Key PointsPatients on hemodialysis do not sleep enough, and there is large variation in the sleep duration among them.Dialysis timing plays a major role in sleep duration; morning shift is associated with decreased sleep duration on the day of dialysis.Patients on hemodialysis sleep the longest on Sundays compared with other days of the week and irrespective of the dialysis schedule.BackgroundIn patients on hemodialysis, the effects of determinants of sleep duration are not widely studied. Using wearable activity trackers, we aimed to characterize natural and hemodialysis-imposed temporal patterns of nocturnal sleep.MethodsIn this yearlong prospective observational study, patients on in-center hemodialysis were equipped with activity trackers (Fitbit Charge 2). Nocturnal sleep duration was assessed according to dialysis start time (early starters: before 8 AM; late starters: others), dialysis versus interdialytic days (postdialysis day and second interdialytic day), weekdays, and seasons. Clinical, laboratory, and hemodialysis treatment data were extracted from electronic medical records. Linear mixed-effects models were constructed to determine the effect of various time patterns and predictors of nocturnal sleep duration.ResultsOne hundred nine patients contributed data (age 54 +/- 12 years, 73% male, 23% diabetic). Sleep duration was 276 +/- 91 minutes; 102 (94%) patients slept on average less than the recommended 420 minutes per night. On dialysis days, participants slept 55 (95% confidence interval [CI], 51 to 59) and 48 (95% CI, 43 to 54) minutes less compared with postdialysis and second interdialytic days, respectively. Early starters slept on average 40 (95% CI, 6 to 74) minutes less compared with late starters. On dialysis days, early starters slept 86 (95% CI, 55 to 118) minutes less compared with late starters. We observed greater sleep-wake disturbance in early starters. Irrespective of dialysis schedule, patients slept on average 26 (95% CI, 19 to 33) to 32 (95% CI, 24 to 40) minutes longer on Sundays. In winter, sleep was 7 (95% CI, 1 to 13) to 10 (95% CI, 5 to 16) minutes shorter. In multivariate analysis, higher BP and higher serum creatinine were significantly associated with shorter sleep duration.ConclusionsOn average, patients on hemodialysis slept less than the recommended amount of time. The timing of hemodialysis treatment has pronounced effects on sleep duration and could be considered in patient care.PodcastThis article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/K360/2025_05_29_KID0000000761.mp3

Use of Home Dialysis (referring to both peritoneal and home haemodialysis throughout this study), is under-exploited and highly variable across Europe, and this is the case both within as well as between countries. Several, predominantly modifiable barriers have been described that explain this inequity of access, but as yet no recommendations have been agreed upon as to how to address the problem. A multi-disciplinary multi-organisational policy forum representing the key stakeholders was held at the EuroPD meeting in Bruges, November 2023 with the purpose of defining solutions and actions that the wider nephrology community should take to reduce disparities in access to home-based therapies. Three key themes were identified by a steering group prior to the forum: Dialysis Provider Motivation, Patient Empowerment and Training and Workforce Issues. Breakout discussion groups for each theme were asked to prioritise up to three actions per theme. These were further refined by the steering group and developed into proposed actions to be taken forward by the kidney failure community. 112 registrants attended the forum representing patients (5%), doctors, (57%) nurses, (13%) industry (7%) and various other roles (18%). The following actions were proposed: (1) a granular European audit of financial disincentives affecting decisions of policy makers, providers, patients and industry; (2) engaging national professional societies to challenge complacency towards uptake of home-based therapies; (3) stimulate networking to support small, inexperienced centres; (4) extending access to assisted peritoneal dialysis; (5) greater involvement of patients (locally and nationally) at every step, especially for advocacy; (6) empowering patients with transparent information; (7) mandating inclusion of training and exposure to Home Dialysis in national curricula; (8) promotion of career sub-specialists (doctors and nurses) with specific qualification in Home Dialysis; (9) promoting access to high quality training resources. The kidney failure community can undertake a number of constructive actions to improve equity of access to Home Dialysis. The Policy Forum steering group who are representative of the key stakeholders have committed to taking this programme forward.

