Patent Application
20050085743
1. Field of the Invention
The present invention relates generally to intraoperative neural monitoring and, more particularly, to apparatus and methods for intraoperative neural monitoring involving monitoring of the spinal cord using motor evoked potentials elicited by electrical stimulation.
2. Brief Discussion of the Related Art
Intraoperative neural monitoring involving intraoperative monitoring of the spinal cord has become accepted as an effective means to avoid neural deficits in patients undergoing various types of surgical procedures in which the spinal cord is at risk of injury. By monitoring the integrity of the spinal cord motor tracts during surgery, impairments in motor function may be detected before they become irreversible and while there is sufficient time to institute corrective measures.
Spinal cord monitoring has traditionally relied on the Stagnara wake-up test, which is ordinarily performed at the conclusion of a surgical procedure and thusly does not provide an early indication of spinal cord dysfunction. Wake-up testing is limited to evaluating gross motor function and fails to identify more subtle spinal cord impairments. Oftentimes administration of the wake-up test is compromised by anesthetic influences. The wake-up test depends on a subjective assessment of a patient's motor responses, and is usually of little value in patients whose motor responses are already impaired by preexisting neural deficits. Additional disadvantages of the wake-up test include the risks of air embolism and self-extubation.
Sensory evoked potentials (SEPs) have also been used for intraoperative spinal cord monitoring, primarily to monitor the dorsal medial tracts within the spinal cord. SEPs are ascending motor volleys elicited by stimulating a peripheral nerve, commonly the posterior tibial nerve at the ankle (medial malleolus), and conducted primarily through the dorsal columns of the spinal cord. SEPs may be detected and recorded as waveforms at various anatomical locations along the nerve tract including peripherally (e.g. popliteal fossa), cervically and cortically. Medically significant changes in amplitude and latency of SEP waveforms during surgery may be indicative of surgically-induced sensory deficits (parathesia). However, it is possible for motor deficits to develop intraoperatively despite the lack of medically significant changes in recorded SEPs, i.e. false negatives. In addition, in some patients it may be difficult or not possible to obtain SEP readings intraoperatively. Being low amplitude, SEP responses require averaging over time such that the readings obtained from SEPs are not as close to real-time as would be desirable. Routine intraoperative spinal cord monitoring using SEPs cannot effectively spatially resolve the loss of certain nerve roots, such as the lumbosacral root, which optimally requires electromyographic (EMG) responses from muscles enervated by the nerve roots.
A more recent form of spinal cord monitoring that addresses many of the disadvantages of the wake-up test and SEPs involves monitoring the spinal cord motor tracts using motor evoked potentials (MEPs). Transcranial electrical stimulation to stimulate the motor cortex has been proposed for eliciting MEPs, which are descending motor volleys conducted along the motor pathways of the spinal cord. The motor cortex can be stimulated non-invasively through an intact skull with electrical current of sufficient magnitude applied via appropriately placed stimulating electrodes. MEPs can be recorded at various anatomical locations including the spine, innervated muscles of the upper and lower extremities (myogenic), and peripheral nerves (neurogenic). Medically significant changes in recorded MEPs during surgery may be indicative of surgically-induced motor deficits (paraplegia), and MEPs are believed to be more sensitive to certain types of spinal cord trauma than SEPs. MEPs recorded from the spinal cord reflect the functional integrity of the corticospinal tract, and MEPs recorded from limb muscles reflect the functional integrity of the motor system from the cerebral cortex to beyond the neuromuscular junction. By stimulating the motor cortex on both sides of the patient's body and recording myogenic MEPs (compound muscle action potential) in muscles on both sides of the patient's body, unilateral neural deficits can be differentiated.
Although magnetic stimulation of the motor cortex can be used to elicit MEPs, transcranial electrical stimulation is generally preferred because magnetic motor evoked potentials are more sensitive to anesthetic-induced depression than electrical motor evoked potentials. Although anesthetics reduce synoptic efficacy and decrease cortical excitability as well as the excitability of spinal motoneurons and interneurons, repetitive or multipulse transcranial stimulation with electrical pulses of sufficiently high current can still elicit MEPs by enhancing temporal summation of the descending input on spinal motoneurons. It is also possible to elicit MEPs by direct electrical stimulation of the spinal cord using epidural electrodes or needle electrodes placed near or in the vertebral bodies with recording accomplished in muscles, nerves and/or the epidural space.
MEPs are large amplitude responses that do not require signal averaging, such that reporting may be accomplished essentially real-time. MEPs provide fast, practical and reliable qualitative information on the functional integrity of the motor tracts of the spinal cord. Because MEPs and SEPs are conducted in different spinal cord pathways having different blood supplies, MEPs may be present in patients when SEPs are absent or ill-defined. MEP monitoring thusly makes it possible to monitor the spinal cord in patients for whom SEP signals are unobtainable. Furthermore, MEPs may better reflect the integrity of the anterior spinal cord than SEPs.
