First non-invasive magnetic phrenic nerve and diaphragm stimulation in anaesthetized patients: a proof-of-concept study

Background: Mechanical ventilation has side effects such as ventilator-induced
diaphragm dysfunction, resulting in prolonged intensive care unit length of stays.
Artificially evoked diaphragmatic muscle contraction may potentially maintain diaphragmatic
muscle function and thereby ameliorate or counteract ventilator-induced
diaphragm dysfunction. We hypothesized that bilateral non-invasive electromagnetic
phrenic nerve stimulation (NEPNS) results in adequate diaphragm contractions and
consecutively in effective tidal volumes.
Results: This single-centre proof-of-concept study was performed in five patients who
were 30 [IQR 21–33] years old, 60% (n = 3) females and undergoing elective surgery
with general anaesthesia. Following anaesthesia and reversal of muscle relaxation,
patients received bilateral NEPNS with different magnetic field intensities (10%, 20%,
30%, 40%); the stimulation was performed bilaterally with dual coils (connected to one
standard clinical magnetic stimulator), specifically designed for bilateral non-invasive
electromagnetic nerve stimulation. The stimulator with a maximal output of 2400
Volt, 160 Joule, pulse length 160 μs at 100% intensity was limited to 50% intensity, i.e.
each single coil had a maximal output of 0.55 Tesla and 1200 Volt. There was a linear
relationship between dosage (magnetic field intensity) and effect (tidal volume,
primary endpoint, p < 0.001). Mean tidal volume was 0.00, 1.81 ± 0.99, 4.55 ± 2.23 and
7.43 ± 3.06 ml/kg ideal body weight applying 10%, 20%, 30% and 40% stimulation
intensity, respectively. Mean time to find an initial adequate stimulation point was 89
(range 15–441) seconds.
Conclusions: Bilateral non-invasive electromagnetic phrenic nerve stimulation generated
a tidal volume of 3–6 ml/kg ideal body weight due to diaphragmatic contraction
in lung-healthy anaesthetized patients. Further perspectives in critically ill patients
should include assessment of clinical outcomes to confirm whether diaphragm contraction
through non-invasive electromagnetic phrenic nerve stimulation potentially
ameliorates or prevents diaphragm atrophy.
Keywords: Respiration, Artificial, Mechanical ventilation weaning, Muscle weakness,
Phrenic nerve, Magnetic field therapy