Case 27 - thyroidectomy Flashcards
how is thyroid hormone produced?
- 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
what is the classic presentation of thyrotoxicosis?
- 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
How does thyroid storm differ from thyrotoxicosis?
- 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)
Are there any other similar presentations to thyroid storm?
DDx
- MH
- neuroletpic malignant syndrome
- sepsis
- pheochromocytoma
What is the tx of thyroid storm?
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
Patient has thyroid cancer and comes for surgery. What are your pre-operative concerns?
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
What are complications of thyroid surgery?
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
What are some anesthetic considerations for thyroid surgery?
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
how do you perform a cervical plexus block for thyroid sx
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