title: Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation.
abstract: BACKGROUND
  Hypoxemia is common during one-lung ventilation (OLV). Atelectasis contributes to the problem. Biologically variable ventilation (BVV), using microprocessors to reinstitute physiologic variability to respiratory rate and tidal volume, has been shown to be advantageous over conventional monotonous control mode ventilation (CMV) in improving oxygenation during the period of lung reinflation after OLV in an experimental model. Here, using a porcine model, the authors compared BVV with CMV during OLV to assess gas exchange and respiratory mechanics.
  
  
  METHODS
  Eight pigs (25-30 kg) were studied in each of two groups. After induction of anesthesia-tidal volume 12 ml/kg with CMV and surgical intervention-tidal volume was reduced to 9 ml/kg. OLV was initiated with an endobronchial blocker, and the animals were randomly allocated to either continue CMV or switch to BVV for 90 min. After OLV, a recruitment maneuver was undertaken, and both lungs were ventilated for a further 60 min. At predetermined intervals, hemodynamics, respiratory gases (arterial, venous, and end-tidal samples) and mechanics (airway pressures, static and dynamic compliances) were measured. Derived indices (pulmonary vascular resistance, shunt fraction, and dead space ventilation) were calculated.
  
  
  RESULTS
  By 15 min of OLV, arterial oxygen tension was greater in the BVV group (group x time interaction, P = 0.003), and shunt fraction was lower with BVV from 30 to 90 min (group effect, P = 0.0004). From 60 to 90 min, arterial carbon dioxide tension was lower with BVV (group x time interaction, P = 0.0001) and dead space ventilation was less from 60 to 90 min (group x time interaction, P = 0.0001). Static compliance was greater by 60 min of BVV and remained greater during return to ventilation of both lungs (group effect, P = 0.0001).
  
  
  CONCLUSIONS
  In this model of OLV, BVV resulted in superior gas exchange and respiratory mechanics when compared with CMV. Improved static compliance persisted with restoration of two-lung ventilation.
authors.affiliation: Anesthesia Research Laboratory, Winnipeg, Manitoba, Canada.
authors.forename: Michael C
authors.initials: MC
authors.lastname: McMullen
authors.forename: Linda G
authors.initials: LG
authors.lastname: Girling
authors.forename: M Ruth
authors.initials: MR
authors.lastname: Graham
authors.forename: W Alan C
authors.initials: WA
authors.lastname: Mutch
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis / Q000379:methods; D008168:Lung / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D012121:Respiration, Artificial / Q000379:methods*; D015656:Respiratory Mechanics / Q000502:physiology*; D013552:Swine