ECMO Circuits and Equipment

Quick Answer

Extracorporeal Membrane Oxygenation (ECMO) is an advanced life support modality that provides temporary support for severe cardiac and/or respiratory failure when conventional therapies fail. ECMO circuits consist of vascular access cannulae, a centrifugal pump, a membrane oxygenator (with integrated heat exchanger), and connecting tubing. VV-ECMO (venovenous) provides isolated respiratory support for severe ARDS (P/F ratio <80, refractory hypoxemia), while VA-ECMO (venoarterial) provides both cardiac and respiratory support for cardiogenic shock or cardiac arrest. Anticoagulation with unfractionated heparin (target ACT 180-220 seconds) or bivalirudin is essential to prevent circuit thrombosis. Key complications include bleeding (10-40%), limb ischemia (10-15% in peripheral VA), recirculation (VV-ECMO), and differential hypoxia (VA-ECMO). ECMO survival rates are approximately 55-65% for VV-ECMO and 40-50% for VA-ECMO. Australian ECMO retrieval services (ECMO Response, CareFlight, MedSTAR) provide mobile ECMO cannulation for interhospital transfer.

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CICM Exam Focus

What Examiners Expect

Second Part Written (SAQ):

Common SAQ stems:

• "A 45-year-old patient with severe ARDS has a P/F ratio of 60 despite optimal ventilation and prone positioning. Outline the indications, contraindications, and initial management of VV-ECMO."
• "A patient on peripheral VA-ECMO develops cyanosis of the upper body with pink lower limbs. Explain the pathophysiology and outline your management."
• "Discuss the components of an ECMO circuit and the principles of troubleshooting common circuit problems."
• "Compare the indications, configurations, and complications of VV-ECMO and VA-ECMO."
• "A patient on VV-ECMO has low PaO2 despite high flow and FdO2. Outline your approach to diagnosis and management."

SAQ scoring expectations:

• Systematic classification of ECMO configurations (VV vs VA)
• Understanding of circuit components and their functions
• Evidence-based indications and contraindications
• Anticoagulation targets and monitoring
• Complication recognition and management
• Familiarity with ELSO guidelines and EOLIA trial evidence

Second Part Hot Case:

Typical presentations:

• Patient on VV-ECMO for severe ARDS with ongoing hypoxemia
• Patient on VA-ECMO post-cardiac surgery with signs of recovery
• ECMO patient with suspected circuit complication (thrombosis, hemorrhage)
• Assessment of patient for ECMO weaning trial

Examiners assess:

• Systematic assessment of ECMO circuit and patient parameters
• Interpretation of ECMO flows, pressures, and blood gases
• Recognition of complications (recirculation, differential hypoxia, limb ischemia)
• Safe adjustment of ECMO parameters
• Weaning assessment and readiness criteria
• Communication with ECMO specialists and family

Second Part Viva:

Expected discussion areas:

• Physiology of VV-ECMO vs VA-ECMO
• Circuit components and their functions
• Anticoagulation strategies (heparin vs bivalirudin)
• Management of differential hypoxia in VA-ECMO
• ECMO for refractory cardiac arrest (ECPR)
• Evidence base for ECMO (CESAR, EOLIA trials)
• Weaning strategies and decannulation criteria
• Australian ECMO retrieval systems

Examiner expectations:

• Safe, consultant-level ECMO knowledge
• Understanding of when to involve ECMO specialists
• Evidence-based decision-making
• Knowledge of ELSO guidelines
• Awareness of Australian ECMO networks

Common Mistakes

• Confusing VV-ECMO (respiratory only) with VA-ECMO (cardiac + respiratory)
• Not understanding the pathophysiology of differential hypoxia
• Failing to consider recirculation as a cause of hypoxemia in VV-ECMO
• Not monitoring for limb ischemia in peripheral VA-ECMO
• Incorrect anticoagulation targets (ACT too high/low)
• Not recognizing oxygenator failure (increased transmembrane pressure gradient)
• Confusing access (deoxygenated blood out) and return (oxygenated blood in) cannulae
• Not understanding the concept of ECMO flow vs native cardiac output in VA-ECMO

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Key Points

Must-Know Facts

1. VV-ECMO Configuration: Drains deoxygenated blood from venous system (typically femoral/jugular), passes through oxygenator, returns oxygenated blood to venous system (right atrium). Provides respiratory support only; patient must maintain own cardiac output (PMID: 27010949).

2. VA-ECMO Configuration: Drains deoxygenated blood from venous system, returns oxygenated blood to arterial system (femoral artery or ascending aorta). Provides both cardiac and respiratory support. Creates retrograde flow in peripheral VA (PMID: 26585095).

3. Circuit Components: Drainage cannula → Pump (centrifugal) → Oxygenator (with heat exchanger) → Return cannula. Modern oxygenators use polymethylpentene (PMP) hollow fiber membranes with integrated heat exchangers (PMID: 26457743).

4. Anticoagulation Targets: Unfractionated heparin most common - target ACT 180-220 seconds (ELSO guidelines). Bivalirudin alternative for HIT. Lower targets (ACT 160-180) acceptable if high bleeding risk (PMID: 34115980).

5. Recirculation in VV-ECMO: Oxygenated return blood immediately re-enters drainage cannula without systemic circulation. Measured by (SvO2 pre-oxygenator - SVC) / (SaO2 post-oxygenator - SVC). Target recirculation <20%. Managed by repositioning cannulae or adjusting flows (PMID: 29067112).

6. Differential Hypoxia in VA-ECMO: Upper body (coronary, cerebral) supplied by native cardiac output (potentially hypoxemic), lower body supplied by ECMO (well-oxygenated). Detected by right radial ABG saturation lower than femoral saturation. Managed by adding upper body oxygenation (VAV configuration) or central cannulation (PMID: 29067112).

7. ECMO Flow Targets: VV-ECMO: 60-80 mL/kg/min (4-6 L/min) to achieve SaO2 >88-90%. VA-ECMO: 2.0-2.4 L/min/m² (50-80 mL/kg/min) for adequate organ perfusion. Higher flows require adequate drainage (RPM increase) (PMID: 27010949).

8. Limb Ischemia in Peripheral VA: Occurs in 10-15% of peripheral VA-ECMO. Femoral arterial cannula obstructs distal flow. Prevention: Prophylactic distal perfusion cannula (DPC) at cannulation. Treatment: Urgent DPC insertion or surgical fasciotomy (PMID: 28506685).

9. Weaning Criteria VV-ECMO: Improving native lung function (P/F >150-200 on low ECMO support), tolerated sweep gas reduction, adequate spontaneous ventilation, resolving underlying cause. Trial: Reduce sweep to 0-1 L/min, maintain blood flow, assess for 1-4 hours (PMID: 32366514).

