INTRAOPERATIVE NEUROPHYSIOLOGICAL MONITORING (IONM) A BRIEF OVERVIEW OF SCIENCE & BENEFITS F AISAL R . J AHANGIRI MD, CNIM, D.ABNM, FASNM VICE PRESIDENT OF CLINICAL AFFAIRS AXIS NEUROMONITORING LLC RICHARDSON, TX
LEARNING OUTCOME Intraoperative Neurophysiological Monitoring (IONM) helps in better patient outcomes by minimizing risks related to the functional status of the nervous system during surgical procedures. An IONM alert to the surgical team during the surgery can help them to identify the cause and take an immmediate corrective action. Learning about the advantages of IONM, as well as the potential legal risks.
INTRODUCTION
INTRODUCTION The term "neurophysiological monitoring" is defined by the American Society of Neurophysiological Monitoring (ASNM) as: “ Any measure that is used to assess the functional integrity of the peripheral or central nervous system either in the Operating Room, the Intensive Care Unit or other Acute Care setting” .
PURPOSE The purpose of IONM is to reduce the incidence of iatrogenic and randomly induced neurological injuries to patients during surgical procedures. IONM consequently confers possible benefits at many levels including: – Improved patient care – Reduced time of temporary deficits – Reduced revision procedures – Reduced rehabilitation and recovery times – Reduced hospital stay and medical costs – Reduced overall insurance burden – Reduce liability (maximum protection of patient nervous system)
BENEFITS OF IONM 1. Increased safety of the surgical procedure. IONM has been shown to play a significant role in reducing patient morbidity and mortality. Early irritation or impending injury can often be detected by measuring spontaneous or elicited (evoked) electrical signals produced by the nervous system or attached muscle groups during surgery. 2. Increased ability to accommodate more complex cases. IONM helps to identify new neurological impairment early enough to allow prompt intraoperative correction of the cause. This "early warning" system provides surgeons with the comfort necessary to perform complex cases. 3. Decreased risk of adverse surgical outcomes. IONM guides the degree of surgical intervention and provides a means for assessing the likelihood of post-operative complications.
NEUROPHYSIOLOGICAL MONITORING ✓ Diagnostic / Clinical: • NM can be used clinically for diagnosis of various diseases. Such as: Epilepsy, Multiple Sclerosis, Neuropathies, Myopathies, Hearing Deficits, Visual Deficits, Intracranial Vasospasms, etc. ✓ Prognostic: • NM can be used in an Intensive Care Units (ICU) for diagnosis and prognosis of various diseases. Such as: Status Epilepticus, Sub-clinical Seizures, Induced Coma, Brain Death studies, Stroke, etc. ✓ Therapeutic: • NM can be clinically for therapeutic purpose. Such as treatment of: Parkinson’s, Spasticity, Acute Stroke, Trigeminal Neuralgia, etc. ✓ Intraoperative (IONM): • NM is used intraoperatively for protection of neural pathways. Such as preventing mechanical & ischemic injuries.
MODALITIES
MODALITIES IN IONM • Modalities are specific types of electrophysiological tests that can used for testing specific neurological / functional pathways during different types of surgeries. • Various modalities are utilized intraoperatively for protection of neural pathways in high risk surgical procedures, such as: • SSEP - for protecting Sensory (Ascending) pathways TCeMEP - for protecting Motor (Descending) pathways • • EMG - for protecting Cranial and Peripheral nerves Free Run EMG (s-EMG) • • Triggered EMG (t-EMG) EEG/ECoG - for protecting brain ischemia • • BAER - for protecting auditory pathway VEP - for protecting visual pathway • • TCD - for protecting brain ischemia DECS - for protecting motor cortex • • MER - for microelectrode recordings
MULTIMODALITY IONM • Multi-modality intraoperative neurophysiologic monitoring (IONM), in general, can prevent or lower the risk of devastating neurologic deficit in a wide variety of cases which place neural structures at risk. • And although they all have advantages and disadvantages, they are, in combination, an effective means for providing patient protection.
