MODEL N-1 FACIAL NERVE LOCATOR and MONITOR Instructions for Use

Copyright GRASS INSTRUMENT COMPANY, 1985 Reproduction in whole or in part must not be made without the written permission of GRASS INSTRUMENT CO.

GRASS INSTRUMENT COMPANY 1O1 OId Colony Avenue @1985

Tel. 617-773-OOO2

. P.O. Box 516 . Quincy, MA 02169

PRECAUTIONS:

The surgeons should be aware that the Model NL-I can malfunction for reasons

such as random component failure in either the instrument itself or the associated cables and probes. A standby Nerve Locator and Monitor, Input

Cable, Isolation Unit and sterilized Stimulating Probe are recommended if equipment malfunction is a significant risk to the patient.

@GRASS INSTRUMENT CO. 1985

MODEL NL-1 FACIAL NERVE LOCATOR AND MONITOR Table of Contents

SECTION 1

SPECIFICATIONS

SECTION 2

DESIGN FEATURES 2.I Design Features

SECTION 3

DESCRIPTION

3.1

3.2 3.3

Descriptions and Functions of Front Panel Controls

3.1.1 Power 3.L.2 Input Probe Connector 3.1.3 CRO Amplifier Gain 3.L.4 Audio 3.1.5 Noise Clipper 3.1.6 Active LED Indicator (YELLOW) 3.1.? Stimulus Volts 3.1.8 Stimulus Isolation 3.1.9 Stimulus LED Indicator (RED) 3.1.i0 Oscilloscope Monitor 3.1.11 Sweep ms/div 3.L.12 Delay ms 3.1.13 Input Mode Description of Rear Panel 3.2.I AC Power Cable 3.2.2 Foot Switch Connector

Descriptions and Functions of Accessories 3.3.1 Input Probe and Cable 3.3,2 Foot Switch 3.3.3 Stimulus Isolation Unit and Cable 3.3.4 Exploratory Stimulating Probe

SECTION 4

INSTALLATION AND SAFETY 4.I Required Reading 4.2 Leakage Currents 4.3 Use with Electrosurgical Units (ESUs) 4.4 Choice of Recording Electrodes 4.5 Intensity and Safety of Stimulus Current at Probe Electrode 4.6 Sterilization

SECTION 5

OPERATIONAL PROCEDURES 5.1 First O.R. Procedure

5.2 5.3 5.4

5.5 SECTION 6

Check List for Proper Function of the NL-l During the Operation Adjustment of Delay MS Control

TROUBLESHOOTING AND MAINTENANCE

.1 6.2 6

SECTION 7

Pre-operative Checkout Procedure Placement and Application of Recording Electrodes

Maintenance

Troubleshooting

SERVICE POLICY WARRANTY M456A87 '. GRASS INSTRUMENT CO 1985

DESIGN FEATURES

Section 2.1

2

DESIGN FEATURES

2.1

Design Features

the surgeon without divertit g his visual attention from the surgical field . In ad ditioo , the response is displayed visually on a b uilt-in oscilloscope.

THE G RASS MODEL N L-l F ACIAL and Monitor is N ERVE LOCATO R intended to locate the facial nerve during the surgical removal of medium and larg e acoustic neuromas. This is accomplished by amplifying the facial muscle EMG and audio monitoring the response of these muscles to stimulation by an exploratory probe manipulated by the surg€orl Thus the surgeon can "-aprr out the facial nerve by listening to the facial EMG, while probing with the exploratory stimulation probe. Portions of tumor not responsive can safely be removed by 2.1.1

This instrument was developed in collaboration with Drs. Mo1ler and Jannetta, who conceived and perfected this method Moller and of locating the facial r€rv€ . Jannettars first sy s tem consisted of g eneral purpose Grass equipment: a Grass P511 Neuro2.L.2

physiological Preamplifier, a Grass AM?/AM8 Audio Monitor, a Grass SD9 Stimulator and Stimulus Isolation Unit and a Tektronix general purpose

o

oscilloscope.

*66o;?'"

M

Foot Switch

-oooo_oo

o-oooo

13.NL-A

Out

lsotated lnput Cable

Stimulus lsolation Unit

(+)

-l-l-r-l

Recording Electrodes

Reference

bot) 0

[_,

Exploratory Stimulating Electrode

i-,

Patient ISO GN D

NL-l SYSTEM FUNCTIONAL BLOCK DIAGRAM FIGURE Z,L.L

@GRASS INSTRUMENT CO. 1985

DESIGN FEATURES

Section 2.1

2.L.3

This compact instrument consists of a s timulator , stimulu s isolation unit, exploratory probe electrode, ?rr input probe with terminals for the facial muscle EMG electrodes, a neurophysiological amplifier r arl oscilloscope, an audio monitor, a stimulus artifact suppression circuit and a foot switch for activation of the audio monitor and suppression of interference generated by the Electrosurgical Unit ( ESU ) . A built-in calibration circuit permits testing the unit prior to the operative procedure so that surgery can be commenced with assurance that the u nit is f ully operation al . 2.L.4

The NL-I Facial Nerve Locator and Monitor is designed for table or shelf

placement. It can also be rackmounted. A retractable stand is included on the bottorn of the unit to raise the front panel upward for easy viewing . To use the stan'd, simply raise the front of the unit and pull the stand toward you u ntil it s nap s in plac e .

