Impairments in consciousness are seen on a daily basis in the neuroscience ICU. While we tend to think about these as fixed impairments, it is important to realize consciousness is fluid and dynamic process in the acute phase of recovery and can be impacted through the critical illness milieu.
Coma:
An unarousable and unresponsive with eyes remaining closed. Once you progress to eye opening or attempted eye opening, you are no longer in a comatose state.
Unresponsive Wakefulness syndrome (UWS) aka Vegetative State:
When a person is awake but is showing no signs of awareness.Clinically, the patient may open their eyes, wake up and fall asleep at regular intervals, and have basic reflexes such as withdraw of limbs to noxious stimulations. However, the do not show any meaningful responses, such as following an object with their eyes or responding to voices.
a continuing vegetative state when it's been longer than 4 weeks
a permanent vegetative state when it's been more than 6 months if caused by a non-traumatic brain injury, or more than 12 months if caused by a traumatic brain injury
Minimally Conscious State:
Condition of severely altered consciousness in which minimal, but definite, behavioral evidence of self or environmental awareness is demonstrated. So what does this look like? In 2002, Giacino et al published their working criteria for making the diagnosis in Neurology's Green Journal. (Neurology Feb 2002, 58 (3) 349-353; DOI: 10.1212/WNL.58.3.349)
To make the diagnosis of MCS, limited but clearly discernible evidence of self or environmental awareness must be demonstrated on a reproducible or sustained basis by one or more of the following behaviors:
Following simple commands.
Gestural or verbal yes/no responses (regardless of accuracy).
Intelligible verbalization.
Purposeful behavior, including movements or affective behaviors that occur in contingent relation to relevant environmental stimuli and are not due to reflexive activity. Some examples of qualifying purposeful behavior include: – appropriate smiling or crying in response to the linguistic or visual content of emotional but not to neutral topics or stimuli – vocalizations or gestures that occur in direct response to the linguistic content of questions – reaching for objects that demonstrates a clear relationship between object location and direction of reach – touching or holding objects in a manner that accommodates the size and shape of the object – pursuit eye movement or sustained fixation that occurs in direct response to moving or salient stimuli
A Couple of parting points for the minimally conscious state:
Distinguishing between VS and MCS is often difficult because the diagnosis is dependent on observation of behavior that show self or environmental awareness and because those behavioral responses are markedly reduced
Clinical experience indicates that MCS after an acute injury can exist as a transitional or permanent state. Many patients that are categorized as being in a peristent vegagtartive state state, may infact be in a minimally conscious state if evalauted by those with aporpriate experitise.
image adapted from Mayo Clinic 2006
Failure of Arousal and Awareness
Due to:
1.Bilateral hemispheric damage
2.Brainstem dysfunction that disrupts the ARAS
3.or both
If only the constructs of consciousness were as simple as the above diagram! Our understanding of disorders of consciousness has evolved over the past 15-20 years, and has challenged our very understanding and definition of consciousness. Below is a brief timeline of just some of the advancements and achievements in the ever evolving field
1990s – early 2000s
Improved Image acquisition techniques
Identification of additional structural networks involved in consciousness: DMN, ECN
Cortical processing of painful stimuli in VS
Understanding of cerebral metabolism in various states of injury
Early 2000s – 2010s
Understanding of cerebral metabolism in various states of injury
Refinement of Functional MRI and improvement in EEG availability
Task based studies with image acquisition
Cortical Processing
In 2002 Laureys et al would publish their findings on cortical processing of painful stimulation in vegetative state patients.
15 nonsedated patients and in 15 healthy controls. Evoked potentials were recorded simultaneously. The stimuli experienced was highly unpleasant in controls. Brain glucose metabolism was also studied with [(18)F]fluorodeoxyglucose in resting conditions.
In PVS patients, overall cerebral metabolism was 40% of normal values. Nevertheless, noxious somatosensory stimulation-activated midbrain, contralateral thalamus, and primary somatosensory cortex in each and every PVS patient, even in the absence of detectable cortical evoked potentials!!!
Covert Consciousness
In 2006, Owen at al would publish a landmark case where they were able to detect awareness in a patient with persistent unresponsive wakefulness syndrome.
This study involved a 23yr-old woman who had previously been diagnosed with unresponsive wakefulness syndrome (UWS) / vegetative state (VS) following a severe traumatic brain injury due to MVC.
After 5 months, she remained unresponsive but with preserved sleep-wake cycles, thus satisfying criteria for UWS / VS.
She was then given as series of verbal prompts such as "imagine playing tennis" or "imaging walking through your home". When she through about tennis, the supplemental cortex showed clear activation, and when prompted to walk through her home her parahippocampal gyrus became activated (which plays an essential role in spatial navigation)!
Their findings would suggest that despite fulfilling criteria for UWS / VS, this patient retained the ability to understand spoken commands and to respond to them as evidenced by her brain activation patterns compared to healthy controls.
Detecting Covert Consciousness in the ICU
In 2017, researchers at Mass General would set out to detect awareness in unresponsive wakefulness syndrome patients in the ICU. Researchers performed imaging studies on 16 patients admitted to the ICU for acute severe traumatic brain injury.
The results, reported in 2017 in the journal Brain, underscored the importance of the ability to detect covert consciousness in the ICU. Using fMRI and EEG, the researchers found evidence of such consciousness in four patients, including three whose bedside neurological examinations suggested a unresponsive wakefulness syndrome / vegetative state.
In two other patients who showed no outward signs of language function, imaging with language and music stimuli revealed higher-order cortex responses to the stimuli.
read more here: Edlow et al
Task-based EEG in Coma
In 2019, Claussen et al would publish their findings of task based EEG analysis in 104 patients who were prospectively followed on admission to their Neuroscience ICU and who were not able to follow commands due to coma.
15 % (16) of those patients showed signs of EEG response to command
50% (8) of those patients were able to FC at discharge follow up
44% (6) would go on to achieve GOSE of 4 or higher – functional independence at least 8hrs / day!!!
Coma:
UWS:
MCS(-):
MCS(+):
Confusional State:
Cognitive Dysfunction:
LIS:
CLIS:
Covert Cortical Processing:
Cognitive Motor Dissociation:
