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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3612_Библиотеки_им_академика_М_И_Перельмана
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390
Key Questions in CONGENITAL CARDIAC SURGERY
Figure 2. Centrifugal pump consisting of control monitors, primary and
back-up control panels, rotating driver devices and centrifugal impellers.
Reproduced with permission from Abbott, © 2020. All rights reserved. CentriMag™,
Thoratec Corporation and Thoratec Corporation Logo are trademarks of Abbott or
its related companies.
11 Extracorporeal membrane oxygenation
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1
6
10
7
8
9
2
3
4
5
391
Figure 3. Membrane oxygenator and its connections.
1 = vent port; 2 = water outlet; 3 = oxygen supply tube; 4
= membrane oxygenator; 5 = water inlet; 6 = sampling
ports; 7 = recirculation port; 8 = arterial outlet; 9 = flow
sensor; 10 = venous inlet.
392
Key Questions in CONGENITAL CARDIAC SURGERY
Figure 4. Air and oxygen blender, with sweep gas
regulator.
Figure 5. Bridge between the arterial and venous
cannulae in an open state.
9 Describe the different types of pump that are used in
an extracorporeal membrane oxygenation circuit
Semi-occlusive roller pumps are rarely used currently, as they are
•
more traumatic to blood components, especially when used for
longer periods.
11 Extracorporeal membrane oxygenation
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They have been replaced by magnetically levitated centrifugal
•
pumps, which are mounted on a rotating magnet driver (Figure 6).
393
Figure 6. Centrifugal propeller.
This pump provides less trauma to blood components and can be
•
employed for longer period of times.
By spinning, a vortex effect is created with low pressure in the apex
•
of the pump removing blood from the patient. The vortex creates a
positive pressure at the bottom of the pump, returning blood to the
patient.
Therefore, centrifugal pumps are preload-dependent and afterload-
•
sensitive.
Given the prolonged use and dependency of the patient’s circulation
•
and respiratory function, drivers are always provided with a back-up
for quick replacement in case of failure (Figure 7).
394
Key Questions in CONGENITAL CARDIAC SURGERY
Figure 7. Centrifugal pump mounted on the rotating
magnetic device, with the mandatory back-up device
adjacent for immediate transfer of the propeller.
10 What are the main factors affecting extracorporeal
membrane oxygenation flow?
The pump provides a blood flow rate (L/min) delivered at a given
•
amount of revolutions per minute (rpm).
Factors that can affect the blood flow rate include:
•
a) preload and afterload;
b) size of the cannulae;
c) size of the cannulated vessels and compliance;
d) body surface area (BSA) of the patient;
e) haematocrit;
f) transmembrane gradient (which represents the pressure
gradient across the oxygenator).
11 What is pump cavitation?
The pump generates a negative pressure on the patient’s venous
•
side, which drives the flow rate, as it provides the inflow into the
propeller.
Past the point of maximal inflow, the negative pressure in the venous
•
system causes the venous vessels or the right atrial wall to
temporarily collapse, potentially occluding blood inflow altogether.
When the pressure in the venous side builds back up again, the
•
pump is able to flow again, which might generate a pulsing blood
flow and cavitation of the pump.
The first intervention to avoid further cavitation is to reduce the pump
•
rpm and therefore the suction effect on the venous return.
11 Extracorporeal membrane oxygenation
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Other manoeuvres that might be needed to maintain pump blood
•
flow include:
a) correcting the hypovolaemia status;
b) changing the positioning of the patient;
c) ensuring that there is no kinking or malposition of the cannula;
d) checking for the presence of thrombus or clotting in the circuit;
e) increasing the size of the venous cannulae or adding additional
venous access for drainage.
12 What is recirculation?
Recirculation is a phenomenon that occurs in VV ECMO when a
•
single intra-atrial double-lumen cannula is used, where reinfused
oxygenated blood is withdrawn through the venous drainage cannula
and therefore does not reach the systemic circulation (Figure 8).
AB
RA
Double-lumen cannula
RV
Figure 8. Flow within a single VV ECMO double-lumen cannula: A) in
the correct position and functioning properly, the cannula draws
deoxygenated blood from the inferior vena cava and right atrium, while
the outlet lumen ejects fully oxygenated blood towards the tricuspid
valve. This increases forward flow with high oxygen saturation across the
pulmonary circulation to reach the left atrium; B) recirculation occurring
with the arterial output drained from the cannula instead of reaching the
right ventricle, resulting in reduced forward flow to the pulmonary valve
and reduced oxygen saturation. RA = right atrium; RV = right ventricle.
