Anesthesia for Endocrine Surgery Flashcards
The thyroid gland is formed by two lateral lobes connected by the _________ at about the second tracheal ring
Thyroid Isthmus
Thyroid Isthmus is ANTERIOR to the trachea
What sensory nerves innervate above the vocal cords?
Internal Laryngeal Branch of Superior Laryngeal Nerve
What sensory nerves innervate below the vocal cords?
Recurrent Laryngeal Nerve
Motor innervation to most of the intrinsic muscles of the larynx is supplied by which nerve?
This nerve does not innervate which structure of the larynx?
- Recurrent Laryngeal Nerve
- Cricothyroid Muscle
What nerve supplies motor innervation to the cricothyroid muscle?
External Laryngeal Branch of Superior Laryngeal Nerve
Colloid-filled follicles store what substance?
Thyroglobulin
Parafollicular cells produce what substance?
Calcitonin
What mineral fuels the production of thyroid hormones?
Iodine
What are the peripheral effects of Thyroid Hormone?
- Heat generation
- Stimulates ATP formation
- Influences flux of ions
- Stimulates metabolic processes ( Basal metabolic rate, protein synthesis, regulation macro metabolism)
What are the cardiac effects of Thyroid Hormone?
- ↑ LV contractility
- ↑ LV EF
- Tachycardia
- ↑ SBP and ↓ DBP
- Chronic hyperthyroidism can lead to Heart Failure, AF, Dysrhythmias
Parasympathetic innervation of the thyroid comes from which nerve?
Vagus Nerve
Sympathetic innervation of the thyroid comes from which nerve?
Superior, Middle, and Inferior Ganglia of the Sympathetic Trunk
Sympathetic nerve fibers will run through the thyroid via what plexus?
- Cardiac periarterial plexus
- Superior and inferior thyroid plexus
What hormone regulates thyroid gland secretion?
Where does this hormone come from?
- TSH
- Anterior Pituitary Gland
What are the three sources of blood supply to the thyroid gland?
- Superior thyroid artery (branch of ext carotid)
- Inferior thyroid artery (branch of subclavian)
- Thyroid ima
Venous drainage location of the thyroid gland.
- Superior thyroid vein (IJ)
- Middle thyroid vein (IJ)
- Inferior thyroid vein (brachiocephalic)
What is the normal level of TSH?
0.4-5.0 milliunits/L
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Hyperthyroidism
T4:
T3:
TSH:
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Hyperthyroidism
T4: Elevated
T3: Elevated
TSH: Normal/Low
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Primary Hypothyroidism
T4:
T3:
TSH:
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Primary Hypothyroidism
T4: Decrease
T3: Decrease/Normal
TSH: Increase
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Secondary Hypothyroidism
T4:
T3:
TSH:
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Secondary Hypothyroidism
T4: Decreased
T3: Decreased
TSH: Decreased
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Pregnancy
T4:
T3:
TSH:
Give the anticipated lab values for the following thyroid disease/condition.
Dx: Pregnancy
T4: Elevated
T3: Normal
TSH: Normal
What type of cancer has the fastest rising incidence?
Thyroid cancer
What factors determine the prognosis of thyroid cancer?
- Age of patient
- Sex
- Presence of metastases
- Tumor size
- Local invasion
What is the mainstay of thyroid cancer?
Surgical Treatment
Surgical options for thyroid cancer
- Lobectomy
- Total thyroidectomy
- Total thyroidectomy plus lymph node dissection
What are the risks of thyroid surgery?
- RLN injury (biggest risk)
- Hypoparathyroidism (mostly temporary)
- Bleeding
Unilateral RLN - hoarseness, global sensation, temporary
Bilateral RLN - AIRWAY issue
A syndrome caused by excessive secretion of TH when there is an overactive thyroid gland.
