Simulating ECMO.
Andy Pybus
St George Private Hospital
Sydney
Conflict of interest:
MSE (Aust) PL
www.ecmosimulation.com
Presentation plan:
• Rationale for simulation.
• Components of a simulator.
• Interactive scenarios.
Rationale for simulation.
Why simulate?
• Education.
• Training.
• Competency assessment.
• Therapeutic / contingency planning.
– (What will happen if ??)
Components of a simulator:
• Physiological models.
• Pharmacological models.
• Equipment models.
Chronotrop
y
ECG
Mechanical
Pumps
Respiratory
Mechanics
Hb
Dissociatio
n
Inotropy
Baro Reception
V:Q
Relationshi
p
Hypoxic
Responses
Thermal
Behaviour
Blood
Gases
Cannula
Flow
Model
PK Models
NM
Transmissi
on
Myocardial
Contractility
CO2
Sensitivity
Fluid
Spaces
Vascular
Pressures
BIS
Starling
Behaviour
VV ECMO Paradigm:
Aims:
• To ‘arterialise’ as great a
proportion of the
venous return as is
possible.
• To ‘rest’ the native lung.
VA ECMO Paradigm:
Aims:
• Circulatory Support.
• (Respiratory
Support.)
Your Resources:
The Patient:
The patient is a 24 year-old man, weighing 75 kgs, who has been admitted to
your Intensive Care Unit for ongoing care.
When he came in, he gave a 4 day history of increasing respiratory distress,
fever and a productive cough. He deteriorated rapidly and required intubation
and ventilation shortly after admission.
Sputum cultures grew a sensitive staphylococcus aureus. Despite treatment
with appropriate antibiotics, the use of prone ventilation, permissive hypercarbia
and inhaled nitric oxide, his condition has not improved…
The clinical picture:
His blood gases on 100% oxygen are:
PaO2
45 mm Hg
PaCO2
58 mm Hg
pH
7.18
SaO2
74%
Hb
85 g/L
You calculate his Total Static Lung Compliance as:
10 ml/cm H2O
You calculate his ‘Shunt’ and ‘Deadspace’ as:
Qs/Qt
0.70
Vd/Vt
0.80
You estimate his oxygen consumption to be:
200 ml/min.
The clinical picture:
His blood gases on 100% oxygen are:
PaO2
45 mm Hg
PaCO2
58 mm Hg
pH
7.18
SaO2
74%
Hb
85 g/L
You calculate his Total Static Lung Compliance as:
10 ml/cm H2O
You calculate his ‘Shunt’ and ‘Deadspace’ as:
Qs/Qt
0.70
Vd/Vt
0.80
You estimate his oxygen consumption to be:
200 ml/min.
Subsequently…
The decision is made to put the patient on VV ECMO. This is successfully
implemented using a ‘Quadrox’ hollow-fibre lung and a dual-cannula drainage
system.
The patient is sedated, heparinised and ventilated on 70% oxygen with a PEEP
of 10 cms H2O, a tidal volume of 350 mls and a rate of 8 bpm.
The artificial lung is ventilated with 100% oxygen at a gas flow rate of 2.0 lpm.
and ECMO blood flow rate of 3.5 lpm.
Dual drainage Cannula system:
SVC drainage
Atrial return
IVC drainage
After 10 minutes on ECMO, you do some blood gases…
PaO2: 55 mm Hg, PaCO2: 55 mm Hg
You'd like to see the PCO2 a bit lower and ask your registrar
what he thinks you should do. He suggests increasing the
patient’s tidal volume to 600 mls and upping the rate to 15
bpm.
Is this appropriate?
The clinical picture:
His blood gases on 100% oxygen are:
PaO2
45 mm Hg
PaCO2
58 mm Hg
pH
7.18
SaO2
74%
Hb
85 g/L
You calculate his Total Static Lung Compliance as:
10 ml/cm H2O
You calculate his ‘Shunt’ and ‘Deadspace’ as:
Qs/Qt
0.70
Vd/Vt
0.80
You estimate his oxygen consumption to be:
200 ml/min.
VV ECMO: PaCO2 and Gas
Flow:
Blood Flow: 5.0 lpm
Blood Flow: 5.0 lpm
You also think that you'd like the patient’s SaO2 a bit higher
and ask your registrar what he thinks you should do.
He suggests increasing the blood flow through the ECMO
system.
Could he be right (this time)?
PaO2 and Blood Flow:
You contemplate cooling the patient to 35Oc in order to further
improve oxygenation.
You discuss this plan with the registrar (who has a lot of
experience with these kind of cases). He tells you that
reducing the patient’s temperature will have no effect on his
SaO2.
Is he right?
