Intraoperative neuromonitoring (IONM) allows surgeons to monitor vulnerable nerves like the facial, recurrent laryngeal, and vagus nerves during head and neck surgery. IONM is done using electromyography to provide real-time information about the functional integrity of nerves. Electrodes are placed on muscles innervated by the nerves of interest and the nerves can be stimulated during surgery to ensure their function is being preserved. IONM helps reduce patient morbidity from nerve injuries during surgery.

4.  Intraoperative neuromonitoring (IONM) is a relatively recent
advance in electromyography (EMG) applied to
otolaryngology-head and neck surgery.
 Its purpose is to allow real-time identification and functional
assessment of vulnerable nerves during surgery.
 The nerves most often monitored in head and neck surgery are
the motor branch of the facial nerve (VII), the recurrent or
inferior laryngeal nerves (X), the vagus nerve (X), and the
spinal accessory nerve (XI), with other cranial lower nerves
monitored less frequently.
 Morbidity from trauma to these nerves is significant and
obvious, such as unilateral facial paresis.

5.  Avoidance of intraoperative nerve injury is of para- mount
importance in order to reduce patient morbidity. In addition,
both RLN and facial nerve paralysis are common reasons for
litigation following otolaryngology surgery.

6.  Krause first described facial nerve monitoring in 1912
using a faradic stimulation during cochlear nerve section
for tinnitus. Twitching of the ipsilateral facial muscles
during stimulation helped him preserve the facial nerve, and
the patient had transient facial weakness postoperatively.
 In the 1960s, dedicated facial nerve monitoring systems were
developed. The Hilger stimulator was used principally in
the assessment of facial paralysis, but was also used during
surgery.
 Further developments in facial nerve monitoring occurred in
the 1970s and 1980s. Delgado and colleagues described the
use of electromyography (EMG) monitoring in
cerebellopontine angle (CPA) surgery.

7.  Moller and Jannetta combined the specificity of EMG
recording with the advantage of acoustic feedback to the
surgeon.

8.  The underlying principle for intraoperative monitoring
is that some types of injury can be reversed.
 Facial nerve monitoring can be useful to identify
the facial nerve when it is not clearly visible in the surgical
field.
 Localizing distal nerve fragments in trauma cases, and
identifying sites of nerve compression, as long as wallerian
nerve degeneration has not completely occurred.
 Otologic procedures in which the nerve is at risk include
cochlear implantation, revision tympanomastoidectomy, and
repair of external auditory canal bony stenosis.

9.  Monitoring may augment safety in cases where the anatomy is
altered by infection, trauma, or congenital malformation.
 It may also be beneficial in training centers where some
portions of operations are performed by less experienced
surgeons.

10.  Many facial nerve monitoring systems are available
commercially, including the Nerve Integrity Monitor
(Xomed, Inc., Jacksonville, FL), Neurosign
100 (Smith & Nephew Richards, Inc., Memphis, TN),
Brackmann II (WR Medical Electronics Co., Stillwater,
MN), and NEI (Grass Instrument Co., Quincy, MA).
 All of these devices use EMG. The Silverstein Facial Nerve
Monitor (WR Medical Electronics Co.,) is an example
of a motion detector device.
 Some systems, such as the Silverstein Monitor, include the
ability to electrify instruments to aid with monitoring.

11.  The electrodes have to be placed in the muscles supplied by
the facial nerve.
 Four electrodes are placed in frontalis, orbicularis oculi,
orbicularis oris and mentalis muscles.
 The ground electrodes are placed over sternum.
 There are stimulators which can stimulate the nerve or could
map the course of the nerve. One could adjust the strength of
the current by which nerve could be stimulated.
 A low current is used when nerve is stimulated directly so
there is no damage to the nerve.

