neurologic disorders
Overview of Coma and Impaired Consciousness
Prognosis
Prognosis for patients with impaired consciousness depends on the cause, duration, and depth of the impairment of consciousness. For example, absent brain stem reflexes indicates a poor prognosis after cardiac arrest, but not always after a sedative overdose. In general, if unresponsiveness lasts<6 hours, prognosis is more favorable. After coma,the following prognostic signs are considered favorable: Early return of speech (even if incomprehensible) Spontaneous eye movements that can track objects Normal resting muscle tone Ability to follow commands If the cause is a reversible condition (eg, sedative overdose, some metabolic disorders such as uremia), patients may lose all brain stem reflexes and all motor response and yet recover fully. After trauma, a Glasgow Coma Scale* score of 3 to 5 may indicate fatal brain damage, especially if pupils are fixed or oculovestibular reflexes are absent. clinicians must exclude major confounders of coma, including sedatives, neuromuscular blockade, hypothermia, metabolic derangements, and severe liver or kidney failure. If brain stem reflexes are absent at day 1 or lost later, Diagnosis is indicated. Prognosis is poor if patients have any of the following: Myoclonic status epilepticus (bilaterally synchronous twitching of axial structures, often with eye opening and upward deviation of the eyes) that occurs within 24 to 48 hours after cardiac arrest No pupillary light reflexes 24 to 72 hours after cardiac arrest No corneal reflexes 72 hours after cardiac arrest Extensor posturing or no response elicited by painful stimuli 72 hours after cardiac arrest No response 20 milliseconds (N20) after stimulation of somatosensory evoked potential (SEP) Serum neuron-specific enolase level of > 33 mcg/L Preexisting disorders such as coronary artery disease, hypertension, and diabetes mellitus If patients who are unresponsive after cardiac arrest have been treated with hypothermia (often for about 24 hours after arrest), 72 hours should be added to the above times because hypothermia slows recovery of brain metabolism. If any of the above criteria is met, outcome is usually (but not always) poor; thus, whether to withdraw life support may be a difficult decision. Patients may also have other neurologic and nonneurologic complications, depending on the cause and duration of impaired consciousness. For example, a drug or disorder causing metabolic coma may also cause hypotension, arrhythmias, myocardial infarction, or pulmonary edema. Prolonged hospitalization in an ICU may also result in polyneuropathy, myopathy, and other complications (eg, pulmonary embolism, pressure ulcers, urinary tract infection). 