anaesthesia in thyroid disease

1. anaesthesia in thyroid disease www.anaesthesia.co.inanaesthesia.co.in@gmail.com

2. ANATOMY • 2 lateral lobes connected by an isthmus, lie at the level C5-C7 • Very vascular organ • Surrounded by a sheath from pretracheal layer of deep fascia • Closely attached to thyroid cartilage & to upper end of trachea – thus moves on swallowing • Embryologically – originates from base of tongue & descends to middle of neck

3. Blood supply: I) superior thyroid artery ii) inferior thyroid artery iii) thyroidea ima

4. Normal function of thyroid gland – directed to secretion of T3 & T4 • Insufficient hormone secretion – hypothyroidism /myxedema • Excessive secretion – hyperthyroidism • Hormone action:- - influence the growth & maturation of tissues - “cell respiration & total energy expenditure - “ turnover of essentially all substrates, vitamins, & hormones

5. PHYSIOLOGY • Recommended daily intake – 140ug • The synthesis depends on: I) quantities of iodine ii) normal iodine metabolism in the gland iii) synthesis of thyroglobullin • Dietary iodine – absorbed by GIT – converted to iodide ion – actively transported into thyroid gland • Once inside – iodide is oxidized back to iodine, which is bound to tyrosine • End results – triiodothyronine (T3) & thyroxine (T4)

6. T4 released more than T3, but T3 is more potent & < protein-bound • Most T3 is formed peripherally from partial deiodination of T4 • In plasma, >90% of T4 & T3 is bound to hormone-binding proteins • Only free hormone available for tissue action

7. PHYSIOLOGY OF HYPOTHALAMIC-PITUITARY-THYROID AXIS 1- TRH released in hypothalamus – stimulates TSH release from pituitary 2- TSH stimulates TSH receptor in the thyroid, to synthesis both T4, T3 & stored hormone  increased plasma levels of T4 & T3 3-  serum levels of T3 & T4 & conversion of T4 to T3 4- T3 & T4 will enter cells & bind to nuclear receptors & promote  metabolic & celular activity

8. Hypothalamus TRH Pituitary TSH Thyroid T3 Tri-iodothyronine Thyroxine T4 PeripheralTissues Physiological Effects

9. Patients with thyroid disease can present for: i) surgery to the thyroid gland ii) Surgery to pituitary gland iii) Any incidental surgery

10. Problems in anaesthesia…. • Airway - tracheal compression/ deviation – difficult intubation - Infiltration by thyroid gland tumour • Tracheomalacia 2) Endocrine status • hyperthyroidism – thyroid crisis • Hypothyroidism - sensitivity to anaesthetic agents with delayed recovery; poor tolerance to blood loss & other stresses

11. 3) Surgery • head & neck surgery with  accessibility to airway • Injury to recurrent laryngeal nerve • Venous air embolism • Hypocalcaemia • Haematoma • hypothyroidism

12. HYPERTHYROIDISM Causes: - Grave’s disease, toxic multinodular goitre, thyroiditis, pituitary tumours, functioning thyroid adenomas, overdosage of thyroid replacement hormone Clinical manifestations: - weight loss, heat intolerance, muscle weakness, diarrhea, hyperactive reflexes, nervousness,fine tremor, exophthalmos, sinus tachycardia, atrial fibrillation, CCF Diagnosis:- abnormal TFT

13. Medical Tx • PTU, methimazole (inhibit hormone synthesis) • Potassium, sodium iodide (Prevent hormone release) • Propranolol (Mask signs of adrenergic overactivity) • Radioactive iodine 2) Surgery

14. Anaesthetic Considerations • PREOPERATIVE • Postpone all elective cases till patient is rendered euthyroid with medical tx • Airway • Determine ease of intubation • Compression Sx:- hoarseness of voice, stridor, dysphagia • Cervical x-ray – tracheal deviation / compression

