CRRT (Continuous renal replacement therapy)
There are two forms of RRT.
IRRT: intermittent renal replacement therapy
<24 hours
HD (hemodialysis)
SLEDD (sustained low efficiency daily dialysis)
used for less stable patients; little slower than HD
CRRT: continuous, >24h
Good for those who are unstable/acute; slow and gentle.
Typical net fluid removal 0-200 cc/hour
Fluid (flow rates) 15-60 cc/min (into patient)
Fluid used: dialysate + replacement
Blood flow 150-200 cc/min
Clinical Indications
AKI
can be defined as:
SCr increase by >/= 0.3 mg/dL within 48 hours, OR
SCr increased to >/= 1.5 times baseline within 7 days, OR
Urine volume <0.5 cc/kg/hour in 6 hours
CRRT: hemodynaically unstable patients or patients with brain edema
Fluid overload
Access
First choice: Right Internal Jugular (15cm, 14fr)
Second choice: femoral (24cm)
Third choice: Left Internal Jugular (20 cm)
Fourth choice: Subclavian
Always use a 20mL syringe to assess patency. Change lego (yellow) caps q7 days. Can be tunneled (with cuff) or non-tunneled
RRT Transport Mechanisms
Ultra filtration: movement of fluid through a semi-permeable membrane driven by hydrostatic pressure
Removes water from fluid overloaded patients - no electrolyte balancing
Adsorption: molecular adherance to the surface o the interior membrane (solute removal)
M60. M100. M150 - positively charged filters, attracts positively charged molecules to stick to it
HF series: neutrally charged filters (does not work through adsorption)
Diffusion (hemodialysis): movement of solutes from high --> low concentration usin gdialysate solution
Uses dialysate to remove small molecules.
Prismasate - does not mix w/patients blood, pulls through semipermeable membranes
Convection/Hemofiltration: the forced movement of solutes with fluid (fluid will drag the solutes)
Removes large and medium (and small) molecules by increasing pressure gradient
Mixes w/patients blood: drug (Prismajol/Phoxillum)
Pre-filter replacement: deivers to circut access blood line before hemofiltere (to increase filter life)
Blood will be diluted (decreased Hct)
Decreased clearance
The replacement "fluid volume" will be removed by the effluent pump
The Hemofilter
Filters waste products from the blood (mimics kidneys)
Dialysate goes in the green line and comes out the yellow line as effluent
Is used for diffusion/electrolyte balance
Once it comes out yellow line it is color of urine
Blood goes in the red access line, pulls from patient
Blood goes out the blue return line, returns to patient
replacement/substitute solution goes into the purple (for pre-replacement) or white (for post-replacement) line
Citrate
"Paralyzes" calcium as soon as it is removed from the patient; once the citrate is metabolized by liver, can be utilized again. This prevents filter clotting
This calcium/citrate complex turns into bicarb
May add a calcium infusion post-filter to be returned back to patient
Essential for contractility in heart and blood vessels; used w/ a pump, start at 90 cc/hour
Concerns for using citrate:
Alkalosis (with trisodium citrate)
In acidosis: liver failure and lactic acidosis may decr body's ability to metabolize the Calcium/citrate complex, thus accumulating citrate = toxicity risk
Pressors may decrease the ability to metabolize the citrate/calcium complex
Citrate Toxicity
Calcium ratio = total Ca (mg/dL) * 0.25 / systemic iCa (mmol/L)
Detection: rising anion gap
Worsening metabolic acidosis
Falling systemic ionized calcium
Escalating Ca+ infusion requirements
Total Ca+: Systemi ion Ca ratio >2.1
Modes of therapy
Slow Continuous Ultrafiltration (SCUF)
goal is to remove patient fluid
Continuous veno-venous hemofiltration (CVVH)
goal for small, medium, and large molecule clearance. Involves patient fluid removal. No dialysate/diffusion
Continuous veno-venous hemodialysis (CVVHD)
goal to achieve small molecule clearance, remove patient fluid
Continuous veno-venous hemodiafiltration (CVVHDF)
goal for small, medium and large molecule clearance and patient fluid removal. Uses dialysate to pull solutes through diffusion.
CRRT Policy - Piedmont
Prior to starting CRRT:
Discontinue all electrolyte replacement protocols
D/c all diuretic orders
Draw an ionized calcium, BMP, mag, phos, PT/PTT, CBC
Have an ABG within last six hours
Unspoken roles: patients potassium + potassium we should give should be ~7
If potassium>5, consider using K of 2
If potassium<3, consider using K of 4
Fluid Balance
start fluid removal at 0 cc/hour for first 10-15 min
Titrate fluid removal every 15 min guided by blood pressure