Thyroid Gland and Anesthetic Management

7/28/2019 Thyroid Gland and Anesthetic Management

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Thyroid Gland and Anesthetic

Management

Daniel Stairs CRNA, MSN, MBA

Excela Health School of Anesthesia


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Thyroid Gland is H-shaped

Right and left lobe with isthmus


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Location of Thyroid Gland

Anterior to trachea

Just below cricoid cartilage

Covering second through fourth trachealrings

Thyroid gland weighs about 20 gm


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Blood Supply to Thyroid Gland

4 to 6 cc/min/gm

Arterial supplyvia inferior and superior

arteries

Venous supplyvia inferior, middle, and

superior thyroid veins


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Nerve Supply

Two superior laryngeal nervesand two recurrent laryngeal

nervessupply the entiresensory and motor innervations

to the larynx.


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Innervation


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Recurrent Laryngeal Nerve

Most common nerve injured inthroidectomy

Motor supply

Sensation below vocal cords

With selective injury to abductor fibers:

(1) hoarseness

(2) bilateral injury

(3) obstruction


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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


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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


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Essential Thyroid Hormones

Thyroxine orT4

Triiodothyronine orT3

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 byits transient nature


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Thyroid Hormones

Nearly all circulating T3 is derived fromperipheral conversion of T4

Major Functions of Thyroid

Hormones:(1) calorigenic effects

(2) growth and cellular differentiation

(3) metabolic effects(4) muscular effects


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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


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Thyroid Hormones

Thyroxine

normal serum range is 5-12 mcg/dL

Triiodothyroninenormal serum range is 70-90 ng/dL


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Laboratory Testing of Thyroid

Hormone

Five General Categories

(1) Direct tests of thyroid function

(2) Tests relating to the concentration andbinding of thyroid hormones in blood

(3) Metabolic indexes

(4) Tests of homeostatic control of thyroid

function(5) Miscellaneous tests


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(1) Direct Tests

In-vivo administration of radioactive iodine

Thyroid Radioactive Iodine Uptake (RAIU) isthe most common

RAIU is measured 24 hours afteradministration of isotope

Normal is 10-30% of administered dose after

24 hours Values above normal indicate thyroid

hyperfunction


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(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


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(3) Metabolic Indexes

Although measurement of the metabolicimpact of thyroid hormones have value inthe investigative setting, none is

sufficiently sensitive, specific, and easilyperformed for routine use

Measurements of oxygen consumption inthe BMR were once a mainstay in thediagnosis of thyroid disease, but nottoday


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(4) Tests of Homeostatic Control

Basal serum TSH concentration

Thyrotropin-releasing hormone

Thyroid suppression test


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(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 inthe concentration of the hormones


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Hyperthyroidism

Clinical symptomsinclude: nervousness,

palpitations, intolerance to heat, weight loss,

muscle weakness, and fatigue

Physical exam: smooth, moistskin,exopthalmus, presence of goiter,

tachycardia, and hyperactive tendon reflex.

Skin temperature is elevated, and there is fine

tremor of the extended hands or a coursetremor and jerking of trunk.


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Hyperthyroidism

Long-standing thyrotoxicosis

Mild anemia and lymphocytosis are

common

Approximately 20% will have reduction in

total WBC count


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Hyperthyroidism

Affects approximately 2% of women and

0.2% of men


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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


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Causes of Hyperthyroidism

Iatrogenicsecond most common

cause. May result from administration of

T3/T4

Toxic nodular goiternodules

functioning independently of normal

feedback regulation

Thyroiditisinflammation-induced

release of thyroid hormones


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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 aremission or achieving euthyroidism before

surgery


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Pregnant females should be treated withpropylthiouracil(of antithyroid drugs it crossesplacenta least), minimizing the risk of goiterany hypothyroidism in fetus

Serious side effects of antithyroid drugsinclude agranulocytosis

Intraoperative bleeding, from drug-inducedthrombocytopenia or hypoprothrombinemia

has been reported in patients onpropylthiouracil

Hypothyroidism is a risk of antithyroid drugs sopatient may receive supplemental T4


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Beta-Adrenergic Antagonists

useful adjunctive therapies for patientswith Graves disease diminish some of

the S/S (tachycardia, anxiety, tremor)more rapidly than can antithyroid drugs

Nadololand atenololhave a longer

duration than propranolol These drugs do not block the synthesis

and secretion of thyroid hormones


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Inorganic Iodine

Iodine in pharmacologic doses (Lugolssolution, 5% iodine, 10% potassium

iodide in water) inhibits the release of T3and T4 for a limited time (days to weeks)after which its antithyroid activity is lost

Inorganic iodine is principally used toprepare pts. for surgery and treatthyrotoxic crisis


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Radioiodine Therapy

Often selected as tx of choice forhyperthyroidism that recurs following therapywith antithyroid drugs

Objective is to destroy sufficient thyroid tissueto 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


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Subtotal Thyroidectomy

Used to treat Graves disease whenradioiodine is refused, or for rare pts. Withlarge goiters causing tracheal compression orcosmetic concerns

