1,721,094 research outputs found
Intravascular volume after aneurysmal subarachnoid hemorrhage
No full textIntravascular volume after aneurysmal subarachnoid hemorrhage A subarachnoid hemorrhage (SAH) from a ruptured cerebral aneurysm is a devastating disorder with an often poor prognosis. The occurrence of delayed cerebral ischemia (DCI) is one of the most important factors determining outcome in patients who have survived the first hours after the hemorrhage. Hypotension and hypovolemia have been associated with an increased risk for DCI after SAH. The aim of the research presented in this thesis was to study the relation between the presumed and the actual condition of the systemic circulation and thereby find a way to improve hemodynamic management after aneurysmal SAH. In a prospective observational study in 50 patients, we assessed the effectiveness of fluid balance guided fluid therapy (current standard therapy) in maintaining normovolemia. Circulating blood volume (CBV) was measured with pulse dye densitometry (PDD) on alternating days during the first two weeks after SAH. We found that hypo- and hypervolemia occurred frequently but found no association between CBV and the daily fluid balance or between CBV and a cumulative fluid balance, adjusted for insensible loss through perspiration and respiration. In a next study on 43 patients, we asked ICU- and Medium Care Unit nurses to predict the present volume status as hypo-, normo- or hypervolemic. They could base their assessments on all usually available hemodynamic data. These assessments were compared with the actual CBV, that was measured daily during the first ten days after SAH. The results showed that deviations from normovolemia occurred frequently but that most instances were not recognized as such, which resulted in a very low sensitivity of the predictions. In a prospective controlled study in 102 patients with recent SAH we compared fluid management guided by daily measurements of CBV to conventional fluid balance guided fluid therapy, during the first 10 days after SAH. In the intervention group, with fluid management guided by CBV, fewer measurements were in the severe hypovolemic range (6.7% versus 17.1%) and a smaller part of patients had measurements indicating severe hypovolemia (39% versus 54%). Pulmonary edema (PED) after SAH is often seen as a sign of hypervolemia and treated as such with diuretics, inotropics and a reduction in fluid intake. We prospectively studied CBV, fluid balance and cardiac index and compared it between patients who did or did not develop PED. The results showed that patients developing PED had actually a lower mean CBV than those without PED and had CBV measurements in the hypovolemic range. Patients with PED after SAH must be considered as hypovolemic and measures taken to counteract the pulmonary edema must be balanced against the risk of worsening hypovolemia. Results from the studies in this thesis show that a normal volume status after SAH is not easy to achieve or to maintain. A probable cause is that SAH results in multiple organ dysfunctions and a systemic inflammatory response syndrome (SIRS). A coordinated multidisciplinary approach of the SAH patient would be appropriate, in research as well as in patient care
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
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
Measuring standardised mortality ratios of hospitals: Challenges and recommendations
No full textObjectives of this thesis This thesis has the following objectives: - To study the effects of ‘referral bias’ and ‘casemix and coding issues’ on the current Dutch HSMR calculation. - To identify potential adjustments in the estimation of the HSMR to improve its validity as a performance indicator. Outline of this thesis The thesis starts with investigating the theoretical method underlying the calculation of the HSMR, the so-called indirect standardisation method. In chapter 2, the indirect standardisation method is compared with the direct standardisation method. Also, pitfalls of HSMR resulting from the indirect standardisation method are discussed, and recommendations are given to reduce the shortcomings of this method. Subsequently, the thesis investigates potential modifications of the currently used model for HSMR calculation. To adjust for casemix differences between hospitals, parameters of comorbidities are included in the model underlying the HSMR calculation. In chapter 3, the commonly used Charlson comorbidity measure is compared with the Elixhauser comorbidity measure. Discriminative performance of the casemix correction models based on these two comorbidity measures is compared and their effects on the HSMRs of individual hospitals are explored. The Dutch HSMR is currently based on in-hospital mortality. However, discharge patterns, average length of hospital stay, and transfers all affect inhospital mortality. In chapter 4, effects of the inclusion of post-discharge mortality on HSMRs are compared with those of in-hospital mortality. In the