Presentation on theme: "Intraoperative Monitoring"— Presentation transcript:
1Intraoperative Monitoring Behrouz Zamanifekri, MD Neurophysiology Fellow KUMC March 2013
2Intraoperative monitoring The most primitive method of monitoring the patient 50 years ago were continuous palpation of the radial pulsations throughout the operation or wake up test!!
3History 1921, Dr Penfield, intraoperative neurophysiology research 1950s, Dr Penfield, electrical stimulation to find epileptic foci1970s, Dr Brown used SSEP for scoliosis operation1974 , among 7,800 operations conducted with Harrington instrumentation, 87 patients had subsequently developed significant spinal cord problemsEarly 1980, IOM in operations for large skull base tumors1980, the American Society for NeurophysiologicalMonitoring [ASNM])
4Introduction What is IOM ? use of neurophysiological recordings for detecting changes caused by surgically induced insultsassess the function of specific parts of the nervous system continuously during an operationIt is becoming part of standard medical practice
5What is the purpose of IOM? 1. Reduce the risk of postoperative neurological deficits2. Identify specific neuronal structures and landmarks that cannot be easily recognized3. Research purposes in basic science, pathophysiology and therapeutic management
6What are the most common types of recording? Spontaneous activityEEGEMGEvoked responses (through external stimulation of a neural pathway)Sensory : 1- visual2-auditory3-somatosensoryMotorThe type of test to be used and the sites of recording and stimulation are chosen on a case by case
7Complications during surgery ischemiamechanical insult
9Spinal MonitoringSpinal cord, nerve roots, and blood vessels are frequently placed at risk for injuryElectrophysiological modalities for monitoring:SSEPsMEPsfree run or spontaneous EMG (sEMG)triggered EMG (tEMG)
10Spine Surgery:surgical insults to the ventral parts of the cord, using motor evoked potentials (MEPs)dorsal columns of the spinal cord , SEPthe purpose of IOM is to detect response changes due to surgery, not to make a clinical diagnosis
11Monitoring of Somatosensory Evoked Potential Earliest used method in IOM1970s in operations for scoliosisStimulation of peripheral nerve and recorded from scalpOnly monitor dorsal(sensory) spinal cordpatient sensory examination for position and vibration is recommended prior to surgery
12SSEP By electrical stimulation of peripheral nerves Median nerve at wrist for injury above C8Posterior tibial nerve at ankle for injury below C8
13spinal cord through the dorsal roots, ascending pathways, thalamusand, finally, to theprimary sensory cortex
16Location of the stimulating and recording posterior tibial nerve SEPs.
17It is important to note- Earlier peaks tend to be less sensitive to anesthesia- used to differentiate SSEP monitoring changes resulting from anesthetic effects from surgical manipulation.
18Alarm criteria -50% reduction in amplitude -10% increase in latency Factors that affect the SSEP amplitude include halogenated agents, nitrous oxide, hypothermia, hypotension, and electrical interference
19Normal SSEPs from median nerves and posterior tibial nerves
20SSEP in Peripheral nerves? sciatic nerve injury during pelvic fractureInjuries to brachial plexus in positioning of pt is commonProlong latency of all peaks and decrease amplitude
21Nerve rootSSEP: insensitive to changesin nerve root functionWhy?
22SSEP in nerve root injury? SSEP used during placement of pedicle screwsRisk of spinal nerve root injuryIf one root damaged, no change inSSEPDermatomal stimulation is better
23Inhalational anesthetics, cortical responses Intravenous Agents- Propofol increases the latency by approximately10%- Benzodiazepines reduce the amplitude of cortical SEP- Etomidate : cortical SEP amplitude augmented 200–600%,increases SEP latencies- Opiates, cause a slight increase in SEP latency- Muscle relaxants, not affect SEPs
24SEP changes due to surgical maneuvers (e. g SEP changes due to surgical maneuvers (e.g., spinal distraction) or ischemia (e.g., after placement of an artery clamp) are abrupt and localized and only one side of the body may be affectedwhereas changes due to anesthesia or body temperature changes are relatively slower
25Detection of cord injury due to misplaced instrumentation just after placement of instrumentation,both the cortical (peak N45) andcervical (peak N30) responses disappear
26SEPs obtained after cross-clamping of the internal carotid ,which resulted in ischemia (time 9:45) that later deteriorated (9:55). After placement of a shunt, response amplitude is restored to within normal limits (time 10:01).
