1. Thyroid Gland and Anesthetic Management
Daniel Stairs CRNA, MSN, MBA
Excela Health School of Anesthesia

2. Thyroid Gland is H-shaped Right and left lobe with isthmus

3. Location of Thyroid Gland
Anterior to trachea
Just below cricoid cartilage
Covering second through fourth tracheal rings
Thyroid gland weighs about 20 gm

4. Blood Supply to Thyroid Gland
4 to 6 cc/min/gm
Arterial supply via inferior and superior arteries
Venous supply via inferior, middle, and superior thyroid veins

5. Nerve Supply
Two superior laryngeal nerves and two recurrent laryngeal nerves supply the entire sensory and motor innervations to the larynx.

6. Innervation

7. Recurrent Laryngeal Nerve
Most common nerve injured in throidectomy
Motor supply
Sensation below vocal cords
With selective injury to abductor fibers:
(1) hoarseness
(2) bilateral injury
(3) obstruction

8. Recurrent Laryngeal Nerve
Selective injury to adduction fibers
Post-operative assessment after thyroidectomy is via laryngoscopy and having patient phonate letter “e”
Most common nerve injury

9. Superior Laryngeal Nerve
Motor supply to cricothyroid muscle (SLN external branch)
Internal branch provides sensation above the vocal cords
Injury causes possible risk for aspiration and hoarseness

10. Essential Thyroid Hormones
Thyroxine – or T4
Triiodothyronine – or T3
Release of these hormones into circulation stimulated by TSH
T3 is less firmly bound to carrier proteins and disappears from circulation quicker
T3 is 3-5 times as potent as T4 but is limited by its transient nature

11. Thyroid Hormones
Nearly all circulating T3 is derived from peripheral conversion of T4
Major Functions of Thyroid Hormones:
(1) calorigenic effects
(2) growth and cellular differentiation
(3) metabolic effects
(4) muscular effects

12. Other Functions of Thyroid Hormones
Working with growth hormone, they ensure proper development of the brain
Increase protein breakdown and glucose uptake by cells, enhance glycogenolysis. and depress cholesterol levels
In excess… they may interfere with ATP synthesis and thus speed the exhaustion of energy in muscle tissues

13. Thyroid Hormones Thyroxine normal serum range is 5-12 mcg/dL
Triiodothyronine
normal serum range is ng/dL

14. Laboratory Testing of Thyroid Hormone
Five General Categories
Direct tests of thyroid function
Tests relating to the concentration and binding of thyroid hormones in blood
Metabolic indexes
Tests of homeostatic control of thyroid function
Miscellaneous tests

15. (1) Direct Tests In-vivo administration of radioactive iodine
Thyroid Radioactive Iodine Uptake (RAIU) is the most common
RAIU is measured 24 hours after administration of isotope
Normal is 10-30% of administered dose after 24 hours
Values above normal indicate thyroid hyperfunction

16. (2) Tests Related to Hormone Concentration and Binding
Are radioimmunoassays
Highly specific and sensitive radioimmunoassays to measure serum T3 and T4
Highly sensitive TSH assay is the most sensitive of thyroid function

17. (3) Metabolic Indexes
Although measurement of the metabolic impact of thyroid hormones have value in the investigative setting, none is sufficiently sensitive, specific, and easily performed for routine use
Measurements of oxygen consumption in the BMR were once a mainstay in the diagnosis of thyroid disease, but not today

18. (4) Tests of Homeostatic Control
Basal serum TSH concentration
Thyrotropin-releasing hormone
Thyroid suppression test

19. (5) Miscellaneous Tests
These do not assess thyroid function but are if value in defining the nature of the thyroid disorder or in planning therapy
Example: some patients with autoimmune thyroid disease develop circulating antibodies against T3 and T4 resulting in sporadic highs and lows in the concentration of the hormones

20. Hyperthyroidism
Clinical symptoms include: nervousness, palpitations, intolerance to heat, weight loss, muscle weakness, and fatigue
Physical exam: smooth, moist skin,exopthalmus, presence of goiter, tachycardia, and hyperactive tendon reflex. Skin temperature is elevated, and there is fine tremor of the extended hands or a course tremor and jerking of trunk.