SIDE VIEW OF NL-I CHASSIS

FIGURE 2.L .4

Mdller, A . R. and P. J. Jannetta . Preservation of facial function during removal of acoustic rl€rlrornds . Journal of Neurosurgerv 61 : 7 57' 7 60, 19 84. Delgado, T. E . , et al . Intraoperative monitoring of facial muscle evoked responses by stimula-

tion of the facial nerve.

Neurosurgery lz

4Lg-42L, L979 .

et gl. Technical and instrumental improvements in the surgical treatment of acoustic neuromas. Journal of Neurosurgerv 57 z 747-752, L982.

Su gita,

OGRASS INSTRUMENT CO. 1985

K.,

DESCRIPTION

Section 3.1

sltMurljs

'GRASS NERI,E LOCATOR AND MONITOR

IHtS rlrslturtrl rust (lxtY 8t ltPtnAIt0 tY ?tns(lls IlAlrt0

rr rIs PuRP0St ll0 tulcll0t ust tnrss ts0l.lIt0

lrPut Pt(lEt oxtY

AMPLITITR INPUT

v0

tIs

mrmsrrY f r

ooooo oooooo ooooooo oooooo ooooo

@@

rocus a@ sr{rEP Ms/orv.

AUOI O

5-

0ll

o

orr@o* 6Rr5S tllslnUrtrl

C0.

qurlcY. rrss.. u.s.r.

t00il. It stRrAl.

v0rIs

tnt0. 50 - 60

I

-

llUI IO

O 'tott/llflui*,t @

,6:

TTIIS

POWIR

@,-

FRONT PANEL CONTROLS

FIGURE 3.1

3

DESCRIPTION

CAUTION :

OnIy a Grass Model I3-NL-A INPUT

PROBE should be used. If other probe models or 3.1

brands are used, padent isolation and safety

Descriptions and Functions of Front Panel Controls

may be severely compromised.

POWER AC power for the NL-l is supplied via a low leakag e nonshielded cable, 15 feet long , terminate d with an Operating Room Hospital Grade Plu g . The POWER tog gle switch located on the right hand side turns the NL-I orr, and the GREEN LED indicator lamp above the POWER switch will illuminate when the POWER switch is in the O N positioo 3.1.1

e

AMPLIFIER INPUT CONNECTOR The input probe cable is connected to the AMPLIFIER INPUT CONNECTOR, located on the 3.L .2

lower left side of the NL-I front panel . The recordit",.g elec trodes are connected to the terminals on the IN PU T PRO BE. ( See Section 3.3.1. )

CRO AMPLIFIER GAIN

Adjusts the vertical sensitivity of the oscilloscope display of the facial muscle (nUC ) response When this b y adju sting the amplifier gain . control is maximum counterclockwise, the EMG CRO deflection factor is 100 0 microvolts per division, corresponding to an amplifier gain of about I, 00 0. When this control is maximum clockwise, the EMG C RO deflection f actor is 200 microvolts per division (amplifier gain = 5,000). The CRO AMPLIFIER GAIN control should be adiusted to provide a deflection of about 4 divisions on the oscilloscope for the facial muscle response. Once this setting has been cietermined, it is unlikely th at it will have to b e ad ju ste d on subsequent operations. Do not use the CRO AMPLIFIER GAIN control to adjust the loudness of the facial muscle EMG response once the CRO arnplifier gain is established. 3.1.3

OGRASS INSTRUMENT CO. 1985

DESCRIPTION

Section 3.1

AU DIO

This is a volume control for the Au dio Monitor portion of the NL-l and does not affect the oscilloscope display. This volume control varies the loudness by a factor of 30. Once the CRO AN,IPLIFIER GAIN setting has been determined as in Section 3.1.3, the AU D IO control is then ad justed for a comfortable Iistening level for interpretation of the response by the surgeon. Once the setting of the AU D IO control has been determined , it is u nlikely th at it will have to b e ad ju ste d on subsequent operations unless the O. R. is unu sually noisy . 3.L.4

sIrMur.t,s VO LIS

A ,,

AUDIO AND STIMULUS CONTROLS 3.L4 to 3.1.9 FIGURE

3.1.8 3.1.5

NOISE CLIPPER

clip pin g

circ uit

tog gle

This two position activa te s a noise

s witc h which suppresses

back ground

noise .