10. EOLIA Trial Evidence: VV-ECMO in severe ARDS did not reduce 60-day mortality (35% vs 46%, p=0.09) but high crossover rate (28%). Post-hoc analysis and meta-analysis suggest mortality benefit (RR 0.73). Supports ECMO as rescue therapy for refractory ARDS (PMID: 29791822).

Memory Aids

ECMO-SAFE - Essential ECMO Monitoring:

• ECMO flows and pressures (inlet pressure -50 to -100 mmHg, avoid air entrainment)
• Coagulation (ACT 180-220, platelets >50, fibrinogen >1.5)
• Membrane function (pre/post oxygenator gases, transmembrane pressure <50 mmHg)
• Oxygenation (SaO2, SvO2, lactate, mixed venous saturation)
• Sweep gas (adjust for CO2 clearance, independent of blood flow)
• Anticipate complications (bleeding, thrombosis, hemolysis, infection)
• Flow (60-80 mL/kg/min target, adjust RPM)
• Evaluate for weaning daily

ECMO RED FLAGS - Complications to Watch:

• Recirculation (low SaO2 despite high flows)
• Embolism (air, thrombus)
• Differential hypoxia (upper body desaturation)
• Flow problems (low flow, high pressures)
• Limb ischemia (pale, pulseless, painful limb)
• Anticoagulation issues (bleeding, thrombosis)
• Gas exchange failure (oxygenator clot)
• Systemic complications (stroke, infection, renal failure)

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Definition & Epidemiology

Definition

Extracorporeal Membrane Oxygenation (ECMO) is a form of temporary extracorporeal life support that provides gas exchange (oxygenation and CO2 removal) and/or circulatory support for patients with severe cardiac and/or respiratory failure refractory to conventional management.

ECMO Classification:

ECMO Intent:

Epidemiology

International Data (ELSO Registry):

• Annual ECMO runs globally: ~17,000 (2022 data) (PMID: 35915992)
• Neonatal: 30%, Pediatric: 15%, Adult: 55%
• Adult respiratory ECMO: 55-65% survival to discharge
• Adult cardiac ECMO: 40-50% survival to discharge
• ECPR (E-CPR): 30-40% survival to discharge
• Total ELSO registry cases (1989-2022): >200,000

Australian/NZ Data (ANZICS ECMO Registry):

• Australian ECMO centers: 15 (major centers: The Alfred Melbourne, Royal Prince Alfred Sydney, St Vincent's Sydney, Prince Charles Hospital Brisbane, Fiona Stanley Perth) (PMID: 30929575)
• NZ ECMO centers: 3 (Auckland City Hospital primary, Wellington, Christchurch)
• Annual ECMO runs (Australia): ~500-600 adults
• VV-ECMO for COVID-19 (2020-2022): >800 patients nationally
• Mobile ECMO retrieval: ECMO Response (Victoria), CareFlight (NSW/national), MedSTAR (SA)
• Median ECMO run duration: 7-10 days (respiratory), 4-5 days (cardiac)

Risk Factors for ECMO Mortality:

Pre-ECMO Factors:

• Age >65 years (PMID: 33069320)
• Mechanical ventilation >7 days before ECMO (PMID: 29791822)
• Immunocompromised state
• BMI >40 or <18.5
• Multiorgan failure (SOFA >12)
• Pre-existing renal failure

On-ECMO Factors:

• Bleeding requiring >4 units PRBC/day
• Renal replacement therapy
• Infection
• Neurological complications
• ECMO duration >14 days

High-Risk Populations:

• Aboriginal and Torres Strait Islander peoples: Limited data but likely underrepresented in ECMO services due to geographic barriers to tertiary care access; higher rates of cardiac disease and severe pneumonia
• Māori and Pacific Islander peoples: Higher rates of severe respiratory illness; geographic barriers to NZ ECMO centers
• Remote/rural populations: Significant delays in access to ECMO services; mobile ECMO retrieval essential

Outcomes:

• VV-ECMO survival (ARDS): 55-65%
• VV-ECMO survival (COVID-19): 50-55% (PMID: 33131360)
• VA-ECMO survival (cardiogenic shock): 40-50%
• VA-ECMO survival (post-cardiotomy): 35-45%
• ECPR survival (OHCA): 30-40%
• Long-term functional recovery: 70-80% of survivors return to baseline at 1 year

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Applied Basic Sciences

This section bridges First Part basic sciences with Second Part clinical practice

Physics of Extracorporeal Circulation

Blood Flow Dynamics

ECMO blood flow follows principles of fluid dynamics:

Flow Equation: Q = ΔP / R

Where:

• Q = Flow rate (L/min)
• ΔP = Pressure gradient (pump outlet - patient venous pressure)
• R = Resistance (circuit resistance + vascular resistance)

Determinants of ECMO Flow:

1. Pump Speed (RPM): Primary determinant; higher RPM = higher flow
2. Preload (Venous Drainage): Adequate intravascular volume essential
3. Afterload (Return Pressure): High arterial pressure limits VA-ECMO flow
4. Cannula Size: Follows Poiseuille's law - flow ∝ r⁴ (larger cannulae = higher flow)
5. Blood Viscosity: Hematocrit, temperature, fibrinogen affect viscosity

Poiseuille's Law Applied to ECMO:

Q = (π × ΔP × r⁴) / (8 × η × L)

Practical implications:

• 25Fr cannula allows ~6 L/min flow
• 21Fr cannula allows ~4 L/min flow
• Resistance proportional to length, inversely to radius⁴
• Hypothermia increases viscosity, reduces flow

Negative Pressure and Air Entrainment:

• Drainage limb operates under negative pressure
• Target inlet pressure: -50 to -100 mmHg
• Excessive negative pressure (<-300 mmHg) causes:
  • Air entrainment through cannula insertion site
  • Venous collapse ("suck down")
  • Hemolysis
  • Cavitation in pump head

Oxygenator Physiology

Membrane Oxygenator Design:

Modern oxygenators use hollow fiber membrane technology:

• Material: Polymethylpentene (PMP) - gas-permeable, plasma-resistant
• Surface area: 1.5-2.5 m² (adult)
• Blood flows outside hollow fibers
• Oxygen flows inside hollow fibers
• Gas exchange occurs across membrane by diffusion

Fick's Law of Diffusion:

V = (D × A × ΔP) / T

Where:

• V = Volume of gas transferred
• D = Diffusion coefficient
• A = Membrane surface area
• ΔP = Partial pressure gradient
• T = Membrane thickness

Oxygen Transfer:

• Determined by: Blood flow rate, FdO2, hemoglobin concentration, membrane surface area
• Maximum O2 transfer: ~400-500 mL O2/min at 5 L/min blood flow
• O2 delivery = ECMO flow × 1.34 × Hb × (SaO2 post - SvO2 pre) + dissolved O2
• Target: SaO2 post-oxygenator >95%

CO2 Removal:

• More efficient than oxygenation (CO2 20× more diffusible than O2)
• Primarily determined by sweep gas flow (not blood flow)
• Sweep gas = 100% O2 flowing through hollow fibers
• CO2 removal ∝ sweep gas flow (Fsweep)
• Double sweep gas → approximately double CO2 removal