15. ii) Cardiovascular system • heart rate & rhythm ( <85 bpm ), atrial fibrillation • Heart failure • Ischemic heart disease iii) Endocrine status • palpitations, tachycardia (awake & sleeping pulse) • Bruit over thyroid gland • Problems with CVS instability & thyroid storm • Latest thyroid function test

16. iv) Current treatment • continue medication & serve on morning of surgery v) Indirect laryngoscopy • ENT review on vocal cord function as a baseline finding Premedication • no premedication in pt with airway obstruction • Pt adequately sedated to prevent anxiety & apprehension ( BDZ / narcotic premedication ) • Emergency surgery – esmolol infusion • (50-150ug/kg/min)

17. B) INTRAOPERATIVE • Anaesthetic options: A-No difficulty anticipated: - usual iv induction & intubation (fentanyl, STP, non-depolarizing muscle relaxant B- possible difficulty in intubation: - iv induction, test ventilation when pt is unconscious, intubation +- suxamethonium C- definite intubation problem / evidence of airway obstruction - awake fibreoptic intubation - inhalational induction - choice of ETT- armoured ETT (< risk of kinking) important measures: - closely monitor pt’s CVS function & body temperature - eyes protection - to raise head of operating table 15-20 degrees to aid venous drainage (although risk of venous air embolims)

18. choice of anaesthetic agents: - induction agent – thiopentone - muscle relaxant – atracurium, vecuronium - volatile agent – isoflurane - narcotic analgesics – fentanyl, morphine - anaesthetic technique – balanced anaesthesia with N2O-O2-isoflurane-muscle relaxant-narcotic analgesics --- IPPV • No controlled study has demonstrated clinical advantages of any anaesthetic drug over another – Miller * University of California (1968-1982)- all anaesthetic agents & techniques have been employed without adverse effects being even remotely attributable to agent / technique

19. Precautions: • avoid ketamine, pancuronium, indirect-acting adrenergic agonists & other drugs that stimulate the sympathetic nervous system • Prone to exaggerated hypotensive response on induction • Achieve adequate anaesthetic depth before laryngoscopy / any surgical stimulation • Administer neuromuscular blocking agent cautiously ( thyrotoxicosis a/w incidence of MG & myopathies ) • Hyperthyroidism does not  anaesthetic requirements

20. Reversal: • uncomplicated cases: reverse & extubate as usual

21. C) POSTOPERATIVE Possible problems • Thyroid crisis / storm • decompensated hyperthyroidism with excessive release of thyroid hormone • Onset – intraoperative / 6-24 hours after surgery • Sn & Sx:- hyperpyrexia, tachycardia or atrial fibrillation, hypotension, vomiting, dehydration, tachypnoea, acute abdominal pain simulating an acute abdomen, agitation, psychosis • May mimic malignant hyperthermia

22. Precipitants • infection, surgery, poorly prepared thyroid surgery, diabetic ketosis, radioiodine therapy in a poorly prepared pt, MI

23. management: A) supportive B) medical Tx 1- investigate for precipitants – FBC, BUSE, blood glucose, FT4, FT3 2) hyperthyroidism: i- inhibition of thyroid hormone formation - PTU 900-1200mg/day orally / NG in 3-4 divided doses OR - carbimazole 60-120mg/day 3-4 divided doses orally / NG

24. ii) Inhibition of thyroid hormone release: • sodium iodide IV 1gm/24hr – slow infusion or • oral potassium iodide 100mg 6hrly • Given 1hr after 1st dose PTU/carbimazole 3) Steroids - iv dexamethasone 2mg 6hrly • inhibits thyroid hormone release & peripheral conversion

25. 4) Receptor blockade ( in the absence of HF) • Iv propranolol 1-2mg slowly 4-6hrly / oral propranolol 40-80mg 6hrly 5) Cardiac failure - diuretics, digoxin, O2 +-propranolol if d/t uncontrolled AF with good LV function 5) Hyperpyrexia • fans, tepid sponge, PCM 6) Dehydration • IVD, CVP 7) Anticoagulation • heparin infusion in AF • Other pt – s/c heparin 5000U 2-3x dly 8) Severe agitation – chlorpromazine 150mg 8hrly PO / 25mg 8hrly IM 9) Exchange transfusion / PD/HD • If pt fails to improve within 24-48hrs

