Case 27 - thyroidectomy

Question 1

how is thyroid hormone produced?

Answer 1

• hypothalamus –> produces thyrotropin releasing horomone –> ant pit
• Ant Pit –> secretes TSH
• TSH binds to receptors of thyroid to produce T3 and T4
• T3 is active form
• TSH levels good screening tools for thyroid function

Question 2

what is the classic presentation of thyrotoxicosis?

Answer 2

• thyroid hormone affect metabolic function –> facilitate biochem reactions that increase heat production and O2 consumption
• upregulates beta receptors and enhance catecholamine effects

Thyroidtoxicosis s/sx

• nervousness/anxiety
• weight loss
• tremor
• a-fib
• CHF
• MI

Question 3

How does thyroid storm differ from thyrotoxicosis?

Answer 3

• thyroid storm is a state of decompensation from thyrotoxicosis (more severe).
• precipitated by stress (MI, surgery, trauma, DKA)

s/sx

• high grade fever
• severe tachy / a fib
• CHF
• HTN
• agitation / altered mental status
• hypovolemic hypotension (fluid losses from n/v, diarrhea, profuse sweating)

Question 4

Are there any other similar presentations to thyroid storm?

Answer 4

DDx

• MH
• neuroletpic malignant syndrome
• sepsis
• pheochromocytoma

Question 5

What is the tx of thyroid storm?

Answer 5

Four principles: 1) block thyroid hormone production and secretion, 2) stop conversion of T4 to T3, 3) antagonize beta adrenergic effects, 4) supportive measures.​

1) block thyroid hormone production and secretion:

• propylthiouracil (PTU)
• Methimazole
• Iodine (blocks secretion)
  
  • see an inital increase in prouction and exacerbates thyroid storm

2) Block T4 to T3 conversion
* Hydrocortisone
3) Beta adrenergic effects

• esmolol
• propranolol
• diltiazem

4) supportive measures

• fluids, cooling –> hypotension
• demerol –> shivering
• Tylenol –> fever

Question 6

Patient has thyroid cancer and comes for surgery. What are your pre-operative concerns?

Answer 6

1) Airway

• examine airway
• listen for dysphonia (vocal cord involvement)
• imaging studies for tracheal deviation or tracheal compression

2) retrosternal goiter?

• large size can cause SVC syndrome –> facial swelling, JVD
• can compress nearby artery –> cerebreal hypoperfusion

3) is it a medullary carcinoma / concern for MEN
* medullary carncioma often coexist with pheochromocytoma (MEN 2a and 2b)
4) patient optimized medically? Euthyroid?

• beta blockers
• iodine and antithyroid meds
• Emerget surgery –> start beta blocker and antithyroid meds intra-op (do not delay sx)
• dehydrated from sweating, diarrhea, n/v –> give fluids and pressors

Question 7

What are complications of thyroid surgery?

Answer 7

most severe complication is respiratory distress.

Resp distress

• recurrent layrngeal nerve injury
  
  • ​b/l injury - vocal cords 2-3 mm from midline (unopposed adduction from sup lary n)
  • unilateral -> hoarseness
• Hypocalcemia
  
  • ​hypoparathyroidism
  • Chvostek (facial spasm); trousseau (carpal spasm)
  • assoc with larygneal muscle tetany
  • effects seen 24-72 hrs after surgery
• Tracheal compression
  
  • ​hematoma
• tracheomalacia
• phrenic N injury
  
  • ​hemidiaphragmatic paralysis

Other complications: hypothyroid, thyroid storm

Question 8

What are some anesthetic considerations for thyroid surgery?

Answer 8

1) airway
* trachea compression, hoaressness
2) HD status
* hypovolemic (fever, htn, diarrhea) –> fluids and pressors
3) acute thyoid crisis during induction

• similar s/sx to MH = increase HR, BP, EtCO2
• MH assoc with muscle rigidity and inc CPK (not seen in acute thyroid crisis)

4) muscle relaxants vs high dose opioids
* remifentanil gtt if intraop nerve monitoring
5) avoid HTN and tachycardia
6) careful eye protection (Grave disease pts); proptosis
7) smooth emergence
* avoid coughing/bucking due to increase risk of hematoma and resp distress
8) post-op resp monitor
* variety of resp distresscomplications assoc with surgery

Question 9

how do you perform a cervical plexus block for thyroid sx

Answer 9

Superficial cervical plexus

• provide sensory innervation (C1 to C4)
• main nerves: supraclavicular N (side of neck and upper chest) & transverse cervical N (neck)
• field block post border of SCM at mid point of muscle body. inject cephalad and caudad along post border of SCM.

Deep cervical plexus

• provides muscle innervation (C1 to C4)
• just above ant surface of C4 TP
• 10 cc injected, shuould spread along paravertebral space
• risks: phrenic nerve block, vertebral A injection, epidural or spinal, horner syndrome, recurrently laryng n injury