Combining surface effects and non-local two variable refined plate theories on the shear/biaxial buckling and vibration of silver nanoplates

Micro & nano letters

article

Morteza Karimi¹  Hojjat Allah Haddad¹  Ali Reza Shahidi¹ 

[1] Department of Mechanical Engineering, Isfahan University of Technology

关键词: nanostructured materials;    silver;    buckling;    vibrations;    nanomechanics;    surface effects;    nonlocal two variable refined plate theories;    shear-biaxial buckling;    vibration;    silver nanoplates;    rectangular nanoplates;    silver sheet;    numerical analysis;    Gurtin-Murdoch theory;    differential quadrature method;    Navier method;    Ag;   

DOI  :  10.1049/mnl.2014.0651

学科分类：计算机科学（综合）

来源: Wiley

【 摘 要 】

Aims and Background: To prolong postoperative analgesia many adjuvants has been used opioids and alpha-2 agonists are very popular among them. This study was aimed at comparing the sensory, motor, hemodynamic, sedative and analgesic properties of epidural administration of fentanyl and dexmedetomidine as an adjuvant to ropivacaine. Methodology: With Institutional ethical committee clearance this study was conducted at our hospital. After obtaining informed and written consent, a total of 60 patients scheduled for elective percutaneous nephrolithotomy (PCNL) were randomly allocated into two groups of 30 each. Patients of both genders, aged 21-60 y, ASA physical status I and II were enrolled. Group RD received 28 ml of inj ropivacaine 0.5% + dexmedetomidine 1 μg/kg and Group RF received 28 ml of ropivacaine 0.5% + inj fentanyl 1 μg/kg epidurally. Hemodynamic parameters, sedation scores, and time to onset of sensory loss, complete motor blockade, two segmental dermatomal regression and time of first rescue analgesic were recorded. Data were compiled systematically and analyzed using unpaired t-test, Chi‑square and Mann-Whitney U test. P < 0.05 was considered significant. Results: The demographic profile of patients was comparable in both groups. Onset of sensory analgesia up to T10 was 6.8 ± 2.8 min vs. 8.7 ± 2.7 min and time to reach maximum motor block was 19.8 ± 5.8 min vs. 23.9 ± 4.9 min in Group RD and Group RF respectively, which was significantly less in the Group RD. Postoperative analgesia was significantly prolonged in the Group RF as compared to Group RD, e.g. 394.5 ± 36.5 vs. 268.5 ± 28.3 min respectively. Sedation scores were better in the Group RD and highly significant on statistical comparison (P < 0.001). Incidence of hypotension, nausea and vomiting was high in the Group RF, while incidence of dry mouth was higher in the Group RD. Conclusion: Dexmedetomidine is a better adjuvant than fentanyl when added to epidural ropivacaine in terms of early onset of sensory and motor block, prolonged postoperative analgesia and better sedation with less side effects.   Declaration: The data have been presented in part at 63rd ISACON,Jaipur; Dec 2015 Received: 26 Dec 2016; Reviewed: 18, 25 Feb 2017; Corrected & accepted: 24 Mar 2017 INTRODUCTION: Pain in the postoperative period is one of the major factors that impede recovery from anesthesia and surgery. Percutaneous nephrolithotomy (PCNL) can be performed under general anesthesia (GA) or regional anesthesia. PCNL under epidural anesthesia has some unique advantages over GA, such as lesser postoperative pain, lower dose requirement for analgesic drugs, and avoidance of the side effects from multiple medications during GA.1-7 Thus, epidural anesthesia has many advantages of providing analgesia for prolonged duration with repeated top-ups and also it is the preferred technique of choice for providing excellent postoperative analgesia. Ropivacaine is a S-enantiomer with less cardiotoxic effect and with less propensity to block motor fibers. Hence this drug is a better alternative to bupivacaine. Combination of opioids and local anesthetic (LA) for epidural anesthesia and analgesia has been used in many studies with reported benefits like decreasing the dose of LA, rapid onset and decreasing side effect of each drug when used alone.8 Epidural fentanyl has been commonly used in neuraxial blockades as a better alternative to morphine to attenuate the side effects like respiratory depression. The adjuvants like central alpha-2 agonists acts by opioid independent mechanism. Dexmedetomidine is a selective alpha-2 agonist with sympatholytic, sedative, amnesic and analgesic