Asst.professor in Anaesthesiology , Kanyakumari govt. medical college, Nagercoil .

1. Asst.professorin Anaesthesiology, Kanyakumarigovt. medical college, Nagercoil. HYPOTHYROIDISM AND OBSTETRIC ANAESTHESIA DR A. Vasukinathan MD DA

2. Hypothyroidism is a clinical condition resulting from inadequate circulating levels of thyroid hormones. • The prevalance in pregnancy is 0.3%.

3. OBSTETRIC COMPLICATIONS • Anaemia • Pre-eclampsia • IUGR • Placental abruption • PPH • Fetal Distress during labour

4. Causes • Primary • Auto immune hypothyroidism (Hashimoto’s Thyroiditis) • Iatrogenic • - 131I treatment • - Thyroidectomy • - Irradiation therapy of neck for lymphomas • Iodine deficiency

5. Transient • Withdrawal of thyroxine treatment in patients with intact thyroid • Sub acute thyroiditis • Secondary • Hypopituitarism • Isolated TSH deficiency • Hypothalamic disease

6. DIAGNOSIS • Normal T4 in Pregnancy-8-16mg/dl(<2.8) • Normal TSH in Pregnancy<10mIU/dl(>88) • Primary Hypothyroidism has a low T3 , T4 and a raised TSH level. • Secondary Hypothyroidism has a low T3 , T4 and TSH levels

7. TREATMENT • Levothyroxine - 1.5µg/kg (100-150 µg/day) orally similar to non pregnant woman –no adverse effects on fetus. • TSH measurements are done 2 months after initiation of treatment.

8. IMPORTANCE TO THE ANAESTHETIST • General– Weight gain ,obesity and its complications

9. Cardiovascular – • Earliest clinical manifestations • Hypodynamic cardiovascular system • Reduced – Heart Rate Stroke Volume Cardiac Output Myocardial contractility • Increased – PVR , BP • Angina, Cardiac failure, Pericardial effusion, Conduction abnormalities. • Unresponsive Baroreceptor reflexes.

10. Pulmonary – reduced surfactant production. • Ventilatory drive in response to hypoxia and hypercarbia is reduced. • MBC and diffusion capacity are reduced. • Pleural effusion.

11. Blood – Secondary Anemia • Plasma volume is reduced and circulation rate is slow. • Coagulation abnormalities-Platelet dysfunction-reduced clotting factors • Adrenal Cortex – Atrophy with reduced Cortisol production. • Inappropriate ADH secretion- water retention and hyponatremia. • CNS – Lethargy, delayed tendon reflexes. • GIT – Delayed gastric emptying, constipation, Ileus and ascites. • Temperature regulation – increased susceptibility to cold. • Metabolism– Decrease in BMR. • Musculoskeletal System- abnormal response to peripheral nerve stimulator.

12. COMPLICATIONS • Increased sensitivity to anaesthetic drugs • Secondary to reduced cardiac output, • Decreased blood volume, • Abnormal baroreceptor function • Decreased hepatic metabolism • Decreased renal excretion.

13. Complication related to the airway • Airway compromise • Secondary to myxedematous swelling of the upper airway • Macroglossia • Edematous vocal cords • Goiter • The risk of regurgitation and aspiration • Delayed gastric emptying time

14. SYMPTOMS • Tiredness Weakness • Dry Skin Feeling cold • Hair loss Poor memory • Constipation Dyspnea • Hoarseness of voice Menorrhagia • Paresthesia • Weight gain with poor appetite • Difficulty in concentration

15. SIGNS • Dry coarse skin • Cold peripheral extremities • Puffy face and feet • Macroglossia • Bradycardia • Hypertension • Delayed Tendon Reflexes.

16. MANAGEMENT OF ANAESTHESIA • Sensitivity to depressant drugs. • Hypodynamic cardiovascular system characterized by decreased cardiac output due to reduction in Heart rate and Stroke Volume. • Slowed metabolism of drugs particularly opioids. • Unresponsive baroreceptor reflexes. • Decreased intravascular fluid volume

17. Impaired Ventilatory response to arterial hypoxemia and / or hypoxia. • Delayed gastric emptying. • Impaired clearance of free water resulting in hyponatremia. • Hypothermia. • Anemia. • Hypoglycemia. • Primary adrenal insufficiency.

