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

Abstract

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.

Is faster better? A randomised crossover study comparing algorithms for closed-loop automatic oxygen control

“…Our initial concern that fast FiO 2 responses to SpO 2 changes result in more episodes of hypoxaemia and/or hyperoxaemia was not confirmed in our study. Sadeghi Fathabadi et al 16 found a median delay in first order responses in SpO 2 following FiO 2 increments or decrements of 22 s and 40 s, respectively, which virtually fits our present waiting time of 30 s. However, some SpO 2 responses to an FiO 2 change occur after this wait time, which may increase the risk of hypoxaemia or hyperoxaemia. In our study, Target% was distinctly higher during CLAC slow compared with CLAC fast in five patients (see online supplementary figure 2S).…”

The Time Delay of Air/Oxygen Mixture Delivery After the Change of Set Fio2: An Improvement of a Neonatal Mathematical Model

“…The time delay we measured can be compared with patient data published by Fathabadi et al [12] and in Krone's master thesis [11]. The time delay presented in Table 1 and demonstrated in Figure 4 shows irregularities in the decreasing trend.…”

Comparison of two devices for automated oxygen control in preterm infants: a randomised crossover trial

“…Original research significant time delay between FiO 2 adjustment and when SpO 2 reaches a new stable level. 11 Given both the importance and difficulty of SpO 2 targeting, automated oxygen control (AOC) is a logical improvement on current practice. In essence, the concept is of an SpO 2 input to a device holding a set of computational instructions (an algorithm), which then gives an output, an updated value for FiO 2 .…”