Oxygenator Performance Monitoring:

Pump Physiology

Centrifugal Pump Principles:

Modern ECMO circuits use constrained vortex centrifugal pumps:

• Impeller rotates within pump housing
• Creates vortex that accelerates blood
• Non-occlusive design (no valves)
• Flow dependent on RPM and resistance

Pump Characteristics:

Common Centrifugal Pumps:

Anticoagulation Pharmacology

Unfractionated Heparin (UFH):

• Mechanism: Potentiates antithrombin III → inactivates thrombin (IIa) and factor Xa
• Half-life: 60-90 minutes (dose-dependent)
• Monitoring: ACT (bedside) or aPTT (laboratory)
• Target ACT: 180-220 seconds (ELSO guidelines) (PMID: 34115980)
• Target aPTT: 60-80 seconds (1.5-2.5× normal)
• Dosing: 50-70 U/kg bolus → 10-30 U/kg/hr infusion
• Reversal: Protamine 1 mg per 100 U heparin
• Complications: Bleeding, HIT (2-5%), osteoporosis (long-term)

Bivalirudin:

• Mechanism: Direct thrombin inhibitor (binds thrombin active site)
• Indication: Heparin-induced thrombocytopenia (HIT), heparin resistance
• Half-life: 25 minutes (hepatic metabolism, renal elimination)
• Monitoring: aPTT (target 60-80 seconds) or ACT
• Dosing: 0.03-0.2 mg/kg/hr infusion (no bolus typically)
• Reversal: No specific reversal agent (short half-life)
• Advantages: No HIT, more predictable response
• Disadvantages: Stagnant blood clots (requires continuous flow), cost (PMID: 30024654)

Argatroban (Alternative):

• Direct thrombin inhibitor
• Hepatic metabolism (use in renal failure)
• Half-life: 39-51 minutes
• Dosing: 0.2-0.5 μg/kg/min (reduced in hepatic impairment)

Anticoagulation-Free ECMO:

• Considered in severe bleeding, recent surgery, trauma
• Requires high blood flows (>4 L/min) and heparin-bonded circuits
• Increased thrombosis risk but feasible short-term (PMID: 29067112)

Hemodynamics of VA-ECMO

Circulatory Effects:

VA-ECMO profoundly alters hemodynamics:

Afterload Increase:

• Retrograde arterial flow increases LV afterload
• Mean arterial pressure increases
• LV wall stress increases
• Increased myocardial oxygen demand

LV Distension Risk:

• Impaired LV ejection against increased afterload
• LV distension → increased LVEDP → pulmonary edema
• Risk factors: Severe LV dysfunction, aortic regurgitation, inadequate ECMO support

Management of LV Distension (ECMELLA Strategy):

Native Cardiac Output Assessment:

• Pulse pressure on arterial waveform indicates native LV ejection
• Echocardiography: Aortic valve opening, LV function
• Mixed venous saturation: >65-70% indicates adequate DO2
• Lactate: <2 mmol/L suggests adequate perfusion

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Clinical Presentation

ICU Admission Scenarios for ECMO

Scenario 1: Refractory Hypoxemia in Severe ARDS

• History: 42-year-old with influenza pneumonia, intubated 5 days, P/F ratio 55 despite prone positioning, PEEP 14, FiO2 1.0
• Examination: Intubated, sedated, bilateral crackles, hypotensive on noradrenaline
• Severity: Severe ARDS (Murray score 3.5), candidate for VV-ECMO

Scenario 2: Refractory Cardiogenic Shock

• History: 58-year-old with massive anterior STEMI, post-PCI, worsening shock despite IABP and inotropes
• Examination: Cold, mottled peripheries, MAP 55 mmHg on multiple vasopressors, oliguric
• Severity: Cardiogenic shock (SCAI Stage D-E), candidate for VA-ECMO

Scenario 3: Out-of-Hospital Cardiac Arrest (ECPR)

• History: 55-year-old witnessed VF arrest, bystander CPR, refractory VF despite 4 shocks and antiarrhythmics
• Examination: Ongoing CPR 35 minutes, end-tidal CO2 25 mmHg, pupils 4 mm reactive
• Severity: Refractory cardiac arrest, candidate for ECPR

Scenario 4: Massive Pulmonary Embolism

• History: 38-year-old post-operative day 5, sudden cardiovascular collapse
• Examination: Pulseless, dilated right ventricle on echo, no response to thrombolysis
• Severity: Massive PE with cardiac arrest, candidate for VA-ECMO + surgical embolectomy

ECMO Indications

VV-ECMO Indications (ELSO Guidelines 2022) (PMID: 32366514):

VA-ECMO Indications (PMID: 26585095):

ECMO Contraindications

Absolute Contraindications:

• Irreversible underlying disease with no transplant option
• Unwitnessed cardiac arrest with prolonged no-flow time
• Advanced malignancy with poor prognosis
• Severe irreversible neurological injury
• Chronic severe organ dysfunction (severe liver cirrhosis, dialysis-dependent CKD)
• Uncontrolled bleeding or contraindication to anticoagulation

Relative Contraindications:

• Age >70 years (consider on individual basis)
• Mechanical ventilation >7-10 days
• BMI >45 or <18
• Immunocompromised state
• Aortic dissection or aortic regurgitation (VA-ECMO)
• Limited vascular access
• Unknown neurological status post-arrest

Severity Scoring

RESP Score (Respiratory ECMO Survival Prediction) (PMID: 24693864):

Predicts survival for VV-ECMO in ARDS:

Risk Classes:

• Class I (≥6 points): 92% survival
• Class II (3-5 points): 76% survival
• Class III (-1 to 2 points): 57% survival
• Class IV (-5 to -2 points): 33% survival
• Class V (≤-6 points): 18% survival

SAVE Score (Survival After Veno-Arterial ECMO) (PMID: 26341508):

Predicts survival for VA-ECMO:

Risk Classes:

• Class I (>5): 75% survival
• Class II (1-5): 58% survival
• Class III (-4 to 0): 42% survival
• Class IV (-9 to -5): 30% survival
• Class V (≤-10): 18% survival

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Investigations

Pre-ECMO Workup

Essential Investigations:

Echocardiography for ECMO Assessment:

Pre-VV-ECMO:

• LV function (must be adequate for VV-ECMO)
• RV function and size
• Pulmonary artery pressures
• Intracardiac thrombus
• Patent foramen ovale (risk of paradoxical embolism)

Pre-VA-ECMO:

• LV/RV function
• Aortic regurgitation (contraindication to peripheral VA)
• LV thrombus
• Pericardial effusion

Vascular Assessment:

• Peripheral pulses (dorsalis pedis, posterior tibial)
• Ultrasound of femoral vessels (size, patency)
• CT angiography if peripheral vascular disease suspected
• Measure vessel diameter for cannula sizing

