The investigators conducted a prospective study to compare the respiratory mechanics of patients with moderate to severe ARDS according to the NMB depth, using an oesophageal pressure catheter (NutriVent®, Sidam) for transpulmonary pressure (PL) assessment, and facial train of four (TOF) for neuromuscular blockade monitoring. The oesophageal balloon was calibrated according to the method recently described to estimate the individual target volume which is assumed to be more adequate. Each patient was analysed at two different times: deep NMB (TOF = 0) and intermediate to light NMB (TOF > 0). The mechanical ventilation parameters were identical for these two measurements. The primary endpoint was the proportion of patients with expiratory transpulmonary pressure (PLexp) greater than or equal to 0 according to the NMB level, in order to assess the risk of region-dependent atelectasis and alveolar opening/closing injury (atelectrauma). Secondary endpoints included: the impact of the depth of NMB on other partition parameters of respiratory mechanics, and the variability of results according to the type of oesophageal balloon calibration.
Neuromuscular blockade (NMB) is proposed in patients with moderate to severe acute respiratory distress syndrome (ARDS). The supposed benefit of these muscle relaxants could be partly linked to their effects on respiratory mechanics by reducing ventilator induced lung injuries (VILI), especially the so called atelectrauma. Although its monitoring is recommended in clinical practice, data about the depth of NMB necessary for an effective relaxation of the thoracic and diaphragmatic muscles and, therefore, the reduction of the chest wall elastance, are scarce. The investigators hypothesised that complete versus partial NMB can modify respiratory mechanics and its partitioning.