Natus Medical Incorporated
Additional Safety and Accessory Reference Information
Natus Intra-Operative Safety Guidelines Rev 07 Aug 2013
Intra-Operative Safety Guidelines
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Intra-Operative Safety Guidelines For Intra-Operative Monitoring when using Nicolet™ Brand EEG systems (Chapter 1) and For Intra-Operative Monitoring when using Nicolet™ Brand EP/EMG/IOM systems (Chapter 2)
IMPORTANT SAFETY INFORMATION Please Read Carefully August 23, 2013
Part Number 269-488001 Rev 07
© 2010 - 2013 Natus Medical Incorporated or one of its subsidiaries. All rights reserved. Natus is a registered trademark of Natus Medical Incorporated. All product names appearing on this document are trademarks or registered trademarks owned, licensed to, promoted or distributed by Natus Medical Incorporated, its subsidiaries or affiliates. All other trademarks are the property of their respective owners.
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Safety Guidlines for Natus Neurology Incorporated EEG Intra-Operative Monitoring
Contact information Technical Support Natus Neurology Incorporated 1850 Deming Way Middleton, WI USA 53562-3530 608-829-8500 1 800-356-0007 Fax: 608-829-8589 www.Natus.com European Authorized Representative Natus Europe GmbH Robert-Koch-Str. 1 82152 Planegg Germany Phone: 0049 (0) 180 501 5544 Fax: 0049 (0) 89 839 42 777 Email: [email protected]
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Domestic Natus Neurology Incorporated 1850 Deming Way Middleton, WI USA 53562 1-800-356-0007 [email protected] www.Natus.com International Natus Neurology Incorporated Phone: 0049 (0) 180 501 5544 Fax: 0049 (0) 89 83942777 Email: [email protected] www.Natus.com
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Table of Contents
For Intra-Operative Monitoring When Using Nicolet brand EEG Systems Safety precautions ...1-3 Summary ...1-4 Introduction ...1-4 Electrical safety features of the monitoring system...1-5 Risks associated with the use of electrosurgical units ...1-6 Selection of recording and stimulating electrodes ...1-10 Positioning of recording and stimulating electrodes ... 1-11 Nicolet Cortical Stimulator...1-12 Stimulus/electrode switching device ...1-12 Current Limit ...1-12 Stimulus Control Unit (SCU) ...1-13
For Intra-operative Monitoring When Using Nicolet brand EP/EMG/IOM Systems Safety precautions ...2-3 Summary ...2-4 Introduction ...2-4 Electrical safety features of the monitoring system...2-5 Risks associated with the use of electrosurgical units ...2-6 Selection of recording and stimulating electrodes ...2-9 Positioning of recording and stimulating electrodes ...2-10 Connection of external custom electrode and/or stimulus switching devices ... 2-11
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For Intra-Operative Monitoring When Using Nicolet EEG Systems
This chapter is intended for the following Nicolet brand systems:
• Nicolet EEG System: Used with and without the Nicolet Cortical Stimulator
• Stand-alone Nicolet Cortical Stimulator Also see the “1 - Safety Guidelines for Nicolet EEG Intra-Operative Monitoring” card at the end of this guide.
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Safety Guidlines for Natus Neurology Incorporated EEG Intra-Operative Monitoring
Safety precautions The following items are suitable for the Intra-Operative patient environment: EEG main unit, Nicolet VikingQuest Combo EEG, OR amplifiers - including Nicolet EEGwireless 32/64 channel amplifier, Nicolet Cortical Stimulator, Natus Neurology Incorporated cart, Natus Neurology Incorporated isolation transformer, and all approved Natus Neurology Incorporated cables for use with the system. Only Natus Neurology Incorporated approved peripheral devices should be used with this system. Devices not specifically approved by Natus Neurology Incorporated are not suitable for the Intra-Operative patient environment. Do not use extension cords to power the system. Extension cords can cause system to be over the ground integrity and leakage current limits. When used simultaneously with high frequency surgical equipment, burns may occur at the site of any recording or stimulation electrode. Electrodes of inadequate size or unsuitable application could provoke skin reactions or burns. Natus Neurology Incorporated recommends the use of disposable, pre-gelled, silver/silver chloride electrodes with a contact area of 20 mm diameter or larger. These electrodes contain an adhesive that maintains the electrode skin position and contact during electrical stimulation and contact during recording and electrical stimulation. During direct nerve stimulation with the Nicolet VikingQuest EEG combo unit (i.e., stimulation of an exposed nerve or nerve root), it is recommended that a "low level stimulator output" be used if available. If not, limit the duration to 100 us or less and the intensity to 10 mA or less. Avoid using constant voltage. Electrode burns to the patient are variable due to numerous conditions that must be understood and monitored during the use of the equipment. Some variables to be aware of, but not limited to, are:
• Time of exposure (All connections should be checked periodically when used in excess of 30 minutes in one place.
