Neurosign 100 Procedure Sheets Oct 2011

CONTENTS These sheets are set out by surgical procedure in the following order: Parotid surgery Acoustic Neuroma surgery Thyroid and Parathyroid surgery Mastoid surgery Middle Ear surgery Submandibular Gland surgery Facial nerve monitoring during a Cochlear Implant

This is not an exhaustive list of the procedures which may involve the Neurosign 100, and additional sheets will be added as these procedures are developed. Advice upon, and contributions to, these notes are welcomed.

Using the Neurosign 100 during surgery of the parotid gland This information is intended for theatre staff and for those demonstrating this equipment.

Follow this check list to ensure that you are using the Neurosign to its best advantage.

+ve CH 1

Frontalis

-ve Reference

Temporal branch Orbicularis oculi Zygomatic branch

Buccal branch

Reference CH 2

Pes

+ve -ve

Anserinus

Levator labii superioris Mandibular branch

Parotid gland Orbicularis oris

Electrode placement for use during surgery of the parotid gland

Submandibular or cervical branch

Distribution of the facial (VIIth) nerve

Setting Up

Surgical Procedure Information

Ÿ Look at the right hand diagram to see where the facial nerve lies anatomically, and then at the left hand diagram to see the muscles which are used to monitor the various branches. Ÿ Note the names of the muscles and their relationship to the nerve branches which control them. Ÿ Ensure that that the electrodes are inserted into the muscles as shown with the wires leading away from the surgical site. The needles must be in the muscle proper and not simply under the skin. Ÿ Secure the electrodes with tape, allow 5cm of free cable for movement and then secure again with tape before leading the electrode wires to the preamplifier pod. Ÿ To check that electrode impedance is OK, switch on both channels and check that the bargraph does not show any lit segments. The bottom segment may flicker - this is a normal muscle reaction to the needle and will die down in a few minutes. Tap the face to demonstrate that the electrodes and monitor is connected. Ÿ Set the stimulator to 30Hz and 0.5mA. This current is used to locate the nerve at its trunk near the stylomastoid foramen. Once located the current can be reduced to a minimum of 0.2mA. Ÿ The concentric probe P/N 4600-00 is recommended. It is very accurate, does not stimulate through tissue, and is excellent for stimulating the small interconnecting fibres between the branches.

Ÿ The operation is normally a superficial parotidectomy, where the tumour lies on top of the facial nerve. The tumour, together with a margin of healthy tissue, is removed leaving the facial nerve lying on top of the remaining gland. Ÿ Occasionally, the tumour extends below the facial nerve; this is termed a deep-lobe parotidectomy. The facial nerve needs to be mobilised so that the tumour can be removed from above and below the nerve. This is technically more difficult and the facial nerve is at greater risk. Ÿ The usual way to find the facial nerve is to follow the digastric groove and find the pes anserinus, the point at which the nerve trunk divides, and then to follow the branches until sufficient space has been created to provide access. Ÿ Use the concentric probe set to 0.5mA to find the nerve trunk; once located, reduce the current to 0.3mA and ultimately to 0.2mA once the branches are identified. Ÿ Note that because the Neurosign 100 only has 2 channels, and you are monitoring 4 branches, the monitor can only discriminate between upper and lower bifurcations, and not the individual branches. As each branch only has a single needle inserted into the relevant muscle, it is possible for the surgeon to stimulate fine interconnecting branches, for part of the face to twitch, but not to see any response from the monitor. This is simply a limitation of using 2 channels where 4 would be more appropriate. It is advised that the face is covered in OpSite or similar material, and left visible so that any twitches can be observed. October 2011

Using the Neurosign 100 during acoustic neuroma surgery This information is intended for theatre staff and for those demonstrating this equipment.

Follow this check list to ensure that you are using the Neurosign to its best advantage.

