Anaesthesia for hypothyroid patient

anesthesia

1. ANAESTHESIA FOR HYPOTHYROID PATIENT MODERATOR-Dr.RAGHURAM PROFESSOR DEPARTMENT OF ANAESTHESIA PRESENTOR-Dr. S.SARAH SHAHNAZ

2. INTRODUCTION

3. THYROID GLAND Endocrine gland in the anterior and lateral aspects of the neck Bi-lobed connected by the isthmus Upper border of isthmus is below the cricoid cartilage Weighs about 20 grams Highly vascular gland-with rich capillary permeation Recurrent laryngeal gland , external laryngeal nerve are in close proximity to the gland

4. Innervated by adrenergic and cholinergic nervous system The gland is made of follicles with proteinaceous colloid Colloid has thyroglobulin-iodinated glycoprotein-substrate for thyroid hormone synthesis It bears parafollicular C cells-calcitonin The hypothalamo-pituitary-thyroid axis plays an important role in body metabolism

5. BLOOD SUPPLY OF THYROID GLAND

6. LYMPHATIC DRAINAGE

7. RELATIONAL ANATOMY

8. HYPOTHALAMO-PITUITARY-THYROID AXIS

9. THYROID DISORDERS Hyperthyroidism Hypothyroidism Goitre- single nodular multinodular Thyroid tumors follicular carcinoma papillary carcinoma medullary carcinoma anaplastic carcinoma

10. parameter Values units Serum TSH 0.5-5 micro units/ml total T4 50-150 nanomol/litre Total T3 1.5-3.5 nanomol/litre Free T4 12-28 picomol/litre freeT3 3-9 picomol/litre thyroglobulin <1-35 micrograms/litre

11. HYPOTHYROIDISM

12. HYPOTHYROIDISM Relatively common in adult population Could be of two types primary hypothyroidism secondary hypothyroidism euthyroid sick syndrome

13. Primary hypothyroidism Decreased production of thyroid hormones inspite of adequate or increased levels of TSH seen most commonly TRH administration causes exaggerated TSH elevation Secondary hypothyroidism reduced levels of freeT4,T3,T4 and reduced TSH level TRH stimulation confirms pituitary as cause which shows absent or blunted reflex

14. Euthyroid sick syndrome abnormal thyroid function tests in critically ill patients with significant non thyroid illness Low level of T3 T4 and normal TSH level With deterioration of the disease,T3 and T4 level decreases further Stress induced as a physiological response during surgery No treatment is needed Serum TSH > 10milliunits/L implies hypothyroidism <5 milliunits/L implies euthyroidism

15. ETIOLOGY Surgery-most common cause Radioactive iodine ablation Idiopathic Autoimmune

16. FEATURES OF HYPOTHYROIDISM Apathy Arthralgia Cardiac failure cardiomegaly Carpal tunnel syndrome Constipation Decreased sweating

17. Deep hoarse voice Dry skin Intolerance to cold Impaired free water clearance-hyponatremia Lethargy Menorrhagia Non pitting edema Pleural and pericardial effusion Periorbital edema

18. Sleep apnea Slow gastric emptying Slow mental functions Slow movement Weight gain –coarse facial features -large tongue

19. TREATMENT Levothyroxine sodium commonly used Response to therapy sodium and water diuresis reduction in TSH level Patient with cardiomyopathy shows measurable improvement in myocardial function with therapy Angina if already present may worsen hence angiogram is needed before hormone replacement

20. HYPOTHYROIDISM AND ANESTHESIA

21. HYPOTHYROIDISM AND ANAESTHSIA Mild to moderate thyroid dysfunction has minimal impact peri-operatively Features expressed in hypothyroid state directs the precautions to be taken peri-operatively and intra-operatively Hypothyroidism reduces anaesthetic requirement slightly Determination of medical treatment is important

22. Changes in thyroid function have been documented in uncomplicated acute myocardial infarction, congestive heart failure, cardiopulmonary bypass. Significant T3 depression occurs which may not get corrected with T3 administration Patient taking amiodarone are at risk of hypothyroidism and needs a thyroid function test before surgery

23. PREOPERATIVE PERIOD Euthyroid state is ideal for surgical procedures For chronic thyroid disorder a preoperative thyroid function test is needed Reliable report - if it is less than 6 months Thyroid stimulating hormone (TSH) is the best to evaluate hypothyroidism Surgical stress may precipitate myxedema or thyroid storm in untreated or severe cases

24. Elective surgeries must be postponed until the patient is euthyroid Emergency surgeries must be done after consultation with endocrinologist Chest x-ray or CT is used to rule out tracheal or mediastinal involvement Continuation of drug on the day of surgery is important

25. In patients with no history of prior thyroid dysfunction but with present history its symptoms-TSH alone could be done Full replacement dose of levothyroxine-1.6micrograms/kg/day -elderly or those with coronary artery disease the initial dose -25 µg daily -increase every 2 to 6 weeks until euthyroid state Half life of the drug is 7 days

