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

Abstract

IntroductionAssessment of respiratory system compliance (Crs) can be used for individual optimization of positive end-expiratory pressure (PEEP). However, in patients with spontaneous breathing activity, the conventional methods for Crs 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 Crs during assisted spontaneous breathing.MethodsAfter 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 cmH2O after every fifth breath during PSV. This was repeated five times, until a total PEEP increase of 5 cmH2O was reached. Subsequently, PEEP was reduced in steps of 1 cmH2O in the same manner until the original PEEP level was reached. Crs 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 Crs(low-flow) was calculated as the slope of the pressure-volume loop between the pressure that corresponded to the selected PEEP and PEEP +5 cmH2O. For additional reference, Crs during CMV (Crs(CMV)) was calculated as expired tidal volume divided by the difference between airway plateau pressure and PEEP.ResultsRespiratory system compliance calculated from the PEEP wave (Crs(PEEP wave)) correlated closely with both reference measurements (r = 0.79 for Crs(low-flow) and r = 0.71 for Crs(CMV)). No significant difference was observed between the mean Crs(PEEP wave) and the mean Crs(low-flow). However, a significant bias of +17.1 ml/cmH2O was observed between Crs(PEEP wave) and Crs(CMV).ConclusionAnalyzing a PEEP wave maneuver with EIT allows calculation of global and regional Crs 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 materialThe online version of this article (doi:10.1186/s13054-014-0679-6) contains supplementary material, which is available to authorized users.

Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations: consensus statement of the TRanslational EIT developmeNt stuDy group

“…EIT can determine regional C rs during this ventilation31 and uncover potentially harmful excessive regional V T , even in the context of a ‘protective’ V T delivered to the whole lung 22. The detection of this ‘pendelluft’ phenomenon by EIT is shown in figure 4.…”

“…A non-periodic change may be caused, for example, by an overall increase in gas volume induced by raising the positive end-expiratory pressure (PEEP) during mechanical ventilation. [29][30][31] The magnitude of the impedance changes associated with spontaneous breathing or mechanical ventilation is approximately one order of magnitude larger than the changes induced by heart action and lung perfusion. 32 Besides physiological and pathological effects, EIT waveforms may also display artefacts originating from, for example, body movement 33 or interference with some medical devices.…”

Characterisation and imaging of cortical impedance changes during interictal and ictal activity in the anaesthetised rat

“…Electrical Impedance Tomography (EIT) is an emerging medical imaging method that produces images of the internal electrical impedance of a subject from multiple surface impedance measurements ( Holder, 2005 ). EIT has recently entered into clinical use for lung imaging in hospital ICUs ( Becher et al, 2014 ), and has the potential for imaging brain function or pathological conditions ( Boone et al, 1994 , Oh et al, 2011 ). Localisation of the seizure onset zone has been proposed as a possible application of EIT ( Boone et al, 1994 ); it is based on the well-established rise of impedance of cerebral tissue during seizure activity ( Van Harreveld and Schade, 1962 , Elazar et al, 1966 ).…”

Electrical impedance tomography (EIT) for quantification of pulmonary edema in acute lung injury

“…Electrical impedance tomography (EIT) is a noninvasive, radiation-free imaging technology that can be used for various purposes [ 23 , 24 ]. To date, functional EIT has been investigated mostly to visualize ventilation and to optimize ventilatory therapy in critically ill patients [ 25 – 27 ]. So far, only a single attempt to quantify pulmonary edema by means of EIT has been described, in 1999 [ 28 ].…”