+ve CH 1

Frontalis

-ve Temporal branch

Reference Orbicularis oculi

Zygomatic branch

CH 2

Buccal branch

Reference +ve -ve

Levator labii superioris

Pes Anserinus

Mandibular branch Parotid gland

Orbicularis oris

Electrode placement for use during acoustic neuroma surgery

Setting Up

Submandibular or cervical branch

Distribution of the facial (VIIth) nerve

Surgical Procedure Information

Ÿ Look at the right hand diagram to see where the Ÿ Acoustic neuromas arise from mutated cells growing from the end of the myelination surrounding the VIIIth nerve inside the internal facial nerve lies anatomically, and then at the auditory canal (IAC). They grow to fill this space, surrounding the Viith left hand diagram to see the muscles which are and VIIIth nerves, destroying hearing in the process, and expand out of used to monitor the various branches. the meatus towards the brainstem. Tumours greater than 2cm are Ÿ Note the names of the muscles and their considered large, less than 2cm, medium, and those contained within relationship to the nerve branches which the IAC intra-caninicular. control them. Ÿ Ensure that that the electrodes are inserted into Ÿ As these tumours grow slowly, they are often referred to radio-surgery or simply scanned every year to check on the rate of growth. Surgical the muscles as shown with the wires leading removal is the only way to actually remove a tumour; radio-surgery away from the surgical site. The needles must aims to kill the cells, leaving the dead cells behind to be reabsorbed be in the muscle proper and not simply under into the body over time. Small tumours generally respond best to the skin. radio-surgery, so typically it is the larger tumours which come to Ÿ Secure the electrodes with tape, allow 5cm of surgery. free cable for movement and then secure again with tape before leading the electrode wires to Ÿ There are 3 standard approaches to these tumours, depending on the degree of hearing remaining, size of tumour and preference of the preamplifier pod. surgeon. The translabyrinthine approach destroys the inner ear; the Ÿ To check that electrode impedance is OK, switch sub-occipital and retro-sigmoid both provide a possibility of preserving on both channels and check that the bargraph hearing. does not show any lit segments. The bottom Ÿ In the translabyrinthine approach, the facial nerve can be identified at segment may flicker - this is a normal muscle an early stage and the concentric probe will be most useful when reaction to the needle and will die down in a stimulating in the internal auditory canal, although the precision few minutes. Tap the face to demonstrate that bipolar probe should be used to stimulate through bone. the electrodes and monitor is connected. Ÿ In the other approaches the tumour capsule should be stimulated at a Ÿ Set the stimulator to 30Hz and 0.05mA. This high current (1mA - 2mA) as soon as the dura is opened and the current is used to locate the nerve at the tumour exposed, to confirm that the facial nerve is not lying on the brainstem or internal auditory meatus, anterior surface. The nerve normally gets pushed behind the tumour, depending on the surgical approach. If the but is on the surface in about 5% of cases. surgeon is using a translabyrinthine approach, Ÿ The tumour is usually debulked to provide operating space and then the current may need to be higher to start the nerve is located at the internal auitory meatus and later at the (0.5mA - 3mA), but reduce to 0.05mA as soon brainstem. The surgeon now has 2 points to stimulate the nerve - 1 as the nerve is located. point distal to the tumour, where the surgery does not affect the nerve Ÿ The concentric probe P/N 4600-00 is (unless the IAC is to be opened); and 1 point at the brainstem proximal recommended. It is very accurate, does not to the tumour. Stimulation at the brainstem therefore stimulates stimulate through tissue, and is excellent for through the portion of the nerve affected by the tumour. If stimulation stimulating the unmyelinated nerve. If at this point gives the same level of response at 0.05mA at the end of operating in the mastoid, either use a higher the procedure as at the first stimulation, then the patient is likely to current or use the precision bipolar probe P/N wake with normal nerve function. If a higher current is required, the 4604-00 set to 0.5mA - 1mA. patient is likely to wake with a paresis, the time taken to resolve depending on the degree of increased stimulation required. October 2011

Using the Neurosign 100 during surgery of the thyroid and parathyroid This information is intended for theatre staff and for those demonstrating this equipment.

