Hylke Salverda

55 3 Comparison of two devices for automated oxygen control in preterm infants Automated oxygen control algorithms The CLiO2 algorithmembedded in the AVEA ventilator is a hybrid rule-based adaptive controller. It makes initial FiO2 adjustments that are proportional to the difference between the measured SpO2 and the limits of the SpO2 TR. Subsequent adjustments also take into account this difference, as well as the SpO2 trend and basal oxygen requirement, the baseFiO2. The baseFiO2 is periodically updated by interrogation of 5 minutes of recent SpO2 and FiO2 data where specific conditions are met, averaged along with the current baseFiO2 value. 26 The OxyGenie algorithm embedded in the SLE6000 ventilator is an adaptive proportional-integral-derivative (PID) controller. The P, I and D terms each have separate coefficients, and in each case are adjusted from raw values to better suit the physiology of a neonate and account for the limitations of pulse oximetry. The basal FiO2, referred to as Reference FiO2, is calculated every 30 minutes using 60 minutes of preceding FiO2 and SpO2 values. Study procedures A crossover design was used to study each infant on the same respiratory support mode. Infants received two consecutive study periods of 24 hours each, one with oxygen therapy under the control of the CLiO2 algorithm and the other with the OxyGenie algorithm, in random sequence. Web-based randomisation by Castor EDC (Castor, Amsterdam, The Netherlands) was used, stratified by mode of respiratory support (invasive or non-invasive) using variable (4, 6) block sizes. After the first study period the alternative ventilator was substituted, and a wash-out period of 1 hour was applied before data recording re-started to prevent a carry-over bias. The study was completed when automated oxygen control with each device had been applied for 24 hours, with standard respiratory management thereafter resuming. The SpO2 TR for both study periods was 91%-95%. No other extra interventions were given. Infants did receive all standard treatments, and ventilation settings were at the discretion of the caregiver. Data collection and analysis Baseline characteristics were noted for each infant, including details on respiratory support and clinical state. The primary outcome was the proportion of time spent within the SpO2 TR (91%-95% with supplemental oxygen, or 91%-100% without supplemental oxygen). SpO2 and intended FiO2 values were recorded each second