Renal Replacement Therapy

Question 1

What are the different varities of continous renal replacement therapy?

Answer 1

CVV - continous veno-venous (from vein to vein)

CVVHD - haemodialysis
CVVHF - haemofiltration
CVVHDF - haemodiafiltration

Question 2

What are some differences between CRRT and IHD

Answer 2

CRRT vs IHD

• slow vs rapid
• continous vs intermittent
• flow 50-200mls/min vs 500ml/min
• haemodynamic consequences stable vs destabilising
• patient populations

Question 3

What are some physiological principles re: dialysis

Answer 3

Diffusion - molecules move down the concentration gradient across a semi-permeable membrane. HDx involves diffusion to normalise electrolytes/waste products.

Ultrafiltration - movement of fluid through semi-permeable membrane driven by pressure changes. Removal of excess fluid, with some solutes too (convection).

Convection - passive movement of small to medium size solutes across semi-permeable membrane - ‘solvent drag’

Question 4

What are some indications for CRRT in ICU?

Answer 4

• number of indications (AEIOU)
• severity of derangement (pH, electrolytes)
• rate of change
• expected recovery
• goals of care

Question 5

What is required to initiate CRRT?

Answer 5

Access - 
vascath
- wide bore, 
- two lumens
- locations R) IJ, L) IJ, Femoral (requires more length/recirculation - cycling of blood products) 
- lasts (jug 2-3weeks, femoral 3-7days)

Question 6

What are some things you can measure on a dialysis machine?

Answer 6

Pressure gauges along the circuit
Transmembrane pressure
Effluent

Question 7

What are the different types of dialysate and fluid options of CRRT? What about anticoagulant?

Answer 7

Dialysate fluid - concentration gradient to facilitate diffusion

• prismocal (no calcium) - used with prismocitrate
• haemosol
• phoxillum - contains PO4 and K+

Replacement fluid (citrate will produce bicarb if we want to raplace it)

• prismocitrate - citrate anticoag, used in combo with prismocal and CaCl (to replace calcium)
• haemosol
• phoxillum
• saline

Anticoagulant

• citrate (increasingly first line)
• low dose heparin
• heparin-protamine

patients on citrate still need DVT prophylaxis

Question 8

How do you know what fluid/dialysate to choose?

Answer 8

Citrate anticoagulation will automatically dictae prismocitrate and prismocal

Citrate is contraindicated in shock and liver failure

Haemosol/Phoxilium will depend on PO4 level.

Citrate anticoagulation
- prismocitrate, phosilium, prismocal

Non-citrate (low dose hep or systemic) - high PO4 and normal PO4
- hemosol with or without K+ if PO4 high phoxilium if its normal

can change from hemosol to phoxilium after a few hours

Question 9

Describe how the different dialysates work

Answer 9

Prismocitrate

• pre-filter replacement fluid with citrate (regional anticoag and a buffer)
• anticoag - binds free ionised Ca preventing coagulation (thus requiring CaCL replacement)
• buffer - converted to HCO3 improving acidosis

Hemosol
- used in severe AKI with high PO4 and K+

PhoXilium
- similar to Hemosol but with PO4 and K+ - used if PO4 <1.5

Question 10

What are some complications from haemodialysis?

Answer 10

Access
Air embolism, bleeding, infection, arterial cannulation (from central line)

Blood outside body
Hypotension
Hypothermia

Anticoag
Bleeding (from anticoag)
HITTS
Citrate - hypocalcemia, citrate toxicity

Overdoing dialysis
Hypokalemia, hypophosphatemia, hypomagnesia
loss of medications
loss of water soluble vitamins