The effect of changes in intra-compartmental bioimpedance measurements with early intra-dialytic hypotension during haemodialysis

INTRODUCTION

Intra-dialytic hypotension (IDH) remains the commonest problem associated with routine haemodialysis treatments. Fluid shifts from intracellular(ICW) and extracellular(ECW) compartments to refill plasma volume during haemodialysis with ultrafiltration.

METHODS

We studied the effect of relative changes in ICW and ECW indifferent body segments using multifrequency segmental bioimpedance during haemodialysis and IDH episodes.

RESULTS

Of 42 haemodialysis patients,16 patients (38.1%) developed IDH within the first hour of dialysis. Patients with and without early IDH were well-matched for demographics and starting bioimpedance measurements. However, after 60 min, the relative change in in ECW/ICW ratio between the non-fistula arm and leg was significantly different for the early IDH group median -1.07 (-3.33 to 0.8) versus 0.61 (-0.78 to 1.8), p < 0.05, whereas there no differences in ultrafiltration rate, relative blood volume monitoring or on-line clearance.

CONCLUSION

Monitoring serial changes in fluid status in different body compartments with bioimpedance may potentially prevent IDH in the future.

Relative Blood Volume Monitoring during Continuous Renal Replacement Therapy: A Prospective Observational Study

INTRODUCTION

Hematocrit monitoring during continuous renal replacement therapy (CRRT) allows the continuous estimation of relative blood volume (RBV). This may enable early detection of intravascular volume depletion prior to clinical sequelae. We aimed to investigate the feasibility of extended RBV monitoring and its epidemiology during usual CRRT management by clinicians unaware of RBV. Moreover, we studied the association between changes in RBV and net ultrafiltration (NUF) rates.

METHODS

In a cohort of adult intensive care unit patients receiving CRRT, we continuously monitored hematocrit and RBV using a pre-filter noninvasive optical sensor. We analyzed temporal changes in RBV and investigated the association between RBV change and NUF rates, using the classification of NUF rates into low, moderate, or high based on predefined cut-offs.

RESULTS

We obtained >60,000 minute-by-minute measurements in >1,000 CRRT hours in 36 patients. The median RBV change was negative (decrease) in 69% of patients and the median peak change in RBV was -9.3% (interquartile range: -3.9% to -14.3%). Moreover, the median RBV decreased from baseline by >5% in 40.2% of measurements and by >10% in 20.6% of measurements. Finally, RBV decreased significantly more when patients received a high NUF rate (>1.75 mL/kg/h) compared to low or moderate NUF rates (5.32% vs. 1.93% or 1.97%, p < 0.001).

CONCLUSION

Continuous hematocrit and RBV monitoring during CRRT was feasible. RBV decreased significantly during CRRT, and decreases were greater with higher NUF rates. RBV monitoring may help optimize NUF management and prevent the occurrence of intravascular volume depletion.

Dynamics of Plasma Refill Rate and Intradialytic Hypotension During Hemodialysis: Retrospective Cohort Study With Causal Methodology

Key Points

Directly studying plasma refill rate (PRR) during hemodialysis (HD) can offer insight into physiologic mechanisms that change throughout HD. PRR at the start and during HD is associated with intradialytic hypotension, independent of ultrafiltration rate. A rising PRR during HD may be an early indicator of compensatory mechanisms for impending circulatory instability.

Background

Attaining the optimal balance between achieving adequate volume removal while preserving organ perfusion is a challenge for patients receiving maintenance hemodialysis (HD). Current strategies to guide ultrafiltration are inadequate.

Methods

We developed an approach to calculate the plasma refill rate (PRR) throughout HD using hematocrit and ultrafiltration data in a retrospective cohort of patients receiving maintenance HD at 17 dialysis units from January 2017 to October 2019. We studied whether (1 ) PRR is associated with traditional risk factors for hemodynamic instability using logistic regression, (2 ) low starting PRR is associated with intradialytic hypotension (IDH) using Cox proportional hazard regression, and (3 ) time-varying PRR throughout HD is associated with hypotension using marginal structural modeling.