• Concentration of currents (burns are caused by current density). Always use the largest possible of contact surface.
• Patient condition.
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Summary This document is intended to inform you about some of the most commonly applicable safety precautions as they relate to the use of Nicolet brand EEG monitoring systems for Intra-Operative Monitoring applications. As more electrical and electronic devices are introduced into this hostile environment, there will be the potential for harm to you and/or the patient. At Natus Neurology Incorporated, commitment to safety and quality is paramount. For this reason, we are providing the following information about the use of Nicolet brand EEG systems for neurophysiological monitoring during various surgical procedures. Please refer to IOM Safety Guide and Card for additional details.
Introduction There are a number of unique requirements related to the surgical monitoring environment that must be satisfied before a monitoring system can be used safely for Intra-operative Monitoring. These requirements concern the safety of both the patient and the person operating the monitoring system. Remember to follow all the cautions and warnings for your system. The reason we suggest using the OR head-box for intra-operative monitoring is to provide the patient with protection from potential burns at the electrode skin tissue sites caused by radio frequency currents from the electro-surgical units. Remember to follow all the cautions and warnings for your system. We believe that the risk of an accident or an injury to either person can be minimized if you are knowledgeable about the safety issues and guidelines discussed on the following pages.
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Safety Guidlines for Natus Neurology Incorporated EEG Intra-Operative Monitoring
Electrical safety features of the monitoring system Every hospital requires that electrodiagnostic systems be safety-inspected by qualified biomedical engineering personnel prior to use for any Intra-operative Monitoring. Typically, this inspection includes, but may not be limited to:
• • •
Evaluation of the ground connection on the system’s line power cord, Measurement of the system’s leakage current to ground, Measurement of the source and sink leakage current of the patient isolation section of the amplifier subsystem.
Procedures for making these assessments and levels of acceptable leakage have been defined in the United States (UL 60601 standard) and internationally (IEC/EN 60601-1 standard). If your biomedical personnel are not familiar with these standards or cannot make leakage current measurements, please contact either Natus Neurology Incorporated’s Technical Support in Middleton, Wisconsin, or your local Natus Neurology Incorporated representative for assistance. All system components that the operator can contact are either grounded or isolated. In addition, the amplifier and electrical stimulator subsystems meet safety isolation requirements to protect the patient. It is important, however, that the integrity of the ground lead on the system main power cable be maintained at all times. For this reason, it is important that system ground lead integrity be checked and verified before a system is used for Intra-operative Monitoring. We also recommend that ground lead integrity be checked at least every six months. Depending on how often the system is used for monitoring and how often it is moved, more frequent verification of ground lead integrity may be warranted. Although most surgical facilities’ power lines conform to the hospital building safety codes, we recommend that you always insure that any line power outlets or receptacles that provide the power to the system be properly grounded in accordance with IEC 606011-1. The isolation circuits in the amplifier subsystem are evaluated by measuring their leakage current. Although Natus Neurology Incorporated measures and documents the leakage current of each system prior to shipment, we expect you to have leakage current checked by biomedical personnel prior to any Intra-operative Monitoring usage. Source and sink leakage current should be measured for both the physiological amplifier subsystem and the electrical stimulating subsystem because both subsystems connect to the patient through the recording and stimulating electrodes, respectively.