If elective, pt. needs to be rendered euthyroidwith drugs

In emergency, pts. can be prepared forsurgery in less than 1 hour by IVadministration of esmolol

T t t t R d H th id


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Treatments to Render Hyperthyroid

Pts. Euthyroid Prior to Surgery

Emergency SurgeryEsmolol 100-300 mcg/kg/min IV until heart rate


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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 unilateralhoarseness, and

paralyzed vocal cord assuming an

intermediate position


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Bilateral recurrent nerve injury results inaphonia and paralyzed vocal cords

The cords can collapse together,

producing total airway obstruction duringinspiration

Selective injury of adductor fibers of

recurrent laryngeal nerves leaves theadductor fibers unopposed andpulmonary aspiration a hazard


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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 ahematoma


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Hypoparathyroidism resulting from accidentalremoval of parathyroid gland rarely occursafter subtotal thyroidectomy

If damage to parathyroids does occur,hypocalcemia typically develops 24 to 72hours postop, but may manifest as early as 1-3 hours postop

Laryngeal muscles sensitive tohypocalcemiamay go from inspiratory stridorprogressing to laryngospasm. Prompt IVcalcium till laryngeal stridor ceases is tx.


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Thyroid Storm (Thyrotoxic Crisis)

Medical Emergencycharacterized by

abrupt appearance of clinical signs of

hyperthyroidism (tachycardia,

hyperthermia, agitation, skeletal muscleweakness, CHF, dehydration, shock)

due to the abrupt release of T4 and T3

into the circulation Can occur intraop but is more likely to

occur 16-18 hours postoperative


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When thyroid storm occurs intraop it maymimic malignant hyperthermia

Treatment includes cooled crytalloids

and continuous IV infusion of esmolol tomaintain heart rate at acceptable level(usually < 100/min)

When hypotension is persistent, theadministration of cortisol, 100-200 mg IVmay be a consideration


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Propylthiouracilis given in dose of100mg every 6 hours po or by NG tubeto take advantage of the drugs ability to

inhibit extrathyroidal conversion of T4 toT3

Potassium Iodide is also administered toblock the release of T4 to T3

Also important to treat any suspectedinfection in these patients


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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 anacceptable heart rate


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When surgery cannot be delayed in

symptomatic hyperthyroid patients,

the continuous infusion ofEsmolol,

100 to 300 mcg/kg/min IVmay be

useful for controlling cardiovascular

responses evoked by thesympathetic nervous system


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Preoperative Medication:

(a) benzodiazepines

(b) use of anticholinergics notrecommended as these drugs could

interfere with the bodys own heat-

regulating mechanisms and contribute to

an increased heart rate


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Preoperative:

Evaluation of the upper airway forevidence of obstruction (goiter

compressing on trachea) is extremelyimportant

Be prepared and have available in the

O.R. needed equipment for a difficultairway and difficult intubation


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Induction:

Propoful/Pentothal for induction

Ketamine is nota likely selection as it canstimulate the sympathetic nervous

system leading to a tachycardia

Succinylcholine or non-depolarizers that

do not affect the cardiovascular system

for intubation (would avoid pancuronium)


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Maintenance of Anesthesia

Goals in maintenance of anesthesiain patients with hyperthyroidism are:

(a) Avoid administration of drugs that

stimulate that stimulate the sympatheticnervous system

(b) Provide sufficient anesthetic-induced

sympathetic nervous systemdepression to prevent exaggeratedresponses to surgical stimulation


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Volatile anesthetics:

(a) isoflurane, desflurane, sevoflurane, are good

as they offset adverse sympathetic nervous

system responses to surgical stimulation, butdo notsensitize the heart to catecholamines

(b) Remember sevoflurane and potential

concern with nephrotoxicity caused by an

increased production of fluoride owing toaccelerated metabolism of this anesthetic


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Monitor and keep track of patients bodytemperature (keep in mind thyroid storm)

Vigilant monitoring of vital signs

Pts. With exopthalmos prone to cornealulcerations

For antagonism of neuromuscular

blockade with anticholinergics, it is bestto avoid atropine and use glycopyrrolateas it has fewer chronotropic effects


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Treatment of Hypotension:

(a) When using sympathomimetic drugs must

consider the possibility of exaggerated

responsiveness of hyperthyroid pts. toendogenous or exogenous catecholamines

(b) Therefore, decreased doses of direct-acting

vasopressors such asphenylephrine may be

a better choice than ephedrine, which acts in

part by provoking the release of

catecholamines

Regional Anesthesia for


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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 ofsympathetic nervous system blockade



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Hyperthyroid Patients

If hypotension occurs, decreased

doses ofphenylephrine are

recommended

Epinephrine should not be added

to local anesthetics, as systemic

absorption of this catecholaminecould produce exaggerated

circulatory responses


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Hypothyroidism

Decreased circulating concentrationof 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


