Fluid Loading Research Articles

Best-estimate water hammer simulations to avoid the calculation of unrealistically high loads or unphysical pressure and force peaks

For safety-related systems fluid loads due to fluid transients have to be quantified for subsequent structural analyses to ensure their integrity or function, as required. Usually transient fluid loads in pipe systems are determined with one-dimensional water hammer software. For single-phase liquid flow, the method of characteristics (MOC) is often used that gives in this case appropriate results. For the consideration of local vapor bubbles, the MOC is combined with the discrete vapor cavity model (DVC). The DVC model may generate unrealistic pressure spikes due to the calculation of the collapse of multi-cavities in scenarios, where only one vapor bubble should actually occur. The application of a two-phase code may improve the calculation results. One requirement for the latter codes is the ability to calculate the propagation of steep gradients without suffering from numerical diffusion to exclude the underestimation of fluid loads. This is commonly attained by applying higher-order numerical schemes. However, the application of a numerical method of pure 2nd order leads to the calculation of unphysical oscillations at steep gradients causing severe problems during the solution. To exclude this, numerical methods with flux limiters can be used. With their application, the calculation of unrealistically high loads due to numerical deficiencies can be minimized. In addition, the consideration of further physical effects, that lead to the reduction of loads during transient flow processes, allows for a more realistic calculation of the loads. These are unsteady friction, widening of the pipe caused by pressure increase, fluid-structure interaction at junctions and due to friction, degassing of gas that is initially dissolved physically in a liquid and thermodynamic non-equilibrium during vapor bubble collapse. The in-house code DYVRO applies a second-order accurate scheme with flux limiters based on the Godunov method and can account for the above-described physical phenomena. It is shown by comparison of calculation results obtained by DYVRO with experimental data from literature that with modeling of these physical effects the loads can be calculated more realistically. Generally, these loads are lower than the results calculated by simplified models, which do not account for these effects. Considering that these loads are applied in subsequent structural analyses, cost-intensive oversizing of pipes and their supports can be avoided, by ensuring the necessary safety.

Case report of pharmacokinetic analysis of continuous intravenous infusion of fentanyl in a patient with severe burn: burn shock stage complicates pain management

BackgroundFentanyl is widely used as an analgesic and sedative for patients with severe burn injuries in intensive care units. However, pharmacokinetic (PK) data for fentanyl, particularly for continuous intravenous infusion during the acute phase of burn injuries, are limited. Here, we report the clinical course and changes in blood fentanyl concentrations during the acute phase in a patient with severe burns treated with continuous intravenous infusion of fentanyl.Case presentationA woman in her 40s, with burns caused by a gas cylinder explosion, was transported to our hospital. The patient had burn wounds on face, neck, shoulders, and all four extremities, with a total burn area of 39.0%. For pain relief, the patient received a continuous infusion of 0.01 mg/mL fentanyl (20–30 µg/h) with a target blood concentration of 1.0–1.5 ng/mL, but continued to suffer from pain due to burning during the acute phase. We measured the blood fentanyl concentrations and found that all concentrations obtained during the acute phase were subtherapeutic. Notably, during the burn shock stage, blood concentrations of fentanyl were 0.50 ng/mL on day 1 and 0.66 ng/mL on day 2, indicating that the blood concentration did not rise sufficiently for the dosage. From days 0 to 2, the patient was administered a massive fluid load for burn shock. After the burn shock stage resolved, fentanyl concentrations gradually approached the target range, and the pain rating scale improved, even though the fentanyl administration rate remained unchanged (30 µg/h).ConclusionsMajor changes in the fluid volumes of body compartments that occur with large burns might increase the volume of fentanyl distribution, thereby lowering its concentration when a standard dose is administered. Our findings indicate that the PK of fentanyl in patients with severe burns can be substantially affected, especially during the shock phase, implying the importance of titrating analgesics for clinical efficacy in the acute phase.

