Haemofiltration and dialysis

Shares
Cite this article as:
Anders, M. Haemofiltration and dialysis, Don't Forget the Bubbles, 2013. Available at:
http://doi.org/10.31440/DFTB.3735

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+ 140 mmol/l, Ca++ 2 mmol/l, Mg++ 0.5 mmol/l, Cl 110 mmol/l, HCO3 32 mmol/l, Lactate 3 mmol/l
  • For non-citrate anticoagulation and lactate free: Na+ 140 mmol/l, Ca++ 1.75 mmol/l, Mg++ 0.5 mmol/l, Cl 113.5 mmol/l, HCO3 35 mmol/l, K+ 4 mmol/l, glucose 5 mmol/l
  • For citrate anticoagulation: Na+ 136 mmol/l, Cl 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?


All Marc’s PICU cardiology FOAM can be found on PICU Doctor and can be downloaded as a handy app for free on iPhone or AndroidA list of contributors can be seen here.

Print Friendly, PDF & Email

About 

Marc Anders is a paediatric intensivist.

Author: Marc Anders Marc Anders is a paediatric intensivist.

Leave a Reply