Relative Blood Volume Research Articles

CHANGES IN RENAL HEMODYNAMICS DURING A COLD PRESSURE TEST ARE DETECTABLE BY DOPPLER AND CONTRAST-ENHANCED ULTRASOUND

Objective: The cold pressure test (CPT) is a classic cardiovascular stress test known to increase blood pressure and heart rate secondary to an increase in nervous sympathetic activity. Its effect on renal hemodynamics using both Doppler ultrasound (DU) and contrast-enhanced ultrasound (CEUS) has not been reported previously. We hypothesized that a CPT would induce changes in renal hemodynamics detectable by DU and CEUS. The objective was to measure the renal responses during a CPT using DU and CEUS. Design and method: This was a single center prospective study in healthy participants. Renal resistive index (RRI) and mean acceleration time (MAT) were measured 4 times during 2 minutes baseline conditions (water at body temperature) and 4 times during 2 minutes CPT conditions (water at 4°C). The same protocol was then repeated after 5 minutes washout period for the measurement of the perfusion index (PI), relative blood volume and mean transit time using CEUS. Renal hemodynamic responses during baseline and CPT were compared using a t-test or a Wilcoxon matched-pair signed-rank test if variables were not normally distributed. Results: 24 healthy participants (15 women, 9 men) were included. Mean age and body mass index were respectively (mean ± standard deviation) 33.9 ± 11.8 years and 24.3 ± 3.4 kg/m2. The CPT increased mean blood pressure by 19.8 ± 4.4 mmHg, heart rate by 14.0 ± 3.8 beats per min. The CPT decrease RRI from 0.60 ± 0.04 to 0.58 ± 0.04 (p = 0.018). This decrease was associated with the systolic blood pressure (rho: -0.43, p = 0.038) and heart rate response (rho = -0.52, p = 0.009). Mean acceleration time did not change. Perfusion index (median and interquartile range) increased from 2578 UI (1789; 4901) to 4148UI (2499; 6739) (p < 0.001). Relative blood volume increased, but mean transit time did not change. Conclusions: This is the first demonstration that the CTP induces detectable changes in renal hemodynamics using both DU and CEUS. The CPT combined to DU and CEUS may be a valuable tool to assess the renal response to increased sympathetic drive in hypertensive or chronic kidney disease patients.

The time of onset of intradialytic hypotension during a hemodialysis session associates with clinical parameters and mortality

Intradialytic hypotension (IDH) is a common complication of hemodialysis, but there is no data about the time of onset during treatment. Here we describe the incidence of IDH throughout hemodialysis and associations of time of hypotension with clinical parameters and survival by analyzing data from 21 dialysis clinics in the United States to include 785682 treatments from 4348 patients. IDH was defined as a systolic blood pressure of 90 mmHg or under while IDH incidence was calculated in 30-minute intervals throughout the hemodialysis session. Associations of time of IDH with clinical and treatment parameters were explored using logistic regression and with survival using Cox-regression. Sensitivity analysis considered further IDH definitions. IDH occurred in 12% of sessions at a median time interval of 120-149 minutes. There was no notable change in IDH incidence across hemodialysis intervals (range: 2.6-3.2 episodes per 100 session-intervals). Relative blood volume and ultrafiltration volume did not notably associate with IDH in the first 90 minutes but did thereafter. Associations between central venous but not arterial oxygen saturation and IDH were present throughout hemodialysis. Patients prone to IDH early as compared to late in a session had worse survival. Sensitivity analyses suggested IDH definition affects time of onset but other analyses were comparable. Thus, our study highlights the incidence of IDH during the early part of hemodialysis which, when compared to later episodes, associates with clinical parameters and mortality.

Absolute blood volume variations during hemodialysis: Does dialysate temperature play a role?

Vascular refilling occurs to preserve hemodynamic stability during hemodialysis (HD). Recent studies report a feasible and noninvasive method to determine absolute blood volume (ABV), and estimate vascular refilling during HD. The objective of this study is to analyze if lowering dialysate temperature modifies variations in ABV during HD. The study was performed in 50 patients under HD. During two different sessions, relative blood volume was assessed using dialysate temperatures of 35.5°C (cool dialysate) and 36.5°C (neutral dialysate). ABV and vascular refilling were calculated using Kron et al methodology. Thirty-nine intradialytic morbid events (IMEs) were observed in 30 patients, 14 under cool dialysate and 25 during neutral dialysate. We did not found statistically differences in ABV or in refilling volume between cool and neutral temperature. When analyzing apart only those patients who presented IME, we observed lower drop in ABV in the 35.5°C dialysate treatments (0.57L) versus 36.5°C dialysate treatments (0.71L). When cool dialysate was used, the vascular refilling fraction tended to be higher, but data did not turn statistically significant. In selected groups of patients the use of cool dialysate induces lower ABV variations that could improve hemodynamic stability during HD treatments.

