A strain-mediated corrosion model for bioabsorbable metallic stents.

This paper presents a strain-mediated phenomenological corrosion model, based on the discrete finite element modelling method which was developed for use with the ANSYS Implicit finite element code. The corrosion model was calibrated from experimental data and used to simulate the corrosion performance of a WE43 magnesium alloy stent. The model was found to be capable of predicting the experimentally observed plastic strain-mediated mass loss profile. The non-linear plastic strain model, extrapolated from the experimental data, was also found to adequately capture the corrosion-induced reduction in the radial stiffness of the stent over time. The model developed will help direct future design efforts towards the minimisation of plastic strain during device manufacture, deployment and in-service, in order to reduce corrosion rates and prolong the mechanical integrity of magnesium devices. STATEMENT OF SIGNIFICANCE: The need for corrosion models that explore the interaction of strain with corrosion damage has been recognised as one of the current challenges in degradable material modelling (Gastaldi et al., 2011). A finite element based plastic strain-mediated phenomenological corrosion model was developed in this work and was calibrated based on the results of the corrosion experiments. It was found to be capable of predicting the experimentally observed plastic strain-mediated mass loss profile and the corrosion-induced reduction in the radial stiffness of the stent over time. To the author's knowledge, the results presented here represent the first experimental calibration of a plastic strain-mediated corrosion model of a corroding magnesium stent.

Liberal perioperative fluid administration is an independent risk factor for morbidity and is associated with longer hospital stay after rectal cancer surgery.

INTRODUCTION Recent studies have advocated the use of perioperative fluid restriction in patients undergoing major abdominal surgery as part of an enhanced recovery protocol. Series reported to date include a heterogenous group of high- and low-risk procedures but few studies have focused on rectal cancer surgery alone. The aim of this study was to assess the effects of perioperative fluid volumes on outcomes in patients undergoing elective rectal cancer resection. METHODS A prospectively maintained database of patients with rectal cancer who underwent elective surgery over a 2-year period was reviewed. Total volume of fluid received intraoperatively was calculated, as well as blood products required in the perioperative period. The primary outcome was postoperative morbidity (Clavien-Dindo grade I-IV) and the secondary outcomes were length of stay and major morbidity (Clavien-Dindo grade III-IV). RESULTS Over a 2-year period (2012-2013), 120 patients underwent elective surgery with curative intent for rectal cancer. Median total intraoperative fluid volume received was 3680ml (range 1200-9670ml); 65/120 (54.1%) had any complications, with 20/120 (16.6%) classified as major (Clavien-Dindo grade III-IV). Intraoperative volume >3500ml was an independent risk factor for the development of postoperative all-cause morbidity (P=0.02) and was associated with major morbidity (P=0.09). Intraoperative fluid volumes also correlated with length of hospital stay (Pearson's correlation coefficient 0.33; P<0.01). CONCLUSIONS Intraoperative fluid infusion volumes in excess of 3500ml are associated with increased morbidity and length of stay in patients undergoing elective surgery for rectal cancer.

Combining cycloisomerization with trienamine catalysis: a regiochemically flexible enantio- and diastereoselective synthesis of hexahydroindoles.

The synthesis of polysubstituted hexahydroindoles through trienamine-organocatalyzed cycloadditions of pyrrolidinyl dienals, prepared by palladium-catalyzed cycloisomerization, is reported. The cycloadditions of this novel class of dienals proceed with excellent levels of enantio- and diastereoselectivity, with the regioselectivity of cycloaddition with respect to the tethering ring readily tuned through design of the cycloisomerization substrate. This work culminates in the first examples of double-stereodifferentiating trienamine catalysis, where catalyst stereocontrol dominates facial selectivity in the cycloaddition, affording azacyclic products that are specifically functionalized at every position.

Pulse transit time as a quick predictor of a successful axillary brachial plexus block.

BACKGROUND: It can take up to 30 min to determine whether or not axillary block has been successful. Pulse transit time (PTT) is the time between the R-wave on electrocardiography (ECG) and the arrival of the resulting pressure pulse wave in the fingertip measured with photoplethysmography. It provides information about arterial resistance. Axillary block affects vasomotor tone causing loss of sympathetic vasoconstriction resulting in an increased PTT. Early objective assessment of a block can improve efficacy of operating room time and minimize patient's fear of possible conversion to general anesthesia. This study explores whether PTT can objectively, reliably and quickly predict a successful axillary block. METHODS: Forty patients undergoing hand surgery under axillary block were included. A three-lead ECG and photoplethysmographic sensors were placed on both index fingers. Measurements were made from 2 min before until 30 min after induction of the block or less if the patient was transferred for operation. Afterwards, PTT was calculated as the time between the R-wave on ECG and a reference point on the photoplethysmogram. To assess the change in PTT caused by the block, the PTT difference between the control and blocked arm was calculated. Sensitivity and specificity of PTT difference were calculated using receiver operating characteristic analysis. RESULTS: In a successful block, the mean PTT difference significantly increased after 3 min by 12 (standard error of the mean 3.9) ms, sensitivity 87% and specificity 71% (area under the curve 0.87, P = 0.004). CONCLUSIONS: PTT is a reliable, quick and objective method to assess whether axillary block is going to be successful or not.

