Dorsal recruitment with flow-controlled expiration (FLEX): an experimental study in mechanically ventilated lung-healthy and lung-injured pigs

Silke Borgmann,Josef Guttmann,Stefan Schumann,Joerg Haberstroh,Ulrich Goebel,Johannes Schmidt

doi:10.1186/s13054-018-2168-9

Silke Borgmann, Josef Guttmann + Show 4 more

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https://doi.org/10.1186/s13054-018-2168-9

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Abstract

BackgroundConcepts for optimizing mechanical ventilation focus mainly on modifying the inspiratory phase. We propose flow-controlled expiration (FLEX) as an additional means for lung protective ventilation and hypothesize that it is capable of recruiting dependent areas of the lungs. This study investigates potential recruiting effects of FLEX using models of mechanically ventilated pigs before and after induction of lung injury with oleic acid.MethodsSeven pigs in the supine position were ventilated with tidal volume 8 ml·kg− 1 and positive end-expiratory pressure (PEEP) set to maintain partial pressure of oxygen in arterial blood (paO2) at ≥ 60 mmHg and monitored with electrical impedance tomography (EIT). Two ventilation sequences were recorded - one before and one after induction of lung injury. Each sequence comprised 2 min of conventional volume-controlled ventilation (VCV), 2 min of VCV with FLEX and 1 min again of conventional VCV. Analysis of the EIT recordings comprised global and ventral and dorsal baseline levels of impedance curves, end-expiratory no-flow periods, tidal variation in ventral and dorsal areas, and regional ventilation delay index.ResultsWith FLEX, the duration of the end-expiratory zero flow intervals was significantly shortened (VCV 1.4 ± 0.3 s; FLEX 0.7 ± 0.1 s, p < 0.001), functional residual capacity was significantly elevated in both conditions of the lungs (global: healthy, increase of 87 ± 12 ml, p < 0.001; injured, increase of 115 ± 44 ml, p < 0.001; ventral: healthy, increase of 64 ± 11 ml, p < 0.001; injured, increase of 83 ± 22 ml, p < 0.001; dorsal: healthy, increase of 23 ± 5 ml, p < 0.001; injured, increase of 32 ± 26 ml, p = 0.02), and ventilation was shifted from ventral to dorsal areas (dorsal increase: healthy, 1 ± 0.5%, p < 0.01; dorsal increase: injured, 6 ± 2%, p < 0.01), compared to conventional VCV. Recruiting effects of FLEX persisted during conventional VCV following FLEX ventilation mostly in the injured but also in the healthy lungs.ConclusionsFLEX shifts regional ventilation towards dependent lung areas in healthy and in injured pig lungs. The recruiting capabilities of FLEX may be mainly responsible for lung-protective effects observed in an earlier study.

Highlights

Concepts for optimizing mechanical ventilation focus mainly on modifying the inspiratory phase
For a patient suffering from acute respiratory distress syndrome (ARDS), the injured respiratory system determines the processing of the expiration phase, leading to high expiratory peak flow rates and rapid lung deflation as a consequence of the short time-constant of passive expiration
It has been found that flow-controlled expiration (FLEX) results in lower positive end-expiratory pressure (PEEP) requirement, improved dynamic lung compliance and could better attenuate experimental ARDS compared to conventional volume-controlled ventilation (VCV) in a porcine lung injury model [5]

Summary

Introduction

Concepts for optimizing mechanical ventilation focus mainly on modifying the inspiratory phase. We propose flow-controlled expiration (FLEX) as an additional means for lung protective ventilation and hypothesize that it is capable of recruiting dependent areas of the lungs. This study investigates potential recruiting effects of FLEX using models of mechanically ventilated pigs before and after induction of lung injury with oleic acid. Analysis of the EIT recordings comprised global and ventral and dorsal baseline levels of impedance curves, end-expiratory no-flow periods, tidal variation in ventral and dorsal areas, and regional ventilation delay index. It has been found that FLEX results in lower PEEP requirement, improved dynamic lung compliance and could better attenuate experimental ARDS compared to conventional volume-controlled ventilation (VCV) in a porcine lung injury model [5]. We assessed the regional ventilation using electrical impedance tomography (EIT) during mechanical ventilation in the volume-controlled mode with and without FLEX in a pig model before and after induction of lung injury

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