Low-Intensity Intradialytic Exercise Attenuates the Relative Blood Volume Drop Due to Intravascular Volume Loss during Hemodiafiltration

Introduction: Patients in hemodiafiltration (HDF) eliminate volume overload by ultrafiltration. Vascular volume loss is among the main mechanisms contributing to adverse events such as intradialytic hypotension. Here, we hypothesize that the intradialytic exercise (IDEX) is an intervention that could improve the acute response of physiological mechanisms involved during vascular volume loss. To test this hypothesis, we evaluated the hemodynamic response to mild aerobic exercise during HDF. Methods: Nineteen end-stage renal disease (ESRD) patients (11 women: 40 ± 10.8 years old, and 8 men: 42 ± 21 years old) receiving HDF thrice a week, with 6 months of previous physical conditioning, participated in this study. Three HDF sessions were scheduled for each patient: 1 resting in supine position, 1 resting in sitting position, and 1 doing aerobic exercise. The first 2 sessions were taken as control. The ultrafiltration rate was set to 800 mL/h in each session. The hemodynamic response was monitored through the relative blood volume (RBV), and cardiovascular variables measured noninvasively by photoplethysmography. Adequacy variables such as Kt/V and percentage reduction of urate, urea, creatinine (Cr), and phosphate were also monitored. Findings: The decrease rate of the RBV was smaller in the session with IDEX compared to the sessions with no exercise. No differences were found neither in the cardiovascular variables nor in the adequacy variables among the 3 sessions. There were no hypotension events during the session with exercise, and 8 events during the sessions without exercise (p = 0.002). Discussion: Mild exercise during HDF decreased the RBV drop and was associated with less hypotension events. The lack of differences in the hemodynamic variables suggests an adequate acute response of cardiovascular compensation variables to intradialytic hypovolemia.

Photoplethysmography (PPG) Scheming System Based on Finite Impulse Response (FIR) Filter Design in Biomedical Applications

Photoplethysmography (PPG) is a non-invasive technique that measures relative blood volume changes in the blood vessels close to the skin. This research work intends to design a real-time filtering system. There are two main parts in this heart rate detection system: the data-gathering portion and real-time processing. Both processing includes preprocessing and filtering in which PPG signals derive from the pulse sensor in the data-gathering stage. It filters from PPG signal in real-time processing. In the data-gathering stage, the PPG signal is first derived from the pulse sensor, and then it is preprocessed to remove noise and enhance the signal quality to collect the paired-pulse index (PPI). After the signal has been preprocessed, the PPI is extracted from the signal, and this signal with features is collected as a data point to give an input signal for Raspberry Pi to draw the heat rate plot. In this system implementation, the pulse sensor is used to detect the heart-beat information of blood stream. This computer-aided system may also help patients save their time being spent waiting for doctors’ decisions. Biomedical analysis, digital signal processing, image processing, and data analysis become important factors for the automatic diagnosis system.

Algorithm and device testing for quantitative analysis of skin fluorescence with regard to a relative blood volume in it on the example of radiation-induced erythema in animals

Algorithm and device testing for quantitative analysis of skin fluorescence with regard to a relative blood volume in it on the example of radiation-induced erythema in animals

Quantitative Imaging Parameters of Contrast-Enhanced Micro-Computed Tomography Correlate with Angiogenesis and Necrosis in a Subcutaneous C6 Glioma Model.

