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

Background: Oxygen saturation (SpO(2)) targeting in the preterm infant may be improved with a better understanding of the SpO(2) responses to changes in inspired oxygen (SpO(2)). Objective: We investigated the first-order FiO(2)-SpO(2) relationship, aiming to quantify the parameters governing that relationship, the influences on these parameters and their variability. Methods: In recordings of FiO(2) and SpO(2) from preterm infants on continuous positive airway pressure and supplemental oxygen, we identified unique FiO(2) adjustments and mapped the subsequent SpO(2) 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 (inter-quartile range)], we identified 993 unique FiO(2) adjustments followed by a first-order SpO(2) response. All response parameters differed between FiO(2) 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 SpO(2) instability, and was diminished with increasing severity of lung dysfunction. Intra-subject variability in all parameters was prominent. Conclusions: First-order SpO(2) responses show variable gain, influenced by the direction of FiO(2) 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 FiO(2) for SpO(2) targeting in preterm infants. (C) 2015 S. Karger AG, Basel