27 de agosto de 2013

Artigo recomendado: Effect of Intraoperative High Inspired Oxygen Fraction on Surgical Site Infection, Postoperative Nausea and Vomiting, and Pulmonary Function

Systematic Review and Meta-analysis of Randomized Controlled Trials

Frédérique Hovaguimian, Christopher Lysakowski, Nadia Elia, Martin R. Tramèr

Anesthesiology 2013; 119:303-16; Hovaguimian et al.


Background: Intraoperative high inspired oxygen fraction (Fio2) is thought to reduce the incidence of surgical site infection (SSI) and postoperative nausea and vomiting, and to promote postoperative atelectasis.

Methods: The authors searched for randomized trials (till September 2012) comparing intraoperative high with normal Fio2 in adults undergoing surgery with general anesthesia and reporting on SSI, nausea or vomiting, or pulmonary outcomes.

Results: The authors included 22 trials (7,001 patients) published in 26 reports. High Fio2 ranged from 80 to 100% (median, 80%); normal Fio2 ranged from 30 to 40% (median, 30%). In nine trials (5,103 patients, most received prophylactic antibiotics), the incidence of SSI decreased from 14.1% with normal Fio2 to 11.4% with high Fio2; risk ratio, 0.77 (95% CI, 0.59–1.00). After colorectal surgery, the incidence of SSI decreased from 19.3 to 15.2%; risk ratio, 0.78 (95% CI, 0.60–1.02). In 11 trials (2,293 patients), the incidence of nausea decreased from 24.8% with normal Fio2 to 19.5% with high Fio2; risk ratio, 0.79 (95% CI, 0.66–0.93). In patients receiving inhalational anesthetics without prophylactic antiemetics, high Fio2 provided a significant protective effect against both nausea and vomiting. Nine trials (3,698 patients) reported on pulmonary outcomes. The risk of atelectasis was not increased with high Fio2.

Conclusions: Intraoperative high Fio2 further decreases the risk of SSI in surgical patients receiving prophylactic antibiotics, has a weak beneficial effect on nausea, and does not increase the risk of postoperative atelectasis.

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23 de agosto de 2013

Artigo recomendado: Phrenic Nerve Function after Interscalene Block Revisited

Now, the Long View
Quinn H. Hogan
Anesthesiology 2013; 119:250-2, Quinn H. Hogan

Anesthesiologists are very good at immediate observation and intervention. For instance, hemodynamic disorders or inadequate ventilation are apparent to us in real time with customary vigilance and modern monitoring. Less evident are the delayed consequences of our actions. Only relatively recently we have become suspicious that volatile anesthetics might alter immunological function or neurological development months after administration. Similarly, in the realm of plexus and peripheral nerve blocks, we have long understood the immediate risks of injecting local anesthetic into the systemic circulation, which included vessel damage leading to bleeding, neural trauma, and anesthetization of unintended targets. Our focus of care is to avoid these immediate dangers. In contrast, delayed harm after blocks is less subject to our scrutiny. A case series reported in the current issue of Anesthesiology suggests that our attention should also extend into the long-term time frame regarding phrenic nerve function after interscalene blockade (ISB).

Acute loss of diaphragmatic activity after block of the phrenic nerve during ISB has been recognized as a predictable hazard since the landmark study by Urmey et al. in 1991. Now, Kaufman et al. report a series of 14 patients referred to them for treatment of chronic diaphragmatic paralysis that was clearly due to phrenic nerve damage after ISB. Few conclusions can be made from a case series with certainty, but their observations support several preliminary hypotheses.

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20 de agosto de 2013

Artigo recomendado: General Anesthesia with Sevoflurane Decreases Myocardial Blood Volume and Hyperemic Blood Flow in Healthy Humans

Carolien S. E. Bulte, Jeroen Slikkerveer, Otto Kamp, Martijn W. Heymans, Stephan A. Loer, Stefano F. de Marchi, Rolf Vogel, Christa Boer, R. Arthur Bouwman

Anesth Analg 2013;116:767–74

Background: Preservation of myocardial perfusion during general anesthesia is likely important in patients at risk for perioperative cardiac complications. Data related to the influence of general anesthesia on the normal myocardial circulation are limited. In this study, we investigated myocardial microcirculatory responses to pharmacological vasodilation and sympathetic stimulation during general anesthesia with sevoflurane in healthy humans immediately before surgical stimulation.

Methods: Six female and 7 male subjects (mean age 43 years, range 28–61) were studied at baseline while awake and during the administration of 1 minimum alveolar concentration sevoflurane. Using myocardial contrast echocardiography, myocardial blood flow (MBF) and microcirculatory  variables were assessed at rest, during adenosine-induced hyperemia, and after cold pressor test–induced sympathetic stimulation. MBF was calculated from the relative myocardial blood volume multiplied by its exchange frequency (ß) divided by myocardial tissue density (ρT), which was set at 1.05 g·mL-1.

