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Beginning and Ending Continuous Renal Replacement Therapy in the Intensive Care Unit


Objectives

This chapter will:

  • 1.

    Discuss the definitions of early versus delayed initiation of continuous renal replacement therapy.

  • 2.

    Discuss the rationale of early versus delayed initiation of continuous renal replacement therapy.

  • 3.

    Present the evidence for the timing of initiation of continuous renal replacement therapy, including data from recent randomized trials.

  • 4.

    Present the evidence for the ending of continuous renal replacement therapy and clinical decision tools for the successful weaning from continuous renal replacement therapy.

Acute kidney injury (AKI) is a common and increasingly common complication of critical illness, occurring in approximately two thirds of patients admitted to the intensive care unit (ICU). In an estimated 8% to 10% of critically ill patients, more severe AKI occurs and renal replacement therapy (RRT) is necessary. The use of RRT has increased steadily; recent data suggest use has grown by more than 10% per year over the last decade. Continuous renal replacement therapy (CRRT) is the most common initial modality prescribed in ICU settings.

The timing of initiation of CRRT for critically ill patients remains uncertain. Identifying the ideal circumstances for when to initiate CRRT remains an important unachieved goal and is currently a high research priority in the field of critical care nephrology. Among patients faced with life-threatening complications of AKI, such as severe hyperkalemia, marked metabolic acidosis, uremia, and/or fluid overload, the decision to urgently start CRRT is generally unequivocal. However, the occurrence of life-threatening complications attributable to AKI have become less commonly triggers for starting CRRT in ICU settings. Indeed, in the absence of overt or impending life-threatening complications, the optimal time to start CRRT is unknown. Similarly, few studies have evaluated the optimal circumstances for when and how to wean patients from CRRT or discontinue therapy. Not surprisingly, given this knowledge gap, there is wide variation in clinical practice for the timing for starting and discontinuation of CRRT. This practice heterogeneity, driven partly by gaps in evidence to guide practice, contributes to suboptimal quality of care.

Defining the Timing of Initiation of Continuous Renal Replacement Therapy

There is currently no consensus on when optimally to start CRRT or on how to define timing of initiation of CRRT. Studies evaluating the timing of starting CRRT have used a broad range of definitions for terms such as “early,” “accelerated,” “delayed,” “late,” and “standard” initiation of CRRT. In addition, studies have been characterized by variable designs and methodologic quality. The terms “early” and “late” should be recognized as relative. For example, what may represent “early” CRRT for a given clinical context for one patient may be “late” for another, characterized by different clinical features, case-mix, and illness severity. Timing definitions have integrated physiologic parameters (e.g., urine output), biochemical parameters (e.g., serum creatinine, urea, kidney damage biomarkers), time relative to diagnosis of AKI (also variably defined), time relative to hospital or ICU admission, and time relative to the development of a complication related to AKI or “conventional” indications for starting CRRT, such as hyperkalemia, acidosis, or fluid overload. Importantly, the majority of studies evaluating the timing of CRRT in AKI consider comparison of patients with AKI who did not receive CRRT. It is plausible that a conservative strategy consisting of supportive management and initiation of CRRT in response to development of conventional indications would result in some patients with severe AKI recovering kidney function without need for CRRT. Indeed, this was shown recently in a Canadian multicenter pilot RCT, in which 25% of patients randomized to a conservative strategy of standard initiation of RRT recovered kidney function without receiving RRT, and in a French multicenter randomized controlled trial (RCT), in which 49% of patients randomized to a conservative strategy of standard initiation of RRT did not receive RRT.

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