OUI IO

SllIu[US

tsoultot unr

S TIMULUS

ISCLATIO N

The connector

for the Stirnulu s Isolation Unit is to the left of the POWER switch. An interlock in this connector prevents any ground referenced voltage from being connected to the stimulating electrodes .

ACTIVE LED INDICATOR (YELLOW) The YELLOW LED indicator to the right of the AU DIO volume control illuminates when the NL-l is in the ACTIVE state and permits the audio EMG response to be heard. This is controlled by the FO O T SW I TC H . See Section 3 .3 .2 . 3.1.6

3.L ,7

STIMULUS VOLTS This large dial has graduations from 0.1 to 1 volts and

the intensity of the stimuhls. The pulse rate is fixed at 10 per second, and the p uls e duration is fixed at 0 . I millico n trols

s tim ulu s

seconds.

Do not defeat the interlock in the Stimulus Isolation Unit connector; safe patient isolation may be compromised. CAUTION I

STIMULUS LED TNDTCATOR ( npO ) The RED LED indicator is illuminated every time the NL-l delivers a stimulus to the It illuminates only Stimulus Isolation Unit. when the NL-l is in the ACTIVE state (see Section

3.r.9

3.3.2 FOOT SWITCH ). Since the stimulus rate is 10 per second, the indicator will flash 10 times per second, and will illuminate even if the Stimulus Isolation Unit is disconnected.

OGRASS INSTRUMENT CO. 1985

DESCRIPTION

Section 3.1

DELAY MS Please ref er to Timing Diagram, Figure 3. I .L2. For the first 10 milliseconds of each cycle, the Audio Monitor 3.1 ,L2

fr @

OSCILLOSCOPE MONITOR

FIGURE 3.1.10

3.I.10

A built-in C RO monitor provides a visual display of the stimulus artifact, as well as the facial mu scle response . The stimulus artifact suppres sion circuit for Audio Monitor ( silent period ) does not ef fec t the visual display shown on the OSCILLOSCOPE MONITOR

OSC ILLOSCOPE MONITOR. Appearance of stimulus

artifact on the oscilloscope is partial proof of the integrity of the entire detection system. The INTENSITY, FOCUS, VERTICAL and HORIZONTAL POSITIONING CONTROLS are screw-

driver adjustments located to the right of the display. An upward deflection on the CRO correspond s to a positive wave at the input probe electrode lead terminal marked GI; and corresponds to a negative wave at the terminal marked G2.

3.1.11

SWEEP MS/DIV SWITCH

This three position s witc h is loc ate d b elow the oscilloscope, and sets the oscilloscope horizontal time base deflection factor as follows: MS/ DIV 2

TIME FOR FULL SWEEP IO DIVISIONS 20 milliseconds 0 milliseconds

5

5

10

10

0 milliseconds

This control does not change the timing of the stimulus or Audio lv{onitor silence period ; it only chan ges the time scale of the CRO display.

is silenced. After a delay of 8 milliseconds from the beginning of the silence period, the stimulus occurs and the CRO sweep begins. Due to unavoidable electrostatic and electroconductive coupling through the body between the stimulus and recording electrodes , a rrstimulus artifacttr always occurs at the recording electrodes simul-' taneou s with the stimulu s r and subsides about L millisecond after the onset of the stimullt s r or: about l millisecond before the end of the Audio Monitor silence period . This audio silence period is fixed at 10 milliseconds , and suppresses the stimulus artifact from reaching the audio monitor and prevents it from being heard by the surg eon . If there is a response from the facial muscle, it will be heard by the surgeon on the Audio Monitor because it occurs after the end of the silent period, and is amplified by the Audio Monitor.

THE DELAY MS CONTROL PERMITS THE ADJUSTMENT of the stimulus delivery time relative to the beginning of the Audio iv{onitor silencit g period , over a range of I to 10 millisecond.s . By reference to Figure 3. I .LZ it can be seen that this adjustment permits the stimulu s artifact to be silenced while allowing the facial muscle EMG response to be heard. Initial experimentation will determine the optimum setting of the DELAY MS control in accordance with the typical response latencies experienced. Once initially determined, the setting of the DELAY MS control should not require subsequent adjustment . The DELAY M S control is f actory set at 8 milliseconds, which delivers the stimulus 2 milliseconds prior to the end of the Audio Monitor silence period, thereby permitting the suppression of the stimulus artifact in the Audio

OGRASS INSTRUMENT CO. 1985

DESCRIPTION

Section 3.1

Basic 1O Hz

Timing Rate EMG Response on the CRO

lOms Audio Silence Period

Sync for CRO Sweep

ll

Fr <Audio Silence Period I

2 ms/div. (time)

lOOps Stimulus Pulse

Recordings from the facial muscles vary widely from patient to patient and depend on the exact placement of the recording electrodes, and thus shown recording must be regarded as an example only.