HYPERTHYROIDISM
Clinical Manifestation of Hyperthyroidism
Thyrotoxicosis
Cause of Hyperthyroidism
- Graves disease (most common)
- Thyroid adenoma
- Thyroid carcinoma
- TSH pituitary adenomas
- Iatrogenic
Symptoms of Hyperthyroidism
- Tachycardia/ Palpitations
- Nervousness
- Heat intolerance/ ↑ Sweating
- Fatigue and weakness
- ↑ Metabolism/ Weight loss
- Hyperdefication
Signs of Hyperthyroidism
- Thyroid enlargement
- Tachycardia
- Atrial fibrillation
- Systolic hypertension ( wide pulse pressure)
- Eye signs (exophthalmos)
Which gender is more prone to hyperthyroidism?
Female (age 20-40)
Possible treatments for hyperthyroidism
- Anti-thyroid Drugs
- β-blockers
- Steroid/ Glucocorticoids
- Radiation
- Surgery
Normal T4 level
60-120 nmole/L
Factors that increase T4 level
- Hyperthyroidism
- Thyroditis
- Early hepatitis
- Pregnancy
- Oestrogen therapy
- Exogenous T4
Factors that decrease T4 level
- Hypothyroidism
- Androgens
- Salicylates
- Sulphonamides
Normal T3 level
0.92-3 nmole/L
Factors that increase T3 level
Hyperthyroidism
Factors that decrease T3 level
- Hypothyroidism
- Cirrhosis
- Uremia
- Malnutrition
What condition will increase TSH level?
Primary Hypothyroidism
What condition will decrease TSH level?
Hyperthyroidism
Give examples of Anti-thyroid drugs.
MOA.
- PTU
- Methimazole
- Carbimazole
- MOA: Inhibition of synthesis of TH by blocking the action of peroxidase, also inhibits the T4 → T3 conversion
MOA of how glucocorticoids treat hyperthyroidism
- Decreases Release of hormone
- Inhibits conversion T4 → T3
MOA of how radioactive iodine treats hyperthyroidism
- Destroys follicular cells
- Remission Rate: 80% +
- 40% - 70% hypothyroid within ten years
What is the last resort for hyperthyroidism treatment?
- SURGERY
- Remission 95%
- 10% - 30% hypothyroid w/i 20 yrs
Indications for Thyroid Surgery
- Large goiter
- Compressive symptoms
- Kids
- CA pt or suspicious nodules
- Allergy to anti-thyroid drugs
- Pregnant and those with a desire to conceive soon
- Moderate to severe ophthalmopathy
- Cosmetic desire of the patient
Pre-op assessment for patients undergoing thyroid surgery
- Assessment of upper airway & tracheal deviation
- Thoracic inlet X-ray, CT scan
- Patient must be EUTHYROID
- Use anti-thyroid drugs and β-blockers
- Resting pulse rate 85-90 bpm
What drugs should you avoid during thyroid surgery?
- Atropine
- Pancuronium
- Halothane
- Ketamine
These drugs may activate the SNS
Drug of choice for induction of a hyperthyroid patient.
- Etomidate
- Propofol
- Barbituates
Choice of muscle relaxant for hyperthyroidism
- Atracurium
- Vecuronium
Cardio stability
Choice of VA for hyperthyroid patient
Isoflurane
Cardio Protective
What type of infusion will typically be started on thyroid patients to keep HR in check?
Esmolol infusion 50-150 mcg/kg/min
What is a postoperative concern for thyroid surgery patients?
Thyroid storm/ crisis
An acute exacerbation of hyperthyroidism with excessive release of thyroid hormone
When will the patient experience a thyroid storm/ crisis?
Onset can be intraoperative or 6-24 hours after surgery
Signs and Sx of Thyroid Storm
- Hyperpyrexia,
- Tachycardia or atrial fibrillation
- Hypotension
- Vomiting/ Dehydration,
- Tachypnea
- Acute abdominal pain
- Agitation/ psychosis
Need to R/O: MH, Pheochromocytoma, or Light Anesthesia
How will Thyroid Storm be managed?
- PTU
- Carbimazole
- Sodium Iodide/ Potassium Iodide
- Steroids
- Receptor blockade (propanolol)
- Tx Cardiac failure (diuretics, dig, O2)
- Tx Hyperpyrexia
- Tx Dehydration (IV fluids)
What is the triad of concerns for patients undergoing thyroid surgery?
- Airway obstruction
- Tetany
- RLN Injury
What are the possible causes of airway obstruction in a hyperthyroid patient?