Representative discussions of transcranial electrical stimulation to elicit MEP responses for monitoring the spinal cord during spinal surgery are set forth in “Cotrel-Dubousset Instrumentation in Children Using Simultaneous Motor And Somatosensory Evoked Potential Monitoring” by Stephen, Sullivan, Hicks, Burke, Woodforth and Crawford, Threshold-level repetitive transcranial electrical stimulation for intraoperative monitoring of central motor conduction” by Calancie, Harris, Brindle, Green and Landy, “A comparison of myogenic motor evoked responses to electrical and magnetic transcranial stimulation during nitrous oxide/opioid anesthesia” by Ubags, Kalkman, Been, Koelman, and de Visser, “lntraoperative monitoring of spinal cord function using motor evoked potentials via transcutaneous epidural electrode during anterior cervical spinal surgery” by Gokaslan, Samudrala, Deletis, Wildrick and Cooper, “lntraoperative spinal cord monitoring for intramedullary surgery: an essential adjunct” by Kothbauer, Deletis and Epstein, “Improved amplitude of myogenic motor evoked responses after paired transcranial electrical stimulation during sufentanil/nitrous oxide anesthesia” by Kalkman, Ubags, Been, Swaan and Drummond, “Repetitive vs. single transcranial electrical stimulation for intraoperative monitoring of motor conduction in spine surgery” by Haghighi and Gaines, “Monitoring of motor evoked potentials with high intensity repetitive transcranial electrical stimulation during spinal surgery” by Haghighi, “Monitoring scoliosis surgery with combined multiple pulse transcranial electric motor and cortical somatosensory-evoked potentials from the lower and upper extremities” by MacDonald, Zayed, Khoudeir and Stigsby, “Intraoperative motor evoked potentials to transcranial electrical stimulation during two anaesthetic regimens” by Pelosi, Stevenson, Hobbs, Jardine and Webb, “The effect of sevoflurane on myogenic motor-evoked potentials induced by single and paired transcranial electrical stimulation of the motor cortex during nitrous oxide/ketamine/fentanyl anesthesia” by Kawaguchi, Inoue, Kakimoto, Kitaguchi, Furuya, Morimoto and Sakaki, “Threshold-level multipulse transcranial electrical stimulation of motor cortex for intraoperative monitoring of spinal motor tracts: description of method and comparison to somatosensory evoked potential monitoring” by Calanci, Harris, Broton, Alexeeva and Green, “Motor evoked potential monitoring during spinal surgery: responses of distal limb muscles to transcranial cortical stimulation with pulse trains” by Jones, Harrison, Koh, Mendoza and Crockard, “Transcranial high-frequency repetitive electrical stimulation for recording myogenic motor evoked potentials with the patient under general anesthesia” by Pechstein, Cedzich, Nadstawek and Schramm, and “Intraoperative Spinal Cord Monitoring” by Houlden. A representative discussion relating to direct electrical stimulation of the spinal cord to elicit MEPs is set forth in “Intra-operative monitoring during surgery for spinal deformity” by Moore and Owen.
Since myogenic MEPs may not indicate motor injury of individual nerve roots, such as the lumbosacral root, it is advantageous in many surgical procedures in which the spinal cord is monitored to also perform neural monitoring involving individual nerve roots. For example, some spinal procedures entail internal fixation with medical devices that may irritate or injure nerve roots, such as the lumbar root, when placed in a patient's body during an operative procedure. Nerve irritation or injury may occur and remain undetected even while standard MEP testing appears normal. It is therefore beneficial to intraoperatively detect dysfunction in individual nerve roots by electrically stimulating the nerve or the anatomical area in the vicinity of the nerve, and monitoring electromyographic (EMG) responses in muscles innervated by the nerve. When electrical stimulation is applied to anatomical tissue at or reasonably near the nerve of interest, the stimulation signal is transmitted through the nerve to excite the related muscle. Excitement of the muscle causes an electrical impulse to be generated within the muscle (EMG) which may be detected by a monitoring or recording electrode in the muscle, thereby providing an indication as to the location and/or integrity of the nerve. Locating a nerve during surgery allows the area of the nerve to be avoided so that it is protected and preserved. Providing an indication of nerve integrity allows nerve irritation or trauma to be detected early, so that the source of irritation or trauma can be identified and corrected. Accordingly, it is beneficial in many types of surgical procedures to perform neural monitoring by monitoring both the spinal cord, using elicited MEPs, and individual nerves/nerve roots, using evoked EMG. The stimulation current for evoked EMG is ordinarily delivered at lower current amperage than the stimulation required to elicit MEPs. In addition to monitoring EMG responses when electrical stimulation is applied, it is also desirable for neural intraoperative monitoring systems to permit neural monitoring involving continuous monitoring of EMG activity from certain muscles at rest and/or when no electrical stimulation is being applied. It would therefore be desirable to provide a single intraoperative neural monitoring system capable of performing multiple modalities of neural monitoring including MEP monitoring and continuous and evoked EMG monitoring.