Simple SummaryContrast-enhanced (CE) X-ray imaging techniques have been used to assess angiogenesis in patients and animal models of cancer in order to overcome the limitations of histological quantification of angiogenesis, such as spatial and temporal heterogeneity of tumors. Some studies have compared the quantitative imaging parameters obtained with static and dynamic CE X-ray imaging techniques, but their association with histological biomarkers of angiogenesis has never been directly compared. This study aimed to provide such a comparison in a suitable animal model for the study of angiogenesis, namely, the subcutaneous C6 glioma model. We found an agreement among the quantitative imaging parameters obtained with these techniques, and we also found an association between a set of them with angiogenesis and necrosis descriptors. This set of quantitative imaging parameters demonstrated a high potential to describe angiogenesis and could be used to assess treatment response in further studies with this animal model.The aim of this work was to systematically obtain quantitative imaging parameters with static and dynamic contrast-enhanced (CE) X-ray imaging techniques and to evaluate their correlation with histological biomarkers of angiogenesis in a subcutaneous C6 glioma model. Enhancement (E), iodine concentration (CI), and relative blood volume (rBV) were quantified from single- and dual-energy (SE and DE, respectively) micro-computed tomography (micro-CT) images, while rBV and volume transfer constant (Ktrans) were quantified from dynamic contrast-enhanced (DCE) planar images. CI and rBV allowed a better discernment of tumor regions from muscle than E in SE and DE images, while no significant differences were found for rBV and Ktrans in DCE images. An agreement was found in rBV for muscle quantified with the different imaging protocols, and in CI and E quantified with SE and DE protocols. Significant strong correlations (Pearson r > 0.7, p < 0.05) were found between a set of imaging parameters in SE images and histological biomarkers: E and CI in tumor periphery were associated with microvessel density (MVD) and necrosis, E and CI in the complete tumor with MVD, and rBV in the tumor periphery with MVD. In conclusion, quantitative imaging parameters obtained in SE micro-CT images could be used to characterize angiogenesis and necrosis in the subcutaneous C6 glioma model.

Abstract 14688: Relative Blood Volume Change After Single Doses of a Loop Diuretic to Assess Volume Status: A Patient Level Meta-analysis

Background: In patients with congestive heart failure administration of an intravenous diuretic results in increased urine production and, depending on the volume status, an immediate change in relative blood volume (RBV). Changes in RBV are already applied clinically to monitor fluid removal and better guide diuresis in patients who undergo peripheral ultrafiltration. Using individual level patient data, we explored whether it is possible to measure changes in RBV after a single intravenous dose of loop diuretic through the measurement of serial hematocrit values. Based on normally occurring variation in volume-stable patients, the smallest change in RBV that would be detectable by routine serial hematocrits ranges from 6.4% to 8.6%. Methods and Results: Electronic databases were queried for articles that contained predefined MeSH terms in order to identify all studies in which patients received intravenous diuretics. The 764 studies that met our entry criteria were systematically reviewed and manually screened. We then conducted a meta-analysis from 14 studies that provided individual, patient-level data from at least 2 time points: just before and within 3 hours of administration of an intravenous loop diuretic. We found that among a total of 240 patients, RBV decreased by 11% (95% CI 10 to 12%) at 2 hours after an intravenous loop diuretic was given (Figure); there was no significant difference in this finding based on whether or not patients had heart failure. Conclusion: We found that anticipated RBV change with single doses of intravenous loop diuretics exceeds the smallest detectable change in RBV that can be obtained by serial hematocrits. This implies that routine hematocrits can be used to track RBV change across serial doses of intravenous loop diuretics, potentially providing a target for a dry interstitium in acute heart failure.

NIMG-41. VARIATION IN PERFUSION AND PERMEABILITY MRI DEPENDING ON VASCULAR INPUT FUNCTION SELECTION

Abstract BACKGROUND According to the updated RANO criteria, MRI contrast enhancement and peritumoral edema during the initial 12 weeks within the radiation field following chemoradiation may be pseudoprogression (PP) or true progression (TP). This ambiguity results in diagnostic uncertainty and delays in effective therapies. MRI perfusion and permeability imaging markers, including relative blood volume (rBV), and volume transfer constant (Ktrans), may be useful in differentiating PP from TP. Both techniques rely on identification of a vascular input function (VIF) to produce reliable output maps. METHODS Perfusion and permeability maps were acquired from 7 patients on a Siemens 3T Verio MRI as part of an ongoing prospective study on glioblastoma multiforme. Patients received standard surgical resection with concurrent chemo-radiotherapy treatment and MRI follow-up at one and every 2 months. Maps were based on the follow-up MRI. The 3D contrast enhancing lesion (CEL) was segmented from the T1-Post-Gd MRI. VIF pixels were identified in the internal carotid artery (ICA), the M2 segment of the middle cerebral artery (MCA2), the superior sagittal sinus (SSS), automatically using software (Olea Sphere 3.0.22), and auto-edited (removed pixels from the auto VIF definition that were outside the brain). RESULTS For the different VIF pixel selections (ICA, MCA2, SSS, Auto, Auto-edited), mean Ktrans values from CEL were 0.32, 0.48, 0.05, 0.09, 0.08, respectively, showing a 10-fold variation. Mean rBV values from CEL were 2.70, 2.36, N/A, 3.10, 3.19, respectively, showing a 1.3-fold variation. CONCLUSIONS VIF pixel selection is a critical step in generating reliable perfusion and permeability MRI maps. Variation of up to a factor of 10 in the Ktrans values, depending on VIF selection, was observed. SSS for the permeability VIF resulted in maps that most closely matched literature values, whereas perfusion imaging showed less sensitivity to VIF selection.

