CKRT: Prescribing

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CKRT:
- Access
- Troubleshooting

Blood Prime (non-normalized)

140 ml in pRBC Adsol + 100 ml 5% albumin mixed by fellow at bedside

Typically for patients < 10kg. Ideal if priming volume is > 20% pt blood volume.

Get an iCa on pt while you’re mixing the blood

Equipment: 3-way stopcock, blood filter tubing, 60mL syringe, ***

Have PRN calcium (10-20mg/kg) and bicarbonate available at bedside
Prime with blood Qb 30, Qd 3600 x 6-7 min. (can also do Qb 60 x 4 min but gives the dialysis nurse less time to check the line and set up citrate/Ca before the blood runs out)

For hypotension after starting, can consider increase in vasopressor drips, PRN calcium or bicarb based on iSTAT before starting, fluid bolus

When starting, set patient fluid removal to 0mL/hr, and gradually advance

5% albumin prime for patients between ~10-20 kg or if hemodynamic instability.

Otherwise normal saline prime

Dialysate composition

PrismaSol BGK 2/0 (baseline 2K, 0Ca, 32HCO3)
- Can be customized with up to additional 2 KCl, 1.5 MgSO4, 2 NaPhos.
- Adjust to keep patient physiologic, choose starting value based on pre-CRRT electrolytes
Sometimes use PrismaSol BK 0/0/1.2 (baseline 0K, 0Ca, 32HCO3) for intraoperative CRRT with concern for hyperkalemia (typical in massive transfusions and liver transplants). Cannot be ordered in EPIC, must call pharmacy.
Sometimes use PrismaSol B22GK 4/0 (baseline 4K, 0Ca, 22HCO3) which has less bicarb (22mEq/L vs 32mEq/L) and more K (default 4mEq/L vs 2mEq/L). Can be ordered in EPIC, see indications below.
- Can still be customized with Phos/Mag as above
Single pass albumin dialysis - for indirect (unconjugated) hyperbilirubinemia and other protein-bound solutes.
- Custom order by adding 5 g/L of 25% albumin to DIALYSATE fluid bag only

Regional anticoagulation

Calcium and citrate gtt ordered in orderset. Should be ready at bedside before starting prime. HD nurse or bedside nurse work together on getting it set up before pt is put on CRRT.
- Citrate binds to calcium in the blood and reduces the iCa of the blood going into the circuit
- Calcium is given to patient to replenish their levels after blood returns. Ideally given through a separate line (PICC or something), but sometimes we give through venous port due to access limitations.
Citrate gtt at 1.5x blood flow (starting) and circuit iCa sliding scale (typical target 0.2-0.3)
- Can go higher 0.3-0.4, even 0.4-0.5 if concern for citrate toxicity
Calcium gtt at 0.4x citrate gtt (starting). Pt iCa sliding scale (1.1-1.2)
- Can go higher on calcium target (per Cards request, typically)

How to prescribe CKRT (Prismaflex)

Prescribed flow rates

Blood flow (Qb): 3-6 mL/kg/min
Dialysate rate (Qd): *** mL/h/1.73m²
Pre-blood pump (PBP): *** mL/h/1.73²
- AKA Pre-filter replacement
Post-filter replacement: *** mL/h/1.73²
- Minimum of 50 mL/h/1.73²
Effluent rate ("clearance"): 35-45 mL/kg/h
- Automatically calculated by the machine based on the settings and patient size
- May exceed this recommended clearance target in certain situations (e.g., rapid treatment of hyperkalemia, hyperammonemia, etc.)

Dialyzer type

HF20
- For patients <20 kg
- Priming volume: 60 mL (filter set: includes filter [18 mL] and lines)
- Maximum Qb: 100 mL/min
- Maximum dialysate rate: 2500 mL/h
- Maximum UF rate (PBP + replacement + fluid removal):
  - Qb 20: 9 mL/min
  - Qb 50: 17 mL/min
  - Qb 100: 24 mL/min
HF1000
- Priming volume: 165 mL (filter set: includes filter and lines)
- Maximum Qb: 400 mL/min
  - Minimum Qb per specifications: 75 mL/min (but able to program it to run lower than this)
- Maximum dialysate rate: 8000 mL/h

Extracorporeal volume (lines/tubing, dialyzer)

Total extracorporeal blood volume (ECV) = filter set volume
- The filter set includes the lines (tubing) and the dialyzer
Dialyzer priming volumes:
- HF1000: 165 mL
- HF20: 60 mL

Priming solution

Blood, albumin, or normal saline (NS)
Blood prime: used if extracorporeal blood volume (ECV) >10% of estimated blood volume (or 8 mL/kg of body weight, as EBV ≈ 80 mL/kg)
- As a general rule, usually use blood prime if <10 kg
- For blood prime, we mix 140 mL of Adsol-preserved PRBCs (Hct ~55%) with 100 mL of albumin to bring Hct close to physiologic
NS prime: used if ECV ≤10% of EBV and hemodynamically stable
Albumin: used if ECV ≤10% of EBV but hemodynamically unstable
If NS or albumin prime was used, you will return the prime (i.e., rinse back the extracorporeal volume) if possible

Dialysate composition

Two options:
- "Normal bicarb" bags (BGK 2/0) and "low bicarb" bags (B22GK 4/0)
  - BGK2/0: HCO

Anticoagulation (AC)

