The following vital capacity measurements were obtained every 4 hours from a patient with suspected Myesthenia-Gravis. Based on this data, what should the respiratory therapist recommend?

0800Vital Capacity = 2.0 Liters
1200Vital Capacity = 1.4 Liters
1600Vital Capacity = 0.8 Liters
  1. Retest the vital capacity in 2 hours
  2. 2 LPM nasal cannula
  3. Non-invasive mask ventilation
  4. Nasotracheal suctioning

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3. Non-invasive mask ventilation


  1. Incorrect. Waiting to retest the patient in two hours will delay care for a patient who is in impending respiratory failure.
  2. Incorrect. There is no indication the patient is hypoxemic, therefore, a 2 LPM nasal cannula is not indicated.
  3. Correct. The vital capacity measurements show a downward trend indicating the patient’s ventilatory muscle strength is weakening. A vital capacity less than 1 Liter is generally considered unacceptable as a rule of thumb. As a result, this patient requires ventilatory assistance, which can be provided non-invasively.
  4. Incorrect. Nasotracheal suctioning is not indicated, as there is no indication the patient has secretions.

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