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Anaesthetic considerations for thyroid dysfunction Dr. Pramod Kohli Professor

Anaesthetic considerations for thyroid dysfunction Dr. Pramod Kohli Professor Lady Hardinge Medical College New Delhi. www.anaesthesia.co.in anaesthesia.co.in@gmail.com. Iodine cycle. 5000 µ g of iodine in the body, 90% in thyroid Iodine  Iodide 

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Anaesthetic considerations for thyroid dysfunction Dr. Pramod Kohli Professor

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  1. Anaesthetic considerations for thyroid dysfunction Dr. Pramod Kohli Professor Lady Hardinge Medical College New Delhi www.anaesthesia.co.inanaesthesia.co.in@gmail.com

  2. Iodine cycle 5000 µg of iodine in the body, 90% in thyroid Iodine  Iodide  (TSH +) Iodide trapping (thiocyan & perchlor -) per  oxidase Iodine  Coupling to form MIT, DIT, T3 & T4(thioureas -) Pro  teases Release of hormones and iodine

  3. Effects of thyroxine • Induces transcription of cellular enzymes,  the metabolism. • Modifies energy use - glucose mobilization - insulin secretion - free fatty acid mobilization  BMR:  HR,  CO, vasodilatation, tissue perfusion  O2 consumption,  CO2 production

  4. Tests for glandular function RAIU(n = 5 – 30 %) • Used to confirm hyperthyroidism • As a part of TSH stimulation test. • As a part of Thyroid suppression test Not a good indicator of hypothyroidism Urinary RAI excretion (n = 60 -80 %) •  to < 35 % in hyperthyroidism •  in hypothyroidism

  5. Hormone assay • T4 n = 4 – 11 µg % • T3 n = 90 – 160 ng % • Free T4 n = 1 – 2 ng % • Free T3 n = 0.2 – 0.4 ng % Good indicator of hyperthyroidism Poor indicator of hypothyroidism

  6. RT3U ( n = 25 – 35 %) Quantifies % saturation of thyroglobulin Uptake inversely proportional to concentration of unoccupied sites on thyroglobulin •  in hyperthyroidism •  in hypothyroidism

  7.  levels Pregnancy Neonates Oral contraceptives Viral hepatitis Chr active hepatitis Ac intermittent porphyria T4 , T3 , RT3U  Free T4 & FTI N  levels Androgens Corticosteroids Cirrhosis Nephrotic syndrome Severe illness Phenytoin therapy T4, T3  RT3U  Free T4 N/, FTI N Factors affecting TBG

  8. Test independent of TBG Free thyroxine index n = 55 – 145 •  in hyperthyroidism •  in hypothyroidism

  9. TSH (n = < 5 µU / ml) •  in hypothyroidism - best indicator •   / negligible in hypothyroidism of pituitary or hypothalamic origin

  10. The stimulation tests TSH stimulation test:5 U given s/c X 3 days • RAIU done to assess thyroid reserve • No  in hypothyroidism of thyroid origin •  in hypothyroidism of pituitary origin TRH stimulation test:400 µg given, TSH  in 10mins, peaks at 20 – 45 mins, then falls rapidly • Subnormal response in pituitary hypothyroidism and thyrotoxicosis • Supranormal response in hypothyroidism of thyroid origin

  11. Thyroid suppression test 100 µg of T3 given daily x 10 days, RAIU done • No in thyrotoxicosis (n =  by 50 %) False results in 50 % treated Grave’s disease & if some autonomous nodule / area suppresses the rest of the gland

  12. Radio-imaging Thyroid scan • Delineates the active thyroid tissue. • Diagnostic for retro-sternal extension.

  13. Other tests • BMR after 12 hrs fasting • Ultrasonography • FNAC • Venography • Antibody titres - anti T3 - anti T4 - thyroid antimicrosomal - anti thyroglobulin

  14. T4 T3 RT3U TSH Hyperthyroidism    N Hypothyroidism     Pit. Hypothyrodism     Pregnancy   N N

  15. A 32 year old female with a large swelling in front of neck, reports for PAC for an elective surgery …..

  16. Is it a mid-line / lateral swelling ? • What could it be ? – D/d of neck swellings. • Could it be a thyroid swelling ? • If yes – is it eu, hyper or hypo-thyroid ? • Is it causing compressionof soft tissues ?

