Neuromonitoring
Encyclopedia
Intraoperative neurophysiological monitoring (IONM) or intraoperative neuromonitoring is the use of electrophysiological methods
such as electroencephalography
(EEG), electromyography
(EMG), and evoked potential
s to monitor the functional integrity of certain neural structures (e.g., parts of the brain
, spinal cord
and peripheral nerves) during surgery. The purpose of IONM is to reduce the risk to the patient of iatrogenic
damage to the nervous system
, and/or to provide functional guidance to the surgeon
and anesthesiologist
.
single unit and local field recordings, SSEP, transcranial electrical motor evoked potentials (TCeMEP), EEG, EMG, and auditory brainstem response
(ABR). For a given surgery, the set of modalities used in depends on which neural structures are at risk. Transcranial Doppler Imaging
(TCDI) is also becoming more widely used to detect vascular emboli
. TCDI can be used in tandem with EEG during vascular surgery
. IONM techniques have significantly reduced the rates of morbidity and mortality
without introducing additional risks. By doing so, ONM techniques reduce health care costs.
To accomplish these objectives, a member of the surgical team with special training in neurophysiology
obtains and co-interprets triggered and spontaneous electrophysiologic signals from the patient periodically or continuously throughout the course of the operation. Patients who benefit from neuromonitoring are those undergoing operations involving the nervous system
or which pose risk to its anatomic or physiologic integrity. In general, a trained neurophysiologist attaches a computer system to the patient using stimulating and recording electrode
s. Interactive software running on the system carries out two tasks:
The neurophysiologist can thus observe and document the electrophysiologic signals in realtime in the operating during the surgery. The signals change according to a various factors, including anesthesia, tissue temperature, surgical stage, and tissue stresses. Various factors exert their influence on the signals with various tissue-dependent timecourses. Differentiating the signal changes along these lines with particular attention paid to stresses is the joint task of the surgical triad: surgeon, anesthesiologist, and neurophysiologist.
or to a peripheral nerve. Most neuromonitoring is utilized by spine surgeons or neurosurgeons, but vascular, orthopedic, otolarygologists and urology surgeons have all utilized neuromonitoring as well.
The most common applications are in neurosurgery
such as spinal surgery; selected brain surgeries; carotid endarterectomy
; ENT
procedures such as acoustic neuroma
resection; and peripheral nerve surgery. Motor evoked potentials have also been used in surgery for TAAA (thoracic-abdominal aortic aneurysms).
Intraoperative monitoring is used
For example, during any surgery on the thoracic or cervical
spinal column, there is some risk to the spinal cord. Since the 1970s, SSEP (somatosensory evoked potentials) have been used to monitor spinal cord function by stimulating a nerve distal to the surgery, and recording from the cerebral cortex or other locations rostral to the surgery. A baseline is obtained, and if there are no significant changes, the assumption is that the spinal cord has not been injured. If there is a significant change, corrective measures can be taken; for example, the hardware can be removed.
More recently, transcranial electric motor evoked potentials (TCeMEP) have also been used for spinal cord monitoring. This is the reverse of SSEP; the motor cortex is stimulated transcranially, and recordings made from muscles in the limbs, or from spinal cord caudal to the surgery. This allows direct monitoring of motor tracts in the spinal cord.
EEG electroencephalography is used for monitoring of cerebral function in neurovascular cases (cerebral aneurysms, carotid endarectomy) and for defining tumor margins in epilepsy
surgery and some cerebral tumors.
EEG measures taken during anesthesia exhibit stereotypic changes as anesthetic
depth increases. These changes include complex patterns of waves with frequency slowing accompanied by amplitude
increases which typically peak when loss of consciousness
occurs (loss of responses to verbal commands; loss of righting reflex). As anesthetic depth increases from light surgical levels to deep anesthesia, the EEG exhibits disrupted rhythmic waveforms, high amplitude burst suppression activity, and finally, very low amplitude isoelectric or 'flat line' activity. Various signal analysis
approaches have been used to quantify these pattern changes and can provide an indication of loss of recall, loss of consciousness and anesthetic depth. Monitors have been developed using various algorithm
s for signal analysis and are commercially available, but none have as yet proven 100% accurate. This is a difficult problem and an active area of medical research.
EMG is used for cranial nerve monitoring in skull base cases and for nerve root monitoring and testing in spinal surgery.
ABR (aka BSEP, BSER, BAEP, etc.) is used for monitoring of the acoustic nerve during acoustic neuroma and brainstem tumor resections.
on occupational regulation. Worldwide, there are at least two private certifications available: CNIM (Certified in Neurophysiological Intraoperative Monitoring) and D.ABNM (Diplomate of the American Board of Neurophysiological Monitoring). Though not governmentally regulated, certain health care facilities have internal regulations pertaining to neuromonitoring certifications (see below). The CNIM is a more widely known credential throughout the United States.
The Certification for Neurophysiological Intraoperative Monitoring (CNIM) is awarded by the American Board of Electroencephalographic and Evoked Potential Technologists. As of 2010, minimum requirements include 1) a B.A., B.S.(Path 2) 2)R.EP.T or R.EEG.T Credential(Path 1) 3) A minimum of 150 surgeries. Path 1 is a 200 question exam costing $350. Path 2 is a 250-question exam. A 4-hour multiple-choice computer-based exam is offered twice a year. Currently, there are a little over 2000 board certified clinicians.
