Ravindra L. Mehta

Starting and Stopping Renal Replacement Therapy in the Critically Ill

Abstract Most cases of acute kidney injury (AKI) in critical care settings are caused by effective volume depletion, sepsis syndrome, and nephrotoxicity. Although these are generally reversible processes, a significant number of patients require renal replacement therapy (RRT) to replace renal function and support other organs during the disease process. When renal replacement or renal support is required, there is a far worse prognosis than with lesser degrees of renal injury. 1 , 2 , 3 Several dialysis techniques are now available for RRT to manage AKI. Acute intermittent hemodialysis, peritoneal dialysis, and continuous techniques are the main treatment modalities. Considerable debate has ensued over the choice of modality, the amount and frequency of dialysis, and the duration of therapy in the acute setting, especially for the critically ill patients. There is a paucity of information on the criteria for initiating and stopping RRT. Timing of the intervention or the criteria used to start therapy is based on individual preferences and experience, and no set guidelines are followed. This chapter addresses the pertinent issues that should be considered for initiating and stopping RRT in the critically ill patient.

Principles of Anticoagulation in Extracorporeal Circuits

Abstract Intermittent and continuous dialysis therapies depend on adequate anticoagulation in their extracorporeal circuit (ECC) to maximize circuit and filter longevity, which will increase clearance and lessen costs and nurse time requirements. Insufficient anticoagulation results in decreased filter performance, clotting, and blood loss. Excessive anticoagulation leads to bleeding complications, which occur in 5% to 26% of treatments. Patients with acute kidney injury (AKI) are at risk for hemorrhagic and thrombotic complications. The goal of the nephrologist remains prolongation of ECC life in the safest manner possible for the patient. Use of replacement fluids in prefilter mode and avoidance of excessive ultrafiltration and blood flow reductions also can lead to improved circuit patency. Although unfractionated heparin remains the most commonly used anticoagulant, there are now an increasing number of other options; these include low-molecular-weight heparin, heparinoids, direct thrombin inhibitors, prostanoids, and serine protease inhibitors. When choosing the type of anticoagulation for renal replacement therapies in AKI, the clinician must consider several aspects, such as the half-life, how to monitor, how to reverse the effect in case of severe bleeding, if the anticoagulant is dialyzable or not, and how to balance the benefits and risk of each drug.

Community- and Hospital-Acquired Acute Kidney Injury

Abstract In population studies, the incidence of hospital-acquired acute kidney injury (AKI) has risen in the last two decades. This rise appears to be multifactorial, being due to improved survival of patients with diabetes mellitus and ischemic heart disease, a growing elderly population, and better care of high-risk surgical and intensive care patients. There is still uncertainty regarding the true incidence of community-acquired AKI in the developing world. AKI in the developed world is encountered more commonly in patients with multiple organ failure, whereas infections, toxins, and obstetric complications are the main causes of AKI in the developing world.

Components of Fluid Balance and Monitoring

Abstract Fluid administration is frequently used in hospitalized patients. The most common reasons for fluid administration include hypotension, shock, sepsis, hypovolemia, replacement of fluid losses, and oliguria. Prompt resuscitation of patients with hypoperfusion with intravenous fluids has been shown to improve outcomes. However, approximately 50% of hemodynamically unstable patients will respond to fluid administration. For many clinicians, the current approach to fluid resuscitation focuses on blood pressure and cardiac output (CO). Bedside echocardiographic assessment also can be useful. If a patient responds to a fluid challenge of 250u202fmL by a 10% to 15% increase in stroke volume (SV) or CO, further fluids can be given as long as there is a positive response. This approach allows avoiding excessive fluid administration, which has been associated with worse cardiopulmonary and kidney outcomes, delayed wound healing, and decreased survival. Therefore, even if an initial fluid resuscitation is required, subsequent approaches aiming for neutral and negative fluid balance can be required, including conservative fluid administration, diuretics, and/or dialysis. In conclusion, fluid therapy in critically ill patients is a dynamic process. Individual assessment of fluid requirements and timing of fluid administration are needed, as well as frequent reassessment of response and ongoing needs. Studies are required to assess the benefits of conservative, hemodynamically guided fluid resuscitation strategy and early use of vasopressors, as well as to optimize techniques to manage fluid overload. In this chapter, we review physiologic aspects related to fluid status, the four phases of fluid resuscitation, and assessment of fluid volume, fluid responsiveness, and fluid overload. We also summarize the pathogenesis of fluid overload and its association with adverse outcomes and comment on practical issues regarding fluid administration, removal, and monitoring.

Indications for Continuous Renal Replacement Therapy: Renal Replacement Versus Renal Support

Abstract Continuous renal replacement therapy (CRRT) is a key component of management of critically ill patients with acute kidney injury (AKI). In current practice, the decision to dialyze is based most often on clinical features of volume overload and biochemical features of solute imbalance. Nevertheless, in the context of AKI, appropriate timing has not been defined, and what constitutes “early” versus “late” initiation has not been established. The question of when to select CRRT over other types of renal replacement therapy (RRT) in critically ill patients with AKI is still a matter of passionate debate among nephrologists. In current clinical practice, modality selection is driven by the availability of treatment, local expertise, and patient characteristics. Although there is usually no hesitation in offering RRT in the presence of life-threatening situations, there is also a tendency to avoid RRT as long as possible. In AKI, classic or renal indications for RRT include severe acidemia, fluid overload with oliguria that does not respond to the use of diuretics, hyperkalemia, or signs of uremia, which in turn also could be related to the concept of “late” dialysis. The approach of waiting for AKI complications may delay dialysis initiation. Nonrenal indications focus on removing various dialyzable substances from the blood such as cytokines in a patient with sepsis, some of these “nonrenal” indications could be related to the concept of “early” dialysis. We favor a strategy to avoid uremic, acid-base electrolytes and volume overload complications, considering RRT as renal support, instead of renal replacement, and aiming to maintain normal acid-base, electrolyte, and fluid status. In this chapter we discuss the traditional or classic indications for RRT, the concept of renal support, and if it could potentially modify outcomes.