On-ECMO Monitoring

Continuous Monitoring:

Intermittent Laboratory Monitoring:

Imaging on ECMO:

• Daily CXR (ETT, cannula position, lung changes)
• Echocardiography (daily if VA, every 2-3 days if VV)
• CT if complications suspected (intracranial bleeding, stroke)
• Limb Doppler if ischemia concerns

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ICU Management

ECMO Cannulation

VV-ECMO Cannulation Configurations:

VA-ECMO Cannulation Configurations:

Cannulation Procedure (Percutaneous Femoral):

1. Preparation: Sterile field, ultrasound, fluoroscopy if available
2. Vascular Access: Seldinger technique, ultrasound-guided
3. Serial Dilation: Sequential dilators to target size
4. Cannula Insertion: Advance over wire under fluoroscopy
5. Position Confirmation: Drainage tip at IVC-RA junction, return tip in right atrium (VV) or iliac artery (VA)
6. Secure Cannulae: Suture, dressing, mark position
7. De-air Circuit: Remove all air before connecting
8. Initiate Flow: Gradual RPM increase to target flow

Distal Perfusion Cannula (DPC):

Essential for peripheral VA-ECMO:

• Indication: Prophylactic (recommended) or therapeutic (limb ischemia)
• Technique: Antegrade 6-8 Fr sheath in superficial femoral artery, connected to arterial return limb via Y-connector
• Flow: 150-300 mL/min typically adequate
• Monitoring: Hourly limb checks (color, temperature, pulses, Doppler signals)

Initial ECMO Settings

VV-ECMO Initial Settings:

VA-ECMO Initial Settings:

Ventilator Management on ECMO

Lung-Protective Ventilation (ELSO Recommendations) (PMID: 32366514):

"Ultra-protective" or "lung rest" strategy:

Goals:

• Minimize ventilator-induced lung injury
• Allow lung healing
• Avoid oxygen toxicity
• Maintain some ventilator cycling (prevents atelectasis)

Hemodynamic Management

VV-ECMO Hemodynamics:

• VV-ECMO does not provide cardiac support
• Patient must maintain adequate cardiac output
• Optimize preload (fluid boluses if hypovolemic)
• May require vasopressors/inotropes for septic shock
• Target MAP 65-75 mmHg

VA-ECMO Hemodynamics:

Monitoring for LV Distension:

• Loss of arterial pulsatility (flat arterial waveform)
• Pulmonary edema on CXR
• Aortic valve not opening on echo
• Dilated LV with elevated filling pressures
• Smoke/thrombus in LV

Management of LV Distension:

1. Reduce ECMO Flow: Allow native ejection
2. Add IABP: Counterpulsation reduces afterload
3. Add Impella: Active LV unloading (ECMELLA)
4. Atrial Septostomy: Decompress left atrium
5. LV Vent: Surgical (central cannulation)

Anticoagulation Management

ELSO Anticoagulation Guidelines (PMID: 34115980):

Heparin Protocol:

HIT Management:

If HIT suspected:

1. Stop heparin immediately
2. Send HIT antibodies (PF4/heparin ELISA)
3. Switch to bivalirudin (0.05-0.15 mg/kg/hr) or argatroban
4. Avoid platelet transfusion unless life-threatening bleeding
5. Maintain adequate anticoagulation (thrombosis risk high)

Bivalirudin Protocol:

Blood Product Management

ELSO Recommendations (PMID: 27010949):

Australian ECMO Retrieval Services

State-Based Services:

Retrieval Considerations:

• Early notification to ECMO center
• Stabilization before transport
• Mode of transport (fixed-wing, rotary, road)
• Mobile cannulation capability
• Transport ventilator and ECMO circuit compatibility
• Blood product availability during transport
• Communication with receiving center

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Monitoring & Complications

ECMO-Specific Monitoring

Circuit Monitoring:

Patient Monitoring:

Complications

Bleeding (Most Common, 10-40%) (PMID: 28506685):

Management Approach:

1. Reduce/hold anticoagulation
2. Transfuse (Hb >10, platelets >100, fibrinogen >2)
3. TXA 1g IV
4. Consider PCC if on warfarin
5. Surgical intervention if ongoing

Thrombosis (5-15%) (PMID: 29067112):

Recirculation (VV-ECMO Specific):

Occurs when oxygenated return blood immediately re-enters drainage cannula.

Diagnosis:

• SaO2 patient low despite high ECMO flows
• SvO2 (pre-oxygenator) approaches SaO2 (post-oxygenator)
• Calculation: Recirculation fraction = (SvO2pre - SVC) / (SaO2post - SVC)
• Target: <20-30%

Causes:

• Cannulae tips too close
• High ECMO flows relative to cardiac output
• Poor cannula positioning

Management:

• Reposition cannulae (increase distance between tips)
• Fluoroscopy/echo-guided repositioning
• Reduce flows if tolerated
• Consider dual-site cannulation

Differential Hypoxia (North-South Syndrome, VA-ECMO Specific) (PMID: 29067112):

Pathophysiology:

• Native cardiac output delivers deoxygenated blood to aortic arch (coronary, cerebral, right arm)
• ECMO return delivers oxygenated blood to descending aorta
• If native lungs impaired, upper body becomes hypoxic while lower body well-oxygenated

Detection:

• Right radial arterial SaO2 lower than femoral SaO2
• Monitor with right radial pulse oximetry
• Difference >10% indicates significant differential hypoxia

Management:

1. Improve native lung function (optimize ventilation)
2. Increase ECMO flow (push mixing zone cephalad)
3. Convert to VAV configuration (add venous return cannula to jugular)
4. Consider central cannulation (antegrade aortic flow)

Limb Ischemia (VA-ECMO, 10-15%) (PMID: 28506685):

Risk Factors:

• Large arterial cannula relative to vessel
• Peripheral vascular disease
• Vasopressor use
• Prolonged ECMO duration

Prevention:

• Prophylactic distal perfusion cannula (DPC) at cannulation
• Use smallest feasible arterial cannula
• Near-infrared spectroscopy (NIRS) monitoring

Detection:

• Hourly limb assessment (6 Ps: Pain, Pallor, Pulselessness, Paresthesia, Paralysis, Poikilothermia)
• Doppler signals (dorsalis pedis, posterior tibial)
• NIRS <40% indicates ischemia

Management:

1. Insert distal perfusion cannula immediately
2. Consider anticoagulation optimization
3. Surgical fasciotomy if compartment syndrome
4. Consider alternative cannulation site
5. Amputation may be required if irreversible

Hemolysis:

Causes:

• Pump thrombosis
• High RPM/flow rates
• Cannula malposition
• Circuit kinking

Detection:

• Plasma-free hemoglobin >50 mg/dL
• Rising LDH
• Hemoglobinuria
• Falling haptoglobin

Management:

• Identify and correct cause
• Reduce flows if possible
• Change pump if pump thrombosis
• Monitor renal function
• Consider circuit change