Feasibility of human spinal cord perfusion mapping using dynamic susceptibility contrast imaging at 7T: Preliminary results and identified guidelines.

To explore the feasibility of dynamic susceptibility contrast MRI at 7 Tesla for human spinal cord perfusion mapping and fill the gap between brain and spinal cord perfusion mapping techniques. Acquisition protocols for high-resolution single shot EPI in the spinal cord were optimized for both spin-echo and gradient-echo preparations, including cardiac gating, acquisition times and breathing cycle recording. Breathing-induced MRI signal fluctuations were investigated in healthy volunteers. A specific image- and signal-processing pipeline was implemented to address them. Dynamic susceptibility contrast was then evaluated in 3 healthy volunteers and 5 patients. Bolus depiction on slice-wise signal within cord was investigated, and maps of relative perfusion indices were computed. Signal fluctuations were increased by 1.9 and 2.3 in free-breathing compared to apnea with spin-echo and gradient-echo, respectively. The ratio between signal fluctuations and bolus peak in healthy volunteers was 5.0% for spin-echo and 3.8% for gradient-echo, allowing clear depiction of the bolus on every slice and yielding relative blood flow and volume maps exhibiting the expected higher perfusion of gray matter. However, signal fluctuations in patients were increased by 4 in average (using spin-echo), compromising the depiction of the bolus in slice-wise signal. Moreover, 3 of 18 slices had to be discarded because of fat-aliasing artifacts. Dynamic susceptibility contrast MRI at 7 Tesla showed great potential for spinal cord perfusion mapping with a reliability never achieved thus far for single subject and single slice measurements. Signal stability needs to be improved in acquisition conditions associated with patients; guidelines to achieve that have been identified and shared.

Hemodialysis crossover study using a relative blood volume change-guided ultrafiltration control compared with standard hemodialysis: the BV-UFC study

BackgroundIt has been difficult to sufficiently achieve body-fluid management using blood volume (BV) monitor during hemodialysis (HD) with constant ultrafiltration (UF) rate. Recently, a relative BV change-guided UF control (BV-UFC) system was developed by combining the concepts of an automatic feedback system that could control the UF rate and profile with real- time monitoring of relative changes in BV (%ΔBV). However, this system has limited application in the clinical setting. Therefore, in this study, we aimed to perform the crossover study on HD with BV-UFC compared to standard HD in terms of hemodynamic stability during HD.MethodsForty-eight patients entered an 8-week crossover period of standard HD or HD with BV-UFC. Prevalence of intradialytic hypotension (IDH) as a primary outcome and changes in blood pressure (BP), differences in %ΔBV, and achievement of the target ultrafiltration volume as secondary outcomes were compared. IDH was defined as a reduction in systolic BP ≥20 mmHg from the baseline value at 10 min after HD initiation.ResultsNo significant differences were found in the prevalence of IDH, frequency of intervention for symptomatic IDH, and achievement of the target ultrafiltration volume between the groups. The %ΔBV was significantly fewer (-12.1 ± 4.8% vs. -14.4 ± 5.2%, p <0.001) in the HD with BV-UFC than that in the standard HD.ConclusionsHD with BV-UFC did not reduce the prevalence of IDH compared with standard HD. The relief of a relative BV reduction at the end of HD may be beneficial in patients undergoing HD with BV-UFC.Trial RegistrationUMIN, UMIN000024670. Registered on December 1, 2016.

Novel Ultrafiltration Rate Feedback Controller for Attainment of Relative Blood Volume Targets During Hemodialysis

Novel Ultrafiltration Rate Feedback Controller for Attainment of Relative Blood Volume Targets During Hemodialysis

Relative blood volume changes during haemodialysis estimated from haemoconcentration markers

Relative blood volume (RBV) monitoring is frequently used in haemodialysis patients to help guide fluid management and improve cardiovascular stability. RBV changes are typically estimated based on online measurements of certain haemoconcentration markers, such as haematocrit (HCT), haemoglobin (HGB) or total blood protein concentration (TBP). The beginning of a haemodialysis procedure, i.e. filling the extracorporeal circuit with the patient’s blood (with the priming saline being infused to the patient or discarded) may be associated with relatively dynamic changes in the circulation, and hence the observed RBV changes may depend on the exact moment of starting the measurements. The aim of this study was to use a mathematical model to assess this issue quantitatively. The model-based simulations indicate that when the priming saline is not discarded but infused to the patient, a few-minute difference in the moment of starting RBV tracking through measurements of HCT, HGB or TBP may substantially affect the RBV changes observed throughout the dialysis session, especially with large priming volumes. A possible overestimation of the actual RBV changes is the highest when the measurements are started within a couple of minutes after the infusion of priming saline is completed.

