Oxygen transport and nonstoichiometry in SrFeO3-delta

Chemical diffusion (D) and surface exchange (k) coefficients for SrFeO3-delta were measured using an electrochemical cell combined with electrochemical impedance spectroscopy (EIS) and potential step technique (PS) in the temperature range of 850-915°C. A value of ~ 4x10-5 cm2/s and a k value of ~ 8x10-5 cm/s were obtained at 900°C. Slow scan (0.5-3 microV/s) cyclic voltametry (CV) was performed in the same temperature range, using the same electrochemical cell to obtain oxygen nonstoichiometry data. The oxygen nonstoichiometry (delta) at 900°C in air was determined as 0.4. A plateau corresponding to delta = 0.5 was observed below an oxygen partial pressure (pO2) of 10-6 atm. These results were shown to be consistent with the literature data. Nonstoichiometry data were further analysed using the existing defect models, and the limits of the independent point defect approximation and the necessity of considering interactions between point defects and clusters were established. Keywords: Strontium Ferrate/Ferrite; Oxygen transport; Oxygen nonstoichiometry

Determination of Chemical Diffusion and Surface Exchange Coefficients of Oxygen by Electrochemical Impedance Spectroscopy

A rigorous mathematical model is developed for the complex impedance of a solid-state electrochemical cell, which is commonly used for the measurement of oxygen transport, oxygen exchange kinetics and thermodynamic properties of nonstoichiometric mixed conducting oxides. The model leads to a simple equivalent circuit for the cell with unambiguous definition of the physical significance of its components. A method is proposed for the analysis of experimental data. The methodology thus developed is validated by comparing the experimental data measured for a well-studied perovskite (SrCo0.5Fe0.503-delta) with the results obtained from the completely equivalent potential-step technique. In addition, various electrochemical properties of the other cell components, such as Pt electrodes and YSZ electrolyte, also obtainable from measurements, show good agreement with the available literature data. The cell design, which significantly minimizes the gas space in contact with the sample, has a clear advantage over similar relaxation cells in terms of reducing the dominating effect of the gas phase capacitance in numerical data analysis. A possible disadvantage, however, is the large impedance of the oxygen pump at low oxygen partial pressures, which may in a similar manner obstruct deconvolution of the sample properties from the measured data

Simultaneous determination of chemical diffusion and surface exchange coefficients of oxygen by the potential step technique

Oxygen diffusion is treated in a dense electronically conducting cobaltate pellet blocked ionically on one surface, electronically on the other, and sealed on its cylindrical periphery. A procedure is developed for extracting the chemical diffusion and surface exchange coefficients for oxygen by use of the asymptotic equations derived for the current response to a potential step at short and long times. It is shown that, while the formation of interfacial phases by reaction between the sample and the electrolyte may affect the surface exchange coefficient, the chemical diffusion coefficient data determined by the present approach are independent of such interfacial phenomena. The consistency of data obtained from several specimens with varying thickness and manner of interfacing with the electrolyte validates the diffusion model and the method used for data analysis. An oxygen permeation cell is also developed in this work as a modification of the diffusion cell. The new cell allows monitoring of the permeation rate by electrochemical means. The steady-state permeation data obtained by the permeation cell are consistent with the chemical-diffusion and surface- exchange coefficients measured by the blocked diffusion cell as long as the assumptions of the related theoretical models are satisfied. This is a further validation of the diffusion model and the related methodology developed here for obtaining the necessary data for characterizing oxygen exchange and transport in such materials

Interventions to improve appropriateness of laboratory testing in the intensive care unit: a narrative review

Healthcare expenses are increasing, as is the utilization of laboratory resources. Despite this, between 20% and 40% of requested tests are deemed inappropriate. Improper use of laboratory resources leads to unwanted consequences such as hospital-acquired anemia, infections, increased costs, staff workload and patient stress and discomfort. The most unfavorable consequences result from unnecessary follow-up tests and treatments (overuse) and missed or delayed diagnoses (underuse). In this context, several interventions have been carried out to improve the appropriateness of laboratory testing. To date, there have been few published assessments of interventions specific to the intensive care unit. We reviewed the literature for interventions implemented in the ICU to improve the appropriateness of laboratory testing. We searched literature from 2008 to 2023 in PubMed, Embase, Scopus, and Google Scholar databases between April and June 2023. Five intervention categories were identified: education and guidance (E&G), audit and feedback, gatekeeping, computerized physician order entry (including reshaping of ordering panels), and multifaceted interventions (MFI). We included a sixth category exploring the potential role of artificial intelligence and machine learning (AI/ML)-based assisting tools in such interventions. E&G-based interventions and MFI are the most frequently used approaches. MFI is the most effective type of intervention, and shows the strongest persistence of effect over time. AI/ML-based tools may offer valuable assistance to the improvement of appropriate laboratory testing in the near future. Patient safety outcomes are not impaired by interventions to reduce inappropriate testing. The literature focuses mainly on reducing overuse of laboratory tests, with only one intervention mentioning underuse. We highlight an overall poor quality of methodological design and reporting and argue for standardization of intervention methods. Collaboration between clinicians and laboratory staff is key to improve appropriate laboratory utilization. This article offers practical guidance for optimizing the effectiveness of an intervention protocol designed to limit inappropriate use of laboratory resources

Implementation of closed-loop-assisted intra-operative goal-directed fluid therapy during major abdominal surgery: A case-control study with propensity matching

BACKGROUND: Goal-directed fluid therapy (GDFT) has been associated with improved patient outcomes. However, implementation of GDFT protocols remains low despite growing published evidence and the recommendations of multiple regulatory bodies in Europe. We developed a closed-loop-assisted GDFT management system linked to a pulse contour monitor to assist anaesthesiologists in applying GDFT. OBJECTIVE: To assess the impact of our closed-loop system in patients undergoing major abdominal surgery in an academic hospital without a GDFT programme. DESIGN: A case-control study with propensity matching. SETTING: Operating rooms, Erasme Hospital, Brussels. PATIENTS: All patients who underwent elective open major abdominal surgery between January 2013 and December 2016. INTERVENTION: Implementation of our closed-loop-assisted GDFT in April 2015. METHODS: A total of 104 patients managed with closed-loop-assisted GDFT were paired with a historical cohort of 104 consecutive non-GDFT patients. The historical control group consisted of patients treated before the implementation of the closed-loop-system, and who did not receive GDFT. In the closed-loop group, the system delivered a baseline crystalloid infusion of 3 ml kg h and additional 100 ml fluid boluses of either a crystalloid or colloid for haemodynamic optimisation. MAIN OUTCOME MEASURES: The primary outcome was intra-operative net fluid balance. Secondary outcomes were composite major postoperative complications, composite minor postoperative complications and hospital length of stay (LOS). RESULTS: Baseline characteristics were similar in both groups. Patients in the closed-loop group had a lower net intra-operative fluid balance compared with the historical group (median interquartile range [IQR] 2.9 [1.6 to 4.4] vs. 6.2 [4.0 to 8.3] ml kg h; P < 0.001). Incidences of major and minor postoperative complications were lower (17 vs. 32%, P = 0.015 and 31 vs. 45%, P = 0.032, respectively) and hospital LOS shorter [median (IQR) 10 (6 to 15) vs. 12 (9 to 18) days, P = 0.022] in the closed-loop group. CONCLUSION: Implementation of our closed-loop-assisted GDFT strategy resulted in a reduction in intra-operative net fluid balance, which was associated with reduced postoperative complications and shorter hospital LOS. TRIAL REGISTRATION NUMBER: NCT02978430.SCOPUS: ar.jinfo:eu-repo/semantics/publishe