Coma, Disorders of Consciousness, and Brain Death

Accurate and competent assessment of the spectrum of disorders of consciousness, and an understanding of the neuroanatomical and neurophysiological mechanisms underlying them, is crucial for guiding treatment plans and prognostication. This chapter describes the various presentations seen in disorders of consciousness; the anatomical and physiological foundations of arousal failure; the clinical approach to a patient presenting with acute coma; treatments in acute and chronic coma; and the approach to a patient with suspected brain death. Impairments of consciousness are manifested by spectrum of clinical syndromes ranging from encephalopathy to coma. They are the final pathway for a broad range of diseases that share the common thread of pathophysiological derangement of the pons, midbrain, and thalamus or simultaneous damage to bilateral thalamocortical projections or bilateral cortices. Encephalopathy is an impairment of normal arousal in which the level of arousal fluctuates. Minimally conscious state is a syndrome where the patient is awake but in which there is only evidence of a minimal awareness of self or environment. Akinetic mutism is a rare form of arousal failure, characterized by an emotionless, frequently motionless state with intact visual tracking, and occurs commonly due to lesions in the bilateral anterior cingulate gyri. Unresponsive wakefulness syndrome, a new name for the previously described persistent vegetative state, is a syndrome where patients are awake (eyes open) but remain otherwise unresponsive, showing only reflexive movements. Coma is a state of complete unresponsiveness to external and internal stimuli, typified by a complete failure of normal arousal. Finally, brain death is defined as the irreversible cessation of clinical brain activity. Clinicians must take care to rule out mimics such as the locked-in syndrome and covert consciousness. In locked-in syndrome, patients have intact arousal and awareness but can only communicate through blinking and/or upward gaze due to severe injury in the ventral pons. Recent studies using EEG have also shown evidence of brain activation to commands in otherwise unresponsive patients, suggesting that there are patients with covert consciousness that don’t have the ability to communicate at all. Physicians must be able to recognize these syndromes, as well as neurological emergencies associated with them. As needed, prompt application of advance cardiac life support (ACLS) and emergency neurological life support (ENLS) algorithms could dramatically impact the course of someone presenting with acute coma. Cerebral herniation associated with a comatose state may require the initiation of a brain code and administration of emergent therapies to decrease ICP including appropriate head of the bed and neck positioning; placement of central access as needed; controlled hyperventilation; and use of hypertonic saline or mannitol. For patients in coma over a longer period of time, new therapies are emerging and being investigated to stimulate patients and maximize their improvement. The final section of this chapter discusses the diagnosis of brain death. It includes criteria and guidance for the clinical exams involved, and an overview of the various ancillary tests that can be done. It also discusses special considerations for patients undergoing targeted temperature management or on extracorporeal membrane oxygenation.