Hemofiltration – Renal Replacement in Intensive Care
Hemofiltration is a renal replacement therapy in which blood is filtered outside the body by a machine. It is primarily used for acute kidney injury in intensive care settings.
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Hemofiltration is a renal replacement therapy in which blood is filtered outside the body by a machine. It is primarily used for acute kidney injury in intensive care settings.
What is Hemofiltration?
Hemofiltration is an extracorporeal renal replacement therapy in which a patient´s blood is passed through a semipermeable membrane outside the body. Water, electrolytes, and uremic waste products are filtered out of the blood and replaced with a specially formulated substitution solution. The procedure partially takes over the function of healthy kidneys and helps remove toxins while regulating fluid and electrolyte balance.
When is Hemofiltration Used?
Hemofiltration is primarily used in patients with acute kidney injury (AKI), especially in the intensive care unit (ICU). Common indications include:
- Acute kidney injury with life-threatening fluid overload
- Severe electrolyte imbalances, particularly hyperkalemia (elevated potassium levels)
- Metabolic acidosis (excess acid in the blood)
- Poisoning with dialyzable substances
- Multi-organ failure in the context of sepsis
Unlike conventional hemodialysis, hemofiltration is often performed as a continuous procedure (CVVH – Continuous Veno-Venous Hemofiltration), which is particularly gentle for hemodynamically unstable ICU patients.
How Does Hemofiltration Work?
During hemofiltration, blood is drawn from the patient via a central venous catheter and passed through a device called a hemofilter. This contains a semipermeable membrane with defined pore sizes. Hydrostatic pressure forces an ultrafiltrate through the membrane, which contains water and dissolved substances up to a certain molecular weight. The filtered blood is then supplemented with a precisely composed substitution solution and returned to the patient.
Difference from Hemodialysis
While hemodialysis primarily relies on diffusion (movement along a concentration gradient) to remove waste products, hemofiltration is based on the principle of convection: solutes are carried through the membrane along with the fluid flow. This allows hemofiltration to remove medium-sized molecules more effectively, which can be advantageous in certain clinical conditions.
Variants of Hemofiltration
- CVVH (Continuous Veno-Venous Hemofiltration): The standard continuous form used in the ICU.
- CVVHD (Continuous Veno-Venous Hemodialysis): A combination of filtration and dialysis.
- CVVHDF (Continuous Veno-Venous Hemodiafiltration): Combines both convection and diffusion principles.
- Intermittent Hemofiltration: Performed at set intervals; less common in critically ill patients.
Possible Risks and Side Effects
Hemofiltration is generally a safe procedure but carries certain risks:
- Bleeding risk due to required anticoagulation (e.g., with heparin or citrate)
- Infections at the catheter insertion site
- Electrolyte imbalances, particularly low potassium, calcium, or magnesium levels
- Hypothermia (low body temperature) from the extracorporeal circuit
- Thrombosis or filter clotting
Monitoring and Care
Patients undergoing hemofiltration are closely monitored. This includes regular checks of blood pressure, heart rate, electrolyte levels, blood counts, and filter system function. Nursing staff and treating physicians continuously adjust the filtration rate and substitution solution composition based on the patient´s condition.
References
- Bellomo R, Kellum JA, Ronco C. Acute kidney injury. Lancet. 2012;380(9843):756-766.
- Kidney Disease: Improving Global Outcomes (KDIGO) AKI Work Group. KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Inter Suppl. 2012;2:1-138.
- Vincent JL, et al. Textbook of Critical Care. 7th edition. Elsevier, Philadelphia 2017.
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Related search terms: Hemofiltration + Haemofiltration + Hemofiltration Therapy