  17. If a goiter, the possible cause ? • Dietary iodine deficiency •  physiological iodine demands – puberty, pregnancy, menopause • Drug induced (iodine containing dyes /drugs) • Inflammatory • Neoplastic

  18. What is the nature of goiter ? • Simple – diffuse / nodular • Toxic – diffuse, nodular, multi-nodular • Retro-sternal (Pemberton’s test)

  19. What is the functional status ? Signs and symptoms of hyperthyroidism • Heat intolerance, warm moist skin, good appetite yet wt loss • Diarrhoea • Anxiety, excitability, tremors •  HR,  BP,  CO,  pulse pressure arrhythmias and heart failure • Myopathy • Eye signs

  20. Eye signs • Exophthalmos • Stellwag’s sign – wide palpebra,blinking • Dalrymple’s sign – lid retraction • Von Graef’s sign – lid lag • Mobius’s sign – inability to converge • Gifford’s sign – difficulty in lid eversion • Joffroy’s sign – loss of wrinkling

  21. Functional status contd… Signs and symptoms of hypothyroidism • Cold intolerance, dry, thick, cold, yellow skin, wt gain in spite of  appetite • Constipation • Menorrhagia • Lethargy, slurred speech,  mentation,  memory •  HR,  BP, pericarditis, pl effusion, ascites • Delayed ankle jerk, polyneuropathy

  22. Compression of soft tissues Airway, SVC, Oesophagus, RLN, symp trunk Rule out / confirm with: - History and examination. - Special tests – Kocher’s, Pemberton’s - Investigations – X-rays, I/L, Ba swallow, Flow-vol curves

  23. Airway obstruction & flow vol curves Fixed Extrathoracic Intrathoracic obstruction obstruction obstruction

  24. Ensure eu-thyroid state Hyperthyroidism • Anti-thyroid drugs • Supportive agents Hypothyroidism • Thyroid hormones • Supportive measures

  25. Anti-thyroid drugs • Thioureas* (propyl & methyl thiouracil) 100 - 400 mg QID x 1 mth, then reduce / adjust • Thiocarbamates* (methimazole & carbimazole) 20 - 40 mg QID x 1 mth, then reduce / adjust * combined with T4 to  the size of goiter cause agranulocytosis and skin rashes • Iodide -  vascularity & hormone synthesis effect peaks after 10 days, then declines • Potassium per-chlorate – high risk of aplastic anaemia, for pts sensitive to other drugs • RAI –  radiation, for elderly

  26. Supportive drugs for hyperthyroidism  blockers - propranolol also blocks conversion of T4 to T3 - esmolol is 1 specific, short t½, better control Reserpine, guanethidine if  blockers are C/I Benzodiazepines

  27. Thyroid hormone supplement • Levothyroxine – 25 µg/day x 2 – 3 weeks by25 µg/day every 2 – 3 wk • L-triiodothyronine • Thyroid extract

  28. Hyperthyroidism: problems anticipated • Potential airway problems • Surgery close to airway • Hyperpyrexia, dehydration and ketosis likely • Hyperdynamic circulation • Arrhythmias common • High blood loss anticipated • Problems due to positioning • Problems of sternotomy • Thyroid storm • Post-operative complications

  29. What is thyroid storm ?

  30. Thyroid storm (6 – 18 hrs post-op) Ac thyrotoxicosis, threatening homoeostasis • Thermoregulatory failure • Cardiovascular collapse • Metabolic failure

  31. Factors precipitating thyroid storm • Radio-iodine therapy, iodinated dyes • Withdrawal of anti-thyroid drugs • Thyroid manipulation • Stress factors: - Infection - Trauma, pain - Non-thyroid surgery - Hypovolaemia - CHF, pulmonary embolism - Diabetic keto-acidosis - Pregnancy, labour

  32. How will you prepare the patient ? • Patient must be euthyroid • Ensure a sleeping pulse rate < 85/min • Examine the patient in laryngoscopy position • Insist on I/L, and Xrays of chest & neck AP & lat • Continue anti-thyroid drugs and  blockers • Lugol’s iodine x 10 days to  vascularity • Arrange blood • Avoid sympathomimetics (atropine) • Good sedation - narcotics and benzodiazepines • No sedation if airway is compromised

