Issues for surgery
Hypothyroid patients undergoing surgery are predisposed to anaemia, hypotension (which can lead to cardiovascular collapse), reduced gastrointestinal motility (which can lead to post-operative ileus) and rarely life-threatening myxedema coma.
Advice in the perioperative period
Elective surgery
Continue.
Patients with known hypothyroidism or who are on treatment for hypothyroidism should have thyroid-stimulating hormone (TSH) checked pre-operatively to determine if treatment is adequate or if dose optimisation is needed before surgery. NB: It can take 4-6 weeks for thyroid function tests (TFTs) to reach steady state after thyroid hormone dose adjustment.
If TSH is significantly outside the normal limits, it may be preferable to defer elective surgery until a euthyroid state is achieved. Discuss with the patient’s endocrinologist.
Emergency surgery
Continue.
If TSH indicates patient is not euthyroid the risks of proceeding with surgery must be balanced against the risks of delaying the surgery. It is suggested that patients with mild or moderate hypothyroidism can proceed with urgent surgery provided the patient is monitored closely for signs of post-operative complications.
Post-operative advice
Patients undergoing thyroidectomy
When starting thyroid hormones after thyroidectomy a baseline (electrocardiogram) ECG should be arranged. Consult product literature for starting dose and titrate accordingly.
Patients undergoing other surgery
Continue usual dose.
If a long nil by mouth (NBM) period is anticipated or if there are concerns regarding enteral absorption see Further information.
Interactions with common anaesthetic agents
None relevant.
Interactions with other common medicines used in the perioperative period
None relevant.
Further information
Risks associated with pre-operative omission and prolonged NBM period
There is a potential risk of exacerbation of hypothyroidism if thyroid hormones are omitted perioperatively. However, the actual risk is dependent on the patient’s TFTs on admission and the length of time that they are omitted. It takes 4 – 6 weeks from being euthyroid to the patient becoming hypothyroid once thyroid hormones are stopped. If there are any concerns regarding the omission or continuation of thyroid hormones during the perioperative period, the patient’s endocrinologist should be consulted.
If oral medications cannot be given post-operatively thyroid hormones can be safely omitted for a few days. The action of liothyronine is expected to persist for 1 to 2 days after it is stopped and levothyroxine has a long half-life, approximately 6-7 days in euthyroid patients. If after this time oral medication still cannot be taken consideration should be given to prescribing an intravenous preparation if there are any concerns regarding the patient’s euthyroid state – consult product literature for preparation and dose.
Unlicensed indications e.g. resistant depression
Whilst this drug record relates to the use of thyroid hormones for endocrinology indications, perioperative continuation of thyroid hormones for other indications is not anticipated to be problematic.
References
Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 26th June 2019]
Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 26th June 2019]
Liothyronine. In: Brayfield A (Ed), Martindale: The Complete Drug Reference. London: The Royal Pharmaceutical Society of Great Britain. Electronic version. Truven Health Analytics, Greenwood Village, Colorado, USA. Available at: http://www.micromedexsolutions.com. [Accessed 26th June 2019]
Palace, M. Perioperative Management of Thyroid Dysfunction. Health Services Insights. 2017; 10: 1-5
Summary of Product Characteristics – Liothyronine Sodium BP 20microgram Tablets. ADVANZ Pharma. Accessed via www.medicines.org.uk 26/06/2019 [date of revision of the text October 2018]