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      Osmolality and blood pressure stability during hemodialysis

      1 , 2 , 3
      Seminars in Dialysis
      Wiley

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          Abstract

          <p class="first" id="P1">Homeostatic regulation of plasma osmolality (POsm) is critical for normal cellular function in humans. Arginine vasopressin (AVP) is the major hormone responsible for the maintenance of POsm and acts to promote renal water retention in conditions of increased POsm. However, AVP also exerts pressor effects, and its release can be stimulated by the development of effective arterial blood volume depletion. Patients with end-stage renal disease on hemodialysis, particularly those with minimal or no residual renal function, have impaired ability to regulate water retention in response to AVP. While hemodialysis can assist with this task, patients are subject to relatively rapid shifts in volume and electrolytes during the procedure. This can result in the development of transient osmotic gradients that lead to the movement of water from the extracellular to the intracellular space. Hypotension may result – both as a consequence of water movement out of the intravascular compartment, but also from impaired AVP release and inadequate vascular tone. In this review we explore the evidence for POsm changes during hemodialysis, associations with adverse outcomes, and methods to minimize the rapidity of changes in POsm in an effort to reduce patient symptoms and minimize intra-dialytic hypotension. </p>

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          Vasopressin: mechanisms of action on the vasculature in health and in septic shock.

          Vasopressin is essential for cardiovascular homeostasis, acting via the kidney to regulate water resorption, on the vasculature to regulate smooth muscle tone, and as a central neurotransmitter, modulating brainstem autonomic function. Although it is released in response to stress or shock states, a relative deficiency of vasopressin has been found in prolonged vasodilatory shock, such as is seen in severe sepsis. In this circumstance, exogenous vasopressin has marked vasopressor effects, even at doses that would not affect blood pressure in healthy individuals. These two findings provide the rationale for the use of vasopressin in the treatment of septic shock. However, despite considerable research attention, the mechanisms for vasopressin deficiency and hypersensitivity in vasodilatory shock remain unclear. To summarize vasopressin's synthesis, physiologic roles, and regulation and then review the literature describing its vascular receptors and downstream signaling pathways. A discussion of potential mechanisms underlying vasopressin hypersensitivity in septic shock follows, with reference to relevant clinical, in vivo, and in vitro experimental evidence. Search of the PubMed database (keywords: vasopressin and receptors and/or sepsis or septic shock) for articles published in English before May 2006 and manual review of article bibliographies. The pathophysiologic mechanism underlying vasopressin hypersensitivity in septic shock is probably multifactorial. It is doubtful that this phenomenon is merely the consequence of replacing a deficiency. Changes in vascular receptors or their signaling and/or interactions between vasopressin, nitric oxide, and adenosine triphosphate-dependent potassium channels are likely to be relevant. Further translational research is required to improve our understanding and direct appropriate educated clinical use of vasopressin.
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            Blood volume controlled hemodialysis in hypotension-prone patients: a randomized, multicenter controlled trial.

            Recently we have devised and tested a biofeedback system for controlling blood volume (BV) changes during hemodialysis (HD) along an ideal trajectory (blood volume tracking, BVT), continuously modifying the weight loss rate and dialysate conductivity. This multicenter, prospective, randomized, crossover study aimed to clarify whether BVT (treatment B) can improve hypotension-prone patients' treatment tolerance, compared with conventional hemodialysis (treatment A). Thirty-six hypotension-prone patients enrolled from 10 hemodialysis (HD) centers were randomly assigned to either of the study sequences ABAB or BABA, each lasting four months. A 30% reduction in intradialytic hypotension (IDH) events was observed in treatment B as compared with A (23.5% vs. 33.5%, P = 0.004). The reduction was related to the number of IDH in treatment A (y = 0.54x + 5; r = 0.4; P < 0.001): the more IDH episodes in treatment A, the better the response in treatment B. The best responders to treatment B showed pre-dialysis systolic blood pressure values higher than the poor responders (P = 0.04). A 10% overall reduction in inter-dialysis symptoms was obtained also in treatment B compared to A (P < 0.001). Body weight gain, pre-dialysis blood pressure, intradialytic weight loss as well as Kt/V did not differ between the two treatments. An overall improvement in the treatment tolerance was observed with BVT, particularly intradialytic cardiovascular stability. Patients with the highest incidence of IDH during conventional HD and free from chronic pre-dialysis hypotension seem to respond better. Inter-dialysis symptoms also seem to improve with control of BV.
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              Improving Clinical Outcomes Among Hemodialysis Patients: A Proposal for a “Volume First” Approach From the Chief Medical Officers of US Dialysis Providers

              Addressing fluid intake and volume control requires alignment and coordination of patients, providers, dialysis facilities, and payers, potentially necessitating a "Volume First" approach. This article reports the consensus opinions achieved at the March 2013 symposium of the Chief Medical Officers of 14 of the largest dialysis providers in the United States. These opinions are based on broad experience among participants, but often reinforced by only observational and frequently retrospective studies, highlighting the lack of high-quality clinical trials in nephrology. Given the high morbidity and mortality rates among dialysis patients and the absence of sufficient trial data to guide most aspects of hemodialysis therapy, participants believed that immediate attempts to improve care based on quality improvement initiatives, physiologic principles, and clinical experiences are warranted until such time as rigorous clinical trial data become available. The following overarching consensus opinions emerged. (1) Extracellular fluid status should be a component of sufficient dialysis, such that approaching normalization of extracellular fluid volume should be a primary goal of dialysis care. (2) Fluid removal should be gradual and dialysis treatment duration should not routinely be less than 4 hours without justification based on individual patient factors. (3) Intradialytic sodium loading should be avoided by incorporating dialysate sodium concentrations set routinely in the range of 134-138 mEq/L, avoidance of routine use of sodium modeling, and avoidance of hypertonic saline solution. (4) Dietary counseling should emphasize sodium avoidance.
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                Author and article information

                Journal
                Seminars in Dialysis
                Semin Dial
                Wiley
                08940959
                November 2017
                November 2017
                July 09 2017
                : 30
                : 6
                : 509-517
                Affiliations
                [1 ]University College Dublin School of Medicine and Medical Science; Dublin Ireland
                [2 ]Renal Division; Department of Medicine; Brigham and Women's Hospital; Boston MA USA
                [3 ]Harvard Medical School; Boston MA USA
                Article
                10.1111/sdi.12629
                5931915
                28691402
                acb195d3-b4fa-4497-b68c-65e588a9e288
                © 2017

                http://doi.wiley.com/10.1002/tdm_license_1.1

                http://onlinelibrary.wiley.com/termsAndConditions#vor

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