Anesthesiology

Thyroidectomy

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What the Anesthesiologist Should Know before the Operative Procedure

Indications for thyroidectomy include thyroid carcinoma, thyroid nodules, goiter (enlarged thyroid) with compressive symptoms, toxic nodule(s) that cannot be controlled medically, and Graves disease.

There are several different thyroidectomy procedures. A total thyroidectomy removes the entire gland and is the most common procedure performed. It is indicated for treatment of carcinoma, especially aggressive forms, and hyperthyroidism due to Graves disease or a toxic goiter. Total thyroidectomy has the advantage of removing microscopic disease from the contralateral side. It has a higher risk of hypoparathyroidism, hypothyroidism, and recurrent laryngeal nerve injury. A subtotal thyroidectomy removes a portion of both lobes and the isthmus and can be considered for low-risk patients with less aggressive disease that is grossly confined to one side. A thyroid lobectomy removes just one lobe of the thyroid and is generally used for non-cancerous nodules. Partial lobectomy or incisional biopsy is rarely performed.

The critical issues related to thyroidectomy include assurance that the patient is euthyroid before surgery, management of the airway in patients with large goiters, and management of specific complications (thyroid storm, recurrent laryngeal nerve damage, hypoparathyroidism, neck hematoma).

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Thyroidectomy is rarely an urgent procedure and then only when dangerous hyperthyroidism cannot be controlled medically.

Thyroidectomy is virtually never an emergency procedure though complications from thyroidectomy, in particular neck hematoma, may require emergency intervention. Rarely, a hyperthyroid patient may not be able to be made euthyroid with medical therapy. There may be intolerable side effects of anti-thyroid medications. Amiodarone-induced hyperthyroidism may be resistant to anti-thyroid medications and the amiodarone cannot be discontinued because of cardiac concerns. In these situations, thyroidectomy may be indicated before thyroid function can be normalized. Such a patient will be at increased risk of cardiovascular instability and thyroid storm.

2. Preoperative evaluation

Thyroid function should be evaluated preoperatively, in particular looking for evidence of hyperthyroidism. Symptoms of hyperthyroidism include weight loss, diarrhea, skeletal muscle weakness and stiffness, warm and moist skin, palpitations, heat intolerance, fatigue, and nervousness. Cardiovascular manifestations include increased left ventricular contractility and ejection fraction, tachycardia, elevated systolic blood pressure, and decreased diastolic blood pressure. Hypercalcemia, thrombocytopenia, and a mild anemia may be present. Laboratory data will show an elevated T4 level and a depressed TSH (thyroid stimulating hormone) level.

An enlarged thyroid (goiter) may compress or deviate the airway and other adjacent structures. Stridor is an indication of significant airway compression. Imaging studies including CXR and neck/chest CT should be reviewed if available to evaluate for any airway narrowing or deviation. Very large or invasive goiters can compress venous structures and cause a superior vena cava syndrome. Signs of head and upper extremity venous hypertension should be sought. Very large or invasive goiters can compress lower airways and cause pathophysiology of an anterior mediastinal mass. Positional dyspnea and positional syncope suggest this pathophysiology. Flow-volume loops can help evaluate for this.

In almost all cases thyroidectomy is an elective procedure and all medically unstable conditions warrant further evaluation and stabilization. In particular, delaying surgery may be indicated if the patient is hyperthyroid. All efforts should be made to return hyperthyroid patients to a euthyroid state prior to surgery. Thyroidectomy is low-risk procedure by ACC/AHA guidelines.

3. What are the implications of co-existing disease on perioperative care?

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b. Cardiovascular system

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c. Pulmonary

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d. Renal-GI:

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e. Neurologic:

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f. Endocrine:

Patients presenting for thyroidectomy may have underlying hyperthyroidism or hypothyroidism.

Hyperthyroidism should be treated prior to thyroidectomy to decrease cardiovascular instability and to decrease the risk of thyroid storm. Mild to moderate hypothyroidism does not appear to increase perioperative risk but should be corrected with thyroid hormone replacement therapy. Severe hypothyroidism must be corrected prior to elective surgery.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

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4. What are the patient's medications and how should they be managed in the perioperative period?

All of the patient's chronic medications should be continued in the perioperative period. Anticoagulants (warfarin) and anti-platelet drugs (aspirin, clopidogrel, non-steroidal anti-inflammatory drugs, garlic and vitamin E) may be held before surgery if not vital for prevention of coronary stent thrombosis or stroke.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Hyperthyroid patients will likely be controlled on several drugs. Anti-thyroid drugs (propylthiouracil or methimazole) should be continued until surgery. Beta-blockers are used to control the adrenergic effects of hyperthyroidism and must be continued through surgery. Iodide may be used in the week preceding surgery to shrink and decrease the vascularity of the gland and should be continued through the day of surgery.

Hypothyroid patients will likely be on thyroid hormone replacement therapy that should be continued throughout the perioperative period though the long-acting effects of synthroid means that missing a dose is not clinically important.

i. What should be recommended with regard to continuation of medications taken chronically?