21. Hyperthyroidism Long-standing thyrotoxicosis
Mild anemia and lymphocytosis are common
Approximately 20% will have reduction in total WBC count

22. Hyperthyroidism
Affects approximately 2% of women and 0.2% of men

23. Causes of Hyperthyroidism
Graves’ disease (diffuse goiter and opthalmopathy) is the most common
Graves’ disease typically occurs in women 20 to 40 years of age
An autoimmune pathogenesis for Graves’ disease is suggested by presence of immunoglobulin G autoantiobodies

24. Causes of Hyperthyroidism
Iatrogenic…second most common cause. May result from administration of T3/T4
Toxic nodular goiter …nodules functioning independently of normal feedback regulation
Thyroiditis …inflammation-induced release of thyroid hormones

25. Treatment of Hyperthyroidism
Antithyroid Drugs
Usual initial medical management
Propylthiouracil,carbimazole, methimazole
These drugs inhibit synthesis of inorganic iodide and coupling of iodothyronines
Graves’ disease often initially treated with antithyroid drugs in hope of inducing a remission or achieving euthyroidism before surgery

26. Treatment of Hyperthyroidism
Pregnant females should be treated with propylthiouracil (of antithyroid drugs it crosses placenta least), minimizing the risk of goiter any hypothyroidism in fetus
Serious side effects of antithyroid drugs include agranulocytosis
Intraoperative bleeding, from drug-induced thrombocytopenia or hypoprothrombinemia has been reported in patients on propylthiouracil
Hypothyroidism is a risk of antithyroid drugs so patient may receive supplemental T4

27. Treatment of Hyperthyroidism
Beta-Adrenergic Antagonists
useful adjunctive therapies for patients with Graves’ disease diminish some of the S/S (tachycardia, anxiety, tremor) more rapidly than can antithyroid drugs
Nadolol and atenolol have a longer duration than propranolol
These drugs do not block the synthesis and secretion of thyroid hormones

28. Treatment of Hyperthyroidism
Inorganic Iodine
Iodine in pharmacologic doses (Lugol’s solution, 5% iodine, 10% potassium iodide in water) inhibits the release of T3 and T4 for a limited time (days to weeks) after which its antithyroid activity is lost
Inorganic iodine is principally used to prepare pts. for surgery and treat thyrotoxic crisis

29. Treatment of Hyperthyroidism
Radioiodine Therapy
Often selected as tx of choice for hyperthyroidism that recurs following therapy with antithyroid drugs
Objective is to destroy sufficient thyroid tissue to cure hyperthyroidism
Permanent hypothyroidism is the only important complication of this therapy
Pregnancy is an absolute contraindication as it may cause ablation of the fetal thyroid gland

30. Treatment of Hyperthyroidism
Subtotal Thyroidectomy
Used to treat Graves’ disease when radioiodine is refused, or for rare pts. With large goiters causing tracheal compression or cosmetic concerns
If elective, pt. needs to be rendered euthyroid with drugs
In emergency, pts. can be prepared for surgery in less than 1 hour by IV administration of esmolol

31. Treatments to Render Hyperthyroid Pts. Euthyroid Prior to Surgery
Emergency Surgery
Esmolol mcg/kg/min IV until heart rate <100/min
Elective Surgery
Oral administration of Beta-adrenergic antagonist (propranolol, nadolol, atenolol) until heart rate <100/min
Antithyroid drugs
Antithyroid drugs plus potassium iodide
Potassium iodide plus Beta-adrenergic antagonist

32. Subtotal Thyroidectomy
Some uncommon complications include damage to recurrent laryngeal nerves, postop bleeding into the neck with resultant tracheal compression, and hypoparathyroidism
Most common nerve injury is damage to abductor fibers of recurrent laryngeal
This injury when unilateral…hoarseness, and paralyzed vocal cord assuming an intermediate position

