There are three critical questions to be answered about a comatose patient. Where is the lesion? What is the cause? Is the coma stable, improving, or worsening? Generally, the physician first determines whether the etiologic category is supratentorial, infratentorial, or metabolic. The next step is to determine the cause within the etiologic category. Obtaining a history, including drug use, from a friend or relative is extremely helpful in placing the patient into an accurate category.

Table 16.2 gives the major clinical features found in each coma category. An elevated temperature and blood white count usually implies an infection (sepsis, pneumonia, or CNS) and a low temperature usually implies patient has been comatose in a cold environment for some period of time. Rapid regular breathing often denotes a metabolic acidosis from a metabolic cause. During the physical examination, attention should be paid to find signs of trauma (especially head or neck trauma), bleeding (external or internal), organ dysfunction (especially lungs, heart, kidney, thyroid), and sepsis. Since mentation, fine sensation, and coordination cannot be tested in a comatose patient, the neurologic exam focuses on spontaneous or pain-induced limb movements, breathing patterns, ocular findings, and cranial nerve function (Tables 16.2 and 16.3).