Follow this check list to ensure that you are using the Neurosign to its best advantage. Electrode positioning Common carotid artery Recurrent Laryngeal Nerve

Parathyroids

Electrode Sensing tracks Vagus nerve

Thyroid anatomy

Active area of electrode

Alternative non-recurrent laryngeals

Black lines Cuff

Setting Up

Surgical Procedure Information

Ÿ Look at the right hand diagram for details on attaching Ÿ Thyroid surgery carries a small risk (1-3%) of the electrode to the endotracheal tube. The left hand permanent injury to the recurrent laryngeal nerves diagram shows the normal anatomy of the recurrent (RLN) which control the vocal cords. Damage to these laryngeal nerves. nerves can lead to hoarseness, difficulty with speech, swallowing and compromise of the airway. More Ÿ Select the correct size of electrode according to the frequent is a subtle change to the voice timbre, which endotracheal tube being used. can be serious for those using their voices Ÿ Attach the electrode to the endotracheal tube as professionally. shown in the instructions for use. If the edge of the Ÿ The surgeon can be at the site of the nerve within 30 electrode is placed against the weld of cuff to tube, the minutes, so it is especially important that the patient is black lines on some tubes will remain visible. Do not not paralysed at this point. grease the tube until the electrode is attached. Ensure ŸBecause of the nature of the Anterior view that the tabbed side of the electrode and the manipulation Epiglottis Ventricular fold electrode is attached first of the larynx during the surgey, the other side will overlap movement artifacts are the tab. common. The purpose of the monitoring it to help identify the Ÿ Intubate as normal, get the RLN using the stimulating probe. patient onto the operating Once identified, the surgeon can table, shoulder bag in place, stay away from it. neck extended, then check that the electrode is ŸThe nerve is usually identified Vocal cord between the cords. If the at Berry’s ligament or in the electrode is next to the weld esophagotracheal groove. of the cuff, then in women ŸThe RLN appears to behave Endotracheal Electrode the tube should be at 19cm, tube differently from the facial nerve mounted on Posterior view and in men at 20cm (allow in that it has a distinct threshold tube surface for patient variation). below which it will not View of the larynx after electrode insertion Ÿ Connect the cable - it can fit stimulate. It is recommended either way round. The 2 that the stimulator be set at yellow wires form 1 channel, 2mA as this threshold varies and the 2 blue wires form the 2nd channel. The green can be as high as 1.5mA. connector can go to either of the Reference connectors on the preamp, leaving 1 connector empty. Ÿ Set the stimulator to 30Hz and 2mA. It should not be necessary to change this value. Ÿ Use the bipolar probe P/N 3601-00.

October 2011

Using the Neurosign 100 during surgery involving the mastoid process This information is intended for theatre staff and for those demonstrating this equipment.

Follow this check list to ensure that you are using the Neurosign to its best advantage.

+ve CH 1

-ve

Frontalis

Reference

Temporal branch Orbicularis oculi Zygomatic branch

Mastoid Buccal branch

Reference CH 2

Pes Anserinus

+ve -ve

Levator labii superioris

Mandibular branch Parotid gland

Orbicularis oris

Sub-mandibular Or cervical branch

Electrode placement used during surgery involving the mastoid process

Distribution of the facial (VIIth) nerve

Setting Up

Surgical Procedure Information

Ÿ Look at the right hand diagram to see where the facial nerve lies anatomically, and then at the left hand diagram to see the muscles which are used to monitor the various branches. Ÿ Note the names of the muscles and their relationship to the nerve branches which control them. Ÿ Ensure that that the electrodes are inserted into the muscles as shown with the wires leading away from the surgical site. The needles must be in the muscle proper and not simply under the skin. Ÿ Secure the electrodes with tape, allow 5cm of free cable for movement and then secure again with tape before leading the electrode wires to the preamplifier pod. Ÿ To check that electrode impedance is OK, switch on both channels and check that the bargraph does not show any lit segments. The bottom segment may flicker - this is a normal muscle reaction to the needle and will die down in a few minutes. Tap the face to demonstrate that the electrodes and monitor is connected. Ÿ Set the stimulator to 30Hz and 0.5mA. A higher current may well be necessary because the surgeon will be stimulating through bone; 0.5mA is a safe value to start. If there is no response at 0.5mA, increase the current until a response is heard. If the anatomy is normal, it may require 5mA to stimulate through the bone. If the nerve is dehiscent, only 0.2mA will be necessary - hence the starting value of 0.5mA. Ÿ The precision bipolar probe P/N 4604-00 is recommended. It is accurate, and the 2 electrodes are identified. The white is the return, the blue is the active stimulator. Place the blue electrode over the nerve. Ÿ The probe can give an indication of depth of bone between probe and nerve. Bearing in mind that stimulation at 0.2mA represents exposed nerve, and 5mA denotes normal anatomy, as the drill is used the stimulation current can be reduced and early warning given when there is very little bone remaining.