Simulation Analysis of Non-concentric Squeeze Film Damper

Squeeze film dampers are components that provide additional damping for rotating motors. In general, in order to achieve the best results of the squeeze film damper, it is necessary to appropriately increase the damping value, reduce the stiffness and set a reasonable eccentricity. In the process of designing the squeeze film damper, we can apply the rotor dynamics module of COMSOL software to model and simulate it, so as to achieve better simulation results and lay a foundation for the subsequent development and design of the product. In COMSOL software, in order to simplify the modeling of rotor components, we usually model squeeze film dampers based on the damping coefficient. The model calculates the damping coefficient for a short squeeze film damper and compares the results with the analytically calculated values. In addition, the damping coefficient depends on the position of the journal in the damper, i.e., the magnitude of the eccentricity. In this paper, by analyzing the dimensionless damping coefficient, bearing stiffness, journal displacement, and fluid load at different eccentricity, and plotting the fluid pressure distribution and the average oil film flow rate of the squeeze film damper, we can find the most suitable range of eccentricity and the damage-prone part of the damper, which can provide an important reference for the actual design of the squeeze film damper.

Efficacy of Combination Therapy Using Crystalloid, Colloid and Ephedrine in Prevention of Post Spinal Hypotension at Cesarean Delivery

Abstract Background Spinal anesthesia is the preferred method for elective cesarean sections due to considerable risks regarding airway management associated with physiological changes of pregnancy. Hypotension is reported to occur in up to 80% of spinal anesthesia cases, it can lead to serious maternal complications as well as impairment of the uterine and placental blood flow. Many approaches have been investigated to prevent spinal hypotension, e.g., fluid loading, vasopressors, or both. Objective To determine the most effective strategy to decrease the incidence and severity of post spinal hypotension by comparing three different combination therapies using crystalloid, colloid and ephedrine at cesarean delivery. Patients and Methods After obtaining approval from the Research Ethical Committee of Faculty of Medicine, Ain Shams University, and written informed consent from all parturients this study was conducted in the operating theatres of Ain Shams Obstetric and Gynecology University Hospitals. Results In our study we found that a combination of an ephedrine infusion at 1.25 mg, minute with a crystalloid co-load was more effective in the prevention of hypotension. Conclusion Employing all mentioned combination treatments reduced the rate of hypotension occurrence following spinal anesthesia in parturients undergoing cesarean delivery. The most effective method was administration of crystalloid coloading plus ephedrine infusion.

The cytochrome P4501A1 (CYP1A1) inhibitor bergamottin enhances host tolerance to multidrug-resistant Vibrio vulnificus infection

PurposeVibrio vulnificus (V. Vulnificus) infection is characterized by rapid onset, aggressive progression, and challenging treatment. Bacterial resistance poses a significant challenge for clinical anti-infection treatment and is thus the subject of research. Enhancing host infection tolerance represents a novel infection prevention strategy to improve patient survival. Our team initially identified cytochrome P4501A1 (CYP1A1) as an important target owing to its negative modulation of the body's infection tolerance. This study explored the superior effects of the CYP1A1 inhibitor bergamottin compared to antibiotic combination therapy on the survival of mice infected with multidrug-resistant V. Vulnificus and the protection of their vital organs. MethodsAn increasing concentration gradient method was used to induce multidrug-resistant V. Vulnificus development. We established a lethal infection model in C57BL/6J male mice and evaluated the effect of bergamottin on mouse survival. A mild infection model was established in C57BL/6J male mice, and the serum levels of creatinine, urea nitrogen, aspartate aminotransferase, and alanine aminotransferase were determined using enzyme-linked immunosorbent assay to evaluate the effect of bergamottin on liver and kidney function. The morphological changes induced in the presence of bergamottin in mouse organs were evaluated by hematoxylin and eosin staining of liver and kidney tissues. The bacterial growth curve and organ load determination were used to evaluate whether bergamottin has a direct antibacterial effect on multidrug-resistant V. Vulnificus. Quantification of inflammatory factors in serum by enzyme-linked immunosorbent assay and the expression levels of inflammatory factors in liver and kidney tissues by real-time quantitative polymerase chain reaction were performed to evaluate the effect of bergamottin on inflammatory factor levels. Western blot analysis of IκBα, phosphorylated IκBα, p65, and phosphorylated p65 protein expression in liver and kidney tissues and in human hepatocellular carcinomas-2 and human kidney-2 cell lines was used to evaluate the effect of bergamottin on the nuclear factor kappa-B signaling pathway. One-way ANOVA and Kaplan-Meier analysis were used for statistical analysis. ResultsIn mice infected with multidrug-resistant V. Vulnificus, bergamottin prolonged survival (p = 0.014), reduced the serum creatinine (p = 0.002), urea nitrogen (p = 0.030), aspartate aminotransferase (p = 0.029), and alanine aminotransferase (p = 0.003) levels, and protected the cellular morphology of liver and kidney tissues. Bergamottin inhibited interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α expression in serum (IL-1β: p = 0.010, IL-6: p = 0.029, TNF-α: p = 0.025) and inhibited the protein expression of the inflammatory factors IL-1β, IL-6, TNF-α in liver (IL-1β: p = 0.010, IL-6: p = 0.011, TNF-α: p = 0.037) and kidney (IL-1β: p = 0.016, IL-6: p = 0.011, TNF-α: p = 0.008) tissues. Bergamottin did not affect the proliferation of multidrug-resistant V. Vulnificus or the bacterial load in the mouse peritoneal lavage fluid (p = 0.225), liver (p = 0.186), or kidney (p = 0.637). ConclusionBergamottin enhances the tolerance of mice to multidrug-resistant V. Vulnificus infection. This study can serve as a reference and guide the development of novel clinical treatment strategies for V. Vulnificus.