33. Subtotal Thyroidectomy
Bilateral recurrent nerve injury results in aphonia and paralyzed vocal cords
The cords can collapse together, producing total airway obstruction during inspiration
Selective injury of adductor fibers of recurrent laryngeal nerves leaves the adductor fibers unopposed and pulmonary aspiration a hazard

34. Subtotal Thyroidectomy
Airway obstruction that occurs soon after tracheal extubation, despite normal vocal cord function, suggests tracheomalacia
This reflects a weakening of tracheal rings by chronic pressure of a goiter
Airway obstruction postop (PACU) may be due to tracheal compression by a hematoma

35. Subtotal Thyroidectomy
Hypoparathyroidism resulting from accidental removal of parathyroid gland rarely occurs after subtotal thyroidectomy
If damage to parathyroids does occur, hypocalcemia typically develops 24 to 72 hours postop, but may manifest as early as 1-3 hours postop
Laryngeal muscles sensitive to hypocalcemia…may go from inspiratory stridor progressing to laryngospasm. Prompt IV calcium till laryngeal stridor ceases is tx.

36. Subtotal Thyroidectomy

37. Thyroid Storm (Thyrotoxic Crisis)
Medical Emergency characterized by abrupt appearance of clinical signs of hyperthyroidism (tachycardia, hyperthermia, agitation, skeletal muscle weakness, CHF, dehydration, shock) due to the abrupt release of T4 and T3 into the circulation
Can occur intraop but is more likely to occur hours postoperative

38. Thyroid Storm (Thyrotoxic Crisis)
When thyroid storm occurs intraop it may mimic malignant hyperthermia
Treatment includes cooled crytalloids and continuous IV infusion of esmolol to maintain heart rate at acceptable level (usually < 100/min)
When hypotension is persistent, the administration of cortisol, mg IV may be a consideration

39. Thyroid Storm (Thyrotoxic Crisis)
Propylthiouracil is given in dose of 100mg every 6 hours po or by NG tube to take advantage of the drug’s ability to inhibit extrathyroidal conversion of T4 to T3
Potassium Iodide is also administered to block the release of T4 to T3
Also important to treat any suspected infection in these patients

40. Management of Anesthesia
Elective surgery should be deferred until the patient has been rendered euthyroid and the hyperdynamic cardiovascular system has been controlled with Beta adrenergic antagonists, as evidenced by an acceptable heart rate

41. Management of Anesthesia
When surgery cannot be delayed in symptomatic hyperthyroid patients, the continuous infusion of Esmolol, 100 to 300 mcg/kg/min IV may be useful for controlling cardiovascular responses evoked by the sympathetic nervous system

42. Management of Anesthesia
Preoperative Medication:
(a) benzodiazepines
(b) use of anticholinergics not recommended as these drugs could interfere with the body’s own heat-regulating mechanisms and contribute to an increased heart rate

43. Management of Anesthesia
Preoperative:
Evaluation of the upper airway for evidence of obstruction (goiter compressing on trachea) is extremely important
Be prepared and have available in the O.R. needed equipment for a difficult airway and difficult intubation

44. Management of Anesthesia
Induction:
Propoful/Pentothal for induction
Ketamine is not a likely selection as it can stimulate the sympathetic nervous system leading to a tachycardia
Succinylcholine or non-depolarizers that do not affect the cardiovascular system for intubation (would avoid pancuronium)

45. Maintenance of Anesthesia
Goals in maintenance of anesthesia in patients with hyperthyroidism are:
Avoid administration of drugs that stimulate that stimulate the sympathetic nervous system
Provide sufficient anesthetic-induced sympathetic nervous system depression to prevent exaggerated responses to surgical stimulation