Ÿ The mastoid process is a section of the skull behind the ear which is like a sponge in structure, being full of cavities. These cavities may become infected and the disease can destroy the bone, in particular the incus, malleus and stapes. The surgical technique is to drill away the bone until fresh, clean bone is exposed, and to seal the cavities to prevent air-borne infection from other tissue. At the same time, prostheses may be fitted to improve hearing and replace missing or destroyed bones. Ÿ The facial nerve runs in a canal on the edge of the mastoid process. It is important that the surgeon does not drill through the canal and the nerve! Sometimes disease may have attacked the canal and the nerve is dehiscent - then the canal will need to be opened in order to clear out disease inside the canal. Ÿ As the surgeon drills, you may hear a high pitched whining which changes frequency with the drill. This is caused by one of two factors; either the drill is vibrating the canal and the nerve is reacting, or the electrodes in frontalis are resting against the bone and the vibration in transmitted directly to them. This is not a fault and no action need be taken. However, if the response continues once the drill has stopped, this is an indication of heating of the nerve and irrigation must be used to cool both the nerve and the drill. Ÿ The nerve is often left within the canal and so the monitor may not appear to be particularly useful. It is guarding against a small but catastrophic risk.

October 2011

Using the Neurosign 100 during surgery of the middle ear This information is intended for theatre staff and for those demonstrating this equipment.

Follow this check list to ensure that you are using the Neurosign to its best advantage.

+ve CH 1

Incus

Frontalis

-ve Reference Orbicularis oculi Stapes

CH 2

Reference +ve -ve

Levator labii superioris

Facial nerve Orbicularis oris Stapes

Electrode placement used during surgery involving the mastoid process

Middle ear anatomy showing course of facial nerve

Setting Up

Surgical Procedure Information

Ÿ Look at the right hand diagram to see where the facial nerve lies anatomically, and then at the left hand diagram to see the muscles which are used to monitor the various branches. Ÿ Note the names of the muscles and their relationship to the nerve branches which control them. Ÿ Ensure that that the electrodes are inserted into the muscles as shown with the wires leading away from the surgical site. The needles must be in the muscle proper and not simply under the skin. Ÿ Secure the electrodes with tape, allow 5cm of free cable for movement and then secure again with tape before leading the electrode wires to the preamplifier pod. Ÿ To check that electrode impedance is OK, switch on both channels and check that the bargraph does not show any lit segments. The bottom segment may flicker - this is a normal muscle reaction to the needle and will die down in a few minutes. Tap the face to demonstrate that the electrodes and monitor is connected. Ÿ Set the stimulator to 30Hz and 0.5mA. A higher current may well be necessary because the surgeon will be stimulating through bone; 0.5mA is a safe value to start. If there is no response at 0.5mA, increase the current until a response is heard. If the anatomy is normal, it may require 5mA to stimulate through the bone. If the nerve is dehiscent, only 0.2mA will be necessary - hence the starting value of 0.5mA. Ÿ The precision bipolar probe P/N 4604-00 is recommended. It is accurate, and the 2 electrodes are identified. The white is the return, the blue is the active stimulator. Place the blue electrode over the nerve. Ÿ The probe can give an indication of depth of bone between probe and nerve. Bearing in mind that stimulation at 0.2mA represents exposed nerve, and 5mA denotes normal anatomy, as the drill is used the stimulation current can be reduced and early warning given when there is very little bone remaining.