Background:Hemodialysis patients are often sedentary, and their life is structured around the dialysis schedule. Wearable activity trackers present an opportunity for long-term continuous monitoring of physical activity. We aimed to characterize dialysis-imposed, weekly and seasonal patterns of physical activity in hemodialysis patients. Methods:In this prospective observational study, patients on in-center hemodialysis in New York City wore the Fitbit® Charge 2™ for 1 year. Physical activity was assessed by weekday, dialysis versus interdialytic days (post-hemodialysis day and second interdialytic day), dialysis start time and season. Linear mixed-effects models with random intercepts between patient were constructed to determine the effect of time-patterns and determinants of physical activity levels. Results:A total of 109 patients on hemodialysis were included (mean age 54 ± 11.6 years, 72% male, 23% diabetic). The observed number of steps was 6590 ± 4014 (mean ± standard deviation) per day; 44 (40%) participants walked <5000 steps/day. Participants walked 912 (95% confidence interval 768, 1057) fewer steps on Sundays and 284 (129, 440) fewer on the second interdialytic day vs dialysis day. Winter activity was reduced by 321 (162, 478) to 455 (312, 598) steps compared with other seasons. Older age, diabetes and higher equilibrated Kt/V were associated with lower physical activity levels; higher albumin was associated with increased physical activity levels. Conclusion:Most hemodialysis patients walked less than recommended level of 10 000 steps/day and physical activity levels vary greatly between and within patients. Dialysis-imposed, weekly and seasonal patterns affect physical activity. Lower physical activity levels on second interdialytic days and Sundays could provide opportunities for improvements of physical activity in shared the decision-making process.

INTRODUCTION:Prevention of hemodynamic complications during hemodialysis remains challenging. Although whole body bioimpedance is well established in fluid status assessment, its use for dynamic or continuous recordings is limited. A segmental approach may serve this purpose better. This study investigates which body segment is best targeted to measure bioimpedance for hemodynamic monitoring. METHODS:In this observational study, serial bioimpedance measurements were conducted on the whole body, lower leg, upper arm, and thorax of 15 patients during two hemodialysis sessions. The resistance component of bioimpedance was used to investigate the relationship with changes in volume and systolic blood pressure (SBP). FINDINGS:Predialysis to postdialysis changes in relative resistance between the two sessions revealed the lowest intraclass correlation coefficient for upper arm (0.023) and the highest for thoracic resistance (0.728). Correlation between ultrafiltration volume and relative resistance was comparable between upper arm and thoracic segment (0.538 [0.447-0.618] and 0.537 [0.446-0.617], both p < 0.001, respectively) and the highest for whole-body and lower leg (0.697 [0.63-0.754] and 0.670 [0.598-0.731], both p < 0.001, respectively). In contrast, the correlation between changes in SBP and relative resistance was the highest in the thoracic segment (-0.33 [-0.432 to -0.219], p < 0.001) and the lowest for whole body measurements (-0.154 [-0.269 to -0.036], p = 0.01). In addition, multiple regression analysis indicated thoracic resistance as the best predictor for changes in SBP (β = -0.261 [-0.353 to -0.126], p < 0.001). DISCUSSION:These findings suggest that the thorax is the most suitable region for segmental bioimpedance measurements to assess hemodynamic parameters. Thoracic bioimpedance may innovate the hemodynamic monitoring of hemodialysis patients.

Repeated single-point measurements of thoracic bioimpedance at a single (low) frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multi-frequency measurements may add in-depth information on the distribution between intra- and extracellular fluid. This study aimed to investigate the feasibility of semi-continuous multi-frequency thoracic bioimpedance measurements by a wearable device in hemodialysis patients. Therefore, thoracic bioimpedance was recorded semi-continuously (i.e., every ten minutes) at nine frequencies (8–160 kHz) in 68 patients during two consecutive hemodialysis sessions, complemented by a single-point measurement at home in-between both sessions. On average, the resistance signals increased during both hemodialysis sessions and decreased during the interdialytic interval. The increase during dialysis was larger at 8 kHz (∆ 32.6 Ω during session 1 and ∆ 10 Ω during session 2), compared to 160 kHz (∆ 29.5 Ω during session 1 and ∆ 5.1 Ω during session 2). Whereas the resistance at 8 kHz showed a linear time pattern, the evolution of the resistance at 160 kHz was significantly different (p < 0.0001). Measuring bioimpedance semi-continuously and with a multi-frequency current is a major step forward in the understanding of fluid dynamics in hemodialysis patients. This study paves the road towards remote fluid monitoring.