FIGURE 3.1.12

Monitor. If this control is not properly adjusted, th; stimulus artifact may not be suppressed, and the stimulus artifact will cause a sound in the Audio Monitor, even when the exploratory stimulating probe is NOT on the facial nerve, and may lead the surgeon to erroneously conclud.e that he is stimulating the facial nerve. It is the suppression of the stimulus artifact that enables the su rg eon to hear when the f acial muscles are being stimulated, and when they are not being stimulated, See Section 5 .5 for proper ad ju stment of DELAY N{ S.

THE STIMULUS-RESPONSE TIMING SEQUENCE is as follows : TIME SEQUENCE ( USE mode ) (ms ) 0.0 Audio Monitor silence period begins 8.0 CRO sweep begins, stimulus and stimulus artifact begin 8.1 9.0 10. 0

14.0 20.0

.0 100.0 20

stimulus ceases stimulus artifact ceases Audio Monitor silence period ends facial EMG response begins ( about 6 milliseconds afte r stimulu s ) facial EMG response ceases ( about 20 milliseconds after stimulus ) Sweep ends (if SWEEP MS/ DIV set to Z) New cycle is repeated repetition rate = 10 / second, (

OGRASS INSTRUMENT CO. 1985

every 100 ms )

DESCRIPTION

Section 3.1

Basic lOHz Timing Rate

Calibration Pulse on the CRO I

,+-+i

8ms Detay

I

Audio Silence Period

Sync for CRO Sweep

ll

F<->r tl

Audio Silence Period

2ms/div. (time)

HsmsDetay

FIGURE 3.1.13

This two position srvitch is located to the far lower left on the front panel, and is labeled : I MV CAL and USE. The USE position is for normal facial nerve location r and the I MV CAL position is u sed to check the circuits in the N L- 1 prior to the operation to assure that the N L-l will be f unctional during the operation, and aids in presetting the DELAY MS control properly.

tion pulse and adjust this delay using the I OrrO" MS control. This enables the operator to preadjust the timing of the stimulus relative to the end of the Aud.io Monitor silence p."{oa for optimum artifact rejection and best audible facial muscle EMG response.

When the INPUT MODE sq/itch is set to the CAL l MV

TIME (ms) 0.0

3.1.13

INPU T MODE SWITCH

position , the C RO sweep starts at the b eginning

of the Audio Monitor silence period ( not coincident with the stimulus ) . See Figure 3. I .13, Calibration Timing Diagram. The 1 MV CAL position places a I millivolt, 0.5 millisecond positive pulse at the amplifier G 1 input in place of the facial muscle EMG response, but at the same time the stimulus would have been delivered. Thus the operator can see the delay on the CRO betwee n the beginning of the Audio Monitor silence period and the beginning of the calibra-

THE CALIBRATION TIMING SEQUENCE is as follows :

8.0 8.5 10 .0 20.0 100.0

OGRASS INSTRUMENT CO. 1985

SEQUENCE

(CAL mode) Audio Monitor silence period begins and CRO sweep begins calibration pulse is applied to amplifier input and stimulus is presented calibration pulse ceases Audio Monitor silence period ends sweep ends (if SWEEP MS/DIV set to 2) new cycle is repeated repetition rate = 10 / second, (

every 100 ms )

DESCRIPTION

Section 3.2

Power Cable

llsVAC 60 Hz

AC Line Fuse 1 amp

t Switch Connector

NL-l REAR PANEL FIGURE 3.2

3.2

Description of Rear Panel

FOOT SWITCH CONNECTOR Connect the plug at the end of the FOOT SWITCH cable to the FOOT SWITCH connector located at the bottom center of the rear panel. 3.2.2

AC POWER CABLE The 15 foot AC power cable enters the rear of the cabinet through a strain relief. In order to provide the convenience of a 15 foot AC cable for the operating room and low chas sis and patient leakage, this cable is a low leakage nonshielded 3.2.1

type. CAUTION i

Do not use any type of extension Patient and Chassis leakages will be increased and patient safety may be compromized.

cords

@GRASS INSTRUMENT CO. 1985

DESCRIPTION

Section 3.3

3.3

Descriptions and Functions of Accessories

INPUT PROBE AND CABLE This cable is approximately 16 feet in length, and is shielded . There are three terminals for the connection of two facial EMG recording electrodes and one patient reference electrode. The .GRASS patient reference elecls0LtTr0il ll{PW cABl.t trode is always connected ilSInUI$tI 00rrc[ nss. t.s.t to the terminal labeled ISOGND. AII three input I00tl, 13'I[-l $rru, terminals have two isolation devices each, which provide a double layer of patient safety. One device is an ISO-SWITCH, MoDEL I3-NL-A ISOLATTON INPUT CABLE and is effective at all FIGURE 3'3'l times. The second device is a relay for added patient protection during periods of Electrosurgical application ( ESUs or Bovies ) - which is a time when facial nerve locating procedure must not be performed. 3.3.1

@r@ @ SnNS

C0.

