Hypothyroidism
Anesthesia Implications
Anesthesia Implications
Surgery cancellation – Severe hypothyroid or hyperthyroid conditions, named myxedema and thyroid storm respectively, should always be cancelled in ELECTIVE cases until the patient is brought as close to euthyroid conditions as possible.
Difficult airway – Large tongue, goiter, and swollen vocal cords are common in these patients and are risks for a difficult airway.
Goiter – Textbooks say that if the patient has a goiter, you should aim for an awake intubation as the best option, and then a spontaneously breathing intubation as the second best.
Aspiration risk – metabolic slowing includes slowing of the GI tract
Hypotension risk – metabolic slowing includes reduced SVR, contractility, HR, SV. This implies use of sympathomimetics (ie. ephedrine) to improve the array of symptoms. Phenylephrine is generally avoided because of the concurrent drop in HR (baroreceptor reflex).
Volatile anesthetics onset – FASTER
MAC – Hypo/Hyperthyroid issues do NOT affect MAC
Higher sensitivity – the more lethargic/slowed/weak the patient is, the more sensitive they will be to anesthetic drugs and neuromuscular blockers
Consider D5NS – These patients typically have impaired clearance of free water – so this is good choice when the patient is hyponatremic.
Slowed offset of drugs – slower metabolism takes longer to excrete drugs cleared by renal/hepatic systems
Labs
Thyroid-stimulating hormone (TSH) – Normal adult range is 0.4-4.5 mIU/mL. Increased levels indicate HYPERTHYROID, while decreased levels indicate HYPOTHYROID.
T4 – Otherwise known as thyroxine level – Normal adult range is 5.0 – 11.0 ug/dL. Low T4 indicates hypothyroidism, whereas high T4 levels indicates hyperthyroidism.
FT4 – Free T4 or free thyroxin – Normal adult range is 0.9 – 1.7 ng/dL. Some proteins may bind to T4, which causes a bad reading. This test is meant to give a more accurate reading in spite of those factors. Low levels indicate hypothyroidism, whereas high levels indicate hyperthyroidism.
T3 – triiodothyronine – Normal range is 100 – 200 ng/dL. Low levels indicate hypothyroidism, whereas high levels indicate hyperthyroidism. Most commonly used in the diagnosis/management of hyperthyroidism.
FT3 – Free triiodothyronine – Normal range: 2.3 – 4.1 pg/mL. Some proteins may bind to T3, which causes a bad reading. This test is meant to give a more accurate reading in spite of those factors.
Additional Notes:
Levothyroxine is the long-term drug used to manage this condition – a great indication that the patient has this condition if not disclosed in the preop interview
Hines. Stoelting’s anesthesia and co-existing disease. 7th edition. 2018. p. 461-463
Nagelhout. Nurse anesthesia. 6th edition. 2018. p. 821-822
Cleveland Clinic. Thyroid blood tests. 2021. link