Exploring kinematic stability of vortex structures: A topological approach to fluid flow around staggered square cylinders

In this study, a detailed fluid dynamics analysis is conducted around two identical square cylinders in a staggered configuration at a Reynolds number (Re) of 40, using a stabilized finite-element method to investigate the kinematic stability of vortex structures. By varying the horizontal spacing (S/D) between 2 and 30 and examining transverse gaps (T/D) of 0.25, 0.8, and 1.25, the research uncovers significant flow behavior variations from the tandem configuration, highlighting complex fluid-structure interactions. The presence of “separation bubbles” at lower S/D values across all T/D ratios indicates the dynamic impact of the upstream cylinder's proximity on the flow field, particularly on the stagnation points of the downstream cylinder. Through a comprehensive topological analysis, the study identifies various flow regimes and topological bifurcations, revealing transitions between stable states that maintain the number of critical points constant, and the kinematic stability of these vortical structures is established by the critical point theory. The effect of cylinder configurations and diverse flow structures on fluid loading is also analyzed by examining surface pressure coefficients. The asymmetry present in the cylinder configuration is manifested through the asymmetric values of lift coefficients.

Observation of the protagonist effect of body fluid load in the pathogenesis of sinonasal polyposis

Background: The objective is to assess the association of body fluid load in the pathogenesis of sinonasal polyposis. Subjects and Methods: The targeted cases with chronic rhinosinusitis (CRS) with nasal polyposis and control of CRS without polyposis were randomly taken from the admitted patients. Two groups of 30 people each were taken. Demographic details such as name, age, and gender were noted. Excess body water was then calculated by subtracting the perfect body water from the total body water (TBW). Results: Of 30 cases and 30 controls aged 18–60, the median was 30.5, and the mean was 34 ± 12.8 years. The gender of the case was 18 males and 12 females, while in control, the males and females were of equal number. The mean TBW was 34.4 ± 5.27 L in cases and 32.4 ± 5.87 L in controls. Total body weight was found to be higher in cases than in controls but not found to be statistically significant (P = 0.160). Excess body water was found in 60% of nasal polyps cases and 46.7% of controls, which was statistically insignificant (P = 0.301). Conclusion: There is a complex interplay between our body fluid dynamics and nasal polyp pathogenesis in CRS with polyposis. While our findings suggest potential trends with small sample sizes, further research with more extensive and diverse populations is needed to authenticate and expand on these observations.

