1,720,975 research outputs found
Cerebral tissue PO2 and SjvO2 changes during moderate hyperventilation in patients with severe traumatic brain injury
No full textObject. The aim of this study was to investigate the effects of moderate hyperventilation on intracranial pressure (ICP), jugular venous oxygen saturation ([SjvO2], an index of global cerebral perfusion), and brain tissue PO2 (an index of local cerebral perfusion).
Methods. Ninety-four tests consisting of 20-minute periods of moderate hyperventilation (27–32 mm Hg) were performed on different days in 36 patients with severe traumatic brain injury (Glasgow Coma Scale score ≤ 8). Moderate hyperventilation resulted in a significant reduction in average ICP, but in seven tests performed in five patients it was ineffective. The response of SjvO2 and brain tissue PO2 to CO2 changes was widely variable and unpredictable. After 20 minutes of moderate hyperventilation in most tests (79.8%), both SjvO2 and brain tissue PO2 values remained above the lower limits of normality (50% and 10 mm Hg, respectively). In contrast, in 15 tests performed in six patients (16.6% of the studied population) brain tissue PO2 decreased below 10 mm Hg although the corresponding SjvO2 values were greater than 50%. The reduction of brain tissue PO2 below 10 mm Hg was favored by the low prehyperventilation values (10 tests), higher CO2 reactivity, and, possibly, by lower prehyperventilation values of cerebral perfusion pressure. In five of those 15 tests, the prehyperventilation values of SjvO2 were greater than 70%, a condition of relative hyperemia. The SjvO2 decreased below 50% in four tests; the corresponding brain tissue PO2 values were less than 10 mm Hg in three of those tests, whereas in the fourth, the jugular venous O2 desaturation was not detected by brain tissue PO2.
The analysis of the simultaneous relative changes (prehyperventilation — posthyperventilation) of SjvO2 and brain tissue PO2 showed that in most tests (75.5%) there was a reduction of both SjvO2 and brain tissue PO2. In two tests moderate hyperventilation resulted in an increase of both SjvO2 and brain tissue PO2. In the remaining 17 tests a redistribution of the cerebral blood flow was observed, leading to changes in SjvO2 and brain tissue PO2 in opposite directions.
Conclusions. Hyperventilation, even if moderate, can frequently result in harmful local reductions of cerebral perfusion that cannot be detected by assessing SjvO2. Therefore, hyperventilation should be used with caution and should not be considered safe. This study confirms that SjvO2 and brain tissue PO2 are two parameters that provide complementary information on brain oxygenation that is useful to reduce the risk of secondary damage. Changes in SjvO2 and brain tissue PO2 in opposite directions indicate that data obtained from brain tissue PO2 monitoring cannot be extrapolated to evaluate the global cerebral perfusion
The use of indomethacin in the treatment of plateau waves : effects on cerebral perfusion and oxygenation
No full textOBJECT: Plateau waves are sudden and steep increases in intracranial pressure (ICP) that can develop in patients with cerebral injuries, reduced pressure-volume compensatory reserve, and preserved autoregulation. They are caused by cerebral vasodilation in response to a reduction in cerebral perfusion and are associated with increased cerebral blood volume and reduced cerebral blood flow. The authors evaluated the hypothesis that administration of indomethacin, a potent cerebral arteriolar vasoconstrictor, could interrupt the vicious cycle that occurs during plateau waves, extinguishing these waves and, ultimately, restoring cerebral perfusion and oxygenation. METHODS: Plateau waves developed in nine patients, seven with severe traumatic brain injury and two with intraparenchymal hemorrhage. One to four episodes of plateau waves per patient were treated with indomethacin (15-20 mg), which was delivered by an intravenous bolus injection. Each patient's mean arterial blood flow (MABP), ICP, cerebral perfusion pressure (CPP), and cerebral tissue PO2 were continuously monitored and the data obtained were stored in a personal computer. Each patient's jugular venous O2 saturation (SjvO2) and venoarterial difference in PCO2 were evaluated by intermittent blood sampling. During five episodes of plateau