Updated January 2, 2015
Author: VerLee

Description: PreOp Assessment & Management, IntraOp Guidleines for parathyroidectomy

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Introduction & Overview

The four parathyroid glands are responsible for maintaining calcium homeostasis via secretion of parathyroid hormone. Parathyroid hormone acts on the bones and kidneys to increase serum calcium and decrease serum phosphate. It stimulates osteoclasts to release calcium and phosphate into the extracellular fluid, and simultaneously increases phosphate excretion and calcium re-absorption in the kidney.

Primary hyperparathyroidism occurs when the PTH level is inappropriately elevated in relation to the serum calcium level. In normal circumstances, a negative feedback loop exists in which the PTH level drops in response to an elevated serum calcium level. This does not occur in the setting of primary hyperparathyroidism.

Secondary hyperparathyroidism occurs when the PTH is elevated as the result of another cause. Vitamin D deficiency and renal failure are the 2 most common causes of secondary hyperparathyroidism.

Tertiary hyperparathyroidism occurs when glands affected by secondary hyperparathyroidism become autonomous and are no longer controlled by the normal feedback mechanisms. An example would be a patient with secondary hyperparathyroidism from chronic renal failure who undergoes a renal transplant that corrects the renal failure but who continues to have inappropriate release of PTH.

Parathyroid surgery

Traditionally, parathyroidectomy involves a collar incision, bilateral exploration of the neck, identification of all four glands, and removal of the diseased gland or glands.
This requires a general anesthetic technique similar to that for thyroid surgery although airway encroachment is rare.
Operating times may be unpredictable, especially if frozen section or parathyroid assays are performed, and active heat conservation should therefore be considered.

Perioperative Considerations

Postoperative Complications

Bleeding: This may result in tense swelling in the neck and respiratory difficulty. Clip removers or stitch cutters must be kept at the bedside to evacuate blood and hematoma, if the patient is in extremis. Otherwise, this is done expeditiously in the OR. Early reintubation is recommended in this situation.

Recurrent laryngeal nerve (RLN) palsy: This may be unilateral or bilateral and present with respiratory difficulty or stridor. With unilateral palsy or partial cord paralysis, the patient may simply complain of hoarseness of voice or have difficulty in phonation. RLN injury may result from ischaemia, contusion, traction entrapment, and actual transection. Traditionally, anaesthetists were taught to inspect the cords under direct vision immediately post-extubation, but this can be difficult and may be unreliable. The laryngeal mask airway and fibrescope has been used to make this technically easier and also to observe the vocal cords during surgery.

Postoperative Care

Serum calcium should be checked at 6 and 24 h after operation. Hypocalcaemia requires supplementation; persisting hypercalcaemia is rare.
Pain is not usually severe and easily controlled with oral analgesia, although NSAIDs should be avoided in patients with renal compromise.

Intraoperative PTH Assay

Intraoperative PTH assay is often employed to predict surgical cure in patients with primary hyperparathyroidism. Guidelines for its use are available from the National Association of Clinical Biochemistry.
Some authors measure preincision PTH levels, and some measure preexcision levels after the abnormal gland has been identified but before it is removed. Some authors check postexcision levels at 5 minutes, 10 minutes, 15 minutes, and 20 minutes after removal of the abnormal gland.
In most situations, 10-15 minutes after the abnormal gland is removed, the PTH sample should be within normal limits and should have decreased by more than 50% from the initial baseline value. If the PTH level does not decrease by 50% and fall into the normal range, the surgeon should continue with 4-gland exploration, or, at least, should continue exploring until additional abnormal parathyroid glands are identified and removed and the PTH level is in the normal range and 50% or more below the starting value.