Amniodrainage-Induced Circulatory Dysfunction in Women Treated for Twin-To-Twin Transfusion Syndrome.

Twin-to-twin transfusion syndrome (TTTS) in monochorionic-diamniotic twin pregnancies usually requires fetoscopic laser ablation (FLA) followed by amniodrainage (AD). Perioperative maternal hemodynamic changes and hemodilution have been observed. Little is known about the underlying pathophysiology. We aimed to evaluate the impact of high volume amniodrainage on intrauterine pressure, placental thickness and maternal blood characteristics. A total of 18 cases of TTTS were included in this prospective pilot study. All patients were treated with FLA and subsequent AD. Intrauterine pressure and placental thickness were assessed before, during and after amniodrainage. Maternal hemoglobin, hematocrit and serum albumin were measured at admission and 24 h after the intervention. Amniodrainage led to a decrease in mean intrauterine pressure (from 30.1 ± 8.1 mmHg to 17.6 ± 3.6 mmHg (p < 0.001)) and an increase in mean placental thickness (from 16.8 ± 6.4 mm to 31.83 ± 8.64 mm (p < 0.001)). There was a positive correlation between changes in placental thickness and the amount of amniodrainage during intervention (Pearson’s Rho 0.73; p = 0.001). Hematocrit decreased from 33.4 ± 3.8 (%) to 28.4 ± 3.5 (%), i.e., an increase in relative blood volume by 18 ± 10.2% (p < 0.001). Albumin decreased from 37.9 ± 0.9 g/L to 30.7 ± 2.2 g/L, i.e., an increase in relative plasma volume by 24 ± 8.1% (p < 0.001). Amniodrainage leads to uterine decompression, increased placental thickness and subsequent maternal hemodilution. We propose the term “amniodrainage-induced circulatory dysfunction” for these specific maternal hemodynamic changes in the treatment of twin-to-twin transfusion syndrome.

Perfusion in hand arthritis on dynamic contrast-enhanced computed tomography: a randomized prospective study using MRI as a standard of reference

ObjectiveTo evaluate the performance of dynamic contrast-enhanced CT (DCE-CT) in detecting and quantitatively assessing perfusion parameters in patients with arthritis of the hand compared with dynamic contrast-enhanced MRI (DCE-MRI) as a standard of reference.Materials and methodsIn this IRB-approved randomized prospective single-centre study, 36 consecutive patients with suspected rheumatoid arthritis underwent DCE-CT (320-row, tube voltage 80 kVp, tube current 8.25 mAs) and DCE-MRI (1.5 T) of the hand. Perfusion maps were calculated separately for mean transit time (MTT), time to peak (TTP), relative blood volume (rBV), and relative blood flow (rBF) using four different decomposition techniques. Region of interest (ROI) analysis was performed in metacarpophalangeal joints II–V and in the wrist. Pairs of perfusion parameters in DCE-CT and DCE-MRI were compared using a two-tailed t test for paired samples and interpreted for effect size (Cohen’s d). According to the Rheumatoid Arthritis Magnetic Resonance Imaging Score (RAMRIS) scoring results, differentiation of synovitis-positive and synovitis-negative joints with both modalities was assessed with the independent t test.ResultsThe two modalities yielded similar perfusion parameters. Identified differences had small effects (d 0.01–0.4). DCE-CT additionally differentiates inflamed and noninflamed joints based on rBF and rBV but tends to underestimate these parameters in severe inflammation. The total dose-length product (DLP) was 48 mGy*cm with an estimated effective dose of 0.038 mSv.ConclusionDCE-CT is a promising imaging technique in arthritis. In patients with a contraindication to MRI or when MRI is not available, DCE-CT is a suitable alternative to detect and assess arthritis.

