Changes In Rate Of Conversion Research Articles

Characteristics of Laparoscopic Surgery for Trauma Patients and Risks of Conversion to Open Laparotomy.

The discussion is ongoing about appropriate indications for laparoscopic surgery in trauma patients. As timing and risks of conversion to laparotomy remain unclear, we aimed to elucidate characteristics of and risks for conversion following laparoscopic surgery, using a nationwide database. A retrospective observational study was conducted, using Japanese Trauma Data Bank (2004-2018). We included adult trauma patients who underwent laparoscopic surgery as an initial surgical intervention. Conversion to laparotomy was defined as laparotomy at the initial surgery. Patient demographics, mechanism and severity of injury, injured organs, timing of surgery, and clinical outcomes were compared between patients with and without conversion. Risks for conversion were analyzed focusing on indications for laparoscopic surgery, after adjusting patient and institution characteristics. Among 444 patients eligible for the study, 31 required conversions to laparotomy. The number of laparoscopic surgeries gradually increased over the study period (0.5-4.5% of trauma laparotomy), without changes in conversion rates (5-10%). Patients who underwent conversion had more severe abdominal injuries compared with those who did not (AIS 3 vs 2). While length of hospital stay and in-hospital mortality were comparable, abdominal complications were higher among patients with conversion (12.9 vs. 2.9%), particularly when laparoscopy was performed for peritonitis (OR, 22.08 [5.11-95.39]). A generalized estimating equation model adjusted patient background and identified hemoperitoneum and peritoneal penetration as risks for conversion (OR, 24.07 [7.35-78.75] and 8.26 [1.20- 56.75], respectively). Trauma laparoscopy for hemoperitoneum and peritoneal penetration were associated with higher incidence of conversion to open laparotomy.

Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils

The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3 catalyst. Intermediates like octadecanal (C18O) and octadecanol (C18OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.

Effect of preheat repetition on color stability of methacrylate- and silorane-based composite resins.

Background. The aim of this study was to investigate the effect of preheating methacrylate- and silorane-based composite resins on their color stability up to 40 times at 55‒60°C. Methods. Seventy-six methacrylate and silorane-based composite resin samples, with a diameter of 10 mm and a height of 2 mm, were divided into 4 groups (n=19). After the samples were prepared, their color parameters were determined using a reflective spectrophotometer. The composite resin samples were separately stored in a solution of tea for 40 consecutive days. Then the samples underwent a color determination procedure again using a spectrophotometer and color changes were recorded. Finally two-way ANOVA was used to study the effect of composite temperature on its staining (P<0.05). Independent-samples t-test was used to evaluate changes in conversion rates of preheated composite resin samples compared to non-heated samples at P=0.005 and P=0.029 for silorane-based and Z250 composite resin samples, respectively. Results. Both composite resin type (P=0.014) and preheating (P<0.001) had significant effects on ΔE. Conclusion. Repeated preheating of methacrylate- and silorane-based composite resin samples, up to 55‒60°C for 40 rounds, resulted in more color changes compared with unheated composite resin samples. After storage in a solution of tea the color change rate in the composite resin samples of silorane-based was higher than the Z250 composite resin samples.

Mechanistic and Structural Insight to an Evolved Benzoylformate Decarboxylase with Enhanced Pyruvate Decarboxylase Activity

Benzoylformate decarboxylase (BFDC) and pyruvate decarboxylase (PDC) are thiamin diphosphate-dependent enzymes that share some structural and mechanistic similarities. Both enzymes catalyze the nonoxidative decarboxylation of 2-keto acids, yet differ considerably in their substrate specificity. In particular, the BFDC from P. putida exhibits very limited activity with pyruvate, whereas the PDCs from S. cerevisiae or from Z. mobilis show virtually no activity with benzoylformate (phenylglyoxylate). Previously, saturation mutagenesis was used to generate the BFDC T377L/A460Y variant, which exhibited a greater than 10,000-fold increase in pyruvate/benzoylformate substrate utilization ratio compared to that of wtBFDC. Much of this change could be attributed to an improvement in the Km value for pyruvate and, concomitantly, a decrease in the kcat value for benzoylformate. However, the steady-state data did not provide any details about changes in individual catalytic steps. To gain insight into the changes in conversion rates of pyruvate and benzoylformate to acetaldehyde and benzaldehyde, respectively, by the BFDC T377L/A460Y variant, reaction intermediates of both substrates were analyzed by NMR and microscopic rate constants for the elementary catalytic steps were calculated. Herein we also report the high resolution X-ray structure of the BFDC T377L/A460Y variant, which provides context for the observed changes in substrate specificity.