Results

During 180,319 HD sessions among 2554 patients, PRR had high within-patient and between-patient variability. Female sex and hypoalbuminemia were associated with low PRR at multiple time points during the first hour of HD. Low starting PRR has a higher hazard of IDH, whereas high starting PRR was protective (hazard ratio [HR], 1.26, 95% confidence interval [CI], 1.18 to 1.35 versus HR, 0.79, 95% CI, 0.73 to 0.85, respectively). However, when accounting for time-varying PRR and time-varying confounders, compared with a moderate PRR, while a consistently low PRR was associated with increased risk of hypotension (odds ratio [OR], 1.09, 95% CI, 1.02 to 1.16), a consistently high PRR had a stronger association with hypotension within the next 15 minutes (OR, 1.38, 95% CI, 1.30 to 1.45).

Conclusions

We present a straightforward technique to quantify plasma refill that could easily integrate with devices that monitor hematocrit during HD. Our study highlights how examining patterns of plasma refill may enhance our understanding of circulatory changes during HD, an important step to understand how current technology might be used to improve hemodynamic instability.

Why is Intradialytic Hypotension the Commonest Complication of Outpatient Dialysis Treatments?

Intradialytic hypotension (IDH) is the most frequent complication of hemodialysis (HD) treatments with a frequency of 10% to 12% for patients with chronic kidney disease attending for outpatient treatments and is associated with both temporary ischemic stress to vital organs, including the heart and brain, and increased patient mortality. Although there have been many different definitions of IDH over the years, an absolute nadir systolic blood pressure (SBP) has the strongest association with patient outcomes. The unifying pathophysiology is one of reduced effective blood volume, resulting in lower plasma tonicity, and if this cannot be adequately compensated for by activation of neurohumeral systems, then arteriolar tone and blood pressure fall. The risk factors for developing IDH are numerous, ranging from patient-related factors, including age and comorbidity with reduced cardiac reserve, to patient compliance with dietary and lifestyle advice, to reactions with the extracorporeal circuit and medications, choice of dialysate composition and temperature, setting of postdialysis target weight, ultrafiltration rate, and profiling. Advances in dialysis machine technology by providing real time estimates of the effective circulating volume and adjusting dialysate composition to maintain vascular tonicity are being developed, but currently require more sophisticated biofeedback loops to be clinically effective in preventing IDH. While awaiting advances in artificial intelligence, the clinician continues to rely on patient education to limit interdialytic weight gains, frequent assessment of the postdialysis target weight, adjusting dialysate composition and temperature, introducing convective therapies to increase thermal losses, and altering dialysis session duration and frequency to reduce ultrafiltration rate requirements.

Monitoring relative blood volume changes during hemodialysis: Impact of the priming procedure

The monitoring of relative blood volume (RBV) changes during hemodialysis is increasingly used to evaluate the effect of dialyzer ultrafiltration on intravascular volume to guide the removal of excess fluid in a manner that maintains hemodynamic stability of the patient. RBV monitoring is typically based on an optical or acoustic sensor placed in the arterial blood line that measures a marker of hemoconcentration, such as hematocrit, hemoglobin, or total blood protein. However, the accuracy of RBV monitors and the impact of their clinical use remain the subject of ongoing debate. Here, we show that, depending on the procedure of filling the extracorporeal circuit with the patient's blood at the beginning of the dialysis session, the indications of an RBV monitor may be misleading as to the actual changes of the intravascular volume. When the blood is first pumped into the dialyzer, the priming fluid (saline) that fills the circuit may be either infused into the patient or disposed of to a drain bag. In the latter case, the intravascular volume is suddenly reduced, which is not accounted for by RBV monitors that track only the subsequent reductions in blood volume due to dialyzer ultrafiltration. We analyzed this general aspect of RBV monitoring using model-based simulations and showed quantitatively how RBV changes calculated using hematocrit differ depending on the priming procedure.

