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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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410
Key Questions in CONGENITAL CARDIAC SURGERY
AB
RA
RA
Cannula
Figure 15. Echocardiographic images demonstrating venous cannula
position for: A) veno-veno extracorporeal membrane oxygenation; and B)
veno-arterial extracorporeal membrane oxygenation. RA = right atrium.
Computed tomography (CT) scanning can be used to investigate the
•
cardiac and respiratory systems, whilst the patient is on ECMO. It is
also useful in assessing the central nervous system, if any
neurological symptoms are present.
CT angiography allows visualisation of cardiac structures and the
•
adequacy of surgical repair. In such cases, a brief period of reduced
or no ECMO flow can be employed to fill the cardiac structures,
while ventilating the patient fully.
Angiography is occasionally used to visualise anatomy and also to
•
perform cardiac interventions, as required.
Ultrasound scanning is used to diagnose involvement of the central
•
nervous system and intra-abdominal organs, and Doppler scanning
to visualise distal limb perfusion in patients with femoral cannulation.
25 What are the ventilation settings on extracorporeal
membrane oxygenation?
Whilst on ECMO, full gas exchange in the lung is not required and
•
ventilation is usually adjusted to rest settings.
This allows for the lungs to be ventilated with lower volumes and
•
pressures, facilitating lung recovery by preventing barotrauma.
The usual settings of a patient on ECMO are FiO230%, PEEP 3-
•
5cm H2O, respiratory rate 5-10 rpm, tidal volume 5-10mL/kg, with
adjustments made according to the patient’s requirements.
11 Extracorporeal membrane oxygenation
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In patients with cardiac ejection whilst on VA ECMO, it is advisable
•
to increase the mechanical ventilation settings, given the increased
pulmonary venous return, to allow for adequate coronary perfusion
with oxygenated blood.
26 What procedures can be performed whilst on
extracorporeal membrane oxygenation?
Chest drain insertion for pneumothorax, haemothorax or chylothorax.
•
Insertion of central lines, arterial lines or a vascular catheter (for
•
haemofiltration).
Orotracheal intubation.
•
Balloon atrial septostomy.
•
Diagnostic or interventional cardiac catheterisation.
•
Computed tomography scan.
•
Transoesophageal and transthoracic echocardiogram.
•
Bronchoscopy.
•
Abdominal procedures and peritoneal dialysis catheter placement.
•
411
27 Describe the principles of anticoagulation
management whilst on extracorporeal membrane
oxygenation
One major advantage of ECMO compared to CPB is the lower
•
heparin requirement and lower activated clotting time (ACT). The
ACT, however, needs to be checked regularly to avoid under- or overheparinisation.
Generally, an ACT of 250 seconds is required to start ECMO and
•
this is obtained with heparin 100 IU/kg administered just prior to
cannulation, depending on local protocols.
Regular checks are carried out at 15-minute intervals for the first 2
•
hours, every 30 minutes for the next hour and finally hourly if the ACT
is within the desired parameters.
A heparin infusion is then started at 0.5mL/hr or 10 IU/kg/hr and
•
titrated accordingly, to maintain an ACT of 220-250 seconds (or 180200 seconds, if bleeding is present).
In the event of a low ACT, the heparin infusion is increased by
•
0.2mL/hr and the ACT is checked every 15 minutes until stable.
If a bolus is required, 5-10 IU/kg is administered in addition to
•
increasing the infusion by 0.2mL/hr and the ACT is rechecked every
15 minutes.
412
Key Questions in CONGENITAL CARDIAC SURGERY
A higher ACT may be required when:
•
a) increasing clot or fibrin formation is visible within the circuit;
b) less than ideal flows are reached;
c) during weaning and trial off ECMO.
A lower ACT may be required in the presence of persistent bleeding,
•
despite optimising clotting factors or after surgical intervention.
If bleeding is persistent, the heparin infusion can be stopped, and
•
correction of the coagulation status is achieved by administration of
platelets, fresh frozen plasma and cryoprecipitate, according to the
clotting results.
