Book 3, Case 7-Thyroidectomy Flashcards
Lithium toxicity is associated with what?
polyuria, skeletal muscle weakness, ataxia, cognitive
changes, widening of the QRS, atrioventricular block, hypotension, and seizures.
How does your anesthetic mgmt differ for a patient who is taking Lithium?
Given the detrimental side effects of lithium toxicity, I would evaluate
the patient for signs of toxicity, such as skeletal muscle weakness, cognitive changes
(sedation), ataxia, widening QRS, atrioventricular heart block, hypotension, and
seizures. In addition to this examination, I would check the patient’s most recent
lithium level and/or order lab work to check her current level. Finally, I would avoid
any drugs that may lead to toxicity (i.e. thiazide diuretics, NSAIDs, ACE inhibitors),
administer sodium containing fluids to prevent excessive renal reabsorption of lithium
(reabsorption occurs in the proximal tubule in exchange for sodium), watch the ECG
for lithium-induced atrioventricular blockade or dysrhythmias, and closely monitor
both anesthetic depth and neuromuscular blockade throughout the case (lithium has
the potential to reduce anesthetic requirements and prolong the effects of both
depolarizing and nondepolarizing muscle relaxants).
What are flow volume loops-like-what do they tell you, and when are you going to order them?
Flow volume loops may be beneficial in determining the effects of positioning on the
airway, whether the obstruction is fixed or variable, and whether the mass is
intrathoracic or extrathoracic. However, I would not necessarily order flow-volume
loops since a CT scan combined with a careful history and physical in which the
patient is observed in both the sitting, supine, and prone positions may provide the
needed information, such as tumor location (substernal extension increases the risk of
worsening tracheal compression with the loss of respiratory muscle tone), the degree
of tracheal compression, and the effects of positioning on mass compression of the
trachea.
What kind of flow volume loop do you expect in this patient?
Patients with large thyroid masses usually have a fixed obstruction
that may be intrathoracic or extrathoracic in location. Airway flow with this type of
obstruction is limited during both inspiration and expiration, with subsequent
flattening of both limbs of the flow-volume loop (regardless of whether the
obstruction is intrathoracic or extrathoracic ).
How can you tell if a patient is euthyroid?
While her tachycardia and hypertension may be due to anxiety
associated with her respiratory distress and/or the upcoming surgery, these symptoms
are concerning since they may represent inadequate treatment and hyperthyroidism.
Therefore, I would perform a history and physical exam to identify additional signs of
inadequately treated hyperthyroidism, such as diarrhea, warm moist skin, heat
intolerance, cardiac arrhythmias, fatigue, skeletal muscle wealmess, fine tremor of the
hands, and hyperactive tendon reflexes. Additionally, I would order a TSH, free T3,
and free T 4, recognizing that c~ hyperthyroid patie~t would likely present with a low
TSH (due to negative feedback) and elevated levels of both free T3 (more active than
T 4) and free T 4.
Patient’s total T4 is elevated, what do you think of this single finding? What other test can you get? What about young women taking OcP can make this unreliable?
While an elevated T 4 may indicate hyperthyroidism, this test (or a
total T3) should never be used alone to evaluate thyroid function, especially for this
patient who is taking an oral contraceptive. While total T4 and T3 levels are often
utilized in the evaluation of thyroid function, thyroid hormone protein binding
influences these concentrations. Unfortunately, the principal binding protein,
thyroxine-binding globulin (TBG), does not remain at a reliably constant level,
increasing with acute liver disease, pregnancy, and estrogen containing drugs (such as
oral contraceptives), and decreasing with chronic liver disease, nephrotic syndrome,
and conditions associated with elevated glucocorticoids. Therefore, total T4 and T3
levels should always be used in conjunction with a test used to assess thyroid
hormone binding, such as a T 4 or T3 resin uptake test. The information from these
tests can then be used to calculate the free T 4 index and/ or free T3 index, which are
proportional to free levels ofT4 and T3 respectively.
YOU WANT THE FREE T4
Does a patient have to be euthyroid to proceed with surgery?
Yes if it’s elective. If not (which you know they won’t let it be):
Therefore, I would discuss my concerns with the surgeon and, if the case was
deemed urgent or emergent, consult an endocrinologist, attempt to medically optimize
this patient’s condition, and proceed to surgery; recognizing that proceeding with
surgery when the patient remains hyperthyroid places her at increased risk for
perioperative complications such as hemodynamic instability (hyperdynamic
circulation), cardiac arrhythmias, and thyroid storm.
Assuming this is an urgent case, how would you optimize this patient’s thyroid
status for surgery?
In optimizing this patient’s thyroid status for urgent surgery, I would
consult an endocrinologist; continue her PTU, which inhibits the organification of
iodide, the synthesis of thyroid hormone, and the peripheral conversion ofT4 to T3;
and administer a 13-blocker (to achieve a normal heart rate), glucocorticoids (to reduce
thyroid hormone secretion and the peripheral conversion ofT4 to T3), and iopanoic
acid (can reduce T3 levels by 50-75% in 6- 12 hours). Additionally, I would provide
adequate hydration and ensure a normal electrolyte balance. I would also consider a
small dose ofbenzodiazepine to relieve anxiety, taking care to avoid respiratory
depression in this patient with apparent airway obstruction. My goal would be to
minimize the risk of hemodynamic instability, cardiac arrhythmias, and thyroid
storm.
