Brainstem evoked potentials are obtained by stimulating the auditory system with click stimuli. The neural action potentials between the cochlea and the medial geniculate body are evaluated based on the brainstem evoked response. Brainstem evoked responses are sensitive to disturbances of the auditory nerve and to retractor disturbances of the brainstem.

Monitorable Structures

Cranial Nerve VIII

Auditory Brainstem Pathways

Surgical Applications

• Acoustic Neuroma Surgery

• Microvascular Decompression of cranial nerves

• Posterior Fossa Surgery

• Skull Base Surgery Requiring Brainstem Retraction

• Vestibular Nerve Section

Near-infrared absorption measurements are used to calculate an index of cerebral venus oxygen saturation

Monitorable Structures

Cortical Perfusion

Surgical Applications

• Cardiopulmonary Bypass

• Carotid Endarterectomy

Language, motor, and sensory areas of the exposed cortex can be identified by direct brain recording or stimulation. The somatosensory response is recorded from the surface of the brain. Language areas are determined by verbal responses during brain stimulation in the awake patient. Motor areas of the cortex and the internal capsule are determined from EMG and evoked by electric brain stimulation.

Monitorable Structures

Motor Cortex and Internal Capsule

Language Areas of the Brain

Sensory Cortex

Surgical Applications

• Brain Tumor Surgery

On going EEG activity from the scalp is recorded from a multi-electrode array and subjected to a fast Fourier transform (FFT) analysis producing a frequency/power spectrum that can be monitored to assess changes in the metabolic state of cortical structures.

Monitorable Structures

Cortex

Surgical Applications

• Aneurysm (including cerebral aneurysm

• Carotid endarterectomy

• Cardiopulmonary bypass

• Evaluation of anesthetic effects

Spinal Nerve Roots: Spontaneous EMG monitoring warns of potential nerve damage during manipulation. Evoked EMG stimulation of the pedicle screws can indicate a misdirected screw placement.

Cranial Nerves: The evaluation of spontaneous and evoked electromyogenic activity can be extremely useful in monitoring cranial nerve function. Spontaneous activity in the distribution of these nerves can signal mechanical disturbance of the cranial nerve.

Peripheral Nerves: The function of peripheral motor nerves can be evaluated during surgery by means of spontaneous and evoked electromyographic activity.

Monitorable Structures

Spinal Motor Roots

Cranial Nerves III, IV, V, VI, VII, IX, X, XI, and XII

Cranial Nerves III, IV, V, VI, VII, IX, X, XI, and XII

Surgical Applications

• Cauda Equina Surgery

• Cervical or Lumbosacral Decompression

• Pedicle Screw Instrumentation Surgery

• Acoustic Neuroma

• Anterior Neck Procedures

• Mastoidectomy

• Microvascular Decompression of Cranial Nerves

• Parotid Surgery

• Middle Ear Surgery

• Skull Base Surgery When Motor Cranial Nerves are at Risk

• Thyroidectomy

• Vestibular Nerve Section

• Monitoring of Femoral and Sciatic Nerve Function during Acetabular Surgery

• Peripheral neuroma Surgery

Somatosensory evoked responses are obtained by stimulating a peripheral nerve at the wrist and/or ankles. The propagation of the sensory action potentials is evaluated along their pathways to the cortex. This modality gives information about the integrity of the sensory pathways. It is also highly correlated with preservation of the spinal cord motor pathways.

Monitorable Structures

Spinal Cord

Lumbar and Sacral Nerve Roots

Monitoring Metabolic Function of Cortical Structures

Brainstem Somatosensory Pathways

Surgical Applications

• Spinal Deformity Surgery

• Spinal Cord Tumor Surgery

• Cervical and Thoracic Decompression, Fusion, and/or Instrumentation Surgeries

• Aortic Aneurysm

• Lumbosacral Decompression, Fusion Surgeries

• Cauda Equina Surgery

• Sacral-iliac Fracture Reduction

• Carotid Endarterectomy

• Cerebral Aneurysm Surgery

• Skull Base Surgery Requiring Retraction

• Acetabular Fracture

Blood flow velocity is measured from intracranial arteries using Doppler ultrasound. This technique is used to detect emboli, vasospasm and inadequate blood flow to cortical structures. Microvascular Doppler can also be used to directly assess blood flow within and through an aneurysm.

Monitorable Structures

Middle Cerebral Artery

Aneurysm Feeder Arteries

Surgical Applications

• Aneurysm Surgery (Cerebral and Ascending Aortic)

• Carotid Endarterectomy

• Cardiopulmonary Bypass

Motor Evoked Potentials are obtained by transcranial electric stimulation of the cortical motor areas. Monitoring the evoked muscle responses or the descending potentials from the spinal cord (The “D” wave) can assess the integrity of the motor pathways.

Monitorable Structures

Spinal Cord Motor Pathways

Surgical Applications

• All Spinal Surgeries that Place the Spinal Cord at Risk Including:

• Spinal Cord Tumor Surgery

• Cervical or Thoracic Decompressions,, Fusion and/or Instrumentation Surgeries

• Thoracoabdominal aortic aneurysm

Visual evoked potentials are obtained from flash stimulation of the eye, and are measured from the occipital region. They may provide useful information regarding the function of the pre-chiasmal visual pathways, but are labile and require careful anesthetic control. Additionally, retrochiasmal functional changes are difficult to assess using flash visual evoked potentials.

Monitorable Structures

Optic Nerve Fuction Anterior to Chiasm

Surgical Applications

• Transsphenoidal Pituitary Tumor Surgery

• Posterior Cerebral Artery Aneurysm