title: Portable mechanical ventilation with closed-loop control of inspired fraction of oxygen maintains oxygenation in the setting of hemorrhage and lung injury.
abstract: BACKGROUND
  Closed-loop controllers (CLCs) embedded within portable mechanical ventilators may allow for autonomous weaning. The ability of CLCs to maintain adequate oxygenation in the setting of hemorrhage and lung injury is unknown. We hypothesized that a portable ventilator with a CLC for inspired fraction of oxygen (FIO2) could provide oxygenation in a porcine model of hemorrhage and lung injury.
  
  
  METHODS
  Female pigs randomized to the study group (n = 6) underwent a pressure-controlled bleed (mean arterial pressure = 40 mm Hg for 30 minutes). Acute lung injury was induced by saline lung lavage followed by intentional infliction of barotrauma. Sham pigs (n = 6) underwent placement of monitoring devices without hemorrhage or lung injury. All pigs were then placed on a portable ventilator modified with a CLC algorithm, which uses feedback from pulse oximetry (SpO2) and FIO2 trends to adjust FIO2 and maintain a target SpO2 of 94% (2%). The initial FIO2 was set at 0.60. Tidal volume, positive end-expiratory pressure, rate, and inspiratory-to-expiratory ratio were constant unless changes were required clinically.
  
  
  RESULTS
  Study pigs had lower mean arterial pressures than shams at all time points except baseline. PaO2/FIO2 ratios were less than 300 and significantly lower than both baseline values and corresponding sham values at all time points. The CLC weaned the FIO2 at a reduced rate in study pigs relative to shams with a final mean FIO2 of 0.54 and 0.29 in study and sham pigs, respectively (p < 0.05). There was a significant divergence in the study and sham FIO2 curves but no significant difference in oxygen saturation or hypoxemia.
  
  
  CONCLUSIONS
  Adequate oxygenation can be maintained in the setting of hemorrhage and lung injury using a portable ventilator embedded with a CLC of FIO2 based on pulse oximetry. These devices may be valuable for providing advanced medical care in resource-limited environments.
authors.affiliation: From the Division of Trauma and Critical Care, Department of Surgery, Institute for Military Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Jernigan
authors.forename: Richard S
authors.initials: RS
authors.lastname: Hoehn
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Blakeman
authors.forename: Judy
authors.initials: J
authors.lastname: Heyl
authors.forename: Bryce R H
authors.initials: BR
authors.lastname: Robinson
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Pritts
authors.forename: Richard D
authors.initials: RD
authors.lastname: Branson
mesh_terms: D000818:Animals; D025461:Feedback, Physiological; D005260:Female; D055370:Lung Injury / Q000628:therapy*; D010100:Oxygen / Q000008:administration & dosage*; D012121:Respiration, Artificial / Q000379:methods*; D012771:Shock, Hemorrhagic / Q000628:therapy*; D013552:Swine; D015300:Ventilator Weaning / Q000379:methods*
chemical_list: D010100:Oxygen