Chapter 25: Dialysis & Renal Replacement Therapy

Indications for Dialysis

Urgent Indications for RRT (AEIOU)

Acidosis: Severe metabolic acidosis (pH < 7.1) refractory to bicarbonate therapy.
Electrolytes: Severe, refractory hyperkalemia with ECG changes.
Ingestions: Certain dialyzable toxins (e.g., salicylates, lithium, ethylene glycol, methanol).
Overload: Refractory fluid overload causing pulmonary edema.
Uremia: Symptomatic uremia, such as pericarditis, encephalopathy, or severe bleeding.

Hemodialysis (HD)

Principles

In HD, blood is pumped from the patient, through an external filter called a dialyzer (the "artificial kidney"), and then returned to the patient. The dialyzer contains thousands of hollow fibers made of a semipermeable membrane. Blood flows through the fibers while dialysate flows around them in the opposite direction (counter-current flow). Waste products and excess electrolytes are removed by diffusion down a concentration gradient, while excess fluid is removed by ultrafiltration using a pressure gradient.

The Hemodialysis Prescription

A typical HD prescription includes the dialyzer type, blood flow rate (Qb), dialysate flow rate (Qd), dialysate composition (e.g., sodium, potassium, bicarbonate, calcium), treatment time, and anticoagulation. A standard in-center prescription is 3-4 hours, three times per week.

Acute Complications During HD

Hypotension: The most common complication, caused by rapid fluid removal exceeding vascular refilling. Managed by reducing the ultrafiltration rate and administering saline.
Muscle Cramps: Related to rapid fluid and electrolyte shifts.
Dialysis Disequilibrium Syndrome: Neurologic symptoms caused by cerebral edema from too-rapid solute removal. More common in the first few treatments.

Peritoneal Dialysis (PD)

Principles

PD uses the patient's own peritoneal membrane as the dialyzer. Dialysate, containing dextrose as an osmotic agent, is instilled into the peritoneal cavity via a PD catheter. Waste products diffuse from the peritoneal capillaries into the dialysate, and excess fluid is removed via osmosis. The used dialysate is then drained out.

Modalities

Continuous Ambulatory Peritoneal Dialysis (CAPD): Manual exchanges performed by the patient 4-5 times throughout the day.
Automated Peritoneal Dialysis (APD): A machine (cycler) performs multiple exchanges automatically overnight while the patient sleeps.

Complications

The most significant complication of PD is peritonitis, an infection of the peritoneal cavity, which presents with cloudy dialysate, abdominal pain, and fever. Prompt treatment with intraperitoneal antibiotics is crucial.

Kidney Transplantation

Kidney transplantation is the treatment of choice for most patients with ESRD, offering the best long-term survival and quality of life. Patients can receive a kidney from a living or deceased donor. The procedure requires lifelong immunosuppressive medication to prevent rejection of the transplanted organ.

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