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Continuous kidney replacement therapy in acute kidney injury

Continuous kidney replacement therapy in acute kidney injury
Literature review current through: Jan 2024.
This topic last updated: Aug 29, 2023.

INTRODUCTION — Kidney replacement therapy (KRT) is commonly required in patients with severe acute kidney injury (AKI). Acute KRTs include intermittent hemodialysis, peritoneal dialysis, continuous kidney replacement therapies (CKRTs), and hybrid therapies such as prolonged intermittent kidney replacement therapies (PIKRTs), which provide prolonged but still intermittent dialysis.

This topic provides an overview of CKRT modalities. Acute intermittent hemodialysis, peritoneal dialysis, and PIKRT are discussed elsewhere:

(See "Acute hemodialysis prescription".)

(See "Use of peritoneal dialysis (PD) for the treatment of acute kidney injury (AKI) in adults".)

(See "Kidney replacement therapy (dialysis) in acute kidney injury in adults: Indications, timing, and dialysis dose".)

(See "Prolonged intermittent kidney replacement therapy".)

INDICATIONS — Indications to perform KRT in AKI are the same for all modalities, but the choice of modality might differ. Specific indications include fluid overload, hyperkalemia, acidosis, and signs of uremia. Indications are discussed elsewhere. (See "Kidney replacement therapy (dialysis) in acute kidney injury in adults: Indications, timing, and dialysis dose".)

In most institutions, intermittent hemodialysis is the standard KRT modality for hemodynamically stable patients [1]. Based on clinical practice patterns, the major indication for choosing CKRT over intermittent hemodialysis is hemodynamic instability. Hypotension is widely believed to be less common with CKRT (although can still occur) because the rates of fluid and solute removal are slower than with intermittent hemodialysis [2-5]. However, randomized trials have not proven that there is improved hemodynamic stability and/or survival among patients treated with CKRT compared with intermittent hemodialysis [6-11]. In addition, the optimal strategy for excess fluid removal in critically ill patients has not been established [12].

CKRT is particularly beneficial for hemodynamically unstable patients who require ongoing, large-volume fluid administration, such as multiple intravenous medications, or total parenteral nutrition. Because CKRT is a continuous therapy, the net solute removal over 48 hours is higher than with intermittent hemodialysis, despite the lower rate.

In many centers, CKRT is preferred to intermittent hemodialysis for patients with acute brain injury or other causes of increased intracranial pressure who have AKI [1,13]. This is because intermittent hemodialysis is more likely to worsen cerebral edema via a decrease in mean arterial pressure (which causes compensatory cerebral vasodilation) and via a rapid removal of urea resulting in a shift of water to the intracellular space. Other special conditions where CKRTs may be preferred include sepsis, burns because of continuous skin fluid losses, heart failure, and liver failure [14]. CKRT may be more practical for treating certain drug toxicities where the agent is dialyzable but slowly transports to the plasma water compartment.

Intermittent hemodialysis rather than CKRT may be better for the treatment of patients with severe hyperkalemia (ie, electrocardiogram [ECG] changes, such as worsening peaked T-waves or QRS prolongation, that are refractory to calcium supplementation), even if the patient requires vasopressors during the treatment. Even with using the highest effluent rates possible with the CKRT, bulk potassium removal with standard intermittent hemodialysis or prolonged intermittent kidney replacement therapy (PIKRT) is much more efficient on a minute-to-minute basis. This requires clinical judgment and often depends on multiple other variables including the availability of dialysis nursing staff.

DEFINITION OF CKRT MODALITY — There are multiple CKRT modalities that differ from each other primarily according to the mechanism of solute transport. In KRTs, solutes are removed by diffusion and/or convection. Diffusion is the primary mechanism that underlies standard hemodialysis, although some convection does occur. Diffusion is driven by solute concentration differences between blood and dialysate. Convection is operative in hemofiltration and is the movement of solute within fluid down a hydrostatic pressure gradient.