- Neck hematoma w/tracheal compression
- Tracheomalacia
- Incomplete reversal of NDMR
- CNS depression
Clinical Manifestation of Tetany
- Circumoral tingling
- Paraesthesia
- Laryngeal spasm,
- Chvostek & Troussau signs
Tetany can result in what type of acid-base imbalance?
Respiratory Alkalolsis
Management for Tetany
- Calcium Replacement
- Slow injection of 10% calcium gluconate 10 mL IV
Clinical Manifestation of Unilateral RLN Injury
- Weak and horse voice croaking
- Coughing when drinking
- Aspiration
- Usually no O2 desaturation
Management of Unilateral RLN Iinjury
- Reintubation & observe for 6-12 minutes
- If the normal function of cords is not returned within 6- 12 minutes Teflon injection
- Speech therapy
Clinical Manifestation of Bilateral RLN Injury
- Usually manifests immediately after extubation.
- Laryngeal stridor
- Acute respiratory distress
- Phonation lost
- O2 desaturation
Management of Bilateral RLN Iinjury
- Reintubation/ muscle paralysis
- Hydrocortisone 100 mg TID
- If extubation fails after 48 hrs, Tracheostomy is warranted
What is Hypoparathyroidism?
Condition when the body tissues are exposed to decreased circulating concentration of thyroid hormones
Causes of Hypoparathyroidism
- Destruction of the thyroid gland
- CNS dysfunction
Management of Hypoparathyroidism
- High dose calcium
- Calcitriol
- Vitamin D
- These are often given to prevent hypocalcemia during thyroidectomy
What lab value can be used to predict hypocalcemia?
Decrease PTH
Signs and Sx of hypothyroidism
- ↓ Metabolic activity
- Cold intolerance
- Lethargy
- ↓ CO up to 40%
- Prolonged circulation time
- Narrow pulse pressure
- ↑ PVR to decrease heat loss
What medication is given to treat hypothyroidism?
Levothyroxine
Severe form of hypothyroidism
Myxedema
Clinical manifestation of Myxedema
- Stupor
- Coma
- Hypoventilation
- Hypotension
- Hypothermia
- Hypernatremia
Myxedema is a medical emergency with a mortality rate of ________%
25-50%
What induction agents will be used for Myxedema?
- Ketamine is a preferable induction agent
- If no severe CVS depression, propofol can be used
- When using relaxants keep in mind that there is a coexisted skeletal muscle weakness, decrease the dose
Myxedema Anesthetic Management
- Hydrocortisone 100mg IV followed by 25 mg IV QID
- Fluid and Lytes Supplementation
- Avoid Hypothermia
- Awake Extubation
- Consider Ketorolac
- Regional Anesthesia preferred over GA
What is the NMBD of choice for Myxedema?
Pancuronium
Pancuronium can precipitate catecholamine release
Factors that cause delayed emergence for myxedema patients
- Hypothermia
- Respiratory Depression
- Slow Drug Biotransformation
What is the best plan to establish an airway if a patient presents with a goiter?
Order or study imagining to determine an airway plan
Which nerve is usually monitored during intraoperative endocrine surgery?
RLN
What type of ETT is used for nerve monitoring for endocrine surgery?
Neural Integrity Monitor (NIM) ETT
Goals of Intraoperative Nerve Monitoring
- Prevent Nerve Injury
- Warn when the nerve is stressed
- Anatomical identification of nerve
Outcomes of Nerve Monitoring
- Does not prevent injury to RLN
- Help confirm that a nerve is functionally intact prior to proceeding to the other side
- Help the surgeon improve nerve handling
- Can have both false-positive and false-negative signals
Catecholamine-secreting adrenal tumors arising from chromaffin cells of the adrenal medulla
Pheochromocytoma
Mass on the kidney
What is a paraganglioma?
Extra-adrenal pheochromocytoma
The adrenal medulla stores what hormone?
- Catecholamines
- 80% as epinephrine
- 20% as norepinephrine
Catecholamines (Epi/NE) are derived from which amino acid?
Tyrosine
Effects of Catecholamines
- Increase glycogenolysis
- Increase gluconeogenesis
- Increase glucagon secretion
- Decrease glucose uptake
How are catecholamines cleared from the body?
