Alveolar pressure estimation in total liquid ventilation during pauses impeded by tube resonance

Abstract

Total liquid ventilation is an innovative experimental method of mechanical assisted ventilation in which lungs are totally filled and then ventilated with a tidal volume of perfluorochemical liquid (PFC) by using a dedicated liquid ventilator. The positive end-inspiratory and end-expiratory pressures (PEIP and PEEP) are static pressure measurements that are critic to the safe and efficient control of the ventilation. However, their measurement is impeded by large oscillations of pressure caused by the propagation of pressure waves along the flexible tubes carrying the PFC to the patient. The aim of this paper is to describe a method to accurately estimate the PEEP and the PEIP from noisy data hindered by flexible tubing resonance during short respiratory pauses. The method developped makes use of the least squares technique to estimate the steady state pressure. Preliminary in vivo validation of the algorithm shows that the method gives accurate estimations with respiratory pauses as short as 0.3 second. I. INTRODUCTIONIn the last decade, a vast array of preclinical studies have shown the efficacy and safety of total liquid ventilation (TLV) in pediatric and adult animal models [1]. In TLV, the lungs are totally filled with a breathable perfluorocarbon (PFC) liquid and then ventilated with a tidal volume of PFC controlled by a dedicated liquid ventilator [2]. TLV offers many advantages over conventional mechanical ventilation (CMV). By eliminating the air-liquid interface, it allows the recruitment of collapsed lung regions ensuring more homogeneous alveolar ventilation [1], an efficient lung lavaging effect [3] and the capability to induce ultra-fast mild therapeutic hypothermia [4].The liquid ventilator Inolivent-5 ( Figure 1) includes different control modes found on conventional ventilators [5], [6]. The use of a volume controlled ventilation during inspiration and of a pressure controlled ventilation during expiration to avoid airway collapsus [7] greatly improves the efficiency and the safety of the ventilator for clinical use [8]. The positive end-inspiratory pressure (PEIP) and the positive endexpiratory pressure (PEEP) are critical parameters for the control of the ventilation. They are static pressure measurements reflecting the alveolar pressure and are related to the endinspiratory (EI) and end-expiratory (EE) lung volume. Usually,