Awake Thyroidectomy under Local Anesthesia and Dexmedetomidine Infusion

INTRODUCTION

Dexmedetomidine (DEX) is an a-2 receptor agonist that has both sedative and analgesic properties. Although it is currently FDA approved for mechanically ventilated patients in the intensive care unit (ICU), much of the recent literature focuses on its use in the perioperative period.1,2 Several case reports have demonstrated the utility of DEX in awake intubations,3,4 as well as in awake neurosurgical cases.5 DEX is uniquely suited for these types of cases because it provides sedation and analgesia while simultaneously preserving the patient's ability to cooperate with the procedure6. DEX causes minimal respiratory depression7 and has opioid sparing properties,8 which make it an ideal agent for patients in whom mechanical ventilation and high doses of opioids should be avoided. Patients with obstructive sleep apnea (OSA) have demonstrated an increased risk for oxygen desaturation following general anestesia. The American Society of Anesthesiology (ASA) Task Force has published guidelines9 recommending the use of regional anesthetic techniques and the avoidance of opioids, when possible, in patients at increased perioperative risk of complications from OSA. Although there are no prospective studies supporting the avoidance of endotracheal intubation in patients with severe chronic obstructive pulmonary disease (COPD) in the acute perioperative setting, there is literature to support the use of noninvasive positive pressure ventilation in acute exacerbations in the intensive care unit.10,11

We report the case of a patient with severe COPD, OSA, unilateral vocal cord dysfunction, and other medical comorbidities undergoing an awake total thyroidectomy under local anesthesia and a DEX infusion.

CASE REPORT

A 64-year-old (67 in, 68 kg) ASA classification IV male was scheduled for total thyroidectomy for papillary carcinoma. The thyroid cancer involved the right recurrent laryngeal nerve (RLN) and was causing preoperative dysphonia. The patient's medical history was significant for obstructive sleep apnea (noncompliant with a continuous positive airway pressure [CPAP] machine), stage III COPD,12 congestive heart failure (with preserved ventricular ejection fraction), gastroesophageal reflux disease, diabetes mellitus type 2, and hypertension. He was dependent on oxygen via nasal cannula at 2 L/min at rest, and required 4-6 L/min of oxygen when walking up a flight of stairs. Spirometry demonstrated an FEVl of 0.61 L (20% predicted), FVC of 2.56 L (63% predicted), FEF of 0.20 L (8% predicted), and a DLCO of 11.0 L (37% predicted). His COPD was maximally medically managed.

The patient's pulmonologist felt that he was at moderate-to-high risk for postoperative respiratory failure (PRF). The respiratory failure risk index (RFRI) is a tool used to predict the risk of PRF.13 The patient had an RFRI score of 36 (neck surgery, age >60, partially dependent functional status, and a BUN >30 mg/dL). His score indicated a predicted probability of 1 1.6% for PRF. General anesthesia has also been found to be an independent risk factor for PRF.14 Therefore, the pulmonologist recommended avoiding intubation, if possible. The patient also expressed a strong desire to avoid intubation.

The patient's surgeon was concerned about possible RLN injury secondary to the surgical procedure and wanted to complete the procedure with die patient awake and under minimal sedation, ensuring die patient would be able to phonate on command. A change in voice quality during surgery indicates tension or retraction on the RLN. Usually, in our institution, diese cases are performed under unilateral or bilateral superficial cervical plexus blocks, as the case dictates. However, in this case, because of the patient's severe COPD, we felt the 30-50% risk of RLN blockade associated with superficial cervical plexus blockade was too high.15·16 Patients with normal pulmonary function can tolerate unilateral RLN blockade. The ability of this patient to tolerate RLN blockade was less likely. As a result of the need to have the patient phonate, the possibility of using a laryngeal mask airway was not an option.

The decision was made to proceed with an awake thyroidectomy. The tiryroid tumor was approximately 1.8 × 1.2 × 1.0 cm in its largest dimension. The patient had a Mallampati class II airway. The radiographic images of his neck did not exhibit tracheal manipulation by the tumor. The patient did not have any physical exam findings of tracheal compression. The team elected to perform the anesthetic via local anesthetic infiltration by the surgeon, as well as a DEX infusion. The DEX infusion was chosen to provide analgesia and allow for a cooperative patient to phonate on command. The patient was counseled extensively by both the surgeon and the anestiiesia team of the details of the anesthetic plan.

