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Abstract
Neuro-ICU’s are unique in that they bring together specially-trained physicians and nurses and advanced technology, all with a focus on treating life-threatening neurological diseases. Neurological diseases tend to be complex and uncommon, and are best treated by specialists that have experience in applying neuroimaging and critical care techniques to the specific needs of neurological patients. Another major advantage to care in a neuro-ICU is the constant observation and immediacy of action that is required to detect and treat neurological deterioration. Constant surveillance by neuro-nurses, and the immediate availability of neuroimaging, on-call physicians, and specialized interventions, make it possible to act immediately to correct or reverse worsening medical conditions that might otherwise lead to permanent brain damage.
Advanced monitoring techniques used in a neuro-ICU allow the identification of critical problems before permanent neurologic injury occurs. A neuro-ICU also offers many specialized therapeutic options for patients with serious neurologic illness. Therefore, the management of such patients in a neuro-1CU is essential towards in achieving a favorable prognosis.
Instruments used to monitor the course of a neurologic illness are crucial for optimizing treatment. Monitoring allows for the establishment of an exact diagnosis. It also permits a patient’s response to drug therapy to be assessed, and allows for complications arising from a disease to be detected early, before the patient’s condition deteriorates, intensive monitoring gives doctors and families an indication of the patient’s prognosis. The following monitoring techniques are unique to a neurologic critical care unit:
• Continuous Electroencephalographic (EEG) Monitoring
• Jugular Venous Oxygen Saturation Monitoring
• Intracranial Pressure Monitoring
• Transcranial Doppler Ultrasonography
• Evoked potentials monitoring
• Electromyography and nerve conduction studies
• Single Photon Emission Computed Tomography (SPECT)
• Invasive Hemodynamic Monitoring
A Neuro-ICU is equipped with advanced treatments capable of improving prognosis in serious neurological illness. Many of these treatments must be administered early in the course of illness to be effective.
Recent clinical experience suggests that the use of continuous EEG (CEEG) monitoring techniques can greatly enhance the neurologic assessment and care of critically ill patients.
Continuous EEG monitoring in the intensive care unit (ICU) can now provide timely and therapeutically im¬portant data regarding cerebral function. These data are most often used in decision making regarding anti epileptic ¬drug (AED) manipulations, the need for immediate neuroimaging studies, and alterations in therapy to assure adequate cerebral perfusion. Additional areas of potential use include management of metabolic coma and decision making regarding prognosis for cerebral recovery after severe brain injury.
EEG monitoring is becoming increas¬ingly accepted as an ICU monitoring technique. Indica¬tions include the detection of nonconvulsive seizures (NCS) or nonconvulsive status epilepticus (NCSE), the management of status epilepticus (SE) with continuous intravenous antiepileptic drugs (cIV AEDs), the detection of cerebral ischemia, and help in predicting outcome of comatose patients.
It can be applied in either struc¬tural disorders (such as potentially expanding mass le¬sions) or metabolic/physiological disorders (seizures. metabolic encephalopathies, postanoxic injury). Previous difficulties associated with bedside use of the EEG, such as excessive paper use, mechanical malfunctions , and problems in providing real-time review, have been largely eliminated with the advent of computerized digi¬tal recording techniques and data transmission via com¬puter networks. The major remaining problem concerns the availability of expertise for continuous real-time or near real-time interpretation of EEG patterns.
Major advantages of EEG monitoring when compared with popular imaging techniques such as computed tomography, magnetic resonance imaging and single photon emission computed tomography, include its excellent temporal resolu¬tion and its availability at the patient’s bedside.
SjVO2 monitoring is only one of many new approach¬es to cerebral monitoring. Other recently described techniques include cerebral tissue oxygen monitoring, microdialysis and near infra-red spectrophotometry. Whether metabolic monitoring will have an impact on outcome remains to be seen.
Measurements of the jugular venous blood oxygen saturation (SjvO2) allow estimation of the global balance between cerebral oxygen demand and supply.
The jugular venous oxygen saturation can be used to determine the cerebral arteriovenous oxygen content difference (CavDO2), which reflects the oxygen uptake and metabolism in the tissues between the artery and venous structures sampled for the measurement.
Jugular bulb saturation must always be interpreted as a result of the relationship of supply (cerebral blood flow) and demand (cerebral metabolism). The contribution of SjvO2 to monitoring and treatment is to identify ischemia and help optimize the balance of supply and demand.