No specific CKRT modality has been shown to provide better outcomes. In most cases, the choice of CKRT modality within individual institutions depends on equipment and staff availability and the expertise of the clinician. In some settings, the technique depends on the degree to which solutes and/or fluid must be removed. As an example, slow continuous ultrafiltration is used exclusively to remove fluid but is not useful for patients who require solute removal.

All modalities for CKRT used today utilize venovenous circuits with blood flow through the dialyzer/hemofilter driven by an extracorporeal blood pump (figure 1). All require placement of a dual-lumen intravenous hemodialysis catheter.

Arteriovenous modalities, in which blood flow was driven by the gradient between the mean arterial pressure (MAP) and venous pressure, are no longer used because of risks associated with the need for arterial access (embolization, bleeding). The only advantage to arteriovenous modalities was that they did not require a blood pump.

Commonly used modalities are discussed here.

Continuous venovenous hemofiltration (CVVH) — CVVH uses hydrostatic pressure to induce the filtration of plasma water across the hemofilter membrane. Solutes are removed entirely by convection. Dialysate fluid is not used.

The ultrafiltration flow rate is high (20 to 25 mL/kg/hour) [13]. As a result, replacement fluid must be given to prevent volume depletion. The amount of replacement fluid that is given is determined by the net volume removal that is desired.

Small- and middle-molecular-weight molecules (ie, <5000 Daltons), such as urea and electrolytes, are removed in roughly the same concentration as plasma water. There is therefore no change in the plasma concentrations of these solutes by hemofiltration. However, the administration of substitution fluid lowers by dilution the plasma concentrations of solutes such as urea and creatinine that are not present in the substitution fluid.

The removal of urea (and probably other small, lipid-soluble solutes) may also be increased by administering the replacement fluid before the hemofilter; this predilution lowers the plasma urea concentration, thereby allowing urea to diffuse from within red cells into the plasma water [15,16].

Continuous venovenous hemodialysis (CVVHD) — CVVHD primarily removes solute by diffusion. Dialysate fluid is used. As in intermittent hemodialysis, dialysate fluid is run countercurrent to the direction of blood flow at a rate of 1 to 2 L/hour.

By contrast to CVVH, the ultrafiltration rate is generally only 2 to 8 mL/min [13].

The dialysate flow rate is 20 to 25 mL/kg/hour.

In CVVHD, ultrafiltration is limited to the rate at which net fluid removal is desired, and no intravenous fluid replacement is required.

Continuous venovenous hemodiafiltration (CVVHDF) — CVVHDF combines diffusion with convection.

CVVHDF requires infusions of both replacement fluid and dialysis fluid. Similar to CVVH, the ultrafiltration volume is variable, and replacement fluid must be given to maintain euvolemia. The amount of replacement fluid that is given is determined by the net volume removal that is desired.

Slow continuous ultrafiltration (SCUF) — SCUF is used to treat isolated fluid overload. SCUF is not useful in patients who are uremic or hyperkalemic, because solute removal is minimal. SCUF can safely remove up to 8 L of fluid per day. Neither replacement fluid nor dialysate fluid is used.

Convective solute loss is limited since the ultrafiltration rate is low compared with CVVH. There is no diffusive solute loss since dialysate fluid is not used.

The blood flow is generally 100 to 200 mL/min and the ultrafiltration rate 2 to 8 mL/min.

VASCULAR ACCESS — CKRT requires reliable vascular access capable of blood flows of at least 200 to 250 mL/min. The standard is a double-lumen tunneled or nontunneled dialysis catheter. (See "Central venous catheters for acute and chronic hemodialysis access and their management".)

Among end-stage kidney disease patients who have arteriovenous fistulas (AVFs) or arteriovenous grafts (AVGs) for maintenance hemodialysis, the fistulas or grafts should not be used for CKRT unless no other access is possible, because of the risks of dislodging the needle and causing bleeding or injury to the AVF or AVG [13].

