Awareness During Coma

 Awareness During Coma

Doctors missing consciousness in vegetative patients

If there's one thing worse than being in a coma, it's people thinking you are in one when you aren't. Yet a new comparison of methods for detecting consciousness suggests that around 40 per cent of people diagnosed as being in a vegetative state are in fact "minimally conscious".

In the worst case scenario, such misdiagnoses could influence the decision to allow a patient to die, even though they have some vestiges of consciousness. But crucially it may deprive patients of treatments to make them more comfortable, more likely to recover, or to allow them to communicate with family, say researchers.

In a vegetative state (VS), reflexes are intact and the patient can breathe unaided, but there is no awareness. A minimally conscious state (MCS) is a sort of twilight zone, only recently recognised, in which people may feel some physical pain, experience some emotion, and communicate to some extent. However, because consciousness is intermittent and incomplete in MCS, it can be sometimes very difficult to tell the difference between the two.

In 2002 Joseph Giacino at the JFK Rehabilitation Institute in New Jersey and colleagues released the first diagnostic criteria for MCS. Then in 2004, Giacino released a revised coma recovery scale (CRS-R) – a series of behavioural tests based on criteria that can be used to distinguish between the two states.

 

Alarm 'appropriate'

To see if the revised scale improves diagnoses, Giacino and Caroline Schnakers of the Coma Science Group at the University of Liege in Belgium, with colleagues, spent two years using CRS-R to re-diagnose patients admitted to a network of Belgian intensive care units and neurology clinics with head injuries that resulted in some kind of disturbance to consciousness.

The clinics and units all used a "clinical consensus" agreed by a range of specialists to diagnose patients. Some of the specialists relied on qualitative, "bedside" observations to diagnose patients, others used older diagnostic tools, but none used the CRS-R – the only one designed specifically to distinguish between MCS and VS.

Of the 44 patients diagnosed as being in a vegetative state by the clinicians, the researchers diagnosed 18, or 41 per cent, as being in a MCS according to the CRS-R.

"We may have become much too comfortable about our ability to detect consciousness," concludes Giacino. "I think it's appropriate for there to be some level of alarm about this."

Giacino concedes that, because there is no objective way to measure consciousness, he cannot exclude the possibility that the reason for the discrepancy is that the CRS-R is over-diagnosing MCS.

Examiner bias

However, Schnakers argues that CRS-R should be more accurate because it specifies how many times each test must be repeated – and how many responses are needed to give an indication of consciousness.

This, she says, guards against missing awareness in someone who pops in and out of consciousness, or mistaking a reflexive response for a response based on consciousness. It should also control for "examiner bias", where someone subjectively decides whether the patient is conscious or not, adds Giacino.

What's more, the revised scale also makes use of some new insights. One sign of consciousness is whether someone follows the path of a moving object, known as "visual pursuit". Many clinicians simply look at whether someone follows a moving pen or person, says Schnakers.

The CRS-R specifies the use of a mirror, which she argues may prompt a reaction in someone who is conscious, but who does not respond to a moving pen. "When you move an object, it is less powerful," she says.

 

'Death or survival'

So why do clinicians still use the qualitative assessment? "Their focus is more typically on death or survival" and on biological factors that need treatment, such as how long a patient needs to be in an intensive care unit, says John Whyte of the Moss Rehabilitation Research Institute in Philadelphia, Pennsylvania, who was not involved in the study. "For their purposes, the distinction [between MCS and VS] doesn't matter much."

For the patient and the family, the difference between MCS and VS can make a huge difference, though. Drug treatments, painkillers, physical therapies designed to stimulate the brain, as well as techniques for encouraging communication, are more likely to be given to someone in a MCS.

In some jurisdictions, whether food can be withdrawn may depend on whether or not they are in a VS, says Whyte. "It's very important to be sure of the diagnosis," says Schnakers.

12:47 21 July 2009 by Celeste Biever

For similar stories, visit the The Human Brain Topic Guide

Journal reference: BMC Neurology (DOI: 10.1186/1471-2377-9-35)

From New Scientist

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