In a patient with myasthenia gravis on mechanical ventilatory support, what should be monitored if MIP changes from -30 cm H2O to -18 cm H2O?

• A. FEV1.0/FVC ratio
• B. FEV1.0 sec
• C. Measure tidal volume and vital capacity
• D. SpO2

Answer: (C)

Monitoring the tidal volume and vital capacity in a patient with myasthenia gravis on mechanical ventilatory support is crucial, particularly when there is a significant change in maximum inspiratory pressure (MIP), such as a decrease from -30 cm H2O to -18 cm H2O.

A decline in MIP indicates a potential worsening of respiratory muscle strength, which can lead to inadequate ventilation. By measuring tidal volume and vital capacity, healthcare providers can assess the patient’s ability to effectively breathe and maintain adequate gas exchange. This information is vital for determining the need for changes in ventilatory support or additional interventions to improve respiratory function.

Monitoring vital capacity specifically can help in evaluating the progression of respiratory muscle fatigue, a common concern in patients with myasthenia gravis. If these measurements show a corresponding decline, it could warrant further clinical considerations, such as increasing ventilatory support or exploring alternative treatments.

The other choices, while relevant in certain situations, do not directly assess the immediate capability of the patient in terms of ventilation and respiratory muscle strength. Thus, focusing on tidal volume and vital capacity is the most appropriate action in this context.