Indications:
- Correction of water overload
- To remove larger quantities of water from the body than the kidney is able to achieve in order to enable the administration of therapeutic fluids such as parenteral nutrition
- To remove excess electrolytes
- Correction of disorders of acid/base homeostasis, including inborn errors of metabolism, particularly metabolic acidosis
- Liver failure (but it does not substitute liver function!)
- Removal of urea and other waste products of metabolism in cases of renal failure or hypercatabolic state
- Removal of ingested poisons, drugs or toxins in sepsis
Most common used: continuous veno-venous haemofiltration (CVVH or CVVHF) or continuos veno-venous haemodiafiltration (CVVHDF).
In CVVHF the filtrate depends on blood flow rate (aim for 3-5 ml/kg/min), the transmembrane pressure – TMP (change in oncotic pressure along the filter), prefilter dilution (decreases urea-/creatinine clearance) and the sieving coefficient (ratio between filtrate concentration and plasma concentration for a given molecule, e.g. urea=1, albumin=0).
The filtrate is replaced by a glucose/electrolyte solution (replacement fluid). In CVVHDF the clearance of small and middle sized molecules is enhanced by counter-current dialysate flow (diffusion).
Anticoagulation:
- UFH/anticoagulation, aim ACT 160-180 secs
- UFH/protamine: 1 mg protamine post-filter for every 100 U Heparin administered pre-filter
- Citrate anticoagulation: 1ml citrate per 30 ml blood flow, aiming for pre-filter Ca++<0.4 mmol/l and replace post-filter with Ca++>1.2 mmol/l (Mg++, citrate accumulation → acidosis)
Replacement fluid:
- For non-citrate anticoagulation: Na+Â 140 mmol/l, Ca++Â 2 mmol/l, Mg++Â 0.5 mmol/l, Cl–Â 110 mmol/l, HCO3–Â 32 mmol/l, Lactate 3 mmol/l
- For non-citrate anticoagulation and lactate free: Na+Â 140 mmol/l, Ca++Â 1.75 mmol/l, Mg++Â 0.5 mmol/l, Cl–Â 113.5 mmol/l, HCO3–Â 35 mmol/l, K+Â 4 mmol/l, glucose 5 mmol/l
- For citrate anticoagulation: Na+Â 136 mmol/l, Cl–Â 106 mmol/l, citrate 10 mmol/l, citric acid 2 mmol/l
Catheter/blood Flow/filter:
Always aim blood flow/filtrate flow ratio > 5:1
| Patient size | Catheter Size | Usual Blood Flow Rate | Maximum recommended Blood Flow |
Haemofilter |
| < 3 kg | 5.0F | 5 ml/kg/min | 50 mL/min | HF20; Filtrate 200-300mL/hr |
| < 8 kg | 6.5F | 5 ml/kg/min | 75 mL/min | HF20; Filtrate 200-300mL/hr |
| 10 – 15 kg | 8.0F | 5 ml/kg/min | 150 ml/min | ST60; Filtrate 900-1400mL/hr |
| >15 kg | 11F | 5 ml/kg/min | 300 ml/min | ST100; Filtrate 6000mL/hr |
| Adult | 14F | 5 ml/kg/min | 2000 ml/min | ST150; Filtrate 6000mL/hr |
Patient monitoring:
- Electrolytes (glucose, Na+, K+, Cl–, HCO3–, Ca++) every 4 hrs, hourly for 1st 4 hours if they were abnormal
- Magnesium and phosphate twice daily
- Fluid balance per hour = IV fluids in per hour + enteral feeds per hour – urine – insensible losses – drain losses – patient Fluid removed per hour
| Mode | Clinical Use | QDF (Diffusion) | UFR (Convection) | QRF | Total Clearance |
| SCUF | Water removal | Nil | =Filtrate flow | Nil | UFR |
| CVVH | Clearance depends on TMP, QBF, Sieving | Nil | =Filtrate flow | = QRF | UFR |
| CVVHD | Clearance depends on QBF, QDF | QDF | =QDF + UFR (small) | Nil | QD + UFR (small) |
| CVVHDF | Improved clearance of small and middle size | QDF | =QDF + UFR | = QRF | QDF + UFR |
References:
[1] Pediatr Nephrol 2012 Feb28: Sutherland et al: Continuous renal replacement therapy
[2] Curr Opin Pediatr 2011 Apr;23(2)181-5: Goldstein: Continuos renal replacement therapy: mechanism of clearance, fluid removal, indications and outcome
[3] Crit Care 2011 Jan 24;15(1)202: Oudemans-van-Straaten et al: Clinical review: anitocagulation for continuous renal replacement therapy – heparin or citrate?
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