A safety estimand for late phase clinical trials where the analysis period varies over the subjects.

BACKGROUND/AIMS: Evaluating safety is as important as evaluating efficacy in a clinical trial, yet the tradition for safety analysis is rudimentary. This article explores more complex methodologies for safety evaluation, with the aim of improving the interpretability, as well as generalizability, of the results. METHODS: For studies where the analysis periods vary over the subjects, using the International Council for Harmonisation estimand framework, we construct a formal estimand that could be used in the setting of safety surveillance that answers the clinical question of 'What is the magnitude of the increase in risk of experiencing an adverse event if the treatment is taken, as prescribed, for a specific period of time?'. Estimation methodologies for this estimand are also discussed. RESULTS: The proposed estimand is similar to that found in the efficacy analyses of time to event data (e.g. in outcome studies), with the key difference of utilization of hypothetical intercurrent event strategy for the intercurrent event of treatment discontinuation. This is motivated by what we perceive to be a key difference for the safety objective compared to efficacy objectives, namely a desire for sensitivity (i.e. greater possibility of detecting a negative impact of the drug, if such exists) as opposed to the need to prove a positive effect of the drug in a conservative manner. CONCLUSION: It is valuable, and possible, to use the International Council for Harmonisation estimand framework not only for efficacy but also for safety evaluation, with the estimand driven by an interpretable, and relevant, clinical question.

Occurrence of Batrachochytrium dendrobatidis in Sweden: higher infection prevalence in southern species.

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused worldwide declines in amphibian populations. While Bd is widespread in southern and central Europe, its occurrence and distribution in northernmost Europe is mostly unknown. We surveyed for Bd in breeding anurans in Sweden by sampling 1917 amphibians from 101 localities and 3 regions in Sweden (southern, northern and central). We found that Bd was widespread in southern and central Sweden, occurring in all 9 investigated species and in 45.5% of the 101 localities with an overall prevalence of 13.8%. No infected individuals were found in the 4 northern sites sampled. The records from central Sweden represent the northernmost records of Bd in Europe. While the proportion of sites positive for Bd was similar between the southern and central regions, prevalence was much higher in the southern region. This was because southern species with a distribution mainly restricted to southernmost Sweden had a higher prevalence than widespread generalist species. The nationally red-listed green toad Bufotes variabilis and the fire-bellied toad Bombina bombina had the highest prevalence (61.4 and 48.9%, respectively). Across species, Bd prevalence was strongly positively, correlated with water temperature at the start of egg laying. However, no individuals showing visual signs of chytridiomycosis were found in the field. These results indicate that Bd is widespread and common in southern and central Sweden with southern species, breeding in higher temperatures and with longer breeding periods, having higher prevalence. However, the impact of Bd on amphibian populations in northernmost Europe remains unknown.

Eroded swimmeret syndrome in female crayfish Pacifastacus leniusculus associated with Aphanomyces astaci and Fusarium spp. infections.

We describe a novel syndrome in crayfish, eroded swimmeret syndrome (ESS), affecting wild female signal crayfish Pacifastacus leniusculus. ESS causes partial or total swimmeret erosion. We observed ESS only in female signal crayfish larger than 40 mm carapace length, i.e. sexually mature and probably having carried eggs at least once. The eroded swimmerets were melanised, indicating a crayfish immune system response. We isolated Fusarium tricinctum species complex (SC), F. sambucinum SC, Saprolegnia parasitica and S. australis from the melanised tissue of the eroded swimmerets. ESS includes chronic Aphanomyces astaci infection and a secondary infection by Fusarium sp. In Sweden, we found female signal crayfish with ESS in 6 out of 11 populations with a prevalence below 1% in lakes with commercially productive signal crayfish populations and higher than 29% in lakes with documented signal crayfish population crashes. In Finland, the ESS prevalence was from 3.4 to 6.2% in a commercially productive population. None of the sampled male signal crayfish showed signs of ESS. A caging experiment indicated that females with at least 1 lost swimmeret carried on average 25% fewer fertilized eggs compared to females with intact swimmerets. ESS could significantly reduce individual female fecundity and thus could also affect fecundity at the population level. The decline in reproductive success due to ESS could be among the factors contributing to fluctuations in wild signal crayfish populations.

Estimand Framework and Statistical Considerations for Integrated Analysis of Clinical Trial Safety Data.

