Warm anaesthesia greetings Dr. S. Parthasarathy MD., DA., DNB, MD (Acu), Dip. Diab. Dip. Software statistics PhD ( physiology), IDRA , FICA

THYROID AND ANAESTHESIA Why should we know?? Patients can come to us with thyroid diseases for thyroid surgery and Non thyroid surgery

THYROID AND ANAESTHESIA Second most common endocrine disease. Discuss under Some physiology. Hypothyroid for anaesthesia Thyrotoxicosis for anaesthesia For thyroidectomy

Physiology

Synthesis Iodide trapping Organification tyrosine + iodine = MIT or DIT Coupling MIT + DIT = T3 DIT + DIT = T4 No coupling then - Deiodinase to revert iodine back to the gland

Actions So varied in all systems as visitors of marina beach

hypothyroidism Neonatal hypothyroidism -> cretinism with physical and mental retardation

Adult manifestations weight gain, cold intolerance, muscle fatigue, lethargy, constipation, hypoactive reflexes, dull facial expression, depression, decreased heart rate, contractility, stoke volume, cardiac output,

cool, mottled extremities (peripheral vasoconstriction), pleural, pericardial, abdominal effusions Almost all systems

Hypothyroid patients low free T4, TSH elevated in primary hypothyroidism Treatment thyroid hormone administration several days for physiologic effect 4- 6 weeks until definite clinical improvement

Anaesthetic Considerations Preoperative Make euthyroid before any elective case. Continue usual thyroid hormone Points to note. Slow gastric emptying Prone to drug-induced respiratory depression

Susceptible to induction hypotension If refractory hypotension, consider additional adrenal insufficiency Ketamine may be good induction agent prone for sedatives

Hypothyroid - tips Inhalation induction faster with decreased cardiac output No significant effect on MAC Large tongue and problems Associated obesity

Hypothyroid Other potential problems hypoglycemia anemia hyponatremia hypothermia Delayed emergence/recovery respiratory depression,slowed drug biotransformation

Hypothyroid send lak Go for regional / local always. Less sedatives Less narcotics. Expect excess bleed. Difficult airway. Acid aspiration prophylaxis. Ketamine better.

Thyrotoxicosis weight loss, heat intolerance, diarrhea, hyperactive reflexes, nervousness, fine tremor, exophthalmos or goiter, tachycardia, atrial fibrillation, congestive heart failure  Muscle weakness, proximal myopathy  Lid retraction or lag Irregular menstrual bleed

elevated serum total thyroxine, triiodothyronine and/or free thyroxine Decreased TSH

Medical Treatment Inhibit hormone synthesis (propylthiouracil, methimazole) Prevent hormone release (potassium, sodium iodine) Mask signs of adrenergic overactivity (propranolol) Destroy thyroid cell function (radioactive iodine)

Anaesthetic Considerations Preoperative Postpone elective surgery until patient euthyroid-- Normal thyroid function studies A low TSH value should not be a contraindication to surgery Resting heart rate < 85 Continue antithyroid medications and beta-blockers through day of surgery

Intraoperative Plan local or regional Closely monitor Cardiovascular function Temperature Eyes (exophthalmos of Graves' disease) prevent sympathetic stimulation increased inhalational anaesthetic requirement due to increased cardiac output, increased temperature Induce and recover smooth

Emergency in thyrotoxic pt. Emergency case the use of an intravenous β-blocker, ipodate, cortisol, or dexamethasone and PTU is usually necessary control Go for regional Be ready for thyrotoxic crisis

Patients for thyroidectomy -Preoperative History Identify abnomality of thyroid function, Make patients euthyroid Associated endocrine disorders concurrent cardiorespiratory disease.

Preop history specifically enquire about dysphagia or respiratory difficulties associated with a change in posture which may indicate tracheal compression ENT opinion (possible ease of larynx vision) (medicolegal)

Clinical Assess the airway, observe pharyngeal structures and neck mobility Look for signs of SVC obstruction which may indicate retrosternal goitre Spontaneous breathing – obstruction ?? Look for euthyroid status. Sleeping pulse rate ≤ 85/min.

