Automatic control of blood oxygen saturation in premature infants

This paper describes research into the development of a controller that regulates blood oxygen saturation (SaO₂) in premature infants. The patient´s SaO₂ is measured by a pulse oximeter and fed into the controller which adjusts the neonate´s inspired air-oxygen (FiO₂) mixture by actuating a motorized gas blender. This oxygen therapy is used to prevent incidents of hypoxemia and hyperoxemia. A simplified physiological model is described. The designers use a unique control algorithm based on the sign of the error magnitude, velocity and acceleration as inputs. The algorithm applies these inputs to a state machine that determines the trend of the error. This trend defines the next state and an associated FiO₂ adjustment and time delay. The controller was verified on eight neonates, each over a six hour study period. During automatic oxygen therapy the controller significantly increased the duration of time the patient spent at normal SaO₂ levels as compared to manual therapy. The numbers of manual interventions were also greatly reduced when the neonates were under automatic oxygen therapy