Serum albumin levels monitoring in ICU in early days and mortality risk association in patients with moderate to severe COVID-19 pneumonia.

Objective: To establish correlation between serum albumin during early days of ICU admission and risk of death in COVID-19 pneumonia. Methods: In this retrospective study, we included 76 patients hospitalized in ICU, who stayed for at least four days with COVID-19 pneumonia, from May 1, 2020 to June 30, 2020 in Lahore Health Care Hospital and Al-Shafi Hospital. Patients were labelled as COVID-19 pneumonia on radiological basis as bilateral 'ground-glass opacity' in lower zones and RT-PCR positive result in nasopharyngeal swab. All patients were oxygen dependent, either on high flow oxygen via non rebreathing mask or invasive positive pressure ventilation support. Serum albumin levels were measured daily from first day to fourth day of ICU admission. The data was analyzed using SPSS version 26 and Microsoft excel 2016. Results: Out of 76 patients of COVID-19 pneumonia admitted in ICU who stayed for more than four days, 38 patients expired. The mean age of all the patients was 58.9±12.56 years, 38(50%) of the patients were ≥60 years and 49 (62%) of them were male. On day four of ICU admission, mean serum albumin of discharged patients was 3.83±0.22 g/dl while mean serum albumin level of expired patients was 2.96±0.46 g/dl. Strong negative correlation (r = -767) was found between decrease in serum albumin level and increase number of deaths from COVID-19 pneumonia. Weak correlation was observed between increase in serum CRP and increase number of deaths in the same patients. Conclusion: Daily monitoring of serum albumin level of COVID-19 pneumonia patients can be used as a biological marker for monitoring of cytokine storm and risk of death in COVID-19 pneumonia.

Prediction of Epitaxial Grain Growth in Single-Track Laser Melting of IN718 Using Integrated Finite Element and Cellular Automaton Approach.

The mechanical properties of selective laser melting (SLM) components are fundamentally dependent on their microstructure. Accordingly, the present study proposes an integrated simulation framework consisting of a three-dimensional (3D) finite element model and a cellular automaton model for predicting the epitaxial grain growth mode in the single-track SLM processing of IN718. The laser beam scattering effect, melt surface evolution, powder volume shrinkage, bulk heterogeneous nucleation, epitaxial growth, and initial microstructure of the substrate are considered. The simulation results show that during single-track SLM processing, coarse epitaxial grains are formed at the melt-substrate interface, while fine grains grow at the melt-powder interface with a density determined by the intensity of the heat input. During the solidification stage, the epitaxial grains and bulk nucleated grains grow toward the top surface of the melt pool along the temperature gradient vectors. The rate of the epitaxial grain growth varies as a function of the orientation and size of the partially melted grains at the melt-substrate boundary, the melt pool size, and the temperature gradient. This is observed that by increasing heat input from 250 J/m to 500 J/m, the average grain size increases by ~20%. In addition, the average grain size reduces by 17% when the initial substrate grain size decreases by 50%. In general, the results show that the microstructure of the processed IN718 alloy can be controlled by adjusting the heat input, preheating conditions, and initial substrate grain size.

3D Multi-Track and Multi-Layer Epitaxy Grain Growth Simulations of Selective Laser Melting.

An integrated simulation framework consisting of the 3D finite element method and 3D cellular automaton method is presented for simulating the multi-track and multi-layer selective laser melting (SLM) process. The framework takes account of all the major multi-physics phenomena in the SLM process, including the initial grain structure, the growth kinetics, the laser scanning strategy, the laser-powder and laser-matter interactions, the melt flow, and the powder-to-liquid-to-solid transformations. The feasibility of the proposed framework is demonstrated by simulating the evolution of the epitaxy grain structure of Inconel 718 (IN718) during a 15-layer SLM process performed using a bi-directional 67° rotation scanning strategy and various SLM process parameters. The simulation results are found to be in good agreement with the experimental observations obtained in the present study and in the literature. In particular, a strong (001) texture is observed in the final component, which indicates that the grains with a preferred <001> orientation win the competitive epitaxy grain growth process. In addition, the size and shape of the IN718 grains are governed primarily by the cooling rate, where the cooling rate is determined in turn by the SLM parameters and the build height. Overall, the results show that the proposed framework provides an accurate approach for predicting the final microstructures of SLM components, and therefore, it can play an important role in optimizing the SLM processing parameters in such a way as to produce components with the desired mechanical properties.