Assessment of respiratory system compliance with electrical impedance tomography using a positive end-expiratory pressure wave maneuver during pressure support ventilation: a pilot clinical study

INTRODUCTION: Assessment of respiratory system compliance (C(rs)) can be used for individual optimization of positive end-expiratory pressure (PEEP). However, in patients with spontaneous breathing activity, the conventional methods for C(rs) measurement are inaccurate because of the variable muscular pressure of the patient. We hypothesized that a PEEP wave maneuver, analyzed with electrical impedance tomography (EIT), might be suitable for global and regional assessment of C(rs) during assisted spontaneous breathing. METHODS: After approval of the local ethics committee, we performed a pilot clinical study in 18 mechanically ventilated patients (61 ± 16 years (mean ± standard deviation)) who were suitable for weaning with pressure support ventilation (PSV). For the PEEP wave, PEEP was elevated by 1 cmH(2)O after every fifth breath during PSV. This was repeated five times, until a total PEEP increase of 5 cmH(2)O was reached. Subsequently, PEEP was reduced in steps of 1 cmH(2)O in the same manner until the original PEEP level was reached. C(rs) was calculated using EIT from the global, ventral and dorsal lung regions of interest. For reference measurements, all patients were also examined during controlled mechanical ventilation (CMV) with a low-flow pressure-volume maneuver. Global and regional C(rs)(low-flow) was calculated as the slope of the pressure-volume loop between the pressure that corresponded to the selected PEEP and PEEP +5 cmH(2)O. For additional reference, C(rs) during CMV (C(rs)(CMV)) was calculated as expired tidal volume divided by the difference between airway plateau pressure and PEEP. RESULTS: Respiratory system compliance calculated from the PEEP wave (C(rs)(PEEP wave)) correlated closely with both reference measurements (r = 0.79 for C(rs)(low-flow) and r = 0.71 for C(rs)(CMV)). No significant difference was observed between the mean C(rs)(PEEP wave) and the mean C(rs)(low-flow). However, a significant bias of +17.1 ml/cmH(2)O was observed between C(rs)(PEEP wave) and C(rs)(CMV). CONCLUSION: Analyzing a PEEP wave maneuver with EIT allows calculation of global and regional C(rs) during assisted spontaneous breathing. In mechanically ventilated patients with spontaneous breathing activity, this method might be used for assessment of the global and regional mechanical properties of the respiratory system. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13054-014-0679-6) contains supplementary material, which is available to authorized users.