A representative monitoring or recording electrode for detecting EMG responses in muscles is disclosed in U.S. Pat. No. 5,161,533 to Prass et al. Representative monopolar and bipolar stimulating probes for electrically stimulating a nerve or anatomical tissue in the vicinity of a nerve are disclosed in U.S. Pat. No. 4,892,105 to Prass and U.S. Pat. No. 6,292,701 B1 to Prass et al. Prior nerve integrity monitoring systems for recording EMG activity from muscles and alerting a surgeon when a nerve has been activated by an electric stimulus are represented by U.S. Pat. No. 6,334,068 B1 to Hacker and U.S. Pat. No. 6,306,100 B1 to Prass. The entire disclosures of U.S. Pat. Nos. 4,892,105, U.S. Pat. No. 5,161,533, U.S. Pat. No. 6,292,701 B1, U.S. Pat. No. 6,306,100 B1, and U.S. Pat. No. 6,334,068 B1 are incorporated herein by reference.
Prior intraoperative neural monitoring systems are either not designed to provide electrical current of sufficient magnitude to elicit MEPs or are not designed to provide automatic biphasic electrical stimulation sequences between the stimulating electrodes. Biphasic electrical stimulation sequences between stimulating electrodes placed in a patient's body in correspondence with the anatomical areas to be stimulated allow the anatomical areas to be sequentially alternatingly stimulated. Where the stimulated anatomical areas, such as the left and right motor cortex, generate MEPs respectively detectable as EMG responses on opposite sides, i.e. left and right, of the patient's body, unilateral neural deficits can be differentiated. However, where the direction or polarity of current flow between the stimulating electrodes is fixed, providing monophasic electrical stimulation in one direction or polarity between the stimulating electrodes, the anatomical areas cannot be sequentially alternatingly stimulated without manually reversing the locations of the stimulating electrodes with respect to the anatomical areas or electromechanically reversing the lead polarities for the stimulating electrodes each time polarity or direction of current flow between the stimulating electrodes is to be reversed.
The Digitimer D185 Multipulse Stimulator of Digitimer Ltd. allows the direction or polarity of current flow between the stimulating electrodes to be reversed, but not automatically. Rather, a polarity selection switch having “normal” and “reverse polarity” settings must be operated each time the direction or polarity of the stimuli is to be reversed. Operation of the polarity selection switch is in addition to operation of a separate trigger switch that activates the delivery of electrical pulses to the output stimulating electrode. Operation of the trigger switch effects delivery of only one phase (positive or negative) of electrical pulses since the polarity selection switch must be operated in order to deliver pulses of the opposite phase. Another operation of the trigger switch is required to effect delivery of the opposite phase pulses.
Prior intraoperative neural monitoring systems used to elicit MEPs and/or the stimulators used to elicit MEPs are therefore associated with various disadvantages including additional operational steps which increase the duration of the surgical procedures to the detriment of patients and medical personnel, increased complexity and confusion attendant with intraoperative neural monitoring, the possible occurrence of false negative responses due to stimulation on the wrong side of the body, and the need for greater human and/or mechanical intervention. Prior intraoperative neural monitoring systems used to elicit MEPs and/or the stimulators used to elicit MEPs have further drawbacks including failing to provide both positive and negative monophasic and automatic biphasic sequenced outputs from a single stimulator, failing to present left and right EMG waveforms simultaneously and correlated in time to biphasic electrical stimulation to allow a more complete interpretation of neurological motor responses, and the inability to efficiently integrate multiple neural monitoring modalities.
Accordingly, it is a primary object of the present invention to overcome the aforementioned disadvantages of prior intraoperative neural monitoring systems and prior electrical stimulators used to elicit MEPs for intraoperative neural monitoring.
Another object of the present invention is to automatically provide biphasic electrical stimulation sequences to left and right areas of the motor cortex to elicit MEPs for spinal cord monitoring.
A further object of the present invention is to eliminate the need for human and/or electromechanical intervention to reverse the direction or polarity of current flow between the stimulating electrodes of an electrical stimulator used in intraoperative neural monitoring system.
An additional object of the present invention is to automatically deliver biphasic stimulation sequences between a pair of stimulating electrodes from an electrical stimulator of an intraoperative neural monitoring system.
Furthermore, it is an object of the present invention to deliver a complete cycle of biphasic electrical stimulation from a stimulator in response to an activation performed at the beginning of the complete cycle.
It is also an object of the present invention to reduce the duration and complexity of surgical procedures involving intraoperative neural monitoring including spinal cord monitoring using MEPs.
The present invention has as another object to increase the safety and efficiency of surgical procedures involving intraoperative neural monitoring including spinal cord monitoring using MEPs.
Moreover, it is an object of the present invention to provide both positive and negative monophasic and automatic biphasic sequenced electrical outputs from a single stimulator used in an intraoperative neural monitoring system.
Yet a further object of the present invention is to facilitate the adjustment of various parameters of positive and negative monophasic and automatic biphasic electrical stimulation delivered from a stimulator for intraoperative neural monitoring.
Still another object of the present invention is to display EMG activity detected on the left and right sides of a patient's body simultaneously and correlated in time in response to biphasic electrical stimulation for enhanced intraoperative neural monitoring.
The present invention has as an additional object to automatically reverse the direction or polarity of stimulating current flowing between left and right areas of the motor cortex in transcranial electrical stimulation.
Furthermore, it is an object of the present invention to integrate a high current stimulator providing monophasic and automatic biphasic electrical stimulation sequences in an intraoperative neural monitoring system to expand the available modalities of neural monitoring.
