Re-inspiration of CO2 from ventilator circuit: effects of circuit flushing and aspiration of dead space up to high respiratory rate

Introduction Dead space negatively influences carbon dioxide (CO2) elimination, particularly at high respiratory rates (RR) used at low tidal volume ventilation in acute respiratory distress syndrome (ARDS). Aspiration of dead space (ASPIDS), a known method for dead space reduction, comprises two mechanisms activated during late expiration: aspiration of gas from the tip of the tracheal tube and gas injection through the inspiratory line - circuit flushing. The objective was to study the efficiency of circuit flushing alone and of ASPIDS at wide combinations of RR and tidal volume (VT) in anaesthetized pigs. The hypothesis was tested that circuit flushing and ASPIDS are particularly efficient at high RR.