ECMO- Basic values and catastrophic complications

Question 1

V-V ECMO
Q* Initiation
Q. Subsequent titration

Answer 1

->* Titrate RPM ↑ gradually over 1–5 minutes.
* Target = predicted blood flow = BSA × 1.8 L/min/m².

->Subsequent titration
* Adjust RPM to minimum flow needed to maintain adequate systemic oxygenation.
* Typically ≈ 5 L/min early on.
* ⚠️ High pump flows → ↑ recirculation fraction → may not improve oxygenation beyond threshold.

Question 2

Pump speeds VA vs VV

Answer 2

Question 3

Blood flows VA vs VV

Answer 3

Add increased risk of Recirculation in the risks asso with higher flows in VV

Question 4

P Venous
Q.what is it?
Q.What does it reflect?
Q.What is the targetPven?
Q. what is the consequence of excessively negative Pven?

Answer 4

1. Pven (Venous/Pre-pump Pressure, P1)
   
   • Pressure before blood enters the pump.
   • Reflects suction required to drain venous blood through cannula/tubing.
   • ⚠️ Target: -<100 mmHg (Red Book 6e).
   • Excessively negative → hemolysis, vessel trauma.

Question 5

Causes of excessively negative Pven (Drainage insufficiency)

Answer 5

->Inadequate preload:
* Hypovolemia
* ↑ Intrathoracic pressure (e.g. pneumothorax, high mean airway pressure)
* ↑ Intra-abdominal pressure (Mx-sedation, cannula above diaphragm)
* Variable intrathoracic pressure (coughing, bucking ventilator → treat with synchrony, ↑ sweep to ↓ drive, opioids)

->VA ECMO-specific: competing preload (native cardiac recovery), tamponade compressing RA

->Cannula/tubing issues:
* Kinked, malpositioned, clotted, too small → may need second drainage cannula

->Excessive pump speed

Answer 6

Management
* Reduce pump speed (may paradoxically improve flow if suction relieved)
* Assess hemodynamics & causes of drainage insufficiency
* Last resort: add additional drainage cannula
( see complications- access insufficiency)

Question 7

2. Pint (Internal/Post-pump Pressure, P2)

Answer 7

• Highest pressure in the ECMO circuit.
• Reflects pressure to push blood through membrane, tubing, and back to patient.
• Goal: <300 mmHg (hemolysis risk rises >250 mmHg).

Question 8

3. Part (Arterial/Post-membrane Pressure, P3)

Answer 8

• Pressure in arterial return tubing after oxygenator.
• Reflects resistance through arterial tubing/cannula.
• ⚠️ Very high (>300 mmHg) → risk of hemolysis.

Question 9

4. ▵P (Transmembrane Pressure)

Answer 9

-> ▵P = Pint – Part
* Normal: <40–50 mmHg
*** **▵P >60 mmHg or steadily rising (without ↑ circuit flow) → membrane lung dysfunction **⚡️
* **▵P >100 mmHg → strongly suggests oxygenator failure ⚡️

Question 10

Return obstruction (↑Part, ↑Pint, stable ▵P)

Answer 10

1)* High cannula resistance: compression, kink, clot, malposition, cannula too small
2)* ↑ Vessel pressure:
* VV ECMO → ↑ CVP (e.g. tamponade, tension pneumothorax)
* VA ECMO → systemic hypertension (MAP»_space;65 mmHg)

=>Management of return failure
* Check for kinks/external compression
* Evaluate listed causes
* Consider vascular imaging

Question 11

5. Sweep Gas Flow
   Q. Purpose
   Q. Typical setting
   Q Indications where you might start at a different setting

Answer 11

• Typical range: 1–9 L/min
  
  • Determines CO₂ clearance.
  • Does not affect oxygenation, unless sweep <0.5 L/min.

Initial sweep setting
* Usually 50–100% of ECMO flow.
* Historically = ECMO flow; with modern oxygenators, 50% flow is often sufficient.

