Any patient with myasthenia gravis who is noted to be confused, irritable, difficult to arouse, has a low oxygen saturation by oximetry, or has a slow or shallow respiratory rate should be continuously observed for respiratory failure due to myasthenic crisis or cholinergic crisis. The key is ensuring ventilatory support if needed.
The following is the abstract from Reference (1):
A serious complication of myasthenia gravis is respiratory failure. This may be secondary to an exacerbation of myasthenia (myasthenia crisis) or to treatment with excess doses of a cholinesterase inhibitor (cholinergic crisis). Managing respiratory failure and differentiating a myasthenia from a cholinergic crisis is reviewed. Due to the unpredictable development of respiratory failure, hospitalization is recommended for most patients with exacerbations or complications of myasthenia gravis.
The following is from Reference (2):
The most important aspect of emergent management of myasthenia gravis is the detection and treatment of the myasthenic crisis.
Patients with myasthenia gravis who are in respiratory distress may be experiencing a myasthenic crisis or a cholinergic crisis. Before these possibilities can be differentiated, ensuring adequate ventilation and oxygenation is important. Patients with myasthenic crisis can develop apnea very suddenly, and they must be observed closely. Evidence of respiratory failure may be noted through ABG determination, pulmonary function tests, or pulse oximetry [or clinically by decreased level of consciousness or slow respiratory rate].
Open the airway by suctioning secretions after positioning the jaw and tongue. Administer high-flow oxygen, and measure oxygen saturation by pulse oximetry. If respirations remain inadequate, ventilate by bag-valve mask while preparing to intubate. In the patient without an intact gag reflex, an oral airway may be placed.
Rapid sequence intubation should be modified, because depolarizing paralytic agents (eg, succinylcholine) have less predictable results in patients with myasthenia gravis. The relative lack of ACh receptors makes these patients relatively resistant to succinylcholine; therefore, higher doses must be used to induce paralysis. Once paralysis is achieved, it may be prolonged.
A rapid-onset, nondepolarizing agent (ie, rocuronium, vecuronium) is the preferred paralytic agent for these patients. Although nondepolarizing agents delay the onset of paralysis, compared with succinylcholine, these medications do not result in unwanted prolonged paralysis. Following paralysis, intubation is accomplished as usual. ABG sampling guides ventilator settings.
(1) Myasthenia gravis: myasthenia vs. cholinergic crisis. [PubMed Abstract] Pediatr Emerg Care. 2005 Aug;21(8):546-8; quiz 549-51.
(2) Emergent Management of Myasthenia Gravis from Emedicine Medscape