title: Ventilator gas flow rates affect inspiratory time and ventilator efficiency index in term lambs.
abstract: BACKGROUND
  Despite increasing survival in the smallest preterm infants, the incidence of chronic lung disease has not decreased. Research into ventilatory strategies has concentrated on minimising barotrauma, volutrauma and atelectotrauma, but little attention has been paid to the role of bias gas flow rates and the potential for rheotrauma or shear stress injury. Ventilated preterm infants frequently receive relatively high gas flow rates.
  
  
  OBJECTIVE
  We hypothesised that altering bias gas flow rates would change the efficiency of ventilation and thereby affect ventilatory parameters.
  
  
  METHODS
  We tested this hypothesis using an artificial lung followed by ventilation of 8 term lambs.
  
  
  RESULTS
  Between flows of 2 and 15 l/min, inflation time (Ti) in the artificial lung was inversely related to the bias gas flow rate. In the ventilated lambs, Ti was inversely related to flow rates up to 10 l/min, with no statistically significant effect at flow rates >10 l/min. There were no adverse effects on gas exchange or cardiovascular parameters until a flow rate of 3 l/min was used, when inadequate gas exchange occurred.
  
  
  CONCLUSIONS
  Ti is inversely associated with the bias gas flow rate. Flow rates much lower than those used in many neonatal units seem to provide adequate ventilation. We suggest that the role of ventilator gas flow rates, which may potentially influence shear stress in ventilator-induced lung injury, merits further investigation.
authors.affiliation: Liggins Institute, University of Auckland, Auckland, New Zealand.
authors.forename: Katinka P
authors.initials: KP
authors.lastname: Bach
authors.forename: Carl A
authors.initials: CA
authors.lastname: Kuschel
authors.forename: Mark H
authors.initials: MH
authors.lastname: Oliver
authors.forename: Frank H
authors.initials: FH
authors.lastname: Bloomfield
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D004195:Disease Models, Animal; D006801:Humans; D007231:Infant, Newborn; D007320:Inspiratory Capacity / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D008954:Models, Biological; D011175:Positive-Pressure Respiration; D012119:Respiration; D012121:Respiration, Artificial; D012127:Respiratory Distress Syndrome, Newborn / Q000517:prevention & control; D012756:Sheep; D013997:Time Factors; D012122:Ventilators, Mechanical