46. Maintenance of Anesthesia
Volatile anesthetics:
isoflurane, desflurane, sevoflurane, are good as they offset adverse sympathetic nervous system responses to surgical stimulation, but do not sensitize the heart to catecholamines
Remember sevoflurane and potential concern with nephrotoxicity caused by an increased production of fluoride owing to accelerated metabolism of this anesthetic

47. Maintenance of Anesthesia
Monitor and keep track of patient’s body temperature (keep in mind thyroid storm)
Vigilant monitoring of vital signs
Pts. With exopthalmos prone to corneal ulcerations
For antagonism of neuromuscular blockade with anticholinergics, it is best to avoid atropine and use glycopyrrolate as it has fewer chronotropic effects

48. Maintenance of Anesthesia
Treatment of Hypotension:
When using sympathomimetic drugs must consider the possibility of exaggerated responsiveness of hyperthyroid pts. to endogenous or exogenous catecholamines
Therefore, decreased doses of direct-acting vasopressors such as phenylephrine may be a better choice than ephedrine, which acts in part by provoking the release of catecholamines

49. Regional Anesthesia for Hyperthyroid Patients
Causes a sympathetic nervous system blockade
May be a useful choice in hyperthyroid patients, assuming there is no evidence of high-output congestive heart failure
Continuous epidural may be preferable to spinal because of the slower onset of sympathetic nervous system blockade

50. Regional Anesthesia for Hyperthyroid Patients
If hypotension occurs, decreased doses of phenylephrine are recommended
Epinephrine should not be added to local anesthetics, as systemic absorption of this catecholamine could produce exaggerated circulatory responses

51. Hypothyroidism Decreased circulating concentration of T3 and T4
Present in 0.5% to 0.8% of adults
Diagnosis based on clinical S/S plus confirmation of decreased thyroid gland function as demonstrated by appropriate tests

52. Hypothyroidism
Causes: The etiology of hypothyroidism is categorized as…
Primary…destruction of the thyroid gland
Secondary…central nervous system dysfunction
Chronic thyroiditis (Hashimoto’s thyroiditis) is the most common cause

53. Etiology of Hypothyroidism
Primary Hypothyroidism
Thyroid Gland Dysfunction
Hashimoto’s thyroiditis
Previous subtotal thyroidectomy
Previous radioiodine therapy
Irradiation of the neck

54. Etiology of Hypothyroidism
Primary hypothyroidism
Thyroid hormone deficiency
Antithyroid drugs
Excess iodide (inhibits release)
Dietary iodine deficiency

55. Etiology of Hypothyroidism
Secondary hypothyroidism
Hypothalamic dysfunction
Thyrotropin-releasing hormone
deficiency
Anterior pituitary dysfunction
Thyrotropin hormone deficiency

56. Hypothyroidism Signs and Symptoms -Decreased metabolic activity
-Lethargy is prominent
-Intolerance to cold
-Cardiovascular changes are often the earliest clinical manifestations
-bradycardia
-decreased stroke volume and contractility
-decreased cardiac output

57. Hypothyroidism -increased SVR
-systemic hypertension, especially diastolic hypertension occurs in about 15% of hypothyroid patients
-narrow pulse pressure
-increased circulating concentrations of catecholamines
-overt CHF is unlikely, but if present may indicate co-existing heart disease

58. Hypothyroidism
Patients with hypothyroidism are predisposed to pericardial effusions
The EKG may reveal low voltage, prolonged PR, QRS, and QT intervals due to pericardial effusion
Conduction abnormalities may predispose patients to ventricular tachycardia, especially torsades de pointes

59. Hypothyroidism
Thyroid hormone is necessary for normal production of pulmonary surfactant
Chronic hypothyroidism is associated with pleural effusions
Ventilatory drive to hypoxia and hypercapnia is decreased in patients with severe hypothyroidism
BMR can be decreased up to 50% due to the hypothermia that occurs

60. Hypothyroidism
Peripheral vasoconstriction characterized by cool, dry skin
There is often atrophy of the adrenal cortex and associated decreases in the production of cortisol
Inappropriate secretion of ADH can result in hyponatremia owing to the impaired ability of renal tubules to excrete free water