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Risks associated with the use of electrosurgical units Electrosurgical units (ESUs) typically use radio frequency (RF) signals to perform ESU and electrocoagulation. The energy of these RF signals applied to the patient is substantial. There is a potential risk for tissue to be heated, and a burn(s) to occur on the patient in areas other than where the ESU is intentionally applied, especially if there is improper usage of the ESU devices, which is discussed later in this section. ESUs are typically described as being either of the monopolar or bipolar type according to the way in which the signal is applied to the patient. Some ESUs may even contain both monopolar and bipolar types of circuitry within a single instrument. Bipolar units present the RF signal through a bipolar, forceps-like hand piece held by the surgeon. Since both the active and return electrodes are mounted in the same hand piece, the amount of tissue involved in the electrosurgical circuit is limited. That is, most of the current in the RF signal entering the patient is localized to the small area where the hand piece contacts the patient. Bipolar applications usually involve only surgical desiccation in confined areas where the surgeon desires to control and limit the desiccation. Because delicate tissues require less heat to desiccate, bipolar applications are typically done using much lower power as compared to the monopolar applications (described below). While it may be said that bipolar ESUs are far less likely to produce burns at any of the electrode sites connected to the system, it must not be assumed that such burns will never be caused by bipolar applications. Monopolar units apply the RF signal through a unipolar hand piece, thereby requiring a separate return electrode or connection to the patient. This ESU return electrode is often referred to as the “Bovie ground.” However, it is not a “ground” electrode because it makes no connection to earth ground. Furthermore, this electrode cannot serve as the patient ground for the amplifier subsystem. The ESU return electrode is an extremely important item in terms of: a. Its function to the ESU. b. Its connection to the patient. c. Its location relative to the location of the systems’s stimulating and recording electrodes. In general, the ESU return electrode is a large pad-like electrode. The large surface area serves to provide a low-impedance connection to the patient. This electrode is often positioned on the thigh or buttocks of a patient.
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Safety Guidlines for Natus Neurology Incorporated EEG Intra-Operative Monitoring
Although some ESUs contain circuitry that will detect if the return electrode is not making proper contact with the patient and will activate an alarm in such cases, we strongly recommend that you independently verify the return electrode status. In the event of loss of the return electrode connection, the RF signal from the ESU will seek another pathway back to the ESU. As a result, any and all electrodes (both stimulating and recording), which connect the patient to the system, or any other device connected to the patient, could potentially provide such a pathway. If the ESU signal flows through these EEG electrodes, then a high density RF current may flow through the tissue to the EEG electrode interface and an “electrode burn” can result. Electrode burns to the patient are variable due to numerous conditions that must be understood and monitored during the use of the equipment. Some variables to be aware of, but not limited to, are: • Time of exposure (All connections should be checked periodically when used in excess of 30 minutes in one place.
•
Concentration of currents (burns are caused by current density). Always use the largest possible of contact surface.
•
Patient condition.
Also, it should never be assumed that there is no possibility of an electrode burn occurring when the system power is off. Even when the system is turned off, a passive pathway for RF currents to flow may exist and allow the ESU signal to produce electrode burns. All system components that the operator can contact are either grounded or isolated. In addition, the amplifier and electrical stimulator subsystems meet safety isolation requirements to protect the patient. Natus Neurology Incorporated has designed the system to minimize the risk of such pathways being established and causing burns.
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Natus Neurology Incorporated has designed the system to minimize the risk of such pathways being established and causing burns. a. First, in every amplifier subsystem, the patient is safety isolated from earth ground. b. Second, special RF choke or resistive devices, which act to inhibit the flow of RF currents through the recording electrodes, are included as part of Natus Neurology Incorporated’s “O.R. approved Amplifiers and Head boxes.” Models of these head boxes specifically designed for Natus Neurology Incorporated products are:
• Nicolet EEG System: 1. C64 OR Amplifier 2. C64 OR/SSU Amplifier 3. Nic36 OR Headbox and Amplifier 4. V44 OR Headbox 5. Nicolet Cortical Stimulator 6. Nicolet EEG Wireless Amplifier 32/64 Channel
• Nicolet Cortical Stimulator: As a stand alone unit c. Third, use of these amplifiers or head boxes is mandatory in all Intra-operative Monitoring uses of the systems, and all recording electrodes must be plugged into these. d. Finally, RF choke devices have also been included in the electrical stimulator subsystem. Use of this approved stimulator is mandatory any time Nicolet brand systems are used for Intra-operative Monitoring.
