Abstract
BackgroundIn obese patients, high closing capacity and low functional residual capacity increase the risk for expiratory alveolar collapse. Constant expiratory flow, as provided by the new flow-controlled ventilation (FCV) mode, was shown to improve lung recruitment. We hypothesized that lung aeration and respiratory mechanics improve in obese patients during FCV.MethodsWe compared FCV and volume-controlled (VCV) ventilation in 23 obese patients in a randomized crossover setting. Starting with baseline measurements, ventilation settings were kept identical except for the ventilation mode related differences (VCV: inspiration to expiration ratio 1:2 with passive expiration, FCV: inspiration to expiration ratio 1:1 with active, linearized expiration). Primary endpoint of the study was the change of end-expiratory lung volume compared to baseline ventilation. Secondary endpoints were the change of mean lung volume, respiratory mechanics and hemodynamic variables.ResultsThe loss of end-expiratory lung volume and mean lung volume compared to baseline was lower during FCV compared to VCV (end-expiratory lung volume: FCV, − 126 ± 207 ml; VCV, − 316 ± 254 ml; p < 0.001, mean lung volume: FCV, − 108.2 ± 198.6 ml; VCV, − 315.8 ± 252.1 ml; p < 0.001) and at comparable plateau pressure (baseline, 19.6 ± 3.7; VCV, 20.2 ± 3.4; FCV, 20.2 ± 3.8 cmH2O; p = 0.441), mean tracheal pressure was higher (baseline, 13.1 ± 1.1; VCV, 12.9 ± 1.2; FCV, 14.8 ± 2.2 cmH2O; p < 0.001). All other respiratory and hemodynamic variables were comparable between the ventilation modes.ConclusionsThis study demonstrates that, compared to VCV, FCV improves regional ventilation distribution of the lung at comparable PEEP, tidal volume, PPlat and ventilation frequency. The increase in end-expiratory lung volume during FCV was probably caused by the increased mean tracheal pressure which can be attributed to the linearized expiratory pressure decline.Trial registrationGerman Clinical Trials Register: DRKS00014925. Registered 12 July 2018.
Highlights
In obese patients, high closing capacity and low functional residual capacity increase the risk for expiratory alveolar collapse
Gender, American Society of Anesthesiologists (ASA) physical status, predicted and actual body weight and body mass index (BMI) were comparable between the two interventional groups (Table 1)
No significant differences in tidal volume, ventilation frequency, Plateau pressure (PPlat), Peripheral oxygen saturation (SpO2) and Quasi-static compliance of the respiratory system (CRS) were found between flow-controlled ventilation (FCV) and volume-controlled ventilation (VCV)
Summary
High closing capacity and low functional residual capacity increase the risk for expiratory alveolar collapse. As provided by the new flow-controlled ventilation (FCV) mode, was shown to improve lung recruitment. We hypothesized that lung aeration and respiratory mechanics improve in obese patients during FCV. An emerging ventilation technique to linearize expiratory flow is flow-controlled ventilation (FCV), provided by the new ventilator Evone (Ventinova Medical B.V., Eindhoven, the Netherlands). This device provides a constant positive flow during inspiration and a constant negative flow during expiration. Since FCV is a new emerging technique comparative clinical studies in humans, in patients with impaired respiratory system mechanics, are lacking
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