27Procedures involves the ICA, MCA, PCA, P.Com, or BA? Median nerve SEPsprocedure involves theACA or the A.Com artery?Posterior tibial nerve
29Introduction SSEP for sensory pathway MEP for motor SSEP + MEP: Small reversible changes in SSEP that occur when motor pathway are injured
30MEP 1990s, TC-MEP as a method to monitor the corticospinal tracts Prior to MEP monitoring,the only way to assess corticospinaltract during surgery was wake-up test
31TC-MEPsstimulation through the skull with signal recording at the level ofmuscle (CMAP)nerve (neurogenic MEP)spinal cord ( D-wave )-the newer technologies is continuous free-running EMG throughout the surgery
32Recording of Muscle Evoked Potentials Stimulation of cortex, activation of coticospinal, EMG of distal( Hand m., abd hallucis, tibialis anterior)Muscle relaxant can not be used
34Interpretation of MEP Recording 4 methods :1) all-or-nothing criterion: the most used method,complete loss of the MEP signal from a baseline recording is indicative ofa significant event2) amplitude criterion: 80% amplitude decrement in at least 1out of 6 recording sites3) threshold criterion: increases in the threshold of 100 V or morerequired for eliciting CMAP responses that are persistent for 1 h or more4) morphology criterion: changes in the pattern and duration of MEPwaveform morphology
35TcMEP monitoring contraindicated in -deep brain stimulators or cochlear implantsTongue biting is the most common complication
37Recording of the response from spinal cord(D, I wave) Recording from epiduralelectrodesD (direct activation ofcorticospinal)I ( indirect, through transsynaptic)Not affected by muscle relaxants, but latencies increase with coolingSubdural electrodes can be substituted for epidural electrodesNeedle electrodes can be place in interspinous ligaments both sides of surgery areamajor benefits reported during intramedullary spinal cord tumor resectiona complete loss of MEPs with at least 50% preservation of the D-wave amplitude generally results in a transient paraplegia
38Spontaneous EMG monitor nerve roots recording electrodes placed in the musclesno stimulation is performedmonitoring of 2 muscles is recommendedC5 nerve root injury, The deltoid and biceps brachiiMEPs be obtained intermittently
39sEMG no paralytic agents train-of-4 testing should indicate that at least 3 out of 4Myasthenia gravis, Botox treatments, and muscular dystrophy are classic conditions that interfere with EMG
40Abnormal sEMG spikes Bursts trains Trains are continuous, repetitive EMG firingcaused by continuous force applied to the nerveroot.
41Example of EMG activity indicating irritation of the nerve Baseline recordings. Note the low amplitude background activity High amplitude spikes are present
42Artifacts may be mistaken for spikes or trains a neurostimulatorthe surgical tablethe surgeon’s head lightbipolar electrocautery device
44Triggered EMG (Pedicle Screw Stimulation) used to determine whether screws have breached the medial or inferior pedicle wall and thus pose a risk to the exiting nerve root at that levelWhen a pedicle screw is accurately placed, the surrounding bone acts as an insulator to electrical conduction, and a higher amount of electrical current is thus required to stimulate the surrounding nerve root.When a medial pedicle wall breach occurs, the stimulation threshold is significantly reduced
45False negative response muscles relaxantsfluid, blood, or soft tissue around the head of the screw , shunt current away from the screwit is important that the stimulation probe be placed directly on the top of the screw and not the tulip, as these 2 structures are not structurally fusedPresence of preexisting nerve root injury. Injured nerve roots will have higher triggering thresholds,
46Due to the variation in thickness and shape between thoracic and lumbar pedicles, different stimulation thresholds exist for these regionsA threshold < 10 mA for screw stimulation, suggest a medial wall breach in the lumbar pediclesA thresholds > 15 mA indicate a 98% likelihood of accurate screw positioningFor thoracic pedicle screw placement, stimulation threshold < 6 mA suggest a medial pedicle breach
47In cervical and thoracic procedures, the spinal cord are of greater importance Conversely, in lumbar or sacral procedures the nerve roots are at greater risk of injury
49ConclusionsMultimodality neurophysiological monitoring is extremely valuable in the prevention of neurological injuryKnowledge of the benefits and limitations of each modality helps maximize the diagnostic value of IOM during spinal procedures
50Neurosurg Focus / Volume 27 / October 2009 A concise guide to intraoperative monitoring / George Zouridakis, Andrew C. Papanicolaou.2001Intraoperative neurophysiological monitoring / Aage R. Moller. -- 2nd ed.