Multiple Modalities Monitoring EMG TOF SSEP TCeMEP BAEP EEG
INTERVENTION Surgical Site No Intervention Needed Intervention Injury Needed
SOMATOSENSORY EVOKED POTENTIALS (SSEP) This test stimulates the patient distally (hands & feet) and records along the pathway as the ▪ nerve pulse travels to the brain. By recording at multiple locations we can determine the anatomic and functional integrity at different locations along the somatosensory pathway as the pulse travel from periphery to the cortex. Optimal for protection of the patient’s ascending sensory spinal pathways ▪ Useful in detection of mechanical and ischemic changes in the peripheral nerves, spinal cord and ▪ somatosensory cortex. Particularly in posterior spinal cord. 95 to 98% specificity to sensory neurological events ▪
SOMATOSENSORY EVOKED POTENTIALS (SSEP)
MOTOR EVOKED POTENTIALS (TCeMEP) Trans Cranial Electrical Motor Evoked Potentials (TCeMEPs): Transcranial electrical stimulation of the cerebral cortex has existed for nearly five decades. • A variety of stimulation and recording techniques have been used to transcranially produce a motor potential. • • Merton and Morton, Nature 285(5762):227, 1980. • Zentner, Funct Neurol 4(30):299-300, 1989. • Kothbauer et al., Pediatr Neurosurg 26(5):247-54, 1997. • Calancie et al., J Neurosurg 88(3): 457-470, 1998. • Deletis et al., Clin Neurophysiol 112(3):438-452, 2001. • Osburn, Am J Electroneurodiagnostic T echnol 46:98-158, 2006. Szelenyi et al., Clin Neurophysiol 118(7):1586-1595, 2007. • • Contraindicated in patients with epilepsy, cardiac pacemakers or other implanted pumps • Require that neuromuscular blockade be minimized or avoided. Can be obtained with seconds.
MOTOR EVOKED POTENTIALS (TCeMEP) Epidural D-Wave 20 mS Muscle MEPs 100 mS
LOSS OF TCeMEP DUE TO A MALPOSITIONED SCREW (Jahangiri, FR et al 2014)
ELECTROMYOGRAPHY (EMG) Electromyography (EMG) are recorded from the distal muscles. Activity recorded is associated with nerve and • nerve root mechanical insult. Used when Spinal Roots, Peripheral Nerves or Cranial Nerves are at risk • Free-Run EMG (S-EMG) Passive continuous recording of activity in muscle • Mechanical or thermal nerve irritation causes s-EMG activity • Evoked or Triggered EMG (CMAP/T -EMG)) Monopolar, Bipolar or Tripolar stimulation • Identification of nerve tissue • Testing pedicle screws • Electrical stimulation with a probe can activate nerve fibers in the surgical field causing a muscle response •
BRAINSTEM AUDITORY EVOKED POTENTIALS (BAER) Preservation of Hearing ▪ It measures the auditory nerve and brainstem pathways ▪ It is useful during posterior or middle fossa cranial procedures for hearing preservation in acoustic neuroma surgeries Neurological Protection: ▪ VI VII V o Cochlea Protection IV o Cranial Nerve Protection I III II o Brainstem Protection ▪ An abnormal or absent BAER is often seen even in patients with minor preoperative hearing loss.
It is a continuous recording of brain activity from the scalp (EEG) ELECTROENCEPHALOGRAPHY Useful measurement of the cortical perfusion Can also provide gross measure of depth of anesthetic
PEDICLE SCREW STIMULATION T-EMG Triggered electromyography are recorded from the distal muscles. Activity recorded is associated with nerve, nerve root and pedicle screw electrical stimulation. T-EMG 4 mA triggered pedicle stimulation response. Indicating probably pedicle wall breach
Pedicle Screw Stimulation Outcome Studies Edward C. Benzel, SPINE Surgery; Volume 2, T echniques, Complication, Avoidance and Management, Chapter 95, Intraoperative Electromyography Monitoring Monitored and non-monitored outcome studies • Separated into 2 groups • Group I(n=185) without monitoring • Group II (n=205) with monitoring • Group I: Incidence of surgically induced radiculopathies was 9.6% • Group II: Incidence of surgically induced radiculopathies was <1.0% •
CNS at Risk in Skull Base Surgeries The goal of CN monitoring is to Identify, Trace, Protect and confirm the Integrity of the nerves. • Below are the cranial nerves at risk during skull base surgeries (posterior fossa surgeries): • V: Trigeminal • VI: Abducens • VII: Facial • VIII: VestibuloCochlear • IX: Glossopharyngeal • X: Vagus • XI: Accessory • XII: Hypoglossal • SOURCE : NETTER MEDICAL ILLUSTRATION
CORTICAL MAPPING ▪ Intra-operative neurophysiological monitoring (IONM) with sensory & motor mapping, as well as Electrocorticography (ECoG) is a well recognized method to identify the central sulcus & surrounding eloquent tissues in order to decrease the risk of neurological injury. ▪ IONM provides real-time feedback to the surgeon during resection & is advantageous over pre-operative imaging modalities.
WHAT IS FUNCTIONAL CORTICAL MAPPING ? Mapping of the Somatosensory Cortex Mapping of the Motor Cortex Mapping of the Language Cortex Mapping of the Epilepsy Foci Microelectrode Recordings (MER)
Cortical Sensory Mapping – Phase Reversal Jahangiri, FR et al, Dec 2011
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