In general, all chronic medications should be continued through the perioperative period. Anti-thyroid drugs and iodine can be discontinued after surgery.

Anticoagulants (warfarin) and anti-platelet drugs (aspirin, clopidogrel, non-steroidal anti-inflammatory drugs) may be held before surgery if not vital for prevention of coronary stent thrombosis or stroke.

j. How To modify care for patients with known allergies -

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k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

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l. Does the patient have any antibiotic allergies- - Common antibiotic allergies and alternative antibiotics]

Antibiotic prophylaxis is not indicated for thyroidectomy.

m. Does the patient have a history of allergy to anesthesia?

If a patient has a history of allergy to an anesthetic drug that drug should not be administered. There are several alternatives for every class of drug.

If a patient has a history of malignant hyperthermia, succinylcholine and potent inhalation agents are contraindicated. A total intravenous anesthetic with propofol with or without nitrous oxide is perfectly suitable for thyroidectomy.

5. What laboratory tests should be obtained and has everything been reviewed?

If the thyroidectomy is being performed for Graves disease or a toxic nodule, preoperative T4 and TSH levels should be obtained. Otherwise there are no special laboratory data required except as dictated by the patient's chronic medical conditions.

Patients being treated for hyperthyroidism should have a preoperative electrocardiogram, electrolyte levels, and a complete blood count.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Thyroidectomy is most commonly performed under general endotracheal anesthesia. This is most comfortable for the patient, provides a still surgical field, and assures a secure airway during laryngeal and tracheal manipulation.

Routine noninvasive monitors (ECG, NIBP, pulse oximeter, end-tidal gas analysis, temperature) are sufficient unless there are severe cardiopulmonary co-morbidities. Thyroidectomy is not a very stimulating procedure and is not associated with large blood loss or fluid shifts.

The patient is positioned supine with the arms tucked at the sides. Care must be taken to protect the ulnar nerves at the elbow. Foam should be placed in the palms. Intravenous tubing connections including extensions should be tight. The neck will be extended with a roll behind the neck and shoulders. Hyperextension must be avoided. Care must be taken to assure that the head is supported at the occiput and not dangling.

Any well controlled induction technique may be used with consideration of the patient's co-morbidities. If the surgeon will be monitoring recurrent laryngeal nerve function intraoperatively, persistent muscle relaxation must be avoided. Intubation may be facilitated with succinylcholine or a small dose or non-depolarizing muscle relaxant which can be reversed if necessary. Deep general anesthesia will allow intubation without the use of muscle relaxants.

Recurrent laryngeal nerve (RLN) function can be monitored in two ways. A nerve stimulator may be used by the surgeon to stimulate suspicious structures and contraction of the laryngeal muscles noted. Alternatively, the NIM (Nerve Integrity Monitor) endotracheal tube (Medtronic Xomed) can be used. This endotracheal tube has two pairs of electrodes embedded in the shaft of the endotracheal tube just above the cuff. When properly positioned the electrodes will be in contact with the vocal cords and an electromyographic signal can be monitored. Muscle relaxants and topical laryngeal anesthesia must be avoided to obtain appropriate signals.

Goiters that are associated with airway deviation or narrowing, especially if symptomatic, may warrant non-routine airway management. The concern is that the reduction in muscle tone associated with induction of general anesthesia and use of muscle relaxants might cause airway collapse and that positive pressure bag-mask ventilation would be ineffective. There is also the concern that with significant tracheal deviation visualization of the larynx by direct laryngoscopy will be difficult. These are rare situations but can be catastrophic if they occur. There are no evidence-based guidelines to decide which patients need an awake intubation or a fiberoptic-assisted intubation. Certainly, symptomatic patients, especially those with dyspnea or stridor on recumbency, are at higher risk.

Substernal goiters pose additional risks as they can compress the trachea, carina, bronchi, and intrathoracic vascular structures. This obstruction can worsen with induction of general anesthesia, use of positive pressure ventilation, and use of muscle relaxants.

During emergence and extubation, coughing should be avoided to decrease the risk of neck hematoma. This may be facilitated by deep extubation, intravenous lidocaine, or generous intravenous opioids.

a. Regional anesthesia

Regional anesthesia is a consideration for thyroidectomy though it is rarely utilized.

Cervical epidural blockade can provide satisfactory anesthesia for thyroidectomy. This is a technically challenging procedure. The benefit is avoidance of general anesthesia. The drawbacks include the risk of spinal cord injury during needle placement, diaphragmatic paresis or paralysis, and the need for a motivated patient and skilled surgeon.