Prediction of fluid responsiveness in spontaneously breathing patients with hemodynamic stability: a prospective repeated-measures study

Evaluating fluid responsiveness with dynamic parameters is recommended for fluid management. However, in hemodynamically stable patients who are breathing spontaneously, accurately measuring stroke volume variation via echocardiography and passive leg raising is challenging due to subtle SV changes. This study aimed to identify normal SV changes in healthy volunteers and evaluate the precision of hemodynamic parameters in screening mild hypovolemia in patients. This prospective, repeated-measures, cross-sectional study screened 269 subjects via echocardiography. Initially, 45 healthy volunteers underwent a fluid challenge test, the outcomes of which served as criteria to screen 215 ICU patients. Among these patients, 53 underwent additional fluid challenge testing. Hemodynamic parameters, including medians of maximum velocity time integrals (VTImaxs), peak velocity of VTImax (PV), internal jugular vein diameters (IJVD), and area (IJVA) were repeatedly measured first at a 60° upper body elevation (UBE), second in a supine position, third at UBE, fourth in a supine position, and lastly in a supine position after fluid loading. The hemodynamic responses to the position changes were compared between 83 fluid non-responders and 15 fluid responders. Fluid responsiveness was defined as fluid-induced medians’ change of VTImaxs (fluid-induced median VTImax change) ≥ 10%. None of the healthy volunteers showed the mean value of repeatedly measured medians of VTImaxs ≥ 7%, following either UBE position (UBE-induced median VTImax change) or fluid loading (fluid-induced median VTImax change). UBE-induced median VTImax and PV changes were significantly correlated with fluid responsiveness (p < 0.001, AUC 0.959; p < 0.001, AUC 0.804). The significant correlations were demonstrated via multivariable analysis using binary logistic regression (p = 0.001, OR 90.1) and the correlation coefficient (R2 = 0.793) using linear regression analysis. UBE-induced median VTImax changes (≥ 11.8% and 7.98%) predicted fluid-induced median VTImax changes ≥ 10% and 7% (AUC 0.959 and 0.939). The collapsibility and variation of IJVD and IJVA showed no significant correlation. An increase in the mean value of medians of repeatedly measured VTImaxs transitioning from an UBE to a supine position, effectively screened mild hypovolemia and demonstrated a significant correlation with fluid responsiveness in spontaneously breathing patients maintaining hemodynamic stability.

High intraoperative fluid load associated with prolonged length of hospital stay and complications after non-cardiac surgery in neonates

Inappropriate perioperative fluid load can lead to postoperative complications and death. This retrospective study was designed to investigate the association between intraoperative fluid load and outcomes in neonates undergoing non-cardiac surgery. From April 2020 to September 2022, 940 neonates who underwent non-cardiac surgery were retrospectively enrolled and their perioperative data were harvested for further analysis. According to recorded intraoperative fluid volumes defined as ml.kg−1 h−1, patients were mandatorily divided into quintile with fluid load as restrictive (quintile 1, Q1), moderately restrictive (Q2), moderate (Q3), moderately liberal (Q4), and liberal (Q5). The primary outcomes were defined as prolonged length of hospital stay (LOS) (postoperative LOS ≥ 14 days), complications beyond prolonged LOS, and 30-day mortality. Secondary outcomes included postoperative complications within 14 days of hospital stay. The intraoperative fluid load was in Q1 of 6.5 (5.3–7.3) (median and IQR); Q2: 9.2 (8.7–9.9); Q3: 12.2 (11.4–13.2); Q4: 16.5 (15.4–18.0); and Q5: 26.5 (22.3–32.2) ml.kg−1 h−1. The odd of prolonged LOS was positively correlated with an increase fluid volume (Q5 quintile: OR 2.602 [95% CI 1.444–4.690], P = 0.001), as well as complications beyond prolonged LOS (Q5: OR 3.322 [95% CI 1.656–6.275], P = 0.001). The overall 30-day mortality rate was increased with high intraoperative fluid load but did not reach to a statistical significance after adjusted with confounders. Furthermore, the highest quintile of fluid load (26.5 ml.kg−1 h−1, IQR [22.3–32.2]) (Q5 quintile) was significantly associated with longer postoperative mechanical ventilation time compared with Q1 (Q5: OR 2.212 [95% CI 1.101–4.445], P = 0.026). Conclusion: Restrictive intraoperative fluid load had overall better outcomes, whilst high fluid load was significantly associated with prolonged LOS and complications after non-cardiac surgery in neonates. Trial registration: Chictr.org.cn Identifier: ChiCTR2200066823 (December 19, 2022).What is Known:• Inappropriate perioperative fluid load can lead to postoperative complications and even death.What is New:• High perioperative fluid load was significantly associated with an increased length of stay after non-cardiac surgery in neonates, whilst low fluid load was consistently related to better postoperative outcomes.