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Hypothyroidism

Causes: The etiology of

hypothyroidism is categorized as

(a) Primarydestruction of the thyroid

gland

(b) Secondarycentral nervous system

dysfunction

Chronic thyroiditis (Hashimotos thyroiditis)

is the most common cause


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Etiology of Hypothyroidism

Primary HypothyroidismThyroid Gland Dysfunction

Hashimotos thyroiditisPrevious subtotal thyroidectomy

Previous radioiodine therapy

Irradiation of the neck


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Primary hypothyroidism

Thyroid hormone deficiency

Antithyroid drugsExcess iodide (inhibits release)

Dietary iodine deficiency


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Secondary hypothyroidism

Hypothalamic dysfunction

Thyrotropin-releasing hormonedeficiency

Anterior pituitary dysfunction

Thyrotropin hormone deficiency


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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


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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


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Hypothyroidism

Patients with hypothyroidism arepredisposed to pericardial effusions

The EKG may reveal low voltage,

prolonged PR, QRS, and QT intervalsdue to pericardial effusion

Conduction abnormalities maypredispose patients to ventriculartachycardia, especially torsades depointes


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Hypothyroidism

Thyroid hormone is necessary for normalproduction of pulmonary surfactant

Chronic hypothyroidism is associated

with pleural effusions Ventilatory drive to hypoxia and

hypercapnia is decreased in patientswith severe hypothyroidism

BMR can be decreased up to 50% dueto the hypothermia that occurs


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Hypothyroidism

Peripheral vasoconstrictioncharacterized by cool, dry skin

There is often atrophy of the adrenal

cortex and associated decreases in theproduction of cortisol

Inappropriate secretion of ADH canresult in hyponatremia owing to theimpaired ability of renal tubules toexcrete free water

H h idi


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Hypothyroidism

Treatment-Oral administration of T4

-Pts. With ischemic heart disease and

hypothyroidism may not tolerate even modestamounts of T4 without developing angina

-If angina appears or worsens during T4

therapy, coronary angiography and CABGmay be necessary before adequate T4 therapy

can be achieved

M d C


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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

M d C


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Myxedema Coma

Treatment is with IV administration of T3,which exerts a physiologic effect within 6hours

Digitalis, as used to treat CHF, is usedsparingly because the hypothyroidpatients heart cannot easily performincreased myocardial contractile work

Fluid therapy is important, but rememberthese patients may be vulnerable towater intoxication and hyponatremia

H th idi


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Hypothyroidism


-Elective surgery should be deferred ifsymptomatic

-T4 drug has long half-life (7 days) andadministration of it on day of surgery isoptional

-T3 drug has shorter half-life (1.5 days) soit may be prudent to have pt. take it onday of surgery

H th idi


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Hypothyroidism

-Opioid premedication may be

exaggerated in the hypothyroid patient

-Supplemental cortisol may be considered

if there is concern that surgical stresscould unmask decreased adrenal

function that may accompany

hypothyroidism

M i t f A th i


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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

M i t f A th i


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Often achieved with nitrous oxide +

short-acting opioids, benzodiazepines, or

ketamine

Volatile anesthetics may not berecommended in overtly symptomatic

hypothyroid pts. for fear of inducing

exaggerated cardiac depression

M i t f A th i


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Vasodilation produced by anesthetic drugs in

the presence of hypovolemia could result in

abrupt decrease in systemic blood pressure

Pancuronium, because of its mildcardiovascular stimulating effects, may be

selected for skeletal muscle paralysis

Intermediate and short-acting NDMRs are

good as they are less likely to produce aprolonged neuromuscular blockade

M i t f A th i


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Monitoring hypothyroid pts. during

anesthesia is intended to facilitate

prompt recognition of exaggerated

cardiovascular depression, and detectionof onset of hypothermia

Consider arterial line for long surgical

procedures, or those associated withsignificant blood loss

M i t f A th i


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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 5.0mg IV

Phenylephrine could adversely increase

SVR in the presence of a heart thatcannot reliably increase its contractility

M i t f A th i


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Suspect acute adrenal insufficiency

when hypotension persists despite

treatment with fluids and/or

sympathomimetic drugs Maintain patients body temperature with

use of a warming blanket or convection

system, and warming of IV fluids

P i ti P i d P ibiliti


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Perioperative Period Possibilities

Increased sensitivity to depressant drugs

Hypodynamic cardiovascular systemresponsesdecreased heart rate,

decreased cardiac output Slow metabolism of drugs

Hypovolemia

Delayed gastric emptying Hyponatremia



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Impaired ventilatory responses to arterial

hypoxemia or hypercarbia

Hypothermia

Hypoglycemia

Adrenal insufficiency

Postoperative Management


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Postoperative Management

Recovery from sedative effects ofanesthetic drugs may be delayed

Tracheal extubation should be delayed

until the hypothyroid patient respondsappropriately and their body temperatureis near 37 degrees C

Due to increased sensitivity to opioids,may want to consider nonopioidanalgesic

Extreme Goiter


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Extreme Goiter

Goiter


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Goiter

Shift of Trachea from Enlarged Right


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g g

Lobe of Thyroid Gland

Thyroid Gland and Anesthetic Management

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