Careful management of the circuit with monitoring of clot formation
•
and fibrous strands within the circuit should be performed. The
membrane oxygenator is the most vulnerable component of the
circuit at risk of clotting. Monitoring of the transmembrane gradient is
paramount to prevent sudden clotting of the oxygenator, causing the
pump to acutely fail.
Once bleeding is corrected, the heparin infusion should be restarted,
•
as above.
28 What are the principles of weaning a patient from
extracorporeal membrane oxygenation?
Weaning a patient from ECMO is a complex and difficult procedure,
•
which requires a multidisciplinary team approach. The respiratory,
cardiac, renal and general status of the patient need to be taken into
consideration before attempting separation from cardiorespiratory
support.
Prior to the commencement of a weaning trial, the following
•
conditions should be evaluated:
a) pulmonary function — to assess chest mechanics, the
presence of any pleural effusions, pneumothorax, pleural
effusions, residual lesions and airway problems by chest
radiography, and lung compliance by manual ventilation of the
patient. Occasional, inhaled nitric oxide may be required to
reduce pulmonary vascular resistance;
b) cardiac function — by serial echocardiography to assess
regional and global function, myocardial contractility and
ventricular compliance at rest before the weaning process. In
cases where ECMO is required for cardiac failure, a more indepth analysis of cardiac function in response to progressive
loading might be required before embarking on a full weaning
process (i.e. 12-24 hours before). This is called a ‘stress echo’
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and it is achieved by temporarily increasing the ACT to 250
seconds, starting conventional ventilation and progressively
reducing the flow by 25% decrements until the circulation is
stopped for 30-60 seconds. In cases where a left heart vent is
present, it is reasonable to clamp it for the duration of the stress
echo which should be kept short (2-3 minutes) to avoid clot
formation in the circuit. While the ECMO flows are reducing, an
echocardiogram is continuously performed to assess myocardial
systolic and diastolic function, global and regional contractility
and any valve dysfunction. In our experience, a stress echo
provides important information about progression in the recovery
of cardiac function and the timing of the ECMO wean;
c) renal function — where alternative strategies should be
considered following a successful weaning (peritoneal dialysis,
peripheral CVVH), if replacement therapy was used on ECMO
via the side ports;
d) fluid balance — increasing oncotic pressure and the use of
vasopressor drugs may be required to limit or reverse fluid
extravasation as a consequence of the inflammatory response
to ECMO;
e) vascular function — with inotropic and vasopressor support,
started before an attempt at weaning;
f) metabolic status — with worsening lactic acidosis, unstable
glycaemia and evidence of worsening multi-organ failure on
ECMO being poor predictors of a successful wean;
g) neurologic status — where head ultrasound or magnetic
resonance imaging may be required to document intracranial
anatomy and functional status;
h) infective conditions — where worsening signs of sepsis prior
to weaning is a poor predictor of outcomes.
413
The ACT is generally raised to 300 seconds by increasing the heparin
•
infusion, to reduce clot formation in the cannulae and circuit whilst
reducing flow.
The process of weaning requires a gradual reduction of the flow, so
•
that over the course of 1-2 hours, the ECMO flow is reduced in steps
of 25%.
During the weaning period, blood gas analysis is performed regularly
•
and the ventilation parameters are adjusted accordingly. Systemic
lactate levels are taken into account as part of the assessment of
systemic perfusion.
Weaning from the ECMO circuit is completed by clamping the
•
venous line, unclamping the bridge and then clamping the arterial
line, following which the child is isolated from the circuit and the heart
takes over the systemic perfusion.
414
Key Questions in CONGENITAL CARDIAC SURGERY
The cannulae are left in place and the ECMO circuit continues to run
•
via the bridge, in case the child fails the weaning trial.
Every 15-20 minutes, the cannulae are flushed to avoid blood
•
stagnation and clot formation.