395
396
Key Questions in CONGENITAL CARDIAC SURGERY
If the patient is dependent on ECMO for oxygenation, recirculation
•
can pose a clinical problem. In this situation, solutions to be
considered include:
a) changing the position of the cannulae;
b) changing the configuration of the cannulae by adding an extra
drainage cannula;
c) changing the position of the reinfusion cannula;
d) decreasing ECMO flow (if possible).
13 What is Harlequin syndrome?
Harlequin syndrome represents a phenomenon occurring in VA
•
ECMO, when there is significant residual native cardiac output with
impaired native gas exchange.
In such cases, poorly oxygenated blood ejected from the heart will
•
supply the upper body, whereas the lower body is perfused by
oxygenated blood from the arterial cannula of the ECMO circuit, in
particular when a femoral cannula is employed.
Blood returning to the venous drainage is more saturated than
•
expected and may be interpreted as a form of recirculation, but as
the blood has already passed through the systemic circulation, it is
not considered recirculation.
Possible solutions to this include:
•
a) increasing the ECMO flow;
b) increasing ventilation support (if possible);
c) repositioning the arterial cannula more proximally in the aorta (if
central cannulation has been used) or adding an additional arterial
cannula for the upper body, such as an axillary artery cannula;
d) improving left atrial decompression with a left atrial vent or
atrial septostomy.
14 Describe the types of extracorporeal membrane
oxygenation arterial cannulae that are used
ECMO is instituted using specific cannulae that are produced to be
•
site-specific. Most centres use a uniform size to flow ratio, according
to the patient’s body weight or body surface area (Tables 2 and 3).
The size and shape of the venous and arterial cannulae vary when
•
used for central or neck cannulation, as compared to peripheral
sites, such as the femoral vein (Figures 9 and 10).
The use of heparin-coated cannulae and heparin-bonded circuits is
•
variable.
11 Extracorporeal membrane oxygenation
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Table 2. Arterial cannula size chart according to flow and body weight.
cäçï=
EãiLãáåF=
0-400
400-700
700-1200
1200-1700
1700-2000
2000-2500
2500-3500
>3500
páòÉ=
EcêF=
8
10
12
14
15
17
19
>21
bснЙке~д=
Зб~гЙнЙк=EггF
2.66
3.33
4
4.66
5
5.66
6.33
>7
_зЗу=пЙбЦЬн
EвЦF
<2
2-5
5-10
10-20
20-30
>40
`~ååìä~
ëáòÉ=EcêF
8 to 10
10 to 14
12 to 16
14 to 19
17 to 21
>21
Table 3. Venous cannula size chart according to flow and body weight.
cäçï=
EãiLãáåF=
0-350
350-600
600-1000
1000-1400
750-1000
1000-1500
1500-2000
2000-2500
2500-3000
3000-3600
3600-4500
4500-
páòÉ=
EcêF=
8
10
12
14
15
17
19
21
23
25
27
29
bснЙке~д=
Зб~гЙнЙк=EггF
2.66
3.33
4
4.66
5
5.66
6.33
7
7.66
8.33
9
9.66
_зЗу=пЙбЦЬн
EвЦF
<2
2-5
5-10
10-20
20-30
>40
`~ååìä~
ëáòÉ=EcêF
8 to 10
10 to 16
14 to 17
17 to 19
19 to 23
21 to 28
397
398
Key Questions in CONGENITAL CARDIAC SURGERY
A
B
Figure 9. Arterial cannulae used for paediatric extracorporeal
membrane oxygenators: A) an 8Fr cannula used for central and neck
cannulation, with a single orifice at the cannula tip, which is placed in the
aortic arch or root of the right brachiocephalic artery; B) a 15Fr cannula
used for femoral cannulation, with a multi-orifice tip, that is more
effective in the abdominal aorta.
Generally, venous cannulae tend to be larger than the arterial
•
cannulae to prevent venous collapse and to accommodate the higher
distensibility of the venous vessels.
In respiratory ECMO, when the VA set is used, the cannulae tend to
•
be of the same size.
11 Extracorporeal membrane oxygenation
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A
B
399
Figure 10. Venous cannulae used for paediatric extracorporeal
membrane oxygenators: A) an 8Fr cannula used for neck cannulation,
with multiple openings and markers to identify the cannula position within
the superior vena cava, right atrium (RA) and inferior vena cava (IVC); B)
a long 15Fr cannula used for femoral vein cannulation, with a multiorifice tip, that is placed at the RA-IVC area.
Although single cannulae (double-lumen) are used in VV ECMO,
•
their use in small babies is limited (Figures 11 and 12).
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