title: FIx controller: an instrument to automatically adjust inspired oxygen fraction using feedback control from a pulse oximeter.
abstract: OBJECTIVE
  To develop an instrument to help prevent pulmonary O2 toxicity, a syndrome that manifests itself in adult intensive care patients.
  
  
  METHODS
  We designed, built, and tested a device that controls FIO2 exposure using oxygen saturation measured with a pulse oximeter (SpO2) in a negative feedback control system. A target SpO2 is designated by the clinician and the system adjusts the FIO2 from a mechanical ventilator so as to minimize the difference between the measured SpO2 and the target. Important elements of the system include a conservative artifact rejection algorithm, a gainscheduled sampled-data proportional-integral-derivative (PID) controller, and a safety system to prevent inspired mixtures with undesirably low FIO2 due to device failure.
  
  
  RESULTS
  The control system was tuned in a series of animal experiments. Acceptable clinical response of the system was obtained using a gain-scheduled controller algorithm whereby the gain of the proportional term of a PID controller was adjusted based on the error signal and measured minute ventilation. Also, the artifact rejection algorithm and safety systems were successfully tested using simulation.
  
  
  CONCLUSIONS
  Testing the effectiveness of this instrument will require comparison with manual control of FIO2 in an appropriately designed trial.
authors.affiliation: Department of Anesthesia, Massachusetts General Hospital, Boston 02114, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Raemer
authors.forename: X B
authors.initials: XB
authors.lastname: Ji
authors.forename: G P
authors.initials: GP
authors.lastname: Topulos
mesh_terms: D000465:Algorithms; D000818:Animals; D016477:Artifacts; D004285:Dogs; D005246:Feedback; D010092:Oximetry; D010100:Oxygen / Q000008:administration & dosage*; D012121:Respiration, Artificial
chemical_list: D010100:Oxygen