Hemodialysis patients with less extracellular water overload and smaller cardiac atrial chamber sizes are at greater risk of a fall in blood pressure during dialysis

Intradialytic hypotension is the most common complication of hemodialysis (HD) treatments. Excessive ultrafiltration results in reduced cardiac preload. We aimed to determine whether a fall in systolic blood pressure during HD was greater in patients starting HD with (a) less overhydration measured by extracellular water (ECW) and (b) lower cardiac preload by cardiac magnetic resonance imaging (MRI). Pre-HD measurements of ECW and total body water (TBW) were performed using multifrequency bioimpedance (MFBIA). Cardiac chamber sizes and functions were determined by MRI. Twenty-six patients, 18 males (69.2%), 11 (42.3%) with diabetes, mean age 63.9 ± 15.9 years were studied. Systolic blood pressure (SBP) fell in 15 (57.7%) patients, and either did not change or increased in 9. There was no difference in demographics between groups. Patients with a fall in SBP had lower pre-HD ECW/TBW (0.400 ± 0.018 vs 0.418 ± 0.021), indexed right ventricular end-diastolic volume (81.2 ± 37.6 vs 100.8 ± 33.7 mL/m² ), and indexed left atrial size (13.7 ± 3.9 vs 18.3 ± 5.0 mL/m² ), all P < .05, respectively. There were univariate correlations between the change in SBP and pre-HD ECW/TBW for the trunk (r = .50, P = .009) and indexed left atrial volume (r = .54, P = .005). A fall in blood pressure occurred more commonly in patients starting HD with lower overhydration as measured by bioimpedance, and those with smaller cardiac chamber sizes. Patients with the lowest ECW/TBW and smallest cardiac chamber sizes had the greatest falls in SBP. This study reinforces the importance of determining physiological target weights and avoiding inappropriately low target weights for HD patients.

Pilot Study to Detect Changes in Blood Flow in the External Auditory Meatus During Hemodialysis

Blood flow to internal organs is reported to fall during hemodialysis (HD). As such, noninvasive monitoring devices are required to detect changes in perfusion, which could then be used for therapeutic interventions. We report on a pilot study monitoring blood flow in the outer auditory meatus. We measured the maximum pulse wave amplitude and indicators of blood flow by analyzing red and green color changes in the outer auditory meatus from video recordings made using an otoscope fitted with a digital camera during HD treatments. We studied 61 patients, 43 (71.5%) male, mean age 64.9 ± 12.7 years. Weight fell from 72.8 ± 22.5 kg predialysis to 71.5 ± 22.1 kg postdialysis (P < 0.001). BP did not significantly change (predialysis 142 ± 29/67 ± 18 to 143 ± 25/68 ± 17 mm Hg postdialysis). The maximum pulse wave amplitude in the external auditory meatus fell from 0.21 (0.1-0.55) to 0.14 (0.04-0.4) after 90 min, P < 0.001, and remained low thereafter, and the change at the end of the dialysis session was associated with percentage weight loss (r = -0.37, P = 0.003). Green and red pixel values did not change (predialysis 0.339 [0.333-0.345] to 0.302 [0.291-0.33] post, and 0.301 [0.293-0.328] predialysis to 0.339 [0.334-0.347] post, respectively). This pilot study showed that the maximum pulse wave amplitude measured in the external auditory meatus fell during the dialysis session, and that the fall was associated with fluid removal. This could potentially lead to the development of a monitoring device, which could fit in the ear and record during the dialysis session.

A feedback system that combines monitoring of systolic blood pressure and relative blood volume in order to prevent hypotensive episodes during dialysis

Hypotensive Episodes (HEs) are one of the most common complications during dialysis. Occurrence of HEs can be reduced by applying physiological closed loop systems that monitor physiological parameter(s) and adjust dialysis related parameter(s). We developed a physiological closed loop control system (PCLCS) that monitors systolic blood pressure (sysBP) and relative blood volume (RBV) and calculates the net fluid removal (nfr) rate during dialysis. The performance of PCLCS was compared in the laboratory to a feedback system that monitors only RBV (BVFS). A laboratory test setup was developed to test the feedback systems. The test setup simulates nfr-rate and refilling of a patient's intravascular fluid. We studied the impact of the feedback systems PCLCS and BVFS on the number of HEs (sysBP < 90 mmHg), on the variance of sysBP and RBV, on pre to post sysBP and RBV and on the achievement of the nfr-volume. PCLCS allowed 80% less HEs than BVFS (p < 0.001). Variance of sysBP and RBV were reduced by 41.8% and by 52% (p < 0.001), respectively, when using PCLCS. There were no differences between pre to post sysBP nor between pre to post RBV when comparing PCLCS to BVFS. The nfr-volume was achieved by both feedback systems.

