To the Editor:
Diaphragm pacing, as obtained by phrenic nerve stimulation through implanted electrodes, is a valid alternative to positive pressure mechanical ventilation (PPV) in patients with high spinal cord injuries [1]. Diaphragm pacing allows such patients to be weaned from PPV, but, to date, the respective effects of diaphragm pacing and PPV on gas exchange have not been compared. PPV is known to reduce ventilation in the lung bases [2]. By contrast, diaphragm pacing, like spontaneous breathing, should direct a larger proportion of the inspired volume to the lung bases. This should improve ventilation/perfusion matching. If this is the case, diaphragm pacing could be of interest as an adjunct to PPV in patients with lung injury. Indeed, in this setting, preserving diaphragmatic activity during mechanical ventilation can improve arterial oxygenation [3]. However, this can be difficult to achieve from a comfort point of view. In a proof-of-concept perspective, we compared blood gases and energy expenditure during PPV and diaphragm pacing in 10 quadriplegics.
10 consecutive, stable and well-nourished tracheotomised quadriplegic patients were studied (six males, aged 15–46 years, mean±sd body mass index 21.9±4.0 kg·m−2). All had a phrenic nerve stimulator (Atrostim; Atrotech, Tampere, Finland) implanted at least 6 months earlier and were considered fully reconditioned. They were studied during planned routine visits, after approval of the ethics committee of the French Learned Society for Intensive Care Medicine. All patients gave their informed consent. Measurements were performed at least 3 h after a meal, with the tracheal cuff inflated. Oxygen consumption (V′O2), carbon dioxide production (V′CO2) and respiratory quotient were …