11.1 Sequential UF, Hemofiltration and Hemoperfusion

Match the Method to the Problem

BONENT's outline explicitly includes sequential ultrafiltration, hemoperfusion, hemofiltration, bicarbonate dialysis and high-sodium techniques. These are not interchangeable versions of ordinary HD. The nurse must understand the dominant transport process, the clinical purpose and the added monitoring requirements. A method that improves volume control may not provide adequate solute removal, and a method useful for one toxin may be ineffective for another.

Isolated ultrafiltration removes plasma water under pressure without the usual dialysate-mediated diffusion. Small solutes move with the removed water, but the net clearance is limited by the removed volume. It is primarily a volume-removal strategy. Sequential treatment may deliver an isolated-UF phase followed or preceded by a diffusive phase. The order identifies the sequence, duration, fluid goal and monitoring. Do not count an hour of isolated UF as an hour of ordinary urea clearance.

Sequential UF and Hemodynamic Tolerance

During conventional HD, both osmotic change and volume removal affect vascular stability. Separating them can help selected patients, but isolated UF can still cause hypotension if removal exceeds plasma refill. It is not an automatically gentle or risk-free alternative. Assess symptoms, pressure, access and cumulative removal. A patient with low perfusion, active bleeding or severe cardiac dysfunction may tolerate neither rapid UF nor large additional fluid shifts.

Suppose a prescription has thirty minutes of isolated UF and three hours of HD. Record each delivered phase and its removal. If the patient has symptomatic hypotension during the first phase, implement the protective protocol and clarify the remaining plan. Continuing merely because the dialysate is off ignores the physiology. The final assessment includes congestion, symptoms and solute adequacy rather than celebrating a reached weight alone.

Convection and Replacement Fluid

Hemofiltration passes plasma water and dissolved solutes across a permeable membrane. The filtration volume may greatly exceed the net fluid removed from the patient, because prescribed sterile replacement fluid restores much of that volume. Hemodiafiltration (HDF) combines this convective process with dialysate diffusion. Small-solute and middle-solute removal depend on membrane properties, effective flows, filtration and dilution.

Replacement before the filter reduces hemoconcentration but dilutes solute concentration at the membrane. Replacement after the filter preserves concentration for removal but increases hemoconcentration within it. The choice affects achievable filtration, clotting and effective clearance. Follow the prescribed replacement location and the device's filtration limits. Monitor pressure trends, clotting, fluid balance and access performance; a displayed total filtration volume is not the patient's net weight loss.

Adsorption and Hemoperfusion

Hemoperfusion circulates blood through an adsorptive cartridge, historically charcoal or resin and now other adsorbers for specific purposes. Adsorption binds molecules to a surface instead of requiring them to cross a dialysis membrane. Protein binding or molecular characteristics may make adsorption useful when ordinary dialysis removes an agent poorly, but the actual toxin, distribution volume, exposure timing and cartridge performance determine benefit.

Poison-control and specialist consultation are essential for intoxication. Do not infer that every protein-bound drug is treatable with every cartridge. Cartridge saturation can reduce removal over time; platelets, calcium or medications may also be affected depending on the product. Verify anticoagulation, circuit compatibility, laboratory surveillance and the endpoint. Treatment may be combined with dialysis, but each component has a distinct purpose.

Buffer and Sodium Strategies

Bicarbonate dialysis replaces an important buffer deficit without relying entirely on acetate metabolism. Verify the delivered bicarbonate formulation and total buffer contribution from the acid concentrate. A label setting is not always the entire final buffer exposure. Excess alkalinization can alter ionized calcium, potassium and ventilation. Reassess symptoms and laboratory trends rather than selecting a universally high bicarbonate bath.

A high-sodium bath or sodium profiling may preserve osmolality during treatment and reduce symptoms in selected circumstances, but it can cause positive sodium balance, thirst, larger weight gain and hypertension. It requires an explicit individualized order. Do not automatically raise sodium for every cramp or hypotensive episode. The apparent short-term improvement must be weighed against the next interdialytic interval.

Exam Reasoning

When a question proposes changing modality, ask what problem is being treated: water excess, small-solute burden, middle-solute clearance or a specific poison. Then identify what the method cannot solve. A fluid-overloaded patient with dangerous hyperkalemia still needs a plan for definitive potassium removal; isolated UF alone is inadequate. A patient receiving HDF needs safe substitution fluid and correct balance, not a casual instruction to increase net UF. The nurse verifies the complete order and evaluates both efficacy and tolerance.

Sources: NIDDK hemodialysis, KDIGO AKI guidance.