Anesthesiology and Perioperative Management of Patients Presenting for Surgical Excision of Endocrine Tumors

Epidemiology

Thyroid cancer is now the most common endocrine malignancy worldwide. The incidence increased from 1.5 cases per 100,000 in 1953 to 7.5 cases per 100,000 in 2002. Developments in diagnostic capabilities, including neck ultrasonography, fine needle aspiration, computed tomography, and magnetic resonance imaging, may have contributed to this apparent increase in the diagnosis of thyroid cancer. Ninety percent of all thyroid tumors are indolent, with the estimated mortality rate at just 0.6 deaths per 100,000 person years. Benign thyroid disease requires treatment only in the presence of dysfunction or local compressive symptoms.

Preoperative Management

A comprehensive history and examination should assess for signs of severe hypothyroidism hyperthyroidism, or complications of thyroid disease, as outlined in Table 28.1 .

Enlarged thyroid glands or goiters as seen in Fig. 28.1 can lead to tracheal compression and difficult airway management. Airway assessment should include thyromental distance, assessment of neck movement, and visualization of pharyngeal structures.

Investigations recommended prior to thyroid surgery are outlined in Table 28.2 .

Interpretation of the Thyroid Function Test

Intraoperative Management

Thyroid surgery is almost always performed under general anesthesia with tracheal intubation. General anesthesia may be induced in a standard manner. Awake fiberoptic intubation should be considered with a large goiter if it is causing tracheal compression, or in a retrosternal goiter with compressive symptoms, or vocal cord dysfunction.

Regarding the endotracheal tube itself, as the surgical field is focused on the head and neck, a simple endotracheal tube could potentially be at risk of kinking under the pressure of surgical handling in the upper neck. For this reason, some anesthesiologists prefer to use a wire-reinforced endotracheal tube, but there is no evidence that this affects patient outcomes.

A study of over 3000 thyroidectomies found that difficult intubation occurred in 6% of cases. Patients undergoing thyroid surgery are at risk of injury to the recurrent laryngeal nerve.

Short acting muscle relaxants can be used to facilitate tracheal intubation and allow for recurrent laryngeal nerve monitoring during the surgery.

Patients are positioned for surgery in neck extension with a head-up table tilt of 25% to reduce blood loss. As visualizing the patient’s face is often not possible intraoperatively, careful attention must be paid to securing the endotracheal tube and protecting the eyes.

Intraoperative monitoring of blood loss is required, via regular assessment of estimated blood loss and weighted swabs, especially in patients with large goiters.

Surgical technique involves raising of skin flaps, muscle retraction, superior pedicle mobilization, ligation and dissection of vessels, and hemostasis and wound closure.

Complications include the following.

Postoperative Management

Measures should be undertaken to prevent straining on tracheal extubation where possible, because this can cause venous engorgement of airway tissues and hence airway edema. It can also rupture small blood vessels directly, leading to hematoma formation and airway compromise. Options to prevent this include tracheal extubation under deep anesthesia, topical use of lidocaine, and the use of an intravenous narcotic such as remifentanil.

Epidemiology

A Danish population-based study found that the incidence of pheochromocytomas has doubled in the last two decades (0.2 per 100,000 person years to 0.4 per 100,000 person years). Similarly, a systematic review in the Netherlands found that the incidence rate increased from 0.29 to 0.46 per 100,000 over the same time period, while age at diagnosis increased. These trends are likely related to improved diagnosis, including imaging studies and advances in biochemical testing, with up to 40% of all pheochromocytomas now diagnosed incidentally on imaging.

Approximately 40% of pheochromocytomas are hereditary and more likely to be bilateral and present at a younger age. The 5-year survival rate for localized and metastatic pheochromocytomas is 95% and 60%, respectively. Biochemical diagnosis and precise tumor localization are required, and the definitive treatment is complete surgical excision (see Table 28.3 ).

Preoperative Management

Pheochromocytomas cause symptoms in approximately 50% of patients. A comprehensive history and clinical exam should include the following :

• Signs and symptoms of a pheochromocytoma

  • Episodic headaches

  • Diaphoresis

  • Abdominal pain

  • Vomiting or diarrhea

  • Weakness

  • Weight loss

• Cardiorespiratory signs of pheochromocytomas

  • Tachycardia

  • Dyspnea

  • Palpations

  • Hypertension

  • Orthostatic hypotension

Preoperative investigations and their clinical indications are included in Table 28.4 .

Intraoperative Management

Endotracheal intubation is advised in all patients undergoing surgical removal of a pheochromocytoma because of the extent and duration of surgery and its intraabdominal location. Preoperative alpha and beta blockade regimens should be continued. Laparoscopic adrenalectomy is sufficient in up to 95% of patients; however, large (>6 cm) or invasive tumors may require open resection. ^, Where open surgical technique is utilized, epidural anesthesia attenuates intraoperative stress-mediated catecholamine surges and postoperatively reduces pain.