CHAPTER 17 ■ COMA ERIC W GLISSMEYER, DOUGLAS S NELSON INTRODUCTION Consciousness refers to the state of being awake and aware of oneself and one’s surroundings It is a basic cerebral function that is not easily compromised; impairment of this faculty may therefore signal the presence of a life-threatening condition An altered level of consciousness (ALOC) is not in itself a disease but a state caused by an underlying disease process Coma refers to a state lacking wakefulness and awareness from which a patient cannot be roused; this represents the most extreme form of ALOC Lesser levels of impairment are described using other terms whose meanings may overlap Lethargy refers to depressed consciousness resembling a deep sleep, from which a patient can be aroused but into which he or she immediately returns A patient is said to be stuporous or obtunded when he or she is not totally asleep but demonstrates greatly depressed responses to external stimuli Not all ALOC states produce a diminished mental state, but may include abnormal activation of consciousness such as in delirium (see Chapter 13 Agitated Child ) Because neurologic status may vary dramatically over time, it may be difficult to summarize such symptoms using a single descriptor Therefore, recording the comatose patient’s specific response (e.g., body movement, type of vocalization) to a defined stimulus (e.g., a sternal rub) is preferable ( Table 17.1 ) PATHOPHYSIOLOGY The state of wakefulness is mediated by neurons of the ascending reticular activating system (ARAS) located in the brainstem and pons Neural pathways from these locations project throughout the cortex, which is responsible for awareness If the function of these neurons is compromised or if both cerebral hemispheres are sufficiently affected by disease, an ALOC will result Proper function of the ARAS and cerebral hemispheres depends on many factors, including the presence of substrates needed for energy production, adequate blood flow to deliver these substrates, absence of abnormal serum concentrations of metabolic waste products or extraneous toxins, maintenance of body temperature within normal ranges, and the absence of abnormal neuronal excitation or irritation from seizure activity or central nervous system (CNS) infection