61. Hypothyroidism Treatment -Oral administration of T4
-Pts. With ischemic heart disease and hypothyroidism may not tolerate even modest amounts of T4 without developing angina
-If angina appears or worsens during T4 therapy, coronary angiography and CABG may be necessary before adequate T4 therapy can be achieved

62. Myxedema Coma Rare complication of hypothyroidism
Manifests as loss of deep tendon reflexes, spontaneous hypothermia, hypoventilation, cardiovascular collapse, coma, and death
Sepsis in elderly or exposure to cold may be an initiating event

63. Myxedema Coma
Treatment is with IV administration of T3, which exerts a physiologic effect within 6 hours
Digitalis, as used to treat CHF, is used sparingly because the hypothyroid patient’s heart cannot easily perform increased myocardial contractile work
Fluid therapy is important, but remember these patients may be vulnerable to water intoxication and hyponatremia

64. Hypothyroidism Management of Anesthesia
-Elective surgery should be deferred if symptomatic
-T4 drug has long half-life (7 days) and administration of it on day of surgery is optional
-T3 drug has shorter half-life (1.5 days) so it may be prudent to have pt. take it on day of surgery

65. Hypothyroidism
-Opioid premedication may be exaggerated in the hypothyroid patient
-Supplemental cortisol may be considered if there is concern that surgical stress could unmask decreased adrenal function that may accompany hypothyroidism

66. Maintenance of Anesthesia
Induction with pentothal, ketamine, or propoful
Tracheal intubation with succinylcholine, or NDMR, but keep in mind that co-existing skeletal muscle weakness could be associated with an exaggerated drug effect

67. Maintenance of Anesthesia
Often achieved with nitrous oxide + short-acting opioids, benzodiazepines, or ketamine
Volatile anesthetics may not be recommended in overtly symptomatic hypothyroid pts. for fear of inducing exaggerated cardiac depression

68. Maintenance of Anesthesia
Vasodilation produced by anesthetic drugs in the presence of hypovolemia could result in abrupt decrease in systemic blood pressure
Pancuronium, because of its mild cardiovascular stimulating effects, may be selected for skeletal muscle paralysis
Intermediate and short-acting NDMRs are good as they are less likely to produce a prolonged neuromuscular blockade

69. Maintenance of Anesthesia
Monitoring hypothyroid pts. during anesthesia is intended to facilitate prompt recognition of exaggerated cardiovascular depression, and detection of onset of hypothermia
Consider arterial line for long surgical procedures, or those associated with significant blood loss

70. Maintenance of Anesthesia
IV fluids used should contain sodium to decrease likelihood of hyponatremia
To treat hypotension it is best to use small increments of ephedrine 2.5 to 5.0 mg IV
Phenylephrine could adversely increase SVR in the presence of a heart that cannot reliably increase its contractility

71. Maintenance of Anesthesia
Suspect acute adrenal insufficiency when hypotension persists despite treatment with fluids and/or sympathomimetic drugs
Maintain patient’s body temperature with use of a warming blanket or convection system, and warming of IV fluids

72. Perioperative Period Possibilities
Increased sensitivity to depressant drugs
Hypodynamic cardiovascular system responses…decreased heart rate, decreased cardiac output
Slow metabolism of drugs
Hypovolemia
Delayed gastric emptying
Hyponatremia

73. Perioperative Period Possibilities
Impaired ventilatory responses to arterial hypoxemia or hypercarbia
Hypothermia
Hypoglycemia
Adrenal insufficiency

74. Postoperative Management
Recovery from sedative effects of anesthetic drugs may be delayed
Tracheal extubation should be delayed until the hypothyroid patient responds appropriately and their body temperature is near 37 degrees C
Due to increased sensitivity to opioids, may want to consider nonopioid analgesic

75. Extreme Goiter

76. Goiter

77. Shift of Trachea from Enlarged Right Lobe of Thyroid Gland