Comparison of the ability of short time low PEEP challenge and mini fluid challenge to predict fluid responsiveness in patients undergoing open pancreaticoduodenectomy: an observational cohort study.

The mini-fluid challenge (MFC), which assesses the change in stroke volume index (SVI) following the administration of 100 mL of crystalloids, and the short-time low positive end-expiratory pressure (PEEP) challenge (SLPC), which evaluates the temporary reduction in SVI due to a PEEP increment, are two functional hemodynamic tests used to predict fluid responsiveness in the operating room. However, SLPC has not been assessed in patients undergoing abdominal surgery, and there is no study comparing these two methods during laparotomy. Therefore, we aimed to compare the SLPC and MFC in patients undergoing open pancreaticoduodenectomy. All patients received a standard hemodynamic management. The study protocol evaluated the percentage change in SVI following the application of an additional 5 cmH2O PEEP (SVIΔ%-SLPC) and the infusion of 100 mL crystalloid (SVIΔ%-MFC). Challenges that resulted in an increase of more than 15% in SVI after the 500 ml of fluid loading were classified as positive challenges (PC). Areas under the receiver operating characteristics curves (ROC AUCs) were used for the comparison of the methods. Thirty-three patients completed the study with 94 challenges. Fifty-five (58.5%) of them were PCs. The ROC AUC of SVIΔ%-MFC was observed to be significantly higher than that of SVIΔ%-SLPC (0.97 vs. 0.64, p < 0.001). The best cut-off value for SVIΔ%-MFC was 5.6%. If we had stopped the bolus fluid administration when SVIΔ%-MFC ≤ 5% was observed (lower limit of the gray zone), we would have postponed the fluid loading in 35 (89.7%) of 39 negative challenges. The amount of fluid deferred would have corresponded to up to 40% of the total fluid given. SVIΔ%-MFC predicts fluid responsiveness with high diagnostic performance and is better than SVIΔ%-SLPC in patients undergoing open pancreatoduodenectomy. Additionally, the use of SVIΔ%-MFC has the potential to defer up to 40% of the total fluid given. gov: NCT05419570.

Up-and-Down Determination of Different Crystalloid Coload Volumes on the ED 90 of Prophylactic Norepinephrine Infusion for Preventing Postspinal Anesthesia Hypotension During Cesarean Section.

Fluid loading improves hemodynamic stability and reduces the incidence rate of post-spinal anesthesia hypotension when prophylactic vasopressors are administered. We investigated the impact of different crystalloid coload volumes on the 90% effective dose (ED) of prophylactic norepinephrine infusion for preventing post-spinal anesthesia hypotension in non-hypertensive patients undergoing cesarean section. Patients were randomly allocated to receive one of the different crystalloid coload volumes (0mL/kg [0mL/kg Group], 5mL kg [5mL/kg Group], and 10mL kg [10mL/kg Group]) in combination with prophylactic norepinephrine infusion immediately after the induction of spinal anesthesia. The prophylactic norepinephrine infusion doses were determined using the up-and-down sequential allocation methodology, with an initial dose of 0.025 μg/kg/min and a gradient of 0.005 μg/kg/min. The primary endpoint was the effective dose at which 90% (ED 90) of patients responded to prophylactic norepinephrine infusion for preventing post-spinal anesthesia hypotension. The estimated effective dose of norepinephrine infusion, at which 90% (ED 90) of patients responded, was found to be 0.084 (95% CI, 0.070 to 0.86), 0.074 (95% CI, 0.059 to 0.077), and 0.063 (95% CI, 0.053 to 0.064) μg/kg/min in the three groups, respectively. A crystalloid coload of 5 mL/kg or 10 mL/kg, as opposed to the groups receiving 0 mL/kg crystalloid coloads, resulted in a reduction of approximately 11.9% and 25.0%, respectively, in the ED90 of prophylactic norepinephrine infusion for preventing post-spinal anesthesia hypotension during cesarean section.

