Oximetry feedback flow control simulation for oxygen therapy

Conservative versus conventional oxygen therapy in type I acute respiratory failure patients in respiratory intensive care unit, Zagazig University

The present study aimed to assess the effect of a conservative (permissive hypoxemia) versus conventional (normoxia) protocol for oxygen supplementation on the outcome of type I respiratory failure patients admitted to respiratory intensive care unit (ICU). This randomized controlled clinical trial was carried out at the Respiratory ICU, Chest Department of Zagazig University Hospital, for 18 months, starting in July 2018. On admission, 56 enrolled patients with acute respiratory failure were randomized in a 1:1 ratio into the conventional group [oxygen therapy was supplied to maintain oxygen saturation (SpO2) between 94% and 97%] and the conservative group (oxygen therapy was administered to maintain SpO2 values between 88% and 92%). Different outcomes were assessed, including ICU mortality, the need for mechanical ventilation (MV) (invasive or non-invasive), and ICU length of stay. In the current study, the partial pressure of oxygen was significantly higher among the conventional group at all times after the baseline reading, and bicarbonate was significantly higher among the conventional group at the first two readings. There was no significant difference in serum lactate level in follow-up readings. The mean duration of MV and ICU length of stay was 6.17±2.05 and 9.25±2.22 days in the conventional group versus 6.46±2.0 and 9.53±2.16 days in the conservative group, respectively, without significant differences between both groups. About 21.4% of conventional group patients died, while 35.7% of conservative group patients died without a significant difference between both groups. We concluded that conservative oxygen therapy may be applied safely to patients with type I acute respiratory failure.

Automated Home Oxygen Delivery for Patients with COPD and Respiratory Failure: A New Approach

Long-term oxygen therapy (LTOT) has become standard care for the treatment of patients with chronic obstructive pulmonary disease (COPD) and other severe hypoxemic lung diseases. The use of new portable O₂ concentrators (POC) in LTOT is being expanded. However, the issue of oxygen titration is not always properly addressed, since POCs rely on proper use by patients. The robustness of algorithms and the limited reliability of current oximetry sensors are hindering the effectiveness of new approaches to closed-loop POCs based on the feedback of blood oxygen saturation. In this study, a novel intelligent portable oxygen concentrator (iPOC) is described. The presented iPOC is capable of adjusting the O₂ flow automatically by real-time classifying the intensity of a patient’s physical activity (PA). It was designed with a group of patients with COPD and stable chronic respiratory failure. The technical pilot test showed a weighted accuracy of 91.1% in updating the O₂ flow automatically according to medical prescriptions, and a general improvement in oxygenation compared to conventional POCs. In addition, the usability achieved was high, which indicated a significant degree of user satisfaction. This iPOC may have important benefits, including improved oxygenation, increased compliance with therapy recommendations, and the promotion of PA.

Credibility Evidence for Computational Patient Models Used in the Development of Physiological Closed-Loop Controlled Devices for Critical Care Medicine

Physiological closed-loop controlled medical devices automatically adjust therapy delivered to a patient to adjust a measured physiological variable. In critical care scenarios, these types of devices could automate, for example, fluid resuscitation, drug delivery, mechanical ventilation, and/or anesthesia and sedation. Evidence from simulations using computational models of physiological systems can play a crucial role in the development of physiological closed-loop controlled devices; but the utility of this evidence will depend on the credibility of the computational model used. Computational models of physiological systems can be complex with numerous non-linearities, time-varying properties, and unknown parameters, which leads to challenges in model assessment. Given the wide range of potential uses of computational patient models in the design and evaluation of physiological closed-loop controlled systems, and the varying risks associated with the diverse uses, the specific model as well as the necessary evidence to make a model credible for a use case may vary. In this review, we examine the various uses of computational patient models in the design and evaluation of critical care physiological closed-loop controlled systems (e.g., hemodynamic stability, mechanical ventilation, anesthetic delivery) as well as the types of evidence (e.g., verification, validation, and uncertainty quantification activities) presented to support the model for that use. We then examine and discuss how a credibility assessment framework (American Society of Mechanical Engineers Verification and Validation Subcommittee, V&V 40 Verification and Validation in Computational Modeling of Medical Devices) for medical devices can be applied to computational patient models used to test physiological closed-loop controlled systems.

Physiological closed-loop control in intelligent oxygen therapy: A review

BACKGROUND AND OBJECTIVE

Oxygen therapy has become a standard care for the treatment of patients with chronic obstructive pulmonary disease and other hypoxemic chronic lung diseases. In current systems, manually continuous adjustment of O₂ flow rate is a time-consuming task, often unsuccessful, that requires experienced staff. The primary aim of this systematic review is to collate and report on the principles, algorithms and accuracy of autonomous physiological close-loop controlled oxygen devices as well to present recommendations for future research and studies in this area.

METHODS

A literature search was performed on medical database MEDLINE, engineering database IEEE-Xplore and wide-raging scientific databases Scopus and Web of Science. A narrative synthesis of the results was carried out.

RESULTS

A summary of the findings of this review suggests that when compared to the conventional manual practice, the closed-loop controllers maintain higher saturation levels, spend less time below the target saturation, and save oxygen resources. Nonetheless, despite of their potential, autonomous oxygen therapy devices are scarce in real clinical applications.

CONCLUSIONS

Robustness of control algorithms, fail-safe mechanisms, limited reliability of sensors, usability issues and the need for standardized evaluating methods of assessing risks can be among the reasons for this lack of matureness and need to be addressed before the wide spreading of a new generation of automatic oxygen devices.

Adaptive pulse width control and sampling for low power pulse oximetry

Remote sensing of physiological parameters could be a cost effective approach to improving health care, and low-power sensors are essential for remote sensing because these sensors are often energy constrained. This paper presents a power optimized photoplethysmographic sensor interface to sense arterial oxygen saturation, a technique to dynamically trade off SNR for power during sensor operation, and a simple algorithm to choose when to acquire samples in photoplethysmography. A prototype of the proposed pulse oximeter built using commercial-off-the-shelf (COTS) components is tested on 10 adults. The dynamic adaptation techniques described reduce power consumption considerably compared to our reference implementation, and our approach is competitive to state-of-the-art implementations. The techniques presented in this paper may be applied to low-power sensor interface designs where acquiring samples is expensive in terms of power as epitomized by pulse oximetry.

A sub-mW fully-integrated pulse oximeter front-end

This paper presents the implementation of the first fully integrated pulse oximeter front-end with a power consumption lower than 1 mW. This is enabled by system- and block-level noise optimisation, also detailed in the manuscript. The proposed design features an analogue feedback loop that enables fast and accurate regulation of the detected photocurrent level and a serial-to-parallel interface allowing for extensive programmability of several operation parameters. The front-end was fabricated in the AMS 0.35 μm technology and occupies an area of 1.35 mm(2). Extensive measured results, both electrical and physiological from human subjects are reported, demonstrating an estimated SNR of 39 dB and ability to detect 2% changes in SpO2, similar to commercial pulse oximeters. This is despite the constrained power consumption which amounts to 0.31 mW for the LEDs and 0.53 mW for the rest of the front-end from a 3.3 V supply. Statistical results from 20 chips verify good matching across the Red and Infrared channels of the front-end and the accurate operation of the proposed analogue feedback loop.