Background
Respiratory failure in myasthenia gravis may be life-threatening, but there are few objective metrics, beyond blood gas measurements, which may not show CO₂ retention until late stages. Weakness of respiratory muscles may be monitored with breath counts, negative inspiratory force (NIF), forced vital capacity (FVC), and/or neck flexion weakness, but these are all effort-dependent. Average Volume-Assured Pressure Support (AVAPS) data collected during sleep provides effort-independent, continuous measurement of respiratory function at home or in the hospital, and we hypothesized that this data might correlate with response to successive cycles of plasma exchange.
Objective
To describe how AVAPS ventilator data, including peak inspiratory pressure (PIP), can be used to monitor response to treatment in a pediatric patients with myasthenia gravis.
Results
During one exacerbation in a 12 year-old patient with generalized, AChR receptor antibody-positive myasthenia gravis, we observed worsening NIF (from −38 to −27 cm H₂O) with rising PIP (21 to 35 cm H₂O), reduced minute ventilation (4.0 to 3.0 L/min), and a drop in spontaneous triggered breaths to 0% at nadir, coinciding with worsening weakness. The patient underwent 10 cycles of plasma exchange, with nadir reached at the time of the third cycle, improvement beginning after the fourth cycle, and steady improvement in PIP with each subsequent cycle and return to 100% spontaneous breaths by the 9th cycle. Data from a second exacerbation show similar changes with elevated PIP above baseline, lower % spontaneous triggered breaths and increasing MG-ADL scores prior to plasma exchange, with improvement after the third cycle of plasma exchange .
Conclusions
AVAPS data show steady improvement in PIP with successive cycles of plasma exchange, and appear to provide a reproducible, effort-independent method to monitor respiratory weakness and response to treatment. We propose that AVAPS may be used as an objective measure of diaphragm weakness in patients with respiratory weakness caused by myasthenia gravis, and perhaps other neuromuscular disorders, and may be used to determine the effectiveness of therapeutic interventions and duration of treatment. With collection of baseline data for a particular patient, it may also help the care team determine timing of treatment and to avoid progression to a myasthenic crisis.