The document discusses thyroid disorders including hyperthyroidism, hypothyroidism, and thyroid storm and their implications for anesthesia such as increased sensitivity to drugs, risks of tachycardia and arrhythmias, and need for careful monitoring of cardiac and respiratory function. It provides guidance on preoperative preparation, intraoperative management, and postoperative care for patients with thyroid disorders undergoing surgery.

1. THYROID DISORDERS AND ANAESTHESIA
PRESENTOR :DR. RAJESH CHOUDHURI
MODERATOR: DR. C.R. MONDAL, PROF. & HOD
PGT, DEPARTMENT OF ANAESTHESIOLOGY
AGMC & GBP HOSPITAL, AGARTALA

2. THYROID GLAND
• Thyroid Gland is H-shaped ,Right and left lobe with isthmus.
• Location ofThyroid Gland: Anterior to trachea.
Just below cricoid cartilage.
Covering second through fourth tracheal rings
Thyroid gland weighs about 20 gm.
• Blood Supply toThyroid Gland: 4 to 6 cc/min/gm.
Arterial supply via inferior and superior arteries.
Venous supply via inferior, middle, and superior thyroid veins.
• Nerve Supply: Two superior laryngeal nerves and two recurrent laryngeal
nerves supply the entire sensory and motor innervations to the larynx.
•

3. THYROID GLAND
• Histological structure:
• composed of numerous follicles filled
proteinaceous colloid.
Also contains parafollicular C cells, which
produce calcitonin.
•
• Regulation of thyroid secretion

4. THYROID HORMONE SYNTHESIS

5. THYROID HORMONE: PHYSIOLOGY
-T4/T3 ratio in blood is 10:1. -
-In blood,T4 andT3 bind reversibly to three major proteins:TBG (80%),
prealbumin(10%) and albumin ( 5% to 10%).
-T3 is 3-4 times more active thanT4.
SITE OF ACTION: Cell nucleus → stimulates m RNA synthesis → controles protein synthesis.
Mitochondria→ oxidative phosphorylation and ATP formation.
Plasma membrane→influences transcellular flux of substrate and cations.
FUNCTIONS: 1. stimulates all metabolic processes.
2. influences growth and maturation of tissues, enhance tissue function.
3. stimulates protein synthesis ; carbohydrate and lipid metabolism.
4. Cardiac: acts directly on cardiac myocytes and vascular smooth muscle
cells. Increases myocardial contractility, decreases SVR, increases intravascular volume,
increases number of beta adrenergic rceptor.
5. CNS: effect on neuronal function and reflexes. Reaction time of stretch
reflex is shortened in hyperthyroidism. Also affects RAS.

6. SICK EUTHYROID SYNDROME
 Abnormal thyroid function tests that occur in the setting of acute and severe
nonthyroidal illness without pre-existing hypothalamic-pituitary and thyroid gland
dysfunction.
 Most common findings are a lowT3,T4 andTSH.
 Reversible after recovery from the illness.
 Partly caused by cytokines or other inflammatory mediators acting at the
hypothalamus, pituitary, thyoid gland and hepatic deiodinase system.
 Degree of abnormality correlates with the disease severity.
 Administration of thyroid hormones in this situation is controversial and has not been
shown to improve outcomes.

7. HYPERTHYROIDISM
• CAUSES: 1. Graves disease—most common cause.
2. toxic multinodular goiter.
3. TSH secreting pituitary tumor.
4. functioning thyroid adenomas.
5. overdose of thyroid replacement medications.
6. S/E of amiodarone/ irradiation thyroiditis.
• DIAGNOSIS: made by abnormal TFTs, elevated total and free T4, T3, low TSH,
raised free thyroxine index.
A TSH level of 0.1-0.4 munits/L with normal level of FT3 and FT4 is
diagnostic of subclinical hyperthyroidism.
A TSH level of less than 0.03 munits/L with elevated T3 and T4 is diagnostic
of overt hyperthyroidism.

8. HYPERTHYROIDISM
• CLINICAL MANIFESTATION:
classical symptoms: hyperactivity, weight loss and tremor.
Other symptoms: palpitation, anxiety/nervousness, diarrhea,
intolerance to heat, large muscle group weakness, menstrual abnormalities.
Signs: tachycardia ( ↑ sleeping PR), warm moist skin, irregularly
irregular pulse, fine brittle hair, ↑ CO, IHD, HF .
Eye signs: 1. Eyelid retraction.
2. Lid lag sign.
3. Joffroy sign-absence of wrinkling.
4. Mobius sign-difficulty in convergence.
5. Stellwag’s sign-absence of blinking.

