Probing 'dry weight' in haemodialysis patients: 'back to the future'.

In the early 1960s, correcting fluid overload and hypertension were already a priority target assigned to haemodialysis treatment adequacy by the Scribner’s group [1, 2]. In the early days of renal replacement therapy, antihypertensive drugs were scarce and the control of extracellular fluid volume by sodium depletion was the only efficient tool for controlling severe and/or accelerated hypertension in end-stage renal disease patients [3]. The concept of volume-dependent hypertension elaborated by the Seattle’s group led to a very practical issue summarized in the ‘dry weight’ achievement [4]. In its basic definition, the dry weight is clinically established and usually reflects the lowest post-dialytic weight that a patient can tolerate without intra-dialytic symptoms and hypotension in the absence of fluid overload while achieving a near normal arterial pressure. Over time, the beneficial effects of adhering to a tight and regular control of the dry weight have been largely proved and considered as a crucial adequacy target for haemodialysis patients [5]. The leading nephrologists of Tassin trained at the Seattle school have kept this important message in mind and transformed this simple concept into a ‘doctrine’ group for their daily clinical practice [6]. In keeping with this concept, dialysis treatment schedules were customized to specific patient needs and to haemodynamic tolerance and then justifying the regular use of long slow dialysis treatment programmes (6–8 h thrice weekly). This old-fashioned haemodialysis modality was also accompanied by a strict salt-restricted diet and the use of a low dialysate sodium concentration. Based on this simple and pragmatic policy, the Tassin group has clearly proved that the regular correction and strict control of fluid volume by dialysis were able to control adequately the arterial pressure in the vast majority of dialysis patients (>80%) without requiring the use of anti-hypertensive drugs. In addition, the same group showed that a tight control of dry weight over a long period of time was associated with a significant reduction in the risk of cardiovascular mortality [5]. Several other studies found the association between chronic fluid overload and higher risks of all-cause and cardiovascular mortalities in haemodialysis patients [7, 8]. It is now well recognized that fluid and sodium homeostasis might be restored in dialysis patients, by lengthening the dialysis treatment time and/or by customizing dialysis treatment programmes (more frequent dialysis sessions, longer treatment time, isolated and/or adjunctive ultrafiltration, blood volume control, etc.) [9, 10]. Furthermore, the correction of the fluid overload has several beneficial effects on the long-term outcomes: it facilitates arterial pressure control; it minimizes the use of anti-hypertensive drugs; it reduces the left ventricular volume and left ventricular mass; it reduces the microinflammation [11] and it improves patient survival [12, 13]. This is why assessing and probing the dry weight should remain a priority objective in the quest for treatment adequacy. In contrast to this physiological approach and customized renal replacement therapy, in the 1970s and 1980s, a different model of haemodialysis has been developed based on short and highly efficient dialysis, easily integrated into the patient’s daily life, more productive and profitable but no longer meeting the individual needs [14, 15]. Interestingly, ultrashort treatment schedules ( 3 h thrice weekly) assessed in the 1980s in order to push back the barriers of treatment time have failed to achieve fluid volume control [16]. All these facts tend to prove that sodium and fluid volume removal are related to patient haemodynamic tolerance and compliance to a low-salt diet and are more easily achieved with a weekly longer treatment time [17]. Today, for economical and practical reasons, short haemodialysis treatment schedules based on 4-h thrice-weekly sessions still represent the most common form of haemodialysis worldwide. In addition, to comply with societal changes and patient requests, the medical prescription to dialysed patients has become more liberal, the dietary salt restriction has been neglected, anti-hypertensive drugs have been used more frequently than the older and the strict compliance to dry weight has been forgotten. Such differences in dialysis practices are clearly shown in large observational studies [18]. For example, comparison of a large amount of registry data shows that the use of anti-hypertensive drugs varies from 20 to 90% of patients according to the countries or dialysis facilities [19]. In addition, the extensive use of anti-hypertensive drugs is frequently supported by fallacious arguments claiming that these drugs have some specific cardioprotective effects. In this perspective, it is interesting to note that some cohort studies have reported some beneficial effects of agents acting on the renin–angiotensin axis (beta-blockers or angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers) but