BACKGROUND: Safety analyses play a pivotal role in drug development, ensuring the protection of patients while advancing innovative pharmaceuticals to market. A single study generally does not have sufficient sample size to evaluate all important safety events with reasonable precision and may not cover the full target population for the investigational treatment. Integrated analyses (pooled or meta-analysis) over several studies may be helpful in that regard. But without a structured conscious workflow accompanied with appropriate statistical methods for the integrated analysis, this can easily take a route compromising the interpretation. METHODS: In this article we apply the ICH estimand framework to clinical trial integration and summarize respective critical statistical assumptions to ensure the integrated analyses are interpretable. RESULTS: The estimand framework is valuable for developing principles for a deeper understanding of the critical statistical aspects of planning an integrated safety analysis. Our principles address the clinical question of interest, estimand and estimation. Special focus was given to the criteria for inclusion and exclusion of the component studies in the integrated analysis, and to integration of estimates pertaining to signal detection. CONCLUSION: Performing an integrated analysis and its preparatory steps calls for a good understanding of the clinical question of interest and its estimand, care and sound practice, to enable interpretation and avoid introducing unnecessary bias. It is valuable to use the estimand framework not only for efficacy evaluations, but also for safety evaluations in clinical trials and for integrated safety analyses.

Southern introgression increases adaptive immune gene variability in northern range margin populations of Fire-bellied toad.

Northern range margin populations of the European fire-bellied toad (Bombina bombina) have rapidly declined during recent decades. Extensive agricultural land use has fragmented the landscape, leading to habitat disruption and loss, as well as eutrophication of ponds. In Northern Germany (Schleswig-Holstein) and Southern Sweden (Skåne), this population decline resulted in decreased gene flow from surrounding populations, low genetic diversity, and a putative reduction in adaptive potential, leaving populations vulnerable to future environmental and climatic changes. Previous studies using mitochondrial control region and nuclear transcriptome-wide SNP data detected introgressive hybridization in multiple northern B. bombina populations after unreported release of toads from Austria. Here, we determine the impact of this introgression by comparing the body conditions (proxy for fitness) of introgressed and nonintrogressed populations and the genetic consequences in two candidate genes for putative local adaptation (the MHC II gene as part of the adaptive immune system and the stress response gene HSP70 kDa). We detected regional differences in body condition and observed significantly elevated levels of within individual MHC allele counts in introgressed Swedish populations, associated with a tendency toward higher body weight, relative to regional nonintrogressed populations. These differences were not observed among introgressed and nonintrogressed German populations. Genetic diversity in both MHC and HSP was generally lower in northern than Austrian populations. Our study sheds light on the potential benefits of translocations of more distantly related conspecifics as a means to increase adaptive genetic variability and fitness of genetically depauperate range margin populations without distortion of local adaptation.

Thiopurine therapy is associated with postoperative intra-abdominal septic complications in abdominal surgery for Crohn's disease.

PURPOSE: Thiopurines are important as maintenance therapy in Crohn's disease, but there have been concerns whether thiopurines increase the risk for anastomotic complications. The present study was performed to assess whether thiopurines alone, or together with other possible risk factors, are associated with postoperative intra-abdominal septic complications after abdominal surgery for Crohn's disease. METHODS: Prospectively registered data regarding perioperative factors were collected at a single tertiary referral center from 1989 to 2002. Data from 343 consecutive abdominal operations on patients with Crohn's disease were entered into a multivariate analysis to evaluate risk factors for intra-abdominal septic complications. All operations involved either anastomoses, strictureplasties, or both; no operations, however, involved proximal diversion. RESULTS: Intra-abdominal septic complications occurred in 26 of 343 operations (8%). Thiopurine therapy was associated with an increased risk of intra-abdominal septic complications (16% with therapy; 6% without therapy; P = 0.044). Together with established risk factors such as preoperative intra-abdominal sepsis (18% with sepsis; 6% without sepsis; P = 0.024) and colo-colonic anastomosis (16% with such anastomosis; 6% with other types of anastomosis; P = 0.031), thiopurine therapy was associated with intra-abdominal septic complications in 24% if any 2 or all 3 risk factors were present compared with 13% if any 1 factor was present, and only 4% in patients if none of these factors were present (P < 0.0001). CONCLUSIONS: Thiopurine therapy is associated with postoperative intra-abdominal septic complications. The risk for intra-abdominal septic complications was related to the number of identified risk factors. This increased risk should be taken into consideration when planning surgery for Crohn's disease.

Canadian Association of University Surgeons annual symposium: Continuity of care: Toronto, Ontario, Sep. 6, 2007.

