Airway Patency
Key Questions:
- Does the patient need intubation?
- Does the patient have a satisfactory swallow?
Because the muscle weakness associated with NMJ dysfunction in MG fluctuates, no single parameter can be used to determine when an MG patient needs respiratory support.
Non-invasive ventilation
Non-invasive ventilation (bilevel positive airway pressure or BiPAP) may prevent the need for intubation in myasthenic patients who have not developed marked hypercapnia [8]. Hypercapnia reflects a more severe degree of neuromuscular respiratory failure than hypoxia alone [19].
The decision to intubate can be straightforward in an MG patient with stridor or history of regurgitation and aspiration. However, other patients have subtle signs of deterioration.
Oxygen saturations can be misleading in patients receiving O2 therapy.
Learning bite
BiPAP should be considered in selected patients with MC who have respiratory compromise (without hypercapnia) and with the ability to synchronise with the machine [22]. A trial of BiPAP before the development of hypercapnia can prevent intubation and prolonged ventilation, reducing pulmonary complications and the lengths of ICU and hospital stay [22].
Endotracheal intubation
Endotracheal intubation may be necessary prior to differentiating between MC and CC [12].
Where there is doubt, the cause of respiratory failure can best be determined after the airway and ventilation have been secured.
Learning bite
The criteria for endotracheal intubation for mechanical ventilation in patients with MC is not well defined and decisions are based on physicians preferences and clinical judgement [19].
Direct laryngoscopy/nasoscopy
Direct laryngoscopy/nasoscopy may be useful to demonstrate vocal cord paralysis when bulbar myasthenic findings are not otherwise obvious [8].
Debate exists as to the best method of rapid sequence induction (RSI) in the MG patient. Several strategies can be used. As these patients are weak to start with, the simplest strategy is to use an induction agent and no muscle relaxant [18].
In untreated MG patients, decreased AChR cause succinylcholine (depolarising drug) resistance but increased sensitivity to nondepolarising agents. However, in treated patients these effects can be unpredictable [18]. Therefore, if muscle relaxants are to be used, either the physician must use a larger dose of succinylcholine (1.5-2 mg/kg), or a smaller dose (by factor of 50%) of a rapid onset nondepolarising relaxant, such as rocuronium.