- Urine
- Peripheral enzymatic degradation
- Uptake at nerve endings
Receptor: β1
Activity:
Symptoms:
Receptor: β1
Activity: Chronotrope, Inotrope, Lipolysis, Sweat Release
Symptoms: Tachycardia, Diaphoresis
Receptor: β2
Activity:
Symptoms:
Receptor: β2
Activity: SM relaxation, vasodilation, glycogenolysis, gluconeogenesis, insulin secretion
Symptoms: Hypotension, Hyperglycemia
Receptor: α1
Activity:
Symptoms:
Receptor: α1
Activity: SM contraction, glycogenolysis, gluconeogenesis, Na+ reabsorption, sweat release.
Symptoms: Hypertension, Hyperglycemia, Diaphoresis
Receptor: α2
Activity:
Symptoms:
Receptor: α2
Activity: Inhibit the release of NE, vasoconstriction, stimulates cognition
Symptoms: Pallor
Signs and Sx of Pheochromocytoma
- HTN
- Tachycardia
- HA
- Diaphoresis
- N/V
- Anxiety
Pretty much the feeling you get during your first day at clinical
Dx of Pheochromocytoma
- Frequently asymptomatic
- Incidental CT Scan
- Confirmed by biochemical testing
What are the Biochemical studies for Pheochromocytoma?
- Plasma Metanephrines
- 24 hour catecholamines
- Elevated serum epinephrine
What substance will be measured in the 24-hour urine catecholamines test?
- NE
- EPI
- Dopamine
- Metabolites (Metanephrine, Normetanephrine, Vanillylmandelic Acid)
Board Question
Where can Phenylethanolamine N Methylating Enzyme be found?
- Adrenal Medulla
- Organ of Zuckerkandl
Perioperative Management Goal of Pheochromocytoma
- Treat hypertension w/ α-blockade
- Volume expansion
- Control cardiac arrhythmia w/ β-blockade
What two main drugs are used for α-blockade for pheochromocytoma?
- Phenoxybenzamine
- Doxazosin
When will Phenoxybenzamine be initiated before resection of the pheochromocytoma?
1-3 weeks before resection
What S/E may the pheochromocytoma patient experience once they are adequately α blocked?
- Fluid Retention
- Weight Gain
- Orthostatic Hypotension
When should β-blockade be initiated for pheochromocytoma patients?
AFTER α-blockade
If beta blockers are given first, it would block the beta receptors of the vascular smooth muscle repsonsible for vasodilation. This will cause a net effect of vasoconstriction which can worsen hypertension or pulmonary edema.
What anesthetic drugs should be avoided in pheochromocytoma patients b/c they can precipitate catecholamine release?
- Ketamine
- Pancuronium
Which anesthetic agents are the least cardiac depressant?
- Isoflurane
- Enflurane
- Nitroprusside
- Phentolamine
During which trimester will a pheochromocytoma be resected in a pregnant patient?
During the 2nd trimester
If pheochromocytoma is noted late into pregnancy, what should be the delivery method?
- C-section
- Vaginal delivery may precipitate a hypertensive crisis
What cells make up the parathyroid gland?
- Chief Cells (majority of parathyroid gland)
- Oxyphil Cells
- Fat Cells
What does the Chief Cell secrete?
PTH
When do Oxyphil cells begin to appear?
Puberty
How many amino acids make up the PTH?
84 amino acids
When will PTH be secreted?
PTH will be secreted from the parathyroid gland increase to low calcium levels.
Maintenance of Ca2+, Phos, and Mag homeostasis is under the influence of which two polypeptide hormones:
- Parathyroid hormone(PTH)
- Calcitonin
Which hormone acts directly on the bones and kidneys and indirectly on the intestine. Its production is regulated by the concentration of serum-ionized calcium.
PTH
Which hormone is released by the “C” cells (Para follicular cells in the thyroid gland) in response to small increases in plasma ionic calcium. It acts on the kidneys and bones to restore the level of calcium to just below a normal set point, which, in turn, inhibits the secretion of the hormone.
