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

Abstract

<p>Oxygen therapy is an essential treatment of premature infants suffering from hypoxemia. Normoxemia is maintained by an adjustment of the fraction of oxygen (FiO<sub>2</sub>) in the inhaled gas mixture that is set manually or automatically based on peripheral oxygen saturation (SpO<sub>2</sub>). Automatic closed-loop systems could be more successful in controlling SpO<sub>2</sub> than traditional manual approaches. Computer models of neonatal oxygen transport have been developed as a tool for design, validation, and comparison of the automatic control algorithms. The aim of this study was to investigate and implement the time delay of oxygen delivery after a change of set FiO<sub>2</sub> during noninvasive ventilation support to enhance an available mathematical model of neonatal oxygen transport. The time delay of oxygen delivery after the change of FiO<sub>2</sub> during the noninvasive nasal Continuous Positive Airway Pressure (nCPAP) ventilation support and during the High Flow High Humidity Nasal Cannula (HFHHNC) ventilation support was experimentally measured using an electromechanical gas blender and a physical model of neonatal lungs. Results show the overall time delay of the change in the oxygen fraction can be divided into the baseline of delay, with a typical time delay 5.5 s for nCPAP and 6.5 s for HFHHNC s, and an exponential rising phase with a time constant about 2–3 s. A delay subsystem was implemented into the mathematical model for a more realistic performance when simulating closed-loop control of oxygenation.</p>

Reducing the time delay of oxygen transport to the neonate on continuous positive airway pressure support: A bench study

“…We validated our concept using the full spectrum of available non-invasive (CPAP) ventilators with recommended interfaces across the full spectrum of adjustable pressures (flow rates), including the low nCPAP which admittedly has little clinical relevance. The measured delays without O 2 -FS matched those measured in our earlier study ( 16 ). It could be concluded that the connection of the system in the off state does not affect the normal function of the CPAP ventilatory support.…”

“…This study demonstrates that there is a feasible technical solution to the problem of the delay of oxygen distribution to a neonate after a change in a set FiO 2 . Previous studies found a significant delay between the change in the set FiO 2 and the actual oxygen delivery to neonates ( 16 , 17 ). However, we demonstrated that a system with a controlled electromechanical valve that delivers extra oxygen directly to the point where a non-invasive ventilatory support interface connects to a ventilator circuit reduces the delay of oxygen distribution to the neonate significantly.…”

“…The overshoot may be better described by the second-order response function rather than the exponential. We preferred the exponential fit due to it was used in previous studies ( 10 , 16 , 17 ) and for this study we considered the overshoot relatively unimportant compared to the rise time described by the time constant.…”

“…The experiment was conducted in laboratories of the Faculty of Biomedical Engineering in Kladno under standard laboratory conditions. The protocol of the experimental procedure validation was derived from our previous study that described the time delay in the distribution of oxygen in a ventilator circuit ( 16 ).…”

“…Third, a part of the time delay is related to the properties of the blender and the ventilator circuit. This physical delay has been measured to be between 20 and 40 s ( 16 , 17 ). Finally, fourth, the physiological delay in the distribution of oxygen depends on many physiological factors, including the active alveolar surface area, diffusion across the alveolar-capillary membrane, and the state of the cardiovascular system (e.g., blood volume, Hb concentration, HbF/HbA ratio, cardiac shunts, peripheral circulation, and other factors affecting oxygen flow).…”