This 2007 symposium of the Canadian Association of University Surgeons brought together surgeons from a number of jurisdictions to discuss the challenges and opportunities that reduced physician work hours will bring to the care of the surgical patient. Dr. Brian Taylor, president of the association, underscored the need to find a balance between the benefits of diminished workloads/work hours and the loss of continuity of care. He opined that Canada needs to learn from our European colleagues' experience. Dr. Per-Olof Nyström, professor of surgery, presented the modern Swedish model of surgical care, which had to be developed as a consequence of the European Union's legal restrictions on the amount of time an individual surgeon may work. Sweden employs a team-based shared-care model driven by the individual surgeon's expertise rather than the "village factory" model of the multiskilled, multitasking approach of surgical care more prevalent in Canada. Dr. Chris de Gara, secretary treasurer of the association, presented the evidence base for (and against) work-hour restrictions and how well-designed systems can ensure effective continuity of care. Dr. Stewart Hamilton illustrated how one such system for the delivery of the emergency general surgical services has evolved at the University of Alberta Hospital, which demonstrated its effectiveness in providing quality surgical continuity of care. Dr. Debrah Wirtzfeld underscored the importance of trainee lifestyle and how modern Web-based technologies can ensure reduced errors with the implementation of a "sign-out" system.

Perioperative prophylaxis with granulocyte colony-stimulating factor (G-CSF) in high-risk colorectal cancer patients for an improved recovery: A randomized, controlled trial.

BACKGROUND: We aimed to improve the postoperative outcome of high-risk patients (American Society of Anesthesiologists class 3 and 4) recovering from colorectal cancer surgery by using recombinant human G-CSF (filgrastim) as perioperative prophylaxis. METHODS: In a double-blinded, placebo-controlled trial, 80 patients undergoing left-sided colorectal resection were randomized to filgrastim or placebo. Filgrastim (5 mug/kg) or placebo was administered in the afternoon on day -1, 0, and +1 relative to the operation. Primary endpoints were in a hierarchic order: quality of life (QoL) over time (determined at discharge, 2 and 6 months after operation with the European Organization for Research and Treatment of Cancer questionnaire) and the McPeek recovery score, which measures death and duration of stays in the intensive care unit and hospital. Predefined secondary endpoints were global QoL, subdomains of QoL, postoperative recovery, duration of stay, 6-month overall survival, complication rates, and cellular and immunologic parameters. RESULTS: There were no significant differences in both primary endpoints between the treatment groups. A significant improvement (P < .05) was obtained by filgrastim prophylaxis in the QoL subdomain family life /- social functioning,; thus, more patients recovered to their preoperative state (14 vs 4 with placebo) as determined by structured interviews. Duration of hospital stay (14 vs 12 days) and noninfectious complications were decreased from 8% to 3%. CONCLUSIONS: High-risk patients undergoing major operation for colorectal cancer profited from filgrastim prophylaxis with regard to duration of hospital stay, noninfectious complications, social QoL, and subjective recovery from operation. These endpoints, however, were secondary, and the primary endpoints (overall QoL and the McPeek index) did not show comparable benefits. A new confirmatory trial with the successful endpoints of this trial, as well as a cost analysis, will be needed to confirm the results before a general recommendation for the prophylactic use of G-CSF in high-risk cancer patients can be given.

Persistent organic pollutants (POP) in a benthic omnivore--a comparison between lake and stream crayfish populations.

We investigated the accumulation of PCB and DDT in crayfish populations in 10 streams in southern Sweden. The results were compared with an earlier study on crayfish in lakes from the same area. We found that the concentration of pollutants in crayfish did not differ between the two types of systems. Variation in body burden was higher in stream living crayfish probably because of the higher influence from pollutants deposited in the catchment area and the more dynamic transport in streams. In streams, p,p'-DDE concentrations were positively correlated to trophic status (total phosphorous) while PCB did not show any correlation with the nutrient regime. Further, mean SigmaPCB and p,p'-DDE concentrations in crayfish did not correlate in streams. We suggest that the sources of the two pollutants differ for stream living crayfish. The results indicate that crayfish in streams are affected to a higher degree to pollutants in the catchment area and the precipitation regime. In lakes, internal processes govern uptake of pollutants in crayfish.

Antithrombotic effects of ximelagatran plus acetylsalicylic acid (ASA) and clopidogrel plus ASA in a human ex vivo arterial thrombosis model.

