Search

Study Design: Retrospective cohort study.Objective: There is only limited data on the outcome of primary surgery of lumbar disk herniation (LDH) in Dutch patients. The objective of this study is to describe undesirable outcomes after primary LDH.Methods: The National Claims Database (Vektis) was searched for primary LDH operations performed from July 2015 until June 2016, for reoperations within 18 months, prescription of opioids between 6 to 12 months and nerve root block within 1 year. A combined outcome measure was also made. Group comparisons were analyzed with the Student’s t-test.Results: Primary LDH surgery was performed in 6895 patients in 70 hospitals. Weighted mean of reoperations was 7.3%, nerve root block 6.7% and opioid use 15.6%. In total, 23.0% of patients had one or more undesirable outcomes after surgery. The 95% CI interval exceeded the 50% incidence line for 14 out of 26 hospitals with less than 50 surgical interventions per year. Although the data suggested a volume effect on undesired outcomes, the t-tests between hospitals with volume thresholds of 100, 150 and 200 interventions per year did not support this (Pvalues 0.078, 0.129, 0.114).Conclusion: This unique nationwide claims-based study provides insight into patient-relevant undesirable outcomes such as reoperation, nerve root block and opioid use after LDH surgery. About a quarter of the patients had a serious complication in the first follow up year that prompted further medical treatment. There is a wide variation in complication rates between hospitals with a trend that supports concentration of LDH care.

Activated clotting time (ACT) measurements are frequently used to monitor unfractionated heparin activity during noncardiac arterial procedures (NCAP). Accuracy of ACT-guided heparinization is mandatory to prevent heparin under and overdosing, thereby minimizing thrombo-embolic complications (TECs) and bleeding risk. The main objective of this study was to investigate accuracy of ACT to monitor heparin activity during NCAP using the Hemostasis Management System Plus (HMS) with high-range (HR) cartridges. ACT values were compared with anti-Xa measurements, regarded as the standard test to measure active heparin.

Purpose: Previous studies have shown that activated clotting time (ACT)–guided heparinization leads to better anticoagulation levels during noncardiac arterial procedures (NCAP) than a standardized bolus of 5000 IU. Better anticoagulation should potentially result in lower incidence of thrombo-embolic complications (TEC). Comparative investigations on clinical outcomes of these heparinization strategies are scarce. This study investigated clinical outcomes of ACT-guided heparinization with a starting dose of 100 IU/kg in comparison with a single standardized bolus of 5000 IU heparin during NCAP.Materials and methods: Analysis from a prospectively collected database of patients undergoing NCAP in 2 vascular centers was performed. Patients receiving ACT-guided heparinization were matched 1:1 with patients receiving 5000 IU heparin using propensity score matching (PSM). Primary outcomes were TEC, bleeding complications, and mortality within 30 days of procedure or during the same admission.Results: A total of 759 patients (5000 IU heparin: 213 patients, ACT-guided heparinization: 546 patients) were included. Propensity score matching resulted in 209 patients in each treatment group. After PSM, the groups were comparable, with the exception of a higher prevalence of peripheral arterial disease in the ACT-guided heparinization group (103 patients, 49% vs 82 patients, 39%, p=0.039). The target ACT (>200 seconds) was reached in 198 patients (95%) of the ACT-guided group versus 71 patients (34%) of the 5000 IU group (p<0.001), indicating successful execution of the ACT-guided protocol. Incidence of TEC (13 patients, 6.2% vs 10 patients, 4.8%, p=0.52), mortality (3 patients, 1.4% vs 0 patients, p=0.25), and bleeding complications (32 patients, 15% vs 25 patients, 12%, p=0.32) did not differ between patients receiving ACT-guided heparinization and 5000 IU heparin. Protamine was administered in 118 patients (57%) in the ACT group versus 11 patients (5.3%) in the 5000 IU group (p<0.001), but did not influence incidence of TEC (17 patients, 5.9% vs 6 patients, 4.7%, p=0.61) or bleeding complications (34 patients, 12% vs 22 patients, 17%, p=0.14).Conclusion: No difference in TEC, bleeding complications, or mortality was found between ACT-guided heparinization and a single bolus of 5000 IU heparin during NCAP.Clinical Impact Previous studies have shown that activated clotting time (ACT)-guided heparinization leads to better anticoagulation levels during non-cardiac arterial procedures (NCAP) then a standardized bolus of 5000 IU. Comparative investigations on clinical outcomes are scarce. This study focussed on clinical outcomes of both protocols in NCAP in a propensity score matched cohort. Thrombo-embolic complications (TEC), bleeding complications and mortality within 30 days after NCAP or during the same admission were comparable between groups. Future studies should focus on optimizing ACT-guided protocols, specifically in patients with a high risk of TEC and bleeding complications.

