may be able to recover.
Part two of this series focuses on this last category of consciousness and how pioneering research is aiming to tackle a multitude of confounds in order to generate reliable tests to determine signs of awareness in patients.
1: Schnakers, Caroline, et al. “Diagnostic accuracy of the vegetative and minimally conscious state: clinical consensus versus standardized neurobehavioral assessment.” BMC neurology 9.1 (2009): 35.