P1079NOVEL ULTRAFILTRATION RATE FEEDBACK CONTROLLER FOR ATTAINMENT OF RELATIVE BLOOD VOLUME TARGETS DURING HEMODIALYSIS

Abstract Background and Aims Preciado et al. have identified half-hourly relative blood volume (RBV) targets (at 30, 60…180 min) during hemodialysis (HD) that are associated with significantly improved patient survival. Attainment of these RBV targets would necessitate incessant adjustments to the ultrafiltration rate (UFR) by the dialysis nurse, which is logistically not feasible. We developed a novel proportional-integral controller that takes RBV data from the commercially available CLiC® device as an input and provides UFR suggestions to guide the RBV curve into the desired targets. The clinician specifies the desired UF goal and the maximum allowed upward/downward deviation from this goal, and the Controller then optimizes the RBV trajectory within the limits allowed by the clinician’s prescription. The present study is aimed to characterize the behavior of this novel feedback controller. Method We conducted a single-arm, prospective, interventional pilot study in subjects on chronic HD at three Avantus Renal Therapy Dialysis Centers in New York City. Subjects were treated with Fresenius 2008T HD machines. RBV was measured with the CLiC® device. CLiC® and HD machine data were fed into a research laptop running the UFR Feedback Controller software. The UFR recommendations (generated every 10 minutes) were evaluated by dialysis nurses who then either implemented or rejected them as they deemed clinically appropriate. The nurses were instructed to only override Controller recommendations if medically indicated, but not in an attempt to manage the subjects’ RBV trajectories themselves. Results Fifteen subjects (58.9 ± 15.3 years, 33% white, 53% black, dialysis vintage 4.1 ± 2.4 years, baseline interdialytic weight gain 2.6 ± 0.8 L, treatment time 222 ± 28 min) were studied (63 study visits, 4.2 ± 1.9 visits per subject). Of 300 analyzed RBV target timepoints, 63% had RBVs within the desired target range, 33% of the RBVs were above and 4% were below target. Stratified by timepoint, the on-target percentage increased from 37% at 30 min to 73% at 180 min into HD, while the proportion of RBVs above or below target decreased. In subjects with at least 4 complete study visits (N=8), looking at each of their first 4 complete visits, on average 71.8% of subjects were within the desired RBV target at 180 min into HD. The rate of intradialytic morbid events did not appear to be outside of the ordinary. There was no indication of adverse events related to the use of the UFR Feedback Controller. The Figure shows an example study visit where the UFR Feedback Controller modulates the UFR on an ongoing basis throughout the treatment to keep the RBV curve close to the ideal target trajectory (red line, defined by connecting the RBVs associated with the lowest all-cause mortality). Solid black line: RBV curve (left y-axis); dashed black line: UFR (right y-axis); green boxes: half-hourly RBV target ranges associated with improved survival. Conclusion The UFR Feedback Controller behaves as expected, steering the patients’ RBV curves toward the predefined target ranges where possible, while simultaneously guaranteeing that the prescribed fluid removal goal will be achieved. Preciado et al. had reported approx. one third of patients within the favorable RBV target range at 3h into HD. In contrast, while our pilot study was relatively small, with use of our novel UFR Feedback Controller, approx. 72% of subjects were within the desired RBV target range at 3h into HD. This novel UFR feedback control technology holds great promise for improving fluid management and clinical outcomes in HD patients without requiring additional staff time.

P1124A NOVEL ALGORITHM TO IDENTIFY PRESUMABLY FLUID OVERLOADED HEMODIALYSIS PATIENTS

Abstract Background and Aims Adequate volume control is a major challenge in hemodialysis (HD) patients, as both fluid overload and depletion are associated with increased morbidity and mortality. In many cases, fluid overloaded patients may require further interventions, e.g. increasing ultrafiltration volume, treatment time or additional HD sessions to achieve their prescribed target weight. Relative blood volume (RBV) monitoring is widely used in HD patients, and past evidence suggests that flat RBV slopes indicate fluid overload [1,2]. The goal of this study was to develop an algorithm that would allow clinicians to identify presumably fluid overloaded HD patients based on a small number of consecutive RBV recordings. Method We based our analysis on the 842 prevalent HD patients enrolled in our previously published multicenter study [1], where RBV (Crit-Line®, Fresenius Medical Care, Waltham, MA) was assessed over a 6-month baseline period and all-cause mortality recorded during a median follow-up of 30.8 months; we found in this study that attainment of a RBV between 86 and 92% three hours into the HD session was associated with significantly better patient survival. The goal of our current research was to develop an algorithm that would require an observation period much shorter than 6 months yet yield clinically meaningful sensitivity and specificity to identify (presumably fluid overloaded) patients with flat RBV profiles (“flat” being defined as RBV &amp;gt; 92% at 3 hours.) We categorized patients in study [1] as either “positive” (their mean RBV at 3 hours was &amp;gt;92%) or “negative”. We computed sensitivities and specificities relative to the “positive” and “negative” cases for 1 to 15 HD sessions and various rates of treatments with flat RBV curves (30, 40, 50 and 60%). Results Sensitivities, specificities, and Youden’s indices (= sensitivity + specificity – 1) for 1 to 15 treatments and across the different rates of “positive” RBV curves are shown (Figure 1). We found a sensitivity of 92%, a specificity of 80%, and a Youden’s index of 73% when &amp;gt;=50% of 10 preceding treatments were “positive”. Based on these results we propose an RBV based algorithm to identify “positive” cases (i.e. patients with a flat RBV profile) (Figure 2). Conclusion Our algorithm requires only a small number (10) of RBV readings to identify presumably fluid overloaded patients with a clinically acceptable sensitivity (92%) and specificity (80%). It would be of interest to compare the performance of this algorithm with volume status as determined by bioimpedance; however, bioimpedance has not yet been approved for use in HD patients in the U.S.