It was the objective of this study to compare the antithrombotic effects and bleeding profiles of the oral direct thrombin inhibitor ximelagatran, an anticoagulant, and the antiplatelet agent clopidogrel on top of steady-state acetylsalicylic acid (ASA) in a human arterial thrombosis model. Healthy male volunteers (n=62) received ASA (160 mg once daily), plus either clopidogrel for 6 days (loading dose 300 mg, then 75 mg once daily), or a single dose of ximelagatran (36 or 72 mg) on Day 6. Changes in total thrombus area (TTA) under low shear rate (LSR; 212 s(-1)) and high shear rate (HSR; 1690 s(-1)) conditions were measured, using the ex vivo Badimon perfusion chamber model pre-dose and 2 and 5 hours after dosing on Day 6, and capillary bleeding times (CBT) were determined. Ximelagatran plus ASA significantly reduced TTA under LSR and HSR, compared with ASA alone. Ximelagatran plus ASA reduced TTA more than clopidogrel plus ASA under LSR after 2 hours (36 mg, P=0.0011; 72 mg, P<0.0001) and 5 hours (72 mg, P=0.0057), and under HSR after 2 and 5 hours (72 mg, P<0.05). Compared with ASA alone, CBT was markedly prolonged by clopidogrel plus ASA (ratio 6.4; P<0.0001) but only slightly by ximelagatran plus ASA (72 mg ximelagatran, ratio 1.4; P=0.0010). Both drug combinations were well tolerated. Oral ximelagatran plus ASA has a greater antithrombotic effect in this human ex vivo thrombosis model and a less pronounced prolongation of bleeding time than clopidogrel plus ASA.

Pharmacokinetics and pharmacodynamics of the oral direct thrombin inhibitor ximelagatran in young healthy Japanese men.

BACKGROUND AND OBJECTIVE: The direct thrombin inhibitor ximelagatran, which is rapidly bioconverted to its active form melagatran after oral administration, is being developed for the prevention and treatment of thromboembolism. This study assessed the effects of food and repeated dosing on the pharmacokinetics and pharmacodynamics of melagatran after oral administration of ximelagatran to young healthy Japanese males. METHODS: In part one of the two-part study, volunteers (n = 24) were randomised to receive in a crossover fashion a single oral dose of ximelagatran 48mg with or without breakfast on 2 days separated by a 2- to 7-day washout period. In the second part of the study, all volunteers received oral doses of ximelagatran 48mg every 12 hours for 5 days followed by a single dose on the morning of day 6. RESULTS: The area under the plasma concentration-time curve (AUC), peak plasma concentration (C(max)) and urinary excretion of melagatran did not differ as a function of whether ximelagatran was taken with or without food. The relationship between the melagatran plasma concentration and activated partial thromboplastin time (aPTT, which reflects the thrombin inhibitory effect of melagatran) was also independent of concomitant food intake. During repeated dosing, steady-state plasma concentrations of melagatran were achieved after the second dose of ximelagatran on day 1 and remained stable through the rest of the dosing period. The melagatran AUC and C(max) increased slightly (by 18% and 22%, respectively) on day 6 compared with day 1. The interindividual variability in the melagatran AUC and C(max) remained low, as reflected by coefficients of variation of <20% on both day 1 and day 6. The amount of melagatran excreted in urine remained stable over the 6 days of repeated dosing. CONCLUSION: The pharmacokinetics, pharmacodynamics, safety and tolerability of melagatran after oral administration of ximelagatran were not affected by food or repeated dosing in healthy Japanese volunteers.

Comparable pharmacokinetics and pharmacodynamics of melagatran in Japanese and caucasian volunteers after oral administration of the direct thrombin inhibitor ximelagatran.

OBJECTIVES: Two studies were conducted to elucidate the pharmacokinetics and pharmacodynamics of melagatran after administration of the oral direct thrombin inhibitor ximelagatran to Caucasian and Japanese volunteers. METHODS: In study 1, with a single-blind, parallel-group design, young Japanese and Caucasian male volunteers were randomised to receive four single escalating oral doses of ximelagatran (12, 24, 36 and 60mg on separate days; n = 27 per ethnic group) or placebo (n = 6 per ethnic group). In study 2, with an open-label design, elderly Japanese male volunteers (n = 12) received three single escalating oral doses of ximelagatran (12, 24 and 36mg on separate days). RESULTS: Regardless of the ethnicity or age of the volunteers, ximelagatran given in single oral doses was rapidly absorbed and bioconverted to melagatran, and the melagatran area under the plasma concentration-time curve (AUC) and peak plasma concentration (C(max)) increased in proportion with the ximelagatran dose, with only small deviations from absolute linearity. Higher melagatran AUC and C(max) were observed in young Japanese volunteers compared with young Caucasian volunteers, and in elderly Japanese volunteers compared with young Japanese volunteers. These results appear to be attributed to weight- and age-related decreases in renal elimination of melagatran rather than to absorption of ximelagatran and formation of melagatran. The pattern of metabolites in plasma and urine was comparable between young Japanese and Caucasian volunteers, and between young and elderly Japanese volunteers. The melagatran plasma concentration-activated partial thromboplastin time (aPTT, an ex vivo coagulation time measurement used to demonstrate inhibition of thrombin) relationship did not differ significantly between young Japanese and Caucasian volunteers or between young and elderly Japanese volunteers. CONCLUSIONS: Ethnicity does not affect the absorption of ximelagatran or the formation of melagatran or the melagatran plasma concentration-aPTT relationship. The elimination of melagatran is correlated with renal function.

