446 - A Novel Device for Measurement of the Actual Percent Oxygen Delivered via Nasal CPAP in Neonates

Poster Number: 446
Publication Number: 446.228

Michael D. Weisner, Equilibrated Bio Systems, Inc., Smithtown, NY, United States; Sarah Perez, UAMS, Little Rock, AR, United States; David N. Matlock, University of Arkansas for Medical Sciences, Little Rock, AR, United States; Thomas Wiswell, Kaiser Permanente Moanalua Medical Center, Middle River, MD, United States; Sherry Courtney, University of Arkansas for Medical Sciences College of Medicine, Little Rock, AR, United States

Background: Leaks at the nose and mouth make it difficult to determine the actual inspired oxygen concentration supplied during nasal CPAP (nCPAP).

Objective: The aim of this study is to measure the actual oxygen concentration delivered to the hypopharynx during nCPAP. To assess inspired oxygen within this space in a neonate, samples must be small and drawn synchronously with breathing.

Design/Methods: A system was designed to make small sequential inspiratory phase measurements combined in a recirculating loop (Figure 1). The average oxygen concentration was measured by an oxygen analyzer, managed by a respiratory gated sampling technique. A medium speed, highly stable paramagnetic oxygen analyzer and a solid-state pressure transducer were integrated with a small Linux-based computer, to provide real-time graphics, a touch control user interface and the synchronized sampling component (Equilibrated Bio Systems E0211R, Figure 2). The system connects to a dual lumen endotracheal tube (ETT, Vygon 2.5) placed through the mouth into the hypopharynx. The smaller and larger ports of the ETT are attached to the pressure sensor and the oxygen analyzer sampling input, respectively. Sampling is triggered by sensing inspiration either by pressure change or manual activation. The output signals from the oxygen analyzer, pressure sensor and sampling state are recorded by a data acquisition system (BioPac). A bench study was completed to verify proper operation. Once the system was validated, calibrated, and IRB approval was obtained, it was tested on two preterm infants.

Results: Infant A was born at 27 weeks, birth weight 750g, and studied at 31 days of life at 1190g on 35% FiO2/nCPAP 6cmH2O (Fischer-Paykel). Infant B was born at 25 weeks, birth weight 560g, and studied at 93 days at 2305g on 30% FiO2/nCPAP 7cmH2O. In both infants, the pressure sensor did not reliably trigger due to leaks at the mouth that could not be effectively controlled. The manual trigger worked extremely well but depended on the ability of the operator to reliably recognize and respond to inspiration. The device recorded measurable drops in inspired O2 in the hypopharynx in both infants (Infant A, Figure 3).Conclusion(s): This novel device provides excellent opportunities to measure inspired oxygen under circumstances where provision of oxygen may vary dramatically from that set by the operator. This may include all forms of non-invasive ventilation in any age patient. However, the control of leaks is important to optimal performance of the system. Infants on nCPAP appear to receive less oxygen than the percent set by the caregiver.
Figure 1The design of the system illustrates the connection to the infant through a dual lumen endotracheal tube to sample the air pressure and fractional concentration of oxygen within the hypopharynx.
Figure 2The device incorporating the oxygen analyzer and sampling system (c) is shown with closeups of the display screen during the bench study (a) and during real-time operation (b).