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Safety Guidlines for Natus Neurology Incorporated EEG Intra-Operative Monitoring
As stated previously, misuse of the ESU by members of the surgical team can also cause burns at the electrode locations. For example, unnecessary and prolonged activation of the ESU should be avoided to reduce the possibility of burns caused by RF leakage currents. Also, activation of the ESU when the hand piece either is not making contact with the patient (i.e., "open circuit" usage) or is applied very near (for example, less than 20 cm) to any of the recording and stimulating electrodes should never be done. It is also highly recommended to minimize electrode length before the protective headbox. A maximum electrode length of 12 inches (30 cm) is recommended to minimize RF leakage currents. Most ESU manufacturers’ user documentation advises that the patient should not come into direct contact with any grounded metal objects (for example, the surgical table frame, instrument table, etc.). In some surgical procedures (for example, those involving the use of non-insulated head frames), it may not be possible to prevent contact between the patient and a grounded metal object. Use of extreme caution to maximize patient safety is advised in these situations. Never intentionally “ground” a patient by connecting them to a grounded metal object or earth ground in order to overcome interference problems in your monitoring. On occasion, two or more ESUs may be connected to a patient and in use simultaneously. For dual monopolar ESU applications, the location of each ESU return electrode is particularly important. ESU manufacturers advise that each ESU return electrode should be positioned as close as possible to the respective site of surgery (that is, the point of application of the ESU signal to the patient) and care should be taken to avoid the possibility of the two ESU return electrodes touching. Given that the responsibility of the set up and use of the ESUs lies with the surgical team, assurance that these and other cautions against ESU misuse (as described by the ESU manufacturers) are heeded and followed is not the responsibility of the person performing neurophysiological monitoring. Being aware of these cautions, however, may help you to minimize the risks of injury to the patient.
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Selection of recording and stimulating electrodes In the event of failures/disconnection of the ESU return electrode or the occurrence of any other condition in which there is stray current applied to the patient, there is a potential for a burn to occur at each electrode site. If the surface area of the electrode is small, such as is the case for needle and “hook-wire” electrodes, the degree of a burn could be quite severe, because the current density at the tissue-to-electrode interface is high. Heating occurs due to the high contact impedance between the electrode and tissue. In contrast, surface electrodes having larger surface areas and lower contact impedance would be less likely to cause burns because the current is spread over a larger area, thereby reducing the heat. User documentation from at least one ESU device manufacturer does not recommend the use of needle electrodes as monitoring electrodes connected to monitoring systems during electrosurgical procedures. Regardless of whether needle, hook-wire, or surface electrodes are selected for monitoring, we strongly recommend that the electrode used for the system patient ground has the largest of a tissue-to-electrode contact area as is practically feasible. However, you should never assume that using only surface electrodes is a 100% guarantee against electrode burns. We also recommend that the surface electrodes used for recording be disposable, nonmetallic, self-stick type. Use of reusable metallic surface electrodes increases the likelihood of RF burns since the tissue contact area and the distribution of the electrolyte gel may not be uniform. This may result in an electrode inducing a high impedance “point” contact with the patient resulting in higher current density and possible RF burns.
