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Is it time for an autoregulation-oriented therapy in head-injured patients?
No full textOptimization of cerebral perfusion
pressure (CPP) is a cornerstone
of the management
of head-injured patients in
intensive care. Unfortunately, there is
still no consensus on the best strategies
to manipulate CPP. Which should we
modify first: blood pressure or intracranial
pressure (ICP)? Which is the most
appropriate drug? What are the pressure
thresholds?
Recent guidelines suggest that “CPP
<50 mm Hg should be avoided, and that
minimally invasive, efficient, and accurate
methods of determining and following
the relationships between CPP
and autoregulation and between CPP
and ischemia in individual patients are
needed” (1).
For the last 20 yrs, the Cambridge
University group has been working
on techniques to measure cerebral
autoregulation in real time and has
proposed many indexes retrospectively
related with clinical and prognostic data
(2–6). In the current issue of Critical
Care Medicine, the retrospective, single-
center study by Aries et al (7) adds
new information for a bedside practical
identification of an “optimal” value
of CPP (CPPopt), which is measured as
the CPP corresponding to the best cerebral
vasoreactivity (8). The main result
has been to develop an algorithm for
the computerized, automated, and continuous
updating of CPPopt, derived
from a time window recording of 4 hrs.
In their study, vasoreactivity has beencalculated as a linear correlation coefficient
between spontaneous fluctuations
of mean arterial pressure and ICP (PRx).
Results are based on some theoretical
considerations:
Firstly, PRx is an index of vasoreactivity,
which means that variations of ICP
induced by CPP changes should be related
to cerebral blood volume variations. In
fact, if ICP is unchanged, cerebral blood
volume should also remain unchanged.
This is not always true, as the same authors
state. In case of decompressive craniectomy,
it is likely that spontaneous fluctuations
of CPP do not induce ICP increase,
even in the presence of significant raises
in cerebral blood volume. The same can
happen when cerebrospinal drainage is
present, or cerebral compliance is high.
Secondly, according to the authors, the
best PRx should correspond to CPPopt.
From a theoretical point of view, it is
reasonable to consider that the best CPP
for individual patients matches with the
best cerebral vasoreactivity, but prospective
validation studies are still lacking. In
particular, we do not know if patients with
high vasoreactivity present the best metabolic
and perfusion indexes. For example,
hypocapnia increases PRx, but may be
dangerous for head-injured patients and
may represent an important confounding
factor that needs to be taken into account
(9). An important step in the knowledge
of this phenomenon is represented by Jaeger
et al (10), who have found that brain
tissue oxygen pressure increases according
to CPP, only when measured CPP was
below or equal to CPPopt. When measured
CPP was higher than CPPopt, brain tissue
oxygen pressure did not change, becoming
independent from any increase in CPP.
Even if brain tissue oxygen pressure is just
a surrogate of cerebral blood flow, this
could suggest that driving CPP in excess
of CPPopt does not improve cerebral perfusion,
at least in the area where the brain
tissue oxygen pressure probe is inserted.
Furthermore, we do not know if drugs
such as mannitol, vasopressors, or other
variables, such as hyperthermia, hypothermia,
and fluctuations in sedation
could impact on PRx and eventually on
CPPopt extrapolation (11).
In addition, even if a correlation
between PRx and prognosis was reported
by several studies, it was only retrospectively
investigated (4–6). We do not know
if optimizing CPP could improve prognosis,
or if it simply reflects such a derangement
of physiological parameters that is
associated with poor outcome.
Beside these theoretical limitations,
there are important practical problems due
to technical acquisition of arterial blood
pressure and ICP and prospective artifact
exclusion. Furthermore, independently
from the quality of the pressure signal, in
a significant number of cases a correlation
between arterial blood pressure and ICP
was lacking, consequently PRx was not
available. In addition, technical difficulties
in identifying CPPopt with an automated
system are reported by the authors.
The purpose of this study is ambitious
and fascinating because it suggests
an autoregulation-oriented strategy
to identify individualized threshold of
CPPopt, which correlates with patients’
prognosis. Such an approach has been
already highlighted on head-injured
patients by Howells et al (12). In an
interesting article, they retrospectively
compared the effects of ICP- and CPPoriented
therapy in patients with continuous
monitoring of cerebrovascular
pressure reactivity. They found that
CPP-oriented therapy was superior to
ICP-oriented therapy when cerebrovascular
reactivity was normal, but it
was the reverse when cerebrovascular
reactivity was impaired. The authors
estimated that the correct CPP- or
ICP-directed treatment could have, on
average, increased the probability of a
favorable outcome from 45% to 64%.
This hypothesis is intriguing and needs
a prospective validation.
So far, no prospective randomized
study has been done, and therefore, no
definitive evidence supports the use
of this technology in general practice.
We look forward to an autoregulationoriented
prospective randomized multicenter
study in the near future
Echography in brain imaging in intensive care unit: State of the art
Full text linkTranscranial Sonography (TCS) is an ultrasound-based imaging technique, which allows the identification of several structures within the brain parenchyma. In the past it has been applied for bedside assessment of different intracranial pathologies in children. Presently, TCS is also used on adult patients to diagnose intracranial space occupying lesions of various origins, intracranial hemorrhage, hydrocephalus, midline shift and neurodegenerative movement disorders, in both acute and chronic clinical settings. In comparison with conventional neuroimaging methods (such as Computed Tomography or Magnetic Resonance), TCS has the advantages of low costs, short investigation times, repeatability, and bedside availability. These noninvasive characteristics, together with the possibility of offering a continuous patient neuro-monitoring system, determine its applicability in multiple emergency and non-emergency settings. Currently, TCS is a still underestimated imaging modality that requires a wider diffusion and a qualified training process
Anaesthesia for total knee arthroplasty: efficacy of single-injection or continuous lumbar plexus associated with sciatic nerve blocks--a randomized controlled study
No full textTotal knee arthroplasty (TKA) often results in marked postoperative pain. We compared in a randomized controlled study tramadol consumption, postoperative pain and patient satisfaction after primary TKA in patients who received a single injection lumbar plexus and sciatic nerve blocks or a continuous lumbar plexus and sciatic nerve blocks. Forty-four patients scheduled for unilateral total knee arthroplasty were allocated to the single shot group (group A) or to the catheter group (group B). All patients (in both groups) reported being satisfied with their anaesthetic management. Although pain scores and tramadol consumption appeared lower in the active infusion group, the differences did not reach statistical significance. This study confirms that either single injection or continuous infusion of Ropivacaine in lumbar plexus provides reliable and long-acting anaesthesia and analgesia
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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