The Diplomate of the American Board of Neurophysiologic Monitoring (D.ABNM) is awarded by the American Board of Neurophysiological Monitoring. As of January 1, 2011 the minimum requirements include: 1) a doctorate in a health science related field 2) an experience base of 300 surgeries that spans at least 3 years of primary responsibility, and 3) two surgeon-signed attestation forms. The exam includes a written portion, which must be passed first, and an oral portion. The 250 question, 4 hour written exam is offered twice a year, as is the oral exam. As of 2007-02, there are 104 D.ABNM certified individuals.
Clinical neurophysiology
Clinical neurophysiology is a medical specialty that studies the central and peripheral nervous systems through the recording of bioelectrical activity, whether spontaneous or stimulated....
such as electroencephalography
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
(EEG), electromyography
Electromyography
Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...
(EMG), and evoked potential
Evoked potential
An evoked potential is an electrical potential recorded from the nervous system of a human or other animal following presentation of a stimulus, as distinct from spontaneous potentials as detected by electroencephalography or electromyography .Evoked potential amplitudes tend to be low, ranging...
s to monitor the functional integrity of certain neural structures (e.g., parts of the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
, spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
and peripheral nerves) during surgery. The purpose of IONM is to reduce the risk to the patient of iatrogenic
Iatrogenesis
Iatrogenesis, or an iatrogenic artifact is an inadvertent adverse effect or complication resulting from medical treatment or advice, including that of psychologists, therapists, pharmacists, nurses, physicians and dentists...
damage to the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
, and/or to provide functional guidance to the surgeon
Surgeon
In medicine, a surgeon is a specialist in surgery. Surgery is a broad category of invasive medical treatment that involves the cutting of a body, whether human or animal, for a specific reason such as the removal of diseased tissue or to repair a tear or breakage...
and anesthesiologist
Anesthesiologist
An anesthesiologist or anaesthetist is a physician trained in anesthesia and peri-operative medicine....
.
Methods
Neuromonitoring employs various electrophysiologic modalities, such as extracellularExtracellular
In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...
single unit and local field recordings, SSEP, transcranial electrical motor evoked potentials (TCeMEP), EEG, EMG, and auditory brainstem response
Auditory Brainstem Response
The auditory brainstem response is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The resulting recording is a series of vertex positive waves of which I through V are evaluated...
(ABR). For a given surgery, the set of modalities used in depends on which neural structures are at risk. Transcranial Doppler Imaging
Transcranial doppler
Transcranial Doppler is a test that measures the velocity of blood flow through the brain's blood vessels. Used to help in the diagnosis of emboli, stenosis, vasospasm from a subarachnoid hemorrhage , and other problems, this relatively quick and inexpensive test is growing in popularity in the...
(TCDI) is also becoming more widely used to detect vascular emboli
Embolism
In medicine, an embolism is the event of lodging of an embolus into a narrow capillary vessel of an arterial bed which causes a blockage in a distant part of the body.Embolization is...
. TCDI can be used in tandem with EEG during vascular surgery
Vascular surgery
Vascular surgery is a specialty of surgery in which diseases of the vascular system, or arteries and veins, are managed by medical therapy, minimally-invasive catheter procedures, and surgical reconstruction. The specialty evolved from general and cardiac surgery...
. IONM techniques have significantly reduced the rates of morbidity and mortality
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
without introducing additional risks. By doing so, ONM techniques reduce health care costs.
To accomplish these objectives, a member of the surgical team with special training in neurophysiology
Neurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
obtains and co-interprets triggered and spontaneous electrophysiologic signals from the patient periodically or continuously throughout the course of the operation. Patients who benefit from neuromonitoring are those undergoing operations involving the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
or which pose risk to its anatomic or physiologic integrity. In general, a trained neurophysiologist attaches a computer system to the patient using stimulating and recording electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s. Interactive software running on the system carries out two tasks:
- selective activation of stimulating electrodes with appropriate timing, and
- processing and displaying of the electrophysiologic signals as they are picked up by the recording electrodes.
The neurophysiologist can thus observe and document the electrophysiologic signals in realtime in the operating during the surgery. The signals change according to a various factors, including anesthesia, tissue temperature, surgical stage, and tissue stresses. Various factors exert their influence on the signals with various tissue-dependent timecourses. Differentiating the signal changes along these lines with particular attention paid to stresses is the joint task of the surgical triad: surgeon, anesthesiologist, and neurophysiologist.
Surgical Procedures
Patients benefit from neuromonitoring during certain surgical procedures, namely any surgery where there is risk to the CNSCentral nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
or to a peripheral nerve. Most neuromonitoring is utilized by spine surgeons or neurosurgeons, but vascular, orthopedic, otolarygologists and urology surgeons have all utilized neuromonitoring as well.