ECMO and Temperature:
Blood Flow: 5.0 lpm
VV ECMO: Basic Manipulations:
Gas Flow
Blood Flow
Temperature (VO2)
“A simple technique for use in
a complex environment.”
• Adjusting Gas Flow will
affect the PaCO2.
• Adjusting Blood Flow will
affect the PaO2.
• Adjusting Temperature will
affect the SvO2.
VV ECMO: The Effect Of Gas Flow:
Gas Flow
Blood Flow
Temperature (VO2)
• Gas flow is analogous to
minute ventilation
• PaCO2 is ≅ to 1/gas flow
• PaCO2 is easily controlled
– CO2 ‘Dissociation’ curve
VV ECMO: The Effect Of Blood Flow:
Gas Flow
Blood Flow
Temperature (VO2)
• PaO2  to blood flow
• Blood flow as a fraction
of cardiac output
• Limits of achievable
PaO2
– Effect of cardiac output
– Effect of Hb dissociation
curve
VV ECMO: The Effect Of Temperature:
Gas Flow
Blood Flow
As Temperature falls:
• VO2
↓
• SvO2 ↑
• PaO2 ↑
• Oxygenator Efficiency ↑
But: SvO2 is also importantly
affected by Hct and CO.
Temperature (VO2)
You’re still worried about the patient’s saturation.
Your registrar tells you that further increasing the gas flow
through the artificial lung will increase the SaO2.
Is he right?
You’ve now been a bit worried about hypoxia all day and
you notice that the patient has a haematocrit of 25%
The registrar (who has a lot of experience with these kind
of cases) suggests that you transfuse the patient.
The registrar (who’s now beginning to get on your nerves)
also points out that the patient’s last known cardiac output
was over 9 lpm.
He suggests that reducing the patient’s output will increase
his arterial PO2.
Could he be right??
VV ECMO: The Effect of Cardiac Output:
Competing influences:
• PaO2 tends to rise because:
– As CO ↑, so SvO2 ↑.
– As SvO2 ↑ , so SaO2 ↑ .
VV ECMO: The Effect of Cardiac Output:
Competing Influences:
• PaO2 tends to fall because:
– As CO ↑, so fraction of CO
passing through the oxygenator ↓.
– As CO ↑, so Qs/Qt ↑.
Lynch JP, Mhyre JG, Dantzker DR.
Influence of cardiac output on intrapulmonary shunt.
J Appl Physiol. 1979 Feb;46(2):315-21.
VV ECMO: The Effect of Cardiac Output:
Net Effect:
As CO ↑, so PaO2 ↓.
You want to go home after a long day, but need to know that
the registrar can change the oxygenator if he really has to.
You ask him how long it will take him. He tells you “30
seconds”.
You then ask him how long it will take before the patient
desaturates profoundly. He tells you “Five minutes or so”…
Is his confidence well-founded?
On the ward round the following day, you’re discussing the
concept of ‘Resting’ the lung.
The registrar asserts that: “If VV ECMO is working very well,
there’s no requirement for tidal ventilation.”
Could he be right?
VV ECMO: Resting the lung:
PaO2
Parameter
Befor
e
After
ECMO Blood Flow (lpm)
5.0
5.0
ECMO Gas Flow (lpm)
2.5
5.0
Ventilator Tidal Volume (mls)
500
200
Ventilator Frequency (bpm)
15
4
Ventilator PEEP (cm H2O)
10
10
Ventilator FiO2
1.0
0.6
PaCO2
The registrar then goes on to say:
“Even at low blood flow rates, VV ECMO can usually control
arterial PCO2.”
Surely, he’s not right again?
You’re now getting pretty exasperated with the registrar. He’s
getting far too many answers right!! In desperation, you ask
him how he thinks the patient would respond to VA ECMO.
You’re not sure what size of arterial return cannula should be
used. The registrar tells you a 15F cannula will be fine.
Is he right?
Return (Arterial) Cannula:
Basis for recommendation:
Blood Flow: 5.0 lpm
?
So here I’ve started the patient on VA ECMO at a blood flow
rate of over two lpm.
I do a blood gas and note that the PaO2 is only ~ 70 mm Hg.
The registrar tells me that the oxygenator is probably failing.
Could he be right?
VA ECMO: Differential
Circulation:
If peripheral arterial cannulation is used, then in
the ‘proximal’ circulation:
• PaO2 is set by adjusting FiO2 / PEEP to native
lung.
• PaCO2 is set by adjusting oxygenator settings.
• Requirement for tidal ventilation reduced.
VA ECMO: Special problems:
•
•
•
•
•
•
The ‘unclamped’ circuit.
Pump flow : Pre-load nexus.
Differential circulation.
Afterload dependence.
Left heart stasis.
Limb ischaemia.
Presentation available at:
www.ecmosimulation.com
‘Downloads’ section.