Ÿ The risk of injury to the facial nerve during stapedectomy and other middle ear procedures is small but usually occurs because of a dehiscence in the fallopian canal above the oval window, which allows the facial nerve to lie unprotected outside its normal anatomy. The use of the monitor allows this condition to be verified at an early stage. Ÿ If the nerve is not visible under the microscope, the surgeon can use the precision bipolar probe to stimulate the canal and gain a response, verifying that the nerve is in its normal position. The nerve is dehiscent in about 50% of cases presenting for surgery; the current should be set to 0.2mA if the nerve is dehiscent, and in the range 0.5mA - 5mA depending on the thickness of intervening bone if it is not dehiscent. Starting at 0.5mA and then increasing or decreasing the current is recommended. Ÿ As the surgeon drills, you may hear a high pitched whining which changes frequency with the drill. This is caused by one of two factors; either the drill is vibrating the canal and the nerve is reacting, or the electrodes in frontalis are resting against the bone and the vibration in transmitted directly to them. This is not a fault and no action need be taken. However, if the response continues once the drill has stopped, this is an indication of heating of the nerve and irrigation must be used to cool both the nerve and the drill. Ÿ Once the nerve has been identified, the monitor is not likely to be used further. Its purpose in this surgery is primarily to guard against the risk to the nerve before it has been located, and so prevent accidental injury.

October 2011

Using the Neurosign 100 during surgery involving the submandibular gland This information is intended for theatre staff and for those demonstrating this equipment.

Follow this check list to ensure that you are using the Neurosign to its best advantage.

Temporal branch Trigeminal nerve

Reference for CH 1

and ganglion Orbicularis oculi Reference CH 2

Lingual nerve

+ve -ve

Levator labii superioris

Orbicularis oris CH 1

+ve -ve

Zygomatic branch

Buccal branch

Mandibular branch

Parotid gland Nerve to mylohyoid

Mylohyoid

Sub-mandibular

(under chin)

or cervical branch

Electrode placement used during surgery involving the submandibular gland

Pes Anserinus

Submandibular gland

Distribution of the facial (VII��) and trigeminal (V��) nerves

Setting Up

Surgical Procedure Information

Ÿ Look at the right hand diagram to see where the the facial nerve and the mylohyoid branch of the trigeminal nerve lie anatomically, and then at the left hand diagram to see the muscles which are used to monitor the various branches. Ÿ Note the names of the muscles and their relationship to the nerve branches which control them. Ÿ It may be desirable to preserve the submandibular or cervical branch of the facial nerve. Insert electrodes into the platysma muscle when this has been exposed. The hypoglossal nerve may also be involved; this can be monitored by inserting electrodes into the lateral aspect of the tongue. If all the above nerves have to be monitored, place one active electrode in each muscle. Ÿ Ensure that that the electrodes are inserted into the muscles as shown with the wires leading away from the surgical site. The needles must be in the muscle proper and not simply under the skin. Ÿ Secure the electrodes with tape, allow 5cm of free cable for movement and then secure again with tape before leading the electrode wires to the preamplifier pod. Ÿ To check that electrode impedance is OK, switch on both channels and check that the bargraph does not show any lit segments. The bottom segment may flicker - this is a normal muscle reaction to the needle and will die down in a few minutes. Tap the face to demonstrate that the electrodes and monitor is connected. Ÿ Set the stimulator to 30Hz and 0.2mA. A higher current of 0.5mA may be to locate the nerve. Ÿ The precision bipolar probe P/N 4604-00 is able to stimulate through a layer of tissue. For greater accuracy, use the concentric probe P/N 4600-00.