Yet an additional object of the present invention is to combine a stimulator capable of delivering high current electrical stimulation via stimulating electrodes and a unit capable of delivering lower current electrical stimulation via stimulating probes in a single intraoperative neural monitoring system.
The aforesaid objects are achieved individually and in combination, and it is not intended that any of the objects be combined unless expressly required by the claims attached hereto.
Some of the advantages of the present invention are that the electrical stimulation is maintained within safe limits; electrical stimulation can be delivered to various anatomical locations; responses to electrical stimulation may be recorded using recording electrodes at various anatomical locations; the intraoperative neural monitoring system allows a more complete interpretation of neurological motor responses; unilateral motor deficits may be differentiated; false negative responses due to stimulating the wrong side of the motor tracts are avoided; polarity is reversed for the stimulator without a diminishment in current amplitude; artifactual changes in recorded activity are distinguished from true EMG responses; various event thresholds may be selected for detected EMG responses to establish the level of EMG activity at which an event is signaled; the stimulator may be used to stimulate various types of anatomical tissue including anatomical tissue having a cortical element or characteristics; the stimulator and the intraoperative neural monitoring system in which the stimulator is incorporated may be used in various surgical procedures in which the spinal cord may be placed at risk; the stimulator and the intraoperative neural monitoring system in which the stimulator is incorporated are particularly beneficial for use in spinal surgery and especially those procedures entailing internal fixation with medical devices such as pedicle screws; the intraoperative neural monitoring system in which the stimulator is incorporated facilitates multiple modalities of stimulation and neural monitoring including continuous EMG monitoring, evoked EMG monitoring, nerve root stimulation monitoring, pedicle screw stimulation monitoring, anterior and posterior spinal cord monitoring through spinal bone and discs, epidermal spinal cord monitoring and transcranial MEP monitoring; the stimulator is particularly useful for applying electrical stimulation requiring a high current; and the intraoperative neural monitoring system in which the stimulator is incorporated may include various types of low current stimulators, stimulating probes or electrodes, and recording electrodes.
These and other objects, advantages and benefits are realized with the present invention as generally characterized in an intraoperative neural monitoring system comprising a power source and a stimulator powered by the power source to deliver a complete cycle of biphasic electrical stimulation to a patient via stimulating electrodes connected to the stimulator and applied to the patient. The complete cycle of biphasic electrical stimulation is delivered from the stimulator as a first group of a selected number of positive phase or negative phase pulses automatically followed by a second group of a selected number of pulses of reverse phase or polarity to the pulses of the first group. The first group of pulses is delivered to a first stimulating electrode for return via a second stimulating electrode in the positive phase and is delivered to the second stimulating electrode for return via the first stimulating electrode in the negative phase. The intraoperative neural monitoring system includes an activator actuatable by a user to perform an activation to initiate delivery of the first group of pulses, and the activation effects delivery of the entire cycle of biphasic electrical stimulation. The stimulator may alternatively be activated to deliver a complete cycle of monophasic electrical stimulation comprising a selected number of pulses that are all positive phase or all negative phase.
Various parameters for the electrical stimulation delivered by the stimulator are selectable including mode, i.e. biphasic or monophasic, current amplitude, pulse width, delay between successive pulses, and number of pulses. The stimulator is capable of delivering electrical stimulation having a current amplitude in the range of 0 to 200 mA to elicit MEPs in the patient. The stimulator is electrically connectible with a power console, which may serve as the power source for the stimulator, and the power console includes a touch screen by which the parameters may be selected. The activator may include a control option on the touch screen or a hand switch.
The intraoperative neural monitoring system may also include a patient interface unit electrically connectible with the power source for delivering electrical stimulation to the patient via a monopolar or bipolar stimulating probe connected to the patient interface unit. The electrical stimulation delivered by the patient interface unit comprises constant current monophasic pulses delivered continuously for so long as a tip of the probe is in contact with anatomical tissue. Various parameters for the electrical stimulation delivered by the patient interface unit, including current amplitude, pulse width, and repetition, are selectable and may be selected via the touch screen. The patient interface unit is capable of delivering electrical stimulation having a current amplitude in the range of 0 to 30 mA to evoke EMG activity in the patient. The patient interface unit comprises a plurality of monitoring channels for the connection of monitoring or recording electrodes to be applied to the patient to detect EMG activity.
The touch screen provides various displays including a setup display, a nerve root selection display, a montage display, monitoring displays and an electrodes display. The monitoring displays display waveforms representative of EMG activity detected by the monitoring electrodes. A monitoring display for electrical stimulation applied via the stimulator includes a waveform display area that displays waveforms representative of EMG activity detected for the positive and negative phases of electrical stimulation, and the waveforms are displayed simultaneously and correlated in time.
