Comparative effects of flow vs. volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in pigs

Jakob Wittenstein,Martin Scharffenberg,Pia Michler,Robert Huhle,Thomas Kiss,Thomas Bluth,Thea Koch,Marcelo Gama De Abreu,Xi Ran,Diana Keller,Raphael Theilen,Sebastian Tauer

doi:10.1186/s40635-020-00308-0

Jakob Wittenstein, Martin Scharffenberg + Show 10 more

Open Access

https://doi.org/10.1186/s40635-020-00308-0

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Abstract

BackgroundFlow-controlled ventilation (FCV) allows expiratory flow control, reducing the collapse of the airways during expiration. The performance of FCV during one-lung ventilation (OLV) under intravascular normo- and hypovolaemia is currently unknown. In this explorative study, we hypothesised that OLV with FCV improves PaO2 and reduces mechanical power compared to volume-controlled ventilation (VCV). Sixteen juvenile pigs were randomly assigned to one of two groups: (1) intravascular normovolaemia (n = 8) and (2) intravascular hypovolaemia (n = 8). To mimic inflammation due to major thoracic surgery, a thoracotomy was performed, and 0.5 μg/kg/h lipopolysaccharides from Escherichia coli continuously administered intravenously. Animals were randomly assigned to OLV with one of two sequences (60 min per mode): (1) VCV–FCV or (2) FCV–VCV. Variables of gas exchange, haemodynamics and respiratory signals were collected 20, 40 and 60 min after initiation of OLV with each mechanical ventilation mode. The distribution of ventilation was determined using electrical impedance tomography (EIT).ResultsOxygenation did not differ significantly between modes (P = 0.881). In the normovolaemia group, the corrected expired minute volume (P = 0.022) and positive end-expiratory pressure (PEEP) were lower during FCV than VCV. The minute volume (P ≤ 0.001), respiratory rate (P ≤ 0.001), total PEEP (P ≤ 0.001), resistance of the respiratory system (P ≤ 0.001), mechanical power (P ≤ 0.001) and resistive mechanical power (P ≤ 0.001) were lower during FCV than VCV irrespective of the volaemia status. The distribution of ventilation did not differ between both ventilation modes (P = 0.103).ConclusionsIn a model of OLV in normo- and hypovolemic pigs, mechanical power was lower during FCV compared to VCV, without significant differences in oxygenation. Furthermore, the efficacy of ventilation was higher during FCV compared to VCV during normovolaemia.

Highlights

Flow-controlled ventilation (FCV) allows expiratory flow control, reducing the collapse of the airways during expiration
In a model of one-lung ventilation (OLV) in normo- and hypovolemic pigs, mechanical power was lower during FCV compared to volume-controlled ventilation (VCV), without significant differences in oxygenation
The efficacy of ventilation was higher during FCV compared to VCV during normovolaemia

Summary

Introduction

Flow-controlled ventilation (FCV) allows expiratory flow control, reducing the collapse of the airways during expiration. The performance of FCV during one-lung ventilation (OLV) under intravascular normo- and hypovolaemia is currently unknown. In this explorative study, we hypothesised that OLV with FCV improves PaO2 and reduces mechanical power compared to volume-controlled ventilation (VCV). During one-lung ventilation (OLV) the incidence of hypoxemia can be as high as 10% and may lead to adverse outcomes [1]. In the presence of atelectasis, the tidal volume is distributed across a reduced lung volume, possibly resulting in hyperdistension of lung zones, or volutrauma [4]. Atelectrauma and volutrauma can increase the transfer of energy per time from the ventilator to the lungs (mechanical power [5]), which might result in ventilator-induced lung injury (VILI) [6]. The risk of VILI is increased during thoracic procedures compared with non-thoracic procedures [7]

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