final part of the thesis we zoom in onto the mortality ratios of specific patient populations, rather than that of an entire hospital population. In chapter 5, the focus is on SMRs of specific diagnosis groups requiring specialised care offered by specialised hospitals. The SMRs of specialised and nonspecialised hospitals are compared and the influence of referral patterns on SMRs is investigated. Current HSMR calculation is based on administrative databases and said to lack important clinical predictors. In chapter 6, the casemix adjustment model for cardiac surgery patients, based on an administrative database, is compared with the validated clinical EuroSCORE prediction model, based on a clinical database. Also influences of the two models on eventual SMRs are compared. Finally, in chapter 7, the results and implications of this thesis are summarised and discussed together with insights and recommendations to improve the validity and utility of HSMRs
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Advanced Cardiovascular Monitoring
No full textThe Frank-Starling curve (the curvilinear relation between cardiac output (CO) and preload) can be used for optimalization of the blood circulation and tissue oxygenation, in order to decrease morbidity and mortality in high risk surgery and critically ill patients. Measurement of CO and preload with a pulmonary artery catheter (PAC) does not lead to diminished morbidity and mortality, partly because of the complications described from the PAC. CO can be measured with sufficient validity with intermittent transpulmonary thermodilution or lithium dilution and continuously with pulse contour cardiac output or arterial waveform analysis (Vigileo), as long as a sufficient arterial pulse wave is available. Bioimpedance CO can be used in children to track changes in CO, but is not sufficient in adults. The prediction of an improvement of the circulation by fluid infusion (fluid responsiveness) is the primary endpoint for preload optimalization. SPV, PPV and SVV as dynamic preload parameters are adequate predictors of fluid responsiveness, as long as patients are mechanically ventilated continuously with closed chest and without arrhythmias. Volumetric preload parameters, such as GEDV and ITBV are not useful, as well as CVP and PCWP measured with the PAC, because of a diminished cardiac and pulmonary vascular compliance in the presence of pathology. It is preferable to combine less invasive CO monitoring with a dynamic preload parameter for the optimalization of the ciculation and tissue oxygenation
Nerve identification and prevention of intraneural injection in regional anesthesia
No full textThis thesis deals with techniques to more reliably identify nervous structures and subsequently prevent intraneural injection in the practice of regional anesthesia. To identify nerves of the brachial plexus and sciatic nerve, both conventional techniques such as nerve stimulation, as well as ultrasound are described. The first chapters deal with nerve identification techniques using nerve stimulation and ultrasound. Nerve stimulation is used to reliably identify various nervous structures in the vertical infraclavicular brachial plexus block. Ultrasound is applied in the infragluteal region of the lower extremity to reliably detect sciatic nerve. The subsequent chapters concern identification and prevention of intraneural needle tip placement and outcome after intraneural injection in the practice of regional anesthesia. The aim of the individual chapters can be summarized as follows: in chapter 2, the authors provide a redirection protocol for the vertical infraclavicular block to effectively block all cords of the brachial plexus. Chapter 3 describes the identification of the infragluteal sciatic nerve using consistently visible and easy identifiable tendinous fibers in the proximal long head of biceps femoris. In chapter 4 and 5, an extensive overview is given about the sonoanatomy of the brachial plexus and the sciatic nerve. In these reviews, imaging modalities such as anatomy, histology and ultrasonography are optimally matched. In chapter 6, the authors conducted a systematic review of the relation between intraneural injection of local anesthetics and neurological sequelae. Chapters 7 and 8 describe the results of an extensive, quantitative analysis of the internal architecture of the brachial plexus and the sciatic nerve. In chapter 9, the hypothesis was tested whether nerve stimulation is reliable to distinguish between intraneural and extraneural environment in supraclavicular ultrasound-guided brachial plexus block. In chapter 10, the authors investigated the accuracy of ultrasound to detect intraneural injection after injection of small amount of dye in both brachial plexus and sciatic nerve blocks. Finally, in chapter 11, the findings of the studies presented in this thesis are discussed in light of the available data and some recommendations are given for future investigations
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