  33. What is thyroid steal ?

  34. Monitoring • ECG for HR and arrhythmias • NIBP • Temperature • SpO2 and EtCO2 • Urine out put • Neuromuscular monitoring (optional) • CVP and intra-arterial BP only if +ve h/o CHF, thyroid storm or hypotension

  35. Induction and intubation • Pre-oxygenation • Thiopentone good due to antithyroid action Avoid ketamine • Add halothane / sevoflurane and N2O • Must obtund pressor response • Suxamethonium / vecuronium / rocuronium for intubation • Intubation must be smooth, reinforced tube • Tube must extend beyond the thyroid gland

  36. Positioning Head end up, head extension, arms by the side • Protect eyes • Pad the elbows • Ensure easy IV access

  37. Maintenance • Maintain adequate depth of anaesthesia - supplemental narcotics (fentanyl, morphine) - isoflurane (does not sensitize heart) - adequate muscle relaxants • Meticulous fluid replacement

  38. Intra-operative problems • Bradyarrhythmias (carotid body stimulation) -do not give atropine - stop surgery & lignocaine infiltration • Excessive bleeding - hyperextension of head - hypercarbia • Acute hypotension - use direct sympathomimetics /  agonists • Air embolism • Thyroid storm

  39. Thyroid storm – causes in OT • Inadequate depth of anaesthesia • Hypoxia • Hypovolaemia • Pulmonary embolism • Surgical manipulation

  40. S/s of thyroid storm on OT table •  EtCO2 •  temp •  HR •  BP •  sweating • Arrhythmias • Soda lime exhaustion

  41. S/s of thyroid storm - awake patient • Restlessness • Tachypnoea •  higher functions • Vomiting and abdominal colic • Dilated pupils •  temp •  HR •  BP •  sweating • Arrhythmias

  42. Differential diagnosis of thyroid storm • Malignant hyperpyrexia • Phaeochromocytoma • Carcinoid crisis

  43. You suspect thyroid storm on OT table……. ……How will you manage ?

  44. Treatment of thyroid storm •  O2,  depth of anaesthesia, change soda lime • Esmolol infusion (100 – 300 µg/kg/min) propranolol – (0.5 – 1 mg iv every 1 - 5 mins) •  temperature - cooling mattress, ice packs - cold iv fluids, cold irrigation - Acetaminophen (no aspirin) • Thioureas followed by sodium iodide • Correct fluid, electrolyte and acid-base • Steroids – inhibit conversion of T4 to T3 • Frusemide, digoxin, inotropes if needed

  45. Reversal and extubation • Ensure total reversal of n/m blockade • Use glycopyrrolate with neostigmine • Avoid atropine • Extubate while deep (volatile agent) • Fibreoptic bronchoscopy through the ETT to assess tracheal collapse during extubation • See vocal cord movements after extubation • Observe on table for stridor or airway obstruction

  46. Post-operatively • Ensure an alert yet pain free patient good analgesia without over sedation • Oxygen • Continue monitoring SpO2, ECG, NIBP, temperature, I/O

  47. 5 min after shifting the patient from OT, you are asked to see the patient as she is having a noisy breathing ….. …..What do you suspect ?

  48. Post-op respiratory compromise Early • Haematoma (keep suture cutter ready) • Oedema • Recurrent laryngeal nerve palsy • Tracheal collapse • Pneumothorax Late • Hypocalcaemic stridor (12 – 72 hrs) • Sup laryngeal nerve palsy  aspiration

  49. Laryngeal nerve palsies Rec laryngeal N close to inf thyroid A • Bilat incomplete RLN palsy  Ac stridor with both vocal cords in mid line - large goiter - malignant goiter - retrosternal goiter Ext br of sup laryngeal N close to sup thyroid A • Gruffness of voice, aspiration

  50. Role of regional anaesthesia For incidental surgery • Main concern is anxiety and symp activity • Always rule out impending heart failure • Sedate the patient well • Do not use adrenaline containing solutions • Epidural preferred over sub-arach block • Prevent hypotension – meticulous fluids • Smaller doses of vasopressors for  BP

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