Pilot study of the air-Q intubating laryngeal airway in clinical use.

The air-Q Intubating Laryngeal Airway (ILA) is a newly introduced extraglottic airway device. In this pilot study, we evaluated its use as a routine airway device during positive pressure ventilation. Ease of endotracheal intubation through the device was also assessed. Fifty-nine ASA I and II patients undergoing elective surgery received an air-Q ILA and an endotracheal tube where indicated. Insertion, ventilation and intubation characteristics were noted, as well as throat morbidity and occurrence of adverse events. An air-Q ILA was successfully inserted in 100% of patients. Mean leak pressure was 19 +/- 5 cmH2O. Endotracheal intubation was indicated in 19 patients and successful in 58% on the first attempt and 74% in total. Ten percent of the study patients were noted to have dysphagia. One patient was diagnosed with bilateral lingual nerve injury but made a complete recovery in four weeks. The air-Q ILA is an adequate extraglottic airway device in terms of insertion and ventilation. However the proposed advantage of ease of endotracheal intubation requires further investigation.

Modafinil reduces patient-reported tiredness after sedation/analgesia but does not improve patient psychomotor skills.

BACKGROUND: Early recovery of patients following sedation/analgesia and anesthesia is important in ambulatory practice. The aim of this study was to assess whether modafinil, used for the treatment of narcolepsy, improves recovery following sedation/analgesia. METHODS: Patients scheduled for extracorporeal shock wave lithotripsy were randomly assigned to one of four groups. Two groups received a combination of fentanyl/midazolam with either modafinil or placebo. The remaining groups received remifentanil/propofol with either modafinil or placebo. Modafinil 200 mg was administered to the treatment group patients 1 h before sedation/analgesia. Groups were compared using the digital symbol substitution test (DSST), trail making test (TMT), observer scale of sedation and analgesia (OAA/S) and Aldrete score. Verbal rating scale (VRS) scores for secondary outcome variables e.g. energy, tiredness and dizziness were also recorded before and after treatment. RESULTS: Sixty-seven patients successfully completed the study. Groups received similar doses of sedation and analgesic drugs. No statistically significant difference was found for DSST between groups. No significant adverse effects occurred in relation to modafinil. No statistically significant difference between groups was identified for TMT, OAA/S and Aldrete scores. The mean VRS score for tiredness was lesser in the modafinil/fentanyl/midazolam group [1.3 (2.0)] compared with the placebo group [3.8 (2.5)], P=0.02. Such a difference was not found between the remifentanil/propofol groups [placebo 2.6 (2.2) vs. modafinil 3.1(2.7)], p>0.05. Dizziness was greater in the modafinil/remifentanil/propofol group 1.7 (2.0) vs. placebo 0.0 (0.5), p<0.05. CONCLUSION: Modafinil reduces patient-reported tiredness after sedation/analgesia but does not improve recovery in terms of objective measures of patient psychomotor skills.

A combination of lidocaine and nitrous oxide in oxygen is more effective in preventing pain on propofol injection than either treatment alone.

BACKGROUND AND OBJECTIVE: Propofol is an intravenous (i.v.) anaesthetic agent that possesses many of the qualities of an ideal anaesthetic agent. The most significant side-effect associated with propofol is pain on injection. Despite optimal therapy, the incidence of pain on propofol injection remains a problem. This prospective, randomized, double blinded study evaluated the effect of three different treatment strategies in decreasing pain on propofol injection. METHODS: We studied 102 adult, ASA I-II patients, scheduled for elective surgical procedures. Combination of i.v. lidocaine and nitrous oxide (N2O) in oxygen (O2) inhalation pre-treatment was compared with either treatment alone in the prevention of pain on propofol injection. A standard propofol injection technique and scoring system, to measure the pain on injection was used. RESULTS: Demographic variables were similar between the groups. The incidence of no pain on propofol injection was similar in the lidocaine and N2O groups (63.6% vs. 57.5%) (95% confidence interval (CI): 0.17-0.29, P = 0.61). Combination therapy was associated with a greater incidence of no pain on injection (84% vs. 63.6%) (95% CI: 0.06-0.48, P = 0.04). CONCLUSION: Combination of i.v. lidocaine and N2O in O2 inhalation pre-treatment is more effective than either treatment alone in decreasing pain on propofol injection.

Challenging the precepts of family-centered care: testing a philosophy.

