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Question No. 2
Q: Why does blood clot during RRT and what are the consequences?
Answer No. 2
- All modes of RRT (with the exception of PD) utilise an extracorporeal circuit
- Contact of blood with the foreign surface results in:
- Activation of both the intrinsic and the extrinsic pathway of coagulation
- Activation of platelets
- Exacerbated by pro-coagulopathic effects of AKI
- When the filter clots:
- Partially – the filter performance is reduced
- Completely – the filter is lost and treatment us interrupted with loss of the filter, circuit and blood contained within
Question No. 3
Q: What is the average circuit life span?
Answer No. 3
- The average circuit lifespan varies according to patient groups and anticoagulation used
- In observational studies mean lifespans of 38 - 124 hours have been reported
Question No. 4
Q: Which factors can increase the risk of circuits clotting?
Answer No. 4
- Poor vascular access
- Kinking of lines and tubes
- Reduced blood flows
- Convective rather than diffusive therapies
- Coagulopathic patient
- Poor anticoagulant choice/dose
- Bio-incompatible filter
Question No. 5
Q: What are the advantages and disadvantages of anticoagulation in RRT?
Answer No. 5
- The goal of anticoagulation with RRT is to:
- Prevent clotting of the filter
- Prevent reduced membrane permeability
- This ensures adequate RRT can be achieved and prevents blood loss in the clotted filter
- Any benefits must be weighed against:
- Risk of bleeding
- Economic issues, such as workload and costs
Question No. 6
Q: What are the types of anticoagulation that can be used for RRT?
Answer No. 6
Mechanical
- Optimising CVP
- Pre-dilution replacement fluid
- High flowrates
- Reducing air-blood contact in the bubble trap
Regional
- Heparin
- Citrate
Systemic
- Heparin
- LMWH
- Prostacyclin
- Thrombin Inhibitors:
- Argatroban
- Lepirudin
- Fondaparinux
- Heparinoids
- Warfarin
Question No. 7
Q: What are the advantages and disadvantages of each mode?
Answer No. 7
Advantages
Disadvantages
No / Mechanical Anticoagulation
- Reduced bleeding risk
- ↓ cost
- ↑ risk of filter clotting:
- Shorter filter lifespan
- Reduced adequacy of RRT
- Not suitable for patients with HIT who are pro-thrombotic
Unfractionated Heparin
- Easily titratable
- Easily monitored
- Can be reversed with protamine
- ↑ bleeding risk
- Risk of HIT
LMWH
- ↓ cost
- ↑ familiarity
- ↑ bleeding risk
- Not titratable
- No reversal agent
Prostacyclin
- Reduced bleeding risk
- Shorter filter life
- Causes systemic hypotension
Citrate
- Good regional anticoagulation with reversal by calcium
- Reduced bleeding risk
- Associated with metabolic complications (Hypernatraemia, hypocalcaemia, metabolic alkalosis)
- Special dialysate required
- Contraindicated in liver failure
- Labour intensive
Question No. 8
Q: Who should receive anticoagulation for RRT?
Answer No. 8
Anticoagulation should be used in all patients requiring RRT for AKI unless:
- There is an ↑ risk of bleeding
- They are already receiving systemic anticoagulation
Question No. 9
Q: Which mode of anticoagulation should be used during RRT?
Answer No. 9
If No Increased Risk of Bleeding
- Regional citrate rather than heparin as first line unless contraindicated
- If citrate contraindicated or as a second line alternative either unfractionated or low molecular weight heparin
If Increased Risk of Bleeding
- Regional citrate unless contraindicated
- Regional heparin should not be used
Question No. 10
Q: Which mode of anticoagulation should be used in Heparin Induced Thrombocytopenia (HIT)?
Answer No. 10
- All heparins should be stopped but anticoagulation should be continued during RRT as they are pro-thrombotic
- The direct thrombin inhibitor argobatran is recommended as first-line
- Other options include Factor Xa inhibitors such as danaparoid or fondaparinux
Question No. 11
Q: How does citrate anticoagulation work?
Answer No. 11
- Calcium (factor IV) is an essential substrate for all 3 clotting pathways
- Citrate is added to blood prior to the filter in the form of trisodium citrate:
- Chelates calcium forming a complex
- Prevents the involvement of calcium in the clotting cascade
- Regional anticoagulation of the filter only is ensured through several mechanisms:
- Citrate-calcium complexes are small molecules and freely pass through the filter (via diffusion or convection)
- Residual citrate in the blood is delivered to the patient and metabolised by the liver to bicarbonate
- Calcium ions are infused post-filter to replace that lost in effluent, normalising levels and clotting function
Question No. 12
Q: What are the advantages of citrate anticoagulation?
Answer No. 12
- Superior anticoagulation to UFH
- Prolonged filter lifespan
- Avoidance of any systemic anticoagulation reducing bleeding complications
Question No. 13
Q: What are the complications of citrate anticoagulation?
Answer No. 13
- Hypocalcaemia – due to chelation
- Hypomagnesaemia - Mg2+ is also chelated
- Hypernatraemia – high sodium load in hyperosmolar trisodium citrate
- Metabolic alkalosis - citrate is metabolised to bicarbonate
- Metabolic acidosis (RAGMA) - caused by the citrate accumulation if there is impaired metabolism (e.g. liver failure)
Question No. 14
Q: How can filter life be extended if no anticoagulation is used?
Answer No. 14
From KDIGO Guidance:
- Good vascular access allowing high blood flows to be reliably achieved
- Reducing blood viscosity through the filter
- Predilution fluids
- Treatments that involve diffusion as opposed to ultrafiltration
- Reducing blood-air contact in the bubble trap
- Ensuring prompt response to the filter alarms resulting in rapid correction of any suboptimal filter conditions which may have arisen
Other
- Prime the circuit with saline or heparin
- Give intermittent 0.9% saline flushes (50-200ml every 30-60mins)