Purpose: Unfractionated heparin is widely used to lower the risk of arterial thromboembolic complications (ATECs) during interventions for peripheral arterial disease (PAD), but it is still unknown which heparin dose is the safest in terms of preventing ATECs and bleeding complications. This study aims to evaluate the incidence of complications during interventions for PAD and the relation between this incidence and different heparinization protocols.Materials and Methods: A retrospective analysis of a prospective multicenter cohort study was performed. Between June 2015 and September 2022, 355 patients who underwent peripheral interventions for PAD were included. All patients who were included before July 2018 received 5000 international units (IU) of heparin (group 1). Starting from July 2018, all included patients received an initial dose of 100 IU/kg, with potential additional heparin doses based on activated clotting time (ACT) values (group 2). Data on ACT values and complications within 30 days post-procedurally were collected.Results: In total, 24 ATECs and 48 bleeding complications occurred. In group 1, 8.7% (n=11) of patients suffered from ATEC, compared with 5.7% (n=13) in group 2. Thirteen percent of patients (n=17) in group 1 had a bleeding complication, compared with 14% (n=31) in group 2. Arterial thromboembolic complications were more often found in patients with peak ACT values of <200 seconds, compared with ACT values between 200 and 250 seconds, 15% (n=6) versus 5.9% (n=9), respectively, p=0.048. Patients with peak ACT values >250 seconds had a higher incidence of bleeding complications compared with an ACT between 200 and 250 seconds, 24% (n=21) versus 9.8% (n=15), respectively, p=0.003. Forty-four percent of patients (n=23) in group 1 reached a peak ACT of >200 seconds, compared with 95% (n=218) of patients in group 2 (p=0.001).Conclusion: ATEC was found in 6.8% (n=24) and bleeding complications in 14% (n=48) of patients who underwent a procedure for PAD. There was a significantly higher incidence of ATECs in patients with a peak ACT value <200 seconds, and a higher incidence of bleeding complications in patients with a peak ACT value >250 seconds. The findings obtained from this study may serve as a basis for conducting future research on heparinization during procedures for PAD, with a larger sample size.Clinical Impact Heparin is administered during arterial interventions for peripheral arterial disease (PAD) to decrease the risk of arterial (thrombo)embolic complications (ATEC) during or shortly following surgery. The effect of heparin is unpredictable in the individual patient, and the optimal dosage of this anticoagulant has not yet been established. Using the activated clotting time (ACT), the anticoagulatory effect of heparin can be monitored periprocedurally. Previous research on the incidence of both ATEC and bleeding complications, or on the optimal dosage of heparin administration, is scarce. This study aims to investigate the incidence of ATEC and bleeding complications between 2 different dosage protocols of heparin—a standard bolus of 5000 IU or ACT-guided heparinization—and thereby provide clarity on the optimal dose of heparin during peripheral arterial interventions for PAD.

