Monitoring Modalities


Biotronic’s extensive collective experience and large clinical staff of over 200 technologists enables us to provide monitoring services for every conceivable type of neurophysiologic intraoperative monitoring that may be required by physicians.


Biotronic offers several monitoring modalities:

Somatosensory Evoked Potentials

Somatosensory evoked responses are obtained by stimulating a peripheral nerve at the wrist or the 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 spinal cord motor pathways.

Dermatome Sensory Evoked Potentials

Dermatome sensory evoked potentials can also be useful in evaluating segmental nerve root function. This is accomplished by stimulating the cutaneous dermatome areas measuring the response at the cortex.

Spinal Cord Evoked Potentials

Mixed motor and sensory evoked potentials can be obtained by electrical depolarization of the spinal cord in the operative field. These are commonly known as NMEP potentials. They are mediated pre-dominantly by the sensory pathways.

Transcranial Motor Evoked Potentials

Motor evoked potentials are obtained by transcranial electrical stimulation of the cortical motor areas. Monitoring the evoked muscle responses or the descending potential from the spinal cord can assess the integrity of the motor pathways.

Cortical Mapping

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 internal capsule are determined from EMG evoked by electric brain stimulation.

Deep-Brain Single Unit Recordings

Globus pallidus and thalamus structures can be identified by the unique single unit activity recorded from microelectrodes inserted into these structures. The nearby optic tracts can also be located.

Auditory Evoked Potentials

Brainstem evoked potentials are obtained by stimulating the auditory system with click stimuli. The neural action potentials between the cochlea and the median 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.

Visual Evoked Potential

Visual evoked potentials are obtained from flash stimulation of the eye, and are measured from the optical 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.

EEG and Computer Enhanced EEG

Ongoing EEG activity from the scalp is recorded from a multi-electrode array. Or, computer enhanced EEG is obtained by subjecting the EEG waves to FFT analysis. The resulting spectrum is then sampled and monitored at 10-second intervals. Changes in the amplitude or power of the EEG components are correlated with the metabolic state of the cortical structures.

Transcranial Doppler

Blood flow velocity is measured from intracranial arteries using ultrasonic 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.

Cerebral Venous Oxygen Saturation

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


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.

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

Peripheral Nerve Action Potential (Intraoperative Nerve Conduction Study): Peripheral nerves are evaluated by eliciting and recording whole-nerve or individual fascicle action potentials to assess peripheral nerve function and the extent of injury.

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