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Intraoperative Monitoring of the Recurrent Laryngeal Nerve During Single-Lung Ventilation in Esophagectomy

2001; Lippincott Williams & Wilkins; Linguagem: Inglês

10.1097/00000539-200103000-00021

1526-7598

Thomas M. Hemmerling, Joachim Schmidt, Klaus Jacobi, Peter Klein,

Voice and Speech Disorders

The recurrent laryngeal nerve supplies motor function for the intrinsic muscles of the larynx. Thyroid surgery (1,2) and surgery of the esophagus (3,4) are common types of surgery with postoperative impairment or damage of the recurrent laryngeal nerve. The reported incidence of postoperative permanent paralysis of the recurrent laryngeal nerve from esophagus surgery varies greatly depending on the degree and spread of cancer, and the type of surgery and surgical technique, but can be as frequent as 34% after transhiatal esophagectomy (3). Perhaps, monitoring of the recurrent laryngeal nerve during surgery could decrease the incidence of paralysis. The degree of cancer in esophagus surgery, the extent of surgery, and often blunt and blind dissection of areas would make the availability of a reliable system to help identify and monitor the recurrent nerve helpful. Many superficial devices have become available for intraoperative monitoring of the recurrent laryngeal nerve: devices inserted into the upper pharynx (5), specially designed endotracheal tubes (6,7), or surface electrodes attached to the routine tracheal tube (8). These techniques naturally involve the anesthesiologist either actively as part of the monitoring team with collective supervision of the monitoring devices, or passively with providing anesthesia without the aid of neuromuscular blocking drugs or introduction of special tubes. We recently described a technique, based on an electrically stimulated response, in which a superficial disposable electrode attached securely to a routine endotracheal tube acts as a surface electrode and picks up the action potentials from the intrinsic muscles of the larynx in thyroid surgery (8). This case report describes the first use of the surface laryngeal electrode for intraoperative nerve monitoring in single-lung ventilation with the use of a double-lumen endobronchial tube for esophagectomy via abdomino-right-thoracic resection. Case Report A 45-yr-old man (height, 182 cm; weight, 65 kg; ASA physical status I) was admitted to the hospital because of weight loss and difficulty swallowing. Esophagoscopy and gastroscopy revealed a distal esophagus carcinoma starting 37 cm distal to the teeth and obstructing two thirds of the lumen over a distance of 5 cm. Gastroscopy revealed only signs of chronic gastritis. A computerized scan of the thorax and the abdomen showed perigastric enlargement of the lymph nodes up to 3.3 cm in diameter without spread to the liver or lungs. Sonography of the esophagus classified the tumor as uT4, N1. The otorhinolaryngology examination showed normal movement of the vocal cords; there was a suspicion of supraclavicular lymph node infiltration on the left side. Clinical examination revealed good health, sinus cardiac rhythm, and normal lung function with a forced expired volume in 1 s of 3.83 L. All laboratory results including tumor markers were normal. The patient was scheduled for abdomino-right-thoracic esophagectomy and advanced lymph node dissection. The patient was planned to have intraoperative monitoring of the laryngeal recurrent nerve, which was felt to be especially at risk of injury because of the widespread lymph node involvement of the neck, making blunt lymph node dissection of the neck necessary. We planned to use a noninvasive surface electrode on a double-lumen tube for the first time because this type of electrode proved to be a reliable, noninvasive, and easy-to-use device for intraoperative monitoring of the recurrent laryngeal nerve in thyroid surgery (8). The double-lumen endotracheal tube, however, is prone to movement during positioning (supine-left lateral) and possible displacement during surgery and single-lung ventilation. The surface electrode is a commercially available electrode (Magstim Company, Whitland, Wales, UK); the recording part has a detachable strip that needs to be removed to glue that distal electrode part circularly around the tube. Becuase the surface electrode has only a 1.5 × 1.5 cm distal recording part, we planned to attach two surface electrodes on the tube, placed in a 90° to each other and starting two cm above the tracheal cuff to cover the largest possible area (Fig. 1). Intraoperatively, the position of the tracheal tube could not be changed to receive optimal tracing as it can be in thyroid surgery because of the necessity to guarantee optimal single-lung ventilation.Figure 1: Details are shown of the distal recording part of the surface electrode. The recording parts (1.5 cm × 1.5 cm) of two surface electrodes are glued circularly around the tube, beginning approximately 2 cm above the tracheal cuff. To cover the widest area of signal coverage, they are attached rotated in a 90 ° angle to each other. It was assumed that by using two electrodes vertically placed and rotated to each other, signal retrieval should be possible even with lateral or vertical movement of the double-lumen tube as it is done during single-lung ventilationAnesthesia was induced by using remifentanil infusion at 0.375 μg · kg−1 · min−1 and a target-controlled infusion of propofol with a target concentration of 4 μg/mL to be reached within 2 min. After 5 min of controlled ventilation with 100% oxygen, the trachea was then intubated without the aid of neuromuscular blocking drugs by using a left-sided double-lumen endobronchial tube (left Broncho-Cath® Endobronchial Tube, 39F; Mallinckrodt, Bicestor, UK) with the surface electrodes attached to it. Its correct position was verified by using flexible bronchoscopy. A 20-gauge arterial line was inserted into the left radial. Anesthesia was maintained by using a remifentanil infusion at 0.1–0.25 μg · kg−1 · min−1 and a target-controlled infusion of propofol with a target concentration of 3 μg/mL. Throughout