title: Quantitative computed tomography in porcine lung injury with variable versus conventional ventilation: recruitment and surfactant replacement.
abstract: OBJECTIVE
  Biologically variable ventilation improves lung function in acute respiratory distress models. If enhanced recruitment is responsible for these results, then biologically variable ventilation might promote distribution of exogenous surfactant to nonaerated areas. Our objectives were to confirm model predictions of enhanced recruitment with biologically variable ventilation using computed tomography and to determine whether surfactant replacement with biologically variable ventilation provides additional benefit in a porcine oleic acid injury model.
  
  
  METHODS
  Prospective, randomized, controlled experimental animal investigation.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Domestic pigs.
  
  
  METHODS
  Standardized oleic acid lung injury in pigs randomized to conventional mechanical ventilation or biologically variable ventilation with or without green dye labeled surfactant replacement.
  
  
  RESULTS
  Computed tomography-derived total and regional masses and volumes were determined at injury and after 4 hrs of ventilation at the same average low tidal volume and minute ventilation. Hemodynamics, gas exchange, and lung mechanics were determined hourly. Surfactant distribution was determined in postmortem cut lung sections. Biologically variable ventilation alone resulted in 7% recruitment of nonaerated regions (p < .03) and 15% recruitment of nonaerated and poorly aerated regions combined (p < .04). Total and normally aerated regional volumes increased significantly with biologically variable ventilation, biologically variable ventilation with surfactant replacement, and conventional mechanical ventilation with surfactant replacement, while poorly and nonaerated regions decreased after 4 hrs of ventilation with biologically variable ventilation alone (p < .01). Biologically variable ventilation showed the greatest improvement (p < .003, biologically variable ventilation vs. all other groups). Hyperaerated regional gas volume increased significantly with biologically variable ventilation, biologically variable ventilation with surfactant replacement, and conventional mechanical ventilation with surfactant replacement. Biologically variable ventilation was associated with restoration of respiratory compliance to preinjury levels and significantly greater improvements in gas exchange at lower peak airway pressures compared to all other groups. Paradoxically, gas exchange and lung mechanics were impaired to a greater extent initially with biologically variable ventilation with surfactant replacement. Peak airway pressure was greater in surfactant-treated animals with either ventilation mode. Surfactant was distributed to the more caudal/injured lung sections with biologically variable ventilation.
  
  
  CONCLUSIONS
  Quantitative computed tomography analysis confirms lung recruitment with biologically variable ventilation in a porcine oleic acid injury model. Surfactant replacement with biologically variable ventilation provided no additional recruitment benefit and may in fact be harmful.
authors: Department of Anesthesia, University of Manitoba, Winnipeg, Manitoba, Canada. mrgraha@cc.umanitoba.ca
authors: M
authors: M
authors: Ruth Graham
authors: Andrew L
authors: AL
authors: Goertzen
authors: Linda G
authors: LG
authors: Girling
authors: Talia
authors: T
authors: Friedman
authors: Ryan J
authors: RJ
authors: Pauls
authors: Timothy
authors: T
authors: Dickson
authors: Ainsley E G
authors: AE
authors: Espenell
authors: W Alan C
authors: WA
authors: Mutch
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology; D019301:Oleic Acid; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D011663:Pulmonary Surfactants / Q000493:pharmacokinetics / Q000627:therapeutic use*; D011897:Random Allocation; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000139:chemically induced / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics; D034421:Sus scrofa; D013990:Tidal Volume; D036542:Tomography, Spiral Computed
chemical_list: D011663:Pulmonary Surfactants; D019301:Oleic Acid