13.  Once before surgery starts electrodes are tapped, which
produces sound as well as an impulse onthe monitor,
indicating proper fixation and connections of the electrodes.
 During surgery as one reaches close proximity of the facial
nerve, the mechanical pull also produces a sound, warning
surgeon that he is in close vicinity of the nerve, preventing any
accidental damage.
 Once the nerve is exposed, it is stimulated directly to identify
it, which produces a different type of sound and also produces
an impulse [EMG] on the monitor.
 Nerve and branches are stimulated as the surgery proceeds.
When the main trunk is stimulated all the electrodes inserted in
different muscles get stimulated and produce an impulse on the
monitor indicating that main nerve as well as the branches are
intact.

14.  While performing a parotid surgery, one comes accross many
fibrous strands which appears similar to nerve. With use of
nerve stimulator, this situation is avoided and precise
identification of nerve is possible and surgical time is saved.

17.  The nerve integrity monitor (NIM-Response 3.0 System,
Medtronic Xomed, Jacksonville, Florida) is the most widely
used device for laryngeal nerve monitoring providing both
audio and visual evoked waveform information when either
the recurrent laryngeal or vagus nerve is stimulated.
 This nerve monitoring device transforms laryngeal muscle
activity into audible and visual electromyographic (EMG)
signals whenever the RLN or vagus nerve is stimulated
intraoperatively.

19.  During IONM, a low pressure-cuffed silicone
endotracheal tube (NIM Standard EMG Reinforced Tube,
(Medronic Xomed) is used.
 This tube is similar to a standard endotracheal tube but in
addition, it has two integrated stainless steel contact
electrodes on each side of the tube that monitor vocal cord
EMG activity.
 These endotracheal surface electrodes make good contact
with the luminal surface of the true vocal cords.
 Following correct positioning of the endotracheal tube,
the vocal cord electrodes and ground wires are connected
to the NIM 3 monitor via a connector box.

20.  Both the recording electrodes and nerve stimulator probe
require grounding electrodes (adhessive or subcutaneous)
usually placed on the patient’s shoulder or sternum region
closest to the monitor unit.
 NIM 3 monitor has a pulse generator which is connected to the
stimulating probe.
 Neural stimulation occurs via a sterile, handheld probe (Prass
Standard Flush-Tip Probe, Medtronic Xomed).
 Stimulating probes can be monopolar or bipolar.

25.  Neuromuscular blockade interferes with monitoring as it
reduces the EMG amplitude and the optimal laryngeal
response.
 Thus after induction with a short acting neuromuscular
blocking agents, neuromuscular blocking agents should be
avoided for the rest of the case.

26.  Skull base tumours may involve many cranial nerves.
 CN III, IV and VI which control extra ocular muscles, are at
risk in tumours of cavernous sinus.
 Intraoperative monitoring of CN VIII has become the standard
of care for skull base and CPA surgery.
 Motor portions of trigeminal nerve may be involved and CN
IX, X, XI and XII can be involved in large skull base lesions.
 Nerves are localized using the same technique as used for the
facial nerve electrode, employing subdermal needle electrodes
placed with great care.

27.  Subdermal needle electrodes can be placed percutaneously in
extraocular muscles that are innervated by a respective cranial
nerve.
 The opposite forehead serves as a good location for reference
electrode to serve to avoid contamination with EMG potentials
from ipsilateral facial muscles.
 EMG from soft palate (CN IX), sternocleidomastoid or
trapezius muscle (CN XI), or lateral tongue (CN XII) can be
used for the lower cranial nerves.
 CN XII monitoring can be done by placing recording
electrodes spaced 1cm apart in the lateral tongue.

28.  Consultant surgeons find the technology helpful. It is therefore
hoped that increased use of intraoperative nerve monitoring
will be associated with improved patient outcomes.
 Innovative methods of cranial nerve monitoring using
techniques such as intra operative F wave and transcranial
electric motor evoked potential mesurement are being
investigated, but have yet to be widely adopted in
otolaryngology.
 As a cautionary note, it must be emphasised that these devices
do not compensate for poor surgical technique. Visual nerve
identification will continue to be the gold standard for
preventing intraoperative nerve damage.

29. THANK YOU ALL