Critical care dialysis--a Gordian knot (but is untying the right approach?).

Will manipulations of dialytic therapy have any real Dialysis support for the critically-ill patient with acute effect on the devastatingly poor outcome of the renal failure (ARF) is now under scrutiny [1], but condition? despite the increasing attention many crucial questions The consistently high mortality of ICU ARF over remain unanswered. In this article, we examine some the years hides the worsening face of the patient of the reasons for these ambiguities and discuss potenpopulation [10], suggesting that we are gaining ground tial solutions. overall. Although the kidney is usually but one of several failing organs in this setting, ARF contributes disproportionately to mortality [11,12] and leads to an The problems increased risk of developing ‘non-renal’ complications such as bleeding and sepsis [11]. Of encouragement is The ESRF–ARF interface the finding that increasing membrane biocompatibility significantly improves rates of renal recovery [13] and Certain well-defined standards of dialysis support for reduces rates of lethal sepsis [14], highlighting the the patient with end-stage renal failure (ESRF) have potential impact of dialytic manipulations. Van become basic tenets of nephrological practice [2]. Any Bommel and co-workers found the ratio of APACHE suggestion of establishing similar standards in critical II at the time of dialysis initiation to that at ICU care dialysis is obviously premature, but can we generadmission (AP2/AP1) to be highly predictive of death, alize from our experience in ESRF? suggesting that irreversible derangements prior to diaUnfortunately, a number of crucial factors within lysis initiation were still (probably most) important the two, quite distinct populations, make extrapola[15]. Whether these derangements were a consequence tions problematic. of ARF or its precursors is not clear but Levy’s work Firstly, the pace of change in the intensive care unit [11] would point towards the first mechanism. (ICU ) ARF population is very different; critical endpoints are reached in days-to-weeks as opposed to the attrition that we are used to of months-to-years in Choice of modality ESRF patients, so dialysis efficacy will have to be Intuitively, continuous renal replacement therapy judged within a very much shorter time-frame. (CRRT ) is seen as the modality of choice, with sugSecondly, those end-points that concern us may be gested advantages including haemodynamic stability quite different in the two groups—renal recovery and (enhancing fluid removal and hyperalimentation), length of ICU stay [3] as opposed to hypertensive improved dialysis dose delivery, enhanced removal of control [4], for instance. Lastly, the negligible impact inflammatory mediators and an improvement in overall of G, the urea generation rate, and the predictability outcome. Recent experience [16,17], however, warns of urea the volume of distribution of urea, are assumpagainst taking for granted these perceived notions of tions made to implement formal urea kinetic modelling therapeutic superiority in the absence of a good, evid(UKM) in ESRF [5]. Clearly, this may not be the ence base. case in critically ill ARF patients with the potential We will examine each of these potential advantages for marked hypercatabolism [6–8] and large variations in turn but it is worth noting that in Jakob’s extensive in Vurea [9], with major implications when considering review [18] of all 67 published studies dealing with delivered dialysis dose (see later). CRRT that were available to them at that time (1996), only 15 were comparative. In only three of these Correspondence and offprint requests to: Dr N. S. Kanagasundaram, [19–21] were both modality groups studied prospectSection of Dialysis and Extracorporeal Therapy, M82, Cleveland Clinic Foundation, 9500, Euclid Avenue, Cleveland, OH 44195, USA. ively and none had complete randomization. Small