P1556HEALTH CARE STAFF ACCEPTANCE OF ULTRAFILTRATION RATE RECOMMENDATIONS MADE BY A NOVEL FEEDBACK CONTROLLER

Abstract Background and Aims Preciado et al. have identified half-hourly relative blood volume (RBV) targets during hemodialysis (HD) that are associated with significantly improved patient survival. Attainment of these RBV targets would require frequent adjustments to the ultrafiltration rate (UFR) by the dialysis nurse, which is logistically not feasible. We developed a novel proportional-integral controller that takes RBV data from the commercially available CLiC® device as an input and provides UFR suggestions to guide the RBV curve into the desired targets. In this study, we investigated the degree to which the dialysis nurses accepted the UFR recommendations made by this novel feedback controller. Method We conducted a single-arm, prospective, interventional pilot study in subjects on chronic HD at three Avantus Renal Therapy Dialysis Centers in New York City. Subjects were treated with Fresenius 2008T HD machines. RBV was measured with the CLiC® device. CLiC® and HD machine data were fed into a research laptop running the UFR Feedback Controller software. The UFR recommendations (generated every 10 minutes) were evaluated by dialysis nurses who then either implemented or rejected them as they deemed clinically appropriate. Results Fifteen subjects (58.9 ± 15.3 years, 33% white, 53% black, dialysis vintage 4.1 ± 2.4 years, baseline interdialytic weight gain 2.6 ± 0.8 L, treatment time 222 ± 28 min) were studied. Fifty-six study visits (48 complete, 8 partial) from 14 subjects had analyzable data. Out of 1,038 UFR recommendations made by the Controller, 926 (89.2%) were accepted by the dialysis nurses, while 112 (10.8%) were overridden. In 48% of all 48 complete treatments, the Controller ran without a single override by the nurses. Of the other half of the treatments, about a quarter only saw one override per treatment (only half of which were due to low blood pressure or clinical symptoms). Only 1 of 59 study visits was incomplete due to a staff intervention for medical reasons that disengaged the Controller. For the 25 complete study treatments (from 11 subjects) that had at least one Controller suggestion overridden by the nurses, we analyzed the direction and magnitude of disagreement between the Controller-suggested and the implemented UFR (Fig. 1). Out of a total of 109 overridden Controller suggestions, 20 implemented UFRs were greater than the respective Controller-suggested UFRs (i.e., not indicated for medical reasons). Another 70 implemented UFRs were less than 100 mL/h (on average 49.7 mL/h) lower than the Controller-suggested UFRs (i.e., very mild disagreements). Together, these two categories make up 83% of all “disagreements” between healthcare staff and the Controller, leaving only 19 more pronounced disagreements. Of note, of the 109 UFR overrides, 65 (59.6%) were due to staff preference in the absence of low blood pressure or clinical symptoms; 41 were due to low blood pressure, 2 due to hypotension with clinical symptoms, and 1 due to clinical symptoms without low blood pressure. Conclusion The proportion of UFR recommendations generated by this UFR Feedback Controller that were accepted by the nurses was very high (≈90%). Importantly, of the relatively few cases where nurses chose to override the Controller’s recommendation, the majority (≈60%) were due to “staff preference” in the absence of low blood pressure or clinical symptoms. The high rate of “staff preference” overrides is likely owed to the fact that, for this study, the nurses exclusively attended to only one patient (the study subject) at a time for the entire HD session.

