Breathing patterns may provide important clues to the depth, neurologic localization, and etiology of the depressed consciousness. In Cheyne-Stokes respiration, a period of
Gastrointestinal (intussusception) Vasculitis (systemic lupus erythematosus) Hepatic failure Hypertensive encephalopathy Reye syndrome Endocrine disorders (adrenal insufficiency, thyroid disorders) Renal disorders (uremia)
Hypoglycemia Hyponatremia or its correction Hypernatremia or its correction Hyperosmolality or its correction Hypercapnia Hyperammonemia Inborn errors of metabolism Diabetes mellitus—ketoacidosis or hypoglycemia
Routine laboratory testing Glucose Sodium, potassium, chloride, bicarbonate, BUN, creatinine, AST, ALT, blood gases, ammonia Blood and urine analyses for toxic substances
CSF analysis including opening pressure, white and red blood cell counts, protein, glucose, and culture (± viral PCR testing) Neuroimaging
Head CT Brain MRI, MRA, MRV
Secondary laboratory testing (if cause remains unknown) Lead level, pyruvate, lactate, serum amino acids, urine organic acids, acylcarnitine profile
ALT, Alanine aminotransferase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; CSF, cerebrospinal fluid; CT, computed tomography; EEG, electroencephalogram; MRI/MRA/MRV, magnetic resonance imaging/angiography/venography; PCR, polymerase chain reaction; PT, prothrombin time;
PTT, partial thromboplastin time.
hyperventilation with a crescendo-decrescendo pattern alter-The detailed neurologic examination of a comatose patient nates with a shorter period of apnea and is due to the loss of focuses on the integrity of the brainstem which is the location cerebral, thalamic, or hypothalamic modulation of respiration. of the reticular activating system, mediating arousal. Pupillary This pattern also can be seen in patients with metabolic disor-responses assess the midbrain function. Eye movements are ders, heart failure, or primary respiratory disease. A mid-brain observed or elicited with the doll’s eye maneuver (oculocelesion yields central neurogenic hyperventilation, which phalic response) (Chapter 179) or cold caloric stimulation consists of sustained rapid deep breathing. Gasping respira-(oculovestibular response). If the oculocephalic responses tions are irregularly irregular and indicate dysfunction of the are not elicited or unclear, cold water is flushed into the exterlower brainstem (medulla). Gasping is ominous and usually is nal ear canal. In a conscious person, this maneuver elicits followed by terminal apnea. nystagmus to the opposite side and extreme vertigo with vom-
The Glasgow Coma Scale (see Table 42-2) can be used to iting. In a comatose patient, cold water irrigation into the ear assess unresponsive patients regarding their best verbal and canal elicits a tonic eye deviation toward the ear irrigated if motor responses and eye opening to stimulation with a score the brainstem is functioning and the patient is not brain dead. of 3 to 15 points. With complete loss of oculomotor function, the eyes remain in the center of the orbit regardless of any stimulation, indicating brainstem failure.
Body posture at rest and after noxious stimulation can indicate the anatomic level responsible for the alteration of consciousness. Mildly altered mental status may be manifested by a comfortable sleeping posture. Frequent spontaneous readjustments of position, yawns, and sighs are observed. Patients who lie in a flat, extended, unvarying position with eyes half-open exhibit a deeper coma. An asymmetrical posture suggests motor dysfunction of one side. This asymmetry may be subtle, such as mild external rotation of the affected leg.