Low levels of persistent organic pollutants (POPs) in New Zealand eels reflect isolation from atmospheric sources.

Polychlorinated biphenyls (PCBs) and organic pesticides (i.e., DDTs) were measured in long finned eels (Anguilla dieffenbachii) in 17 streams on the west coast of South Island, New Zealand. Very low levels of PCBs and low levels of ppDDE were found. The concentrations of PCBs and ppDDE were not correlated within sites indicating that different processes determined the levels of the two pollutants in New Zealand eels. The PCBs probably originate from atmospheric transport, ppDDE levels are determined by land use and are higher in agriculture areas. The low contamination level of these aquatic systems seems to be a function of a low input from both long and short-range transport as well as few local point sources. No correlation could be found between lipid content and persistent organic pollutants (POPs) concentration (as shown in previous studies) in the eels which could be explained by low and irregular intake of the pollutants.

Oral ximelagatran for secondary prophylaxis after myocardial infarction: the ESTEEM randomised controlled trial.

BACKGROUND: Despite important advances in treatment, the risk of recurrent ischaemic events is high both early and late after an acute coronary syndrome. We aimed to assess the effectiveness of ximelagatran and acetylsalicylic acid for prevention of death, non-fatal myocardial infarction, and severe recurrent ischaemia after a recent myocardial infarction. METHODS: In this placebo-controlled, double-blind, multicentre, multinational dose-guiding study we assessed 1883 patients who had had recent ST-elevation or non-ST-elevation myocardial infarction. Within 14 days after the index event we randomised the participants in the proportions 1/1/1/1/2 to oral ximelagatran at doses of 24 mg, 36 mg, 48 mg, or 60 mg twice daily, or placebo, respectively for 6 months. All patients received acetylsalicylic acid 160 mg once daily. The primary efficacy outcome was the dose response of ximelagatran by comparison with placebo for the occurrence of all-cause death, non-fatal myocardial infarction, and severe recurrent ischaemia. Analysis was by intention to treat. FINDINGS: Oral ximelagatran significantly reduced the risk for the primary endpoint compared with placebo from 16.3% (102 of 638) to 12.7% (154 of 1245) (hazard ratio 0.76, 95% CI 0.59-0.98, p=0.036) for the combined ximelagatran groups versus placebo. There was no indication of a dose response between the ximelagatran groups. Major bleeding events were rare, 1.8% (23 of 1245) and 0.9% (six of 638) (hazard ratio 1.97, 95% CI 0.80-4.84) in the combined ximelagatran and placebo groups, respectively. We recorded no serious clinically adverse outcomes judged related to the investigational drug. INTERPRETATION: Oral direct thrombin inhibition with ximelagatran and acetylsalicylic acid is more effective than acetylsalicylic acid alone in preventing major cardiovascular events during 6 months of treatment in patients who have had a recent myocardial infarction.

Ximelagatran vs low-molecular-weight heparin and warfarin for the treatment of deep vein thrombosis: a randomized trial.