Two peripheral intravenous lines were placed, to ensure a back up intravenous line for continued DEX infusion in case of primary intravenous line failure, and standard ASA monitors were applied. A DEX loading dose of 1 mcg/kg was administered over 10 minutes,7 while the surgical team began to prepare the field and infiltrate local anesdietic. The surgery lasted ~210 minutes. A total of ~20 mL of 1% lidocaine with 1:200,000 epinephrine was used for local infiltration. The patient received 250 pg of fentanyl (-1 pg/kg/hr). The DEX infusion ranged from 0.2 to 1.0 pg/kg/hr. His blood pressure and heart rate remained within 20% of preoperative baseline values, and he did not require medical intervention to raise heart rate or blood pressure. The patient maintained verbal communication throughout the case and was able to cooperate with the surgeon's requests. During less stimulating parts of the operation, the patient would fall asleep, but was easily aroused by calling his name.

The patient was given 7.5 mg of ketorolac, a nonsteroidal anti-inflammatory medication, at the end of the operation for multimodal analgesia. He was monitored in the postanesthesia care unit overnight to observe for any postoperative respiratory distress. His average pain rating in the recovery unit was 2 out of 10. He received two acetaminophen/oxycodone (325/5 mg) tablets by mouth. The patient was evaluated die following morning by the anesthesia team. The patient could recall the entire operation (which he was counseled on before surgery), but did not experience pain and was appreciative of avoiding intubation.

CONCLUSIONS

Several other cases of awake thyroidectomies have been reported.17-19 To our knowledge, however, this is the first case report using DEX in combination with local anesthetic infiltration for the duration of the surgery. There were several factors in this case that supported the decision to perform an awake thyroidectomy rather than a general anesthetic. The patient had a history of severe COPD, as well as poorly controlled OSA, and was at significant risk for PRF. The surgeon was appropriately concerned for local anesthetic spread to the recurrent laryngeal nerves, and therefore ruled out the use of superficial cervical plexus blockade. Our anesdietic goals were to ensure a cooperative patient who was able to phonate on request, avoid respiratory depression, and to decrease the risk of PRF. DEX can provide analgesia through its action at the dorsal horn of the spinal cord, but has also been shown to maintain respiratory drive.7,20 We purposefully avoided the use of midazolam because of concern for respiratory depression, especially in combination with fentanyl. The patient maintained hemodynamic stability throughout the operation. The most stimulating parts of the operative procedure were addressed by using additional local anesdietic while taking care to avoid spread to the recurrent laryngeal nerves, increasing the DEX infusion rate, and using low doses of intravenous fentanyl. Patient selection and extensive preoperative counseling before surgery were key factors in the success of this anesthetic.

The infusion rate of DEX was increased above the recommended FDA dose of 0.7 mcg/kg/hr (0.8-1.0 mcg/kg/hr) during several parts of the procedure. Although the literature does not specifically support this practice, there have been reports of using 10-15 times the maximally recommended infusion rate of DEX without respiratory depression or hemodynamic instability.7 As DEX was the primary anesdietic agent used, higher doses were required during the most stimulating parts of the operation. To minimize the total opioid requirement, we elected to increase the DEX infusion while monitoring the patient carefully for drug-related side effects. The patient's arms were available to us throughout the operation if we felt it necessary to measure invasive blood pressures or obtain an arterial blood gas sample. Verbal communication was maintained throughout the procedure, which helped us monitor the degree of sedation.

The patient's postoperative course was uncomplicated. He received minimal additional analgesic in the first 24 hours and was satisfied with the anesthetic given and postoperative analgesia provided. The surgeon in this case has performed several other awake thyroidectomies at our institution, but all of those were completed under superficial cervical plexus block and all cases received more total opioid despite shorter surgical times. Another important aspect of this case is the patient's acknowledgment of complete surgical recall. The patient was counseled extensively on this possibility before the operation. Recall with DEX has been reported21 previously in ventilated patients during neurologic assessment after anteroposterior spinal fusion. Although DEX has anxiolytic properties, it does not show consistent amnestic properties. Although this case may have been successfully completed with alternative anesthetic regimens, we believe it exemplifies another positive application of DEX in the perioperative period. For challenging medical patients, DEX has consistently shown favorable pharmacodynamic properties. Its minimal effect on respiratory drive and reduction in opioid requirement were key components in our decision to use DEX for this patient with severe COPD and undertreated OSA. Further studies are needed to evaluate the optimal perioperative dosing range for DEX and its effects on hemodynamic and respiratory parameters.

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