The design, development, and validation of an accessible high flow nasal oxygen solution with patient scoring outputs

Reabow, Brandon

The design, development, and validation of an accessible high flow nasal oxygen solution with patient scoring outputs

Thesis / Dissertation

2024

Publisher

University of Cape Town

Department

Department of Human Biology

Faculty

Faculty of Health Sciences

Abstract

Introduction Acute respiratory failure patients are admitted to healthcare units to treat hypoxemic symptoms. High Flow Nasal Oxygen (HFNO) device are medical oxygen therapy devices, with its use emerging through the COVID-19 pandemic and ongoing to treat congenital diseases, to effectively treat poor patient vitals and oxygenate patients. Clinical settings such as the general ward, for which HFNO is suitable, is left to be managed with manual patient monitoring means. Continuous monitoring methods are generally not accessible to these settings. With no high flow devices targeting means to provide this option without sophisticated medical devices, patient care may be limited. Therefore, this study aimed to develop an HFNO device that interfaced with predicate patient vital sign sensors that provided medical professionals with the Respiratory Rate and Oxygenation (ROX) patient score. The score has been validated to aid in early detection of patient deterioration and informing clinicians on treatment prognosis, improving patient care. Materials & Method A standalone HFNO device was designed with subsystems that are characteristic of the common treatment components of HFNO, which included the Oxygen Regulator and Mixer Unit, the Humidification and Heating Unit, and the Patient Airway Device. Additionally, a Patient Vitals Acquisition Unit for acquiring patient vitals was incorporated into the system architecture. The subsystem designs were based on requirements ad specifications informed by the World Health Organisation (WHO) clinical guidance and ISO 8601-2-90:2021 safety and performance requirements. An iterative and fast prototyping approach was adopted, with a Failure Modes and Effects Analysis for assessing risks in safety and failure in performances, to produce design and development outcomes for each unit and the integrated overall device. The study progressed through various processes of verification and validation. The outcomes were verified based on meeting the technical specifications outlined and conducted in the Medical Devices Laboratory (MDL) at the University of Cape Town (UCT) under simulated compressed air inputs. The system was fully integrated and validated by testing the accuracy of oxygen settings guided by ISO 80601-2-90:2021 and interfacing with all peripherals within the clinical setting, simulated within the Groote Schuur Clinical Skills department. The HFNO device with patient vitals were connected to medical oxygen source and the Simman patient simulator to demonstrate the intended use and feasibility within the relevant context. Results and Observations All units were manufactured successfully and tested for essential performance and integral safety. Initial tests with simulated compressed air supply showed flow rate outputs of up to 70 l/min with sufficient automated flow rate control and manual oxygen concentration settings of 21-100%. The humidification unit provided permissible humidification loads of up to 100%RH, and 37°C gas heating which reduced humidification loads to 48%RH at 60 l/min. The patient airway device fit the Laerdal Patient Airway Management trainer effectively. The patient vitals sensors provided respiratory rate capture of 3 to 90 breaths per minute, and the pulse oximetry data connectivity to the system. The maximum error in oxygen flow rates greater than 30 l/min was - 5.69 l/min for 30% FiO2. Maximum errors of +3.2% FiO2 were shown for flow rates less than 15 l/min and greater than 30 l/min. The respiratory rate and pulse oximetry measurements were used to produce the ROX and modified ROX scores in real-time within the clinical setting for simulated patients for unsuccessful and successful treatment pathways. Conclusions A preliminary HFNO solution was developed and performed well amongst performance criteria of commonly used products. The solution was produced affordably within a research and development context and on a basis of materials only. The automatic access to respiratory rate, a good basis for predicted outcomes illustrated the benefit of the system. Ultimately, the results and the solution had implications for improving HFNO within resource-poor settings.

Keywords

Biology

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