Ÿ If the surgeon is to explore the parotid gland as well, then consider putting in the electrodes as shown on the parotid setup and changing them on the preamp at the appropriate stage of the operation. Make sure any temporarily unused electrodes are identified and are accessible. Ÿ The nerve to the mylohyoid muscle is a motor branch of the trigeminal (Vth) nerve. Therefore you may be monitoring branches of both the facial and trigeminal nerves in this procedure, since both these nerves run close to the submandibular gland. If the tumour is extensive, the surgeon may need to consider monitoring the masseter muscle as well, as this is innervated by a different branch of the trigeminal nerve. Ÿ The lingual nerve is a sensory branch of the trigeminal nerve which connects with the lingual gland and supplies mucous membranes on the floor of the mouth and the anterior of the tongue. Being a sensory nerve it cannot be directly monitored using the Neurosign, but it can be differentiated as a sensory nerve rather than a motor nerve. Ÿ The part of the facial nerve at risk are the mandibular and cervical branches which are covered by monitoring the orbicularis oris below the lower lip, but if there is a chance that the buccal branch may be involved, one electrode should be placed above the upper lip. If the surgeon is certain that this branch will not be involved, this needle may also be placed below the lower lip. Ÿ Because you may be monitoring 2 different nerves, you may see a response from only 1 channel of the monitor when using the stimulator. The current required to effectively stimulate the nerve to the mylohyoid may not be the same as that required for the facial nerve, and it may be necessary to increase the current setting to 0.5mA for this nerve.

October 2011

Using the Neurosign 100 during a cochlear implant This information is intended for theatre staff and for those demonstrating this equipment.

Follow this check list to ensure that you are using the Neurosign to its best advantage.

Round window

Frontalis

+ve CH 1

-ve Facial nerve

Reference Orbicularis oculi

Vestibular nerve Cochlea nerve

Reference CH 2

+ve -ve

Levator labii superioris

Orbicularis oris

Electrode placement to be used during a cochlear implant

Setting Up

Surgical Procedure Information

Ÿ The facial nerve is one trunk in its mastoid section and until it leaves the stylomastoid foramen, so the left hand diagram should be used to place the electrodes. Ÿ Ensure that that the electrodes are inserted into the muscles as shown with the wires leading away from the surgical site. The needles must be in the muscle proper and not simply under the skin. Ÿ Secure the electrodes with tape, allow 5cm of free cable for movement and then secure again with tape before leading the electrode wires to the preamplifier pod. Ÿ To check that electrode impedance is OK, switch on both channels and check that the bargraph does not show any lit segments. The bottom segment may flicker - this is a normal muscle reaction to the needle and will die down in a few minutes. Tap the face to demonstrate that the electrodes and monitor is connected. Ÿ Set the stimulator to 30Hz and 0.5mA. A higher current may well be necessary because the surgeon will be stimulating through bone; 0.5mA is a safe value to start. If there is no response at 0.5mA, increase the current until a response is heard. If the anatomy is normal, it may require 5mA to stimulate through the bone. If the nerve is dehiscent, only 0.2mA will be necessary - hence the starting value of 0.5mA. Ÿ The precision bipolar probe P/N 4604-00 is recommended. It is accurate, and the 2 electrodes are identified. The white is the return, the blue is the active stimulator. Place the blue electrode over the nerve. Ÿ The probe can give an indication of depth of bone between probe and nerve. Bearing in mind that stimulation at 0.2mA represents exposed nerve, and 5mA denotes normal anatomy, as the drill is used the stimulation current can be reduced and early warning given when there is very little bone remaining.

Ÿ A cochlear implant comprises two distinct phases; drilling the mastoid process in order to seat the transceiver, and obtaining access to the cochlea so that the electrode can be inserted. It is in the second stage that the monitor is important. The facial nerve may be anomalous, or it is possible to injure it during the drilling of the middle ear. Ÿ The facial nerve lies in a canal on the edge of the mastoid process. It is important that the surgeon does not drill through the canal and the nerve! Vibration from the drilling is often heard and can serve as an early warning that the nerve is nearby. A high pitched whining indicates that either the nerve is affected by the drilling, or that the frontalis electrodes are touching bone and picking up the vibration. If you check the bargraphs, equal amplitude indicates that the nerve is being affected, whereas signals only from channel 1 indicate vibration transferred by the bone and can be ignored. Ÿ The precision bipolar probe will stimulate through bone if sufficient current is used. It is recommended that the nerve is stimulated so that it is known that the monitor and electrodes are functioning correctly. If a nerve is dehiscent, a current of 0.2mA will stimulate it; to stimulate through bone, start at 0.5mA and increase until a response is obtained. This will vary according to the depth of bone, and could require up to 5mA. Place the blue electrode of the probe over the nerve - the white is the return electrode.

October 2011