26. INTRA-OPERATIVE PERIOD Increased risk when hypothyroid patient goes through general or regional anaesthesia Difficult intubation-Swollen oral cavity -edematous vocal cords -goitrous enlargement Aspiration risk and regurgitation risk-decreased gastric emptying

27. Cardiovascular changes hypodynamic circulation Decreased cardiac output Decreased stroke volume Decreased heart rate Decreased baroreceptor reflexes Respiratory changes Enhanced suppression of ventilatory response to hypoxia and hypercarbia

28. Hematologic abnormalities Anemia 25%-50% of patients Platelet dysfunction and coagulation factor abnormalities (factor viii) electrolyte imbalances-hyponatremia Metabolic demands Hypoglycemia is common Hypothermia has quicker onset which is difficult to treat decreased neuromuscular excitability

29. PRECAUTIONS Extremely sensitive to narcotics and sedatives -cautious pre operative sedation is needed Hypothyroidism effects on Minimum Alveolar concentration is negligible Due to decreased hepatic metabolism and renal excretion of drugs- induction agents and neuromuscular blockers must be used with caution

30. Due to cardiovascular instability the patient may need invasive monitoring and transesophageal echocardiography In noncardiac surgery-intraoperative hypotension occurs In cardiac surgery,heart failure was more prevalent

31. GENERAL ANESTHESIA given through oral endotracheal tube Rapid sequence induction or awake intubation done in case of difficult airway Inhalational agents may aggravate myocardial depression Pancuronium is the ideal neuromuscular blocker from cardiovascular standpoint but careful dosing is needed due to reduced skeletal muscle activity and reduced hepatic metabolism

32. Controlled ventilation needed as spontaneous breathing may lead to hypoventilation Intraoperative hypotension is managed by pharmacological agents like ephedrine,dopamine,epinephrine if unresponsive may need supplemental steroid administration Dextrose in normal saline is preferred to avoid hypoglycemia and hyponatremia

33. POST OPERATIVE PERIOD Myxedema coma common in emergency cases Intravenous thyroid replacement therapy should be started intravenous L thyroxine takes 10 to12days to yield peak basal metabolic rate Intravenous tri-iodothyronine effective in 6 hours with peak metabolic rate seen in 36 hours to 72 hours

34. Levo thyroxine 300 to 500 mcg I.V or Levo tri-iodothyronine 25 to 50 mcg I.V is the initial dose Hypothyroidism may be associated with decreased adrenal cortical function,steroid coverage with hydrocortisone or dexamethazone could be given Milrinone phosphodiesterase inhibitor may be effective in the treatment of intraoperative myocardial depression

35. Post operatively ,if still no ability to administer the drug enterally after 5 days, intravenous (IV) levo thyroxine should be administered as 60% to 80% of the oral dose the hypothyroid group has a higher rate of gastrointestinal and neuropsychiatric complications post surgically

36. MYXEDEMA COMA Is a rare severe form of d ecompensated hypothyroidism Mostly seen in elderly women with chronic hypothyroidism Infection , trauma,cold and central nervous system depressant predispose hypothyroidism to myxedema coma Patient is not comatose but often needs mechanical ventilation

37. Hypothermia of less than 27 degree centigrade is a cardinal feature with impaired thermoregulation by hypothyroidism Treatment of choice Intravenous L-thyroxine or L-triiodothyronine Intravenous fluid-glucose containing saline solution Thermoregulation Electrolyte imbalance correction

38. Stabilization of cardiac and pulmonary function Vitals-heart rate ,blood pressure,temprature improve 24 hours Relative euthyroid is achieved in 3 to 5 days Hydrocortisone 100-300mcg/day is given for adrenal insuffiency

39. management in the intensive care unit where proper ventilatory, electrolyte, and hemodynamic support can be given. Passive rewarming, broad spectrum antibiotic coverage and corticosteroids may be needed. The definitive treatment is thyroid hormone replacement administered as IV T 4,  200 to 500 mcg as an initial bolus followed by 50-100 mcg daily

40. Few suggest addition of IV T 3,  10-25 mcg every 8 hours if available. Rapid thyroid hormone replacement may precipitate myocardial infarction, hence caution should be exercised in those with underlying ischemic heart disease. Treatment of the precipitating cause like an infection is critical for rapid recovery.