***Iopanoic acid: potent inhibitor of thyroid hormone release from thyroid gland, as well as of peripheral conversion of thyroxine (T4) to triiodothyronine (T3).
Lithium can result in what as far as sodium/fluid balance?
Lithium can result in vasopressin resistant DI
Go through the process of anesthetizing the airway:
Nebulized what?
Topicalized what?
Nebulized lidocaine to numb above epiglottis
-Topicalize the nose in case a nasal airway becomes
necessary-use phenylephrine spray also.
Pharynx is largely innervated by what?
Larynx is largely innervated by what?
Max Amt of lidocaine for these topicalized treatments:
So, how will you provide nebulized lidocaine?
Pharynx: glossopharyngeal nerve
Larynx: Vagus
Go over this in learning issues section of notebook
Systemic absorption from topical application to the upper airways is lower than expected, so in practice higher doses can be used than the recommended 2 mg/kg.
Adding approximately 5 mL of 4% lidocaine to a nebulizer, then delivering it with oxygen for up to 30 minutes is a safe and noninvasive way to topicalize the airway all the way down to the trachea
How to do a SLN block?
To perform the block using the external approach, the patient is placed in the supine position and will need a degree of neck extension to facilitate identification of the hyoid bone.
Once identified, the hyoid bone is gently displaced to the side where the block is to be performed and a 25-gauge needle is inserted from the lateral side of the neck, aiming toward the greater cornu.
Once contact has been made, the needle is walked off the bone inferiorly, and injecting 2 mL of 2% lidocaine here will block both the internal and the external branches of the superior laryngeal nerve
Aspirate prior to injection.
How to do a RLN block?
The sensory innervation of the vocal cords and trachea is supplied by the recurrent laryngeal nerves.
-Direct recurrent laryngeal nerve blocks are not performed as they can result in bilateral vocal cord paralysis and airway obstruction, as both the motor and the sensory fibers run together. Therefore, this nerve is blocked using the translaryngeal block.
To perform this, the patient should be supine, with the neck extended be identified in the midline, then the palpating finger should be moved in a caudad direction until the cricoid cartilage is palpated. The cricothyroid membrane lies between these two structures, immediately above the cricoid cartilage. The thumb and third digit of one hand should stabilize the trachea at the level of the thyroid cartilage, then a 22 or 20 gauge needle should be inserted perpendicular to the skin with the aim to penetrate the cricothyroid membrane (above the cricoid cartilage) (Figure 12). This should be done with continuous aspiration of the syringe, as the appearance of bubbles will indicate that the needle tip is now in the trachea. At this point, immediately stop advancing the needle; otherwise, the posterior laryngeal wall can be punctured. Rapid injection (and then removal of the needle) of 5 mL of 4% lidocaine will result in coughing, which will help to disperse the local anesthetic and blockade of the recurrent laryngeal nerve
What kind of tubes are you using in thyroids? Also-If a pt with a huge thyroid mass refuses an awake intubation, what are you going to do?
A reinforced tube
-GET THAT NECK PREPPED AND DRAPED IN RISKY PROCEDURES! I would make the patient, her family, and the surgeon aware of my
concerns of possible difficult intubation, mask ventilation, and complete airway
obstruction. At the same time, I would attempt to identify and address the patient’s
concerns with an awake intubation, reassuring her that all steps would be taken to
make the procedure as comfortable as possible. If she still refused this procedure, I
would administer an H2-receptor antagonist and metoclopramide; and ensure the
presence of difficult airway equipment, a rigid bronchoscope, reinforced endotracheal
tubes in various sizes, a tracheostomy kit, and a surgeon capable of performing an
emergency tracheostomy. I would then have the neck prepped and draped, place the
patient in slight reverse trendelenburg position, apply cricoid pressure, provide
minimal sedation, and perform an inhalational induction with sevoflurane with the
goal of maintaining spontaneous respiration until the airway is secured. Finally, I
would pass a reinforced endotracheal tube, ensuring that the distal tip of the tube
extends beyond the point of extrinsic compression.
Anesthetic maintenance in hyperthyroid cases:
I would maintain anesthesia with a balanced technique consisting of
IV narcotics and a volatile agent, being careful to maintain an adequate depth of
anesthesia to prevent exaggerated sympathetic responses to surgical stimulation.
Additionally, I would avoid the administration of any agents that stimulate the central
nervous system, such as atropine, ketamine, desflurane, ephedrine, epinephrine, and
pancuronium. If intraoperative hypotension occurred, I would treat with fluids and a
direct-acting vasopressor such as phenylephrine.and closely monitor the patient for any signs of thyroid storm, such as
hyperthermia, dysrhythmias, tachycardia, myocardial ischemia, congestive heart
failure, and cardiovascular instability.