FOOT SWITCH

The FOOT SWITCH enables the surg eon to alternately unit back and forth between the the switch STANDBY state to the ACTIVE state. Each time the FOOT SWITCH is pressed, the NL-l changes to the other state. When the Yellow LED indicator on the f ront panel is illuminated , the N L- 1 is in the ACTIVE state. 3.3.2

he (or someone directed by him) presses the FooT SWITCH, placittg the NL-l in the ACTIVE state. when finished with location procedures, oR WHEN ELEC TROSURGERY is performed, the FOOT swITcH should be pressed agerin to place the NL-l back into the STANDBY stzrte.

IN THE STAND BY STATE, the relays in the INPUT PROBE provide a high degree of isolation during Electrosurgery b y disconnecting patient electrodes. In the STAND BY state, the relays ground the amplifier input:s, and the Audio Monitor is silenced, so that interference from Electrosu rgery and other devi,:es will not be distracting and annoying. In the, STANDBY state, there is no stimulus delivered to the Stimulus Isolation Unit.

IN THE ACTIVE STATE, the, relays in the INPUT PROBE connect the arnplifier inputs to the electrodes, and the Atrdio Monitor is activated so that the surgeon may listen for facial muscle responses . In the ACTIVE state, stimuli are delivered to the Stimul'us Isolation Unit.

FOOT SWITCH

FIGURE 3.3.2

CAUTION I Patient safety may ber compromised if the surgeon leaves the N:L-I in the ACTIVE state

during application of Electrosurgery. CAUTION I

During the course of surgery, the NL-l should be set to the STAND BY state by the surgeon for maximum safety during Electrosurgery. When the surgeon desires to perform facial nerve location,

The NL-l hras an interlock, which

prevents the NL-l from breing in the ACTIVE state if the FOOT SWITCH is disconrrected from the NL-I. Do NOT attempt to defeat the purpose of this safety interlock.

EGRASS INSTRUMENT CO. 1985

DESCRIPTION

Section 3.3

STIMULUS ISOLATION UNIT AND CABLE - This unit provides isolation of the stimulus from ground, both for patient safetY and for the reduction of artifact in the facial muscle EMG response. It is a constant reRASS voltage type, which has sllrljtus ts0ttlrtlil uiltI been determined to Provide superior spacial anatomical tilss rrslturtrr 0uucl. rlss. 3J.L

3.3.3

c0.

discrimination than constant ru0tt $-rt-r current types. A low leak$rrrt age transformer provides the isolation and provides built in stimulus current limitation by virtue of its MODEL SI-NL-I output impedance of 1000 STIMULUS ISOLATION UNTT FIGURE 3.3.3 ohms, thereby limiting the stimulus current to 1 milliampere (at a maximum stimulus of 1 volt ) . This Stimulus Isolation Unit was specifically designed to be used in this application. Use only a Model SI-NL-A Stimulus Isolation Unit; other models or brands may not provide adequately safe stimulus isolation and/or current limitation.

3.3.4

EXPLORATORY STIMULATING PROBE The probe applies the monopolar

voltage to neural tissue, and perrnits the surgeon to identif y the facial nerve b y exploratory The handle is n'ylon and has a stimulation. solid silver wire electrode.

A single Exploratory Stimulating Probe ( Figure 3.3 .4a) with two different length tips is supplied with every N L-l unit. (Jne tip is Z-L I 4 inches long and the second tip is 3-L I 4 inches Iong. The longer tip is useful for those cases where the operative field is deep and dif ficult to reach . To replace the tip, r;imply twist the threaded collet counterclockwise and remove the tip. Place the new tip in the <:ollet up to the insulation and tighten the coll,et by turning clockwise.

Previously the probe (Figure 3.3.4,b) was designed to allow adjustment of the exposed length of the wire electrode.

CAUTION I

The solid silver wire diameter :ls 0.030 inches ( 0.76mm ) and the shape is easily adjusted by the surgeon to conform to the surgi,:al site without

Z INTERCHANGEABLE TIPS (GOLD) z-31 4n LoNG

L

l2n

3414n LONG I lzn

THIS END GOES TO PROBE COLLET

PROBE (]OVER

EXPLORATORY STIMULATING PROBE AFTER JANUARY, 1987 FIGURE 3.3.4a

DESCRIPTION

Section 3.3

PHONE PLUG

r

ADJUSTABLE ELECTRODE PUSH/PULL WIRE TO ADJUST ELECTRODE LENGTH

I

i I

TWIST CAP TO LOCK/UNLOCK PROBE C;OVER

COMMON ELECTRODE

EXPLORATORY STIMULATING PROBE PRIOR TO JANUARY, 1987

FIGURE 3.3.4b

fatiguing the wire. The silver wire is nickel plated and then plated with 200 millionths of an inch of gold over itrs entire length to prevent any material migration to or toxicity with tissue. The gold plated wire is teflon coated except for the L ll6th inch exposed tip ( 1.6mm ) giving an ef fective stimulating area of 0.043 sg. crl. The probe lead wire is also teflon insulated and is 7 feet long (2L4cm) terminating in a phone plug for connection to the stimulus isolation unit. The probes are supplied with protective covers which should be in place when not being used to protect the flexible silver wire electrode.