9. HYPERTHYROIDISM
TREATMENT:
1. Antithyroid drugs: methimazole or proylthiouracil ( PTU)
-interfere with thyroid hormone synthesis. PTU also inhibits the peripheral
conversion ofT4 toT3.
- euthyroid state can almost always be achieved within 6-8 weeks.
- S/E: agranulocytosis, hepatotoxicity, vasculitis, teratogenicity.
2. Iodide: Inhibit hormone release. Effects occur immediately but short –lived.
Reserved for hyperthyroid patients for surgery, thyroid storm, severe
thyrocardiac disease.
Potassium iodide- 3 drops PO every 8 hrly for 10-14 days.
Lithium carbonate 300 mg PO every 6 hrly .
3. beta adrenergic antagonists: relieve signs and symptoms of increased
adrenergic activity. Propanolol has the added feature-inhibit conversion ofT4 toT3.
4. radioactive iodine and subtotal thyroidectomy: other alternative to
medical therapy.

10. HYPERTHYROIDISM: ANAESTHETIC CONSIDERATIONS
• Pre-operative consideration
Antithyroid medications and beta blockers should be continued through the morning of
surgery.
Miller: ideally patients should be rendered euthyroid prior to any elective procedure .
Begining pre-op antithyroid medication take 2-6 weeks for effect, can use KI with beta-
blockers in addition or alternatively.
Benzodiazepines are good choice for pre-medication.
Carefull evaluation of air-way.

11. HYPERTHYROIDISM: ANAESTHETIC CONSIDERATIONS
• Intra-operative considerations:
No controlled study suggest advantages of particular anaesthetic drug or technique
for hyperthyroid patients, however:
Drugs that stimulate SNS should be avoided because of the possibility of large
increase in BP and HR. Ex-ketamin, pancuronium, atropine, ephedrine.
Thiopental may be the induction agent of choice as it possesses antithyroid activity
at high doses.
Close monitoring of cardiac function and body temperature. Need for invasive
monitoring?
Adequate anaesthetic depth should be obtained prior to laryngoscopy or surgical
stimulation to avoid tachycardia, Htn., ventricular arrhythmia.

12. HYPERTHYROIDISM: ANAESTHETIC CONSIDERATIONS
• Intra-operative considerations:
Anticipate exacerbated hypotensive response during induction as patient may be
hypovolaemic.
Eye protection.
Muscle relaxants can be used safely. Note: patients with autonomic thyrotoxicosis are
associated with increased risk of myopathies and myesthenia gravis.
Reversal with glycopyrolate instead of atropine.
Hyperthyroidism doesn’t increase MAC requirements, volatile agents can be used safely.

13. HYPERTHYROIDISM: ANAESTHETIC CONSIDERATIONS
• Post-operative considerations:
 thyroid storm is the most-serious post operative problem.
Precipitating factors: trauma, infection, medical illness or surgery.
Characterized by: hyperpyrexia, tachycardia, hypermetabolism, altered conciousness and
hypertension.
Incidence is 10% in patients hospitalized for thyrotoxicosis.
Onset is 6-24 hrs after surgery, but can happen intra-operatively mimicking MH.
Thyroid hormone levels may not be significantly higher than during uncomplicated
hyperthyroidism.
Unlike MH, not associated with muscle rigidity, ↑ CPK or marked degree of lactic or
respiratory acidosis.

14. HYPERTHYROIDISM: ANAESTHETIC CONSIDERATIONS
Thyroid storm: treatment
IV hydration with glucose containing crystalloids and cooling measures.
Beta-blockers: IV propanolol ( 0.5 mg increments) , esmolol to control HR until < 90/m.
PTU 200-400 microgram every 8 hrly orally or by NG tube/rectally.
Sodium iodide 1 gm over 12 hrs.
Correction of any precipitating events ( infection).
Dexamethasone 2 mg every 6 hrly or Cortisol 100-200 mg every 8 hrly.
Mortality rate is approximately 20%.

15. ANAESTHETIC CONSIDERATIONS: SUBTOTAL THYROIDECTOMY
• Associated with several complications:
 recurrent laryngeal nerve palsy can cause hoarseness if unilateral , or stridor
if bilateral.
Vocal cord function may be evaluated by DL after deep extubation if there is
concern.
Haematoma formation may cause airway compromise . May require
immediate opening of neck wound.
Hypothyroidism may result from unintentional removal of parathyroid gland .
Hypocalcaemia will result within 24-72 hrs.
Pneumothorax-may be developed.

16. HYPOTHYROIDISM
• INCIDENCE: 0.5%TO 0.8% of adult population; ten times more common in females.
• CAUSES: - primary hypothyroidism—95% of all cases.
-autoimmunue ( Hashimoto’s thyroiditis)
-post radioactive iodine.
-post thyroidectomy.
-overdose of anti-thyroid medication.
- iodine deficiency.
-secondary hypothyroidism( failure of the hypothalamo-pituitary axis)
• DIAGNOSIS: can be confirmed by low free thyroxin levels and elevatedTSH( if free).
ATSH level of 5.0 to 10 milliunits/L with normal levels of FT3 and FT4 is
diagnostic of subclinical hypothyroidism.
ATSH level of more than 20 milliunits/L with reduced levels ofT3 andT4 is
diagnostic of overt hypothyroidism.