The present invention is also generally characterized in a method of intraoperative neural monitoring comprising the steps of activating a stimulator to initiate delivery of a biphasic cycle of electrical stimulation to a patient during an operative procedure, delivering the entire biphasic cycle of electrical stimulation to the patient in response to the activating step, and detecting EMG activity in a muscle of the patient responsive to the electrical stimulation to monitor neural function during the operative procedure. The method may involve eliciting motor evoked potentials in the patient in response to the electrical stimulation. The step of activating may be performed as a two-step procedure executed via a touch screen of a power console connected to the stimulator or via a hand switch connected to the power console. The electrical stimulation may be delivered to the patient at various anatomical locations, and the step of delivering may include delivering the electrical stimulation to the left and right motor cortex and/or to the spinal cord. The step of delivering may include delivering the electrical stimulation to the patient via stimulating electrodes applied to the patient. The method may involve various additional steps including the step of delivering electrical stimulation to the patient via a monopolar or bipolar stimulating probe connected with a patient interface unit that is electrically connected to the power console. The step of detecting may involve detecting the EMG activity via monitoring electrodes placed in muscle of the patient and may involve displaying waveforms representative of the detected EMG activity on a monitoring display of the touch screen
These and other objects and advantages of the present invention will become apparent from the following description of a preferred embodiment taken in conjunction with the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference characters.
An intraoperative neural monitoring system 10 according to the present invention is depicted in
The power console 12 is shown in
As shown in
As further shown in
The patient interface unit 14 is illustrated in
The patient interface unit 14 includes a probe interface 56 for connection of a monopolar or bipolar stimulating probe to the patient interface unit. The probe interface 56 comprises connectors 57a (positive) and 57b (negative) as well as an auxiliary connector 58 (negative). Each probe interface connector 57a, 57b and 58 may comprise a jack or other suitable electrical connector. Two connection diagrams are provided on the housing 44, one connection diagram 59a diagrammatically depicting connection of a monopolar stimulating probe to the probe interface 56 for monopolar Stim 1 electrical stimulation and the other connection diagram 59b diagrammatically depicting connection of a bipolar stimulating probe to the probe interface for bipolar Stim 1 electrical stimulation.
Monopolar and bipolar stimulating probes may be used to provide electrical stimulation in the area of a nerve. If the stimulation is applied at or reasonably near the nerve, the stimulation signal is applied to the nerve and is transmitted through the nerve to excite the related muscle. Excitement of the muscle causes an electrical impulse (EMG) to be generated within the muscle, the impulse being detected by the monitoring electrodes which have been placed in the muscle. Monitoring EMG activity evoked in response to stimulation applied via stimulating probes connected with the patient interface unit 14 allows the location and/or integrity of nerves to be ascertained. The intraoperative neural monitoring system 10 also allows EMG activity at the monitoring electrodes to be continuously monitored even while no electrical stimulation is being applied and nerves are not being manipulated by the surgeon. Continuous EMG monitoring provides at rest or baseline EMG parameters which facilitate identification of potentially significant intraoperative changes in monitored EMG activity.
It should be appreciated that color coding of the patent interface unit to monitoring and ground electrodes and to stimulating probes may be accomplished in various ways. Also, the term “wire” as used herein is intended to encompass a single wire or a plurality of wires. U.S. Pat. No. 6,334,068 B1 to Hacker is incorporated herein by reference as providing teachings pertinent to an understanding of the design and operation of the power console 12 and patient interface unit 14 as well as stimulation via monopolar and bipolar stimulating probes and EMG monitoring via monitoring electrodes. It should also be appreciated that the term “nerve” as used herein is intended to encompass various nerves and nerve roots.
The stimulation delivered from the patient interface unit 14 to the monopolar or bipolar stimulating probe 64, 66 is a first form of electrical stimulation or Stim 1 electrical stimulation. Stim 1 electrical stimulation is continuous monophasic electrical stimulation comprising continuous constant current (DC) square wave pulses. A waveform 70 representing Stim 1 electrical stimulation is shown in
The stimulator 16 is illustrated in
The stimulation delivered to the stimulating output electrode 76a or 76b from the stimulator 16 is a second form of electrical stimulation or Stim 2 electrical stimulation. Stim 2 electrical stimulation is delivered as a monophasic or biphasic stimulation cycle comprising a finite number of constant current (DC) square wave pulses. A waveform 78 representing a single complete cycle of monophasic Stim 2 electrical stimulation is shown in
A waveform 80 representing a single complete cycle of biphasic Stim 2 electrical stimulation is shown in
As explained further below, delivery of Stim 2 stimulation from the stimulator 16 requires activation by the user. In response to an activation completed by the user to start delivery of a Stim 2 stimulation cycle, the stimulator 16 delivers a complete cycle of Stim 2 stimulation in accordance with parameters or settings preselected by the user for the Stim 2 stimulation. The intraoperative neural monitoring system 10 is designed to provide Stim 2 electrical stimulation that may be selected to have a duration A in the range of 100 to 500 microseconds and preferably 100, 250 or 500 microseconds, a level B ranging from 0-200 mA, max 750V compliance, a delay C in the range of 2 to 4 milliseconds and preferably 2, 3 or 4 milliseconds, and a repetition E of 1-8 pulses. For biphasic Stim 2 electrical stimulation, the interval F is a fixed, predetermined interval, preferably about 2 seconds. The stimulator 16 may be considered a high current stimulator of the intraoperative neural monitoring system 10. As explained further below, the touch screen 30 is used to select and/or adjust various parameters or settings for Stim 2 electrical stimulation including mode (monophasic or biphasic), duration A, level B, delay C and repetition E. Once activated, the stimulator 16 will deliver the complete cycle of Stim 2 electrical stimulation, with subsequent cycles of Stim 2 electrical stimulation being delivered by reactivating the stimulator.