Attached to this phone plug is a plastic insulated wire r gr€€n in color , a,lso 7 feet lon g ( 214cm ) , which is terminated in a banana plug. This banana plug is intended to be connected to the return or indifferent stimulerting electrode. It is the userrs responsibility to select and use a safe electrode for this purp()se such as a hypodermic needle ( see Section tI.4 CHOIC E OF RECORDING ELECTRODES - the sarme criteria apply to the selection of an indifferent stimulating electrode as apply to selectiorr of recorditrg electrodes ) . The return stimulating electrode must be located as close to the stimulating site as possible in order to keep the stimulus artifact at low levels. Abnormall.y high stimulus artifact may not be able to be sulppressed by the NL-l silencit g circuitry, and 'will render the unit useless in discriminating tretween a valid response and stimulus artifact.

OGRASS INSTRIJMENT CO. 1985

INSTALLATION AND SAFETY Sections 4.1 '4.2

4

INSTALLATION AND SAFETY

4.2

Leakage Currents

41

Required Reading

ilhe NL-l is NOT intended to be conner:ted directly to the heart, or to an electrical ltathway directly to the heart. Consequently the NL-l is classified as equipment having rrordin aryrr patient connections; as opposed to equipment having Isolated Patient Connections. Therefore, , leakage limits for isolated equipment do not apply; the IlL-l need only rneet leakage limits for rrordinary patient connected equipment. 4.2.1

Preparatory for use , it is hig hly recommended that the surgeon, and the O. R. technician or nurse in charge of the NL-l and the responsible biomedical engineer and technician read the followitrg documents : 4.1.1

THIS N,IANUAL.

CLASSIFICATION

rl

All the Instruction lr,4anuals for any Electrosurgical Devices that will be used on the same patients as the Grass NL-l. Moller, A.R. and P.J. Jannetta. Preservation of facial function during removal of acoustic neuromas . Journal of Neurosurgery 6l : 7 57 7 60, I 994. FPA Standard 99 , Health Care Facilities : Appendix E, The Safe Use of High Frequency Electricity in He alth Care Facilities (ESUs). N

( 1984)

AAMI Standard ESU-D-31 83, Electrosurgical Devic€s .

PRI9R TO INCOIv{ING LEAKAGE TESTIryG, and installation, it is recommended that the responsible biomedical engineer and technician review the followitrg leakage 4.L .2

THESE LIMITS, AND THE LE4S/IGE in microamps ( pA

) of the NL-l are indicated a,s follows:

STANDARD:

CHASSIS

SOURGE

SINK

(operator )

(patient ) pA

(patient)

pA

NFPA 99

100

50'r

AAMI SCL

100

50 50

uL 544

100

CSA

100

50

rEc 6 01

500

500

GRASS NL-I

20

20*

pA

not required not required not required not required 51 0oo

3**

AU values in AC microamperesr RM;S, for rrordinarytt patient connections r 3e opposed t,c Isolated Patient Connectionsr 3e of October, 19840

*With all patient leads connected together and measured to ground. **Measured at only one patient conn,ection at a time.

standards:

NFPA Standard 99, Health Care Facilities ( 19 84 ) ; Ch -9 , Saf e Use of Electricity in Patient Care Areas of Hospitals . AAMI Standard SCLI2l 7 8, Safe Current Limits for Electromedical Apparatus.

OGRASS INSTRUMENT CO. 1985

INSTALLATION AND SAFETY Sections 4.2- 4.3

4.2.2

SCHEDULED INSPECTIONS Scheduled

inspections should be made on the NL-l for condition of the AC cord and plu g , grou nding and Chassis and Patient SOU RCE Leakage in accord ance with the policy of the Hospitalrs Safety Committee. In this regard, it is highly recommended that the hospital follow the recommendations of NFPA Standard 99 ( 1984), Chapter 9, rrSafe Use of Electricity in Patient Care Areas of Hospitalsrr . Althou gh the NL-I classification I'Ordinary ( Patient Connections " ) does not require Patient SI NK Leakage Testing , it is recommended that Patient Sink Leakage be conducted at more frequent intervals than the above inspections for the followirg reason: The patient isolation circuits in the Input Probe and Stimulus Isolation Unit are subjected to exposure to high frequency ESU voltages . If O NLY the low power, BiPoIar mode is used, these isolation circuits should las t indefinitely . If subjected to the voltages associated with high power MonoPolar ESU energ y , the isolation circuits may be compromLzed. The Patient SINK Leakage Test will verify proper patient isolatioo.