17. HYPOTHYROIDISM
• CLINICAL MANIFESTATIONS:
Hypothyroidism in early neonatal development may result in cretinism.
In adults, manifestation can be subtle: weight gain, cold intolerance, muscle fatigue,
lathergy ,constipation, hypoactive muscle reflexes, depression, periorbital or pre-tibial
swelling.
HR, contractility , stroke-volume and CO decreases, extremity may be cold, hair may be
coarse and brittle, large tongue.
Anaemia, hypoglycaemia, hyponatraemia, ↑ cholesterol levels.
ECG: flattened or inverted T waves, low amplitude P waves and QRS
complexes, sinus bradycardia, ventricular dysarrythmia.

18. HYPOTHYROIDISM
• TREATMENT:
• Oral replacements.
• L-thyroxine: started with 50-100 microgram ( 25 mcg in the elderly or in the
patients with IHD)
Titrated by clinical improvement and by monitoring TSH level.
T4 has a half-life of 7 days, onset of action 12 hrs and takes almost 2 weeks
for peak action.
T3 has a half-life of 1.5 days and is available in injected form.

19. HYPOTHYROIDISM: ANAESTHETIC CONSIDERATION
• PRE-OPERATIVE:
Patients with uncorrected severe hypothyroidism ( T4<1 mcg/dl) or
myxedema coma should not undergo elective surgery. Potential for severe
cardiovascular instability intra-operatively and myxedema coma.
If emergency surgery is necessary, in patients with overt ds. Or myxedema
coma , IV thyroxine and steroid coverage.
Euthyroid state is ideal, however, subclinical cases of hypothyroidism has not
been shown to significantly increase risk of surgery.
Continue thyroid replacement medication on morning of surgery.

20. HYPOTHYROIDISM: ANAESTHETIC CONSIDERATION
• PRE-OPERATIVE:
Air-way evaluation : patients tend to be obese, large tongue, short neck, swelling of
upper airway.
Pre-op sedation should be administered cautiously if at all, as patients are more prone
to drug induced respiratory depression from sedation and narcotics.
Consider aspiration prophylaxis-delayed gastric emptying.
Increased incidence of adrenocortical insufficiency and reduced adrenocorticotropic
hormone response to stress—patients should receive hydrocortisone cover during
surgery.
Specific investigations: Hb, platelet count and clotting tests, serum electrolytes, Bld.
Sugar, ECG.

21. HYPOTHYROIDISM: ANAESTHETIC CONSIDERATION
• INTRA-OPERATIVE:
Patients are more sensitive to hypotensive effects of anaesthetic agents because of decreased CO,
blunted baroreceptor reflexes and decreased intravascular vol,; invasive monitoring on a per
patient basis.
Ketamin or etomidate may be induction agent of choice.
Succinylcholine and NDMRs are generally safe for use; monitor with peripheral nerve stimulator.
Controlled ventilation is recommended as patients tend to hypoventilate.
Hypothermia occurs quickly and difficult to prevent and treat.
MAC is essentially unchanged.
Haematological ( anaemia, platelet, coag dusfx) abnormalities, electrolyte imbalance and
hypoglycaemia are common and require close monitoring intra-operatively.

22. HYPOTHYROIDISM: ANAESTHETIC CONSIDERATION
• MYXEDIMA COMA:
Rare form of decompensated hypothyroidism.
Characterised by stupor or coma, hypoventilation, hypothermia, bradycardia,
hypotension and severe dilutional hypontraemia( SIADH) , CHF.
Medical emergency with mortality rate of 15-20%.
Infection, trauma, cold, CNS depressants predispose hypothyroid patients, especially in
elderly.
Treatment: IV thyroxine is indicated( L-thyroxine loading dose 300-500 mcg followed by 50
mcg/day for 24-48 Hrs)
IV hydration with dextrose containing crystalloids , correction of electrolyte
imbalance.
Support cardio-vascular and pulmonary system as necessary.

23. OTHER PERIOPERATIVE CONSIDERATIONS
Eyes should be protected especially if exophthalmos is present.
The patient is positioned slightly head up to help venous drainage.
Neck is hyper extended and should be well-established.
Extension tubing for iv lines and long respiratory hoses may be required.
Valsalva maneuver inTrendelenberg position is carried out to check hemostasis.
Steroids may be given if extensive tracheal handling and edema suspected.
Extubation should be smooth and coughing should be avoided to prevent bleeding.
The possibility of tracheomalacia and vocal cord palsy should be kept in mind.
Surgeon may wish to observe the movement of vocal cord at the end of operation.