Introduction of Renal Replacement Therapies (RRTs)

Indications for RRT (A-E-I-O-U)

Renal Replacement Therapy (RRT) is initiated when the kidneys fail to maintain homeostasis. The common indications are summarized by the mnemonic A-E-I-O-U:

• A – Acidemia: Severe metabolic acidosis (pH < 7.1) that does not respond to medical treatment.
• E – Electrolyte Imbalance: Life-threatening electrolyte disturbances, such as refractory hyperkalemia (K+ > 6.5 mmol/L or ECG changes).
• I – Intoxication: Removal of toxic, dialyzable substances including salicylates, lithium, isopropyl alcohol, magnesium salts, and ethylene glycol.
• O – Fluid Overload: Refractory pulmonary edema not responding to diuretics, leading to respiratory distress.
• U – Uremia: Severe uremic symptoms such as pericarditis, encephalopathy, seizures, and bleeding diathesis.
• Types of Renal Replacement Therapy

RRT is broadly classified into:

• Hemodialysis (HD): Blood is filtered through an extracorporeal circuit.
• Peritoneal Dialysis (PD): Uses the peritoneal membrane as the dialysing surface.

1. Hemodialysis (HD)

A. Intermittent Hemodialysis (IHD)

Indications:

• Hemodynamically stable patients requiring rapid solute/toxin clearance.
• Life-threatening electrolyte disturbances (e.g., severe hyperkalemia).
• Drug overdoses involving dialyzable substances.

Pros:

• Shorter treatment duration (3-4 hours per session, 3-5 times per week).
• Efficient clearance of solutes and fluids.

Cons:

• Requires vascular access (AV fistula, graft, or catheter).
• Risk of hypotension, cramps, and disequilibrium syndrome.
• Not suitable for haemodynamically unstable patients.

B. Prolonged Intermittent Renal Replacement Therapy (PIRRT)

Includes modalities such as Sustained Low-Efficiency Dialysis (SLED, SLEDD, SLEDD-F).

Indications:

• Patients who are haemodynamically unstable but lack access to CRRT.
• AKI patients requiring gentler solute removal over a prolonged period.

Pros:

• Less haemodynamic instability compared to IHD.
• More widely available than CRRT.
• Can be performed in ICUs without dedicated CRRT machines.

Cons:

• Longer duration than IHD (6-12 hours per session).
• Less efficient than IHD for rapid toxin clearance.
• Still requires trained staff and equipment.

2. Continuous Renal Replacement Therapy (CRRT)

Includes four main modalities:

• SCUF (Slow Continuous Ultrafiltration) – Removes only fluid, no significant solute clearance.
• CVVH (Continuous Veno-Venous Hemofiltration) – Primarily removes fluids and large solutes via convection.
• CVVHD (Continuous Veno-Venous Hemodialysis) – Uses diffusion for solute clearance.
• CVVHDF (Continuous Veno-Venous Hemodiafiltration) – Combines convection and diffusion for maximal clearance.

Indications:

• First choice for hemodynamically unstable patients with AKI, septic shock, or multi-organ failure.
• Severe electrolyte imbalances requiring gradual correction.
• Patients with high fluid needs (e.g., sepsis requiring large-volume resuscitation).

Pros:

Maintains stable hemodynamics.

Provides gradual and continuous solute and fluid removal.

Cons:

Expensive and requires specialized equipment.

Needs trained staff (not widely available in all hospitals).

Limited availability in resource-constrained settings.

Choosing the Right Modality

1. If the patient is hemodynamically unstable, CRRT is the first choice.
2. If CRRT is unavailable, PIRRT (SLED, SLEDD, etc.) is the next best option.
3. If the patient is hemodynamically stable and rapid solute removal is needed, IHD is preferred.

Peritoneal Dialysis (PD)

Indications:

• Patients who cannot tolerate HD (e.g., severe cardiovascular disease, lack of vascular access).
• Chronic renal failure patients seeking home-based therapy.

Pros:

• Can be performed at home (improves quality of life).
• Less cardiovascular stress compared to HD.

Cons:

• Risk of peritonitis and catheter-related infections.
• Slower solute clearance than HD.
• Fluid removal can not be controlled like in Hemodialysis.
• Requires patient compliance and manual exchanges (unless using automated PD).