Investigations Thyroid function tests, full blood count, sugar urea & electrolytes, serum calcium,Bl.grouping CXR-look for evidence of tracheal compression or deviation, indirect laryngoscopy- if unsuccessful will indicate difficult intubation. CT or MRI can be used to assess degree of retrosternal goitre. Pulmonary function tests may demonstrate upper airway obstruction in flow-volume loops.

FV loop normal

Variable extrathoracic obstruction sitting or supine !!

Rt. Shift of trachea

ECG,Echo if necessary. sinus tachycardia prolonged PR interval ST depressions, and AF

premed Continue beta blockers and antithyroid drugs Sedatives adequate Atropine , Glyco? Fentanyl,(see HR) Difficult airway ?? Then PPI s Antibiotics.

Induction GA with controlled ventilation – ideal Thiopentone – mild hypothyroid effects Suxa if emergency or difficult airway. Vec + inh. Agent Avoid sympathetic stimulation Pass armoured tube crossing obstruction. nasal RAE also works well Awake fibreoptic – rare cases.

monitoring Pulse, SPO2 BP, ECG, ETCo2 Temperature, NMJ monitoring Blood loss.

Position supine, padding behind shoulders to extend the neck 10 to 15 * head up - some surgeons ask for. Beware ET tube under the drapes. Supplement with ansa cervicalis block. Look for intraop BRADY. Eye protection

Intraop hiccups?? IV access ?? Blood leakage?? Tuck in hands proper to protect. Tight bag after intubation – is it intrathoracic thyroid

Recovery Smooth. Add “Just before end ” narcotics. Possibly look for cord movements.

Postoperative Management: 1. Airway problems Haematoma lymphatic obstruction give O2 and/or CPAP * remove sutures & open the wound * If intubation required for obstruction do reintubate

Recurrent laryngeal nerve palsy Unilateral neuropraxia not uncommon results in voice change and slight stridor Bilateral palsy rare: * 1/30,000 * flaccid cords are drawn together by the Bernouli effect during inspiration * causes complete obstruction requiring reintubation and tracheostomy

Tracheomalacia the tracheal rings can become weakened by the effects of prolonged pressure due to large goitre postoperative collapse of the trachea can cause complete obstruction rare except in areas of endemic goitre with late presentation Prolonged ventilation will help.

Tetany hypocalcaemia typically develops 24 -72 hrs postop hypoparathyroidism can present as laryngospasm monitor serum Ca++ & Mg++ Chvostoek's sign: facial muscle spasm on tapping of the facial nerve

Tetany Trousseau's sign: carpopedal spasm within 4 mins of inflating a blood pressure cuff to >systolic BP Mg++ promotes PTH release Ca++ given immediately if clinically detectable hypocalcaemia

Post op Removal of the thyrotoxic gland does not mean immediate resolution of thyrotoxicosis. The T1/2 of T4 is 7 to 8 days; therefore, β-blocker therapy may need to be continued in the postoperative period

thyroid storm intraop, but usually 6-24 hours postop hyperpyrexia, tachycardia, hypotension agitation, delirium, coma,

Treatment A,B,C,D Antithyroid drugs,Antibiotics Beta-blockade propylthioruacil 250 mg Q6H PO or NG followed by sodium iodide 1 Gm IV over 12 hours Beta-blockade esmolol infusion or propranolol 0.5 mg increments until heart rate < 100 Cooling and Cortisol 100-200 mg Q8H (possible coexisting adrenal gland suppression) Drip

Other options Cervical epidural C7 -C8 space catheter 6 ml of 0.5% bupi Superficial and deep cervical plexus block. Local and acupuncture

message Make euthyroid. Smooth induction and recovery. Plan and precisely give drugs. Use monitors. Beware of postop complications.