Haemofiltration

1. Haemofiltration

2. The History of Haemofiltration / Ultrafiltration • The concept of removing fluid from the intravascular space of patients in renal failure, by the filtration of blood through an ultraporous membrane dates back to 1928. (Brull L. Realization de l’ultrafiltration in vivo. C R Soc Bid-Paris.) • First clinical application in 1952 ( The Artificial Kidney- The efficacy of the dialyser; ultrafiltration for human use.) • During the 1970’s Lee West Henderson began to introduce ultrafiltration during cardiac surgery.

3. Haemodilution during CPB Benefits: • Facilitate tissue perfusion Disadvantages: • Decreased plasma colloidal oncotic pressure • Reduced haematocrit • Increased total body water and interstitual oedema in vital organs. • Hypoxia • Hypotension • Hypocoagulation • Myocardial and cerebral ischemia

4. Why do we use a Haemofilter during CPB? • Reverse haemodilution by removing plasma water and low molecular weight molecules directly across a semipermiable membrane using hydrostatic forces. • Increase haematocrit – Increse oxygen delivery and organ perfusion • Remove excess water (priming fluid and volume overloaded patients) • Long duration of bypass, hypothermia and low body weight increase the risk of oedema and haemodilution. Note: Increasing the transmembrane pressure too much by occluding the outlet of the haemofilter could cause haemolysis.

5. Why do we use a Haemofilter during CPB? Causes of Hyperkalemia during CPB • Renal Impairment • Cardioplegia (size of dose, continuous delivery?) • Haemolysis • Packed red cells Plasma potassium level is critical as it contributes to the recovery of normal sinus rhythm. Potassium may need to be added when a patient without increased potassium levels is haemofiltered.

6. Circuit Design?

7. Circuit Design Cont… • Arterio-venous ultrafiltration • From the recirculation line to the venous reservoir. • From the arterial filter purge line to the venous reservoir. • From the arterial line to the cadioplegia delivery line – using a heat exchanger for MUF in neonates and infants has advantages. • Venous-venous ultrafiltration • From the vent line to the venous reservoir. • From the venous line to venous reservoir • An ultrafilter can be inserted between femoral vein and contralateral femoral vein.

8. Types of Haemofiltration There are three methods for the application of ultrafiltration: • Conventional ultrafiltration • Modified ultrafiltration • Zero-balance ultrafiltration

9. Conventional Ultrafiltration • Inserted into the CPB circuit. • Most common method to maintain moderate haemodilution during CPB and a minimal venous reservoir blood volume. • This technique can be used at anytime during CPB. • High/adequate volume required.

10. Conventional Ultrafiltration Cont… • Higher arterial pump flow to compensate for purge. • The blood reservoir level can be kept at an acceptably minimal but safe operating level. • Consider the disadvantages of removing plasma fluid to then replace with crystalloid /colloid. • Removal of small molecules including Potassium

11. Zero-balance (Z-BUF) Ultrafiltration • An identical circuit to conventional ultrafiltration but with the addition of clear fluid to provide volume. • Usually performed after the rewarming phase by administering a replacement fluid into the venous reservoir. The amount added is equal to the volume of ultrafiltrate. • The most common replacement fluid is Plasmalyte; an isotonic electrolyte solution. • High volume Z-BUF allows control of blood potassium, glucose and lactate levels during CPB. Z-Buf can be manipulated to allow haemoconcentration. Accusol is lactate-free, potassium free and has a 100% bicarbonate buffer that provides all the necessary electrolytes.

12. Zero-balance Continued…. • In paediatric cases where packed red cells are added to the prime Z-Buf can be performed to ‘wash’ the perfusate. • Blood gas analysis of the priming solution is required to determine the Z-Buf end point. • The haemofilter is left in the circuit and can be used for conventional use or MUF. • Maintaining a minimal level in the venous reservoir can be challenging in Paediatric cases. Z buf allows manipulation of volume and flow. • Surgical request to remove certain drugs?