Signs of early failure of an ECMO weaning trial include:
•
a) poor haemodynamic performance with declining systemic
arterial pressure;
b) increasing right and/or left atrial pressure;
c) poor ventricular function on echocardiogram;
d) arrhythmias;
e) poor peripheral perfusion with increasing systemic lactate,
hypoxia, hypercarbia and acidosis;
f) poor oxygenation and high end-tidal CO2.
In some cases, a ‘one-way wean’ strategy is adopted, where ECMO
•
will not be reinstituted in the case of early failure. This is a difficult
decision that must be taken by the most senior multidisciplinary team
and adopted in cases of manifest inadequacy of the native
cardiorespiratory system. Given the nature of active withdrawal of care,
it is important to involve the parents in the decision-making process.
If the trial is successful, the patient is decannulated. In patients with
•
central cannulation via a median sternotomy, a policy of ‘delayed
sternal closure’ is employed. In patients with neck decannulation,
vessel reconstruction should be attempted but if no reasonable
patency is obtained, vessel ligation may be required.
An ACT is then performed and protamine is administered to reverse
•
heparin to reach an ACT of 100-120 seconds.
29 What are the outcomes of patients undergoing
extracorporeal membrane oxygenation following
paediatric cardiac surgery?
In general, survival to hospital discharge following cardiac ECMO is
•
40-50% and is influenced by several factors:
a) time spent on ECMO — where increased duration of ECMO
support is associated with a lower survival. Beyond an ECMO
duration of 7 days, the odds of mortality increase by 12% per
every extra day on ECMO;
b) pre-operative conditions — where low weight, preterm birth,
pre-operative necrotising enterocolitis are recognised risk
factors for mortality;
c) postoperative complications — where renal failure requiring
renal replacement therapy, neurological impairment, bleeding
and developing necrotising enterocolitis whilst on ECMO, all
carry higher mortality;
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d) neurological sequelae — where longer CPB (>400 minutes)
and the use of deep hypothermic circulatory arrest at the
cardiac operation, are determinants of an increased risk of a
neurological insult, if the patient needs VA ECMO
postoperatively.
30 What are the outcomes of extracorporeal membrane
oxygenation in the neonatal paediatric population (Table 4)?
Table 4. Outcomes following paediatric extracorporeal membrane
oxygenation produced by the Extracorporeal Life Support Organization
(ELSO) in 2018.
Neonatal
Pulmonary
Cardiac
ECPR
Paediatric
Pulmonary
Cardiac
ECPR
qçí~ä=êìåë
30,934
7794
1718
8820
10,462
3946
pмкобоЙЗ=b`ip
25,990 84%
5063 64%
1140 66%
5953 67%
7177 68%
2262 57%
pмкобоЙЗ=нз=ЗблЕЬ~кЦЙ=
зк=нк~елСЙк
22,662 73%
3281 42%
708 41%
5131 58%
5447 52%
1675 42%
415
31 What are the potential complications of extracorporeal
membrane oxygenation?
As complications of ECMO are common, each patient is likely to
•
develop an ECMO-related complication. Although circuit-related
complications are rare, they are significant.
Complications that occur during cannulation include:
•
a) damage to the cannulating vessels, including dissection;
b) haemothorax, pneumothorax (Figure 16);
c) haemopericardium and tamponade;
d) accidental dislodgement of the cannulae or malposition;
e) limb ischaemia, especially in femoral cannulation.
Complications that occur whilst the child is on ECMO include:
•
a) bleeding (both minor and major);
b) thrombus in the circuit (tubing, oxygenator), or haemolysis;
Key Questions in CONGENITAL CARDIAC SURGERY
416
Figure 16. Chest radiograph demonstrating a
pneumothorax following venous cannulation for
extracorporeal membrane oxygenation.
Figure 17. An axial computed tomography
scan demonstrating a significant cerebral bleed
in a child whilst on extracorporeal membrane
oxygenation.