Neurological Complications (10-15%):

Monitoring:

• Clinical neurological assessment Q2-4 hours
• CT head if concern
• EEG if seizures suspected
• Pupillometry

Infection (10-20%):

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Prognosis & Outcome Measures

Survival Outcomes

VV-ECMO (ELSO Registry Data) (PMID: 35915992):

VA-ECMO (ELSO Registry Data):

Long-Term Outcomes

Functional Recovery:

• 70-80% of ECMO survivors return to baseline function at 1 year
• 6-minute walk test: 80% of predicted at 6 months
• Pulmonary function: 70-80% of predicted at 1 year (VV-ECMO)
• Cardiac function: Depends on underlying etiology (VA-ECMO)

Quality of Life:

• SF-36 scores: 60-70% of age-matched controls at 1 year
• Return to work: 60-70% at 1 year
• Depression/anxiety: 20-30% at 6 months
• PTSD symptoms: 15-25%

Neurological Outcomes:

• Neurological disability in 10-15% of survivors
• Cognitive impairment: 20-30%
• Motor weakness: 15-20% (ICU-acquired weakness)

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ECMO Weaning

VV-ECMO Weaning (PMID: 32366514)

Prerequisites for Weaning Trial:

• Improving CXR
• Improving lung compliance
• Resolving underlying cause
• Adequate native oxygenation (P/F >150 on FiO2 <0.6)
• Adequate ventilation (minute ventilation achievable)
• Hemodynamically stable

Weaning Trial Protocol:

Decannulation Criteria:

• Tolerated weaning trial 4-6 hours
• PaO2/FiO2 >150-200 on FiO2 <0.5
• pH >7.35 with PaCO2 <50 mmHg
• Plateau pressure <28 cmH₂O
• Minimal vasopressor requirements
• Stable hemodynamics

VA-ECMO Weaning (PMID: 26585095)

Prerequisites for Weaning Trial:

• Evidence of cardiac recovery (improved EF, reduced inotropes)
• Stable rhythm (no ventricular arrhythmias)
• Adequate arterial pulsatility
• Lactate <2 mmol/L
• Resolved underlying cause (if reversible)

Weaning Trial Protocol:

Echocardiographic Weaning Criteria:

• Aortic VTI >10 cm
• LVEF >25-30%
• Lateral mitral annular S' >6 cm/s
• No new wall motion abnormalities
• Tolerable filling pressures

Decannulation Criteria:

• Tolerated minimal flow trial (1-2 hours)
• MAP >65 mmHg with minimal vasopressors
• CI >2.0 L/min/m² on echo
• SvO2 >65%
• Lactate stable or falling
• No significant arrhythmias

Decannulation Procedure

Venous Cannula Removal (VV and VA):

• Apply pressure for 10-20 minutes
• Figure-of-8 suture if bleeding
• Monitor for venous bleeding

Arterial Cannula Removal (VA):

• Options: Surgical cutdown and repair, or percutaneous with closure device (if small cannula)
• Check distal pulses post-removal
• Monitor for pseudoaneurysm

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Progressive Difficulty Assessments

Basic Level (Foundation Knowledge)

Question 1: ECMO Configuration

Q: Define VV-ECMO and VA-ECMO. What type of support does each provide?

A:

• VV-ECMO (Venovenous): Blood drained from venous system (IVC/SVC), passed through oxygenator, returned to venous system (right atrium). Provides respiratory support only (oxygenation and CO2 removal). Patient must maintain own cardiac output.

• VA-ECMO (Venoarterial): Blood drained from venous system, passed through oxygenator, returned to arterial system (femoral artery or aorta). Provides both cardiac and respiratory support. Bypasses heart and lungs.

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Question 2: Circuit Components

Q: List the 5 major components of an ECMO circuit and describe the function of each.

A:

1. Drainage Cannula: Removes deoxygenated blood from patient (venous system)
2. Centrifugal Pump: Generates blood flow through circuit (kinetic energy)
3. Membrane Oxygenator: Gas exchange - adds O2, removes CO2 across hollow fiber membrane
4. Heat Exchanger: Maintains blood temperature (usually integrated with oxygenator)
5. Return Cannula: Returns oxygenated blood to patient (venous in VV, arterial in VA)

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Question 3: Anticoagulation

Q: What is the standard anticoagulant used for ECMO? What is the target ACT range according to ELSO guidelines?

A:

• Standard anticoagulant: Unfractionated heparin (UFH)
• Target ACT: 180-220 seconds (ELSO guidelines)
• Alternative: Bivalirudin for HIT or heparin resistance

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Intermediate Level (Applied Knowledge)

Question 1: Differential Hypoxia Case

Stem: A 48-year-old patient is on peripheral femoral-femoral VA-ECMO for cardiogenic shock post-STEMI. ECMO flow is 4.5 L/min. You note the following saturations:

• Right radial pulse oximetry: 82%
• Left toe pulse oximetry: 98%

Q1: What is the diagnosis? (2 marks)

A1: Differential hypoxia (North-South syndrome)

• Upper body (coronary, cerebral circulation) receiving deoxygenated blood from native cardiac output
• Lower body receiving oxygenated blood from ECMO return

Q2: Explain the pathophysiology. (3 marks)

A2:

• In peripheral VA-ECMO, oxygenated blood is returned to femoral artery (retrograde flow)
• Native cardiac output (if present) ejects blood from LV into ascending aorta
• If native lung function impaired, this blood is poorly oxygenated
• Mixing zone exists in aorta where ECMO and native blood meet
• Upper body structures (coronaries, brain, right arm) receive native (hypoxemic) blood
• Lower body receives ECMO (well-oxygenated) blood

Q3: How would you manage this? (5 marks)

A3:

1. Optimize native lung function: Improve ventilator settings, treat pneumonia/pulmonary edema
2. Increase ECMO flow: Pushes mixing zone cephalad, more oxygenated blood to upper body
3. VAV configuration: Add return cannula to internal jugular vein, splitting flow to provide oxygenated blood to RA
4. Central cannulation: Convert to central VA-ECMO (ascending aorta return) - provides antegrade flow
5. Reduce native cardiac output: If causing significant differential hypoxia (controversial - may worsen LV distension)

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Question 2: Troubleshooting Low Flow

Stem: A patient on VV-ECMO for severe ARDS has a sudden drop in ECMO flow from 5.0 to 2.5 L/min. RPM unchanged at 3500. Inlet pressure is -250 mmHg (previously -80 mmHg).