Indications to start lower sweep
1. Baseline hypercapnia
2. Situations where hypocapnia particularly undesirable

Question 12

FdO2

Answer 12

->It is the Fractional delivered oxygen in the sweep gas that passes through the membrane lung.
->Crucial setting for controlling the amount of oxygen added to the blood, alongside the ECMO blood flow rate, which determines the overall oxygenation of the patient’s arterialized blood.
Oxygenation Parameters in ECMO

->For VV ECMO:
* FdO₂ generally set at 100%.

->For VA ECMO:
* Blood delivered directly to tissues → risk of tissue hyperoxia.
* Adjust FdO₂ to target slight hyperoxemia: Post-oxygenator PaO₂ ~150 mmHg

Question 13

SarO2 (arterial return saturation)
&
ParO2 (pO2 in arterial return)

Answer 13

=>VV ECMO
-> SarO₂: ~100%
-> ParO₂:
* New device: >600 mmHg
* Over time: ParO2 decreases but should remain >250 mmHg
* <150–200 mmHg → abnormal (suggests dysfunction)

=>VA ECMO
->SarO₂: close to 100%
-> ParO₂:
* Avoid marked hyperoxia
* titrate to PaO₂ >60–150 mmHg

Question 14

Causes of Low Circuit Flow

Answer 14

• Inadequate Preload ⚡️Elevated Pven
  
  • Hypovolemia, high intrathoracic/intra-abdominal pressure, tamponade, drainage insufficiency.
• Membrane failure (elevated ▵P) ⚡️
• Afterload excessive (high Part & Pint, stable ▵P) ⚡️
  
  • Return cannula obstruction (kink, clot, malposition).
  • ↑ systemic arterial pressure (VA) or ↑ central venous pressure (VV).
• Inadequate RPMs

Question 15

Causes of Circuit Flow Arrest

Answer 15

1). Clamp left on
2). Pump failure – mechanical / electrical
3). Catastrophic clot – obstructing circuit.
4). Extraluminal cannula/ vessel dissection (check by CXR or ultrasound).
5). Arterial air alarm – pump automatically stops if bubble detector senses air.
6). Pump air lock

Question 16

pump failure

Answer 16

causes

->Console dysfunction:
->Driver failure: Not coupled with the pump head.
->Pump head failure:
Thrombosis (noise may be heard).
Air embolism (pump head airlock).

clinical presentation->Abrupt loss of ECMO flow.

Management:
-Airlock: de-airing.
-Thrombosis: change pump or ECMO circuit.
-Hand crank or backup console (but not for thrombosis or airlock).
-VA ECMO: clamp the circuit to prevent backward flow that may cause a large arteriovenous shunt.
-CPR may be required.

Question 17

Why are the flows higher in VV as compared to VA?

Answer 17

1) Different physiologic targets
* VV ECMO (gas exchange):
You’re trying to replace oxygenation/CO₂ clearance. To keep SpO₂ >90% when the native lung contributes little, you often need a large venous flow fraction (≥60–70% of CO). Real-world factors (recirculation, cannula geometry) push you to higher flows than the BSA×1.8 estimate.
* VA ECMO (perfusion):
You’re augmenting systemic perfusion & MAP, not primarily oxygenation. Starting around ~4 L/min often achieves perfusion targets while avoiding LV afterload/distension and differential hypoxia.

2) Recirculation (VV) vs afterload (VA)
* VV: Increasing flow can be offset by recirculation; to achieve effective oxygen delivery you often run 4.5–6 L/min early, even though BSA×1.8 may calculate ~3–3.5 L/min for many adults.
* VA: Higher flows increase LV afterload, risking LV distension/pulmonary edema. So you typically start lower and titrate to perfusion endpoints.

3) Cannula/equipment constraints
* VV: Large-bore venous drainage/return can often tolerate higher flows with acceptable pressures.
* VA: Arterial return imposes higher circuit/vascular resistance (Part/Pint), raising hemolysis risk at high flows.