With the NL-l in the ACTIVE state ( yellow LED indicato:r illuminated ) , the Patient SINK leakage should measure less than 3 microamperes at any one patient terminal, and typically measures I microamlf ere.

When th e NL-l is switched to the STAND BY state

from the ACTIVE state (using the FOOT SWITCH), the leak.age at any of the terminals at the INPUT

should be reduced ( typically to 0 . 5 indicating that the relay microamperes ), isolation. circuits are functioning properly. PRO BE

If you do not obtain these readingS, the NL-l should be removed from service and exc$anged for another unit from the factory . Recommended Patient SINK Leak age Te ting

is at

least once per month, or eve:rytime

fter high

power MonoPolar ESU has been used an had the NL-l connected to the patient.

has als o

4.3 4.3.L ELECTROSURGICAL UNIT WITH OTHER DE_VICES attached to the patient ( NL-1 ) ,

is that burns may occur at unintended sites, such as at the facial muscle recordirg ele:ctrodes and exploratory prob e electrode . The risk is greatly increased when the ESU is used in a monopolar mode, or when high ESU power settings are used (cut mode). The surgeon rnust be made aware of the consequences of burns that would occur at both the recording electrodes ( facial muscles ) and the exploratory stimulating prob e ( facial nerve ) . Since surgery involvirg the facial nerve does not require use of monopolar ESU, orf ESU for cutting, only low power bipol:rr ESU action is recommended. The risk of burns to critical tissues ( nerve and muscle ) is grr3atly increased if Electrosurg ery is performed sirnultaneou sly with use of the NL-1 exploratory stimulating probe electrode. Isolation of the patientrs facial muscle recording electrodes is always higher when the NL-l is in the STAND BY r;tate ( yellow LED indicator OFF ). The risk of IISU burns at the monitoring or stimulating sitesr is increased if these electrodes or their Iea,J s are in close proximity to the ESU cables, ESU return electrodes, or ESU active prob€s .

@GRASS INSTRUMENT CO. 1985

INSTALLATION AND SAFETY Section 4.3

CAUTION I Use of ESUs on a patient simultaneously connected to the NL-l must be restricted to Iow power bipolar mode for coagulation.

CAUTION I Do not use Electrosurgery simultane-

ously with the use of the NL-l exploratory probe electrode. Always store the exploratory probe away from the wound, and not touching any metalIic object, nor near any ESU instruments and cables while not being used.

CAUTION: Electrosurgery should never be applied when the NL-l is in the ACTIVE state; always deactivate the NL-l to the STANDBY state by use of the FOOT SWITCH whenever Electrosurg ery is in lls€ .

CAUTION:

Always keep the facial muscle

electrode leads, and the exploratory probe elec-

trode lead and its return electrode lead away from ESU cables. Recording electrodes leads should never be longer than 51r' (I30 cm)r preferably shorter. The stimulating probe electrode lead and the indiff erent return lead ( supplied with the NL-l is 3-L 12 feet ( 107 cm ) long, and should never be lengthened.

AAMI STANDARD (ESU-D 3/83): The safe and eff ective u se of electrosurg ery irs d"pendent to a large extent upon factors under the control of the operator and is not entirellr controllable by equipment desig n . It is imp,e1'tant that the instructions supplied with this equipment ( ESU I be read , llnderstood , and follo wed in order to Follow the enhance saf ety and effectivene ss . directions and recommended p:ractices f or the preparatien, placement, surveillance, removal and use of any dispersive electrode. During use of Electrosurgery, the patient should not be allowed to come into contact with metaI parts that are grounded. Un1ess the Electros'ergical leads are the shielded type, they should be positioned so that they cannot contact the patient or other leads connected to the patieot, nor should they run parallel close to other l,eads or to the operating table . The risks of t> urns at the site of stimulating and monitoring electrodes on a patient u ndergoing Electrosu rg (3ry are reduced when all other electrodes are placed as far as possible from the Electrosu rgic:rl site and from the dispersive electrode. Apparent low power output or failure of the Electrosurgical equipment to f unction correctly at otherwise normal setting s may indicate faulty application of the dispersive electrode r or failure of an ( nSU ) electrical lead. Do not increase power output before checking for obviou s def ects or misapplication (of ESU, leads and accessories). Effective contact between patient and the dispersive electrode must be verified wherrever the patient is repositioned after the initi;rl application of the dispersive electrode . rr

rl

OGRASS INSTRUMENT CO. 1985

I

NSTALLATION AND SAFETY

Section 4.4

4.4

SURFACE ELECTRODE9 - There are two surface

Choice of Recording Electrodes

4.4.L

The choice of electrodes for recordittg the facial muscle EMG is the responsibility of the user. Surface discs and subdermal needie ty pes are equally eff ective in obtaining the facial muscle EMG response o

NEEDLE ELECTRODES - Since the recordirg electrodes may not be easily accessible during surg ery , r€application during surgical procedures is not practical . In the choice of recording electrodes and application techniques, the user should be guided by whatever methods allow easy application, and which provide the maximum mechanical inte grrty .

