Thyroid Disease PRE-OPERATIVE ASSSESSMENT • Indications for surgery: Carcinoma, thyrotoxicosis, obstructive symptoms, cosmetic • Airway problems History : Duration of enlargement and symptoms of obstruction (hoarseness, stridor, dysphagia, positional dyspnoea) Examination : Position of trachea and other intubation problems X-ray I CT : Position and narrowing of trachea and retrostemal extension Indirect laryngoscopy I nasendoscopy : vocal cord movement • Thyroid state : (Assess adequacy of control) History : Regression of symptoms with therapy Examination : Sleeping pulse Investigations : TSH, T /f 4 • Cardiovascular status : resting pulse rate, rhythm, blood pressure, ECG • Drug therapy: beta blockers, carbimazole, Lugol's iodine PRE-OPERATIVE PREPARATION • Conversion to euthyroid state is mandatory. • Give Lugol's iodine to minimize bleeding • Blood for grouping, screen for antibodies and save. INTRA-OPERATIVE PERIOD Aims • Maintain a clear airway at all times. • Provide smooth anaesthesia. • Minimize bleeding. • Avoid complications of the thyroid state. Intubation If difficult intubation is anticipated attempt awake intubation under LA. If i. v. or gaseous induction, check ability to ventilate before administering relaxant. Use re-inforced ETT and secure with plaster (not ties). Position neck extension, shoulder and head rest, 20° head up tilt, arms by the side with i.v. extension tube. Eye padding and cover especially for exophthalmos.
Maintenance Give IPPV with non depolarizing muscle relaxants to ensure adequate ventilation. Obtund laryngeal reflexes to avoid too deep a level of anaesthesia. Minimize bleeding: head up tilt, smooth anaesthesia, low Paw, ETC02 30-35mm Hg Bupivacaine infiltration of incision for analgesia Extubate deep without bucking POST-OPERATIVE COMPLICATIONS • Haemorrhage may occur early in the post operative period. May present as stridor as tense haematomas cause laryngeal oedema due to compression of the veins and lymphatics. Needs emergency surgery. Cut sutures of skin, muscles and deep fascia to relieve the pressure, if cyanosed. Intubate and keep the ETT in for at least 24 hours till the oedema subsides. • Hoarseness due to trauma by ETT or recurrent laryngeal nerve damage. Humidified oxygen, steam inhalation, dexamethazone 8 mg i.v. • Stridor after extubation o Laryngeal oedema (maybe immediate or delayed) Ligature of veins in neck and haematoma predispose to oedema Management: (see page 20. 3) o Tracheal collapse (immediate) Due to tracheomalacia (long standing goiter) occurs soon after extubation. If predicted before, deflate ETT cuff, check air leak after partial withdrawal. Re-intubate and keep endotracheal tube in place for 72 hours. Consider tracheostomy ifthe problem recurs. o Nerve damage (immediate) Bilateral partial damage paralyses the abductors causing unopposed adduction. Total damage causes a cadaveric position with some tension of the cords. Re-intubate and consider nasendoscopy and tracheostomy. • Thyrotoxic crisis (see page 8.16) • Tetany due to hypoparathyroidism develops after 24 -48 hours. Symptoms : peri-oral tingling. twitching, carpo-pedal spasms, seizures Trousseau's sign: BP cuff inflation causes spasms. Chvostek's sign: tapping facial nerve causes facial twitching Give calcium gluconate i. v. with oral Ca and vitamin Din the long term.
Thyrotoxicosis Symptoms : Excitability, tremors, sweating, weight loss, palpitations CVS signs : Tachycardia, atrial fibrillation , hypertension, heart failure Other signs Neuropathy, proximal myopathy, exophthalmos and finally coma ANAESTBF.SIA Carbimazole 30mg/day given to achieve euthyroid state before elective surgery to avoid precipitating a thyroid crisis, and Lugol's iodine 10 days prior to reduce vascularity. • Heavy premedication to relieve anxiety (diazepam) and excitability • Beta block throughout the peri-operative period to maintain heart rate <90/min Atenolol 50-1 OOmg morning dose covers 24 hours Propranalol 30-60mg tds (high dose required due to upregulation) Complications • Dysrh)1hmias Bradycardia due to beta blockers should be treated with atropine. Tachyarrhythmias occur if control is poor. Esmolol infusion is useful. Atropine and adrenaline infiltration are contraindicated. Isoflurane is preferable as halothane can exacerbate the dysrhythmias. • Bleeding due to increased vascularity of the gland should be anticipated. • Damage to eyes due to proptosis • Thyrotoxic crisis ''thyroid storm" Signs during anaesthesia : Tachycardia, atrial fibrillation, ventricular tachycardia, and cardiac arrest A hyper metabolic state which resembles malignant hyperthermia Pulmonary oedema may occur due to increased cardiac output, tachycardia or atrial fibrillation, increased blood volume and depression of myocardial function. Signs in the post operative period : Confusion, restlessness, mania, pyrexia and coma Tachycardia, hypertension, nausea, vomiting, diarrhoea and abdominal pain Treatment • Carbimazole 60-120 mg orally or by naso gastric tube (acts within 1 hour). • Kl Na iodide 0.3ml oral tds should only be given lh after carbimazole • Propranolol 20-80 mg 6 hourly orally or 1-5mg i.v. to reduce heart rate • Hydrocortisone 200mg 6 hourly i.v. • Fluids including dextrose i. v. with active cooling • Sources of infection should be sought and empirical antibiotics given
Hypothyroidism Causes : Autoimmune disease, post-thyroidectomy or I 131, pituitary disease Euthyroid state should be achieved prior to surgery with thyroxine 100-200µg /day. Oral thyroxine takes 10 days to take effect, and may precipitate myocardial ischaemia. Emergency surgery may require i. v. thyroxine but myocardial ischaemia may occcur. Since hypothyroidism is often associated with adrenocortical insufficiency, steroid supplementation is recommended in the untreated hypothyroid patient. PROBLEMS 1. Difficult intubation due to a large tongue 2. Reduced blood volume, cardiac output, heart rate, with possible IHD, so that dehydration, haemorrhage and fluid overload are poorly tolerated. 3. TPPV with relaxants is the best technique, but hypocarbia must be prevented. i.v. induction and volatile agents may cause profound hypotension. Narcotics may cause prolonged respiratory depression and delayed recovery. 4. Tendency to hypothermia (use warm blankets and i.v. fluids) 5. Tendency to hypoglycaemia 6. Needs steroid cover (hydrocortisone lOOmg) during anaesthesia. 7. Recovery may be delayed and ventilatory support may be required.