Activation for Stim 2 stimulation may be accomplished via a button or other control option of the touch screen 30 serving as an activator for simulator 16 as described below or remotely via the hand switch 18 illustrated in
During many surgical procedures, an electrified medical instrument such as an electrosurgical or electrocautery instrument may be used as a surgical knife, to assist in hemostasis or for other purposes. High frequency (HF) energy generated by an electrified instrument used during an operative procedure may be transmitted through the patient and picked up by the monitoring electrodes, such that the HF energy may be amplified by the intraoperative neural monitoring system 10 to disturbing volume levels. The one or more muting detectors 22 may be used in the intraoperative neural monitoring system 10 to detect when an electrified instrument or instruments is/are in use which may cause interference with EMG monitoring. A muting detector 22 is depicted in
As shown in
From the high power amplifier 97, controlled current is provided to the primary winding of a transformer 100 as shown in
For safety purposes, a discharge circuit 107 shown in
A watchdog 111, best depicted in
The user interface 21 presents various displays on the touch screen 30 providing information and providing control options for executing various selections, features or functions. Control options may comprise various touch-on or press-on graphics including but not limited to check boxes, radio buttons, adjustment buttons and arrows, scroll buttons and arrows, word commands, information boxes, and LED indicators. Upon start-up, the touch screen normally defaults to a quick setup display 127 as represented in
The nerve root selection display 129 is illustrated in
For a muscle-to-muscle montage, a muscle listed in the recommended montage” window, e.g. Left L5:Extensor Hallucis Longus, may be selected by pressing on the muscle listing and may be assigned to a channel 47, e.g. channel 1, by pressing the electrode assignment box 133a for the positive monitoring electrode input for the channel. The muscle listing will remain in the “recommended montage” window but will also appear in the electrode assignment box 133a of the channel. The corresponding channel label will be set to the location, i.e. L (left) or R (right), and the range of nerve root levels for the muscle, e.g. L5. Another muscle listed in the “recommended montage” window may be selected and assigned in a similar manner to the electrode assignment box 133b for the negative monitoring electrode input of the same channel to complete the montage. The channel label will remain the same, and the listing for the second muscle will appear in the electrode assignment box 133b for the channel. The muscle-to-reference montage is similar to the muscle-to-muscle montage except that “reference” is selected in the “recommended montage” window instead of the second muscle and is assigned to the electrode assignment box 133b for the negative monitoring electrode of the channel. To establish an intra-muscle montage, the same muscle selected and assigned to the electrode assignment box 133a for the positive monitoring electrode input of the channel is selected and assigned to the electrode assignment box 133b for the negative monitoring electrode input of the channel. For each type of montage, the channel label continues to display the location (“R” or “L”) and the range of nerve root levels for the muscle assigned to the positive monitoring electrode input.
Channel assignments may be cleared using a “clear” button on the montage display 132. A channel label may be customized for other nerve roots by pressing an “edit label” button which provides access to a keyboard display for the entry of alphanumeric characters. A “cancel” button may be used to load factory default settings, close the montage display 132 and open the EMG monitoring display. Pressing a “previous” button saves the channel assignments and opens the nerve root selection display 129. An “OK” button is pressed in order to save the channel assignments, close the montage display 132 and open the EMG monitoring display. A “select nerve roots to add” button may be used to save channel assignments and open a display by which additional nerve roots may be entered and added to the montage display 132.
The EMG monitoring display 143 is illustrated in
The channels 47 may be turned on and off by pressing the channel buttons on the EMG monitoring display 143, which also activates and deactivates LED indicators 167 on the channel buttons. Each channel button is identified by the channel number, and the channel button of each channel 47 being used for monitoring displays the location (“L” or “R”) and nerve root level(s) being monitored. During power-up, each channel 47 that is coupled with a patient connected monitoring electrode is automatically turned on. Tone and audio icons 181 for the channel buttons are enabled when a channel mute function is selected via a settings display accessed by pressing a “settings” tab on the EMG monitoring display 143. The icons indicate, respectively, whether event tones and EMG audio are turned on or off.
The EMG monitoring display 143 has an “EMG Stim” box depicting the level (current amplitude) selected for Stim I electrical stimulation. The level is selected by pressing the “EMG Stim” box and then pressing the appropriate up or down coarse or fine adjustment arrow buttons to obtain a level from 0 to 30 mA. The current level will typically be set to zero when Stim 1 electrical stimulation is not in use. When Stim 1 electrical stimulation is delivered to the patient using a monopolar or bipolar stimulating probe as described above, the “measured” current amperage delivered to the patient is displayed adjacent the “EMG Stim” box. Pressing the “0” button will reset the stimulus level to zero.