Pediatric intradialytic hypotension: recommendations from the Pediatric Continuous Renal Replacement Therapy (PCRRT) Workgroup

Intradialytic hypotension (IDH) is a common adverse event resulting in premature interruption of hemodialysis, and consequently, inadequate fluid and solute removal. IDH occurs in response to the reduction in blood volume during ultrafiltration and subsequent poor compensatory mechanisms due to abnormal cardiac function or autonomic or baroreceptor failure. Pediatric patients are inherently at risk for IDH due to the added difficulty of determining and attaining an accurate dry weight. While frequent blood pressure monitoring, dialysate sodium profiling, ultrafiltration-guided blood volume monitoring, dialysate cooling, hemodiafiltration, and intradialytic mannitol and midodrine have been used to prevent IDH, they have not been extensively studied in pediatric population. Lack of large-scale studies on IDH in children makes it difficult to develop evidence-based management guidelines. Here, we aim to review IDH preventative strategies in the pediatric population and outlay recommendations from the Pediatric Continuous Renal Replacement Therapy (PCRRT) Workgroup. Without strong evidence in the literature, our recommendations from the expert panel reflect expert opinion and serve as a valuable guide.

Postdialysis recovery time is extended in patients with greater self-reported depression screening questionnaire scores

INTRODUCTION

Most patients take time to recover after a hemodialysis (HD) session. It has been suggested that recovery time is associated with intradialytic hypotension and rapid solute clearances. Other studies have reported a linkage to depression. We investigated the association between recovery time and intradialytic hypotension and depression.

METHODS

In five UK HD units, we screened for depressive symptoms using the Beck depression inventory-II, Patient Health Questionnaire, and recorded sessional blood pressures and Kt/Vurea.

FINDINGS

Seven hundred and one HD patients were studied; 63.6% male, mean age 64.1 ± 16.6 years, 33.5% diabetic. About 24.1% recovered in <1 hour, 27% 1-4 hours, 15.4% 4-8 hours, 10.7% 8-12 hours, and 22.8% after 12 hours. Systolic blood pressure fell by ≥20 mmHg in 30.9% postdialysis, and to <100 mmHg in 7.6%. In multivariate analysis, patients with recovery times >1 hour were more likely to be female, have high self-reported Beck depression inventory-II scores, a past medical history of depression, and be living without a partner. Longer recovery times were also associated with very low postdialysis systolic blood pressures (<100 mmHg), and higher body weight. However, the model predicted only 18% of the variation in recovery times. We found no association between recovery times and short-term mortality risk.

DISCUSSION

Prolonged postdialysis recovery times are associated with higher self-reported depression scores, and very low postdialysis blood pressure. Future studies investigating changes in dialysis practice and recovery times will need to target strategies to prevent intradialytic hypotension and adjust for patient psychological status.

Promoting Kidney Function Recovery in Patients with AKI Requiring RRT

AKI requiring RRT is associated with high mortality, morbidity, and long-term consequences, including CKD and ESRD. Many patients never recover kidney function; in others, kidney function improves over a period of many weeks or months. Methodologic constraints of the available literature limit our understanding of the recovery process and hamper adequate intervention. Current management strategies have focused on acute care and short-term mortality, but new data indicate that long-term consequences of AKI requiring RRT are substantial. Promotion of kidney function recovery is a neglected focus of research and intervention. This lack of emphasis on recovery is illustrated by the relative paucity of research in this area and by the lack of demonstrated effective management strategies. In this article the epidemiologic implications of kidney recovery after AKI requiring RRT are discussed, the available literature and its methodologic constraints are reviewed, and strategies to improve the understanding of factors that affect kidney function recovery are proposed. Measures to promote kidney function recovery are a serious unmet need, with a great potential to improve short- and long-term patient outcomes.