The preferred catheter access site is the right internal jugular vein, although the femoral vein may be used, if necessary. The subclavian vein should be avoided, if possible, as subclavian catheters have been associated with stenosis of the subclavian vessel, which may prevent placement of future AVFs or AVGs. (See "Central venous catheters for acute and chronic hemodialysis access and their management", section on 'Access site'.)

EQUIPMENT — There are multiple integrated CKRT systems available [17]. Their basic components are similar:

Blood flow and dialysate inflow and outflow are controlled by roller pumps.

Balancing systems provide ultrafiltration control.

Dialysate inflow and outflow are continuously measured and the pump speeds adjusted to maintain the desired flow rates. Using this microprocessor-driven control, ultrafiltration rates can be maintained with high precision.

Many newer machines can be used for all CKRT techniques, although some cannot perform continuous venovenous hemodiafiltration (CVVHDF) [17].

PRESCRIPTION OF CKRT — The prescription of CKRT and parameters for anticoagulation are discussed elsewhere [18]. (See "Prescription of continuous kidney replacement therapy in acute kidney injury in adults", section on 'CKRT Prescription' and "Anticoagulation for continuous kidney replacement therapy".)

DRUG DOSING IN CKRT — The rate at which drugs are removed by CKRT is affected by multiple patient and drug-related variables and by the CKRT modality and prescription. Drug dosing in CKRT is discussed elsewhere. (See "Drug removal in continuous kidney replacement therapy".)

LABORATORY MONITORING — Laboratory abnormalities are common in patients undergoing CKRT, and laboratory values are carefully monitored. The laboratory values and optimal frequency of monitoring are discussed elsewhere. (See "Prescription of continuous kidney replacement therapy in acute kidney injury in adults", section on 'Laboratory monitoring'.)

STOPPING CKRT OR TRANSITIONING TO INTERMITTENT HEMODIALYSIS — There is no standard approach to stopping CKRT. Patients are often transitioned to hemodialysis once they are sufficiently hemodynamically stable and increased mobility is desired.

Alternatively, CKRT may be discontinued when there is sufficient recovery of kidney function [19,20]. This issue is discussed elsewhere. (See "Acute hemodialysis prescription", section on 'Management during recovery of kidney function'.)

COMPLICATIONS OF CKRT — Complications of CKRT are generally the same among CKRT modalities. Complications include electrolyte, mineral, and acid-base imbalances; hypotension; infection; bleeding; and hypothermia [13]. These are discussed elsewhere. (See "Prescription of continuous kidney replacement therapy in acute kidney injury in adults", section on 'Complications'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Acute kidney injury in adults".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

Basics topic (see "Patient education: Acute kidney injury (The Basics)")

SUMMARY AND RECOMMENDATIONS

Indications for continuous kidney replacement therapy (CKRT) – Based on clinical practice patterns, the major indication for choosing CKRT over intermittent hemodialysis is hemodynamic instability. However, randomized trials have not proven that CKRT causes less hypotension than intermittent hemodialysis. (See 'Indications' above.)

CKRT modalities – CKRT modalities include continuous venovenous hemofiltration (CVVH), continuous venovenous hemodialysis (CVVHD), and continuous venovenous hemodiafiltration (CVVHDF). The major difference among modalities is the underlying mechanism that drives solute removal. (See 'Definition of CKRT modality' above.)

Choice of CKRT modality – The choice of CKRT modality depends on availability and the expertise of the clinician. All modalities utilize venovenous circuits with blood flow through the dialyzer/hemofilter driven by an extracorporeal blood pump. Arteriovenous modalities, in which blood flow was driven by the gradient between the mean arterial pressure (MAP) and venous pressure, are no longer routinely used because of risks associated with the need for arterial access (embolization, bleeding). (See 'Definition of CKRT modality' above.)

Vascular access for CKRT – CKRT requires reliable vascular access capable of blood flows of at least 200 to 250 mL/min. The standard is a double-lumen tunneled or nontunneled dialysis catheter. Among end-stage kidney disease patients who have arteriovenous fistulas (AVFs) or arteriovenous grafts (AVGs) for maintenance hemodialysis, we suggest that the AVF or AVG not be used for CKRT unless no other access is possible (Grade 2C). There is a risk of dislodging a needle causing bleeding or injury to the AVF or AVG. (See 'Vascular access' above.)

