Читать книгу Pearls and Pitfalls in Head and Neck Surgery - Группа авторов - Страница 9
ОглавлениеThyroid and Parathyroid Glands
Cernea CR, Dias FL, Fliss D, Lima RA, Myers EN, Wei WI (eds): Pearls and Pitfalls in Head and Neck Surgery. Basel, Karger, 2012, pp 6–7
DOI: 10.1159/000338384
1.3 New Aspects of Nerve Monitoring in Thyroid and Parathyroid Surgery
Gregory W. Randolpha Marco A.V. Kulcsarb Lenine Garcia Brandãoc
aMassachussetts Eye and Ear Infirmary, Thyroid Surgical Division, Harvard Medical School, Boston, Mass., USA; bHead and Neck Surgery in Cancer Institute of São Paulo (ICESP), and cHead and Neck Surgery, São Paulo University Medical School, São Paulo, Brazil
P E A R L S
• Recurrent laryngeal nerve (RLN) monitoring with vagal nerve stimulation helps the identification and protection of the RLN during operations on the central compartment, and is fundamental in reoperations on this area.
• Vagus nerve stimulation may be used to confirm the integrity of the RLN, or to localize the site of an eventual injury.
• It is important to stimulate the contralateral vagus nerve to confirm a real negative vagal response. When no contralateral response is achieved, it probably reflects a problem concerning the functioning of the monitoring system.
• If a true negative response is observed at the end of a lobectomy, it is advised to interrupt the operation and to stage the contralateral lobectomy.
• Pre- and postoperative laryngoscopy are essential to document vocal fold function.
P I T F A L L S
• Nerve monitoring is no substitute for careful dissection and meticulous hemostasis.
• Just the electrical identification of the RLN does not eliminate the need for visual identification of the nerve.
Introduction
One of the complications of thyroidectomy and parathyroidectomy is vocal fold paralysis after the RLN manipulation during the surgery. The incidence of this complication ranges from 0.5 to 5%, and in reoperations this rate increases up to 20% [1]. Thus, careful dissection and positive identification of the RLN is a mandatory step, as demonstrated by numerous studies [2–6]. In order to minimize the risk of nerve injury, numerous methods of identifying the RLN have been proposed. Some authors suggest electrical nerve stimulation and observation contraction of the vocal fold by endoscopy [2]. Others prefer to palpate the posterior cricoarytenoid muscle [3]. Some studies have proposed an objective assessment of vocal fold mobility using contact electrodes attached to an endotracheal tube, generating an electromyographic (EMG) response associated with a sound signal [3–7]. This is the most popular nerve monitoring system, and initially was indicated mainly for reoperations, thyroid cancer, and large goiters. With the evolution of the methodology and better understanding the system, some authors believe that it should be used in all cases of thyroid or parathyroid surgeries [1, 7].
Nerve Monitoring System
There is more than one system, but the most commonly used is one with the endotracheal (ET) tube equipped with bilateral surface electrodes that are in contact with the medial aspect of the true vocal folds. A sterile hand-held stimulator probe is connected to a monitor and this is used to deliver the adjustable stimulus (0.5-2 mA) to the RLN and vagus nerve. This allows passive and evoked monitoring of the thyroarytenoid muscles during thyroid and parathyroid surgery.
Practical Tips
There are several technical aspects to consider [3–5]:
The anesthesiologist must use only short-acting paralytic agents for anesthesia induction.
The position of surface electrodes at the level of the glottis and the ET tube cuff in the subglottis must be confirmed with a laryngoscopy (rigid or flexible), after the final positioning of the patient to surgery.
Check for respiratory variation in baseline EMG tracing, impedance of each electrode (should be less than 0.5 kΩ, with imbalance of less than 1 kΩ).
Monitor settings. Event threshold (EMG response): 100 μV; stimulator probe: 0.5 mA.
Surgical field notes. Test stimulator on strap muscle to confirm twitch and that current is received on the monitor. Dissect the vagus nerve and stimulate it before handling the thyroid lobe and check the vocal fold contraction (V1), with a stimulus of 0.5 mA. Identify the RLN with electrical stimulation and then dissect it for less manipulation; confirm it in the initial stimulation (R1). Ligate or cut any anatomical structure only after dissection and positive identification of the RLN. After lobectomy, perform the final stimulation of the vagus nerve (V2) and RLN (R2).
Monitor response. The response is positive when the amplitude exceeds 100 μV both on the vagus nerve and on the RLN, confirming the safety of performing a contralateral lobectomy, if indicated. Stimulate the contralateral vagus nerve and verify the response when the response is less than 100 μV during the final stimulation (V2, R2). If you have a response from this side, there has probably been an injury of the ipsilateral. Return to the other side and investigate the injury of the RLN. If there is no response after the stimulation of the contralateral vagus nerve is obtained, check all the electrodes and positioning of the endotracheal tube with a laryngoscope, and stimulate the vagus nerve and the RLN with palpation of the cricoarytenoid muscle.
Conclusion
The dissection of the RLN is the gold standard in thyroidectomy and parathyroidectomy, but intraoperative nerve monitoring is a very useful tool for increasing safety and preventing one of the most feared complications - bilateral vocal fold paralysis.
References
1 Dralle H, Sekulla C, Lorenz K, Brauckhoff M, Machens A: German IONM Study Group: Intraoperative monitoring of the recurrent laryngeal nerve in thyroid surgery. World J Surg 2008;32:1358–1366.
2 Kulcsar MAV, Kodaira S, Cernea CR, Ferraz AR, Cordeiro AC: Avaliação funcional das pregas vocais por meio da estimulação do nervo laríngeo inferior durante tireoidectomias e pela ultrasonografia com Doppler colorido no pré e pós-operatorio. Rev Bras Cir Cabeça e Pescoço 2009;3:137–144.
3 Randolph GW, Dralle H, et al: Electrophysiologic recurrent laryngeal nerve monitoring during thyroid and parathyroid surgery: international standards guideline statement. Laryngoscope 2011; 121(suppl 1): S1-S16.
4 Chan WF, Lo CY: Pitfalls of intraoperative neuromonitoring for predicting postoperative recurrent laryngeal nerve function during thyroidectomy. World J Surg 2006;30:806–812.
5 Chiang FY, Lee KW, Chen HC, Chen HY, Lu IC, Kuo WR, Hsieh MC, Wu CW: Standardization of intraoperative neuromonitoring of recurrent laryngeal nerve in thyroid operation. World J Surg 2010;34:223–229.
6 Cernea CR, Brandão LG, Brandão J: Neuromonitoring in thyroid surgery. Curr Opin Otolaryngol Head Neck Surg 2012, E-pub ahead of print.
7 Cernea CR, Brandão LG, Hojaij FC, De Carlucci D Jr, Brandão J, Cavalheiro B, Sondermann A: Negative and positive predictive values of nerve monitoring in thyroidectomy. Head Neck 2012;34:175–179.
Dr. Gregory W. Randolph, MD
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