Overview of CRRT
CRRT (continuous renal replacement therapy)
Frequently, relatively tight control over the fluid balance is a desirable goal in ECMO patients, whether that is for respiratory failure or cardiac failure. Achieving a substantial negative fluid balance however may be challenging. Rapid fluid shifts with diuretic boluses sometimes are not well tolerated and manifest with intermittent access insufficiency. For those reasons there is a relatively low threshold to use CRRT as a means to control fluid balance as well as to replace renal function. Advantageously the CRRT circuit can be attached to the ECMO circuit without any further procedure.
Haemosol versus citrate
Routine mode of CVVHDF with Hemosol BO 5000ml fluid as first line choice for CRRT therapy (PBP – DF – Replacement).
In clinical scenarios where systemic anticoagulation is not possible and there is loss of 2 or more CRRT sets in 24 hours consult with ECLS CNC/ECLS CON for consideration of “Citrate/Ca CRRT” (DF – Prism0Cal B22 5000ml, PBP Prismocitrate 18/0 5000ml, REP Prism0Cal 18/0, Calcium Chloride 10% infusion).
Calcium chloride infusion should be connected to the patients central access and NOT via the ECMO circuit.
All additional management will be as per the non-ECMO cohort.
CRRT connections
For most ECMO configurations, the ECMO circuit provides the optimal access for CRRT and a separate vascath is NOT required. ECMO configurations that may not support CRRT due to excessive circuit pressures are: dual lumen bi-caval (Avalon Elite) configuration in VV ECMO and any VA ECMO configuration with a small return cannulae (e.g. 15 Fr). See next paragraph for management of high pressures.
ECMO trained bedside ICU nurses carry out the connection and disconnection of CRRT from the ECMO circuit. Prior to any CRRT connection/disconnection. Reconfirm arterial bubble intervention is OFF as per daily shift checks.
CRRT connection must always be sited on the positive pressure (post-pump) part of the circuit. No ports exist for connection pre-pump (access) side of any Alfred Hospital ECMO circuit. The same applies to temporary RVAD configurations. Note temporary LVAD should NOT be used for CRRT.
The CRRT machine will access the pressurised post pump blood in the ECMO circuit return limb of the ECMO circuit. For problems with high pressures see next paragraph.
Connection and disconnection for both PLS and HLS consoles and temporary VAD circuits
- The connection and disconnection need to be completed with a dressing regime using a dressing trolley, dressing pack, 2 x 10ml syringes, and red caps
- ONLY ASPIRATE the luer connections on commencement of CRRT
- NEVER flush the luer connectors
- Cap off with sterile red caps
CRRT Blood Return can be practiced as aligned with normal patient practice.
2 Person procedure utilising the same procedure for access/disconnection.
The CRRT circuit is stopped. The 3 way tap turned off to the ECMO circuit and CRRT access limb clamped. Line removed with red cap applied to 3way tap on ECMO circuit and access line handed off to be attached via spike to hanging saline bag.
Utilising the “Saline Recirculation” option as per normal process allows blood return +/- recirculation as per normal practice.
If the recirculation has been successful the CRRT set having followed the normal steps (priming/checks) can be recommenced on the ECMO circuit eg CRRT down for transport.
As with normal practice if there are concerns around the CRRT set itself or it has been stationary for a period of time – do not attempt to return.
PLS circuit connection for CRRT
The access and return lines for CRRT are connected to the two Luer lock connectors between the outlet of the pump head (post-pump) and the oxygenator. The access line for CRRT is attached to the “proximal” (closer to the pump head) connector and the return line for the CRRT circuit is connected to the “distal” (closer to the oxygenator) connector.
The CRRT connection in the PLS circuit is pre-oxygenator with the access (red marked tubing) first and the return second (blue marked-tubing), any micro-bubbles would be caught in the oxygenator.
HLS circuit connection for CRRT
Oxygenator inlet and outlet Luer taps with wide bore extensions are used for CRRT connection. The CRRT access line is connected to the post oxygenator port and the return line for CRRT is connected to the pre oxygenator port. The oxygenator thereby functioning as a potential bubble trap.
The red marked tubing represents the access for the CRRT and is connected post-oxygenator, the CRRT return (blue) connects pre-oxygenator.
Temporary RVAD circuit connection for CRRT
The set up is analogous to the PLS circuit only that the perfusionist has to be asked specifically to splice the side ports into the circuit beforehand. The access and return lines for CRRT are connected to the two Luer lock connectors between the outlet of the pump head (post-pump) and the oxygenator. The access line for CRRT is attached to the “proximal” (closer to the pump head) connector and the return line for the CRRT circuit is connected to the “distal” (closer to the patient) connector (See PLS connections above).
There should be NO CRRT connections in a temporary LVAD circuit.
Plasmapheresis connections for CRRT
Plasmapheresis is the process of separating blood from plasma, plasma exchange (PLEX) or therapeutic plasma exchange often refers to a high ratio of exchange of the patient plasma.
CRRT and Plasmapheresis can run concurrently. Utilising the same access and return 3 way taps as the running CRRT via ECMO circuit. All occurring POST pump and PRE oxygenator in relation to the ECMO circuit.
That is providing access for the PLEX via the same access 3 way tap as CRRT and return for the PLEX via the same return 3 way tap.
Pausing the CRRT briefly during this connection time to clarify/check connections.
There may be haemodynamic instability or increase in vasopressor/inotrope load during such treatments.
Link to PLEX guideline
THERAPEUTIC PLASMA EXCHANGE PROCEDURE
USING OPTIA MACHINE GUIDELINE
The fluid balance as reflected in EMR may reflect more positive than actual.
High return pressure
CRRT pressure alarms
High ECMO circuit pressures can result in CRRT high return positive pressure alarms. This is not uncommon. High ECMO circuit return pressures are expected with higher ECMO blood flow rates. Further factors are smaller ECMO return cannulae (e.g. VA ECMO with 15Fr return cannula; or dual-lumen, bi-caval (Avalon Elite) VV ECMO) and to a lesser degree the systemic blood pressure.
Current software will allow running the CRRT circuit with return pressures consistently below <300 mmHg (Prismax) and <350 mmHg (Prismaflex) respectively. This would be reflected in the pre-oxygenator pressure in the PLS circuit and post-oxygenator pressure in the HLS circuit (see connections above).
A software update for the Prismax is in progress by the manufacturer. Current Prismaflex software will accept these positive pressure ranges after the standard startup.
Options to manage high CRRT pressure alarms on ECMO
For all alternative options risk benefit discussion to occur with ECLS CNC/ECLS CON
- Reduce CRRT blood flow (low risk intervention, blood flow settings between 150 and 250 ml/min usually acceptable) – decreased solute clearance
- Reduce ECMO blood flow (if possible) – decreased patient support
- Replace ST 100 set with ST 150 set (ST 150 now routine)
- PLS/HLS: change CRRT return port to post-oxygenator connection – small effect avoiding the transmembrane pressure component. (increased risk of air emboli)
- Consider inserting a separate vascath
- Consider non-ECMO site for CRRT return – caution high risk (large bore proximal peripheral cannula, note 18G flow ~150ml/min with pressure so ideally 16G and reduce CRRT blood flow, also consider the site of return, ability to observe for extravasation given the high flow rates.)