While physical activity (PA) is understood to promote vascular health, little is known about whether the daily and weekly patterns of PA accumulation associate with vascular health. Accelerometer-derived (activPAL3) 6- or 7-day stepping was analyzed for 6430 participants in The Maastricht Study (50.4% women; 22.4% Type 2 diabetes mellitus (T2DM)). Multivariable regression models examined associations between stepping metrics (average step count, and time spent slower and faster paced stepping) with arterial stiffness (measured as carotid-femoral pulse wave velocity (cfPWV)), and several indices of microvascular health (heat-induced skin hyperemia, retinal vessel reactivity and diameter), adjusting for confounders and moderators. PA pattern metrics were added to the regression models to identify associations with vascular health beyond that of stepping metrics. Analyses were stratified by T2DM status if an interaction effect was present. Average step count and time spent faster paced stepping was associated with better vascular health, and the association was stronger in those with compared to those without T2DM. In fully adjusted models a higher step count inter-daily stability was associated with a higher (worse) cfPWV in those without T2DM (std beta = 0.04, p = 0.007) and retinal venular diameter in the whole cohort (std beta = 0.07, p = 0.002). A higher within-day variability in faster paced stepping was associated with a lower (worse) heat-induced skin hyperemia in those with T2DM (std beta = -0.31, p = 0.008). Above and beyond PA volume, the daily and weekly patterns in which PA was accumulated were additionally associated with improved macro- and microvascular health, which may have implications for the prevention of vascular disease.

Abstract Background and Aims Hemodialysis patients face a high hemodynamic variability in blood pressure and fluid status, which contributes to their cardiovascular mortality. Currently, intradialytic hemodynamic monitoring has to rely on cuff-based blood pressure measurements. During the interdialytic interval, no monitoring system is applied. An interesting alternative to monitor hemodynamics continuously can be found in the bioimpedance technique, and more specifically in bioimpedance measurements of the thoracic segment. Repeated single-point measurements of thoracic bioimpedance at single (low)-frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multifrequency measurements may add in-depth information on the distribution between intra- and extracellular fluid. This study aims to investigate the feasibility of semi-continuous multifrequency thoracic bioimpedance measurements by a wearable device in hemodialysis patients. Method Thoracic bioimpedance was recorded semi-continuously (i.e. every ten minutes) at nine frequencies (8–160 kHz) in 68 patients during two consecutive hemodialysis sessions, complemented by an interdialytic single-point measurement at home. The wearable bioimpedance device was provided by imec, The Netherlands (Fig. 1). A linear mixed model was built to integrate all measurements at frequencies 8 and 160 kHz, incorporating the different dialysis sessions up until 240 minutes after the start of dialysis as well as the home measurement that was performed. Results On average, the thoracic resistance signals increased during the first hemodialysis session, decreased during the interdialytic interval, and increased again during the second hemodialysis session, at all frequencies. The average intradialytic increase was larger at 8 kHz (∆ 32.6 Ω during session 1 and ∆ 10 Ω during session 2) compared to 160 kHz (∆ 29.5 Ω during session 1 and ∆ 5.1 Ω during session 2). By measuring semi-continuously and at multiple frequencies, a different time pattern became clear within and between frequencies. The resistance at 8 kHz followed a linear time pattern, whereas the evolution of the resistance at 160 kHz showed a significant quadratic trend in the first dialysis session (p < 0.0001). During the first interdialytic interval (from the end of the first dialysis session towards the home measurement), the decrease in resistance was more distinct at 8 kHz (∆ −2.27 Ω) compared to a small increase of 0.84 Ω in 160 kHz. This finding reveals a certain inertia in the higher frequencies, mirroring the changes in intracellular volume. Finally, the statistical model could create individual predicting profiles over time, including as well the intradialytic as the interdialytic interval (Fig. 2). Conclusion In this study, we showed that it is feasible to perform semi-continuous and multifrequency bioimpedance measurements by a wearable device during hemodialysis. Semi-continuous and multifrequency measurements provided a broader, and respectively profounder knowledge on the trend of the bioimpedance signal during fluid changes compared to single-point and single-frequency measurements. Measuring thoracic bioimpedance semi-continuously and with a multifrequency current is a major step forward in the understanding of fluid dynamics in hemodialysis patients, by which the road is paved towards remote fluid monitoring and the prevention of hemodynamic instabilities.