Q1: List 3 possible causes. (3 marks)

A1:

1. Hypovolemia (blood loss, dehydration)
2. Cannula malposition (drainage cannula against vessel wall/RA wall)
3. Tension pneumothorax (impaired venous return)
4. Cardiac tamponade (impaired venous return)
5. Cannula kinking

Q2: How would you investigate and manage? (5 marks)

A2: Immediate Assessment:

• Check patient vitals, examine chest
• CXR (pneumothorax, cannula position)
• Bedside TTE/TOE (tamponade, cannula position, volume status)
• Check for external cannula kinking

Management:

1. If hypovolemia: Fluid bolus 500 mL crystalloid, reassess
2. If cannula malposition: Reposition under fluoroscopy/echo guidance
3. If pneumothorax: Immediate needle decompression, chest drain
4. If tamponade: Pericardiocentesis
5. Reduce RPM temporarily if "suck down" (venous collapse) occurring

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Exam Level (CICM Second Part Standard)

See SAQ Practice section for full exam-level questions

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SAQ Practice

SAQ 1: VV-ECMO for Severe ARDS

Time Allocation: 10 minutes Total Marks: 20

Stem: A 42-year-old male is referred to your tertiary ICU with severe influenza pneumonia. He has been intubated for 4 days at the referring hospital.

Current Ventilator Settings:

• Mode: PC-CMV
• Pinsp: 28 cmH₂O, PEEP: 14 cmH₂O
• FiO2: 1.0, RR: 28/min
• Tidal volume: 280 mL (IBW 70 kg = 4 mL/kg)

ABG (on above settings):

• pH: 7.28, PaCO2: 62 mmHg, PaO2: 52 mmHg, HCO3: 28 mmol/L, Lactate: 2.4 mmol/L

P/F Ratio: 52

Additional Information:

• He has been proned twice (16 hours each time) with only transient improvement
• He is receiving neuromuscular blockade
• Hemodynamics: HR 110, BP 105/65 (MAP 78) on noradrenaline 0.1 mcg/kg/min
• No significant past medical history

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Question 1.1 (6 marks)

List the indications for VV-ECMO in this patient and explain why conventional management has failed.

Question 1.2 (6 marks)

Describe the initial ECMO settings and ventilator adjustments you would make after VV-ECMO cannulation.

Question 1.3 (8 marks)

During VV-ECMO, the patient's SaO2 remains at 85% despite ECMO blood flow of 5 L/min and FdO2 1.0. The pre-oxygenator SvO2 is 78% and post-oxygenator SaO2 is 98%. Explain the likely cause and outline your management.

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Model Answer - SAQ 1

Question 1.1 (6 marks total)

Indications for VV-ECMO in this patient (4 marks):

1. Severe hypoxemia (1 mark)

   • P/F ratio 52 (<80 for >3 hours despite optimal therapy)
   • Meets ELSO criteria for VV-ECMO consideration

2. Failure of conventional rescue therapies (2 marks)

   • Prone positioning attempted with only transient improvement
   • Neuromuscular blockade already instituted
   • Optimized ventilation (low VT 4 mL/kg, high PEEP)
   • High FiO2 1.0 with ongoing severe hypoxemia

3. Preserved cardiac function (1 mark)

   • Adequate MAP on low-dose vasopressor (VV-ECMO requires native cardiac output)

Why conventional management has failed (2 marks):

• Severe ARDS with profound V/Q mismatch and intrapulmonary shunt
• Limited ability to increase oxygenation despite:
  • Maximum FiO2 (oxygen toxicity concerns)
  • High PEEP (recruitment optimized, risk of barotrauma)
  • Prone positioning (temporary benefit only)
• Cannot increase minute ventilation without causing VILI (already at lung-protective limits)
• Escalation to ECMO indicated before further deterioration

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Question 1.2 (6 marks total)

Initial VV-ECMO Settings (3 marks):

Ventilator Adjustments ("Lung Rest Strategy") (3 marks):

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Question 1.3 (8 marks total)

Likely Cause: Recirculation (2 marks)

• Pre-oxygenator SvO2 78% approaches post-oxygenator SaO2 98%
• Normal SvO2 should be 65-75% if no recirculation
• Elevated pre-oxygenator saturation indicates oxygenated return blood is being immediately re-aspirated by drainage cannula

Recirculation Calculation (2 marks):

• Recirculation fraction = (SvO2pre - SVC saturation) / (SaO2post - SVC saturation)
• Assuming SVC ~65%: (78 - 65) / (98 - 65) = 13/33 = 39% recirculation (high, target <20%)

Causes of Recirculation (1 mark):

• Cannula tips positioned too close together
• High ECMO flows relative to cardiac output
• Cannula migration

Management (3 marks):

1. Confirm diagnosis:

   • CXR to assess cannula positions
   • TOE/fluoroscopy for precise positioning
   • Measure SVC saturation directly (central line sampling)

2. Reposition cannulae:

   • Increase distance between drainage and return tips
   • Drainage tip in low RA/IVC-RA junction
   • Return tip in mid-right atrium
   • Consider bicaval dual-lumen cannula (Avalon) via IJ

3. Optimize flows:

   • Reduce ECMO flows if hemodynamics tolerate (reduces recirculation)
   • Increase cardiac output (reduce sedation, fluid optimize)

4. Consider cannula change:

   • Femoral-jugular configuration (if not already)
   • Dual-site cannulation reduces recirculation vs single-site

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Common Mistakes:

• Forgetting to calculate recirculation fraction
• Not considering alternative cannulation configurations
• Continuing to increase ECMO flows (makes recirculation worse)
• Not recognizing elevated pre-oxygenator saturation as abnormal

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SAQ 2: VA-ECMO Complications

Time Allocation: 10 minutes Total Marks: 20

Stem: A 55-year-old female is Day 2 on peripheral femoral-femoral VA-ECMO for fulminant myocarditis with cardiogenic shock. A prophylactic distal perfusion cannula was placed at cannulation.

Current Status:

• ECMO flow: 4.0 L/min, RPM: 3200
• MAP: 70 mmHg, noradrenaline 0.15 mcg/kg/min
• Heparin infusion: ACT 195 seconds
• Urine output adequate

You are called because the bedside nurse is concerned about the right leg (cannulated side).

Examination Findings - Right Leg:

• Pale, cool compared to left leg
• No palpable dorsalis pedis or posterior tibial pulse
• Doppler: Weak monophasic signal at ankle
• DPC appears patent, flow 180 mL/min

Left Leg: Warm, normal pulses

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Question 2.1 (6 marks)

What is the diagnosis and what are the possible causes?

Question 2.2 (6 marks)

Outline your immediate assessment and management.

Question 2.3 (8 marks)

Despite your interventions, the leg deteriorates over the next 2 hours with increasing pain and muscle tenderness. What complications are you concerned about and how would you manage this situation?

