Marino The ICU Book 4e, IE

806 Nervous System Disorders

COMA The patient who is comatose (i.e., unarousable and unaware) is one of themost challenging problems in critical care practice, and the management includes not only the patient, but the patient’s family and other intimates as well. Etiologies Coma can be the result of any of the following conditions: 1. Diffuse, bilateral cerebral damage. 2. Unilateral cerebral damage causing midline shift with compression of the contralateral cerebral hemisphere. 3. Supratentorial mass lesion causing transtentorial herniation and brainstem compression. 4. Posterior fossa mass lesion causing direct brainstem compression. 5. Toxic or metabolic encephalopathies (including drug overdose). 6. Nonconvulsive status epilepticus. 7. Apparent coma (i.e., locked-in state, hysterical reaction). The most common causes of coma in one study were cardiac arrest (31%), and either stroke or intracerebral hemorrhage (36%) (20). Bedside Evaluation The bedside evaluation of coma should include an evaluation of cranial nerve reflexes, spontaneous eye and body movements, and motor reflexes (20,21). The following elements of the evaluation deserve mention. Motor Responses Spontaneous myoclonus (irregular, jerking movements) can be a nonspe- cific sign of diffuse cerebral dysfunction, or can represent seizure activi- ty (myoclonic seizures), while flaccid extremities can indicate diffuse brain injury or injury to the brainstem. Clonic movements elicited by flexion of the hands or feet (asterixis) is a sign of a diffuse metabolic encephalopathy (20). A focal motor defect in the extremities (e.g., hemi- paresis or asymmetric reflexes) is a sign of a space-occupying lesion or spinal cord injury. RESPONSE TO PAIN: Painful stimulation that elicits a purposeful response (i.e., localization to pain) is not a feature of the comatose state. The re- sponses to pain in the comatose state are either purposeless or absent. With injury to the thalamus, painful stimuli provoke flexion of the upper extremity, which is called decorticate posturing . With injury to the midbrain and upper pons, the arms and legs extend and pronate in response to pain; this is called decerebrate posturing . Finally, with injury involving the lower brainstem, the extremities remain flaccid during painful stimulation. Eye Opening Spontaneous eye opening is an indication of arousal, and is not consis-

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