18. PRE-OPERATIVE ASSESSMENT • Clinical assessment of the patient • Airway assessment • Hematological – as they are usually anemic • Coagulation Profile • Cardiovascular and pulmonary – Cardiomegaly and pleural effusion • ECG – low voltage complexes, ST , T wave abnormalities • Echo – for LV function and pericardial effusion • Lipid Profile • Thyroid Profile

19. Premedication • Judicious use of opioids - Ventilatory depression • Thyroxine, the morning dose can be given on the day of surgery. • Cortisol supplement is optional. • Perioperative Thyroid hormones in IHD or Valvular Heart Disease- Controversy.

20. ANAESTHESIA - REGIONAL OR GENERAL • Regional anaesthesia is preferred if the location of the surgery permits

21. Regional anaesthesia • Doses of local anaesthetic drugs may be reduced. • Metabolism of amide local anaesthetics is slow leads to development of systemic toxicity. • Land marks difficult to identify. • Hemodynamic side effects are exaggerated

22. General anaesthesia • Induction of anaesthesia- • Ketamine is the ideal induction agent theoretically • Recovery is inconsistent. • Barbiturates or benzodiazepines may produce sudden fall in BP. • Rapid sequence induction is preferred because of delayed gastric emptying. • Succinyl Choline is the preferred drug for intubation.

23. Maintenance of anaesthesia • Nitrous oxide with small doses of a short acting opioids and a non depolarizing muscle relaxant may be used. • Pancuronium is the relaxant of choice because of its mild sympathomimetic effects. • Volatile anaesthetics are not recommended because of • 1.Extreme sensitivity. • 2.Vasodilatation may cause a sudden fall in BP.

24. Monitoring • Early recognition of hypotension, bradycardia, and hypothermia. • 1. Pulse oximetry • 2. ECG • 3. NIBP • 4. CVP • 5. Temperature

25. Hypotension can be treated with vasopressor (ephedrine 2.5-5mg). • Acute primary adrenal insufficiency • Hypotension persists despite treatment with intravenous fluids and sympathomimetic drugs. • Maintenance of body temperature • Increasing the temperature of operating room • Warming inhaled gases • Passing intravenous fluids through a blood warmer.

26. Recovery • Reversal of muscle relaxants • Acetyl cholinesterase inhibitor and an anti cholinergic agent. • Removal of ET tube-should be considered only • When the patient is awake • Maintaining airway • Normothermic • Adequate lung volumes

27. DELAYED RECOVERY • Prolonged effects of anaesthetic drugs • Extreme sensitivity to the Ventilatory depressant effects of opioids.

28. Postoperative period • Prolonged post-operative observation is necessary • Continuous monitoring of temperature pulse, BP, CVP, and oxygen saturation is mandatory. • Maintaining the airway is also important.

29. Myxedematous Coma • Decompensated hypothyroidism-rare • Coma • Hypoventilation • Hypothermia • Bradycardia • Hypotension • Severe dilutional hyponatremia.

30. Predisposing Factors: • Infection, trauma, cold, CNS depressant drugs, and Surgery. • Treatment: • Medical emergency with a mortality rate of 15- 20 % • Immediate aggressive treatment. • Specific Measures: • L-Thyroxine (T4) 300-500µg bolus IV followed by a maintenance dose of 50µg / day. • T3 40µg bolus (slow infusion) followed by a maintenance dose of 10-20µg / day.

31. Supportive measures • Intravenous hydration with a glucose containing saline solution. • Maintenance of Temperature • Electrolyte imbalance correction. • Stabilization of the cardiac and pulmonary system. • Aggressive external warming is not recommended peripheral vasodilatation, hypotension and cardio vascular collapse • Hemodynamic status and hypothermia usually improve within 24 hrs. • I.V. hydrocortisone 100-300 mg / day is prescribed to treat possible adrenal insufficiency.

32. EMERGENCY SURGERY IN SEVERE HYPOTHYROIDISM • Possibility of developing severe CVS instability intraoperatively and myxedematous coma in the post-operative period is high. • I.V. tri-iodothyronine 25-50µg bolus plus a continuous infusion is effective within 6 hours with a peak rise of BMR in 36-72 hrs. • Amrinone, an Inovasodilator may improve myocardial contractility since its mechanism of action does not depend on beta receptors. • Corticosteroid coverage.

33. Conclusion • Well-controlled hypothyroidism do not present much difficulty • Sub clinical or untreated hypothyroidism presenting as an emergency, are at considerable risk. • Do proper preoperative assessment of the patients • Appropriate treatment to avoid complications in the perioperative phase.