An “event threshold” button of the EMG monitoring display 143 is used to adjust an event threshold of the monitoring system 10. The event threshold is enabled by an event threshold filter and assists in defining where monitored EMG activity becomes significant. EMG activity that exceeds the event threshold is considered an “event”, resulting in an audible event tone. The event threshold is adjusted by pressing the “event threshold” button and then pressing the appropriate up or down coarse or fine adjustment arrow buttons. The total adjustable range is preferably 20-2500 microvolts. The level of EMG activity selected as the event threshold, e.g. 100 microvolts as shown by way of example in
An “event capture” button on the EMG monitoring display 143 allows EMG waveforms that exceed the event threshold, i.e. events, to be captured in the waveform display area of the EMG monitoring display. The event capture function is turned on and off by pressing the “event capture” button. When the event capture function is turned on, waveforms that exceed the event threshold are captured on the display and remain captured on the display until replaced by the next captured event. In addition, any channel having EMG activity resulting in a captured event will have the amplitude of the last captured event displayed on its channel button. Having the event capture function turned on also allows a particular event waveform on the display 143 to be pressed, causing the amplitude and time for the event waveform to be displayed. When the event capture function is turned off, the channel buttons display the amplitude of monitored EMG activity. While the event capture function is used to capture current events, a “largest” button may be turned on to effect capture of the largest in a series of events. The “largest” button is turned on and off by pressing and is used with the 50 millisecond or 100 millisecond time scale. For example, if fifteen sequential events occurred and the fourth event was the largest, a trace of the fourth event would be displayed along with “4 of 15”.
The EMG monitoring display 143 is identified by a highlighted “EMG” tab and presents additional tabs for “MEP”, “electrodes”, “settings” and “patient” displays accessible by pressing the corresponding tabs. The EMG monitoring display 143 may have a “freeze” button for freezing a current display, a “print” button for transmitting a current display as image or text to a printer, a “save” button for sending a current display to a compact flash disk, a “?” button (not shown) for opening a “help” screen for a current display, and/or a “volume” control button for adjusting speaker/headphone volume.
Rate, pulse width and artifact delay for Stim 1 electrical stimulation are selected using an EMG Stim settings display, an example of which is depicted at 151 in
An MEP or Stim 2 monitoring display 153 is shown in
The vertical scale of the waveform display area of the MEP monitoring display 153 is the same as the vertical scale of the EMG monitoring display 143 and the reference value for each segment of the display area is selectable as described for the EMG monitoring display 143. The horizontal scale for the waveform display area of the MEP monitoring display 153 has three sections, i.e. left, middle and right, and the MEP monitoring display requires that the “time” button be set at “dual 0.1 s-2 s-0.1 s”. The left section represents 0.1 seconds (100 milliseconds), the middle section is compressed and represents two seconds, and the right section represents 0.1 seconds (100 milliseconds). In monophasic Stim 2 stimulation, all of the pulses in a stimulation cycle and the artifact delay following the last pulse in the cycle are applied within the left section of the display area within the first 12 milliseconds. The next 88 milliseconds of the left section is where EMG events would appear should they occur, and a vertical dashed line in the left section of the waveform display area during stimulation distinguishes the artifact delay from the beginning of actual EMG activity. Following the two second delay in the compressed middle section, monitored EMG activity continues in the right section of the waveform display area during the next 100 milliseconds. In biphasic Stim 2 stimulation, the first group of pulses in a stimulation cycle and the artifact delay following the last pulse of the first group are applied within the left section of the waveform display area as described for monophasic Stim 2 stimulation. The middle section is a compressed time delay allowing the muscles to relax before the second group of pulses in the stimulation cycle is applied. The second group of pulses and the artifact delay following the last pulse of the second group are applied within the right section of the waveform display area within the first 12 milliseconds of the right section. The next 88 seconds of the right section reflects monitored EMG activity where EMG events would appear should they occur.
An MEP Stim settings display 155 shown in
A patient display is accessible via the “patient” tabs on the EMG and MEP monitoring displays for the entry of patient information including patient name and identification number, procedure and comments. Information may be entered using a keyboard which opens on the touch screen 30 as the user interacts with the patient display.
The intraoperative neural monitoring system 10 produces various sounds including EMG audio, event tones, baseline voices, stimulation tones and voices, and help voices which are selectable and/or adjustable using an audio settings display (not shown) accessed via an “audio” tab of the EMG Stim and MEP Stim settings displays 151,155. EMG audio is the amplified sound of muscle activity detected by the monitoring electrodes and may be heard as a low-pitched drumbeat, a high-pitched crackle or a growl. Other EMG audio responses include brief burst responses caused by electrical stimulation, direct nerve contact, irrigation or thermal changes, longer train responses caused by nerve excitation or irritation, irrigation, drying, bumping or anesthesia, and repetitive pulse responses caused by electrical stimulation, tumor mapping or verification of nerve integrity.