The most common applications are in neurosurgery
Neurosurgery
Neurosurgery is the medical specialty concerned with the prevention, diagnosis, treatment, and rehabilitation of disorders which affect any portion of the nervous system including the brain, spine, spinal cord, peripheral nerves, and extra-cranial cerebrovascular system.-In the United States:In...
such as spinal surgery; selected brain surgeries; carotid endarterectomy
Carotid endarterectomy
Carotid endarterectomy is a surgical procedure used to prevent stroke, by correcting stenosis in the common carotid artery...
; ENT
Otolaryngology
Otolaryngology or ENT is the branch of medicine and surgery that specializes in the diagnosis and treatment of ear, nose, throat, and head and neck disorders....
procedures such as acoustic neuroma
Vestibulocochlear nerve
The vestibulocochlear nerve is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium information from the inner ear to the brain...
resection; and peripheral nerve surgery. Motor evoked potentials have also been used in surgery for TAAA (thoracic-abdominal aortic aneurysms).
Intraoperative monitoring is used
- to localize neural structures, for example to locate cranial nerves during skull base surgery;
- to test function of these structures; and
- for early detection of intraoperative injury, allowing for immediate corrective measures.
For example, during any surgery on the thoracic or cervical
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
spinal column, there is some risk to the spinal cord. Since the 1970s, SSEP (somatosensory evoked potentials) have been used to monitor spinal cord function by stimulating a nerve distal to the surgery, and recording from the cerebral cortex or other locations rostral to the surgery. A baseline is obtained, and if there are no significant changes, the assumption is that the spinal cord has not been injured. If there is a significant change, corrective measures can be taken; for example, the hardware can be removed.
More recently, transcranial electric motor evoked potentials (TCeMEP) have also been used for spinal cord monitoring. This is the reverse of SSEP; the motor cortex is stimulated transcranially, and recordings made from muscles in the limbs, or from spinal cord caudal to the surgery. This allows direct monitoring of motor tracts in the spinal cord.
EEG electroencephalography is used for monitoring of cerebral function in neurovascular cases (cerebral aneurysms, carotid endarectomy) and for defining tumor margins in epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
surgery and some cerebral tumors.
EEG measures taken during anesthesia exhibit stereotypic changes as anesthetic
Anesthesia
Anesthesia, or anaesthesia , traditionally meant the condition of having sensation blocked or temporarily taken away...
depth increases. These changes include complex patterns of waves with frequency slowing accompanied by amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
increases which typically peak when loss of consciousness
Unconsciousness
Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...
occurs (loss of responses to verbal commands; loss of righting reflex). As anesthetic depth increases from light surgical levels to deep anesthesia, the EEG exhibits disrupted rhythmic waveforms, high amplitude burst suppression activity, and finally, very low amplitude isoelectric or 'flat line' activity. Various signal analysis
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
approaches have been used to quantify these pattern changes and can provide an indication of loss of recall, loss of consciousness and anesthetic depth. Monitors have been developed using various algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
s for signal analysis and are commercially available, but none have as yet proven 100% accurate. This is a difficult problem and an active area of medical research.
EMG is used for cranial nerve monitoring in skull base cases and for nerve root monitoring and testing in spinal surgery.
ABR (aka BSEP, BSER, BAEP, etc.) is used for monitoring of the acoustic nerve during acoustic neuroma and brainstem tumor resections.
Licensure, certification, and credentialing
In the US, IONM licensure has not been legislated at the state or federal level. Issues of licensure are discussed in ASET's 68-page white paperWhite paper
A white paper is an authoritative report or guide that helps solve a problem. White papers are used to educate readers and help people make decisions, and are often requested and used in politics, policy, business, and technical fields. In commercial use, the term has also come to refer to...
on occupational regulation. Worldwide, there are at least two private certifications available: CNIM (Certified in Neurophysiological Intraoperative Monitoring) and D.ABNM (Diplomate of the American Board of Neurophysiological Monitoring). Though not governmentally regulated, certain health care facilities have internal regulations pertaining to neuromonitoring certifications (see below). The CNIM is a more widely known credential throughout the United States.
The Certification for Neurophysiological Intraoperative Monitoring (CNIM) is awarded by the American Board of Electroencephalographic and Evoked Potential Technologists. As of 2010, minimum requirements include 1) a B.A., B.S.(Path 2) 2)R.EP.T or R.EEG.T Credential(Path 1) 3) A minimum of 150 surgeries. Path 1 is a 200 question exam costing $350. Path 2 is a 250-question exam. A 4-hour multiple-choice computer-based exam is offered twice a year. Currently, there are a little over 2000 board certified clinicians.
The Diplomate of the American Board of Neurophysiologic Monitoring (D.ABNM) is awarded by the American Board of Neurophysiological Monitoring. As of January 1, 2011 the minimum requirements include: 1) a doctorate in a health science related field 2) an experience base of 300 surgeries that spans at least 3 years of primary responsibility, and 3) two surgeon-signed attestation forms. The exam includes a written portion, which must be passed first, and an oral portion. The 250 question, 4 hour written exam is offered twice a year, as is the oral exam. As of 2007-02, there are 104 D.ABNM certified individuals.
Trade-Related Societies
External links
- See a video of the equipment used (Flash video)