1,721,160 research outputs found
Moderate-degree acidosis is an independent determinant of postoperative bleeding in cardiac surgery
No full textBackground. Acidosis is a well-known factor leading to coagulopathy. It has been widely explored as a risk factor for severe bleeding in trauma patients. However, no information with respect to acidosis as a determinant of postoperative bleeding in cardiac surgery patients exists. The aim of this study was to investigate the role of acidosis and hyperlactatemia (HL) in determining postoperative bleeding and need for surgical revision in cardiac surgery patients. Methods. We carried out a retrospective analysis on 4521 patients receiving cardiac operations in two institutions. For each patient the preoperative data and operative profile was available. Arterial blood gas analysis data at the arrival in the intensive care unit were analyzed to investigate the association between acidosis (pH4.0 mMol/L) and postoperative bleeding and surgical revision rate. Results. After correction for the potential confounders, both acidosis (P=0.001) and HL (P=0.001) were significantly associated with the amount of postoperative bleeding. HL was an independent risk factor for postoperative bleeding even in absence of acidosis. Overall, surgical revision rate was 5.6% in patients with HL and no acidosis; 7.7% in patients with acidosis and HL, and 7.2% in patients with acidosis and no HL. All these values are significantly (P=0.001) higher than the ones in patients without acidosis/HL (2%). Conclusions. Even a moderate degree of postoperative acidosis is associated with a greater postoperative bleeding and surgical revision rate in cardiac surgery patients. Correction of acidosis with bicarbonate does not lead to an improvement of the postoperative bleeding asset
FROM A BOUNDARY INTEGRAL FORMULATION TO A VORTEX METHOD FOR VISCOUS FLOWS
No full textFor the numerical solution of flow problems past a solid body it is worth to consider boundary integral techniques for their inherent capability to manage efficiently the far-field boundary conditions as well as the approximation of the solid body contour. However, for the analysis of large Reynolds number flows, of major interest in the applications, several computational difficulties appear when using the integral representation for the velocity or for the vorticity field in its classical form with interpolating functions (BEM). In particular, the evaluation of the volume integrals is a serious drawback while the steepness of their kernel introduces artificial diffusion in the calculation. To satisfy the opposite requirements of the advective and of the diffusive part of the Navier-Stokes equations, we adopt an operator splitting scheme according to the Chorin-Marsden product formula (Chorin et al. 1978), together with a proper vorticity generation scheme at the solid boundary. A solution procedure based on the approximation of the vorticity field by a finite number of point vortices (PVM) follows as a natural evolution of the boundary integral formulation.
The numerical results given by the two methods for the merging of two like-signed vortices in free space reveal the excessive numerical diffusion of BEM. The better accuracy of PVM is also established through the evaluation of some first integrals of motion. Several results are also reported for flows in presence of solid boundaries where the vorticity generation is crucial. In this case accurate solutions are only obtained with PVM, while BEM is even less satisfactory than in free space. Finally, the proposed vortex-like method (PVM) is tested on the classical problem of the wake behind a cylinder, in comparison with other well established techniques
From a Boundary integral formulation to a vortex method for viscous flows
No full textFor the numerical solution of flow problems past a solid body it is worth to consider boundary integral techniques for their inherent capability to manage efficiently the far-field boundary conditions as well as the approximation of the solid body contour. However, for the analysis of large Reynolds number flows, of major interest in the applications, several computational difficulties appear when using the integral representation for the velocity or for the vorticity field in its classical form with interpolating functions (BEM). In particular, the evaluation of the volume integrals is a serious drawback while the steepness of their kernel introduces artificial diffusion in the calculation. To satisfy the opposite requirements of the advective and of the diffusive part of the Navier-Stokes equations, we adopt an operator splitting scheme according to the Chorin-Marsden product formula (Chorin et al. 1978), together with a proper vorticity generation scheme at the solid boundary. A solution procedure based on the approximation of the vorticity field by a finite number of point vortices (PVM) follows as a natural evolution of the boundary integral formulation. The numerical results given by the two methods for the merging of two like-signed vortices in free space reveal the excessive numerical diffusion of BEM. The better accuracy of PVM is also established through the evaluation of some first integrals of motion. Several results are also reported for flows in presence of solid boundaries where the vorticity generation is crucial. In this case accurate solutions are only obtained with PVM, while BEM is even less satisfactory than in free space. Finally, the proposed vortex-like method (PVM) is tested on the classical problem of the wake behind a cylinder, in comparison with other well established techniques
Monitoring prohemostatic treatment in bleeding patients
Get PDFAcutely bleeding patients are commonly found in the trauma and major surgery scenarios. They require prompt and effective treatment to restore an adequate hemostatic pattern, to avoid serious and sometimes life-threatening complications.Different prohemostatic treatments are available, including allogeneic blood derivatives (fresh frozen plasma, platelet concentrates, and cryoprecipitates), prothrombin complex concentrates, specific coagulation factors (fibrinogen, recombinant factor XIII, recombinant activated factor VII), and drugs (protamine for patients under heparin treatment, desmopressin, antifibrinolytics).For decades, prohemostatic treatment of the acutely bleeding patient was based on empirical strategies and clinical judgment, both in terms of a correct diagnosis of the mechanism(s) leading to bleeding, and of an assessment of the effects of the treatment. This empirical strategy may lead to excessive or unnecessary use of allogeneic blood products, as well as to an incorrect, inefficacious, or even dangerous treatment. Different monitoring devices are nowadays available for guiding the diagnostic and therapeutic decision-making process in an acutely bleeding patient. This review addresses the available tools for monitoring prohemostatic treatment of the bleeding patient, with a specific respect for point-of-care tests (thromboelastography, thromboelastometry, platelet function tests, and heparin monitoring systems) at the light of the existing evidence
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Data set from Ranucci M, Barile L, Ambrogi F, Pistuddi V; Surgical and Clinical Outcome Research (SCORE) Group. Discrimination and calibration properties of the hypotension probability indicator during cardiac and vascular surgery. Minerva Anestesiol. 2019 Jul;85(7):724-730. doi: 10.23736/S0375-9393.18.12620-4. Epub 2018 Nov 22. PMID: 30481996.
