Anaesthetic management of a patient with hyperthyroidism for total thyroidectomy

J. Sivagurunathan^*, S. Khaja Mohideen, K. Senthil Kumar

Consultant Anaesthesiologists, Department of Anesthesiology, Kauvery Hospitals, Trichy

Abstract

The most feared complication that can occur in unoptimised or uncontrolled thyrotoxic patient is thyroid storm (TS). TS is an intense life-threatening endocrine emergency that resembles magnified features of thyrotoxicosis. Thyrotoxicosis refers to the clinical condition occurring due to inappropriate activation of thyroid hormone in tissues. It may be triggered by an acute stress event such as abrupt stoppage of anti-thyroid drugs, surgery or infection. Here we report a case of patient with Grave’s disease not controlled with medication posted for total thyroidectomy under general anaesthesia.

Keywords: Hyperthyroidism; Thyrotoxicosis; Thyroid storm; Anti-thyroid drugs.

Case Presentation

60-year-old female with hyperthyroidism for past 2 years came to hospital with complaints of tremors. Thyroid profile done in February 2023 showed Free T3 >20pg/ml, Free T4 8.93pg/ml and TSH of 0.00 micro IU/ml. Pre-admission thyroid profile done on 16/03/24 showed Free T3- 12.15pg/ml, Free T4- 4.46pg/ml and TSH- 0.00 micro IU/ml. Patient had agranulocytosis, may be Tab. Carbimazole induced, and hence the drug was stopped. On admission on 18/03/24 all routine surgical profile was done and thyroid profile was repeated at regular intervals.

Date	Free T3(pg/ml)	Free T4(pg/ml)	TSH(micro IU/ml)
21/03/24	6.93	2.85	-
23/03/24	6.81	2.56	0.008
25/03/24	5.35	2.3	0.008

Patient was started on T. Lithium Carbonate 300mg q8h, T. Propranolol 20mg 2 BD and 5% lugol’s iodine 1ml q6h. Since euthyroid state was not achieved with medical management, total thyroidectomy was planned under general anaesthesia on 26/03/24 under ASA -PS Ⅲ. On the day of surgery, operation room was prepared and anti-thyroid storm measures like cold intravenous fluids, cooling blanket, short acting β blocker, direct vasopressor and propylthiouracil were kept ready.

In operating room, all routine and standard monitors were connected and arterial cannulation was done in left radial artery for invasive blood pressure monitoring. Surgery was performed under balanced general anaesthesia and lasted for approximately 130 minutes and was uneventful throughout. At the end of the procedure patient was extubated and shifted to post anaesthesia care unit for observation. On Post operative day (POD) -1 Serum calcium was 7.85mg/dl and S. PTH was 26.6 pg/ml. Patient was discharged on POD-2 with oral calcium tablet and reviewed on POD-9 and thyroid profile on POD-9 was Free T3- 1.64pg/ml, Free T4-0.87pg/ml and TSH of 0.00μIU/ml.

Discussion

Thyroid gland’s main function is to convert iodine into thyroid hormones. Thyroid cells combine iodine and tyrosine to form T3(triiodothyronine) and T4(thyroxine). Normal thyroid gland produces 80% T4 and 20% T3. Majority of T3 (bioactive form) is produced by enzymatic deiodination of T4 in the peripheral tissues by iodothyronine deiodinases.

Hyperthyroidism is a condition where there is increased synthesis and secretion of thyroid hormone from thyroid gland. Symptoms of thyrotoxicosis include heat intolerance, palpitations, anxiety, fatigue, weight loss, muscle weakness and irregular menstrual cycles in females. Clinical signs include warm and moist skin, tremors, tachycardia and lid lag.

Treatment modalities for hyperthyroidism

Treatment choices for hyperthyroidism includes

Anti-thyroid drugs- Thionamides (Carbimazole, Methimazole, propylthiouracil)
Radioactive iodine
Thyroidectomy

Antithyroid drugs

It’s been around 80 years since the successful administration of thionamides (thio uracils and imidazoles) in hyperthyroid patients for its inhibitory effects on thyroid hormones. Compared to radioactive iodine (RAI), anti-thyroid drugs (ATD) are most preferred in many parts of the world.

Thionamides inhibit the formation of thyroid hormone by inhibiting thyroid peroxidase to prevent incorporation of iodine into tyrosine residues of thyroglobulin. In addition to blocking synthesis, PTU also inhibits the peripheral de-iodination of T4 & T3.

