Adapting automated control of oxygen saturation to apnoea in preterm infants
Creators: name: Marshall, Andrew
Publisher: name: University of Tasmania
Year: 2024

description: Preterm infants face a multitude of challenges as a direct consequence of their prematurity. The fluctuations in inspired oxygen requirement and irregular breathing patterns resulting from an immature respiratory system are of particular concern. Clinical management of blood oxygen saturations in these infants is further complicated by apnoea of prematurity, a condition that affects the majority of preterm infants and which, along with associated intermittent hypoxaemia and bradycardia, has been linked to adverse neurodevelopmental outcomes. Devices to automatically deliver supplemental inspired oxygen are now seeing more general adoption and have demonstrated marked improvements in oxygen saturation targeting and in reducing the incidence of severe hypoxaemia and bradycardia compared with manual titration by bedside staff. However, adapting appropriately to both the gradual variations in basal oxygen requirement between infants and throughout infant development, as well as to the rapid and frequent fluctuations in oxygen requirement associated with apnoea, remains a challenge for automated oxygen controllers. <br>Although apnoea is a well-recognised cause of physiological instability in preterm infants and presents a unique challenge for automated oxygen control, the factors influencing the severity of associated hypoxaemia and bradycardia are not well characterised. In a prospective analysis of apnoeic events in preterm infants receiving supplemental oxygen and non-invasive respiratory support, associations were identified between key situational, clinical and demographic factors and the incidence of subsequent hypoxaemic and bradycardic episodes. In particular, short-lived apnoeic events were found to contribute disproportionately to the overall incidence of physiological instability. From this analysis, a fuzzy inference system was developed to evaluate the risk of post-apnoea physiological instability, incorporating previously identified predictive relationships and expert clinical knowledge. <br>Despite the efficacy of rapidly responsive oxygen controllers in minimising intermittent hypoxaemia, their performance during apnoea is likely to be poor. A controller adaptation was developed to supplement the controller behaviour by providing a pre-emptive proportional increase in inspired oxygen during detected apnoeic events, aiming to improve post-apnoea recovery. Oxygen saturation targeting with this apnoea response module and with standard automated control were evaluated in simulation. Both controllers achieved improved targeting compared with manual control, with the apnoea response module outperforming both, especially when a larger proportional oxygen increase was provided. However, both controllers resulted in significant oxygenation overshoot, increasing the risk of hyperoxaemia. <br>In an interventional crossover study, the performance of a refined version of an adaptive automated oxygen controller was evaluated for the first time in standard clinical conditions. Oxygen saturation targeting was improved with automatic control across all infants, with a 23% increase in time spent in the target saturation range overall while maintaining equivalent exposure to inspired oxygen. In a nested study the developed apnoea response module was evaluated in comparison with standard automated control and with manual control during apnoeic events. Automatic control alone demonstrated marginal improvements over manual control in saturation targeting during apnoea, but was frequently associated with overshoot. Although addition of the apnoea response mod?ule further improved recovery from hypoxaemia, there was a corresponding worsening of overshoot resulting from overestimation of the risk of post-apnoea instability. <br>The limited capacity of existing automated oxygen controllers to achieve acceptable performance and robustness across the vicissitudes of neonatal oxygen requirement, emphasises the need for continued development of adaptive controllers in conjunction with improved models of the underlying oxygen requirement. This is especially true in the case of transient and variable disturbances such as those introduced by apnoea. The apnoea response module, and similar event-specific controller responses, are a potential solution, but their efficacy is dependent on accurate detection of disturbance events and models of the associated changes in oxygen requirement.