Circuit priming

General aspects

Circuit priming needs to be carried out with meticulous attention to sterility, proper connections, and an air-free prime.


Only the ECLS Coordinator, accredited ICU Consultants or a member of the Perfusion Department may perform and / or supervise ECMO circuit priming.

Pre-pump access ports

All ECMO circuits primed at The Alfred have no access ports on the negative pressure (access) side of the circuit to reduce the incidence of air entrainment. PLS circuits do come with two ports on the negative pressure (access) side of the circuit when removed from the box. These ports are cut out of the circuit during the priming process. The CRRT connections are on the return side (positive pressure).

Caution: ECMO circuits that arrive from other centres may have access ports on the negative pressure side of the circuit. These should be immediately secured with Sleek, and consideration given to changing out the circuit within 24 hours of admission to the Alfred ICU for operational and patient safety concerns.

PLS circuit priming


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PLS priming – step by step instructions

Equipment required

Consumables required

ECMO PLS console

PLS Circuit

CO2 cylinder

Large Trolley

Sterile gloves / gown / mask / hat

5 x 3-way tap with extension

2 x 1000ml 0.9% NaCl

2 x Sterile drapes (fenestrated)

Cable ties & cable gun

Lovells Bag

1 x 20ml syringe

Staff 1 sterile primer, 1 non sterile assistant

Trolley and circuit set up

  • Prepare trolley with Viraclean
  • Sterile primer to perform surgical scrub, gown, glove, mask and hat. Hat and mask for assistant
  • Prepare sterile surface with fenestrated drapes (2 x drapes to cover fenestrations with current drapes). Keep smaller drapes to place on floor later
  • Assistant to open PLS circuit box. (Easier to leave box on a chair or low table)
  • Remove Velcro attachments (4x) and move PLS circuit onto sterile surface
  • In addition take out green tubing, large bags, scissors and cable tie
  • Do NOT discard small bags and extensions contained with PLS circuit.

Completing the circuit

  • Cut the 2 x access ports (single cut) out of the access limb of circuit
  • Connect circuit to pump head. Note cable tie must be applied to this connection at the end of the prime.
  • Cut U-bend connector from circuit (2 x cuts).
  • Connect Lovells bag to circuit – Y-limb connects to BLUE (access) limb; RED (return) to the other single line.
  • Connect 5 x 3-way taps with extensions directly to the circuit: 2 between pump and oxygenator, 1 pre-oxygenator, 1 post-oxygenator, 1 onto oxygenator

Carbon dioxide Prime

  • Connect CO2 filter to one 3-way extension between pump and oxygenator, connect green tubing to CO2 filter and hand to assistant to connect to CO2 cylinder.
  • Clamp before or after the 3-way tap and the pump head and oxygenator.
  • Turn on CO2 cylinder and run CO2 at 1-2 L/min.
  • Once Lovells bag is filled with CO2, briefly remove red cap clamp and flush fluid line with CO2 before reapplying clamp.
  • Reduce CO2 flow to 0-1 L/min.
  • Flush each 3-way tap – Sterile primer does this by applying gentle pressure to CO2 reservoir in Lovells bag. Listen for hissing noise from each port.
  • Switch clamp to the other side of the 3-way extension with CO2 attached.
  • Repeat process of flushing each 3-way tap on circuit.
  • Disconnect and discard CO2 priming line from circuit.

Fluid Prime

  • Pass fluid attachment from Lovells bag to assistant. Leave clamped. Attach to first 1000ml bag of 0.9% NaCl.
  • Ensure other ports to Lovells bag are CLAMPED.
  • Fill Lovells bag with ~1500ml of 0.9% NaCl by removing clamp from fluid line (gravity is your friend).
  • When Lovells bag has been filled reapply clamp to fluid line.

ECMO Console (nonsterile step)

Please try to minimize tangling of the lines at this stage.

  • Remove yellow cap from oxygenator but do not discard.
  • Hang up the priming bag and allow to prime by removing clamps on table.
  • Attach oxygenator to holder and place pump head into pump.
  • Use gravity to remove any macroscopic bubbles from circuit. NB. This is likely to require some manipulation of the circuit and briefly removing the pump head from the pump and the oxygenator from its holder.
  • Assistant to plug ECMO console into power and turn on console.
  • Silence alarm. Turn flows up, then down to zero until display shows ‘0’ LPM flow.
  • Gradually increase to approximately 2000RPM until the fluid remaining in the Lovells bag shows evidence of ‘gentle agitation’.
  • Ensure no further bubbles in ECMO circuit.
  • Sterile primer then aspirates from each 3-way tap attachment on circuit using 20ml Syringe.

