ECMO circuit change

Indications and considerations

Common reasons to exchange the ECMO circuit are clot accumulation with or without rise in Delta P. This may be associated with coagulation system activation and inflammation e.g. with rising D-Dimer and falling fibrinogen (< 2). It is less common for the oxygenator to malfunction and fail to oxygenate however post oxygenator PaO2 below 300mmHg should be srutinised and <200mmHg (FiO2 1.0) should lead to a circuit exchange. Gas exchange can also be disturbed by inefficient CO2 clearance. The age of the circuit is an unreliable measure, an indication may occur very early in the run, however replacement is common after 2-3 weeks.

Indications

Emergency*

  • Air embolus
  • Mechanical failure – leakage at membrane oxygenator, connectors or pump head
  • Pump head thrombosis (visible clots, increased noise, haemolysis, reduced platelets)
  • Acute oxygenator thrombosis (visible thrombus, reduced outflow PaO2, increasing transmembrane pressure gradient)

* The urgency is determined by the support and stability of the patient. Clearly a stalling pump from one of these mechanisms requires an immediate change with the Emergency pack – otherwise the procedure is performed semi-electively.

Semi-elective

  • Device-related coagulopathy (local fibrinolysis in membrane, decreased platelet count, hyperfibrinolysis)
  • Worsening gas exchange (oxygenation or CO2 removal)
  • Approaching life span of circuit
  • As part of reconfiguration

Emergency pack

Mostly there is time to properly set up for a circuit change as below under semi-elective exchange. However, in an absolute emergency where the patient is unsupported and deteriorating use the Emergency pack on the console. Commence resuscitating the patient (ensure airway secured, establish full ventilation, apply defibrillator pads), whilst simultaneously setting up for exchange procedure.

This is exceptionally rare but done with simple sterile gloves, cutting the circuit, inserting 3/8 connectors and an underwater seal using the prepacked 10ml NaCl 0.9%.

Semi-elective exchange

Equipment

When setting up for a circuit change, the following equipment is required:

  • Console
  • Primed ECMO circuit + console
  • Trolley
  • Large ECMO trolley
  • Defries pack
  • CVC sterile drape pack
  • ECMO equipment
  • ⅜” x ⅜” connectors (2 required – no side taps)
  • ECMO clamps (8 required)
    • 6 sterile: 4 for old circuit, 2 for limbs of new circuit
    • 2 non-sterile: for console operators to apply
  • General equipment
    • Betadine solution (NOT chlorhexidine)
    • 0.9% Saline 1L
    • Sterile fluid bag spike
    • Heparin (10,000 units or 5,000 units if < 50kg)
    • Sterile scissors x 2
    • 4 x 60ml catheter-tip syringes

Personnel

A standard circuit change requires a team of 8 people, with the following roles:

Proceduralists

Two proceduralists are required for each new connection (i.e. 4 people sterile gowns total)

  • Identify in advance who does what (i.e. clamp, cut, underwater seal, connection)
  • Agree on technique: Routinely ⅜” connectors are attached to the ends of the new circuit. The old circuit is cut, leaving a portion of the old circuit still attached to the cannulae. The new circuit is attached to this portion via underwater seal.
  • Ensure correct orientation of circuit limbs
  • Perform “talk-through”

In exceptional circumstances the old circuit may be removed entirely by slicing the tubing at the connection of the cannulae. The new circuit is then directly attached to the cannula. However, this risks damage to the connector/cannula with the potential for “silent” air embolism.

Console

Allocate responsibility for old and new consoles

Operator

Complete new circuit checks

See initiation of ECMO (link)

Resuscitator

Prepare resuscitation drugs

Identify rapid venous access point

Communicate plans with team leader

Identify and manage deterioration

Team Leader

Overall control and leadership of procedure

Allocate roles, communicate steps

Plan for potential complications

Ensure proceduralists have performed ‘talk-through’

Ensure skill mix and experience of operators is appropriate

Ensure patient and team safety

Ask the team: “does anyone have questions or concerns?”

Procedure

A circuit change requires preparation of the patient, equipment and new circuit, prior to the circuit change procedure itself. Once this is completed, post-procedure checks need to be performed as listed below.

Prepare patient

  • Ensure adequate sedation and muscle relaxant
  • Optimise ventilation and pre-oxygenation
  • Optimise haemodynamic support (± commence inotrope)
  • Position patient

Prepare equipment

  • Proceduralists perform surgical scrub and don PPE
  • Prepare trolley, pour saline into blue bowl via sterile spike, add heparin
  • Commence sterile skin preparation and decontamination of existing ECMO circuit
  • Position sterile drapes, non-fenestrated drape (General Pod – opposite pharmacy) for underneath prepped cannulae, Defries drape over top, enlarge holes to widen field

Prepare new circuit

  • Complete new circuit checks (see initiation)
  • Prepare circuit tubing

PLS

  • Hand new circuit to proceduralists who sterilise with Betadine
  • Proceduralists clamp each limb and cut (hands-width above), ensuring sterility, straight cut

HLS

  • New circuit in sterile tray is opened and offered to proceduralists
  • Operators remove circuit from tray, use provided blue clamps and pre-made connection
  • Cut off connectors

Prepare for procedure

  • Team leader to lead “talk-through” of procedure
  • Ensure correct orientation of circuit limbs
  • Resuscitator ready to titrate vasoactives once clamps on (= off mechanical support)
  • Connect ⅜” connectors to each limb of new circuit

Circuit change procedure

  • Apply clamps to circuit
  • Cut old circuit between clamps
  • Ensure sufficient tubing length to allow easy connection (> 5cm from clamp)
  • Perform underwater seal and check for bubbles

Mandatory checks by cannulator before connection – assistant to remind them

  • Check for obvious air – tubing, oxygenator, pumphead
  • Confirm clamp on the circuit
  • Oxygen connected and turned on

Perform underwater seal connection

  • Check connection for air bubbles
  • Cannulators: CLAMPS OFF
  • Set 1500 RPM and Console operator: CLAMP OFF
  • Steadily increase ECMO support (3000-4000 RPM) to achieve desired blood flow

Confirmation

  • Visualise direction of blood flow from the access cannula to pump head
  • Colour change across the oxygenator confirms gas delivery and function

Post-procedure:

  • Apply cable ties to connections
  • Secure cannulae and tubing with Grip-Locks

Circuit examination prior to disposal

If pump head thrombosis or oxygenator thrombosis were considered as potential causes, the diagnosis should be confirmed by examination of the circuit post exchange.

This is done in the disposal room by flushing the oxygenator and pumphead. Tap water can be aspirated through the access limb by running the circuit until sufficiently flushed.

In the PLS circuit the oxygenator and pump head are easily accessible and can visually be inspected post flushing. The HLS circuit requires a torx key to remove the pump head and expose the inflow side of the the oxygenator as shown below. The key can be found in the ECMO store area.

The torx key [A] is utilised to separate the HLS pump head from the oxygenator. There are 4 screws to unscrew on the pump head plate [B] and 2 on the sidearm [C].

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