Iron deficiency (ID) and anemia often coexist. Recent findings showed ID associates with mortality in chronic kidney disease (CKD) patients not requiring dialysis, irrespective of hemoglobin and ferritin levels (Guedes, et al JASN 2021). It is unclear whether ID associates with outcome in patients initiating peritoneal dialysis (PD). This study explores the association between transferrin saturation (TSAT) levels at the start of PD and mortality risks.

Interest in the use of sorbents in chronic dialysis treatment has undergone a revival in the last decades, for which two major factors are responsible. The first is the potential of sorbents as adjunct therapy for the removal of substances that are difficult to remove by conventional dialysis therapies. The second is their use in regeneration of dialysate, which is of pivotal importance in the design of portable or even wearable treatments, next to the potential for reducing water use during conventional dialysis treatment. Sorbent-enhanced dialysis with synthetic polymers was associated with a reduction in inflammatory parameters as compared to hemodialysis and even associated with improved survival in smaller studies, although this needs to be confirmed in large randomized trials. Incorporation of sorbents within a dialysis membrane (mixed matrix membrane) appears a promising way forward to reduce the complexity and costs of a dual therapy but needs to be tested in vivo. For regeneration of dialysate, at present, a combination of urease, zirconium-based sorbents, and activated charcoal is used. Next to sodium release by the sorbent in exchange for ammonium and the CO2 release by the hydrolysis of urea has been a bottleneck in the design of wearable devices, although short-term trials have been performed. Still, for widespread and flexible application of sorbent-assisted portable or wearable devices, a direct urea sorbent would be a major asset. In the near future, it will likely become apparent whether sorbent-assisted dialysis techniques are feasible for routine implementation in clinical practice.

The increasing prevalence of chronic kidney disease (CKD) is placing a growing burden on healthcare systems, which results in considerable economic and environmental challenges. Sustainable CKD care and optimization of patient outcomes requires a new approach to the organization of healthcare systems, in which home monitoring will have a pivotal role.

Estimation of muscle mass is a pivotal component in the diagnosis of protein-energy wasting and sarcopenia. While bioimpedance spectroscopy is a widely accepted technique for the assessment of lean tissue related to the diagnosis of sarcopenia, to date skeletal muscle ultrasound (US) has not gained full acceptance for this purpose. The aim of this study was to assess the predictive value for mortality of the indexed thickness of the quadriceps vastus intermedius, as measured by US, compared to lean tissue index as estimated by bioimpedance spectroscopy, both combined with handgrip strength in a group of patients with end-stage kidney disease (ESKD) on maintenance hemodialysis (HD). The cut-off values for low handgrip strength were < 27 kg for males and < 16 kg for females. The cut-off value for low lean tissue index was obtained from an age-matched healthy control group, with low lean tissue index being defined as values below the 10th percentile of the distribution of healthy subjects. The cut-off values for low quadriceps vastus intermedius thickness index were < 3.44 mm/m2 for males and < 3.52 mm/m2 for females. Ultrasound and bioimpedance spectroscopy were performed in 99 patients, and handgrip strength was assessed in 64 patients, all on maintenance HD. After a median follow-up of 28 months (interquartile range 19–41 months) 38 patients died. Lean tissue index was not associated with mortality, while low quadriceps vastus intermedius thickness index and low handgrip strength were associated with an increased hazard of death. In the fully adjusted model, only the combination of low handgrip strength and low quadriceps vastus intermedius thickness index was significantly associated with higher mortality. When combined with low handgrip strength, low quadriceps muscle US outperformed low lean tissue index as assessed by bioimpedance spectroscopy in predicting mortality in a cohort of patients on maintenance HD. Ultrasound may be a useful and convenient technique for the assessment of sarcopenia and protein-energy wasting in this patient population.