Conversion of Laparoscopic to open cholecystectomy - six years experience at Shalamar Hospital, Lahore

Background: Laparoscopic Cholecystectomy (LC) is the gold standard treatment for symptomatic Gall Stones. The identification of factors that reliably predict the likely need to convert LC to open procedure would decrease the incidence of intraoperative complications and help in patient counseling about LC before surgery. Methods: Between 2001 and 2006, 300 elective Laparoscopic cholecystectomies were performed from a total of 470 elective cholecystectomies. The change in conversion rate between 200 1 to2003 and 2004 to 2006 was analysed. Factors predictive of higher risk for conversion were also identified. Results: Twelve LCs (4.0%) required conversion. History of acute attack for more than 72hrs was a strong predictor of conversion even if patient has minimal signs and symptoms. The conversion rate from 2001 to 2006 was only slightly changed i.e.; it has decreased for last 3 years. Conclusion: The conversion rate over the last 6 years has decreased with no incidence of intraoperative complications. Age >= 50 years, male patients and acute cholecystitis are the major predictors of conversion.

Structural Basis for Binding of Fluorinated Glucose and Galactose to Trametes multicolor Pyranose 2-Oxidase Variants with Improved Galactose Conversion

Each year, about six million tons of lactose are generated from liquid whey as industrial byproduct, and optimally this large carbohydrate waste should be used for the production of value-added products. Trametes multicolor pyranose 2-oxidase (TmP2O) catalyzes the oxidation of various monosaccharides to the corresponding 2-keto sugars. Thus, a potential use of TmP2O is to convert the products from lactose hydrolysis, D-glucose and D-galactose, to more valuable products such as tagatose. Oxidation of glucose is however strongly favored over galactose, and oxidation of both substrates at more equal rates is desirable. Characterization of TmP2O variants (H450G, V546C, H450G/V546C) with improved D-galactose conversion has been given earlier, of which H450G displayed the best relative conversion between the substrates. To rationalize the changes in conversion rates, we have analyzed high-resolution crystal structures of the aforementioned mutants with bound 2- and 3-fluorinated glucose and galactose. Binding of glucose and galactose in the productive 2-oxidation binding mode is nearly identical in all mutants, suggesting that this binding mode is essentially unaffected by the mutations. For the competing glucose binding mode, enzyme variants carrying the H450G replacement stabilize glucose as the α-anomer in position for 3-oxidation. The backbone relaxation at position 450 allows the substrate-binding loop to fold tightly around the ligand. V546C however stabilize glucose as the β-anomer using an open loop conformation. Improved binding of galactose is enabled by subtle relaxation effects at key active-site backbone positions. The competing binding mode for galactose 2-oxidation by V546C stabilizes the β-anomer for oxidation at C1, whereas H450G variants stabilize the 3-oxidation binding mode of the galactose α-anomer. The present study provides a detailed description of binding modes that rationalize changes in the relative conversion rates of D-glucose and D-galactose and can be used to refine future enzyme designs for more efficient use of lactose-hydrolysis byproducts.

Risk Factors for Conversion during Laparoscopic Cholecystectomy: Retrospective Analysis of Ten Years' Experience at a Single Tertiary Referral Centre

Background/Purpose: Laparoscopic cholecystectomy (LC) is the standard treatment for symptomatic benign gallbladder disease. The identification of factors that reliably predict the need to convert LC to open cholecystectomy (OC) would help with patient education and counseling. Methods: Between January 2000 and December 2009, 4,698 patients underwent cholecystectomy. LC was attempted in 4,434 patients (94.4%) and OC from the start was performed in 264 patients (5.6%). The causes for conversion were evaluated. The change in conversion rate between 2000 and 2004 and between 2005 and 2009 was analyzed. Factors predictive of conversion were identified by univariate and multivariate analysis. Results: Conversion to OC from an initial LC approach was required in 234 patients (5.3%). The main cause for conversion was dense adhesions (54.7%). Independent risk factors in multivariate analysis were male gender (p < 0.001), increased age (p < 0.001), a history of previous upper abdominal surgery (p < 0.001), a WBC count >9 × 10³/μl, and urgently indicated cholecystectomy (p <0.001). The conversion rate decreased significantly from 6.7 to 3.6% over the two time intervals (p < 0.001). Conclusions: Those at highest risk for conversion are elderly male patients with prior abdominal surgery who present emergently with laboratory evidence of biliary inflammation.