41. PREGNANCY AND HYPOTHYROIDISM

42. Pregnancy is a state of excessive thyroid stimulation increase in thyroid size by 10% in iodide sufficient areas and 20-40% in iodide deficient regions Due to physiological and hormonal changes caused by pregnancy and human chorionic gonadotropin (HCG) the production of thyroxin (T4) and triiodothyronine (T3) increase up to 50%

43. 50% increase in daily iodide need, while Thyroid-stimulating hormone (TSH) levels are decreased in first trimester In an iodide sufficient area ,thyroid adaptations during pregnancy are tolerated, as stored inner iodide is sufficient in iodide deficient areas, due to physiological adaptations there are significant changes during pregnancy

44. FEATURES OVERT HYPOTHYROIDISM Abortion Anemia pregnancy-induced hypertension Preeclampsia premature birth low birth weight intrauterine fetal death

45. increased neonatal respiratory distress and infant neuro-developmental dysfunction placental abruption postpartum hemorrhage SUBCLINICAL HYPOTHYROIDISM higher chance of placental abruption preterm birth miscarriage gestational hypertension fetal distress

46. severe preeclampsia neonatal distress diabetes in pregnant women thyroid autoimmunity has effects similar to that of subclinical hypothyroidism Subclinical hypothyroidism is the most common thyroid dysfunction during pregnancy

47. hypothyroidism is very common during pregnancy 2-3% of pregnant women suffer from hypothyroidism 0.3-0.5% overt hypothyroidism and 2-2.5% subclinical hypothyroidism main etiology for hypothyroidism in pregnancy is iodide insufficiency in iodide sufficient areas, its main cause is autoimmune thyroiditis

48. LABOUR COMPLICATION Labor – diskinetic,longer due to the existence of the hypomyotonia and the simultaneous cardio-respiratory problems; hypokinesis Post-partum hemorrhages occur through uterus hypotony and through coagulation disorders Post-partum depression, post-partum thyroiditis, hypogalactia

49. Vitiated pelvis (limit pelvis) which can be the reason of various cephalic-pelvis disproportions Thyroid function test in pregnancy includes free T3 and T4 The free T 4  index (FT 4 I) is an indirect measure of FT 4  and accounts for increase in TBG. FT 4 I= TT 4  ×RT 3 U The reported reference value for FT 4 I is 4.5-12.5mcg/dl.

50. The values associated with hypothyroidism increase in TSH low FT 4 low FT 4 I and variable presence of thyroperoxidase antibodies (TPO) TSH and FT 4 /FT 3  are used to assess and follow thyroid diseases in pregnancy. limit of TSH should be 0.1 mIU/L -2.5 mIU/L in 1st trimester and 0.2 mIU/L -3mIU/L in 2nd and 3rd trimesters

51. If the serum TSH is ≥3 mIU/L, tests are repeated along with FT 4  and TPO. Start levothyroxine meanwhile If declared euthyroid stop levothyroxine If TSH is >3mIU/L and FT4 is normal, then patient should be tested throughout the pregnancy If TSH >3mIU/L along with low FT 4 , then levothyroxin is continued and the dose is titrated to maintain TSH level in the range of 0.5-2.5 mIU/ L

52. MEDICAL MANAGEMENT   pre-existing hypothyroidism, there is 30-50% increase in requirement of levothyroxine during the first trimester. due to increased T 4  metabolism, elevated TBG as well as inhibition of thyroid hormone (TH) absorption from the gut by prenatal iron supplements. Could be treated by iron supplements and TH four hours apart. 

53. hypothyroidism during pregnancy, levothyroxine should be started at a dose of 1-2 mcg/kg/day TSH levels should be reassessed 4-6 weeks following the dose change Treatment goal of TSH in the range of 0.5-2.5 mIU/L . overt hypothyroidism diagnosed in pregnancy, T 4  should be normalised as rapidly as possible by using two to three times the estimated final daily dose. 

54. ANESTHETIC MANAGEMENT During pre operative preparation, anxiolytics and sedatives should be avoided administration of antihistamines like ranitidine and oral sodium citrate solution along with metoclopramide are considered safe. Severe hypothyroidism should be managed with IV T 3 /T 4  

55. Hypothermia should be prevented in the operation room as well as in the post operative period hypothyroidism is associated with qualitative platelet dysfunction- dysfunction-arrangement of fresh frozen plasma or platelets is needed epidural hematoma is a risk and presence of normal coagulation should be confirmed before regional anesthesia

56. Vasopressor response is normal for epinephrine but, decreased for phenylephrine. During surgical stress, hydrocortisone should be given Regional anesthesia should be favoured over general anesthesia Nerve stimulators may not be useful clinically due to abnormal response to the peripheral nerve stimulator, due to depression of neuro muscular junction activities

57. REFERENCES Miller’s ANESTHESIA-volume1-eighth edition Stoelting’s anesthesia and co-existing disease-second south asian edition MAEdiCA-a journal of clinical medicine-2010-Maternal and fetal complications of the hypothyroidism-related pregnancy Iran J Reprod Med-review article-2015-Thyroid dysfunction and pregnancy outcomes Schwartz’s principles of surgery-10 th edition https://www.apicareonline.com/thyroid-disorders-during-pregnancy-and-anesthetic-considerations/

58. HYPO TH YROID AN ESTHESIA K FOR YOU