Family-centered care (FCC) is a model of patient care delivery that encourages the inclusion of the family in the planning and provision of care. Although this model has been discussed extensively in the literature and adopted by some institutions, it is one that many have difficulty implementing. The purpose of this study was to test the elements of a FCC philosophy developed for maternal/child units at a major medical center. Questionnaires developed for this study and translated into four languages were completed by 193 parent/patient participants. The questionnaire asked participants to rate the importance of FCC interventions and report which interventions had been provided. Most of the participants were Caucasian, married, female, had an annual income of $20,000 or less, had 12 or fewer years of education, and were younger than 40 years of age. Overall, "feeling welcome when I come to the hospital" was the highest rated item by parents of hospitalized neonates and children and perinatal patients. Findings from this study will be used to implement a FCC care philosophy.

Unicompartmental knee arthroplasty. Sequential radiographic and scintigraphic imaging with an average five-year follow-up.

Clinical, radiographic, and scintigraphic results of 33 consecutive unicompartmental knee arthroplasties were reviewed after a mean follow-up period of 68 months (range, 24 to 112 months). Clinical grades employing criteria established by the Hospital for Special Surgery showed 74% good to excellent and 11% fair to poor results. Four knees (15%) required revision to a total knee arthroplasty after an average postoperative interval of 7.4 years. Within the subset of surviving medial compartment arthroplasties (23 knees), superior clinical results were associated with a central or slightly medialized mechanical axis (p < 0.05). Periprosthetic radiolucency showed no correlation with clinical scores or failures resulting in revision surgery. There was no radiographic evidence of progressive arthrosis within the unreplaced compartments. Comparative analysis of preoperative and annual postoperative technetium bone scans showed no temporally related changes indicative of impending prosthetic failure or disease progression within the unoperated compartments. The surgically treated compartments maintained uniformly intense femorotibial activity, whereas the unoperated compartments, including the patellofemoral joint, remained scintigraphically quiescent. Disease progression in unreplaced compartments is unusual after contemporary unicompartmental knee arthroplasty. Most failures and poor results arise from mechanical inadequacies amendable to surgical technique and/or future design considerations.

Functional dynamics of the knee joint by ultrafast, cine-CT.

An ultrafast, cine-CT scanner was used to demonstrate the differential mobility of the lateral and medial femoral condyles on their respective tibial plateaus in cadaver knees and to show the kinematic type of motion of the knee joint. Current imaging techniques cannot accomplish this because they do not perform combined quantitative, tomographic, and dynamic studies. Accordingly, this preliminary report presents the data from cine-CT scans of 12 normal intact adult cadaver knees. Scans were obtained at the rate of 14 or 17 per second at 50 or 100 ms exposures through midsagittal planes of the medial and lateral condyles and intercondylar notch. The cine-CT scans were displayed on a CRT and analyzed as closed-loop movies and as isolated images. Each cadaver femoral condyle demonstrated a different combined rolling and gliding motion. Preliminary results on the cadaver knee suggest the lateral femoral condyle moved 2.3 times further on the tibial plateau than its medial counterpart. The percentage of rolling for the lateral condyle was 43%-49%; the percentage of gliding was 51%-57%, with a ratio of rolling to gliding of 1:1.2. The percentage of rolling for the medial condyle was 16%-26%; the percentage of gliding 74%-84% with a ratio of rolling to gliding of 1:3.8. The femoral condyles, tibia, and cruciate ligaments acted as a crossed four-bar linkage in concordance with kinematic theory. The applicability of the cadaver knee results to patient dynamics and diagnosis cannot be determined from this study and awaits further investigations on the in vivo knee. However, ultrafast cine-CT demonstrated the complex knee motion in the cadaver knee joint.

Asymptomatic total hip prosthesis: natural history determined using Tc-99m MDP bone scans.

A prospective study was performed with 97 patients who had undergone total hip replacement surgery and who were not experiencing pain or other symptoms or problems. The study was intended to determine the normal postoperative appearance of radionuclide scans of the hip following administration of technetium-99m methylene diphosphonate. Five areas of the prostheses were evaluated. Results showed that 6 months after implantation activity around the lesser trochanter and prosthesis shaft became insignificant. Activity around the acetabulum, greater trochanter, and prosthesis tip stabilized approximately 2 years after surgery; approximately 10% of patients in the study had persistent activity in these areas. Familiarity with this normal progression is fundamental to interpretation of postoperative bone scans in patients with total hip prosthesis.

Alterations in vertebral growth following prolonged plaster immobilisation.

Long-term immobilisation in serial plasters for scoliosis, including the period of the adolescent growth spurt, leads to an increase in height of the vertebral bodies and a decrease of their height to width ratio. These changes are at the expense of the disc which is reduced in thickness. This stimulating effect on the vertebral body growth is probably due to the changes in mechanical factors.