HYPOTHYROIDISM AND OBSTETRIC ANAESTHESIA DR A. Vasukinathan MD DA Asst.professor in Anaesthesiology, Kanyakumari govt. medical college, Nagercoil.

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

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

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

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

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

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.

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

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.

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

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.

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

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

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

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

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

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.

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

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.

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

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

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.

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.

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

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.

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

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

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.

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

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.

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.

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.

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.