Purpose: Heparin is the most widely-used anticoagulant to prevent thrombo-embolic complications during non-cardiac arterial procedures (NCAP). Unfortunately, there is a lack of evidence and consequently non-uniformity in guidelines on perprocedural heparin management. Detailed insight into the current practice of antithrombotic strategies during NCAP in the Netherlands is important, aiming to identify potential optimal protocols and local differences concerning perprocedural heparinization.Materials and Methods: A comprehensive online survey was distributed electronically to vascular surgeons of every hospital in the Netherlands in which NCAP were performed. Data were collected from September 2020 to October 2021.Results: The response rate was 90% (53/59 hospitals). During NCAP, all surgeons generally administered heparin before arterial clamping. In 74% (39/54) of hospitals, a single heparin dosing protocol was used for all types of patients and vascular procedures. In 40%, there was no uniformity in heparin dosing between vascular surgeons. Depending on the procedure, a fixed bolus heparin, predominantly 5000 IU, was administered in 73% to 93%. In the remaining hospitals (7%–27%), a bodyweight-based heparin protocol was used, with an initial dose of 70 or 100 IU/kg. A minority (28%) monitored the effect of heparin in patients using the activated clotting time add (ACT) after activated clotting time. Target values varied between 180 and 250 seconds or 2 times the baseline ACT.Conclusion: This survey demonstrates considerable variability in perprocedural heparinization during NCAP in the Netherlands. Future research on heparin dosing is needed to harmonize and optimize heparin dosage protocols and contemporary guidelines during NCAP, and thereby improve vascular surgical care and patient safety.Clinical Impact This survey demonstrated persisting intra- and inter-hospital variability in perprocedural heparinization during non-cardiac arterial procedures (NCAP) in the Netherlands. The observed variability in heparinization strategies highlights the need for high quality evidence on perprocedural anticoagulation strategies. This is needed in order to harmonize and optimize heparin dosage protocols and contemporary guidelines and thereby improve vascular surgical patient care. Based on the current results, an international survey will be conducted by the authors to gain additional insight into the antithrombotic strategies used during NCAP, aiming to harmonize anticoagulation protocols worldwide.

Purpose: Smoking is a well-known risk factor for developing arterial diseases and for an increase of complications during and after vascular procedures. Although smoking has a proven effect on hemostasis, no literature is available on the effect of smoking on the activated clotting time (ACT), which is used to monitor the effect of heparin during noncardiac arterial procedures (NCAP). The aim of this study was to examine the effect of smoking on ACT values and the incidence of complications during the same admission or 30 day follow-up of NCAP.Materials and methods: A post hoc analysis of a prospective multicenter cohort study was performed. Patients older than 18 years, who underwent NCAP between December 2016 and April 2021, were enrolled. Patients were divided into 2 groups based on smoking status: never/former smokers and current smokers. Two heparin dosing protocols were used: an initial bolus of 5000 IU or 100 IU/kg bodyweight.Results: In total, 773 patients met the inclusion criteria. Five minutes after administration of 5000 IU of heparin, mean ACT values were 190 and 196 seconds for nonsmokers and smokers, respectively (p=0.078). After 100 IU/kg of heparin, mean ACT values were 229 and 226 seconds for nonsmokers and smokers, respectively (p=0.37). Incidence of complications in the whole study cohort was not significantly different for nonsmokers compared with smokers (arterial thrombo-embolic complication [ATEC] 4.7% vs 5.7% p=0.55; hemorrhagic complications 15% vs 18% p=0.29). In subgroup-analysis, a significant difference between smoking groups was found for hemorrhagic complications after open aneurysm repair (p=0.024). However, after adjusting for confounders, the difference between the smoking groups annulled.Conclusion: The results of this study suggest that smoking does not have a significant effect on ACT values or on the incidence of complications in NCAP. Large-scale studies are required to further analyze potential factors having an effect on the ACT and perioperative and postoperative complications, which could help individualize heparinization strategy.Clinical impact There is high variance between patients in their response on administration of heparin, this is not yet fully understood. This study investigated the effect of smoking in a large prospective multicentre cohort. The results suggests that active smoking does not have an effect on the activated clotting time after administration of heparin. Also no significant effect of smoking could be found on the incidence of all registered complications. Monitoring of the effect of heparin remains important to provide patients with safe anticoagulation during vascular procedures.

This paper reports on a study among 711 Chinese students from the post-reform generation, comparing the subjective wellbeing of urban and rural students from different family income groups, using the Personal Wellbeing Index of the International Wellbeing Group. Urban participants were found to be more satisfied with their standard of living and their life-achievements than their rural counterparts, but no differences were found between these two groups for happiness, overall satisfaction with life, and the other five Personal Wellbeing Index satisfaction domains. In terms of family income level, participants from higher income families were found to be happier than participants from lower income families, and they were significantly more satisfied with their life (overall), as well as with their standard of living, life-achievement, personal relationships, feeling part of the community, and future (financial) security.