the procedure, hemodynamic stability was achieved with a mean blood pressure above 60 mm Hg in this normotensive patient. After fixation of the tracheal tube, the patient was brought into the operating room and positioned in the supine position. Both surface electrodes were connected to the Multiliner® neuromonitor (Toennies, Wuerzburg, Germany); by using a transcutaneous nerve stimulator (Multiliner®) and just lateral of the thyroid notch, both recurrent laryngeal nerves were stimulated and their compound action potential recorded. The evoked responses were both recorded from the upper surface electrode. The compound action potentials were recorded and the surface electrodes connected to the Neurosign® 100 (Magstim Company) for intraoperative nerve monitoring and identification. Surgery commenced with an abdominal incision. After the abdominal dissection, the patient was brought into left lateral position, and single-lung ventilation was commenced. Single-lung ventilation was performed in routine fashion by using at least 50% oxygen in air breathing gas with controlled ventilation of a tidal volume of 6 mL/kg, and the respiratory rate was adjusted to maintain an end expiratory Peco2 of 28–40 mm Hg. Again, transcutaneous stimulation of the recurrent laryngeal nerve took place; the best responses were then obtained from the lower surface electrode, which was subsequently connected to the Neurosign® 100. Spontaneous signals from the vocal cords, evoked by accidental direct or indirect (tear, thermal irritation) nerve contact were used to prevent the surgeon from damaging the nerve. During the blunt dissection of the contralateral (left) cervical side, most of the dissection took place without direct vision. There, a bipolar long stimulation probe (Inomed, Wuerzburg, Germany) was used to deliberately search and identify for the recurrent laryngeal nerve, which could be performed without any problem. The intraoperative stimulation probe was then used to follow the nerve whenever it was necessary during the dissection (Fig. 2). Stimulation took place with 3 Hz, 0–2 mA, and threshold measurements as it is done during thyroid surgery to determine how close the preparation is to the actual nerve (8). Surgery was completed and the ceratinizing squameous cell carcinoma (pT3 pN1 L1 V1 MX, UICC-stadium III) removed.Figure 2: Intraoperative picture of the stimulation probe identifying the nerve; relevant structures are labeledThe patient was transferred to the intensive care unit, and his trachea was extubated 3 h after surgery. The postoperative course was without any problems. There were no laryngeal sequelae detected at routine postoperative direct laryngoscopy. The patient was discharged 2 wk after surgery. Discussion There are different surgical approaches to carcinoma of the esophagus. They can all lead to complications (e.g., anastomotic leaks, respiratory failure, sepsis) including recurrent laryngeal nerve damage, mostly unilateral, which reach the highest percentage in the transhiatal approach (3). Extensive lymph node dissection, especially in the neck area of the contralateral side, can result in nerve injury, even when the abdomino-right-thoracic approach is used. Special endotracheal tubes (6), available for thyroid surgery, cannot be used in esophagus surgery because of the need to use single-lung ventilation for better surgical exposure. To use the surface electrode successfully, meticulous preparation of the double-lumen tube is mandatory. Because adjustment of the position of the tube might become necessary during surgery and single-lung ventilation as a result of changes in patient position or surgical manipulation, we used two surface electrodes glued one after the other. Because position changes might occur not only in the vertical axis but horizontally as well, they were glued in a 90° angle to each other. It is important that reference stimulation is always possible during surgery, either by stimulating the recurrent laryngeal nerve transcutaneously at the neck or, if within the sterile field, by stimulating the vagal nerve by using the bipolar stimulating device, which is used to identify the recurrent nerve. These stimulating probes are available in two lengths; the longer probe (15 cm) is used in esophageal surgery. The evoked response can be heard by using the Neurosign® 100 as it is done during thyroid surgery. Spontaneous continuous monitoring of the nerve status is possible by listening to disturbance noises, which indicate either direct or indirect (e.g., tearing of the nerve), nerve irritation. Monitoring of the spontaneous signals is, however, limited by the absence of any visual monitoring. The main feature of this monitoring device is the direct stimulation of areas where the nerve cannot yet be visualized or exposure is limited, e.g., blunt lymph node dissection of the neck, and where by increasing the stimulating current an even distant (1–2 cm) nerve can be located and secured. Neuromuscular blockade (NMB) limits the degree of the evoked responses; complete blockade makes monitoring impossible. A less-than-complete blockade, e.g., T1% set to be 50% of control response, might still allow the nerve monitoring; for optimal monitoring conditions, however, we opted to not use any neuromuscular blocking drugs. A deep enough anesthesia and skill with endobronchial intubation without the aid of NMB makes intubation even with the large double-lumen tube possible. An alternative is certainly the use of a short-acting neuromuscular blocking drug for intubation and subsequent avoidance of NMB and NMB-monitoring. We conclude that, for the first time, intraoperative nerve monitoring and nerve identification in esophageal surgery and during single-lung ventilation was performed. This was achieved by using a noninvasive, easy-to-use surface electrode attached to a regular double-lumen tube. A successful monitoring and nerve identification can only be done by the active involvement of the anesthesiologist in the intraoperative monitoring. Knowledge of electrophysiologic monitoring and expertise with the electrode in thyroid surgery proved indispensable.