SACCM 178: Renal Replacement Therapies Flashcards
How does timing of initiation of RRT affect survival in humans with AKI?
does not affect survival according to recent systematic review of RCTs
Gaudry et al., 2020, the Lancet
What are the three most commonly prescribed extracorporeal RRT in veterinary medicine?
Continuous renal replacement therapy (CRRT)
Intermittent hemodialysis (IHD)
prolonged intermittend renal replacement therapy
What are the four modalities of CRRT?
- continuous ultrafiltration - convective - fluid removal
- continous venovenous hemofiltration -convective - solute removal
- continous venovenous hemodialysis (CVVHD) - diffusive - solute removal
- continous venovenous hemodiafiltration (CVVHDF) - diffusive and convective - solute removal
solute removal prescriptions can be altered to achieve fluid removal
What is the definition of “Dialysis”?
Dialysis is the movement of solutes between two aqueous solutions separated by a semipermeable membrane
What does the rate of solute removal by diffusion depend on?
- concentration gradient
- solute charge
- solute molecular weight
- surface area
- permability
How do diffusion and convection differ in the size of solutes they remove?
- diffusion removes small molecular weight solutes, e.g., BUN and creatinine, and some middle molecular weight
- convection removed small and middle molecular weight solutes (500 - 60,000 Da) + some large (>60,000)
What is the molecular weight of BUN?
60 Da
What is the molecular weight of creatinine?
113 Da
What is the molecular weight of albumin?
66,400 Da
What does the rate of solute removal by convection depend on?
- amount of water movement across the membrane (osmotic and hydrostatic pressures)
- membrane pore size
- membrane surface area
Does IHD work by diffusion or convection?
primarily diffusion
Explain how dwell time and exchange frequency can be altered to improve removal of small or larger molecular sized molecules during PD.
- Small solutes are cleared by diffusion - therefore to maximize small solute removal freuquent dialysate exchange keeps up a high cc gradient
- Middle to large solutes are removed by convection - therefore longer dwelling times permit better solute equillibration
How is ultrafiltration achieved in IHD and CRRT?
by application of a negative transmembrane pressure to the dialyzer
What are the indications for dialysis?
AEIOU
Why does IHD and CRRT improve electrocardiogram abnormalities rapidly - even if total body K remains elevated?
returning blood with low K levels - returns directly into the right atrium and coronary circulation
Name 3 contraindications and how to adjust for them in IHD and CRRT
- severe hypotension - stabilized with pharmacotherapy and volume restoration
- severe preexisting coagulopathies - adjust anti-coagulatn prescriptions
- small patient size - prime the extracorporeal circuit with colloid solutions, blood, or both
What are contraindications to PD in small animal patients?
- peritonitis
- recent abdominal or thoracic surgery
- hypoalbuminemia
- severe hypercatabolic states
How much heparin should be used to lock the catheter lumens?
100-2000 units/mL depending on the patient’s size
In what dialysis modalities does the dialysate flow countercurrent to the blood?
IHD, CVVHD, CVVHDF
Why do CRRT dialyzers have larger pore sizes than IHD ones?
because CRRT relies on diffusion and convection - solute removal in IHD is mostly by diffusion
What are complications from local citrate anticoagulation?
hypocalcemia
arrhythmias
alkalosis
citrate toxicity
What are the components of the dialysis prescription?
- type of RRT most appropriate for the patient
- dialyzer
- blood flow rate
- dialysis time
- dialysate composition
- flow rate
- ultrafiltration
- type of anticoagulation
What rate should not be exceeded for volume removal by ultrafiltration?
most patients can tolerate < 10 ml/kg/hr
What are clinical signs of excessive rate of ultrafiltration?
- hypotension
- hypothermia
- nausea
- cramping
