In this paper, a simplified model of a Polymer Electrolyte Membrane (PEM) water electrolysis cell is presented and compared with experimental data at 60 °C and 80 °C. The model utilizes the same modelling approach used in previous work where the electrolyzer cell is divided in four subsections: cathode, anode, membrane and voltage. The model of the electrodes includes key electrochemical reactions and gas transport mechanism (i.e., H2, O2 and H2O) whereas the model of the membrane includes physical mechanisms such as water diffusion, electro osmotic drag and hydraulic pressure. Voltage was modelled including main overpotentials (i.e., activation, ohmic, concentration). First and second law efficiencies were defined. Key empirical parameters depending on temperature were identified in the activation and ohmic overpotentials. The electrodes reference exchange current densities and change transfer coefficients were related to activation overpotentials whereas hydrogen ion diffusion to Ohmic overvoltages. These model parameters were empirically fitted so that polarization curve obtained by the model predicted well the voltage at different current found by the experimental results. Finally, from the efficiency calculation, it was shown that at low current densities the electrolyzer cell absorbs heat from the surroundings. The model is not able to describe the transients involved during the cell electrochemical reactions, however these processes are assumed relatively fast. For this reason, the model can be implemented in system dynamic modelling for hydrogen production and storage where components dynamic is generally slower compared to the cell electrochemical reactions dynamics.
(1) Background: This study evaluated the perioperative red blood cell (RBC) transfusion need and determined predictors for transfusion in patients undergoing elective primary lumbar posterior spine fusion in a high-volume center for spine surgery. (2) Methods: Data from all patients undergoing spine surgery between 1 January 2014 and 31 December 2016 were reviewed. Patients’ demographics and comorbidities, perioperative laboratory results, and operative time were analyzed in relation to RBC transfusion. Multivariate logistic regression analysis was performed to identify the predictors of transfusion. (3) Results: A total of 874 elective surgeries for primary spine fusion were performed over the three years. Only 54 cases (6%) required RBC transfusion. Compared to the non-transfused patients, transfused patients were mainly female (p = 0.0008), significantly older, with a higher ASA grade (p = 0.0002), and with lower pre-surgery hemoglobin (HB) level and hematocrit (p < 0.0001). In the multivariate logistic regression, a lower pre-surgery HB (OR (95% CI) 2.84 (2.11–3.82)), a higher ASA class (1.77 (1.03–3.05)) and a longer operative time (1.02 (1.01–1.02)) were independently associated with RBC transfusion. (4) Conclusions: In the instance of elective surgery for primary posterior lumbar fusion in a high-volume center for spine surgery, the need for RBC transfusion is low. Factors anticipating transfusion should be taken into consideration in the patient’s pre-surgery preparation.
BackgroundSpine fusion is a surgical procedure characterized by a significant perioperative bleeding, which often requires red blood cell (RBC) transfusion.MethodsThe incidence and the cost of RBC transfusion were evaluated in all patients undergoing elective surgery for spine fusion in our Institution, a high-volume center for spine surgery, over a period of 3 years. The analysis specifically addressed the RBC transfusion need in all the different spine fusion procedures (atlanto-axial, cervical, dorsal, lumbar, revisions) with the different surgical approaches (anterior, posterior).ResultsDuring the 3 years of observation, a total of 1.882 elective spine fusions were performed. More than half of the procedures (n = 964) were posterior lumbar fusions. Overall, 5% of the patients (n = 103) required RBC transfusion. The cervical fusions were the procedures with the lowest percentage of RBC need (0–5%), while the dorsal and the lumbar ones, with the anterior approach, represented the procedures with the highest rate of transfusion (29% and 25% respectively). More than 60 % of the RBC units were employed in the instance of posterior lumbar fusion, while a variable 1–10% of the units was used in each of the other procedures. The overall transfusion cost was of 46.000 euros, with a distribution of costs that paralleled the amount of units transfused for each procedure.ConclusionsSeveral surgical and patient factors may contribute to the perioperative blood loss. An accurate patient blood management, may efficiently decrease transfusion requirements and ultimately healthcare costs.
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