waves, middle cerebral artery flow velocities were evaluated by transcranial Doppler ultrasonography. Indomethacin extinguished all plateau waves. On average, the ICP decreased from an initial value of 58.9 +/- 11.6 mm Hg to 21.2 +/- 8.6 and 25.8 +/- 13.7 mm Hg after 5 and 10 minutes, respectively (p < 0.01). The MABP did not change significantly. As a consequence the CPP increased by 98 and 81% after 5 and 10 minutes, respectively (p < 0.01). Five and 10 minutes after indomethacin was administered, SjvO2 increased from an initial value of 50 +/- 10.5% to 62 +/- 7.6 and 59.9 +/- 9.3%, respectively (p < 0.01); the cerebral tissue PO2 increased from an initial value of 13.4 +/- 10.6 mm Hg to 23.6 +/- 9.58 and 21.9 +/- 9.2 mm Hg, respectively (p < 0.05); and the venous-arterial PCO2 decreased significantly. The mean and diastolic flow velocities increased significantly, whereas the pulsatility index decreased from 1.39 +/- 0.56 to 1.09 +/- 0.4 at 5 minutes and 1.06 +/- 0.36 at 10 minutes (p < 0.05). CONCLUSIONS: The findings confirm that plateau waves are caused by vasodilation and show that indomethacin, by constricting the cerebral arteries, is effective in extinguishing plateau waves, ultimately restoring cerebral perfusion and oxygenation
Effects of cerebral perfusion pressure on brain tissue PO2 in patients with severe head injury
No full textIschemia causes secondary brain damage after severe head injury (SHI). Cerebral perfusion is commonly estimated by monitoring CPP, but the adequacy of cerebral oxygenation requires further measurements, such as jugular oxygen saturation or, more recently, PtiO2 monitoring. In 7 patients with severe head injury, ICP, MAP, CPP, SjO2 and PtiO2 were monitored for a mean time of 9.0 +/- 2.2 days. Most of the data were in a "normal" range. Focusing on values under the thresholds of 60 mm Hg for CPP and 20 mm Hg for PtiO2, we found a relationship between CPP and PtiO2. Looking at the PtiO2 time-course, we observed a quite constant increasing trend during the first 48 hours of monitoring, then the values remained relatively constant within a normal range. Our data show that decreases of PtiO2 are not uncommon after severe head injury and therefore it seems that monitoring of PtiO2 in SHI may be useful in order to minimize secondary insults
Cerebral perfusion pressure and cerebral tissue oxygen tension in a patient during cardiopulmonary resuscitation
No full textAbstract Objective: To report on
the effects of cardiopulmonary resuscitation
(CPR) instituted immediately
after a cardiac arrest on cerebral
perfusion pressure (CPP) and
cerebral tissue oxygen tension
(PbrO2). Design: Case report.
Setting: ICU of a university hospital.
Patient: A head-injured 17-yearold
man submitted to multimodal
neurological monitoring underwent
sudden cardiac arrest and successful
CPR. Interventions: External chest
compression, 100% oxygen ventilation,
volume expansion and standard
ACLS protocols. Measurements
and results: Heart rate, ECG, mean
arterial blood pressure (MABP),
ETCO2, PaO2, intracranial pressure
(ICP), CPP and PbrO2 were continuously
monitored during CPR and data
recorded at 15-s intervals by a
dedicated personal computer. At the
onset of the cardiac arrest, PbrO2
decreased to zero. The institution of
CPR resulted in a progressive increase
of MABP, CPP and PbrO2.
Assuming, on the basis of previous
experimental and clinical reports,
8 mmHg PbrO2 as a possible ischaemic/
hypoxic threshold value,
during the first 6.5 min of CPR,
PbrO2 values were below this
threshold (range 0–7 mmHg) and
CPP values were <25 mmHg for
81.5% of the time. In the following
5.5 min, more efficient CPR generated
CPP values >25 mmHg for
77.3% of the time. These values
were associated with a PbrO2
>8 mmHg (range 8–28 mmHg)
at all times. Conclusions: In the
clinical setting of a witnessed
cardiac arrest, immediate institution
of CPR can be effective in generating
PbrO2 values above a supposed
ischaemic/hypoxic threshold when
CPP is >25 mmHg. PbrO2 monitoring
by the Licox system is sensitive
and reliable, even at low values, and
can be suitable for evaluating cerebral
oxygenation during experimental
CPR
The importance of protecting the mechanical ventilator during colistin methanesulfonate nebulization.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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