P1091DYNAMICS OF VASCULAR REFILLING IN EXTENDED NOCTURNAL HAEMODIALYSIS

Abstract Background and Aims Refilling volume had not been a measurable parameter in clinical practice so far, because the knowledge of absolute blood volume (BV) is necessary. Recently, we developed a simple method to determine absolute BV, thus enabling quantification of the refilling volume. The overnight dialysis is particularly suitable for studying the refilling process due to negligible external influences and the extended treatment time. Method At the beginning of the dialysis (t=0), before starting the ultrafiltration (UF), a defined online bolus of 240 ml dialysate was infused by pressing the emergency button on the haemodiafiltration (HDF) machine (5008, FMC). The subsequent increase in relative BV (RBVpost-RBVpre) was measured with the integrated BV monitor, and absolute BV at t=0 was calculated: absolute BV in ml = bolus volume 240 ml x 100% / increase in relative BV in%. Absolute BV at any other time t was calculated as: Vt = V0 x RBVt (in %) / 100 At constant UF rate refilling volume (Vref) is given for every hour (h) as: Vref h = UFV h – drop in absolute BVh (beginning – end) The refilling fraction is expressed as refilling/UF ratio: Ref% = Vref/UFV x 100, in % Before treatment, volume overload was evaluated by bioimpedance spectroscopy (BIS) using the body composition monitor (FMC). Results Refilling volume and refilling fraction were studied in 10 stable chronic haemodialysis (HD) patients during an extended (7 hour) nocturnal HD session. Specific BV at treatment start was 74.9 ± 11.8 mL/kg and dropped to 68.6 mL/kg at dialysis end. The constant UF rate was set to 406 ± 120 mL/h (specific UF rate 4.81 ± 1.83 mL/kg/h). In the first hour refilling volume amounted only to 23% of UF volume. Refilling fraction reached its maximum in the 2nd, 3 rd and 4th hour at about mean 90% (91.5%, 88.7%, and 91.1% respectively) of UF volume. From the 5th hour on, refilling volume and refilling fraction decreased (5th hour 81.3%, 6th hour 72.5%, and 7th hour 70.0% of UF volume). In the 5th hour, cumulative UF volume exceeded volume overload (1.1 ± 1.0 L) measured by BIS in 9 of 10 patients. Refilling fraction cumulatively increased up to the 4th hour. Thereafter, cumulative ratio remained constant at 70 – 75% due to the decrease in refilling volume. This did not change during the further course of dialysis. Cumulative refilling volume showed a strong correlation (r2 = 0.88; p&amp;lt;0.001) with UF volume. Conclusion After the first hour, when sufficient refilling takes place, refilling volume is in a stable ratio of approximately 90 % of UF volume. Refilling is low in the first hour, and, therefore, refilling volume amounted cumulatively only about 70 to 75% of UF volume during usual dialysis duration. Thereby, absolute BV will be reduced by approximately 250 to 300 ml per liter UF. This must be taken into account in volume management in order to avoid intradialytic complications. As expected, refilling decreases when volume overload in the interstitial space is removed. Due to the reduced refilling, there will be an additional gap in BV.

P1243ABSOLUTE BLOOD VOLUME VARIATIONS INFLUENCED BY DIALYSATE TEMPERATURE DURING HAEMODIALYSIS

Abstract Background and Aims Intradialytic hypotension is a common complication in haemodialysis. Vascular refilling occurs to preserve haemodynamic stability. Recent studies report a feasible and noninvasive method to determine absolute blood volume, which would allow us to estimate vascular refilling during haemodialysis. During years, it has been proposed that lowering the dialysate temperature could improve intradialytic hypotension outcomes in patients undergoing chronic haemodialysis. The objective of this study is to analyze if lowering dialysate temperature modifies variations in absolute blood volume during haemodialysis. Method The study was performed in 51 patients under haemodialysis treatment. During two different sessions, relative blood volume was assessed using dialysate temperatures of 35.5ºC (cool dialysate) and 36.5ºC (neutral dialysate). Absolute blood volume and vascular refilling were calculated using Kron et al methodology (Hemodial Int. 2016;20(3):484–91). Intradialytic hypotension was defined as a systolic blood pressure below 85 mmHg or a drop of pressure above 20 mmHg accompanied by symptoms. Statistical analysis was performed using paired t-Test or Wilcoxon rank sum. Results 31 episodes of intradialytic hypotension were observed, 14 under cool dialysate and 26 during neutral dialysate. We did not found statistically differences in absolute blood volume or in refilling volume between cool and warm dialysate temperature. In the group of patients with intradialytic hypotension (Table 1) we observed lower drop in absolute blood volume in the 35.5ºC dialysate group (0.59 L) versus 36.5ºC group (0.72 L). Although no statistically significant differences were found in vascular refilling volumes, when cool dialysate was used refilling tended to be higher. Conclusion It seems that in selected groups of patients the use of cool dialysate could improve absolute blood volume stability during HD treatments, although further studies are needed.