The Hemodynamic Changes Induced by Lung Recruitment Maneuver to Predict Fluid Responsiveness in Children during One Lung Ventilation-A Prospective Observational Study.

The prediction of fluid responsiveness in critical patients helps clinicians in decision making to avoid either under- or overloading of fluid. This study was designed to determine whether lung recruitment maneuver (LRM) would have an effect on the predictability of fluid responsiveness by the changes of hemodynamic parameters in pediatric patients who were receiving lung-protective ventilation and one-lung ventilation (OLV). A total of 34 children, aged 1-6 years old, scheduled for heart surgeries via right thoracotomy were enrolled. Patients were anesthetized and OLV with lung-protection ventilation settings was established, and then, positioned on left lateral decubitus. LRM and volume expansion (VE) were performed in sequence. Heart rate (HR), systolic arterial pressure (SAP), mean arterial pressure (MAP) diastolic arterial pressure (DAP), stroke volume (SV), stroke volume variation (SVV), and pulse pressure variation (PPV) were recorded via an A-line based monitor system at the following time points: before and after LRM (T1 and T2) and before and after VE (T3 and T4). An increase in stroke volume (SV) or mean arterial pressure (MAP) of ≥10% following fluid loading identified fluid responders. The predictability of fluid responsiveness by the changes of SV (ΔSVLRM) and MAP (ΔMAPLRM) after LRM and VE were statistically evaluated by receiver operating characteristic curves [area under the curves (AUC)]. SVs in all patients were significantly decreased after LRM (p < 0.01) and then, increased and returned to baseline after VE (p < 0.01). In total, 16 out of 34 patients who were fluid responders had significantly lower SV after LRM compared to that in fluid non-responders. The area under the receiver operating characteristic curves for ΔSVLRM was 0.828 (95% confidence interval [CI], 0.660 to 0.935; p < 0.001) and it indicated that ΔSVLRM was able to predict the fluid responsiveness of pediatric patients. MAPs in all patients were also decreased significantly after LRM, and 12 of them fell into the category of fluid responders after VE. Statistically, ΔMAPLRM did not predict fluid responsiveness when LRM was considered as an influential factor (p = 0.07). ΔSVLRM, but not ΔMAPLRM, showed great reliability in the prediction of the fluid responsiveness following VE in children during one-lung ventilation with lung-protective settings. ChiCTR2300070690.

Vibroacoustic response of a locally resonant coated cylindrical shell semi-submerged or fully submerged at a finite depth near a free sea surface

We study the vibroacoustic response of a coated cylindrical shell semi-immersed or fully submerged close to a free sea surface. Different coating designs corresponding to a uniform coating made of a viscoelastic material and locally resonant coatings composed of the viscoelastic material embedded with cavities or hard inclusions are considered. Analytical models that account for fully coupled fluid-structure interaction between the coated shell, the surrounding fluid domain and the free sea surface are developed. The free surface is treated as a pressure release boundary. For a fully submerged coated shell, the image method is employed. For the semi-immersed coated shell, a partial fluid loading condition is imposed on the wetted coating surface. The combined influence of the different coating designs and free surface on the structural and acoustic responses of the semi- and fully immersed shells are described. The influence of variation in dominant coating parameters that primarily impact the local resonances of the inclusions is also reported.

Topology optimization of incompressible structures subject to fluid–structure interaction

In this work, an algorithm for topology optimization of incompressible structures is proposed, in both small and finite strain assumptions and in which the loads come from the interaction with a surrounding fluid. The algorithm considers a classical block-iterative scheme, in which the solid and the fluid mechanics problems are solved sequentially to simulate the interaction between them. Several stabilized mixed finite element formulations based on the Variational Multi-Scale approach are considered to be capable of tackling the incompressible limit for the numerical approximation of the solid. The fluid is considered as an incompressible Newtonian fluid flow which is combined with an Arbitrary-Lagrangian Eulerian formulation to account for the moving part of the domain. Several numerical examples are presented and discussed to assess the robustness of the proposed algorithm and its applicability to the topology optimization of incompressible elastic solids subjected to Newtonian incompressible fluid loads.

