In a patient with myasthenia gravis requiring ventilatory support, which ventilator settings are most appropriate?

• A. Volume-controlled intermittent mandatory ventilation, f = 12 breaths/min
• B. Pressure-controlled continuous mandatory ventilation, f = 12
• C. Synchronized intermittent mandatory ventilation, f = 10
• D. Assist-control ventilation, f = 12

Answer: (A)

In myasthenic patients who need ventilatory support, the goal is to guarantee reliable ventilation while giving fatigable respiratory muscles moments of rest. A volume-targeted mode delivers a fixed tidal volume on each mandatory breath, so you are sure the patient receives enough ventilation even if their effort wanes. Intermittent mandatory ventilation combines those assured breaths with spontaneous breaths in between, allowing the diaphragm and intercostals to rest periodically while still maintaining overall ventilation. A frequency of about 12 breaths per minute provides adequate minute ventilation without pushing the patient into fatigue or risking CO2 retention.

Other modes can be less ideal in this scenario. Pressure-controlled ventilation relies on airway pressure to set breaths, so tidal volumes can vary with changing compliance or strength, risking under-ventilation during weakness. Modes that rely more on the patient’s own effort (like synchronized intermittent mandatory ventilation) can lead to inconsistent ventilation if the patient tires. Assist-control can deliver full support on every breath, which is good for protection but may reduce the opportunity for rest and fatigue management. The volume-controlled intermittent mandatory approach hits the balance of guaranteed ventilation and patient rest, making it the best choice here.