Coma and brain death

Abstract

Arousal impairment, as manifested by coma, encephalopathy, and brain death, is a common final pathway for a broad range of diseases, which share the common thread of pathophysiological derangement of the pons, midbrain, thalamus, or simultaneous damage to bilateral thalamocortical projections or bilateral cortices. Coma is a state of complete unresponsiveness to external and internal stimuli, which is typified by the complete failure of normal arousal. Encephalopathy is an impairment of normal arousal in which the level of arousal fluctuates. These manifestations of arousal failure are among the most common derangements in hospitalized patients and patients in the ICU and the etiologies of arousal failure are manifold. In this chapter, the anatomical and physiological bases of arousal failure are discussed. The anatomical and physiological foundations of arousal failure are then used as framework to describe the neurological assessment of comatose or encephalopathic patients and how the neurological assessment leads to neuroanatomical localization of the brain injury leading to arousal failure. The approach to etiological diagnosis and management of patients with coma and encephalopathy are then described based on the principles of neurological localization. Brain death is defined as the irreversible cessation of clinical brain activity after exclusion of toxic or metabolic confounders. Although the body continues to function for some finite period of time after brain death, somatic death is imminent. In this chapter, the approach to the suspected genbrain-dead patient is described, within the framework of the anatomical and physiological foundations of arousal failure, neurological assessment, and neuroanatomical localization.