Hemodynamic changes in the prone position according to fluid loading after anaesthesia induction in patients undergoing lumbar spine surgery: a randomized, assessor-blind, prospective study

Introduction A change from the supine to prone position causes hemodynamic alterations. We aimed to evaluate the effect of fluid preloading in the supine position, the subsequent hemodynamic changes in the prone position and postoperative outcomes. Patients and methods This prospective, assessor-blind, randomized controlled trial was conducted between March and June 2023. Adults scheduled for elective orthopaedic lumbar surgery under general anaesthesia were enrolled. In total, 80 participants were randomly assigned to fluid maintenance (M) or loading (L) groups. Both groups were administered intravenous fluid at a rate of 2 ml/kg/h until surgical incision; Group L was loaded with an additional 5 ml/kg intravenous fluid for 10 min after anaesthesia induction. The primary outcome was incidence of hypotension before surgical incision. Secondary outcomes included differences in the mean blood pressure (mBP), heart rate, pleth variability index (PVi), stroke volume variation (SVV), pulse pressure variation (PPV), stroke volume index and cardiac index before surgical incision between the two groups. Additionally, postoperative complications until postoperative day 2 and postoperative hospital length of stay were investigated. Results Hypotension was prevalent in Group M before surgical incision and could be predicted by a baseline PVi >16. The mBP was significantly higher in Group L immediately after fluid loading. The PVi, SVV and PPV were lower in Group L after fluid loading, with continued differences at 2–3 time points for SVV and PPV. Other outcomes did not differ between the two groups. Conclusion Fluid loading after inducing general anaesthesia could reduce the occurrence of hypotension until surgical incision in patients scheduled for surgery in the prone position. Additionally, hypotension could be predicted in patients with a baseline PVi >16. Therefore, intravenous fluid loading is strongly recommended in patients with high baseline PVi to prevent hypotension after anaesthesia induction and in the prone position. Trial number KCT0008294 (date of registration: 16 March 2023)

Survey of Thai Physicians' Practice in Pediatric Septic Shock.

(1) Background: Sepsis management in children is crucial, especially in emergency services. This study aims to evaluate Thai physicians' knowledge gaps in the emergency management of sepsis in children and to evaluate their adherence to the current sepsis clinical practice guidelines. (2) Methods: This is a cross-sectional survey of Thai physicians' management of septic shock in children. The survey was conducted through online questionnaires from March 2019-April 2019. (3) Results: Of the 366 responders, 362 (98.9%) were completed. Most of the responders were general practitioners (89.2%) and pediatricians (10.8%). The time from positive sepsis screening to being evaluated by physicians within 15 min was reported by 83.9%. The most common choice of fluid resuscitation was normal saline solution (77.3%). The practice of a fluid loading dose (20 mL/kg) consistent with the guidelines was 56.3%. The selection of the first vasoactive agent in warm shock (norepinephrine) and cold shock (epinephrine) according to recommendations in the guidelines was 74.3% and 36.2%, respectively. There was a significant difference between general practitioners and pediatricians in terms of knowledge about initial fluid resuscitation and the optimal vasoactive agent in cold shock (p-value < 0.001). In the multivariate model, factors associated with the guideline-based decision-making of vasoactive agent choice for cold shock were specialist training (pediatrician) and the completion of sepsis management training certification, with adjusted odds ratios (AORs) of 7.81 and 2.96, but working experience greater than ten years was inconsistent with the guideline-based decision-making (AOR 0.14). (4) Conclusions: Thai clinicians were unfamiliar with pediatric sepsis therapy standards, specifically the quantity of early fluid resuscitation and the appropriate vasoactive medications for cold shock. To encourage adherence to the guidelines, we propose a regularly required training course on pediatric sepsis management.