13. Modified Ultrafiltration • This technique has been adapted to be used post CPB. • The MUF circuit is completely seperate from the bypass machine. • It is performed in order to concentrate the patients circulating blood by removing excess water and also to salvage blood from the circuit. • Predominant use in paediatric cases. • The ultrafilter is placed with the inlet connected to the arterial line and the outlet connected to the venous line. The noraml arterial pump is simultaneously activated to deliver volume from the reservoir. • MUF must be primed pre CPB and clamped off and isolated during the case.

14. Modified Ultrafiltration Continued…. • Usually performed for a period of 10-20 minutes post CPB. • All members of the team need to be in support; patient needs to be haemodynamically stable. • MUF is completed either when CPB circuit empties or when haematocrit reaches an appropriate level. • Evidence suggests improved cardiac function post cardiac surgery when MUF is used; this improvement may be attributed to haemoconcentration, reduced inflammatory response and reduced myocardial oedema.

15. ECMO Would you add a Haemofilter into an ECMO circuit? • A haemofilter can be placed in-line with an ECMO circuit from the high pressure arterial line to the low pressure venous line. • The goal would be to remove excess water, increase blood osmolarity and regulate fluid-electrolyte and acid-base balance. • Blood gas analysis and clinical situation are essential tools to determine the end point. • Be aware that when blood transfusions are being given, it is critical not to over haemoconcentrate the patient. Remember ECMO is dependent on patient volume status.

16. Hemofiltration and Immunological Response • Hemofiltration appears to remove TNF α and IL-1β,C3a and C5a from the plasma of patients with SIRS. • Reducing the inflammatory response to cardiac surgery could result in better organ perfusion and reduced improved prognosis. • Evidence suggests that a reduced inflammatory response resulting from ultrafiltration is associated with significantly improved pulmonary function. • It is critical to always treat the patient as a whole and not to focus on one aspect.

17. Unconventional uses? Removal of Drugs

18. Unconventional uses? Removal of Drugs ReoPro is a drug used in the field of interventional cardiology especiallyduring coronary angioplasty and coronary stenting. Administration of this monoclonal antibody fragment results in almost total inhibition of platelet aggregation. Cardiac surgery is then dangerous because of the excessive bleeding that may occur in patients who have received ReoPro. ReoPro has a molecular weight of 50 kd which allows it to be removed from the circulation by a haemofilter. Heparin?! Low molecular weight fractions may be removed however most studies report an increased concentration of Heparin. Check ACTs regularly Bivalirudin can be removed by ultrafilotration. There may be other uses in the future?!

19. Current Research and Thoughts... 2009

20. Atrial fibrilation (AF) occurs in 20-50% of patients after cardiac surgery and is associated with increased morbidity and mortality. • A relationship between post cardiac surgery AF and increased CRP, lymphocyte and cytokine concentration has been reported. • Corticosteroids are reported to decrease the incidence, presumably by attenuating inflammation. • It was hypothesised that hemofiltrartion during CPB, which may attentuate inflammation may decrease the incidence of AF. This study did not demonstrate this however further research on this subject may show new findings.

21. Current Research and Thoughts... • Fluid shifts in microcirculation,lymphatics and organ oedema are the “New Frontier” for improving patient outcomes by Perfusionists in cardiac surgery. • There is increasing evidence that albumin levels possess additional effects on organ perfusion, microcirculation, tissue oxygenation, inflammation, endothelial activation, capillary leakage, and tissue oedema that are well beyond just the volume expanding/replacing properties. • Fluid overload is an independent predictor of mortality in cardiac surgical patients as well as an indirect trigger for blood transfusions. • Concentration of post bypass circuit volume by ultafiltration as oppose to cell salvage methods provides higher concentrations of platelets and clotting factors (fibrinogen, prothrombin and factor VII).

22. Hemobag Ultrafiltration (Hemobag) has the benefit of concentrating whole blood quickly and easily saving all the plasma as well as the RBCs. Figures taken from www.mybloodfirst.com/hemobag

23. Hemobag Final Infusion Volume Contents Significant increase in clotting factors delivered to patient. Taken from www.mybloodfirst/hemobag

24. Conclusion • Haemofiltration is a tool that Perfusionists can use to provide optimal patient treatment. • There are clinical implications; use your professional judgement!