FIX CONTROLLER - AN INSTRUMENT TO AUTOMATICALLY ADJUST INSPIRED OXYGEN FRACTION USING FEEDBACK-CONTROL FROM A PULSE OXIMETER

Objective. To develop an instrument to help prevent pulmonary O-2 toxi city, a syndrome that manifests itself in adult intensive care patient s. Methods. We designed, built, and tested a device that controls FIO2 exposure using oxygen saturation measured with a pulse oximeter (SpO( 2)) in a negative feedback control system. A target SpO(2) is designat ed by the clinician and the system adjusts the FIO2 from a mechanical ventilator so as to minimize the difference between the measured SpO(2 ) and the target. Important elements of the system include a conservat ive artifact rejection algorithm, a gain-scheduled sampled-data propor tional-integral-derivative (PID) controller, and a safety system to pr event inspired mixtures with undesirably low FIO2 due to device failur e. Results. The control system was tuned in a series of animal experim ents. Acceptable clinical response of the system was obtained using a gain-scheduled controller algorithm whereby the gain of the proportion al term of a PID controller was adjusted based on the error signal and measured minute ventilation. Also, the artifact rejection algorithm a nd safety systems were successfully tested using simulation. Conclusio ns. Testing the effectiveness of this instrument will require comparis on with manual control of FIO2 in an appropriately designed trial.