• Go Hirabayashi, Yukihiko Ogihara, Shoichi Tsukakoshi, Kiyoshi Daimatsu, Masaaki Inoue, Kiyoyasu Kurahashi, Koichi Maruyama, and Tomio Andoh.
• From the Mizonokuchi Hospital, Teikyo University School of Medicine, Kanagawa (GH, KM, TA), Department of Anaesthesiology, Tokyo Medical University (YO), Department of R&D, Senko Medical Instrument Co., Ltd. (ST), Furrex Co., Ltd., Tokyo, Japan (KD), S.K.I. Net, Inc., Tokyo (MI), and Department of Anesthesiology and Intensive Care Medicine, International University of Health and Welfare, School of Medicine, Narita, Japan (KK).
• Eur J Anaesthesiol. 2018 Apr 1; 35 (4): 307-314.

BackgroundPressure-controlled inverse inspiratory to expiratory ratio ventilation (PC-IRV) is thought to be beneficial for reducing the dead space volume.ObjectiveTo investigate the effects of PC-IRV on the components of dead space during robot-assisted laparoscopic radical prostatectomy (RLRP).DesignA randomised crossover study of three different ventilator modes.SettingA single university hospital from September 2014 to April 2015.PatientsTwenty consecutive study participants undergoing RLRP.InterventionsPatients were ventilated sequentially with three different modes in random order for 30 min: volume control ventilation (VCV; inspiratory to expiratory ratio 0.5), pressure control ventilation (PCV; inspiratory to expiratory ratio 0.5) and PC-IRV. Inverse inspiratory to expiratory ratio was adjusted individually by observing the expiratory flow-time wave to prevent the risk of dynamic pulmonary hyperinflation.Main Outcome MeasuresThe primary outcome included physiological dead space (VDphys), airway dead space (VDaw), alveolar dead space (VDalv) and shunt dead space (VDshunt). VDphys was calculated by Enghoff's method. We also analysed respiratory dead space (VDresp) and VDaw using a novel analytical method. Then, VDalv and VDshunt were calculated by VDalv = VDresp - VDaw and VDshunt = VDphys - VDresp, respectively.ResultsThe VDphys/expired tidal volume (VTE) ratio in PC-IRV (29.2 ± 4.7%) was significantly reduced compared with that in VCV (43 ± 8.5%) and in PCV (35.9 ± 3.9%). The VDshunt/VTE in PC-IRV was significantly smaller than that in VCV and PCV. VDaw/VTE in PC-IRV was also significantly smaller than that in VCV but not that in PCV. There was no significant change in VDalv/VTE.ConclusionPC-IRV with the inspiratory to expiratory ratio individually adjusted by the expiratory flow-time wave decreased VDphys/VTE in patients undergoing RLRP.Trial RegistrationUniversity Hospital Medical Information Network in Japan 000014004.

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