Development and preclinical testing of an adaptive algorithm for automated control of inspired oxygen in the preterm infant.

OBJECTIVE: To assess the performance of a novel algorithm for automated oxygen control using a simulation of oxygenation founded on in vivo data from preterm infants. METHODS: A proportional-integral-derivative (PID) control algorithm was enhanced by (i) compensation for the non-linear SpO2-PaO2 relationship, (ii) adaptation to the severity of lung dysfunction and (iii) error attenuation within the target range. Algorithm function with and without enhancements was evaluated by iterative linking with a computerised simulation of oxygenation. Data for this simulation (FiO2 and SpO2 at 1 Hz) were sourced from extant recordings from preterm infants (n=16), and converted to a datastream of values for ventilation:perfusion ratio and shunt. Combination of this datastream second by second with the FiO2 values from the algorithm under test produced a sequence of novel SpO2 values, allowing time in the SpO2 target range (91%-95%) and in various degrees of hypoxaemia and hyperoxaemia to be determined. A PID algorithm with 30 s lockout after each FiO2 adjustment, and a proportional-derivative (PD) algorithm were also evaluated. RESULTS: Separate addition of each enhancing feature to the PID algorithm showed a benefit, but not with uniformly positive effects. The fully enhanced algorithm was optimal for the combination of targeting the desired SpO2 range and avoiding time in, and episodes of, hypoxaemia and hyperoxaemia. This algorithm performed better than one with a 30 s lockout, and considerably better than PD control. CONCLUSIONS: An enhanced PID algorithm was very effective for automated oxygen control in a simulation of oxygenation, and deserves clinical evaluation.

Characterisation of the Oxygenation Response to Inspired Oxygen Adjustments in Preterm Infants.

BACKGROUND: Oxygen saturation (SpO2) targeting in the preterm infant may be improved with a better understanding of the SpO2 responses to changes in inspired oxygen (FiO2). OBJECTIVE: We investigated the first-order FiO2-SpO2 relationship, aiming to quantify the parameters governing that relationship, the influences on these parameters and their variability. METHODS: In recordings of FiO2 and SpO2 from preterm infants on continuous positive airway pressure and supplemental oxygen, we identified unique FiO2 adjustments and mapped the subsequent SpO2 responses. For responses identified as first-order, the delay, time constant and gain parameters were determined. Clinical and physiological predictors of these parameters were sought in regression analysis, and intra- and inter-subject variability was evaluated. RESULTS: In 3,788 h of available data from 47 infants at 31 (28-33) post-menstrual weeks [median (interquartile range)], we identified 993 unique FiO2 adjustments followed by a first-order SpO2 response. All response parameters differed between FiO2 increments and decrements, with increments having a shorter delay, longer time constant and higher gain [2.9 (1.7-4.8) vs. 1.3 (0.58-2.6), p < 0.05]. Gain was also higher in less mature infants and in the setting of recent SpO2 instability, and was diminished with increasing severity of lung dysfunction. Intra-subject variability in all parameters was prominent. CONCLUSIONS: First-order SpO2 responses show variable gain, influenced by the direction of FiO2 adjustment and the severity of lung disease, as well as substantial intra-subject parameter variability. These findings should be taken into account in adjustment of FiO2 for SpO2 targeting in preterm infants.

Lost without trace: oximetry signal dropout in preterm infants.

Oxygen saturation (SpO2) signal dropout leaves caregivers without a reliable measure to guide oxygen therapy. We studied SpO2 dropout in preterm infants on continuous positive airway pressure, noting the SpO2 values at signal loss and recovery and thus the resultant change in SpO2, and the factors influencing this parameter. In 32 infants of median gestation 26 weeks, a total of 3932 SpO2 dropout episodes were identified (1.1 episodes/h). In the episodes overall, SpO2 decreased by 1.1%, with the SpO2 change influenced by starting SpO2 (negative correlation), but not dropout duration. For episodes starting in hypoxia (SpO2 <85%), SpO2 recovered at a median of 3.2% higher than at SpO2 dropout, with a downward trajectory in a quarter of cases. We conclude that after signal dropout SpO2 generally recovers in a relative normoxic range. Blind FiO2 adjustments are thus unlikely to be of benefit during most SpO2 dropout episodes.