Myasthenia gravis

Question 1

Patient presents for laparoscopic resection of the colon. PT has hx colon cancer and MG on pyridostigmine and prednisone. How to you asses if optimized for surgery

Answer 1

H and P
is disease limited to ocular muscles or involvement of extremities or resp/laryngeal muscles by evidence of trouble chewing, swallowing, or talking

any previous surgery

any prolonged intuations or problems with anesthesia

any episodes of myasthenic crisis

have symptoms been stable recently

assess motor strength

Question 2

what other medical conditions is MG closely associated with?

Answer 2

thymus hyperplasia, thymomas, auto-immune dz like thyroid dz, pernicious anemia, RA

Question 3

Would you get PFTs on this patient and why?

thymoma?

Answer 3

I would not unless severe resp comonent of evidenced by H&P

if they have severe resp sx, negative inspiratory force (NIF) and FVC could be used as reference pt to determine optimal conditions for extubation and need for postop ventilation

could also help determine appropriateness of ambulatory surgery

if pt has thymoma flow volume loops can help demonstrate extent of impairment and if fixed or dynamic

Question 4

Why is this patient on corticosteroids

Answer 4

MG is autoimmune dz so suppresses immune system and abnormal antibody production

usually for more advanced disease

Question 5

Would you administer preop steroids?

Answer 5

Yes, stress dose steroids, hydrocortisone 100mg Q8 hours on DOS and taper postop

I would do this because patient is on chronic steroids

Question 6

Would you sedate this patient preop

Answer 6

yes if needed unless if there was a question of her respiratory reservei

Question 7

is there anything you would tell the patient about her postop course

Answer 7

would tell her and family that sx may worsen perioperatively but usually return to baseline and also mention possibility of postop mechanical ventilation

Question 8

lambert eaton myasthenic syndrome is related to what

Answer 8

paraneoplastic syndrome and SCC of lung

also seen in sarcoidosis

Question 9

Would you select general or regional technique for this patient?

Answer 9

if no contraindications i would prefer regional because it avoids muscle relaxation and need for postop ventilator support so long as the patient agrees with plan

Question 10

would you do epidural or spinal

Answer 10

I say CSE book says epidural

Question 11

how would you induce if she refuses regional

Answer 11

normal stuff

Question 12

how would your induction technique change if patient were at high risk of aspiration?

Answer 12

I would perform RSI with sux at a dose of 1.5-2 mg/kg

Question 13

would you use nerve stimulator during the case? Why or why not?

Answer 13

Yes I would but it may not be reliable in MG pts because of distribution of muscle weakness is often uneven

Question 14

what is the impact of preop cholinesterase inhibitor administration on neuromuscular blockade and reversal

Answer 14

preop pyridostigmine inhibits plasma cholinesterase and succinylcholine may cause a prolonged block. Reversal of residual nondepolarizing neuromuscular blockade at the end of surgery may be unsuccessful because acetylcholinesterase is already maximally inhibited

Question 15

Would you extubate patient at the end of this case?

Answer 15

If they meet extubation criteria and depending on how the case went then yes

Question 16

Get a call from the PACU saying pt is weak. What do you think and what will you do?

Answer 16

Differential dx: residual muscle relaxant, narcotic overdose, residual inhalational anesthetic, myasthenic crisis, cholinergic crisis, hypothermia, hypocarbia and acidosis

would assess pts vital signs and respiratory pattern

reintubate if showing signs of respiratory insufficiency

consider edrophonium test to evaluate if shew was in myasthenic crisis vs cholinergic crisis; sx would improve if myasthenic crisis

Question 17

what is myasthenic crisis and precipitaing factors

Answer 17

severe bulbar or respiratory sx with MG

can be precipitated by infection, recent surgery, emotional stress, interruption in immunosuppressants

hypothermia, acidosis, hypokalemia, hypermagnesemia

Question 18

which drugs can precipitate myasthenic crisis

Answer 18

aminoglycosides, polymyxins, fluorquinolones, clindamycin, anticonvulsants, beta blockers, CCB, corticosteroids, LAs, magnesium, ketamine, neuromuscular blockers, and anticholinergics

Question 19

treatment of cholinergic crisis

Answer 19

cessation of cholinesterase inhibitors
supportive
atropine
intubation