33 2 Automated oxygen control in preterm infants, how does it work and what to expect Commercially available algorithms Details of six commercially available oxygen control algorithms are set out below, with a precis of the known function of the algorithm followed by a section on clinical effect where data are available. Closed-Loop Automatic oxygen Control17 How it works The Closed-Loop Automatic oxygen Control (CLAC) is a rule-based algorithm commercially available in the Leoni ventilator (Löwenstein medical, RheinlandPfalz, Germany). The algorithm deduces two parameters from the SpO2 signal once per second: the state and trend parameters. The state parameter is calculated by taking SpO2 values of the last three minutes, filtering out values far out-of-range, and forming a so-called ‘spread’ from the remaining information: a regression line combined with an adapted standard error. Using the middle of this spread the algorithm labels the state ‘substantially above’, ‘above’, ‘normal range’, ‘below’, or ‘substantially below’ target range, in response to which FiO2 will be adjusted in the range of -0.02 to +0.05 (-0.02, -0.01, +0.01, +0.02 and +0.05). The trend parameter – the slope of SpO2 trend in the last 60 seconds – can postpone an adjustment, dependent on an increasing, stable or decreasing trend. This to account for when the SpO2 is outside the TR but normalising. 17, 24, 25 After making an adjustment the algorithm pauses for 180 seconds to allow the baby to reach a new steady oxygenation state. Recently, the alternative to pause for 30 seconds was added.26 The system can pause for safety (reasons are: adapted standard error above a cut-off value; missing or invalid oximetry input; acute hypoxia (SpO2 < 80%) for more than 4 seconds) during which bedside staff is alerted and can intervene if necessary. Clinical effect Three randomised crossover trials reported the use of the CLAC algorithm (Table 1). While infants spent more time within TR during AOC (90.5% vs 81.7%, P = 0.01) during the first study, the short study span probably led to the high proportion of time in TR in both groups. The reduction in manual adjustments (89%) is however striking and could be beneficial in reducing workload for bedside caregivers.17 In a subsequent multicentre study27 infants on (non)invasive ventilation were studied
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