The novel concept of reverse flow operation with reactor side feeding is studied for selective oxidation of NH3 to produce either N2, N2O, or NO. During normal reverse flow operation, where the feeds are alternately introduced from either end of the reactor, the conversion is always lower when compared to steady state, once-through operation at the same residence time. The novel concept of reverse flow operation with reactor side feeding is therefore proposed to avoid the decrease of conversion. The production rate of the desired product can be kept at a high level, which may even exceed the production of normal reverse flow operation and steady state, once-through operation. The reactor behavior was simulated for three regimes (quasi steady state, dynamic, and relaxed steady state) with varying feed positions. The development of spatiotemporal patterns inside the reactor with side feeding shows completely different behavior compared to normal reverse flow operation and steady state, once-through operation, leading to the possibility of conversion and selectivity manipulations. In addition, the proposed concept also indicates better conversion for the dynamic and relaxed steady-state regimes. The influence of shifting the feed positions to the reactor center is most pronounced if the switching time is shorter. This concept also provides an opportunity to prevent the dead gas volume in the center of the reactor if suitable feed positions can be applied. The catalyst effectiveness in this novel concept is therefore much better than during normal reverse flow operation and steady state, once-through operation, particularly in the relaxed steady-state regime.

Moment‐based analysis was applied to determine successfully inter‐ and intrapellet diffusion coefficients from experimental TAP outlet pulse responses over a one‐zone bed with porous particles. Different temperatures, gas molar masses, and pellet sieve fractions were used to validate the Knudsen diffusion relation for inert gases inside porous catalyst pellets. The zeroth to third moments of the outlet pulse response were analytically derived for rectangular, cylindrical and spherical pellets. The third moment provides a significantly more accurate access to the intrapellet diffusivity than the second moment does. The experimental window of the TAP reactor is explored for porous silica as catalyst support bed filling. The relevance of concentration gradients inside the pellet is illustrated with model simulations.

A high‐resolution magnetic sector mass spectrometer has been developed and used for transient kinetic measurements on reactions that are important for automotive exhaust gas catalysis. This instrument allows separation of the isobaric masses of CO and N2as well as CO2and N2O, which are separately monitored in time at a sampling rate of 48 Hz. The time resolution is sufficient to determine individual kinetic rate parameters for reactions under transient conditions. A description of the experimental set‐up as well as the software used is given. The results are illustrated by the catalytic reduction of NO by CO. To the best knowledge of the authors, this is the first application of a magnetic sector mass spectrometer for kinetic research under dynamic operation conditions. Copyright © 2002 John Wiley & Sons, Ltd.

A method for determining the average cluster size of supported catalysts using low-energy ion scattering (LEIS) data is presented. The method is particularly suitable for determining the average cluster size of atomically dispersed metals and can be used for clusters as large as 10 nm. For Pt/γ-Al2O3 quantitative agreement is shown between the average cluster size as determined with LEIS and that determined with transmission electron microscopy (TEM). In the case of three-way catalysts, classic methods for determining the cluster size, such as TEM or CO chemisorption, often fail or produce ambiguous results because of the presence of ceria. Therefore, LEIS has been applied to determine the average noble metal cluster size of a commercial three-way catalyst. Moreover, it is shown by LEIS that the three-way catalyst contains mixed Pt/Rh clusters, which are strongly enriched in surface Pt after reduction.

A mathematical model of a three-way catalytic converter based on a detailed chemical kinetic model has been created mainly to analyze the converter's dynamic behavior at low temperatures. The light-off process of the converter is analyzed in detail. Competition of species for empty noble metal surface determines the light-off characteristic, as inhibition processes increase light-off temperatures of some exhaust gas components in the complete exhaust mixture. Perturbations of the exhaust gas mixture around stoichiometry can in certain conditions decreasethe effect of inhibition and lower the light-off temperature for some exhaust components.

The transient kinetics of ethylene oxidation by oxygen over a commercial Pt/Rh/CeO2/γ-Al2O3 three-way catalyst were modeled. Experiments were carried out in a fixed-bed microreactor with two separate inlets, enabling alternate feeding of ethylene and oxygen with frequencies up to ¹/4 Hz. The experimental conditions resemble the cold-start period of an Otto engine in a car. Two types of adsorbed ethylene species seem to exist. A selective catalyst deactivation for oxygen adsorption, due to deposition of carbonaceous species, was found. A kinetic model was developed, based on elementary reaction steps, that allows one to describe the experiments quantitatively. Furthermore, this model was combined with the published model for transient carbon monoxide oxidation over the same catalyst,¹ which enables one to predict the results of simultaneous ethylene and carbon monoxide oxidation. Both components react in rather distinct zones, with ethylene being converted only when carbon monoxide oxidation is almost complete.