In this regard, the user may wish to use subdermal electrodes. Subdermal electrodes, while convenient and durable, present specific safety hazard's:

The likelyhood of serious burns is increased by the virtue of the very small surface area presented by needle electrodes rvhen used with ESUs for this reasoo, both the NFPA & AAMI ESU standard s specifically warn against the use of needle electrodes: AAI4I ( ESU-D 31 83) 3.1 .2.2I

disc types : EEG ( applied with a paste ) , or EKG ( preg elled adhesive ) . Grass E5GH (gold ) or Grass E5SH tisilver), are EEG surface disc electrodes, 10 mm in diameter, and are applied with a paste and,/or i1auze and adhesive tape I They require preparertion of the skin to provide low contact impedance, and often

collodion is used to fix the dj sc from coming off and adhesive tape overall. CAUTION : Use of acetone for skjln preparation,

and collodion for securing electrodes are considered flammable and volat.Lle materials. Because they constitute a possible hazard in the O.R., these agents should not be used in the O.R. However, they can be used in patient preparation outside the O. R.

Conventional infant pre geIIecL-adhe sive EKG electrodes, used for O. R. tnorlitoring can also be Follow the directions for application used. by the manufacturer. supplied

rrNeedles should

not be used as monitoring electrodes during such procedures (ESU ) .

rr

NFPA ( Appendix E 1984 ) E- 4.3. 3. I Patient Monitoring Electrodes : rrHigh-frequency current densities at monitoring electrode-to-skin interface can be reduced by the use of a large surfaced electrode. Needle electrodes normally should not be employed during an Electrosurgical procedure but if this mode of monitoring is judged necess ary, it should be done with extreme care. rl

OGRASS INSTRUMENT CO. 1985

INSTALLATION AND SAFETY

Section 4.5

4.5

lntensity and Safety of Stimulus Current at Probe Electrode

The maximum stimulus intensity at the end of the exploratory probe is a function of the applied voltage, the pulse duration, the tissue i-pedance and the square area of the exposed probe tip. The maximum output of the N L- I is 1 volt , with an inte rnal imPedance of 1, 000 ohms, for a duration of 0.1 milliseconds. The minimum expected tissue i-pedance is 3 , 00 0 ohms, and the effective probe stimulation area is 0.043 sq cro. The maximum possible stimulation current under this condition is 250 microamperes' corresponding to a net charg e transfer per pulse of 0.025 microcoulombs. Pudenz ( 1) found that some amount of neural damage is consistently produced in chronic stimulation if the charge per pulse is 0.45 microcoulombs or greater. 4.5.1

Prior experience by lloller ( 4 ,t su g gests that a stimulus intensity of 0.5 vol.ts on the NL-l should be adequate to elicit reliable facial muscle EMG respohse. Althou gh maximum NL-l stimulating intensity is consirl.ered safe ' consistent use at the maximum setting of the STIMULUS VOLTS control should be cause to check equipment, hook uP, stin:ulating electrodes and procedure. During your initial experience you should establish a setting on the l..ll,-l STIMULUS VOLTS control that: is the threshold value; it is recommended that a value not exceedir.g 20% of this threshold be used routinely. It is not expected that the settinE5 of the STIMULU S VOLTS should need adjustment during subsequent operations. 1

.

of the Brain. Brain Barrier.

The maximum possible charge density per pulse under these conditions is 0.59 microcoulombs per sq crn . Brown ( 3 ) su g gested that charg e densities greater than 10 microcoulombs per sq cm not be used to chronically stimulate the human cerebelIar cortex, Consequently, the maximum stimulus intensity is j*dged to be safe, psrticularly considering that

,

Blecrirical Stimulation II . Bffects; on the BloodSurgical Nerrrology 4: 26541.

270, L975.

The maximum possible average power density under

these conditions is 4.4 microwatts per sq clrl . Mortimer (2) concluded that the limit for safe chronic stimulation was 0.05 watts Per sq inch ( 7 , 8 00 microwatts per sq cm ) .

Pudenz , R. H. *

2

. Mortimer, J. T. 9L d. , E::perimental Nondestructive Electrical Stimu],ations of the Brain and spinal cord. Journal of Neurosursgl 32 z 533-559 , 1970. vI

3.

Brown, W.J. -et aI., Tissue Jleaction to LongTerm Electrical Stimulation o:f the Cerebellum

in Monkey s.

Journal of Neurosurgell

47 z

366-379, L977 . 4. Moller, A. R . , Research Profe ssor of Neurological Surgery and Physiology, University of

Pittsburgh School of Medicirl€), Personal Communication to Grass Instrument ComparY.

typical operating intensities are only between f 5% and 50% of maximum values above.

OGRASS INSTRUMENT CO. 1985