The anatomical structures involved in the mechanisms of consciousness are the brainstem (pons and midbrain), bilateral thalamus, hypothalamus, and bilateral cerebral cortical structures.
The initial emergent evaluation and management of a comatose patient include the ABC, general physical examination, and neurologic examination.
The initial neurologic examination should include determination of the level of consciousness, pupillary size and function, eye movements, motor responses (spontaneous and to a painful stimulation), and respiratory patterns.
Computed tomography (CT) scanning of the brain is the most valuable acute imaging test to rule out a structural cause of the coma.
The Uniform Determination of Death Act (UDDA) states that “An individual who has sustained either (1) irreversible cessation of circulatory and respiratory functions, or (2) irreversible cessation of all functions of the entire brain, including the brainstem, is dead.” It also defines that “A determination of death must be made in accordance with accepted medical standards.”
While the determination of Brain Death or Death by Neurologic Criteria is a clinical determination, there are certain circumstances that require an ancillary test to be performed in addition to the clinical examination and apnea testing.
Coma and disorders of consciousness (DoC) are commonly observed neurological conditions that may be related to either a primary neurological or nonneurological disorder. Wang et al found that only 1% of the admissions from the emergency room have been attributed to coma.1 The prevalence of persistent wakefulness without awareness (previously known as vegetative state) and minimally conscious state is 0.2 to 3.4 per 100,000 inhabitants and 1.5 per 100,000 inhabitants, respectively.2 However, wider epidemiological studies in communities are lacking. Despite being frequently encountered by clinicians, understanding DoC, including their pathophysiology and treatment, has been one of the most challenging fields in neurology. This could be attributed in part to the different terms used in the description of DoC and variation among assessments of different providers. The Neurocritical Care Society launched in 2019 an initiative called Curing Coma Campaign (CCC) to address these issues. The CCC focuses on the endotyping of coma and DoC, defining biomarkers, and designing proof of concept clinical trials.3
In this chapter we will focus on the current understanding of coma and DoC, their pathophysiology, and current approaches in treatment and prognostication.
DEFINING DISORDERS OF CONSCIOUSNESS
Disorders of consciousness are a heterogeneous group of disorders, whose definition is ever evolving. Consciousness was first medically defined in 1966 by authors Plum and Posner as the presence of both wakefulness and awareness. These two components have remained part of the subsequent refinements, although wakefulness remains the best defined neurobiologically. Clinically we rely on the observation of a patient’s behavior, whether this is spontaneous or in response to a stimulus, to assess these components. Although here we attempt to define these disorders as discrete entities, it is important to ...