BACKGROUND:Cardiac troponin T (cTnT) is key in diagnosing myocardial infarction (MI) but is also elevated in end-stage renal disease (ESRD) patients. Specific larger cTnT proteoforms were identified for the acute phase of MI, while in serum of ESRD patients solely small cTnT fragments were found. However, others allocated this to a pre-analytic effect due to abundant thrombin generation in serum. Therefore, we investigated the effect of various anticoagulation methods on cTnT composition and concentration and compared the cTnT composition of MI and ESRD patients. METHODS:The agreement of cTnT concentrations between simultaneously collected serum, lithium-heparin (LH) plasma, and ethylenediaminetetraacetic acid (EDTA) plasma was studied using the high-sensitivity (hs-)cTnT immunoassay. cTnT proteoform composition was investigated in a standardized time-dependent manner through spike experiments and in simultaneously collected blood matrixes of MI and ESRD patients. RESULTS:Excellent hs-cTnT concentration agreements were observed across all blood matrixes (slopes > 0.98; 95% CI, 0.96-1.04). Time-dependent degradation (40 kDa intact:29 kDa fragment:15 to 18 kDa fragments) was found in LH plasma and EDTA plasma, and serum in ratios (%) of 90:10:0, 0:5:95, and 0:0:100, respectively (48 h after blood collection). Moreover, gel filtration chromatography (GFC) profiles illustrated mainly larger cTnT proteoforms in MI patients, while in ESRD patients mainly 15 to 18 kDa fragments were found for all matrices. CONCLUSIONS:The extent of cTnT degradation in vitro is dependent on the (anti)coagulation method, without impacting hs-cTnT concentrations. Furthermore, mainly larger cTnT proteoforms were present in MI patients, while in ESRD patients mainly small 15 to 18 kDa cTnT fragments were found. These insights are essential when developing a novel hs-cTnT assay targeting larger cTnT proteoforms.

ObjectiveGlucose metabolism status (GMS) is linked to non-alcoholic fatty liver disease (NAFLD). Higher levels of advanced glycation end products (AGEs) are observed in people with type 2 diabetes mellitus (T2DM) and NAFLD. We examined the association between GMS, non-invasive tests and AGEs, with liver steatosis and fibrosis.MethodsData from The Maastricht Study, a population-based cohort, were analysed. Participants with alcohol overconsumption or missing data were excluded. GMS was determined via an oral glucose tolerance test. AGEs, measured by skin autofluorescence (SAF), were assessed using an AGE Reader. Associations of GMS and SAF with the fibrosis-4 score (FIB-4), Forns index (FI) and fatty liver index (FLI) were investigated using multivariable linear regression, adjusted for sociodemographic, lifestyle and clinical variables.Results1955 participants (56.6%) were analysed: 598 (30.6%) had T2DM, 264 (13.5%) had pre-diabetes and 1069 (54.7%) had normal glucose metabolism. Pre-diabetes was significantly associated with FLI (standardised regression coefficient (Stβ) 0.396, 95% CI 0.323 to 0.471) and FI (Stβ 0.145, 95% CI 0.059 to 0.232) but not FIB-4. T2DM was significantly associated with FLI (Stβ 0.623, 95% CI 0.552 to 0.694) and FI (Stβ 0.307, 95% CI 0.226 to 0.388) but not FIB-4. SAF was significantly associated with FLI (Stβ 0.083, 95% CI 0.036 to 0.129), FI (Stβ 0.106, 95% CI 0.069 to 0.143) and FIB-4 (Stβ 0.087, 95% CI 0.037 to 0.137).ConclusionThe study showed that adverse GMS and higher glycaemia are positively associated with steatosis. FI, but not FIB-4, was related to adverse GMS concerning fibrosis. This study is the first to demonstrate that SAF is positively associated with steatosis and fibrosis.

Chronic kidney disease poses a growing global health concern, as an increasing number of patients progress to end-stage kidney disease requiring kidney replacement therapy, presenting various challenges including shortage of care givers and cost-related issues. In this narrative essay, we explore innovative strategies based on in-depth literature analysis that may help healthcare systems face these challenges, with a focus on digital health technologies (DHTs), to enhance removal and ensure better control of broader spectrum of uremic toxins, to optimize resources, improve care and outcomes, and empower patients. Therefore, alternative strategies, such as self-care dialysis, home-based dialysis with the support of teledialysis, need to be developed. Managing ESKD requires an improvement in patient management, emphasizing patient education, caregiver knowledge, and robust digital support systems. The solution involves leveraging DHTs to automate HD, implement automated algorithm-driven controlled HD, remotely monitor patients, provide health education, and enable caregivers with data-driven decision-making. These technologies, including artificial intelligence, aim to enhance care quality, reduce practice variations, and improve treatment outcomes whilst supporting personalized kidney replacement therapy. This narrative essay offers an update on currently available digital health technologies used in the management of HD patients and envisions future technologies that, through digital solutions, potentially empower patients and will more effectively support their HD treatments.

