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  • Section Writer: Dr. Om J Lakhani
  • Section Editor: Dr. Om J Lakhani

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• Q. Should perioperative thyroid function be done in all patients routinely?
  • No
  • Only in patients with clinical signs and symptoms of thyroid dysfunction and/or a history of prior thyroid disorder
• Perioperative hypothyroidism management
• Q. Which is the chief organ that must be taken care of in the Perioperative state in a Hypothyroid patient?
  • Cardiac involvement
  • Hypothyroidism affects cardiac function predominantly
• Q. What are the cardiac effects of hypothyroidism?
  • 1. Increase Peripheral vascular resistance
  • 2. Reduced cardiac contractility
  • 3. Reduced cardiac output
  • 4. Decreased blood volume
• Q. What are the effects of Hypothyroidism on the cardiac cycle?
  • The Projection phase is prolonged and the Ejection phase is narrowed
  • This leads to a reduction of cardiac output by 30-50%
• Q. Why is there an increase in peripheral vascular resistance?
  • T3 is thought to have a vasodilatory effect which is lost in hypothyroid patients
• Q. Why do hypothyroid patients become hypotensive on exposure to anesthetic agents?
  • This is because there is a loss of change of Cardiac output with the change of intrathoracic pressure and vasalva
• Q. What are the effect of Hypothyroidism on catecholamines?
  • There is catecholamine resistance like effect
  • Catecholamines are increased by a reduced adrenergic tone
• Q. What type of tachyarrhythmia is seen in Hypothyroid patients perioperatively?
  • Torasdes de pointes
  • Ventricular tachycardia is also sometimes seen
  • This is because of prolonged action potential
• Q. Which other test is a must in patients with Hypothyroidism as far as Cardiac function is concerned?
  • A lipid profile should be done
  • It is often abnormal and often associated with perioperative risk of cardiovascular disease
• Q. What is better in MI patients with Hypothyroidism? PTCA or CABG?
  • PTCA
  • Because hypothyroid patients undergoing CABG without achieving euthyroidism have more complications
• Q. What are the effects of Hypothyroidism on a respiratory drive?
  • Both hypoxic and hypercapnic respiratory drive is blunted in hypothyroid patients
• Q. What is its effect on respiratory muscle action?
  • Respiratory muscle weakness is generally seen in most patients
• Q. What is Hoffman’s syndrome?
  • Hypothyroidism with reduce muscle strength but increase muscle size
• Q. Which other respiratory problem is common in hypothyroid patients?
  • Obstructive sleep apnea is common in hypothyroid patients
• Q. What is the problem of medicating in Hypothyroid patients in the perioperative period?
  • Patients with Hypothyroidism have reduced drug metabolism
  • Hence drugs that reduce respiratory function often have prolonged action in these patients
• Q. What is the problem with respiratory in Hypothyroid patients who develop sepsis?
  • They have reduced respiratory surfactant development
• Q. Does T3 have some role in Lung maturation?
  • It is observed that intra-amniotic T3 administration in babies with a high risk of RDS, reduces the risk of RDS
  • PEARL: thyroid hormone induces surfactant synthesis
• Q. Is there an increase or reduced plasma volume in patients with Hypothyroidism?
  • Circulating volume is reduced
  • More fluid moves to interstitial space
  • This is because of increased capillary permeability
• Q. Which electrolyte imbalance is prominent in patients with Hypothyroidism?
  • Hyponatremia
  • ADH is often increases in these patients
• Q. What is the effect on renal function in patients with Hypothyroidism?
  • Hypothyroidism reduces the renal perfusion
  • This may lead to worsening of renal function post-op
• Q. What is the most common CBC abnormality because of hypothyroidism?
  • Anemia
  • It is seen in 25-50% of patients with hypothyroidism
• Q. What type of anemia is commonly seen?
  • Normochromic normocytic
• Q. What is the effect of hypothyroidism on bleeding?
  • It increases the tendency to bleed
• Q. Which clotting factor is dysfunctional in patients with Hypothyroidism?
  • Factor VIII and they often have acquired von Willebrand factor deficiency
• Q. What is the effect of Hypothyroidism on GI perioperatively?
  • Can often lead to ileus and constipation
  • Some people called it myxedema ileus
• Q. What is the effect on QT interval?
  • Prolonged QT interval
• Q. Can hypothyroidism cause cortical insufficiency?
  • Yes
• Q. How much time does it take perioperatively for TSH to normalize?
  • 2 weeks after T4 administration
• Q. Which is the induction agent of choice in Hypothyroidism?
  • Ketamine
  • It has positive inotropic action and increases sympathetic activity
• Q. Which agent is not preferred?
  • Thiopental is not preferred
  • It increases systemic vascular resistance
• Q. In which cases Central hypothyroidism must be suspected ?
  • Patients undergoing neurosurgery for Sellar or nonsellar mass lesions
  • Patients with a history of traumatic brain injury
  • History of cerebrovascular accident
• Q. How does hypothyroidism produce hyponatremia ?
  • By increase of ADH
  • By increase of ANF- atrial natriuretic peptide
  • by decreased RAAS activity
• Q. What is the impact of uncontrolled hypothyroidism on coagulation?
  • It reduced coagulation by decreasing Factor VIII activity
  • Increases the risk of bleeding
• Q. Give an algorithm for the management of perioperative hypothyroidism.
  • 
• Perioperative thyrotoxicosis management
• Q. What is the mainstay of perioperative thyrotoxicosis management?
  • the mainstay is good beta-blocker coverage
• Q. Are thioamides useful?
  • It is important to understand that thioamides block de novo synthesis of thyroid hormones and have little impact on already released hormone
  • Hence in immediate situations thioamides may not have a significant role
• Q. What is the advantage of PTU in this setting?
  • PTU blocks T4 --> T3 conversion in this setting
  • However, it is not popular
• Q. What is the role of iodine in this situation?
  • Iodine is useful in blocking the release of thyroid hormones
  • However, it must be given only 1 hour after giving thioamides to prevent the iodine from being used as a substrate for de novo thyroid hormone synthesis
  • This does not happen in Graves' disease but can occur in Toxic adenoma or Toxic MNG- hence in these situations it is better to give Thionamides first
• Q. What is done if a patient cannot take thionamides orally?
  • Can be given per-rectally also
• Q. What kind of beta-blockers should be preferred?
  • Long-acting ones are better than short-acting ones
  • Hence Atenolol may be better as per this article
  • Starting dose of 25-50 mg and can go up to 200 mg
  • Keep pulse <80
• Q. What type of anesthetic agent is given in a perioperative setting?
  • Sodium thiopental is preferred because it has anti-thyroid action
  • ketamine and ephedrine increase sympathetic activity and must be avoided
• Pearl:
  • hypothyroid patient- prefer Ketamine
  • For hyperthyroid patients - prefer thiopental sodium
• Q. What agent is preferred in this setting for reversing neuromuscular blockage?
  • Glycopyrrolate is preferred over atropine
  • It has less chronotropic action
  • Atropine may cause exaggerated tachycardia
• Q. Why is Aspirin avoided in these scenarios?
  • They displace thyroid hormones from TBG and hence can precipitate a storm
• Summarize the approach to thyrotoxicosis in perioperative settings
  • 

Reference:

1. Malhotra, Bhanu; Bhadada, Sanjay K.. Perioperative Management for Non-Thyroidal Surgery in Thyroid Dysfunction. Indian Journal of Endocrinology and Metabolism: Sep–Oct 2022 - Volume 26 - Issue 5 - p 428-434 doi: 10.4103/ijem.ijem_273_22 & earlier notes