CONTEXT: Ximelagatran, an oral direct thrombin inhibitor with a rapid onset of action and predictable antithrombotic effect, has the potential to be a simple therapeutic alternative to current standard treatment of acute venous thromboembolism. OBJECTIVE: To compare the efficacy and safety of ximelagatran with standard enoxaparin/warfarin treatment for the prevention of recurrent venous thromboembolism. DESIGN, SETTING, AND PATIENTS: Randomized, double-blind, noninferiority trial (Thrombin Inhibitor in Venous Thromboembolism [THRIVE] Treatment Study) of 2489 patients with acute deep vein thrombosis, of whom approximately one third had concomitant pulmonary embolism. The study was conducted at 279 centers in 28 countries from September 2000 through December 2002. INTERVENTIONS: Patients were randomized to receive 6 months of treatment with either oral ximelagatran, 36 mg twice daily, or subcutaneous enoxaparin, 1 mg/kg twice daily, for 5 to 20 days followed by warfarin adjusted to maintain an international normalized ratio of 2.0 to 3.0. MAIN OUTCOME MEASURES: Recurrent venous thromboembolism, bleeding, and mortality. RESULTS: Venous thromboembolism recurred in 26 of the 1240 patients assigned to receive ximelagatran (estimated cumulative risk, 2.1%) and in 24 of the 1249 patients assigned to receive enoxaparin/warfarin (2.0%). The absolute difference between ximelagatran and enoxaparin/warfarin was 0.2% (95% confidence interval [CI], -1.0% to 1.3%). This met the prespecified criterion for noninferiority. Corresponding values for major bleeding were 1.3% and 2.2% (difference, -1.0%; 95% CI, -2.1% to 0.1%), and for mortality were 2.3% and 3.4% (difference, -1.1%; 95% CI, -2.4% to 0.2%). Alanine aminotransferase levels increased to more than 3 times the upper limit of normal in 119 patients (9.6%) and 25 patients (2.0%) receiving ximelagatran and enoxaparin/warfarin, respectively. Increased enzyme levels were mainly asymptomatic. Retrospective analysis of locally reported adverse events showed a higher rate of serious coronary events with ximelagatran (10/1240 patients) compared with enoxaparin/warfarin (1/1249 patients). CONCLUSIONS: Oral ximelagatran administered in a fixed dose without coagulation monitoring, was as effective as enoxaparin/warfarin for treatment of deep vein thrombosis with or without pulmonary embolism and showed similar, low rates of bleeding. Increased levels of liver enzymes in 9.6% of ximelagatran-treated patients require regular monitoring; the mechanism requires further evaluation. Prospective assessment of coronary events in future studies is warranted.

[Difficult to measure results and quality of surgical interventions but length of stay is an important variable]. / Svårt mäta resultat och kvalitet i kirurgi men vårdtiden är en viktig variabel.

No generally accepted measures exist to describe the quality of surgical care. Measures derived from surgical care processes are relatively easy to improve but are often too local to allow comparison with other surgical departments. The final outcome of an operation is often difficult to record objectively or can only be determined after observation. Improving items of the process is often insufficient to markedly improve outcome because process and outcome are logarithmically related. Therefore, a department's surgical balance sheet remains stable over several years. The introduction of new techniques or new concepts of treatment with sufficient potential for change can improve that balance sheet if effectively implemented. Quality of care implies a rating of the outcome relative to a standard or in comparison with the achievement of other surgical departments. It is argued that postoperative hospital stay is an objective, verifiable, and uniformly recorded outcome measure that reflects the combined achievement of the surgical, organisational, and social processes for each patient. Laparoscopic cholecystectomy, a new technique, tension-free inguinal hernia repair, and fast-track surgery, a new concept, all had the potential to shorten the hospital stay. The mode of change seems to be diminished surgical and anaesthetic trauma and therefore fewer complications. The ultimate quality achievement is to be able to operate without causing physiological derangement of the patient, which should eventually allow day-surgery for most elective procedures.

The influence of productivity and width of littoral zone on the trophic position of a large-bodied omnivore.

Omnivory is common in many food webs. Omnivores in different habitats can potentially change their feeding behaviour and alter their trophic position and role according to habitat conditions. Here we examine the trophic level and diet of the omnivorous signal crayfish (Pacifastacus leniusculus) in gradients of trophic status and lake size, both of which have been previously suggested to affect trophic position of predators separately or combined as productive space. We found the trophic position of omnivorous crayfish to be positively correlated with lake trophic status, but found no evidence for any influence of lake size or productive space on crayfish trophic position. The higher trophic position of crayfish in eutrophic lakes was largely caused by a shift in crayfish diet and not by an increase in trophic links in basal parts of the food web. Hence, our results support the "productivity hypothesis," suggesting that food chains can be longer in more productive systems. Furthermore, stable isotope data indicated that larger crayfish are more predatory than smaller crayfish in lakes with wider littoral zones. Wider littoral zones promoted the development of intrapopulation differences in trophic position whereas narrow littoral zones did not. Hence, differences in habitat quality between and within lakes seem to influence the trophic positions of omnivorous crayfish.