Calcitonin
Effects of PTH
- ↑ Activity of osteoclasts causing the release of Ca from bone
- ↑ Ca reabsorption from urine in the kidney
- ↑ Urinary phosphate excretion
- ↑ renal production of Vitamin D3 (calcitriol)
- ↑ GI absorption of calcium
What is the most common cause of hypercalcemia in outpatients?
Primary Hyperparathyroidism
Which gender is more likely to have hyperparathyroidism?
Females are 3x more likely
Causes of Primary Hyperparathyroidism?
- 85% caused by single adenoma
- 10% diffuse hyperplasia
- 5% multiple adenomas
Signs and Sx of Primary Hyperparathyroidism?
- Renal
- Skeletal
- Abdominal
- Cardiovascular
- Psychiatric and neuromuscular
Stones, Bones, Groans, Moans
Neuropsychiatric Manifestations
of Primary Hyperparathyroidism.
- Easy fatiguability
- Depression
- Inability to concentrate
- Memory problems
- Proximal myopathy
What is the only cure for Primary Hyperparathyroidism?
Surgery
Effects of Bisphosphonates on Hyperparathyroidism
- Bisphosphonates can lower calcium
- May increase PTH
Effects of Cinacalcet on Hyperparathyroidism
- Cinacalcet lowers calcium
- Modestly lowers PTH.
Why is surgery to most optimal route for most hyperparathyroidism?
- When end-organ damage occurs, it is irreversible
- Neuropsychiatric symptoms are common and often subtle
- The operation is very effective and has minimal morbidity
What is involved in the surgical treatment for Hyperparathyroidism
- Removal of all affected glands (one or more adenomas)
- For diffuse hyperplasia, removal of all but approximately 50-70 mg of parathyroid tissue
Which hyperparathyroidism surgery has a 100% success rate?
- Directed parathyroidectomy
- Requires intraoperative PTH monitoring (need an arterial line)
What are the different ways to image the parathyroid gland?
- Sestamibi scan
- Ultrasound
- CT (4D CT)
- MRI
Overall sensitivity around 70-80%.
All very poor at multi-gland disease
Preoperative Assessment for Hyperparathyroidism Surgery
- Assess volume status to avoid hypotension during induction
- Hydration w/ NS and diuresis with Lasix to decrease serum Ca levels
- Bone fragility
- Labs and Comorbidities
Anesthetic Considerations for Hyperparathyroidism Surgery
- Titration of muscle relaxants(pre-existing muscle weakness)
- Avoid hypoventilation, acidosis ↑ ionized calcium → cardiac dysrhythmias.
Tracheal manipulation during dissection - Proper patient positioning
- Smooth emergence
- Evaluate for RLN damage
- Pain control
Post-operative complications for Hyperparathyroidism Surgery
- Neck hematoma
- Laryngeal swelling/ glottis edema
- RLN damage
- Hypocalcemia= tetany
- Acute arthritis
- Metabolic acidosis with deterioration of renal function (transient)
- PARATHYROID CRISIS
What Ca2+ level is considered a Parathyroid Crisis?
> 15 mg/dl
Parathyroid Crisis Management
- Requires hydration (dilutes Ca++)
- Followed by diuresis with loop diuretic (promote Ca++ & H2O excretion)
- Glucocorticoids
- Calcitonin
- Dialysis
What is the purpose of intraoperative PTH Assay?
To confirm that all abnormal parathyroid tissue has been removed w/o the need to physically examine all glands
List the times you will draw a PTH during surgery.
- After anesthesia induction but before neck incision (0-min or baseline)
- During the manipulation of a suspected hyperfunctioning gland (pre-excision)
- 5-min after gland excision
- 10-min after gland excision
- 20-min after gland excision
A PTH decline of what percent indicates a successful parathyroid gland excision.
> 50% decline in PTH
Outcomes after hyperparathyroidism surgery
- Approx. 99% success rate
- Increased bone density
- Resolution of hypercalciuria.
- Decreased risk of kidney stones
- Improvement in neurocognitive symptoms
- Improvement in functional ability in the elderly
What is the gold standard surgical technique for hyperparathyroidism?
- Full neck exploration
- 99% success rate
- Requires visualization of all four glands
