Inhaled Nitric Oxide: An Experimental Analysis of Continuous Flow Noninvasive Delivery via Nasal Cannula

• Author / Creator

  Pillay, Kineshta

• Inhaled nitric oxide (iNO) is used to treat pulmonary hypertension and improve oxygenation in critically ill patients. It is primarily delivered via mechanical ventilation to patients in the critical care setting; however, there are several drawbacks to this invasive form of delivery. As a result, there has been increased administration of noninvasive delivery in the critical care setting, as well as investigation into long-term noninvasive administration of iNO to treat pulmonary hypertension associated with chronic lung diseases. Dose delivery of iNO is currently defined in terms of the constant concentration that is maintained in the inspired gas although applying this metric for delivery modes other than ventilation is challenging. Dose delivery for iNO supplied at a constant flow rate through a nasal cannula has not yet been established. This thesis aims to determine the influence of nasal cannula type, supply flow rates, and the patient’s breathing pattern on delivered iNO through a nasal cannula. Additionally, a basis for dosage estimation through this delivery mode is provided. This assessment was conducted in vitro using a realistic adult airway replica and lung simulator.

  The first chapter of this thesis examines and reviews the literature around the applications of iNO and its delivery methods. Chapter 2 examines the theoretical basis for this experimental study of iNO, while the study design and results of experiments are provided in Chapter 3. Chapter 4 summarizes the thesis and provides perspectives for future work.

  In the experiments conducted, carbon dioxide (CO2) was used as a tracer gas to mimic the delivery of nitric oxide at a continuous flow rate. It was supplied through a nasal cannula to a realistic adult nose-throat airway replica. This replica was connected to a lung simulator that imposed breathing patterns representative of patients during rest, sleep and light exercise. A canister of soda lime was used in the system to mimic NO absorption in the lung. CO2 flows were selected to provide targeted tracheal concentrations at rest of 5 or 20 parts per million (ppm) NO and were initially supplied with 2 L/min of supplemental oxygen (O2). Three different cannulas were tested, followed by additional tests with 6 L/min oxygen supply at both CO2 flows. Breathing patterns were later varied to investigate tidal volume and breathing frequency influences independently. Dosage delivery was presented in the form of tracheal NO concentrations, along with NO mass flow rate past the trachea. Delivery efficiency was assessed for each condition and presented an estimate of the NO that was delivered to the trachea in relation to the NO supplied. Delivery results, tracheal NO concentrations and mass flow rates, were compared to predictive equations to determine whether dosage delivery could be reasonably quantified for future applications.

  Tracheal NO concentrations differed significantly based on breathing pattern and supply flow rates. However, for the same test conditions, mass flow rate of NO past the trachea was notably less sensitive to breathing pattern. Provided breathing parameters were known, inhaled tracheal NO concentrations were reasonably predicted using a simple assumption of complete mixing of the NO flow within the inspired breath. Cannula type had a minimal effect on inhaled NO concentrations and mass flow rate. Mass flow rate and delivery efficiency increased when overall minute volume increased. Due to the low variation in delivery across breathing pattern, mass flow rate could provide a stable option as a delivery metric for iNO. The presented information describing inhaled NO concentration, mass flow and delivery efficiency will help in establishing NO dosing for noninvasive continuous flow delivery.

• Subjects / Keywords

  • continuous flow
  • airway model
  • dose delivery
  • tracheal concentration
  • nitric oxide

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-cw50-kr77

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.