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General anesthesia impairs muscle microvascular compliance
No full textIntroduction Drugs used to induce and maintain general
anesthesia have deep effects on the cardiovascular system. To our knowledge there are no studies investigating microvascular
compliance during general anesthesia with a noninvasive approach
based on near-infrared spectroscopy (NIRS) technology.
Methods We randomized 36 healthy subjects undergoing maxillofacial surgery to receive general anesthesia with a sevofluorane–remifentanil (Group S) or a propofol–remifentanil association (Group P). We collected noninvasive measures of hemoglobin concentration from the gastrocnemius muscle of the subjects using a NIRS device (NIMO, NIROX srl, Italy), which performs quantitative assessments of the [HbO2] and [Hb] exploiting precise absorption measurements close to the absorption peak of the water. Data were collected during a series of venous occlusions at different cuff pressures, before and after 30 minutes from induction of general anesthesia. The muscle blood volume and microvascular compliance were obtained with a process previously described elsewhere [1]. Data were analyzed with a one-way analysis of variance test.
Results Demographic data of the 36 subjects were similar in both
Groups S and P. General anesthesia reduced the heart rate and
mean arterial pressure and increased the total muscle blood
volume in both groups (Group S: from 2.4 ± 0.9 to 3.2 ± 1.2 ml/
100 ml; Group P: from 2.4 ± 1.2 to 3.5 ± 1.8 ml/100 ml;
P < 0.05). During general anesthesia, despite no differences in
muscle blood volume between the two groups, sevofluorane–
remifentanil significantly decreased microvascular compliance
(from 0.15 ± 0.08 to 0.09 ± 0.04 ml/mmHg/100 ml; P = 0.001)
whereas propofol–remifentanil did not (from 0.15 ± 0.08 to
0.16 ± 0.11 ml/mmHg/100 ml; P = 0.39)
Effects of midline thoracotomy on pulse pressure variations during pressure-control ventilation
No full textObjective During mechanical ventilation, the heart–lung interaction
induces a cyclic oscillation of the arterial pulse pressure. The measure of this respiratory changes, called pulse pressure variation (PPV), is one of the most reliable index of fluid responsiveness. It is used as a functional hemodynamic monitoring in several conditions (general anesthesia, sepsis, ALI/ARDS). During cardiac surgery, midline thoracotomy significantly alters heart–lung interaction and, consequently,
PPV. The aim of the study was the evaluation of the effects of
sternotomy on PPV during pressure-control ventilation (PCV).
Methods Nineteen patients (age 62 ± 10 years) undergoing elective CABG in a tertiary university hospital were enrolled. A Swan–Ganz catheter, an arterial catheter and a central venous catheter was inserted in order to collect pressure waveforms. After the induction of general anesthesia all the patients were mechanically ventilated (PCV), setting pressure values in order to obtain a tidal volume of 8 ml/kg. Hemodynamic data were collected 5 min before and after sternotomy. PPV was calculated offline from the collected waveforms, according to the formula reported by Michard and colleagues [1].
Results The PPV, cardiac index, stroke volume, mean arterial
pressure, airway pressure and tidal volume did not change after
sternotomy. We subsequently differentiated patients according to
PPV values (Fig. 1). In the subgroup of patients with PPV > 13%
(7/19 patients), we found a good correlation between PPV and
Paw (Pearson correlation 0.861 P = 0.03; R2 = 0.74 P = 0.049);
after sternotomy, PPV was significantly reduced (15.4 ± 2.8% vs
8.2 ± 1.6%, P = 0.043) and it was no more correlated with Paw. In the subgroup of patients with PPV < 13% (12/19 patients), we did not find any correlation between PPV and Paw, and sternotomy
had no effects on hemodynamic data.
Conclusions During PCV, airway pressure affects PPV only when
patients are in a ‘fluid responsive’ status (PPV > 13%); similarly,
sternotomy reduces PPV only when baseline is above the hreshold value of 13%. It may thus be possible that midline thoracotomy makes a ‘fluid responsive’ patient unresponsive to a fluid challenge by leading his heart to work on the plateau portion of theFrank–Starling curve. This hypothesis would be confirmed by the lack of correlation between airway pressure and PPV after opening the thorax.
Reference
1. Michard F, Boussat S, Chemla D, et al.: Am J Respir Crit
Care Med 2000, 162:134-138
General anesthesia impairs muscle microvascular compliance
No full textIntroduction Drugs used to induce and maintain general
anesthesia have deep effects on the cardiovascular system. To our knowledge there are no studies investigating microvascular
compliance during general anesthesia with a noninvasive approach
based on near-infrared spectroscopy (NIRS) technology.
Methods We randomized 36 healthy subjects undergoing maxillofacial surgery to receive general anesthesia with a sevofluorane–remifentanil (Group S) or a propofol–remifentanil association (Group P). We collected noninvasive measures of hemoglobin concentration from the gastrocnemius muscle of the subjects using a NIRS device (NIMO, NIROX srl, Italy), which performs quantitative assessments of the [HbO2] and [Hb] exploiting precise absorption measurements close to the absorption peak of the water. Data were collected during a series of venous occlusions at different cuff pressures, before and after 30 minutes from induction of general anesthesia. The muscle blood volume and microvascular compliance were obtained with a process previously described elsewhere [1]. Data were analyzed with a one-way analysis of variance test.
Results Demographic data of the 36 subjects were similar in both
Groups S and P. General anesthesia reduced the heart rate and
mean arterial pressure and increased the total muscle blood
volume in both groups (Group S: from 2.4 ± 0.9 to 3.2 ± 1.2 ml/
100 ml; Group P: from 2.4 ± 1.2 to 3.5 ± 1.8 ml/100 ml;
P < 0.05). During general anesthesia, despite no differences in
muscle blood volume between the two groups, sevofluorane–
remifentanil significantly decreased microvascular compliance
(from 0.15 ± 0.08 to 0.09 ± 0.04 ml/mmHg/100 ml; P = 0.001)
whereas propofol–remifentanil did not (from 0.15 ± 0.08 to
0.16 ± 0.11 ml/mmHg/100 ml; P = 0.39).
Conclusion General anesthesia affects the microvascular bed of
skeletal muscle. An association between opioid and ipnotic agents
increases the muscle blood volume, whereas microvascular compliance
is reduced only by the sevofluorane–remifentanil association.
Reference
1. De Blasi RA, Palmisani S, Alampi D, et al.: Microvascular
dysfunction and skeletal muscle oxygenation assessed by phase modulation near-infrared spectroscopy in patients with septic shock. Intensive Care Med 2005, 31:1661-1668
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
Sphenopalatine Ganglion Pulsed Radiofrequency for the Treatment of Refractory Chronic SUNCT and SUNA: A Prospective Case Series
No full textWe aimed to evaluate the safety and effectiveness of sphenopalatine ganglion pulsed radiofrequency (SPG-PRF) for the treatment of patients with refractory chronic short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) and with cranial autonomic symptoms (SUNA)
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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