Closed loop control of inspired oxygen concentration in trauma patients

Transport of mechanically ventilated patients in a combat zone presents challenges, including conservation of resources. In the battlefield setting, provision of oxygen supplies remains an important issue. Autonomous control of oxygen concentration can allow a reduction in oxygen usage and reduced mission weight.

Trauma patients requiring ventilation and inspired oxygen concentration (FIO(2)) > 0.40 were evaluated for study. Patients were randomized to consecutive 4-hour periods of closed loop control or standard care. The system for autonomous control consisted of a ventilator, oximeter, and a portable computer. The computer housed the control algorithm and collected data every 5 seconds. The controller goal was to maintain pulse oximetry (SpO(2)) at 94 +/- 2% through discrete changes of 1% to 5% every 30 seconds. Ventilator settings and SpO(2) were recorded every 5 seconds for analysis.

Forty-five patients were enrolled in this study. Oxygen saturation was maintained in the 92% to 96% saturation range 33 +/- 36% of the time during clinician control versus 83 +/- 21% during closed loop control. Time spent at the target SpO(2) 92% to 96% was 193.3 +/- 59.18 minutes during closed loop control and 87.08 +/- 87.95 minutes during clinician control (p < 0.001). Hyperoxemia was more frequent during clinician control (144.29 +/- 90.09 minutes) than during closed loop control (38.91 +/- 55.86 minutes; p < 0.001). There were no differences in the number of episodes of SpO(2) < 88%. Oxygen usage was reduced by 32% during closed loop control.

Closed loop control of FIO(2) offers the opportunity for maximizing oxygen resources, reducing mission weight, and providing targeted normoxemia without increasing risk of hypoxemia in ventilated trauma patients.