properties and so the opioid sparing analgesia can be achieved. Keeping in mind all pharmacological profile of these drugs, we conducted a study with the aim of comparing the sensory, motor, analgesic and sedative properties of dexmedetomidine and fentanyl as an adjuvant to epidural ropivacaine. METHODOLOGY: It was a hospital based double blind, randomized comparative study, done in a tertiary care centre. After approval from the institutional ethical committee and review board, written informed consent was obtained from each patient for performance of epidural anesthesia after complete explanation about the study. We included 60 patients undergoing PCNL who were randomly allocated into two groups of 30 patients in each. Patients of either sex with age between 20-60 years and ASA physical status l and II were included and patients with any contra indication to regional anesthesia and allergy to local anesthetics were excluded from the study. Patients were premedicated with inj. ranitidine 50 mg IV and midazolam 1 mg IV one hour prior to the procedure. Baseline vital signs like NIBP, pulse rate, respiratory rate and SpO2 were recorded. After securing an 18 G IV cannula, preloading was done with 10-15 ml/kg lactated ringer solution. Patients were positioned in left lateral decubitus position assisted by OT staff. Lumbar epidural puncture was performed with 18G Tuohy needle in L1-L2 interspace. The identification of the epidural space was done with loss of resistance technique using normal saline; a test dose of 3 ml of 2% lignocaine plus adrenaline (1:200,000) was given and epidural catheter secured at 3-5 cm in epidural space. The patients were allocated to groups by using lottery method and study drug was loaded by one colleague who was unaware of study design and was administered by the lead author. The drugs were given slowly over one minute with negative aspiration and in incremental doses. A total of 28 ml of inj ropivacaine 0.5%  + dexmedetomidine in Group RD, and an equal volume of ropivacaine 0.5% + fentanyl 1 mg/kg in Group RF, diluted to make a total of 30 ml volume respectively. After injecting patients were turned supine and vital signs were recorded. The patients were given 4 L/min of oxygen by face mask. Sensory and motor parameters were assessed after every 1 min and patient was given prone position only after desired grade of sensory and motor level achieved and surgery was started 30 min after epidural injection. The following parameters were observed Time to onset of sensory block at T10 Maximum sensory level achieved Time taken to achieve the maximum sensory level Time taken to complete motor blockade Time taken to two segmental dermatomal regression Sensory regression to S2 Total duration of analgesia Grading of motor block was done by modified Bromage score, e.g. 0 = no block; 1 = inability to raise extended leg; 2 = inability to flex knees; 3 = inability to flex ankles and feet. The pain score was determined by numerical rating scale (NRS), in which the patient marks the score on a scale numbered from 0 to 10 [0 = no pain, 1-3 = mild pain, 4-6 = moderate pain,7-9 = severe pain, 10 = worst imaginable pain]. Sedation was also assessed at intervals of 10 min intraoperatively and at intervals of 1 hour during postoperative period using Ramsay sedation scale, e.g. 1 = anxious and agitated or restless, 2 = cooperative, oriented and tranquil, 3 = responding to commands only, 4 = brisk response to a light glabellar tap or auditory stimulus, 5 = asleep, sluggish response to light glabellar tap or auditory stimulus and 6 = no response to painful stimulus. The various side effects were noted and managed accordingly. The sample size was calculated as 26 subjects in each group at alpha error of 0.05 and power 80% assuming difference in mean of complete motor block from a pilot study done on 10 patients in each group and considering 10% drop out 30 patients were included in each group. Statistical analysis: It was performed with IBM SPSS Statistics for Windows, Version 21 (SPSS Inc., Chicago, IL, USA). The categorical data were presented as numbers (percent) and were compared among groups using Chi square test. The quantitative data were presented as mean ± standard deviation and were compared by Student’s unpaired t-test. Probability was considered to be significant if less than 0.05.

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