Changing the hemodialysis prescription for hemodialysis patients with subdural and intracranial hemorrhage

Although continuous modalities of renal replacement therapy offer an advantage to the patient with compromised cerebral perfusion and intracranial hypertension, they are generally limited to the intensive care unit setting. Many hemodialysis patients admitted with strokes and subdural hematoma are managed on general wards. As such, these patients are generally treated by intermittent hemodialysis, and their dialysis prescription should be altered to minimize changes in serum osmolality, and fall in blood pressure during dialysis. Such patients require more frequent but shorter dialysis sessions, using minimally bioincompatible small surface area dialyzers with lower blood flows, in combination with higher sodium and cooled dialysate. In patients at risk of intracranial hemorrhage and those with invasive intracranial monitoring, systemic anticoagulants should be avoided, choosing no anticoagulation protocols or regional anticoagulants.

Hemodialysis for infants, children, and adolescents

Children with chronic kidney disease stage 5 requiring dialysis can be treated by peritoneal or hemodialysis. In the United Kingdom nearly twice as many children receive peritoneal dialysis compared with hemodialysis. Technical aspects of pediatric hemodialysis are challenging and include the relative size of extracorporeal circuit and child's blood volume, assessment of adequacy,technical and complications of vascular access. Alternatives to standard hospital-based hemodialysis are also increasingly available. Optimizing nutritional status with the support of specialist pediatric dietitians is key to the management of children receiving hemodialysis. The effects of chronic illness on growth and school achievement, as well as the psychological, emotional, and social development of the child should not be underestimated. This review focuses on the above elements and highlights common pediatric practice in the United Kingdom.

Innovative strategy with potential to increase hemodialysis efficiency and safety

Uremic toxins are mainly represented by blood urine nitrogen (BUN) and creatinine (Crea) whose removal is critically important in hemodialysis (HD) for kidney disease. Patients undergoing HD have a complex illness, resulting from: inadequate removal of organic waste, dialysis-induced oxidative stress and membrane-induced inflammation. Here we report innovative breakthroughs for efficient and safe HD by using a plasmon-induced dialysate comprising Au nanoparticles (NPs)-treated (AuNT) water that is distinguishable from conventional deionized (DI) water. The diffusion coefficient of K₃Fe(CN)₆ in saline solution can be significantly increased from 2.76, to 4.62 × 10⁻⁶ cm s⁻¹, by using AuNT water prepared under illumination by green light-emitting diodes (LED). In vitro HD experiments suggest that the treatment times for the removals of 70% BUN and Crea are reduced by 47 and 59%, respectively, using AuNT water instead of DI water in dialysate, while additionally suppressing NO release from lipopolysaccharide (LPS)-induced inflammatory cells.

Are serum to dialysate sodium gradient and segmental bioimpedance volumes associated with the fall in blood pressure with hemodialysis?

INTRODUCTION

A fall in blood pressure is the most common complication of outpatient hemodialysis. Several factors have been implicated, including serum sodium to dialysate gradient, ultrafiltration rate, and the amount of fluid to be removed during dialysis.

METHODS

We prospectively audited 400 adult patients attending for their routine midweek hemodialysis session, and recorded changes in mean arterial blood pressure (MAP).

RESULTS

Mean age 58.4 ± 16.6 years, 60.9% male, 30.7% diabetic, 36.8% Caucasoid, single pool Kt/V 1.57 ± 0.4, and median percentage change in MAP -6.7% (-14.1 to + 2.8). The percentage fall in MAP was greatest for those starting with higher MAPs (β 0.448 , F 67.5, p<0.001), greater serum sodium to dialysate sodium gradient (β 0.676, F 5.59, p = 0.019), and age (β 0.163, F 5.15, p = 0.024). In addition, the percentage fall in MAP was greater in those with the lowest segmental extracellular water/total body water (ECW/TBW) ratios in the right arm prior to dialysis (β -477.5, F 7.11, p = 0.008).

CONCLUSIONS

Falls in blood pressure are common during dialysis, and greater for those starting dialysis with the highest systolic pressures, greater dialysate to serum sodium concentration gradient, and also those with the least ECW in the arm. As such, segmental bioimpedance may be useful in highlighting patients at greatest risk for a fall in blood pressure with dialysis.