EMG audio may be selected/deselected using a button on the audio settings display. All EMG activity is audible when EMG audio is turned on. Event tones are heard when the monitored EMG amplitude is greater than the event threshold setting. The event tones are different for each monitoring channel, increasing in pitch from channel one to channel eight so that the channels responsible for the event tones may be identified. Event tones are also selected/deselected using a button on the audio settings display. A channel may be configured to produce both EMG audio and event tones, EMG audio alone or event tones alone as enabled via a channel mute button on the audio settings display and as indicated by the icons 181 shown in
Stimulation tones and voices exist in opposite states, i.e. if one is selected the other is disabled. These selections are made using appropriate buttons on the audio settings display. Stimulation voices announce the delivery of stimulus current to the surgical field by voice. Delivery of Stim 1 stimulus may be announced by the word “stimulus” along with the preselected current level. Adjustments in the stimulus current may also be announced by voice. Stimulation tones may announce the delivery of Stim 1 stimulus with a continuous warble tone or a brief three beep tone as selected using buttons on the audio settings display. Delivery of monophasic Stim 2 stimulus may be announced by the word “stimulus”. Delivery of biphasic Stim 2 stimulus may be announced by the word “stimulus” followed by a continuous tone which is followed by the word “stimulus”. Stimulation tones may announce the delivery of monophasic Stim 2 stimulus with a brief three beep tone and may announce the delivery of biphasic Stim 2 stimulus with a warble, followed by a continuous tone followed by another warble.
Baseline voices may include baseline increased, baseline decreased and baseline normal voices used in conjunction with the auto threshold feature when automatic adjustments are made. Help voices for “check electrode” and “muting” may be turned on and off via the audio settings display and operate in conjunction with a bleedle alarm. The bleedle alarm, followed by the “check electrode” help voice, signifies the need to check an electrode. The bleedle alarm followed by the “muting” help voice operates when not in the check electrode mode to indicate that the system has been in the mute mode for more than thirty seconds. A beep alarm is generated to indicate failure of internal microprocessor hardware. The audio settings display may include a control for adjusting volume higher or lower.
The intraoperative neural monitoring system is particularly suited for use during surgeries in which a motor nerve is at risk due to unintentional manipulation. It provides patient-connected neural monitoring for various surgical procedures including but not limited to degenerative treatments, scoliosis and deformity cases, pedicle screw procedures, fusion cages, rhizotomy, orthopedic surgery and open and percutaneous lumbar, thoracic and cervical procedures. EMG activity from muscles innervated by nerves is detected via monitoring electrodes placed in the muscles. EMG activity may be monitored continuously and in response to electrical stimulation of anatomical areas from which an electrical impulse may be transmitted to the monitored muscles. Electrical stimulation delivered by the intraoperative neural monitoring system may be Stim I electrical stimulation delivered to anatomical tissue via monopolar or bipolar stimulating probes connected to the patient interface unit. The probes may deliver Stim 1 electrical stimulation directly to anatomical tissue by directly contacting the tips of the probes with the tissue or indirectly by contacting the tips of the probe with a conductive medical device, such as a pedicle screw, disposed in contact with the tissue. Electrical stimulation delivered by the intraoperative neural monitoring system may alternatively be Stim 2 electrical stimulation applied via stimulating electrodes located in the anatomical tissue to be stimulated and connected with the stimulator. Stim 2 electrical stimulation may be delivered at significantly higher current than Stim 1 stimulation and is particularly well suited for eliciting MEPs which may produce EMG responses detectable by the monitoring electrodes. Stim 2 electrical stimulation may also be used for pedicle screw stimulation when higher stimulation currents are needed.
The anatomical areas to which electrical stimulation is delivered may vary depending on the surgical procedure being performed, the nerves being monitored, and the type of stimulation desired to be effected. Representative anatomical areas for the application of Stim 2 stimulation include the motor cortex and the spine. The stimulating electrodes for Stim 2 stimulation may be placed at anatomical areas appropriate to stimulate the left and right areas of the motor cortex, with biphasic stimulation allowing the left and right areas of the motor cortex to be stimulated sequentially to excite the muscles on the left and right sides of the patient's body. Biphasic stimulation is accomplished automatically in that a group of positive or negative pulses is automatically followed by a group of pulses of opposite polarity delivered as a complete cycle of stimulation with no action by the user other than the activation required to initiate delivery of the complete cycle of stimulation. By reducing the actions required to be taken by the user, the intraoperative neural monitoring system greatly simplifies intraoperative neural monitoring for greater efficiency and patient safety. The locations for the monitoring electrodes may vary depending on the nerves/nerve roots being monitored, and the user interface may display recommended locations for various preset and custom surgical procedures and/or nerve root levels.
EMG activity detected by the monitoring electrodes is displayed as waveforms during Stim 1 stimulation on an EMG monitoring display and during Stim 2 stimulation on an MEP monitoring display. EMG activity is also displayed on the monitoring displays when no stimulation is being applied. Where the Stim 2 stimulation is biphasic, the MEP monitoring display differentiates the EMG activity corresponding to each group of pulses in the stimulation cycle. In addition, EMG activity from the left and right sides of the patient's body may be displayed simultaneously and correlated in time for a more accurate assessment of neurological responses. Various parameters for Stim I and Stim 2 electrical stimulation are adjustable. Various electrical components, circuits and designs may be used in the intraoperative neural monitoring system to effect delivery of Stim 1 and Stim 2 stimulation. Monitoring may be accomplished simultaneously on up to eight monitoring channels.
Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all subject matter discussed above and shown in the accompanying drawings be considered illustrative only and not be taken in a limiting sense.
This application claims priority from prior provisional patent application Ser. No. 60/441,471 filed Jan. 22, 2003, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60441471 | Jan 2003 | US |
