In monitoring a patient with MG, which parameter is crucial to watch for impending ventilatory failure?

• A. Airway pressure monitoring
• B. Complete blood count
• C. Serum electrolytes
• D. Arterial blood gas for acute ventilatory failure

Answer: (D)

In myasthenia gravis, weakness of the chest and diaphragmatic muscles can progress to ventilatory failure, so the best way to detect that danger early is by checking how well the patient is ventilating and managing acid-base status. An arterial blood gas gives a direct read on ventilation by providing PaO2, PaCO2, and pH. A rising PaCO2 with a falling pH indicates hypoventilation from respiratory muscle weakness and signals impending ventilatory failure, often before other signs become obvious. This information helps you decide when to escalate support, such as noninvasive or invasive ventilation.

Airway pressure monitoring is useful when someone is already on a ventilator to ensure adequate delivery, but it doesn’t reliably predict impending failure in a patient who isn’t yet intubated. Complete blood count and serum electrolytes don’t specifically reveal worsening ventilatory status in this context, though they may help identify other problems.