11 Extracorporeal membrane oxygenation
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c) air within the circuit;
d) motor failure, pump failure or console failure;
e) oxygenator failure;
f) tubing rupture or failure of the line components;
g) cerebral bleed, infarction or oedema (Figure 17);
h) infection;
i) accidental displacement and decannulation (Figure 18);
j) complications from other systems, especially renal and
gastrointestinal;
k) general ICU-related complications.
417
Figure 18. Chest radiograph demonstrating
accidental arterial decannulation of a child whilst
on extracorporeal membrane oxygenation.
32 Describe the principles of managing emergency
extracorporeal membrane oxygenation scenarios
Veno-veno ECMO hypoxia:
•
a) check that the pump flow is over two-thirds of the patient’s
cardiac output;
418
Key Questions in CONGENITAL CARDIAC SURGERY
b) administer 100% FiO2from the oxygenator, aiming to achieve
a pO2>150mmHg;
c) increase pump flow;
d) increase ventilation;
e) cool the patient;
f) administer muscle relaxants;
g) maintain haemoglobin levels;
h) add a second access line to reduce the shunt.
Veno-veno ECMO hypercarbia:
•
a) check that the pump flow is over two-thirds of the patient’s
cardiac output;
b) increase the O
rate;
c) increase the pump flow rate (otherwise consider that
recirculation may be occurring);
d) increase ventilation;
e) cool the patient;
f) administer muscle relaxants.
flow to the oxygenator to twice the pump flow
2
Veno-veno ECMO shunting or recirculation:
•
a) observe the cannula position as pump flow may not improve
oxygenation;
b) check that the pre-membrane (venous) pO2is <50mmHg;
c) reposition the cannula (if required).
Veno-arterial ECMO hypoxaemia:
•
a) check the arterial blood gas from the right radial arterial line
and O2saturation measured on the right hand or forehead;
b) ensure proper functioning of the oxygenator return line pO
>150mmHg;
c) increase the pump flow as high as possible;
d) increase ventilation, PEEP and inspired O2concentration;
e) readjust or replace the arterial line, if required.
Veno-arterial ECMO hypercarbia:
•
a) check for adequate pump flow (over two-thirds of the patient’s
cardiac output);
b) adjust the supply of O2to the oxygenator, to twice the pump
flow rate;
2
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c) increase the pump flow rate;
d) increase ventilation;
e) cool the patient;
f) administer a muscle relaxant.
Veno-arterial ECMO bleeding:
•
a) prevention is the primary objective by meticulous haemostasis
and monitoring coagulation status (ACT, APTT, FBC, D-dimer,
fibrinogen);
b) maintain an APTT of 50-75 seconds with a heparin infusion
(but can be withheld if the patient is bleeding). Heparin-coated
circuits can run for a couple days without heparin;
c) transfuse platelets, cryoprecipitate, FFP, packed cells as needed;
d) administer antifibrinolytic agents, such as IV tranexamic acid;
e) consider surgical exploration.
Veno-arterial ECMO haemolysis — which may be caused by a clot in
•
the circuit or near the cannula orifice, obstruction at the circuit,
increased speed of the pump, deranged coagulation cascade or liver
dysfunction. Presenting signs include haematuria, hyperkalaemia, renal
failure, jaundice (late sign) and shaking of the lines due to changes in
pressure (cavitating). Management includes the following:
419
a) monitor haemoglobin, liver function tests, urea & electrolytes
and clotting screen;
b) replace the volume;
c) adjust the pump flow;
d) a transoesophageal echocardiogram (TOE) to ensure that the
cannulae are not obstructed;
e) circuit change, if required.
Unable to maintain veno-arterial ECMO flow:
•
a) check the position of the cannulae and volume status and
improve if possible;
b) check for any kinking of the lines or cannulae;
c) blood sample from pre- and post-oxygenator;
d) perform an echocardiogram and chest radiograph to identify
the intracardiac position of the cannulae;
e) optimise fluid status, preload, afterload and contractility;
f) decrease the pump speed to reduce the suction on the
catheter, followed by increasing the speed to normal as
smoothly and quickly as possible;
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