Background:Abnormal fluid and plasma sodium concentrations are established prognostic factors for patients on hemodialysis. However, the cumulative effects of abnormal salt and water and potential effect modifications and the effect of dialysate sodium remain incompletely understood. Methods:The study followed 68,196 patients on incident hemodialysis from 875 dialysis clinics in 25 countries over 10 years (2010–2020) investigating dose-response patterns between cumulative exposure time of fluid overload/depletion (measured by bioimpedance spectroscopy using the Fresenius Body Composition Monitor), abnormal plasma sodium levels, low dialysate sodium, and all-cause mortality. We calculated time-varying cumulative exposure (in months) of relative fluid overload (any degree; >7% or severe; >13 or >15% in women or men, respectively) and fluid depletion (<−7%), hypo- or hypernatremia (sodium <135 or >145 mmol/L, respectively), low dialysate sodium (≤138 mmol/L), and estimated hazard ratios for all-cause mortality using a multivariable Cox model. Results:Of 2,123,957 patient-months, 61% were spent in any degree of fluid overload, 4% in fluid depletion, 11% in hyponatremia, and 1% in hypernatremia. Any degree of fluid overload was associated with higher all-cause mortality (hazard ratio peak at 3.42 [95% confidence intervals, 3.12 to 3.75] relative to no exposure), and this association with all-cause mortality seemed to be stronger with severe fluid overload. The risk pattern associated with hyponatremia was approximately linear in the first four patient-months and then plateaued after the fourth patient-month. We did not observe effect modification between fluid overload and hyponatremia. Conclusions:Even mild fluid overload was associated with higher mortality in patients on hemodialysis. Whether more stringent fluid management results in clinical improvement requires further investigation.

Background The appropriate prescription of dialysate calcium concentration for hemodialysis is debated. We investigated the association between dialysate calcium and all-cause, cardiovascular mortality and sudden cardiac death.Methods In this historical cohort study, we included adult incident hemodialysis patients who initiated dialysis between 1 January 2010 and 30 June 2017 who survived for at least 6 months (grace period). We evaluated the association between dialysate calcium 1.25 or 1.50 mmol/l and outcomes in the 2 years after the grace period, using multivariable Cox regression models. Moreover, we examined the association between the serum dialysate to calcium gradient and outcomes.Results We included 12 897 patients with dialysate calcium 1.25 mmol/l and 26 989 patients with dialysate calcium 1.50 mmol/l. The median age was 65 years, and 61% were male. The unadjusted risk of all-cause mortality was higher for dialysate calcium 1.50 mmol/l [hazard ratio (HR) 1.07, 95% confidence intervals (CI) 1.01-1.12]. However, in the fully adjusted model, no significant differences were noted (HR 1.05, 95% CI 0.99-1.12). Similar results were observed for the risk of cardiovascular mortality (HR 1.03, 95% CI 0.94-1.13). Adjusted risk of sudden cardiac death was lower for dialysate calcium 1.50 mmol/l (HR 0.81, 95% CI 0.67-0.97). Significant and positive associations with all outcomes were observed with larger serum-to-dialysate calcium gradients, primarily mediated by the serum calcium level.Conclusions In contrast to the unadjusted analysis that showed a higher risk for dialysate calcium of 1.50 mmol/l, after adjusting for confounders, there were no significant differences in the risk of all-cause and cardiovascular mortality between dialysate calcium concentrations of 1.50 and 1.25 mmol/l. After adjustment, a lower risk of sudden cardiac death was observed in patients with dialysate calcium 1.50 mmol/l. A higher serum-to-dialysate calcium gradient is associated with an increased risk for adverse outcomes. Graphical Abstract