Circuit flushing and ASPIDS, which significantly reduce tubing dead space and PaCO 2, merit further clinical studies. ConclusionsĪt high RR, re-breathing of CO 2 from the y-piece and tubing becomes important. ASPIDS reduced PaCO 2 by 33% at RR 40 minutes -1 and by 41% at RR 60 minutes -1. In Part 2, circuit flushing reduced PaCO 2 by 20% at RR 40 minutes -1 and by 26% at RR 60 minutes -1. In Part 1, VD aw, prox was 7.6 ± 0.5% of V T at RR 10 minutes -1 and 16 ± 2.5% at RR 60 minutes -1. In part two, changes in CO 2 partial pressure (PaCO 2) during prolonged periods of circuit flushing and ASPIDS were studied at RR 20, 40 and 60 minutes -1. Proximal dead space in a y-piece and ventilator tubing (VD aw, prox) was measured. In Part 1 of the study, RR and V T were, with a computer-controlled ventilator, modified for one breath at a time without changing minute ventilation. The hypothesis was tested that circuit flushing and ASPIDS are particularly efficient at high RR. The objective was to study the efficiency of circuit flushing alone and of ASPIDS at wide combinations of RR and tidal volume (V T) in anaesthetized pigs. 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. Dead space negatively influences carbon dioxide (CO 2) elimination, particularly at high respiratory rates (RR) used at low tidal volume ventilation in acute respiratory distress syndrome (ARDS).
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