Because jugular bulb oxygen saturation indicates the relationship of metabolism to supply, it is of greatest use in monitoring when global ischemia can occur.
Cerebral oximetry is a noninvasive bedside technology using near-infrared light to monitor cerebral oxygen saturation in an uncertain mixture of arteries, capillaries, and veins. Oximetry using (NIRS) reflects the balance between regional oxygen supply and demand. In dead or infarcted nonmetabolized brain, saturation may be near normal because of sequestrated cerebral venous blood in capillaries and venous capacitance vessels and contributions from overlying tissue. In regionally or globally ischemic but metabolizing brain saturation decreases because oxygen supply is insufficient to meet metabolic demands.
The clinical application of (NIRS) for cerebral oximetry has undergone a long period of experimental development.
Only a few of the numerous methods available for measuring or estimating cerebral blood flow (CBF) are practical in the operating room and the critical care unit. Positron emission tomography (PET), single photon emission computerized tomography (SPECT), stable xenon computerized tomography, and magnetic resonance techniques.
Near-infrared spectroscopy (NIRS) is a noninvasive technique that has been used to measure CBF in adults and children.
This preliminary investigation has demonstrated that bedside estimation of CBF is possible using NIRS and intravenous ICG. Although the absolute values for CBF are low, this noninvasive technique, combining NIRS and pulse dye-densitometry, allows repeated measurements to be made and therefore may be ideal for measuring relative changes in CBF over short periods of time.
Global cerebral blood flow (CBF) is an important yet largely unknown quantity in the treatment of neurological intensive care patients. Color duplex sonography of the extracranial cerebral arteries can be used to measure global CBF volume directly at the bedside. To establish reference data on global CBF volume and to test the influence of sex and age on this parameter.
Monitoring of ICP is recommended for all patients who are comatose as a result of head injuries, even when initial computerized tomography shows no signs of intracranial hypertension. Multimodality monitoring, including such measurements as blood flow velocity in the middle cerebral artery and jugular bulb venous oxygen saturation add valuable information. Still, cerebral perfusion pressure, derived from ICP and intra-arterial pressure measurements, is thought to be the most important monitoring parameter in patients with severe head injuries.
Moniroring of ICP is also valuable in non-traumatic coma. It has been considered essential in managing patients having liver transplantation for fulminant hepatic failure. Epidural transducers may be safest in these patients, even though they are less precise than intraventricular catheters or intraparenchymal fibreoptic pressure transducers. In one study of such patients, fatal hemorrhage occurred in 1 per cent of patients who had epidural ICP monitoring, whereas subdural and intraparenchymal devices were associated with fatal hemorrhage in 5 per cent and 4 per cent of patients respectively.
One of the earliest applications of TCD monitoring is probably the most frequent application in the critical care unit still: detection of intracranial vasospasm following subarachnoid hemorrhage.
Serial TCD recordings in patients with increased intracranial pressures who went on to brain death showed a progressive reduction in flow velocities as intracranial pressure increased and cerebral perfusion pressure decreased.
A new development in transcranial Doppler ultrasonogra¬phv (TCD) monitoring has addressed this issue and achieved promising results.
Evoked potentials (EPs) are the electrophysiological responses of the nervous system to sensory, electrical, magnetic, or cognitive stimulation. They reflect the functional integrity of structures from which potentials arise and of pathways traversed between the site of stimulation and the neural generators of the evoked electrophysiological activity.
Measuring the electrical activity in muscles and nerves can help detect the presence, location and extent of diseases that can damage muscle tissue (such as muscular dystrophy) or nerves (such as amytrophic lateral sclerosis). In the case of nerve injury, the actual site of nerve damage can often be located. EMG and nerve conduction studies are often done together to provide more complete information.
Ideally, EMG recording could be used to monitor any nerve with a motor component such as numerous cranial nerves.
A SPECT scan is primarily used to view how blood flows through arteries and veins in the brain. Tests have shown that it might be more sensitive to brain injury than either MRI or CT scanning because it can detect reduced blood flow to injured sites.
SPECT scanning is also useful for pre-surgical evaluation of medically uncontrolled seizures. The test can be performed between seizures (interictal) or during a seizure (ictal) to determine blood flow to areas where the seizures originate.
This type of scanning is also useful in diagnosing stress fractures in the spine (spondylolysis), blood deprived (ischemic) areas of brain following a stroke, and tumors.