ECMO prime complete

  • Replace yellow cap onto oxygenator.
  • Apply cable tie to attachment made on pump head.
  • Turn off ECMO console.
  • Clamp attachments to Lovells bag using blue clamps included in PLS equipment.
  • Remove cap from oxygen attachment to oxygenator.
  • Cover circuit and return to ECMO area.
  • Complete Priming paperwork and attach to circuit cover.

HLS circuit priming


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General comments

  • The HLS circuit is designed to be primed at the time of ECMO commencement.
  • Sterile attire and CO2 priming are not required.
  • All circuit connections to be performed with no-touch technique.

Equipment required

  • Cardiohelp Pump
  • HLS box with disposable circuit
  • 3-way taps with extension (x3)
  • 2 litres of 0.9% NaCl

Step 1 Connections to Cardiohelp

  • Place Cardiohelp arm in the “up” position & connect module to Cardiohelp
  • Leave de-airing port (yellow cap) off
  • Add 3-way taps with extension tubing to pre (1x) and post (2x) oxygenator ports

  • Connect integrated sensor cable (temperature and pressure) to HLS Module
  • Connect flow probe (bubble sensor) to the return line and ensure the direction of flow is correct
  • Ensure the Venous Probe is connected to the initializing station on the blue handle
  • Lower the Cardiohelp arm and place sterile tray on top (should sit securely) – contents of tray to remain sterile

Step 2 Complete circuit

  • Hang priming bag (alternatively use dedicated priming board to hang the priming bag)
  • Remove ends from both the sterile tray tubing and the priming lines and then connect, pay attention to the direction of the white lip to place your thumb
  • Connect pair of red and blue lines
  • Clamp outlet (blue) of priming bag

Step 3 Pressure zeroing

  • Turn Cardiohelp on
  • Go to second menu at the bottom of the screen
  • Zero 3 pressures Part, Pven and Pint – enter pressure setting and perform zero

Step 4 Priming process

  • Connect filling line to 0.9% saline & transfer almost 2L 0.9% saline to priming bag (Open stop-cocks on the priming bag to de-air the reservoir)
  • Ensure adequate elevation of priming bag (>60cm)
  • Allow priming to occur passively by opening all clamps
  • Wait (!) for priming to occur
  • Run pump at 3000rpm for at least 2 min, then 4000rpm for an additional 1 minute
  • Purge all 3-way taps
  • Ensure all air removed from circuit – no air should be visible and the pump should be virtually silent

Step 5 final checks

  • Close de-airing port (yellow cap)
  • Ensure the taps of the reservoir are all closed (contamination risk)
  • Remove cap from oxygen connection
  • Cover circuit and return to ECMO CPR area
  • Turn off ECMO console and plug in
  • Complete Priming paperwork and attach to circuit cover

Immediate patient connection

  • Clamp both lines from sterile tray
  • Close G-clamps to/from priming bag. Disconnect from the sterile tray tubing
  • Complete loop from sterile tray
  • Open sterile tray and hand tray to cannulator for connection to cannulae
  • Sterile cannulator to place clamps at markings within sterile tray
  • Disconnect from tubing which exits the sterile tray and complete circuit loop
  • Remove sterile tubing from sterile tray
  • Clamp, cut and connect to cannulae with “underwater” seals

Temporary VAD circuit priming

Increasing use of temporary VAD circuits has led to requirements for circuit changes in this patient group e.g. urgently in case of a pump head thrombosis. Timely circuit priming, therefore, is a required skill.

A dedicated temporary VAD box can be found in the ECMO area.

A suggested efficient way of priming the circuit is described in the video and the step-by-step guide below.

link video

Set up and connections

  • Sterile set up with an ECMO pack in anticipation of a circuit change.
  • Insert access ports for renal replacement therapy if required to the return line (2x straight ⅜ connector with luer lock). Ensure connectors are inserted at least 30cm away from the pump.
  • Add 3-way taps with extension tubing to both connectors


  • Place ECMO clamp at the distal end of the access tubing.
  • Connect pump set to Luer lock just above clamp
  • Hand over the pump set to your assistant to connect to 1L 0.9% Saline to prime the line.
  • Carefully continue to prime the circuit in a slow and steady fashion to keep it bubble-free. In particular, the pump head needs to be handled carefully to stay bubble-free. The flow can be regulated by the pump set and height of priming bag but generally, passive filling is sufficient.
  • Clamp once the entire circuit is filled.
  • Prime 3-way extensions before clamping and check for bubbles
  • If no bubbles identified cut out the priming port and leave both ends clamped.
  • For later use you connect the ends with a ⅜ connector with an underwater seal

For circuit changes at the bedside the same principles as in any other ECMO circuit change apply.

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