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Model Answer - SAQ 2

Question 2.1 (6 marks total)

Diagnosis (2 marks):

• Right limb ischemia in a cannulated limb on peripheral VA-ECMO
• Despite prophylactic DPC in situ

Possible Causes (4 marks):

1. Inadequate DPC flow (1 mark)

   • DPC flow 180 mL/min may be insufficient for metabolic demands
   • DPC kinking, thrombosis, or malposition

2. Femoral artery occlusion by cannula (1 mark)

   • Large arterial cannula (typically 15-21 Fr) occludes significant portion of femoral artery
   • Retrograde flow from ECMO does not reach limb (distal to cannula)

3. Arterial thrombosis (1 mark)

   • Clot formation around cannula or within native artery
   • Despite anticoagulation

4. Vasospasm/vasoconstriction (0.5 marks)

   • Vasopressor use (noradrenaline)
   • Cold limb from inadequate perfusion

5. Embolism (0.5 marks)

   • Thromboembolism from circuit or LV

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Question 2.2 (6 marks total)

Immediate Assessment (3 marks):

1. Clinical assessment (1 mark)

   • Complete 6 Ps: Pain, Pallor, Pulselessness, Paresthesia, Paralysis, Poikilothermia
   • Compare with contralateral limb
   • Assess sensory and motor function

2. DPC assessment (1 mark)

   • Confirm DPC patency (flush, check connection)
   • Check DPC flow and position
   • Consider increasing DPC flow if possible

3. Imaging (1 mark)

   • Duplex ultrasound of femoral artery and DPC
   • CTA of lower limb if deteriorating
   • Check for thrombus, cannula position

Immediate Management (3 marks):

1. Optimize DPC (1 mark)

   • Increase DPC flow (adjust Y-connector, increase ECMO flow slightly)
   • If DPC malpositioned or thrombosed, consider replacement
   • Aim for DPC flow 300-500 mL/min if tolerated

2. Reduce vasoconstriction (0.5 marks)

   • Reduce vasopressor dose if hemodynamics allow
   • Warm limb (external warming)

3. Anticoagulation optimization (0.5 marks)

   • Ensure ACT in therapeutic range
   • Consider increasing target if no bleeding

4. Surgical consultation (1 mark)

   • Early vascular surgery involvement
   • May require surgical thrombectomy or fasciotomy
   • Consider alternative cannulation strategy

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Question 2.3 (8 marks total)

Complications of Concern (4 marks):

1. Compartment syndrome (2 marks)

   • Increasing pain (especially passive stretch)
   • Tense compartments
   • Paresthesia, then paralysis
   • Reperfusion injury exacerbates after restoration of flow
   • Irreversible muscle necrosis >6 hours of ischemia

2. Rhabdomyolysis (1 mark)

   • Release of myoglobin, potassium, phosphate, CK
   • Acute kidney injury (myoglobinuric)
   • Cardiac arrhythmias (hyperkalemia)
   • DIC

3. Limb loss (1 mark)

   • May require amputation if irreversible ischemia
   • Balance against overall prognosis

Management Strategy (4 marks):

1. Laboratory assessment (0.5 marks)

   • Urgent CK, potassium, creatinine, lactate
   • ABG (metabolic acidosis, hyperkalemia)

2. Compartment pressure measurement (0.5 marks)

   • If concern for compartment syndrome
   • Absolute pressure >30 mmHg or delta pressure (diastolic - compartment) <30 mmHg

3. Fasciotomy (1 mark)

   • Urgent 4-compartment fasciotomy of lower leg
   • May require thigh fasciotomy
   • Performed at bedside or operating theatre

4. Revascularization options (1 mark)

   • Surgical thrombectomy
   • Larger or repositioned DPC
   • Consider alternative cannulation (axillary artery, contralateral femoral)
   • Central cannulation if ongoing limb issues

5. Renal protection (0.5 marks)

   • Volume resuscitation
   • Maintain urine output
   • Early RRT if oliguric renal failure

6. Multidisciplinary discussion (0.5 marks)

   • Vascular surgery, ICU, cardiology, family
   • Discuss prognosis and goals of care
   • Consider if limb salvage possible vs amputation
   • Balance against overall patient prognosis

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Common Mistakes:

• Not checking DPC patency as first step
• Delaying surgical consultation
• Not measuring compartment pressures when suspected
• Failing to consider systemic complications of limb ischemia

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Viva Questions

Viva 1: ECMO Circuit Components and Troubleshooting

Stem: "You are the ICU consultant covering the ECMO service. A nurse calls you because the ECMO circuit has developed a sudden change in parameters."

Duration: 12 minutes (2 min reading + 10 min discussion)

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Examiner: "Describe the major components of an ECMO circuit and their functions."

Expected Answer (3 minutes):

The ECMO circuit consists of five major components arranged in series:

1. Drainage Cannula

   • Purpose: Removes deoxygenated blood from the patient
   • Location: Femoral vein (IVC), jugular vein (SVC), or right atrium
   • Size: 21-29 Fr (larger = higher flow capacity)
   • Multiple side holes for optimal drainage

2. Centrifugal Pump

   • Purpose: Generates blood flow through the circuit
   • Mechanism: Rotating impeller creates centrifugal force
   • Non-occlusive design - flow depends on RPM and resistance
   • Modern pumps are magnetically levitated (reduced hemolysis)
   • Examples: Maquet Rotaflow, CentriMag

3. Membrane Oxygenator

   • Purpose: Gas exchange - adds oxygen, removes CO2
   • Design: Polymethylpentene hollow fiber membrane
   • Blood flows outside fibers, sweep gas inside fibers
   • Surface area 1.5-2.5 m² for adults
   • Gas exchange by diffusion (Fick's law)
   • Integrated heat exchanger in modern devices

4. Heat Exchanger

   • Purpose: Maintains blood temperature
   • Usually integrated with oxygenator
   • Water circuit heats/cools blood
   • Target normothermia (36-37°C) or therapeutic hypothermia if indicated

5. Return Cannula

   • Purpose: Returns oxygenated blood to patient
   • VV-ECMO: Returns to right atrium (venous)
   • VA-ECMO: Returns to femoral artery or aorta (arterial)
   • Size: 15-21 Fr (arterial), 17-23 Fr (venous return)

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Examiner: "The nurse reports the following: ECMO flow has dropped from 5.0 L/min to 3.0 L/min. RPM unchanged at 3500. Inlet pressure is now -280 mmHg (was -80 mmHg). What is your differential diagnosis?"

Expected Answer (2 minutes):

The high negative inlet pressure with reduced flow indicates inadequate venous drainage. Differential diagnosis:

1. Hypovolemia

   • Most common cause
   • Blood loss, dehydration, third-spacing
   • Assessment: Check Hb, CVP, fluid balance

2. Cannula malposition

   • Drainage cannula tip against vessel wall or RA wall
   • Migration during patient movement
   • Assess with CXR, TOE, fluoroscopy

3. Cannula obstruction

   • Kinking of external tubing
   • Thrombus within cannula
   • Check circuit inspection

4. Impaired venous return

   • Tension pneumothorax
   • Cardiac tamponade
   • Abdominal compartment syndrome
   • Positive pressure ventilation with high PEEP

5. "Suck-down" phenomenon

   • Venous collapse around cannula at high negative pressures
   • Vein walls sucked against cannula drainage holes

---

Examiner: "How would you manage this situation?"

