Assessment of ventilation inhomogeneity during mechanical ventilation using a rapid-response oxygen sensor-based oxygen washout method.

Ido G Bikker,Patricia Specht,Diederik Gommers,Wim Holland,Can Ince

doi:10.1186/2197-425x-2-14

Abstract

PurposeVentilatory inhomogeneity indexes in critically ill mechanically ventilated patients could be of importance to optimize ventilator settings in order to reduce additional lung injury. The present study compared six inhomogeneity indexes calculated from the oxygen washout curves provided by the rapid oxygen sensor of the LUFU end-expiratory lung volume measurement system.MethodsInhomogeneity was tested in a porcine model before and after induction of acute lung injury (ALI) at four different levels of positive end-expiratory pressure (PEEP; 15, 10, 5 and 0 cm H2O). The following indexes were assessed: lung clearance index (LCI), mixing ratio, Becklake index, multiple breath alveolar mixing inefficiency, moment ratio and pulmonary clearance delay.ResultsLCI, mixing ratio, Becklake index and moment ratio were comparable with previous reported values and showed acceptable variation coefficients at baseline with and without ALI. Moment ratio had the highest precision, as calculated by the variation coefficients. LCI, Becklake index and moment ratio showed comparable increases in inhomogeneity during decremental PEEP steps before and after ALI.ConclusionsThe advantage of the method we introduce is the combined measurement of end-expiratory lung volume (EELV) and inhomogeneity of lung ventilation with the LUFU fast-response medical-grade oxygen sensor, without the need for external tracer gases. This can be combined with conventional breathing systems. The moment ratio and LCI index appeared to be the most favourable for integration with oxygen washout curves as judged by high precision and agreement with previous reported findings. Studies are under way to evaluate the indexes in critically ill patients.

Highlights

Mechanical ventilation is critical for the survival of most patients with respiratory failure, it can induce lung damage and may even be the primary factor in lung injury [1].In 1970, Mead et al estimated that forces acting on lung tissue might be 4.5 times higher when lungs are inhomogeneously ventilated [2]
Venous admixture and the ratio of alveolar dead space volume divided by alveolar tidal volume (VDalv/VTalv) were both increased by the induction of acute lung injury (ALI), indicating an increased ventilation-perfusion mismatch (Table 1)
lung clearance index (LCI), mixing ratio, Becklake index and moment ratio were comparable with historical reference values and showed acceptable mean variation coefficients (Table 3)

Summary

Introduction

In 1970, Mead et al estimated that forces acting on lung tissue might be 4.5 times higher when lungs are inhomogeneously ventilated [2] This was confirmed in an experimental work using tomographic microscopy, which generates detailed three-dimensional alveolar geometries [3]. This inhomogeneity raises stress and increases the risk to develop ventilator-induced lung injury (VILI). In the LUFU system developed by Weismann et al, oxygen concentration is measured with a diverting oxygen analyser with response time < 200 ms This method offered the possibility to develop an index of ventilatory inhomogeneity which we believe will be of great potential use in combination with EELV measurement to optimize ventilatory settings at the bedside

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