Neurological Monitoring

Posted by e-Medical PPT Tuesday, September 4, 2012
EEG
Electroencephalogram – surface recordings of the summation of excitatory and inhibitory postsynaptic potentials generated by pyramidal cells in cerebral cortex
EEG:
 Measures electrical function of brain
 Indirectly measures blood flow
 Measures anesthetic effects

Three uses perioperatively:
Identify inadequate blood flow to cerebral cortex caused by surgical/anesthetic-induced reduction in flow
Guide reduction of cerebral metabolism prior to induced reduction of blood flow
Predict neurologic outcome after brain insult
Other uses: identify consciousness, unconsciousness, seizure activity, stages of sleep, coma

Abnormal EEG:
Regional problems - asymmetry in frequency, amplitude or unpredicted patterns of such
Epilepsy – high voltage spike with slow waves
Ischemia – slowing frequency with preservation of amplitude or loss of amplitude (severe)
Global problems – affects entire brain, symmetric abnormalities
Anesthetic agents induce global changes similar to global ischemia or hypoxemia (control of anesthetic technique is important)

Evoked Potentials
Definition: electrical activity generated in response to sensory or motor stimulus
Stimulus given, then neural response is recorded at different points along pathway

Sensory Evoked Potential
Sensory evoked potentials
 Somatosensory (SSEP)
 Auditory (BAEP)
 Visual (VEP)

SSEP – produced by electrically stimulating a cranial or peripheral nerve
If peripheral n. stimulated – can record proximally along entire tract (peripheral n., spinal cord, brainstem, thalamus, cerebral cortex)
As opposed to EEG, records subcortically

Intraoperative SSEPs
Neurologic pathway must be at risk and intervention must be available

Indications:
Scoliosis correction
Spinal cord decompression and stabilization after acute injury
Brachial plexus exploration
Resection of spinal cord tumor
Resection of intracranial lesions involving sensory cortex
Clipping of intracranial aneurysms
Carotid endarterectomy
Thoracic aortic aneurysm repair

Transcranial Doppler
Direct, noninvasive measurement of CBF
Sound waves transmitted through thin temporal bone, contact blood, are reflected, and detected
Most easily monitor middle cerebral artery
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