A 57-year-old woman with known myasthenia gravis is brought to the emergency department after 2 weeks of progressively worsening weakness in her arms and legs, fatigue, and intermittent shortness of breath. She could not eat breakfast today due to difficulty swallowing. Her only other medical problem is hypertension, and her medications include pyridostigmine, olmesartan, and chlorthalidone.
The patient's blood pressure is 122/72 mm Hg, pulse is 78/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical examination shows clear lung fields and normal first and second heart sounds. There is no nasal flaring or usage of accessory respiratory muscles. There is mild proximal weakness (4/5) in the arms and legs. Pinprick and light touch sensations are intact.
Her vital capacity is 25 mL/kg. Laboratory results include serum potassium of 3.8 mEq/L and serum creatinine of 0.8 mg/dL. Her chest x-ray is clear.
Which of the following is the most appropriate way to monitor this patient's respiratory status?

Question

A 57-year-old woman with known myasthenia gravis is brought to the emergency department after 2 weeks of progressively worsening weakness in her arms and legs, fatigue, and intermittent shortness of breath.  She could not eat breakfast today due to difficulty swallowing.  Her only other medical problem is hypertension, and her medications include pyridostigmine, olmesartan, and chlorthalidone.
The patient's blood pressure is 122/72 mm Hg, pulse is 78/min, respirations are 14/min, and oxygen saturation is 98% on room air.  Physical examination shows clear lung fields and normal first and second heart sounds.  There is no nasal flaring or usage of accessory respiratory muscles.  There is mild proximal weakness (4/5) in the arms and legs.  Pinprick and light touch sensations are intact.
Her vital capacity is 25 mL/kg.  Laboratory results include serum potassium of 3.8 mEq/L and serum creatinine of 0.8 mg/dL.  Her chest x-ray is clear.
Which of the following is the most appropriate way to monitor this patient's respiratory status?

Quizplus · Accepted Answer

11ec193a_9664_3600_853d_4584117af022_MD0002_00 This patient's presentation is consistent with myasthenic crisis, defined as severe weakness from myasthenia gravis requiring intubation. Myasthenic crisis is usually due to weakness of the respiratory muscles but can also present as severe oropharyngeal weakness resulting in dysphagia and aspiration. The common precipitants are infection and surgery (Table); however, it can also present as a progression of myasthenia gravis. Patients should be monitored in the intensive care unit with respiratory status checks every 2-4 hours using vital capacity (VC) and maximal inspiratory force (MIF). Both VC and MIF should be interpreted in combination as neither is superior to the other. Patients require intubation for VC <20 mL/kg or MIF >-30 cm H₂O (eg, 0 to -30). Anticholinesterase inhibitors should be stopped temporarily while the patient is on mechanical ventilation to minimize secretions. Rapid treatment involves plasmapheresis or intravenous immunoglobulin (IVIG) in addition to high-dose glucocorticoids (prednisone 60-80 mg/day) due to the short-lived therapeutic effect of plasmapheresis and IVIG. Patients who cannot tolerate glucocorticoids can be started on azathioprine, mycophenolate mofetil, or cyclosporine. Weaning and extubation are considered in patients with improved muscle strength (eg, ability to lift head off bed, VC >20 mL/kg, MIF <-30 cm H₂O). (Choices A, C, D, and E) Arterial PCO₂, oxygen saturation, peak expiratory flow rate, and respiratory rate are not good predictors of impending respiratory failure as they may not show marked abnormalities until late stages. Educational objective: The respiratory status of patients with myasthenic crisis should be monitored using serial measurements of vital capacity (VC) and maximal inspiratory force (MIF). Patients should be electively intubated when VC <20 mL/kg or MIF >-30 cm H₂O (eg, 0 to -30). Treatment includes plasmapheresis or intravenous immunoglobulin, along with high-dose steroids. __________ References: The myasthenic patient in crisis: an update of the management in neurointensive care unit. (http://www.ncbi.nlm.nih.gov/pubmed/24141444)

A 57-Year-Old Woman with Known Myasthenia Gravis Is Brought to the Emergency