Closed-loop control of FiO₂ rapidly identifies need for rescue ventilation and reduces ARDS severity in a conscious sheep model of burn and smoke inhalation injury

Pulmonary injury can be characterized by an increased need for fraction of inspired oxygen or inspired oxygen percentage (FiO2) to maintain arterial blood saturation of oxygenation (SaO2).We tested a smart oxygenation system (SOS) that uses the activity of a closed-loop control FiO2 algorithm (CLC-FiO2) to rapidly assess acute respiratory distress syndrome (ARDS) severity so that rescue ventilation (RscVent) can be initiated earlier. After baseline data, a pulse-oximeter (noninvasive saturation of peripheral oxygenation [SpO2]) was placed. Sheep were then subjected to burn and smoke inhalation injury and followed for 48 h. Initially, sheep were spontaneously ventilating and then randomized to standard of care (SOC) (n=6), in which RscVent began when partial pressure of oxygen (PaO2) < 90 mmHg or FiO2 < 0.6, versus SOS (n=7), software that incorporates and displays SpO2, CLC-FiO2, and SpO2/CLC-FiO2 ratio, at which RscVent was initiated when ratio threshold < 250. RscVent was achieved using a G5 Hamilton ventilator (Bonaduz, Switzerland) with adaptive pressure ventilation and adaptive support ventilation modes for SOC and SOS, respectively. Outcomes: the time difference from when SpO2/FiO2 < 250 to RscVent initiation was 4.7±0.6 h and 0.2±0.1 h, SOC and SOS, respectively (P < 0.001). Oxygen responsiveness after RscVent, defined as SpO2/FiO2 > 250 occurred in 4/7, SOS and 0/7, SOC. At 48 h the SpO2/ FiO2 ratio was 104±5 in SOC versus 228±59 in SOS (P=0.036). Ventilatory compliance and peak airway pressures were significantly improved with SOS versus SOC (P<0.001). Data suggest that SOS software, e.g. SpO2/CLC-FiO2 ratio, after experimental ARDS can provide a novel continuous index of pulmonary function that is apparent before other clinical symptoms. Earlier initiation of RscVent translates into improved oxygenation (reduces ARDS severity) and ventilation.