Myasthenic Crisis

Separate it from cholinergic crisis before you treat - Both present as worsening weakness. Give a single 2 mg IV dose of edrophonium: strength improves or stays unchanged in myasthenic crisis and worsens in cholinergic crisis. Cholinergic crisis also carries the muscarinic picture (SLUDGEM or DUMBELS: salivation, lacrimation, urinary frequency, diarrhea, GI cramping, emesis, miosis, plus diaphoresis, bronchospasm and bronchorrhea) along with fasciculations. Getting this backwards matters, because more anticholinesterase is the first-line treatment for one and deepens the other.

Treating myasthenic crisis - Additional cholinesterase inhibitor first; if there is no improvement, immunoglobulin, plasmapheresis and endotracheal intubation. If the patient cannot take oral pyridostigmine, the parenteral dose is roughly one-thirtieth of the oral dose.

Treating cholinergic crisis instead - Stop the cholinesterase inhibitor and give atropine, roughly 2 mg in an adult or 0.03 to 0.05 mg/kg in a child, titrated to signs of atropinization. Atropine does nothing for the nicotinic weakness, so intubation may still be needed until it resolves.

Who ends up ventilated - The Leventhal risk factors are disease duration over 6 years, coexisting pulmonary disease, pyridostigmine above 750 mg/day, and a preoperative vital capacity under 2.9 L. A history of prior myasthenic crisis and the presence of anti-acetylcholine-receptor antibodies also predict postoperative ventilation. Bulbar symptoms, higher preoperative MGFA class, long surgical time, greater blood loss and thymoma add to the risk of postoperative myasthenic crisis. A preop vital capacity and the daily pyridostigmine dose do most of the work of this conversation, and the possibility of prolonged intubation belongs in the consent.

Neuromuscular blockade - If volatile alone gives you enough relaxation for the case, take it. When paralysis is required choose a nondepolarizing agent for a more predictable block and give a reduced dose. The 2023 ASA guideline recommends quantitative monitoring over qualitative assessment and against clinical assessment alone, at the adductor pollicis rather than eye muscles; in a patient with this little reserve, that is the standard to hold to. These patients are markedly sensitive to nondepolarizers and resistant to succinylcholine, because there are fewer receptors available to depolarize.

Reverse with sugammadex, not neostigmine - The 2023 ASA guideline recommends sugammadex over neostigmine at deep, moderate and shallow depths of rocuronium- or vecuronium-induced block, with neostigmine only a reasonable alternative at minimal depth (train-of-four ratio 0.4 to less than 0.9). In myasthenia gravis the case is stronger still: sugammadex fully reverses rocuronium and vecuronium including the high-dose rocuronium used for RSI, while neostigmine has a ceiling effect in MG, can produce paradoxical weakness at 0.04 to 0.07 mg/kg, above 0.06 mg/kg carries a threefold increase in postoperative complications, and can tip the patient into cholinergic crisis. Reversal even with sugammadex has been variable in reported myasthenic cases, so keep monitoring for weakness after the twitches look fine.

Aspiration - Bulbar involvement affects pharyngeal and laryngeal muscles and raises aspiration risk. Premedicate with a PPI, an H2 blocker or metoclopramide, and manage secretions actively through emergence and into PACU.

Extubation criteria - Beyond the usual: a normal level of consciousness, tidal volume of at least 5 mL/kg, and respiratory rate under 30/min. The part that matters most is absolutely no residual curarization, so confirm a quantitative train-of-four ratio of at least 0.9 before extubation per the 2023 ASA guideline. Clinical assessment alone is too insensitive to rule out residual block, and residual block is what puts a myasthenic straight back on the ventilator. Extubate awake with confirmed ventilatory function.

Drugs that make it worse - Avoid magnesium and calcium channel blockers, both of which impair muscle contraction. Aminoglycosides, beta blockers, lidocaine and procainamide all potentiate weakness. Azathioprine prolongs succinylcholine and inhibits nondepolarizing blockers, so it gets discontinued preoperatively; most other immunosuppressants do not interact with anesthesia.

Opioids and sedatives - These patients are more sensitive to the respiratory depressant effects of benzodiazepines and opioids, so routine premedication with either is out. Postoperatively lean on regional anesthesia and NSAIDs, with small doses of rapid, short-acting opioids only if needed. Pain and physiologic stress themselves exacerbate the disease, so undertreating is not the safe option either.

Blocks near the phrenic nerve - Peripheral nerve blocks help and require smaller local anesthetic doses, but be cautious with interscalene or supraclavicular approaches. Phrenic nerve block paralyzes the hemidiaphragm, and a patient in or near crisis has no reserve to give up.

Keep the MG medications running - Continue pyridostigmine and the immunosuppressants through the perioperative period and restart them early, particularly in generalized or severe disease, where withholding treatment is how patients decline.

Timing and disposition - Schedule elective surgery during a stable phase; if the case is emergent and the patient is unstable, optimize first, with plasmapheresis or IVIG for respiratory or oropharyngeal weakness. Afterwards, avoid reflexive ICU admission and delayed extubation. Thymectomy patients extubated within 6 hours have shorter ICU stays and fewer pulmonary complications. If the patient does deteriorate, get neurology involved immediately.

Myasthenic crisis is an exacerbation of myasthenia gravis (MG) in which weakness progresses to respiratory distress and diaphragmatic failure, often requiring prolonged mechanical ventilation. The underlying lesion is autoimmune destruction of postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction, so the endplate potential generated is too weak to reliably open muscle sodium channels; as receptor reserve falls, bulbar and then respiratory muscles give out.

Precipitants are the things that fill an OR schedule: infection, surgery, physiologic stress and pregnancy, plus drugs including quinidine, calcium channel blockers (verapamil, nifedipine, felodipine) and antibiotics (gentamicin, ampicillin, streptomycin, erythromycin, ciprofloxacin). Older age, slow recognition and the need for intubation predict death. The mimic is cholinergic crisis from excess anticholinesterase, which looks nearly identical but is made worse by the first-line treatment for myasthenic crisis.