title: Effect of inspiratory flow rate on the efficiency of carbon dioxide removal at tidal volumes below instrumental dead space.
abstract: OBJECTIVE
  The ability to ventilate babies with tidal volumes (VTs) below dead space has been demonstrated both in vivo and in vitro, though it appears to violate classical respiratory physiology. We hypothesised that this phenomenon is made possible by rapid flow of gas that penetrates the dead space allowing fresh gas to reach the lungs and that the magnitude of this phenomenon is affected by flow rate or how rapidly air flows through the endotracheal tube.
  
  
  METHODS
  We conducted two bench experiments. First, we measured the time needed for complete CO2washout from a test lung to assess how fixed VTbut different inflation flow rates affect ventilation. For the second experiment, we infused carbon dioxide at a low rate into the test lung, varied the inflation flow rate and adjusted the VTto maintain stable end tidal carbon dioxide (ETCO2).
  
  
  RESULTS
  At all tested VTs, lower flow rate increased the time it took for CO2to washout from the test lung. The effect was most pronounced for VTs below dead space. The CO2steady-state experiment showed that ETCO2increased when the flow rate decreased. Ventilating with a slower flow rate required a nearly 20% increase in VTfor the same effective alveolar ventilation.
  
  
  CONCLUSIONS
  Inflation flow rate affects the efficiency of CO2removal with low VT. Our results are relevant for providers using volume-controlled ventilation or other modes that use low inflation flow rates because the VTrequired for normocapnia will be higher than published values that were generated using pressure-limited ventilation modes with high inflation flows.
authors: Department of Pediatrics, Women and Infants, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA.
authors: Edward H
authors: EH
authors: Hurley
authors: Department of Pediatrics, Women and Infants, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA.
authors: Martin
authors: M
authors: Keszler
mesh_terms: D002245:Carbon Dioxide / Q000502:physiology; D006801:Humans; D008168:Lung / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial / Q000379:methods*; D012126:Respiratory Dead Space / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide
keywords: Respiratory physiology; Tidal volume; Volume guarantee; Volume targeted ventilation