Transcript Thyroid Gland and Anesthetic Management

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 tracheal
rings
 Thyroid gland weighs about 20 gm
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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
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Nerve Supply
 Two
superior laryngeal nerves
and two recurrent laryngeal
nerves supply the entire
sensory and motor innervations
to the larynx.
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Innervation
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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
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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
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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
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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
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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
 Triiodothyronine
normal serum range is 70-90 ng/dL
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Laboratory Testing of Thyroid
Hormone
(1)
(2)
(3)
(4)
(5)
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
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(1) Direct Tests
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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
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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 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
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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 in
the concentration of the hormones
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Hyperthyroidism
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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.
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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
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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
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
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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 a
remission or achieving euthyroidism before
surgery
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Treatment of Hyperthyroidism
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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
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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
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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
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Treatment of Hyperthyroidism
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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
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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
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Treatments to Render Hyperthyroid
Pts. Euthyroid Prior to Surgery
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Emergency Surgery
Esmolol 100-300 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
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Subtotal Thyroidectomy
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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 unilateral…hoarseness, and
paralyzed vocal cord assuming an
intermediate position
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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
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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
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Subtotal Thyroidectomy
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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 13 hours postop
 Laryngeal muscles sensitive to
hypocalcemia…may go from inspiratory stridor
progressing to laryngospasm. Prompt IV
calcium till laryngeal stridor ceases is tx.
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Subtotal Thyroidectomy
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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 16-18 hours postoperative
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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, 100-200 mg IV
may be a consideration
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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
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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 an
acceptable heart rate
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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
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Management of Anesthesia
Preoperative Medication:
(a) benzodiazepines
(b) use of anticholinergics not
recommended as these drugs could
interfere with the body’s own heatregulating mechanisms and contribute to
an increased heart rate
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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
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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)
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Maintenance of Anesthesia
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(a)
(b)
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
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Maintenance of Anesthesia
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Volatile anesthetics:
(a) isoflurane, desflurane, sevoflurane, are good
as they offset adverse sympathetic nervous
system responses to surgical stimulation, but
do not sensitize the heart to catecholamines
(b) Remember sevoflurane and potential
concern with nephrotoxicity caused by an
increased production of fluoride owing to
accelerated metabolism of this anesthetic
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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
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Maintenance of Anesthesia
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Treatment of Hypotension:
When using sympathomimetic drugs must
consider the possibility of exaggerated
responsiveness of hyperthyroid pts. to
endogenous or exogenous catecholamines
(b) 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
(a)
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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
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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
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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
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Hypothyroidism
Causes: The etiology of
hypothyroidism is categorized as…
(a) Primary…destruction of the thyroid
gland
(b) Secondary…central nervous system
dysfunction
Chronic thyroiditis (Hashimoto’s thyroiditis)
is the most common cause
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Etiology of Hypothyroidism
 Primary Hypothyroidism
Thyroid Gland Dysfunction
Hashimoto’s thyroiditis
Previous subtotal thyroidectomy
Previous radioiodine therapy
Irradiation of the neck
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Etiology of Hypothyroidism
 Primary hypothyroidism
Thyroid hormone deficiency
Antithyroid drugs
Excess iodide (inhibits release)
Dietary iodine deficiency
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Etiology of Hypothyroidism
 Secondary hypothyroidism
Hypothalamic dysfunction
Thyrotropin-releasing hormone
deficiency
Anterior pituitary dysfunction
Thyrotropin hormone deficiency
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Hypothyroidism
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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 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
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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
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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
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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
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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
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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
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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
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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 stress
could unmask decreased adrenal
function that may accompany
hypothyroidism
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Maintenance of Anesthesia
Induction with pentothal, ketamine, or
propoful
 Tracheal intubation with succinylcholine,
or NDMR, but keep in mind that coexisting skeletal muscle weakness could
be associated with an exaggerated drug
effect
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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
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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
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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
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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
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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
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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
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Perioperative Period Possibilities
Impaired ventilatory responses to arterial
hypoxemia or hypercarbia
 Hypothermia
 Hypoglycemia
 Adrenal insufficiency
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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
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Extreme Goiter
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Goiter
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Shift of Trachea from Enlarged Right
Lobe of Thyroid Gland
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