No full textData set from Ranucci M, Barile L, Ambrogi F, Pistuddi V; Surgical and Clinical Outcome Research (SCORE) Group. Discrimination and calibration properties of the hypotension probability indicator during cardiac and vascular surgery. Minerva Anestesiol. 2019 Jul;85(7):724-730. doi: 10.23736/S0375-9393.18.12620-4. Epub 2018 Nov 22. PMID: 30481996.
This is the abstract:
Background: Hypotension during surgery is linked to postoperative complications. Recently, a new hemodynamic algorithm intended to predict hypotensive events (hypotension probability indicator [HPI]) has been developed. The aim of the present study is to test the discrimination and calibration properties of the HPI.
Methods: The intraoperative files of 23 patients undergoing cardiac and major vascular surgery receiving the HPI-based hemodynamic monitoring were retrospectively investigated for prediction of hypotensive events (mean arterial pressure <65 mmHg). The HPI was available at 20 seconds intervals; the values of HPI five to seven minutes before a hypotensive event (HPI5-7) were tested for discrimination and calibration.
Results: The HPI5-7 has a fair level of discrimination (area under the curve 0.768) and a poor calibration, due to overestimation of the hypotensive risk. At the observed prevalence, a cut-off value of 85% carries a sensitivity of 62.4% and a specificity of 77.7%, a negative predictive value (NPV) of 97.8% and a positive predictive value (PPV) of 12.6%; a value of 98% has a PPV of 64% and an NPV of 95.3%.
Conclusions: The HPI5-7 may offer some useful insights. Values ≤85% carry a clinically acceptable NPV for hypotensive events at the observed prevalence and may represent a "safe zone" during surgery. Values >85% do not carry enough PPV to trigger hemodynamic interventions, but represent a warning signal. Values >98% are highly suggesting a hypotensive event after 5-7 minutes. Further studies exploring the predictive ability of the HPI at different times are needed
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Accuracy, calibration and clinical performance of the EuroSCORE: can we reduce the number of variables?
No full textBACKGROUND:
The European system for cardiac operative risk evaluation (EuroSCORE) is currently used in many institutions and is considered a reference tool in many countries. We hypothesised that too many variables were included in the EuroSCORE using limited patient series. We tested different models using a limited number of variables.
METHODS:
A total of 11150 adult patients undergoing cardiac operations at our institution (2001-2007) were retrospectively analysed. The 17 risk factors composing the EuroSCORE were separately analysed and ranked for accuracy of prediction of hospital mortality. Seventeen models were created by progressively including one factor at a time. The models were compared for accuracy with a receiver operating characteristics (ROC) analysis and area under the curve (AUC) evaluation. Calibration was tested with Hosmer-Lemeshow statistics. Clinical performance was assessed by comparing the predicted with the observed mortality rates.
RESULTS:
The best accuracy (AUC 0.76) was obtained using a model including only age, left ventricular ejection fraction, serum creatinine, emergency operation and non-isolated coronary operation. The EuroSCORE AUC (0.75) was not significantly different. Calibration and clinical performance were better in the five-factor model than in the EuroSCORE. Only in high-risk patients were 12 factors needed to achieve a good performance.
CONCLUSIONS:
Including many factors in multivariable logistic models increases the risk for overfitting, multicollinearity and human error. A five-factor model offers the same level of accuracy but demonstrated better calibration and clinical performance. Models with a limited number of factors may work better than complex models when applied to a limited number of patients
- …