Towards spatio-temporal prediction of cavitating fluid flow with graph neural networks

In this article, we present a deep learning-based surrogate model for spatio-temporal prediction of cavitating fluid flow. Specifically, we introduce a finite element-inspired rotation equivariant hypergraph neural network for inferring and predicting dynamical behaviors of cavitating flow. We generate ground-truth spatial–temporal data by simulating a full-order variational system based on homogeneous mixture-based cavitation theory. We consider the flow past a NACA0012 hydrofoil to examine the predictive ability of the proposed graph neural network for cavitation dynamics. Results demonstrate that the network achieves stabilized and accurate temporal predictions of the system states, successfully forecasting the evolution patterns of individual cavitation events. Additionally, comparisons of predicted fluid loading coefficients are in good agreements with the ground-truth values. We also discuss some challenges encountered in the long-term prediction of flow patterns across multiple cavitation events. The proposed framework has implications for design optimization, active control and development of a physics-based digital twin of a cavitating marine propeller.

Asymptotic Analysis of an Elastic Layer under Light Fluid Loading

Asymptotic analysis for an elastic layer under light fluid loading was developed. The ratio of fluid and solid densities was chosen as the main small parameter determining a novel scaling. The leading- and next-order approximations were derived from the full dispersion relation corresponding to long-wave, low-frequency, antisymmetric motions. The asymptotic plate models, including the equations of motion and the impenetrability condition, motivated by the aforementioned shortened dispersion equations, were derived for a plane-strain setup. The key findings included, in particular, the necessity of taking into account transverse plate inertia at the leading order, which is not the case for heavy fluid loading. In addition, the transverse shear deformation, rotation inertia, and a number of other corrections appeared at the next order, contrary to the previous asymptotic developments for fluid-loaded plates not assuming a light fluid loading scenario.

Dynamic Analysis of a Moored Spar Platform in a Uniform Current: Fluid Load Prediction Using a Surrogate Model

A moored spar platform, equipped with various instruments, serves as a crucial tool in hydrological monitoring. However, conducting dynamic analyses of a single spar that endures wind and current requires significant amount of computational time. To address this challenge, this study proposes an efficient surrogate model to represent fluid loads. A database is established to capture the relationship between fluid loads, spar displacements and uniform currents based on a numerical model of the spar. Subsequently, an artificial neural network method is employed to construct the surrogate model. Finally, the surrogate model is integrated with a numerical model of the cable, developed using the lumped mass method, to create a coupled model of the moored spar. The dynamic responses of this coupled model align closely with those obtained from the purely numerical model, demonstrating the efficacy of the surrogate model in capturing fluid loads on the spar. In addition to the surrogate model generation approach, this research provides an efficient method to couple the surrogate model with the numerical model in dynamic analysis of floating systems in uniform currents.

An experimental study of oscillations induced by two-phase slug flows of water and air on a flexible catenary shaped submerged pipe

In this paper, an apparatus is described to conduct an experimental study on a small-scale laboratory model of a submerged suspended flexible pipe, in a catenary layout, oscillating in response to the intermittent loads caused by the internal two-phase slug flow of water and air.The slug flows were obtained by injecting water and air into the pipe with sixteen combinations of flow rates. The flexible pipe was set in a catenary configuration inside a water tank with a depth of 2 m. The oscillations of the pipe were recorded by cameras registering the position of fifty-five targets attached to points along the body of the pipe, providing a time-history of the movement of the pipe.The flow rates of the liquid and gas phases, the speed of the slugs and their frequencies were measured, leading to an evaluation of slugs‘ lengths and hold-ups, and to the assessment of the fluid loads applied to the pipe due to gravity and curvature. The video images of the pipe movement were processed to provide the amplitudes and frequencies of oscillation of the pipe.The methodology developed in this work may be used for various geometries and flow regimes, and it could be employed to the validation of physical models and numerical simulations of pipes’ oscillations excited by fluid interactions through the comparison between the experimental results and the computer calculations.The application of the experimental results to offshore pipes in operations, carrying oil and gas from petroleum reservoirs submarine wells to floating facilities in the ocean, may be obtained by the proper scaling up in conjunction with computer simulations.