4 Dialysis in Acute Kidney Injury

Purpose of dialysis in acute kidney injury

Dialysis, also called renal replacement therapy (RRT), temporarily supports kidney function by removing selected waste products and excess fluid and correcting electrolyte and acid–base disturbances. It does not directly repair injured kidneys, so treatment of the underlying cause and correction of reversible problems continue alongside dialysis.

For acute kidney injury (AKI), continue RRT only while it is needed. Stop when kidney function adequately meets the patient’s needs or when treatment no longer fits the goals of care.

When to start renal replacement therapy

Start RRT urgently for life-threatening fluid, electrolyte, or acid–base disturbances. The memory aid AEIOU summarizes common indications:

• Acidosis: severe metabolic acidosis that persists despite appropriate medical treatment.

• Electrolytes: especially severe or refractory hyperkalemia; dangerous abnormalities may recur despite temporary medical measures.

• Intoxications: selected poisonings involving dialyzable substances. The decision depends on the substance, the patient’s clinical condition, and toxicology guidance.

• Overload: fluid overload causing pulmonary edema or other serious effects that does not respond adequately to medical management.

• Uremia: complications attributable to uremia, such as encephalopathy, pericarditis, or bleeding.

Oliguria or anuria, rising laboratory values, and increasing fluid requirements may contribute to the decision. However, no single blood urea nitrogen (BUN) or creatinine value is a universal trigger. Consider symptoms, laboratory trends, fluid balance, the overall clinical condition, and whether RRT can address the problem.

For example, persistent severe hyperkalemia despite medical treatment is a potentially life-threatening concern and an urgent indication to consider RRT. Pulmonary edema despite appropriate medical management represents refractory fluid overload; fluid removal may be needed, with a goal the patient can tolerate. A high creatinine alone does not mean dialysis must begin.

Choosing a dialysis modality

No modality is best for every patient. Choose according to hemodynamic stability, the urgency and type of problem, access, bleeding risk, patient factors, and local expertise and resources. Intermittent hemodialysis (IHD) can be advantageous when rapid solute removal is needed, while continuous renal replacement therapy (CRRT) offers more gradual control of fluid balance. Modalities may be changed as the patient’s condition changes.

Intermittent hemodialysis

Blood passes through an extracorporeal filter for a limited session. IHD clears small solutes and potassium relatively quickly and can remove fluid; it is often suitable for hemodynamically stable patients. Rapid fluid and solute shifts may cause hypotension, and rapid urea removal may cause dialysis disequilibrium. The treatment-free intervals allow mobility and procedures.

Continuous renal replacement therapy

CRRT filters blood continuously or near-continuously, allowing gradual solute and fluid removal. It is often selected for hemodynamically unstable patients or when slow fluid shifts are desirable, including some patients with acute brain injury or raised intracranial pressure. It requires continuous access to the circuit and close monitoring; anticoagulation may be needed. Potential problems include circuit clotting, bleeding, hypothermia, and slower clearance than IHD.

Prolonged intermittent dialysis

Prolonged intermittent dialysis, for example SLED, is a slower, longer treatment combining features of intermittent and continuous therapy. It may be considered when conventional IHD is poorly tolerated and CRRT is unavailable or not preferred. Availability and practice vary, and treatment still requires extracorporeal access and monitoring.

Peritoneal dialysis

Peritoneal dialysis (PD) places dialysate in the abdominal cavity, where the peritoneum acts as the exchange membrane. It may be useful in selected patients, including when extracorporeal treatment is unavailable or difficult. It requires a usable peritoneal cavity and catheter. Clearance and fluid removal may be less predictable; risks include peritonitis, protein loss, and impaired breathing from abdominal fill volume.

Setting goals and monitoring treatment

Set treatment goals before dialysis, including the target for fluid removal and the problems to correct, such as potassium, acid–base status, or uremic symptoms. Avoid removing fluid faster than the patient can tolerate.

For AKI, KDIGO recommends a delivered CRRT effluent volume of $20\text{–}25\,\text{mL}\,\text{kg}^{-1}\,\text{hour}^{-1}$. The prescription may need to be higher to account for interruptions. Adjust treatment to the patient’s goals and to what is actually delivered.

Monitor blood pressure and other vital signs; fluid input and output; weight and clinical volume status; symptoms; access and circuit function; and treatment interruptions. Check electrolytes, acid–base status, and kidney-function trends at intervals appropriate to the patient and modality. Reassess the fluid-removal target and prescription when the patient’s condition changes.

Complications and reassessment

Monitor for hypotension; bleeding or anticoagulation complications; catheter infection or malfunction; circuit clotting; and shifts in potassium, sodium, calcium, phosphate, or glucose. IHD may cause dialysis disequilibrium, while CRRT may cause hypothermia. Respond to abnormalities and revise the prescription as needed.

Regularly assess whether kidney function is recovering and whether RRT remains necessary. Discontinue treatment when kidney function is sufficient for the patient’s needs or when continued treatment no longer aligns with goals of care.