Complications of CKRT – Complications of CKRT include hypotension, infection, bleeding, and hypothermia. Common laboratory abnormalities include hypophosphatemia, hypokalemia, hypomagnesemia, and, depending on the method of anticoagulation, hypocalcemia. (See 'Complications of CKRT' above.)

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  2. Golper TA. Indications, technical considerations, and strategies for renal replacement therapy in the intensive care unit. J Intensive Care Med 1992; 7:310.
  3. Forni LG, Hilton PJ. Continuous hemofiltration in the treatment of acute renal failure. N Engl J Med 1997; 336:1303.
  4. Ronco C. Continuous renal replacement therapies for the treatment of acute renal failure in intensive care patients. Clin Nephrol 1993; 40:187.
  5. Manns M, Sigler MH, Teehan BP. Continuous renal replacement therapies: an update. Am J Kidney Dis 1998; 32:185.
  6. Vinsonneau C, Camus C, Combes A, et al. Continuous venovenous haemodiafiltration versus intermittent haemodialysis for acute renal failure in patients with multiple-organ dysfunction syndrome: a multicentre randomised trial. Lancet 2006; 368:379.
  7. Bagshaw SM, Berthiaume LR, Delaney A, Bellomo R. Continuous versus intermittent renal replacement therapy for critically ill patients with acute kidney injury: a meta-analysis. Crit Care Med 2008; 36:610.
  8. Pannu N, Klarenbach S, Wiebe N, et al. Renal replacement therapy in patients with acute renal failure: a systematic review. JAMA 2008; 299:793.
  9. Augustine JJ, Sandy D, Seifert TH, Paganini EP. A randomized controlled trial comparing intermittent with continuous dialysis in patients with ARF. Am J Kidney Dis 2004; 44:1000.
  10. Mehta RL, McDonald B, Gabbai FB, et al. A randomized clinical trial of continuous versus intermittent dialysis for acute renal failure. Kidney Int 2001; 60:1154.
  11. Nash DM, Przech S, Wald R, O'Reilly D. Systematic review and meta-analysis of renal replacement therapy modalities for acute kidney injury in the intensive care unit. J Crit Care 2017; 41:138.
  12. Murugan R, Bellomo R, Palevsky PM, Kellum JA. Ultrafiltration in critically ill patients treated with kidney replacement therapy. Nat Rev Nephrol 2021; 17:262.
  13. Macedo E, Mehta RL. Continuous Dialysis Therapies: Core Curriculum 2016. Am J Kidney Dis 2016; 68:645.
  14. Davenport A, Honore PM. Continuous renal replacement therapy under special conditions like sepsis, burn, cardiac failure, neurotrauma, and liver failure. Semin Dial 2021; 34:457.
  15. Kaplan AA. Predilution versus postdilution for continuous arteriovenous hemofiltration. Trans Am Soc Artif Intern Organs 1985; 31:28.
  16. Kaplan AA. Clinical trials with predilution and vacuum suction: enhancing the efficiency of the CAVH treatment. ASAIO Trans 1986; 32:49.
  17. Ronco C. Evolution of Technology for Continuous Renal Replacement Therapy: Forty Years of Improvements. Contrib Nephrol 2017; 189:114.
  18. Verma S, Palevsky PM. Prescribing Continuous Kidney Replacement Therapy in Acute Kidney Injury: A Narrative Review. Kidney Med 2021; 3:827.
  19. Wang L, Li J, Sun S, et al. Predictors of successful discontinuation from renal replacement therapy during AKI: A meta-analysis. Semin Dial 2021; 34:137.
  20. Gautam SC, Srialluri N, Jaar BG. Strategies for Continuous Renal Replacement Therapy De-escalation. Kidney360 2021; 2:1166.
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