Results: During sevoflurane anesthesia, MBF at rest was similar to baseline values (1.05 ± 0.28 vs 1.05 ± 0.32 mL·min-1·g-1; P = 0.98; 95% confidence interval [CI], -0.18 to 0.18). Myocardial blood volume decreased (P = 0.0044; 95% CI, 0.01–0.04) while its exchange frequency (ß) increased under sevoflurane anesthesia when compared with baseline. In contrast, hyperemic MBF was reduced during anesthesia compared with baseline (2.25 ± 0.5 vs 3.53 ± 0.7 mL·min-1·g-1; P = 0.0003; 95% CI, 0.72–1.84). Sympathetic stimulation during sevoflurane anesthesia resulted in a similar MBF compared to baseline (1.53 ± 0.53 and 1.55 ± 0.49 mL·min-1·g-1; P = 0.74; 95% CI, -0.47 to 0.35).

Conclusion: In otherwise healthy subjects who are not subjected to surgical stimulation, MBF at rest and after sympathetic stimulation is preserved during sevoflurane anesthesia despite a decrease in myocardial blood volume. However, sevoflurane anesthesia reduces hyperemic MBF, and thus MBF reserve, in these subjects.

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16 de agosto de 2013

Artigo recomendado: Conventional and Kilohertz-frequency Spinal Cord Stimulation Produces Intensity- and Frequency-dependent Inhibition of Mechanical Hypersensitivity in a Rat Model of Neuropathic Pain

Ronen Shechter, Fei Yang, Qian Xu, Yong-Kwan Cheong, Shao-Qiu He, Andrei Sdrulla, Alene F. Carteret, Paul W. Wacnik, Xinzhong Dong, Richard A. Meyer, Srinivasa N. Raja, Yun Guan

Anesthesiology 2013; 119:422-32, Shechter et al.

Background: Spinal cord stimulation (SCS) is a useful neuromodulatory technique for treatment of certain neuropathic pain conditions. However, the optimal stimulation parameters remain unclear.

Methods: In rats after L5 spinal nerve ligation, the authors compared the inhibitory effects on mechanical hypersensitivity from bipolar SCS of different intensities (20, 40, and 80% motor threshold) and frequencies (50, 1 kHz, and 10 kHz). The authors then compared the effects of 1 and 50 Hz dorsal column stimulation at high- and low-stimulus intensities on conduction properties of afferent Aα/β-fibers and spinal wide-dynamic–range neuronal excitability.

Results: Three consecutive daily SCS at different frequencies progressively inhibited mechanical hypersensitivity in an intensity-dependent manner. At 80% motor threshold, the ipsilateral paw withdrawal threshold (% preinjury) increased significantly from pre-SCS measures, beginning with the first day of SCS at the frequencies of 1 kHz (50.2 ± 5.7% from 23.9 ± 2.6%, n = 19, mean ± SEM) and 10 kHz (50.8 ± 4.4% from 27.9 ± 2.3%, n = 17), whereas it was significantly increased beginning on the second day in the 50 Hz group (38.9 ± 4.6% from 23.8 ± 2.1%, n = 17). At high intensity, both 1 and 50 Hz dorsal column stimulation reduced Aα/β-compound action potential size recorded at the sciatic nerve, but only 1 kHz stimulation was partially effective at the lower intensity. The number of actions potentials in C-fiber component of wide-dynamic–range neuronal response to windup-inducing stimulation was significantly decreased after 50 Hz (147.4 ± 23.6 from 228.1 ± 39.0, n = 13), but not 1 kHz (n = 15), dorsal column stimulation.

Conclusions: Kilohertz SCS attenuated mechanical hypersensitivity in a time course and amplitude that differed from conventional 50 Hz SCS, and may involve different peripheral and spinal segmental mechanisms.

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12 de agosto de 2013

Artigo recomendado: Acute Normovolemic Hemodilution in the Pig Is Associated with Renal Tissue Edema, Impaired Renal Microvascular Oxygenation, and Functional Loss

Franziska M. Konrad, Egbert G. Mik, Sander I. A. Bodmer, Bahar Ates, Henriëtte F. E. M. Willems, Karin Klingel, Hilde R. H. de Geus, Robert Jan Stolker, Tanja Johannes

Anesthesiology 2013; 119:256-69, Konrad et al.

Background: The authors investigated the impact of acute normovolemic hemodilution (ANH) on intrarenal oxygenation and its functional short-term consequences in pigs.

Methods: Renal microvascular oxygenation (μPo2) was measured in cortex, outer and inner medulla via three implanted optical fibers by oxygen-dependent quenching of phosphorescence. Besides systemic hemodynamics, renal function, histopathology, and hypoxia-inducible factor-1α expression were determined. ANH was performed in n = 18 pigs with either colloids (hydroxyethyl starch 6% 130/0.4) or crystalloids (full electrolyte solution), in three steps from a hematocrit of 30% at baseline to a hematocrit of 15% (H3).