Thionamides are not available in parenteral preparations. Serum thionamides level reaches peak after 1-2 hr of ingestion.

Methimazole is the desired choice of drug in many situations considering its efficacy and lesser side effects. But has some teratogenic effects – Aplasia cutis, choanal atresia, craniofacial defects and esophageal atresia

There are two strategies available for ATD therapy

Titration regimen – monotherapy with ATD
Block & replace regimen i.e., high dose ATD combined with levothyroxine – associated with higher rate of ATD adverse effects.

Primary goal of antithyroid drugs is rapid restoration of euthyroid state with minimal side effects. Starting dose of methimazole is 5-40 mg in 1-2 divided dose and for PTU it is 100-800mg in 2-3 divided doses based on degree of thyrotoxicosis, Free T4, Free T3, symptoms and goiter grade.

ATD can be down titrated to a daily maintenance dose of 2.5 to 10mg of methimazole or 50 – 150 mg of PTU over several months. Dose titration should be based on periodic biochemical and clinical condition. ATD dose can be reduced by 30-50% if euthyroid state is achieved.

In patients with grave’s disease thyroidectomy is preferred when medical management is inadequate or unresponsive. Preferably patient should be brought to euthyroid state whenever possible. Fewer patients are incapable of taking anti-thyroid drugs due to serious untoward reactions like agranulocytosis, hepatitis, aplastic anemia and lupus like syndrome.

Thyroid storm

Thyroid storm can develop in untreated or poorly controlled hyperthyroidism but more commonly triggered by any stressful events such as abrupt discontinuation of antithyroid drugs, infection, surgery, trauma, preeclampsia, hyperemesis gravidarum, diabetic ketoacidosis and acute iodine overload.

The diagnosis of thyroid storm is challenging due to the nonspecific features and rarity. Diagnosis is further hampered if the patient is under general anaesthesia during surgery. No laboratory abnormalities are specific to thyroid storm.

Mental state changes and gastrointestinal dysfunction will not be evident in patients under general anaesthesia. Tachycardia under anaesthesia has many causes like awareness, haemorrhage, hypovolemia, hypotension, bladder distension or pain. Pyrexia and rise in end tidal carbon dioxide may be a sign of sepsis, neuroleptic malignant syndrome, pheochromocytoma, malignant hyperthermia or anticholinergic syndrome. Hence the diagnosis of thyroid storm is partially a diagnosis of exclusion.

Management of intraoperative thyroid storm

Once the diagnosis of thyroid storm is made, prompt initiation of treatment is utmost important. Management principles can be divided into general and specific considerations as listed in the tabular column below

Optimization prior to surgery

If an elective surgery is planned in patients with hyperthyroidism or thyrotoxicosis, it is advisable that surgery and anaesthesia be postponed until the patient is clinically and biochemically euthyroid. Achieving a euthyroid state may take anytime between 6 weeks to 18 months. In case of emergency surgery, where optimisation is not possible, perioperative thyroid storm should be anticipated and adequately prepared.

Premedication should include beta-blocker (propranolol 0.1-0.15 mg/kg intravenously), antithyroid drug (propylthiouracil 200-400mg orally), and a corticosteroid (hydrocortisone). whenever possible regional anaesthesia and peripheral nerve block should be preferred over general anaesthesia. If the surgical procedure mandates general anaesthesia, it is vital to ensure

That intubation response is blunted
Adequate analgesia and depth of anaesthesia is maintained
Smooth emergence and extubation are performed.

References

A.Farling, Thyroid disease, BJA: British Journal of Anaesthesia, Volume 85, Issue 1, 1 july 2000, pages 15-28.
Mehmet l. Buget, Bilge Sencan, et al. Anaesthetic management of a patient with thyrotoxicosis for non-thyroid surgery with peripheral nerve blockade. Case Rep. Anesthesiol. 2016; 2016:9824762. doi: 10.1155/2016/9824762.
Hengameh Abdi, Atieh Amouzegar, et al. Antithyroid drugs. Iran J Pharm Res. 2019 Autumn; 18(suppl 1): 1-12. doi: 10.22037/ijpr.2020.112892.14005.
Bourcier S, Coutrot M, Kimmoun A, et al. Thyroid storm in the ICU: a retrospective multicenter study. Crit Care Med. 2020; 48:83-90.
Terefe M, Belay BY, BY, Addisu NY, et al. Perioperative management of the thyrotoxic patients: a systematic review. Ann Med Surg. 2022; 81:104487.

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Anaesthetic management of a patient with hyperthyroidism for total thyroidectomy