26. 2) Airway obstruction Possible causes: - neck haematoma with tracheal compression - recurrent laryngeal nerve palsy - tracheomalacia - incomplete reversal - central depression

27. 3) Tetany • clinical manifestations: circumoral tingling, paraesthesia, laryngeal spasm, (+)ve Chvostek & Trousseau signs • May result from respiratory alkalosis, d/t: - over-ventilation in immediate postoperative period - hypocalcemia from hypoparathyroidism Mx • calcium estimation • Slow injection of 10% calcium gluconate 10 mls IV

28. HYPOTHYROIDISM Causes • autoimmune disease, thyroidectomy, radioactive iodine, antithyroid medications, iodine deficiency, failure of hypothalamic-pituitary axis Clinical manifestations: • weight gain, cold intolerance, muscle fatigue, lethargy, constipation, hypoactive reflexes, depression, dull facial expression, • HR, stroke volume, CO • Pleural, abdominal, pericardial effusion Dx: low free T4 level

29. Tx: • oral replacement therapy with a thyroid hormone preparation

30. Myxedema Coma • results from extreme hypothyroidism • Precipitated by – infection, surgery, trauma • C/f: - most pts are female, elderly - impaired mentation - hypoventilation - hypothermia - hypotension - bradycardia - comatose - hyporeflexia - hyponatremia

31. Management i) FT3, FT4, TSH, FBC, ii) Should start on clinical grounds iii) Thyroid hormone replacement - T4:- iv 200 mcg bolus, daily dose 100mcg till pt can take orally - T3:- iv/oral 10-20mcg bd till T4 can be given orally iv)steroids:- iv hydrocortisone 100mg stat, 50-100mg tds

32. v) ventilation: assisted ventilation if RF vi) hypothermia: • do not warm rapidly (>1C/hr)– CVS collapse • Blankets & close temperature monitoring vii) Hypotension viii) Hyponatremia • caused by dilution & redistribution • Fluid restriction ix) Tx of precipitating factors * Full recovery – replacement thyroxine dose titrated once / 2-3 weeks to maintain euthyroid state

33. A) PREOPERATIVE Severe hypothyroidism ( T4 <1mg/dL): • Elective case – to correct first • Emergency case – to treat with thyroid hormone prior to surgery Mild – moderate:- no absolute C/I

34. i- Airway ii- CVS Iii- endocrine status - coarse dry skin, slow mentation, cold intolerance, - CO, hyporeflexia, hypoglycaemia • Increased sensitivity towards anaesthetic agents & central depressants • Hypotension & cardiac arrest following induction • Delayed recovery from GA

35. Premedication: • Do not require much, prone to drug-induced respiratory depression • Histamine H2 antagonists & metoclopramide – d/t slowed gastric emptying times

36. B- INTRAOPERATIVE - > susceptible to hypotensive effect of anaesthetic agents -  CO - blunted baroreceptor reflexes -  intravascular volume • induction agent of choice – ketamine - does not  MAC • Potential problems - hypoglycemia, anemia, hypoNa+ - difficult intubation d/t large tongue - hypothermia d/t low BMR

37. C) POSTOPERATIVE • delayed recovery – hypothermia, respiratory depression, slowed drug biotransformation • Should remain intubated till awake & close to normothermic • Postoperative pain relief – nonopiod (ketorolac)

38. References: i- Maged S. Mikhail: clinical anaesthesiology, Lange 2002 ii- Parveen Kumar: clinical medicine, W.B Saunders,1998 iii- Lee Choon Yee: manual of anaesthesia iv- Braunwald: Harrison’s principles of internal medicine, 1998 V- Soo Hua Huat: Handbook of medical emergencies www.anaesthesia.co.inanaesthesia.co.in@gmail.com