The Impact of Race on Organ Donation Rates in Southern California

The Organ Donation Breakthrough Collaborative began in 2003 to address and alleviate the shortage of organs available for transplantation. This study investigated the patterns of organ donation by race to determine if the Collaborative had an impact on donation rates among ethnic minorities. The following data from the Southern California regional organ procurement organization were reviewed between 2004 and 2008: age, race (Caucasian, African-American, Asian, Hispanic, and other), the numbers of eligible referrals for organ donation and actual donors, types of donors, consent rates, conversion rates, organs procured per donor (OPPD), and organs transplanted per donor (OTPD). Logistic regression was used to determine independent predictors of ≥4 OTPD. There were 1,776 actual donors out of 2,760 eligible deaths (conversion rate 64%). Hispanics demonstrated a significantly lower conversion rate than Caucasians (64% vs 77%, p < 0.001), but a considerably higher rate than African Americans (50%) and Asians (51%, p < 0.05 for both). There were no significant changes in conversion rates over time in any race. Age was a negative predictor (odds ratio [OR] 0.95), and trauma mechanism (OR 2.1) and standard criteria donor status (OR 2.5) were positive independent predictors of ≥4 OTPD. Race did not affect OTPD (all groups, p > 0.05). Conversion rates among all ethnic minorities were significantly lower than the rates observed in Caucasians. However, when controlling for other factors, race was not a significant risk factor for the number of organs transplanted per donor. The Collaborative has not had an identifiable effect on race conversion rates during the 5 years since its implementation. Further intervention is necessary to improve the conversion rate in ethnic minorities in Southern California.

Conversion of elective laparoscopic to open cholecystectomy between 1993 and 2004

Laparoscopic cholecystectomy (LC) is the standard treatment for symptomatic gallbladder disease. The identification of factors that reliably predict the likely need to convert LC to an open procedure would provide short-term benefits in terms of patient education and postoperative expectations. Between 1993 and 2004, 1179 elective LCs were attempted from a total of 1339 elective cholecystectomies. The change in conversion rate between 1993-1999 and 2000-2004 was analysed. Factors predictive of higher risk for conversion were also identified. Eighty-nine LCs (7.5 per cent) required conversion. Gallbladder wall thickness and a history of common bile duct (CBD) stones, treated by preoperative endoscopic sphincterotomy, were predictors of conversion. The proportion of patients who underwent LC was the same in 1993-1999 (87.5 per cent) and 2000-2004 (88.8 per cent), but the conversion rate increased significantly from 5.3 to 10.6 per cent in these two time intervals. In addition, the proportion of patients with a history of CBD stones rose significantly, from 6.4 per cent in 1993-1999 to 11.0 per cent in 2000-2004. The conversion rate increased over the 12-year interval of the study. A history of preoperative endoscopic sphincterotomy and a thickened gallbladder wall contributed to the likelihood of conversion.

Non-michaelian behavior of 5α-reductase in human prostate

An in-depth analysis of the kinetics of 5α-reductase in human prostatic tissue gave findings inconsistent with the claim that the enzyme is michaelian. In both hyperplastic and malignant tissue, the time-course of the conversion of testosterone (T) into dihydrotestosterone (DHT) was non-linear under conditions ensuring less than 15% conversion of substrate and cofactor. An initial rapid phase of conversion was followed by a long steady-state phase. This time-dependent change in conversion rate was not due to enzyme denaturation, fast inhibition by substrate or product effects. It resulted from a true slow transient kinetic process induced in the reactive enzyme by the substrates. Under our experimental conditions at pH5.5, 5α-reductase appeared to undergo a conformational change from an initially highly reactive form to a less reactive form. Since this “hysteretic” behavior was correlated with apparently negative cooperativity in enzyme kinetics, we postulate that, as previously described for other key metabolic enzymes, regulation of 5α-reductase activity in the prostate depends on the molecular flexibility of the enzyme and on changes in the cooperativity of different enzyme forms over time. This original non-michaelian behavior may explain the conflicting kinetics reported so far in the literature for this enzyme. The clinical implications of 5α-reductase hysteresis and its involvement in the damping of DHT production within the prostate are discussed.