Results: ANH with crystalloids decreased μPo2 in cortex and outer medulla approximately by 65% (P < 0.05) and in inner medulla by 30% (P < 0.05) from baseline to H3. In contrast, μPo2 remained unaltered during ANH with colloids. Furthermore, renal function decreased by approximately 45% from baseline to H3 (P < 0.05) only in the crystalloid group. Three times more volume of crystalloids was administered compared with the colloid group. Alterations in systemic and renal regional hemodynamics, oxygen delivery and oxygen consumption during ANH, gave no obvious explanation for the deterioration of μPo2 in the crystalloid group. However, ANH with crystalloids was associated with the highest formation of renal tissue edema and the highest expression of hypoxia-inducible factor-1α, which was mainly localized in distal convoluted tubules.

Conclusions: ANH to a hematocrit of 15% statistically significantly impaired μPo2 and renal function in the crystalloid group. Less tissue edema formation and an unimpaired renal μPo2 in the colloid group might account for a preserved renal function.

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9 de agosto de 2013

Case Scenario: Hypotonia in Infancy - Anesthetic Dilemma

Angela K. Saettele, Anshuman Sharma, David J. Murray

Anesthesiology 2013; 119:443-6, Saettele et al.


Infants with hypotonia of unknown etiology pose a unique challenge as many of the potential diagnoses have major, often conflicting, anesthetic management implications. The differential diagnosis of hypotonia is long and includes possibilities such as Duchenne muscular dystrophy, central core disease, and multiminicore disease. Intravenous anesthetic techniques are recommended because hyperkalemia or malignant hyperthermia is associated with the use of volatile anesthetics. However, the differential diagnosis of infants with hypotonia also includes mitochondrial disorders.

In children with mitochondrial disorders, an intravenous anesthetic technique that includes propofol could lead to metabolic decompensation because propofol alters mitochondrial electron transfer. This dilemma is often encountered when hypotonic infants require anesthesia for diagnostic tests such as magnetic resonance imaging and muscle biopsies for definitive diagnosis.

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5 de agosto de 2013

Artigo recomendado: Integration of Pain Score and Morphine Consumption in Analgesic Clinical Studies

Feng Dai, David G. Silverman,y Jacques E. Chelly, Jia Li, Inna Belfer and Li Qin

Dai et al, The Journal of Pain. 2013 by the American Pain Society

ABSTRACT

In pain clinical trials, the rescue analgesic medication such as patient-controlled analgesia morphine is often made available for patients for breakthrough pain. The patient-controlled analgesia morphine usage decreases the study agent’s effect on pain relative to placebo and introduces greater variability in attainment of pain scores. For assessment of analgesic efficacy, the isolated statistical analysis of pain score or morphine consumption as a surrogate marker for pain not only loses statistical efficiency but also may incur increased false-positive findings because of multiple testing. The aim of this article is to review the research to date for choices of statistical tests for pain or morphine consumption outcome, with a focus on systematically evaluating a means for collective analgesic assessment of pain and morphine consumption using an integrated outcome. A case example is illustrated for data visualization, statistical comparison, and effect size estimation using the new endpoint. Some implications for clinical practice and further research are discussed.
Perspective: This article provides statistical evidence to conclude that an integrated outcome of pain score and morphine consumption provides an efficient means for integrated analgesic assessment.

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2 de agosto de 2013

Artigo recomendado: Surgical Treatment of Permanent Diaphragm Paralysis after Interscalene Nerve Block for Shoulder Surgery

Matthew R. Kaufman, Andrew I. Elkwood, Michael I. Rose, Tushar Patel, Russell Ashinoff, Ryan Fields, David Brown

Anesthesiology 2013; 119:484-7, Kaufman et al.

Unilateral diaphragm paralysis after interscalene nerve block can result in respiratory disturbances that may have a substantial impact on quality of life and increased prevalence of respiratory infections. Several reports have estimated the incidence of transient diaphragm paralysis after routine interscalene blocks for shoulder surgery to be 100%, however, with modified local anesthetic dosing and ultrasound-guided needle placement, more recent data suggest this rate to be lower. Of greater concern is permanent diaphragm paralysis after interscalene nerve block for shoulder surgery. There are isolated reports in the literature regarding long-standing postprocedural diaphragm paralysis, yet the underlying causative mechanism has not been previously sought. Peripheral nerve injury may occur from a variety of mechanical causes, including: transection, piercing, stretching, thermal injury, and compression. Alternatively, a nonmechanical injury can result from the toxic or ischemic effects of pharmacologic agents, such as local anesthetics, epinephrine, or chemotherapeutic agents.

Phrenic nerve injury from many of these causes may be repaired using nerve-reconstruction techniques. We report our experience with 14 patients suffering permanent diaphragm paralysis after interscalene nerve blocks evaluated and treated between 2009 and 2012 at a tertiary referral center for peripheral nerve injuries with a catchment area that includes the entire United States. Parameters for review included: results of comprehensive evaluation, intraoperative findings during phrenic nerve surgery, and outcomes of surgical intervention (using our previously reported surgical treatment algorithm and outcomes study). Successful treatment of the paralyzed diaphragm was based on improvements on: sniff testing, spirometry, nerve conduction testing, electromyography, and patient reporting.

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