Key Learning Points

1. ECMO Blood Flow Depends on Venous Return

• ECMO blood flow is preload-dependent.

• Venous return = (Mean systemic filling pressure – Right atrial pressure) / Resistance.

• Determined by venous tone, intravascular volume, cannula position/diameter, and pump speed.

2. Chattering: Causes and Interpretation

Chattering (cannula swing or collapse) occurs when venous return is insufficient for set pump speed. Causes include:

• Hypovolemia (absolute or relative)

• Cannula malposition

• High intrathoracic/intra-abdominal pressures

• Patient-ventilator asynchrony or agitation

• Circuit thrombus or obstruction

3. Management Algorithm

Step 1: Decrease pump speed — “low and slow” approach to avoid suction and hemolysis.

Step 2: Inspect circuit and cannula — confirm no kinks, clots, or malposition.

Step 3: Optimize sedation — reduce coughing, straining, or spontaneous breaths if premature.

Step 4: Address mechanical complications — rule out tamponade, pneumothorax, IAH.

Step 5: Consider fluid bolus — only if other causes excluded.

Step 6: Add drainage cannula — in refractory cases, increase drainage capacity

Volume Resuscitation: Rational Approach

• Avoid reflex fluid boluses for chattering.

  • Clinical signs

  • Lactate

  • TTE/echo

  • Passive leg raise (PLR)

  • Capillary refill time (CRT)

    Evaluate need based on:

  • Start with crystalloids (e.g., Ringer’s or NS).

  • Albumin and PRBCs only in specific indications.

  • Avoid excessive fluid — positive fluid balance on ECMO day 3 correlates with increased mortality.

    Fluid type:

Special Scenarios Discussed

• Double-lumen cannula: Requires meticulous positioning due to single drainage port.

• Septic patient on VV ECMO with high flow needs: Consider VVA configuration or adding drainage cannula.

Final Message

Chattering ≠ immediate fluid bolus.

Use a structured, physiological approach.

Tailor interventions based on timing, aetiology, and patient-specific context.