Bilateral superficial cervical plexus block can provide satisfactory anesthesia for thyroidectomy. The benefit is the avoidance of general anesthesia. The drawbacks include discomfort, especially during airway manipulation, and the need for a motivated patient and skilled surgeon.

b. General Anesthesia

Thyroidectomy is usually performed under general endotracheal anesthesia. The benefits are a comfortable patient and a secure airway during tracheal and laryngeal manipulations.

c. Monitored Anesthesia Care

Increasingly, thyroidectomy is being performed under monitored anesthesia care (conscious sedation with local infiltration anesthesia). The benefits are avoidance of the complications of general anesthesia and possibly decreased cost and shorter hospital stay. The drawbacks are that it requires a motivated patient and a skilled surgeon.

6. What is the author's preferred method of anesthesia technique and why?

Prophylactic antibiotics are not indicated for thyroidectomy.

The are several different surgical procedures: total thyroidectomy, partial thyroidectomy, lobectomy.

The most feared intraoperative complication is recurrent laryngeal nerve (RLN) injury. The recurrent laryngeal nerves are found immediately posterior to the thyroid gland in association with the inferior thyroid artery. The surgical literature is divided about whether the nerves should be specifically sought and identified. The recurrent laryngeal nerve innervates all the laryngeal muscles except the cricothyroideus muscle and therefore is responsible for abduction of the vocal cords. Unilateral damage to the RLN can cause postoperative hoarseness. Bilateral damage to the RLN can cause postoperative total airway obstruction with the vocal cords paralyzed in the midline. Bilateral damage may require immediate reintubation or tracheostomy.

Rarely, patients who are hyperthyroid (and even sometimes when not) can develop thyroid storm intraoperatively. Thyroid storm is an exaggerated hyperthyroid condition characterized by hyperthermia, tachycardia, hypertension, tremor, sweating, widened pulse pressure, agitation, confusion, dysrhythmias, myocardial ischemia, and congestive heart failure. It must be distinguished from malignant hyperthermia, sepsis, pheochromocytoma and light anesthesia though there are no clear diagnostic criteria. Treatment must be rapid and aggressive to prevent complications. Treatment is largely supportive with oxygenation, ventilation, intravenous fluids, and cooling blankets. Beta-blockers (esmolol, metoprolol, propanolol) are used to treat adrenergic symptoms. Electrolyte and acid-base abnormalities should be treated. Anti-thyroid drugs and iodide are used to treat thyroid storm but, in the context of a thyroidectomy where the thyroid will be removed, they will have limited value.

a. Neurologic:

The recurrent laryngeal nerves are found immediately posterior to the thyroid gland in association with the inferior thyroid artery and can be injured during thyroidectomy.

b. If the patient is intubated, are there any special criteria for extubation?

Extubation of the trachea is usually routine. Excessive or prolonged coughing should be avoided to reduce the likelihood of bleeding.

If there is concern about recurrent laryngeal nerve injury, spontaneous ventilation can be resumed while under general anesthesia and the patient extubated while observing vocal cord movement via direct or fiberoptic laryngoscopy. Both vocal cords should abduct during inspiration.

Long standing or large goiters may cause tracheomalacia that predisposes to tracheal collapse during negative pressure inspiration. This can be evaluated by resuming spontaneous ventilation under general anesthesia and performing fiberoptic bronchoscopy. Significant tracheomalacia may require tracheostomy to maintain a patent airway postoperatively.

c. Postoperative management

There is only minimal to moderate postoperative pain after thyroidectomy. In the immediate postoperative period this can be managed with small boluses of intravenous opioids followed by oral opioids and acetaminophen when the patient is capable of oral intake.

Patients can be safely placed in a regular floor bed postoperatively. Uncomplicated thyroidectomies can be discharged on the same calendar day after an extended period of observation. Some centers are performing selected thyroidectomies on an outpatient basis. Patients who have had intraoperative complications such as tracheomalacia or bilateral recurrent laryngeal nerve injury may need intensive care.

The most important postoperative complication is neck hematoma leading to airway compression. There must be frequent checks on the patient. Measurement of neck circumference may detect a problem early. Neck hematoma is a potentially life-threatening complication of thyroidectomy because it can lead to airway obstruction. Common symptoms of a neck hematoma include neck swelling, neck pain and pressure, dyspnea, and stridor. The initial management of a symptomatic neck hematoma is to open the wound and evacuate the hematoma at the bedside to decompress the airway. The patient can then be returned to the operating room for airway management and re-exploration. Opening the wound may not relieve airway obstruction because a component of the airway obstruction is from venous congestion and edema of the airway. The priority then becomes securing the airway with an endotracheal tube or tracheostomy as soon as possible. Endotracheal intubation is often difficult because of the distorted anatomy.

Hypoparathyroidism and resultant hypocalcemia can occur postoperatively due to devascularization, injury, or accidental removal of the parathyroid glands. Calcium levels should be checked postoperatively though symptomatic hypocalcemia rarely occurs before 24 hours. Some centers are advocating measuring a 4-hour post-thyroidectomy parathormone (PTH) level as an index of likelihood of hypocalcemia and the need to preemptively treat before discharging the patient. Hypocalcemia is treated with intravenous calcium gluconate. Oral calcium and vitamin D supplementation can be used for low-risk patients.

What's the Evidence?

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