Multiple sclerosis (rare) Devic's disease
Guillain-Barre syndrome (with dysautonomia)
Autoimmune cerebritis including giant cell arterits, primary CNS artentis, and hypersensitivity arteritis and autoimmune induced dysautonomic states irom penpheral nervous system involvement including polyartentis and Wegener's granulomatosis. Systemic lupus erythematosus can affect either central or peripheral systems
Cortical contusion, epidural hematomas, subdural hematomas
Traumatic hematomas, post-traumatic epilepsy
All seizures associated with loss of consciousness, i.e., primary and secondary generalized seizures and all complex partial seizures with an alteration in consciousness
Complicated migraine, basilar migraine
Drugs assoeiated with hypotension or seizures
AIDS, Aequired immunodefieiency syndrome; CNS, central nervous system; MELAS, mitochondrial myopathy, encephalopathy, lacticacidosis and strokelike episodes; MERFF, mitochondnal encephalopathy with ragged red fibers; NCL-2, neuronal ceroid lipofuscinosis type 2.
there is no detectable function above the level of the foramen magnum. Any sign of brain stem-mediated function, such as decerebrate posturing, eye movements, pupillary response to light, or coughing, negates the possibility of the diagnosis of death by current brain criteria. Brain stem testing includes an apnea challenge. y
Apnea testing involves observing the brain stem response to hypercapnia without producing hypoxemia. In order to prevent hypoxemia, a period (e.g., 20 minutes) of ventilation with 100 percent oxygen is required before starting the test. Although acidosis, rather than hypercapnia, is the real afferent trigger for ventilation, a PaCO 2 of 60 mm Hg (50 mm Hg in the United Kingdom) is usually the endpoint for this test. In order to reach this endpoint before hypoxemia supervenes, it is advisable to regulate ventilation during the period of preapneic oxygenation so that the PaCO 2 reaches 40 to 45 mm Hg before apnea begins. This period should also be used to ensure that the patient's core temperature is adequate (e.g., above 32 degrees C), and that the results of assays for hypnosedative agents, if indicated, show that intoxication is not the cause of the patient's apparent lack of reflex responses.
Even though the patient has been adequately preoxygenated, some method of supplemental oxygen delivery is still necessary. This may be accomplished either by placing a suction catheter near the carina with a 10 L/min oxygen flow, or by using a continuous positive airway pressure (CPAP) circuit with 10 cm H 2 O pressure. A CPAP circuit does not provide ventilation, so it does not interfere with observation for spontaneous respirations. Even with one of these methods employed, some patients with cardiorespiratory dysfunction may not tolerate the approximately 10 minutes of apnea necessary to raise the PaCO 2 to 60 mm Hg without becoming hypoxemic and hypotensive. In this circumstance, a confirmatory test may be necessary.
Apnea is then allowed under observation until the PaCO2 reaches 60 mm Hg by arterial blood gas analysis. Although it may be possible to predict this point by following the trend in end-tidal CO 2 (PetCO2 ) measurements, there is enough discrepancy between arterial blood PaCO 2 and PetCO2 to indicate use of the arterial measurement. Visual observation is the standard method for detecting respiratory movement; this may be supplemented by airway pressure monitoring. Any respiratory movement negates the diagnosis of apnea. However, if the patient remains apneic despite a PaCO 2 of 60 mm Hg, the diagnosis of apnea is confirmed, and the patient, having met the other conditions cited as prerequisites, is declared dead by brain criteria.
If the patient is unable to tolerate the apnea test, or if some portion of the examination cannot be performed (e.g., trauma has rendered the face too swollen to examine the eyes), then a confirmatory test is necessary if the patient is to be diagnosed as dead. This is usually indicated only for potential organ donors, because there is no requirement that death be diagnosed in order to withdraw supportive measures, but at times may be helpful for the patient's family. Tests of cerebral perfusion (e.g., radionuclide angiography or conventional contrast angiography) are usually employed to show that blood does not flow intracranially above the foramen magnum. In some areas, transcranial Doppler blood flow velocity measurements are considered adequate for this purpose. Electrophysiological studies, such as EEG, have been used for this purpose but are prone to both false-positive (e.g., artifacts that cannot be distinguished from cerebral activity with certainty) and false-negative (due to hypothermia or hypnosedative drug intoxication) results (see Chapter.24 , Fig 24-4 ).
Was this article helpful?