Intraoperative neurophysiologic monitoring for intracranial surgery

Pusan National University Hospital Kim Won Sung Intraoperative neurophysiologic monitoring (IONM) consists of two main categories of techniques.

Monitoring Mapping IONM methods

• Electromyography (EMG) • Evoked Potentials (EP) – Somatosensory Evoked Potential (SSEP) – Brainstem Auditory Evoked Potential (BAEP) – Visual Evoked Potentials (VEP) – Motor Evoked Potentials (MEP) • Electroencephalography (EEG) And Electrocorticography (ECoG)

Electromyography (EMG) Somatosensory Evoked Potential (SSEP)

From Enno Freye. Journal of Clinical Monitoring and Computing Vol 19 Nos 1–2 2005 Brainstem Auditory Evoked Potential (BAEP) Visual Evoked Potentials (VEP) Motor Evoked Potentials (MEP)

From Jameson LC. Anesthe siol Clin 2006; 24:777. Electroencephalography (EEG) And Electrocorticography (ECoG) THE USE OF IONM IN THE MANAGEMENT OF CEREBRAL ANEURYSM SURGERY INTRAOPERATIVE INTRAOPERATIVE INJURY MANAGEMENT

• Vessel injury • Placement of • Vasospasm aneurysm clips • Clip placement • Increases • Hypotension in MAP • Retractor • Adjustment of placement retractors

Immediately! Monitor brain function (detecting ischemia)

• Somatosensory evoked potentials (SSEP) • Motor evoked potentials (MEP) – Transcranial electrical stimulation (TES) – Direct cortical stimulation (DCS) • Brainstem auditory evoked potentials (BAEP) • Electromyography (EMG)

SSEP • Detect ischemia in and to localize specific areas of cortical tissue

– Determine the adequacy of • Collateral blood flow • Blood pressure Advantages

1. Less affected by different anesthetics or neuromuscular blocking agents

2. Less interference to the operation

3. More reliable

in predicting cortical blood supply The vascular distributions

• SSEP monitoring – Common use in operations where the frontal circulation may be compromised

– MCA, ACA, and ICA • Somatosensory cortex and Internal capsule – PCA • Thalamic subcortical activity

• Median nerve SSEP – The primary somatosensory parietal cortex (representing the hand) – Monitoring the MCA or ICA

• Posterior tibial nerve SSEP – The parasagittal somatosensory parietal cortex (representing the leg) – Monitoring the ACA

• Amplitude reduction > 50%

Detecting • Latency delay > 10% ischemia • CCT of >1.0 ms • Complete loss of the waveform MEP Motor impairment not reflected by SSEP.

• SSEP – insensitive to perforating vessel occlusion and subcortical infarcts

• Reductions in blood flow in a perforating artery can result in contralateral hemiplegia, hemianesthesia, and hemianopsia.

• MEP – Technique to detect perforating vessel compromise

During brain aneurysm surgery “Pure motor deficit”

• Paresis on one side in the absence of sensory deficit, homonymous hemianopia, aphasia, agnosia, and apraxia • internal capsule/corona radiate, or brainstem Transcranial electrical Direct cortical stimulation (TES) stimulation (DCS)

• From anesthetic • During peri-rolandic induction to skin closure brain surgery • Directly stimulating • Focal muscle activation, deeper subcortical less movement structures (false negative) • Detect cortical and • Patient movement, bite subcortical ischemia • Relative contraindications • Bridging vein rupture with cardiac pacemaker • Leg area can be hard to • Siezure, arrhythmia reach Neuromuscular blockade

Omit muscle relaxation Partial neuromuscular blockade

Only for induction Tightly controll

Sensitivity of MEP!!! Patient movement!!! Critical MEP thresholds

• If MEPs were stable – Amplitude decreases of > 50% – Latency increases > 10%

• If not – “YES” or “NO” – Total abolishment SSEP vs MEP • MEP is superior to SSEP in most situations in aneurysm surgery.

• “MEP monitoring will replace SSEP monitoring in aneurysm surgery.”

MEP + SSEP =more completely and accurately!!! BAEP • Problems in the external or middle ear • Ischemia of the cochlea • Traction on cranial nerve VIII • Ischemia or neural damage to the auditory pathways in the brainstem

Posterior Fossa Surgery

• Narrow and critical space

– the brainstem – the reticular activating system – the neural networks that underlie crucial protective reflexes BAEP for Posterior circulation monitoring?

• Lam AM et al. – useful during basilar vertebral aneurysm surgery • Friedman et al. – unhelpful during basilar aneurysm surgery

• Combination of monitoring – SSEP, BAEP, and MEP – lower false positive and false negative

EMG (CRANIAL NERVE MONITORING DURING CLIPPING AN ANEURYSM ) M. Ishikawa et al. / Clinical Neurology and Neurosurgery 112 (2010) 450–453 CONCLUSION 1

• There are no RCT showing a favorable effect of IONM on surgical outcome.

• But there is much evidence that it is a useful tool to prevent neurological damage during different surgical procedures. 2

• Monitor by combining multiple modalities of evoked potentials. • For the monitoring team it is of prime importance to be aware of the limitations of their method, and detailed knowledge of IONM failures may help to refine monitoring techniques and improve sensitivity.

Thank you!!

Won Sung Kim [email protected] Pusan National University Hospital Department of Anesthesia and Pain medicine