Electromyographic (EMG) Neuromonitoring in Otolaryngology-Head and Neck Surgery
Section snippets
Scope and definitions
This article focuses on the anesthetic considerations pertinent to IONM of peripheral cranial nerves during otolaryngologic–head and neck surgery. The specific modality of IONM is EMG, both spontaneous and evoked. Spontaneous and evoked EMGs are “cousins” to a modality anesthesiologists commonly use while administering routine anesthetics: neuromuscular junction (NMJ) monitoring. Spontaneous EMG monitors the spontaneous electrical activity of muscle cells, and had its initial application in
History
The first attempt at sparing the facial nerve during parotid surgery was recorded by Thomas Carwardine in 1907.5, 6 He used careful dissection to identify numerous branches of the facial nerve in his patients, and although palsies were common after surgery, these were not permanent or significant in most patients.
Similarly, in early otolaryngologic practice in the 1940s and 1950s, sound anatomic knowledge,7, 8, 9, 10 experience, and especially visual identification of the cranial nerves in the
General anesthetic considerations for all IONM and EMG procedures used in otolaryngologic surgery
Which anesthetic technique is compatible with the type of monitoring used in a given procedure? Several modalities are available for monitoring the central and peripheral nervous system during otolaryngologic and neurotologic surgery. Table 1 and Table 2 list the conventional types of monitoring and the anesthetic agents that affect or have no effect on the specific type of monitoring. For the sake of comparison, other modalities besides IONM (spontaneous and evoked EMG) are included in Table 1
Vagus and recurrent laryngeal nerve monitoring during thyroidectomy, parathyroidectomy, and other anterior cervical surgery
As remotely as 1938,18, 19 and as recently as the present time,4, 9 authors have advocated visual identification of the recurrent20 and superior21 laryngeal nerves during thyroidectomy and other surgeries as a means of avoiding trauma. Riddell10 actually tested (and proved) the hypothesis of visual identification being superior to nonidentification of the recurrent laryngeal nerve as a way to protect it during thyroidectomy. Both visual identification and IONM seem to be a safe and reliable
Anesthetic considerations for NIM tube monitoring during thyroid surgery
Anesthesiologists are usually asked to tailor their technique to allow for efficient placement and accurate positioning of the NIM tube (Fig. 2). Ideally, the surgeon and anesthesiologist will confer at length about the placement and use of the NIM tube.
The overall goals are to (1) provide for a quick induction, intubation, and positioning, including neck extension; (2) allow partial emergence or lightening immediately after intubation so that respiratory variation in the vocalis muscle (ie,
Intraoperative monitoring of the motor branch of the facial nerve during tympanic, mastoid, parotid, and other surgeries
The facial nerve is vulnerable to injury during many otolaryngologic procedures and parotidectomy rhytidectomy, and other head and neck procedures (Fig. 3). The typical IONM operation involving facial nerve monitoring, such as a tympanomastoidectomy, involves preoperative placement of facial nerve monitoring recording electrodes either awake or after induction and intubation. Surface gel or needle electrodes are placed in or overlying the orbicularis oculi and orbicularis oris muscles; these
Anesthetic considerations during IONM of the motor branch of the facial nerve during tympanic, mastoid, parotid, and other surgeries
Patient movement is a primary concern, because of the use of powered surgical instruments and the proximity of the facial nerve to the operative site. As in anterior cervical surgery, valid concerns exist about the use of muscle relaxants and local anesthetics blocking the sensitivity of the IONM being used. Succinylcholine or rocuronium to facilitate intubation can be used initially but not afterward.
The microscopic field causes any blood loss during middle ear surgery to be problematic for
Intraoperative monitoring of cranial and cervical nerves during neck dissection and skull base operations
During neck dissection, many nerves and vessels (including the thoracic duct) are at risk.35, 36, 37, 38 Although the usefulness of the NIM tube in monitoring vagus and recurrent laryngeal nerve function is well established, a NIM tube is only helpful in this setting if revision thyroidectomy with neck dissection is undertaken.37, 39 Otherwise, handheld unipolar and bipolar probes are more commonly used to stimulate nerves and observe the movement of target muscles. Typical nerves monitored in
Anesthetic considerations during neck dissection and skull base operations
Patient movement during neck dissection and skull base surgery may be problematic for several reasons, including its potential to precipitate surgical injury, embolism, or hemorrhage. Assuring adequate depth of anesthesia is important, especially if the Mayfield apparatus or other positioning device is used for craniotomy. Furthermore, if IONM is planned, then muscle relaxants should be used only at induction and intubation. The use of local anesthetics is likewise contraindicated because of
Summary
During otolaryngologic–head and neck surgery, surgeons and anesthesiologists compete for the airway as a part of their cooperative care of the patient. Although it is often brief, this involves intense stimuli (especially to the vocal cords and nearby airway mucosa) alternating with periods of little stimulation. As a goal, anesthetic induction for IONM must be deep enough to ensure patient comfort and lack of awareness, but light enough to allow accurate positioning of a NIM tube, and then
Acknowledgments
The author would like to extend sincere thanks to Gregory W. Randolph, MD, of the Departments of Otolaryngology at Massachusetts Eye and Ear Infirmary and Harvard Medical School for his advice and encouragement.
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