Expected Answer (2 minutes):

Immediate Actions:

1. Reduce RPM slightly to prevent further suck-down and hemolysis
2. Examine patient: Chest, abdomen, lines, cannulae
3. Fluid challenge: 250-500 mL crystalloid bolus

Investigations:

1. CXR: Pneumothorax, cannula position, cardiac size
2. ABG and FBC: Assess Hb, check for hemolysis (plasma-free Hb)
3. Bedside TTE/TOE: Volume status, cannula position, tamponade

Management Based on Cause:

• If hypovolemia: Continue fluid resuscitation, transfuse if Hb low
• If malposition: Reposition cannula under fluoroscopy/echo guidance
• If pneumothorax: Decompress (needle then chest drain)
• If tamponade: Pericardiocentesis
• If suck-down: Reduce flows, volume resuscitate, consider repositioning

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Examiner: "The transmembrane pressure gradient across the oxygenator has increased from 30 mmHg to 120 mmHg over 24 hours. What does this indicate and what would you do?"

Expected Answer (2 minutes):

Interpretation:

• Elevated transmembrane pressure (>100 mmHg) indicates oxygenator thrombosis
• Clot forming on membrane fibers, increasing resistance to blood flow
• Normal TMP: <50 mmHg

Associated Findings:

• Decreased O2 transfer (post-oxygenator PO2 falling)
• Possible hemolysis (elevated plasma-free Hb, LDH)
• Visual clot in oxygenator (dark discoloration)

Management:

1. Confirm diagnosis:

   • Check pre/post oxygenator blood gases
   • Assess oxygenator for visible clot
   • Check anticoagulation adequacy (ACT, aPTT)

2. Optimize anticoagulation:

   • Increase heparin if ACT subtherapeutic
   • Consider antithrombin levels if heparin resistance

3. Plan circuit change:

   • Oxygenator change or complete circuit change
   • Coordinate with perfusion, prepare backup circuit
   • Brief controlled switch (minimize air entrainment)

4. Increase monitoring:

   • More frequent ACT/aPTT
   • Daily D-dimer, fibrinogen
   • Consider anti-Xa levels

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Examiner's Expected Level:

Pass:

• Names major circuit components and their basic functions
• Recognizes high negative inlet pressure indicates drainage problem
• Systematic approach to troubleshooting
• Knows elevated TMP indicates oxygenator clotting

Fail:

• Cannot describe circuit components
• Fails to recognize significance of pressure changes
• Unsafe management (e.g., increasing flows during suck-down)
• No consideration of circuit change for failing oxygenator

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Viva 2: EOLIA Trial and ECMO Evidence

Stem: "A colleague is considering VV-ECMO for a patient with severe ARDS. They ask about the evidence base."

Duration: 12 minutes (2 min reading + 10 min discussion)

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Examiner: "Tell me about the EOLIA trial."

Expected Answer (3 minutes):

EOLIA Trial (Combes et al., NEJM 2018, PMID: 29791822):

Design:

• Multicenter, international RCT (France, 27 centers)
• 249 patients with severe ARDS randomized
• Intervention: Early VV-ECMO within 7 days of intubation
• Control: Conventional management (could crossover to ECMO as rescue)

Inclusion Criteria (severe ARDS):

• P/F ratio <50 mmHg for >3 hours, OR
• P/F ratio <80 mmHg for >6 hours, OR
• pH <7.25 with PaCO2 >60 for >6 hours

Primary Outcome:

• 60-day mortality

Key Results:

• ECMO group: 35% mortality
• Control group: 46% mortality
• Absolute risk reduction: 11% (not statistically significant, p=0.09)
• High crossover rate: 28% of control group crossed to rescue ECMO

Interpretation:

• Trial underpowered due to crossover
• Control group survival included patients rescued by ECMO
• Post-hoc analyses accounting for crossover suggest significant benefit
• Meta-analysis (including CESAR) shows mortality benefit (RR 0.73)

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Examiner: "How do you interpret the EOLIA results for clinical practice?"

Expected Answer (2 minutes):

Clinical Interpretation:

1. ECMO is effective rescue therapy

   • 28% crossover rate shows clinicians believe ECMO works
   • Control patients who received rescue ECMO survived (would have died without)

2. Early ECMO may be better than late rescue

   • Control group who crossed over had worse outcomes than early ECMO
   • Supports early referral to ECMO center

3. ECMO should be considered in severe refractory ARDS

   • When conventional therapy fails (P/F <80 despite optimization)
   • Before prolonged mechanical ventilation (>7 days)

4. ELSO and guidelines recommend ECMO for severe ARDS

   • Based on totality of evidence (CESAR + EOLIA + meta-analyses)
   • When performed in experienced centers

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Examiner: "Tell me about the CESAR trial."

Expected Answer (2 minutes):

CESAR Trial (Peek et al., Lancet 2009, PMID: 19762075):

Design:

• UK-based RCT
• 180 patients with severe ARDS
• Intervention: Transfer to ECMO center (Glenfield, Leicester)
• Control: Continued conventional management at local hospital

Key Difference from EOLIA:

• CESAR randomized to transfer to ECMO center, not to ECMO itself
• Only 75% of patients transferred actually received ECMO

Results:

• Survival without disability at 6 months:
  • "ECMO center: 63%"
  • "Control: 47%"
  • p=0.03 (statistically significant)

Limitations:

• Not all transferred patients received ECMO
• Control group not protocolized (some not lung-protective)
• Single center ECMO expertise

Interpretation:

• Supports benefit of referral to ECMO center
• May reflect expertise of specialized center as well as ECMO itself

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Examiner: "What about ECMO for COVID-19 ARDS?"

Expected Answer (2 minutes):

COVID-19 ECMO Outcomes (PMID: 33131360):

Key Data (ELSO Registry):

• Early pandemic (Feb-May 2020): ~35% mortality
• Later pandemic (May-Dec 2020): ~50% mortality

Worse Outcomes Compared to Non-COVID ARDS:

• Longer ECMO runs (median 15-20 days vs 7-10 days)
• Higher bleeding and thrombotic complications
• Hypercoagulable state of COVID-19
• Resource strain affecting outcomes

Patient Selection:

• Similar criteria to non-COVID ARDS
• Consider MV duration (>10 days associated with poor outcomes)
• Age >65 associated with worse survival
• Avoid in frail or immunocompromised

Australian Experience:

• 800 patients received ECMO for COVID-19 (2020-2022)

• National coordination through state ECMO services
• Survival rates similar to international data (~50%)

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Examiner's Expected Level:

Pass:

• Knows EOLIA showed non-significant mortality reduction (35% vs 46%)
• Understands high crossover rate confounded results
• Can discuss CESAR trial and its limitations
• Applies evidence to clinical decision-making

Fail:

• States EOLIA was "negative" without nuance
• Cannot cite trial details (population, outcomes)
• Unfamiliar with current guidelines
• Does not consider COVID-19 ECMO data