The partial oxidation of methane to synthesis gas over rhodium sponge has been investigated by admitting pulses of pure methane and pure oxygen as well as mixtures of methane and oxygen to rhodium sponge at temperatures from 873 to 1023 K. Moreover, pulses of oxygen followed by methane and vice versa as well as pulses of mixtures of methane and labelled oxygen were applied to study the role of chemisorbed oxygen and incorporated oxygen in the reaction mechanism. The decomposition of methane on reduced rhodium results in the formation of carbon and hydrogen adatoms. During the interaction of pure dioxygen with rhodium the catalyst is almost completely oxidized to Rh2O3. In addition to rhodium oxide, oxygen is also present in the form of chemisorbed oxygen species. During the simultaneous interaction of methane and dioxygen at a stoichiometric feed ratio and a temperature of 973 K only 0.4 wt% Rh2O3is present. The chemisorbed oxygen species are completely desorbed after 2 s. A Mars–Van Krevelen mechanism is postulated: methane reduces the rhodium oxide, which is reoxidized by dioxygen. Synthesis gas is produced as primary product. Hydrogen is formed via the associative desorption of two hydrogen adatoms from reduced rhodium and the reaction between carbon adatoms and oxygen present as rhodium oxide results in the formation of carbon monoxide. The consecutive oxidation of CO and H2proceeds via both chemisorbed oxygen and oxygen present as rhodium oxide. Continuous flow experiments were performed to compare rhodium and platinum. When compared to platinum, rhodium shows a higher conversion to methane at a comparable temperature and also a higher selectivity to both CO and H2, the difference for CO being most pronounced. The observed differences in methane conversion and selectivities for the two catalysts are ascribed to the higher activation energy for methane decomposition on platinum compared to rhodium. An additional explanation for the difference in H2selectivity could be the higher activation energy for OH formation on rhodium compared to platinum.

The adsorption and reaction characteristics of methane, carbon dioxide, carbon monoxide, and hydrogen have been investigated over a ZrO2support and a Pt/ZrO2catalyst by using a temporal analysis of products reactor system. It was observed that on Pt/ZrO2both methane and carbon dioxide dissociate independently of one another. The dissociation of carbon dioxide acts as an oxygen supplier, while the decomposition products of methane scavenge the oxygen from the catalyst. When an abundance of oxygen is present, pulsing of methane leads to the production of carbon dioxide. It is concluded that both the selectivity with which methane produces carbon monoxide or carbon dioxide and the carbon dioxide conversion is determined by the same reaction: COads+Oads⇔CO2,ads.

The oxidative coupling of methane to ethane and ethene has been investigated by admitting pulses of pure methane, pure oxygen, and mixtures of methane and oxygen to MgO, Li/MgO, and Sn/Li/MgO at temperatures ranging from 923 to 1073 K in a Temporal Analysis of Products (TAP) set-up. Moreover, pulses of oxygen followed by pulses of either methane, ethane, ethene, or carbon monoxide were applied to study the role of both adsorbed oxygen and surface lattice oxygen in the reaction mechanism. Two types of reversibly adsorbed oxygen are present on Sn/Li/MgO. The first type is strongly adsorbed oxygen, which desorbs from the surface on a time scale of 3 min at 973 K. This type of oxygen does not seem to be reactive toward methane. The second type of oxygen consists of weakly adsorbed oxygen species with a time scale of desorption amounting to 4 s at 973 K. The weakly adsorbed oxygen species are involved in the direct conversion of methane to carbon dioxide. Surface lattice oxygen is also interacting with the admitted reductants. The percentage of surface lattice oxygen reactive in the methane conversion is less than 0.1% of a theoretical monolayer on MgO at 1023 K. This value amounts to 27% for Li/MgO and 44% for Sn/Li/MgO at the same temperature. On Li/MgO and Sn/Li/MgO two different types of surface lattice oxygen are present. The first is active in methyl radical formation, while the second is involved in the direct conversion of methane to carbon dioxide. Weakly adsorbed oxygen and the second type of surface lattice oxygen are also involved in the nonselective reaction paths of ethane and ethene as well as in the consecutive oxidation of carbon monoxide. Strongly adsorbed oxygen is not involved in these reactions. The observations are consistent with the Lunsford mechanism [Ito, T., Wang, J.-X., Lin, C.-H., and Lunsford, J. H.,J. Am. Chem. Soc.107, 5062 (1985)] for the generation of methyl radicals over MgO-based catalysts. The increasing activity toward methane due to the addition of lithium and moreover tin to MgO can be explained by an increase in the amount of reactive surface lattice oxygen.