Systemic AC is managed by primary team
- At our institution, systemic anticoagulation is rarely initiated solely for CKRT; generally, they are already on systemic AC for another indication
The use of regional (i.e., citrate) anticoagulation is preferred to maximize circuit life
- Can be used in combination with systemic anticoagulation, e.g., bivalirudin or heparin
Citrate anticoagulation:
- Anticoagulant citrate dextrose (ACD)
  - Initial rate = 1.5-2x Qb
- Calcium infusion
  - Initial rate = 40% of citrate rate
  - Uses *** mg/mL concentration rather than standard ICU infusion, to make titration easier
    - If they are already on the standard ICU calcium infusion, that infusion should be discontinued
- Goals:
  - Circuit ionized calcium (iCa)
    - Typically 0.30-0.45 mmol/L
      - Often goals are higher, e.g., if on systemic anticoagulation or having citrate toxicity
    - Patient iCa
      - Typically 1.1-1.3 mmol/L
        Use 1.2-1.4 in cardiac patients
  - Titrate citrate and calcium infusions by increments of 3 mL/h in children <10 kg, 5 mL/h in bigger kids
    - *** example titration

Unintended fluid loss/gain limit

The machine can detect if more or less fluid is being removed per hour than is programmed (i.e., unintended fluid loss/gain)
This setting must be determined before starting treatment
May use a sliding scale to determine
- <10 kg: 150 mL/3 hours
- 10-20 kg: 200 mL/3 hours
- 20-40 kg: 300 mL/3 hours
- 40 kg: 400 mL/3 hours
If the limit is reach, the treatment will end and cannot be resumed; a new circuit must be set up

Generic clearance =
- Mass removal rate / blood concentration
- Effluent flow rate x effluent concentyration/blood concentration
- K = Qe x Ce/Cb
Effluent definition
- CVVH: Total UF = replacement fluid + fluid removal
- CVVHD: dialysate + fluid removal
- CVVHDF: dialysate + fluid removal + replacement fluid
Convection vs diffusion (Brunet et al Am J Kidney Dis 1999;34:486-42)
- Clearance is proportional to effluent rate for small molecular weight solutes
  - Increasing effluent rate increases solute clearance
  - This is true up until your dialysate rate is saturated (Qd = 2-3x Qb)
- CVVH clearance = CVVHD clearance for same effluent rates for small molecules weight solutes
More prefilter replacement = more dilution of solutes = decreased efficiency of solute removal (graph: "Clark WR et al. Dose determinants in continuous renal replacement therapy. Artif Organs. 2003")
Blood flow rate vs post-filter replacement fluid rate
Filtration fraction = total ultrafiltration rate / plasma flow rate
- QtotalUF = total ultrafiltration rate
- Qp = plasma flow rate
- FF = QtotalUF / (Qp + Qprefilter RF)
- Filter clotting more likely with FF >20-25%
- Increasing the blood flow rate decreases the FF
Post-dilution (convective)
- Reinfusion into venous line (post-filter)
- Advantage: clearance directly related to ultrafiltration rate
- Disadvantage: UF rate limited to certain percentage of blood flow rate due to hemoconcentration
Predilution:
- REfusion into arterial line (prefilter)
- Disadvantages: reduction of solute clearances, decreased efficiency
- Advantages: may improve circuit life
Main 2 studies about CKRT dosing: Bellomo, Palevski (ATN trial)
ATN trial: 1124 patients [***Table]
- No difference in either study that suggested a higher dose improved outcome.
- An effluent flow rate of 20-25 mL/kg/h is sufficient so long as there is careful attention to ensuring the target dose of therapy is actually delivered
- For iHD there is no need to provide treatments more than 3x/week so long as target KT/Vurea >1.2 is achieved
Citrate
- Metabolic consequences
  - Metabolic alkalosis: Citrate excess (overdose/toxicity)
    - Management: decrease blood flow rate, or increase dialysate flow rate, or decrease buffer concentration in other CKRT solutions
  - Metabolic acidosis: Citrate toxicity in setting of severe liver disease or hypoperfusion
    - Risk factors:
      - Liver disease
      - Shock liver; severe hypoperfusion states
      - Lactic acidosis (>4)
    - Detection
      - Worsening metabolic acidosis
      - Elevated total calcium
      - Decreased ionized calcium -> increasing Ca++ infusion
      - Total calcium: ionized calcium ratio >2.5 (mmol/L)
    - Management: decrease blood flow rate, or increasing dialysate flow rate, or discontinue citrate
    - Citrate deficit: metabolic conversion of citrate to bicarbonate resulting in insufficient buffer
      - Management: Increase blood flow rate, or decrease dialysate rate, or increase buffer concentration in other CKRT Solutions
  - Hypernatremia: Hyperosmolar citrate solutions
  - Hypocalcemia and hypercalcemia: If calcium infusion not titrated properly
  - Hypomagnesemia: Citrate also chelates magnesium
- Monitoring:
  - Q1h then
Commercial CKRT solutions
- Bicarbonate based (22-35 mmol/L)
  - Sodium: 130-140 mmol/L
  - Chloride: 106.5-120.5 mmol/L
  - Lactate 0-3 mmol/L
  - Potassium: 0-4 mmol/L
  - Calcium: 0-3.5
  - Magnesium: 1-1.5
  - Phosphorus: 0-1
  - Dextrose: 0-110

References

[AMA formatted citations]
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