Simulating ECMO - ECMO Simulator

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24 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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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.

Blood

Gases

Thermal

Behaviour

Vascular
Pressures

Myocardial

Contractility

ECG

Respiratory

Mechanics

V:Q

Relationshi
p

Starling

Behaviour

Baro

-

Reception

CO2

Sensitivity

Hypoxic

Responses

Chronotrop
y

Inotropy

PK

Models

Fluid

Spaces

NM

Transmissi
on

Cannula

Flow

Mechanical

Pumps

BIS

Hb

Dissociatio
n

Model

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 H
2
O


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 H
2
O


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

H
2
O, 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

I
VC drainage

Atrial return

After 10 minutes on ECMO, you do some blood gases…


PaO
2
:
55

mm Hg, PaCO
2
:
55

mm Hg


You'd like to see the PCO
2

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 H
2
O


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: PaCO
2

and Gas
Flow:

Blood Flow: 5.0
lpm

Blood Flow: 5.0
lpm

You also think that you'd like the patient’s SaO
2

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)?

PaO
2

and Blood Flow:

You contemplate cooling the patient to 35
O
c 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
SaO
2
.


Is he right?

ECMO and Temperature:

Blood Flow: 5.0
lpm

VV ECMO: Basic Manipulations:

“A simple technique for use in
a complex environment.”


Adjusting
G
as
F
low will
affect the
PaCO
2
.


Adjusting B
lood
F
low
will
affect the
PaO
2
.


Adjusting T
emperature will
affect the
SvO
2
.

Gas Flow

Blood Flow

Temperature (VO
2
)

VV ECMO: The Effect Of Gas Flow:


Gas
flow is analogous to
minute
ventilation


PaCO
2
is


to
1/gas
flow


PaCO
2
is easily controlled


CO
2

‘Dissociation’ curve

Gas Flow

Blood Flow

Temperature (VO
2
)

VV ECMO: The Effect Of Blood Flow:


PaO
2


to
blood flow


Blood flow as a fraction
of cardiac output


Limits of achievable
PaO
2


Effect of cardiac output


Effect of
Hb

dissociation
curve

Gas Flow

Blood Flow

Temperature (VO
2
)

VV ECMO: The Effect Of Temperature:

As Temperature falls:


VO
2








SvO
2







PaO
2







Oxygenator Efficiency





But: SvO
2

is also importantly
affected by
Hct

and CO.

Gas Flow

Blood Flow

Temperature (VO
2
)

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 SaO
2
.


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 PO
2
.


Could he be right??

VV ECMO: The Effect of

Cardiac Output:

Competing influences:


PaO
2

tends to
rise because
:


As
CO

,
so SvO
2


.


As
SvO
2



,
so
SaO
2



.

Competing Influences:


PaO
2

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:

VV ECMO: The Effect of

Cardiac Output:

Net Effect:

As
CO

, so PaO
2


.

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:

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 H
2
O)

10

10

Ventilator FiO
2

1.0

0.6

PaO
2

PaCO
2

The registrar then goes on to say:



“Even
at low
blood flow
rates
, VV
ECMO can
usually control
arterial
PCO
2
.”



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:



PaO
2
is set by adjusting FiO
2

/ PEEP to native
lung.


PaCO
2
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.