The oxidation of CO by O2was studied for a Pt/γ-Al2O3catalyst and for a commercially available Pt/Rh/CeO2/γ-Al2O3three-way catalyst. Kinetic experiments were carried out in an isothermal fixed-bed microreactor under intrinsic conditions, i.e., in the absence of mass and heat transfer limitations, in the temperature range from 436 to 503 K, with CO and O2inlet partial pressures between 0.12 and 8.3 kPa and H2O and CO2inlet partial pressures between 0 and 10 kPa. For the Pt/γ-Al2O3catalyst, the CO2production rate was found to be essentially proportional to the oxygen and inversely proportional to the carbon monoxide partial pressures, although at large CO and small O2partial pressures deviations occur. A kinetic model, based on elementary reaction steps, was constructed. It was concluded that for the experimental conditions considered, the noble metal surface is almost completely covered with CO, the CO adsorption being in quasi-equilibrium, and that irreversible molecular adsorption of oxygen is the rate-determining step, followed by potentially instantaneous dissociation. The presence of steam was found to enhance the reaction rate. For the experiments carried out over Pt/Rh/CeO2/γ-Al2O3in the presence 10 kPa H2O and 10 kPa CO2, it was found that the CO2production rate becomes zero order in CO at high CO partial pressures. The partial reaction order in O2is approximately 0.5. The experimental observations were explained by the existence of a second bifunctional reaction path next to the reaction path catalyzed by the noble metal only. The bifunctional reaction path involves a reaction between CO adsorbed on the noble metal and oxygen from ceria at the noble metal/ceria interface. The experiments could be described adequately over the investigated range of conditions by a kinetic model incorporating the mono- and bifunctional reaction paths. For the quantification and understanding of the changes in the partial reaction orders in CO and O2as a function of the experimental conditions, a kinetic model based on elementary reaction steps is necessary.

The assumption of irreversible adsorption of a reactant can lead to a structurally unstable kinetic model. The structural instability is caused by the fact that two steadystate solutions intersect in the bifurcation diagram o j for example, the degree of surface coverage of one of the adsorbates us. the partial pressure of one of the reactants. One of the two solutions is a trivial solution, corresponding to a catalyst surface completely covered with the irreversibly adsorbing reactant. The intersection point is a transcritical bifurcation point. A structurally stable kinetic model is obtained i f an arbitrarily small desorption rate coefficient is introduced. Two examples are discussed in which a transcritical bifurcation point is encountered, that is, the total oxidation of ethene in three‐way catalysis and the chemical vapor deposition of refractory metals. The consequences of the existence of a transcritical bifurcation point for kinetic parameter estimation and reactor simulation are emphasized.

Transient kinetic experiments allow to assess quantitatively the rate coefficients of individual elementary steps. Experiments were performed in the temperature range 300–400 K with temporal analysis of products (TAP) for CO oxidation over polycrystalline platinum, initially fully precovered with O adatoms, at varying degrees of CO and O coverage. Experimental evidence for the existence of islands was found. The results were described with an island model, that accounts for CO chemisorption from a precursor state, followed by either CO incorporation into CO islands or by a surface reaction with O adatoms from adjacent O islands. CO chemisorption was not activated and its rate coefficient was estimated as 40 s−1, while the surface reaction was relatively fast. Indications for the size of the CO and O islands were found.

Pt/CoOx/SiO2catalysts consisting of 5 wt% Pt and 3 wt% Co3O4are highly active for CO oxidation below 100°C. In the present study the technique of temporal analysis of products was used to obtain information on the mechanism of the high activity. The behaviour of a 3 wt% CoOx/SiO2and a 5 wt% Pt/SiO2catalyst was compared with that of a Pt/CoOx/SiO2catalyst. Several models proposed to explain the high activity of the Pt/CoOx/SiO2catalyst are discussed.