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Safety Guidlines for Natus Neurology Incorporated EEG Intra-Operative Monitoring
Positioning of recording and stimulating electrodes Natus Neurology Incorporated recommends that all recording electrodes connected to the Nicolet brand system be positioned, if practical, as far away as possible from the ESU return electrode. The user documentation from one ESU manufacturer specifically recommends that both recording electrodes and probes (that is, stimulating electrodes) should be placed as far from the electrosurgical site and from the ESU return electrode as possible. In some cases, this recommendation means that the ESU return electrode may have to be positioned somewhere on the patient other than the thigh or buttocks. Simple communication with the surgical team may be all that is necessary to get the ESU return electrode positioned to a place that is more optimal in terms of patient safety. The nicolet brand system patient "ground" electrode should never be positioned beneath or further away from the recording site than the ESU return electrode. We also recommend, when it is consistent with clinical practice, that the Nicolet brand system patient "ground" electrode not be positioned between the ESU return and the site where the ESU monopolar hand piece is applied to the patient. While electrical interference from a variety of sources within the surgical monitoring environment may interfere with the signals being recorded on the system, you must never attempt to overcome such interference by connecting the system patient "ground" electrode directly to earth ground. Connecting this electrode, or any other stimulating or recording electrode having a direct connection to earth ground, should always be avoided, regardless of the problems experienced with noise or interference.
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Nicolet Cortical Stimulator The Nicolet Cortical Stimulator can be used as a stand alone unit without interfacing it to a Nicolet EEG system. In this case, a disposable Nicolet Cortical Stimulator Bipolar probe is used, which has red and black cathode bands and a 2.2 mm gold plated ball tip. The probe should be placed firmly against the brain to confirm a stable charge density. When using the probe, a continuous stimulating mode is available. The Cortical stimulator as a stand alone unit with probe is not a functional brain stimulator that is intended to be therapeutic or restore body function. This is a device to support transient cortical mapping. Electrical cortical stimulation has become the standard of care for functional localization of at risk eloquent brain structures prior to neurosurgical resection. It is understood the clinician applies cortical stimulation as a tool to support mapping of eloquent brain function to preserve as much eloquent brain tissue as possible. Stimulus/electrode switching device The C64-OR SSU (Stimulus Switching Unit) amplifier includes the ability to automatically switch the stimulus to different electrodes. Current Limit A current limit circuit controls the maximum amount of stimulating current that may flow out of the Stimulus Control Unit. The current may be limited to ±15 mA. It may also be decided in some intraoperative monitoring applications to switch between different electrical stimulating sites. Use of a custom-made or commercially-available stimulus switching apparatus for these applications can introduce a safety risk to the patient in several ways. Such devices typically are simply connected to the output jacks of the electrical stimulator subsystem on a Nicolet brand system. Since these outputs are isolated for reasons of patient safety, the switching device therefore must not provide any connection to earth ground to avoid defeating the safety isolation. Natus Neurology Incorporated has approved electrode and stimulus switching devices available. The wiring and cabling associated with the switching device may also introduce additional capacitance to earth ground and in turn increase current leakage, thereby making the stimulator subsystem no longer conform to the safety standards. Even when packing and cabling for the switching device is carefully managed, the device can still represent a patient safety hazard because it may provide a low impedance path to earth ground for RF currents. The use of a stimulus switching device can affect the system functionality because additional capacitance in the switching device can act to distort the shape of the electrical stimulus pulse being delivered to the patient, thereby altering its effectiveness as a stimulus.
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Safety Guidlines for Natus Neurology Incorporated EEG Intra-Operative Monitoring
Use only Natus Neurology Incorporated-supplied and/or approved electrode and stimulus switching devices. Please see the third paragraph on this page. The applicable stimulation probe is the Natus Neurology Incorporated Bipolar Stimulation Probe with 2.2mm diameter tips. The applicable stimulation electrodes are any commercially available 2.3mm diameter Strip and Grid Electrodes. In the United States only, the stimulation electrodes and stimulation probes must have been cleared to market by the Food and Drug Administration (FDA). Stimulus Control Unit (SCU) The Stimulus Control Unit (SCU) is equipped with built-in controls and a display. It provides isolated constant current stimulation and may be connected to the Acquisition system via a Serial port on the Desktop, Laptop, or Panel PC computer. The Stimulus Control Unit (SCU) can deliver the following stimuli:
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Bi-phasic Constant current Stimulation pulses Trains of stimulation pulses
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