Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3612_Библиотеки_им_академика_М_И_Перельмана
.pdf
370
Key Questions in CONGENITAL CARDIAC SURGERY
19 What are the causes of myocardial injury during
cardiopulmonary bypass for congenital cardiac
surgery?
Cross-clamp ischaemic energy depletion — which may (or may not)
•
be reversible, depending on the length of ischaemia and efficacy of
protection. Damage results from multiple issues, including ischaemia
with resultant lactic acidosis, depletion of high-energy phosphates,
altered intracellular calcium and direct trauma. Chronically, hypoxic
hearts (a common feature in congenital heart disease) are less able
to tolerate this. Late reperfusion activates an inflammatory response
and apoptosis. An intermediate duration of ischaemia may result in
myocardial stunning with delayed recovery.
Following removal of the cross-clamp, reperfusion injury can result in:
•
a) intracellular calcium overload and leucocyte activation;
b) release of oxygen free radicals that activate complement,
thereby causing endothelial injury and an increase in
microvascular permeability, leading to oedema and cell death;
c) superoxide anion production due to increased oxygen
availability, which damages endothelial barriers, and promotes
neutrophil adhesion and activation;
d) inhibition of endothelial nitric oxide production, which
exacerbates coronary artery vasospasm, pulmonary
hypertension and right ventricular failure;
e) intra-coronary air embolism during reperfusion, which causes
further ischaemia, especially in neonates.
Left ventricular distension due to inadequate venting results in a
•
reduced ability of the ventricle to eject against a high afterload.
Failure of myocardial protection caused by long intervals between
•
cardioplegia, particularly during complex cases, or impaired
cardioplegia delivery due to:
a) aortic regurgitation;
b) anomalous coronary arteries arising from the pulmonary artery,
which therefore do not receive cardioplegia;
c) absent coronary sinus — which may be associated with a
persistent left SVC;
d) anomalous connections of the coronary sinus with the left
atrium or coronary arteries;
e) presence of coronary sinusoids — fistulous connections
between coronary arteries and the right ventricle, such as in
patients with pulmonary atresia, thereby shunting of blood
away from the myocardium.
10 Cardiopulmonary bypass
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
Surgical issues — regardless of the underlying congenital condition,
•
direct myocardial injury, coronary injury, prolonged periods of bypass
or cross-clamp all have been reported as causes of reversible and
irreversible myocardial injury.
20 How is the temperature of the patient controlled whilst
on cardiopulmonary bypass?
Heat loss occurs from the skin and mucous membranes by radiation,
•
conduction, convection and evaporation.
The CPB heater-cooler can further manipulate temperature (Figure
•
9). A tank provides temperature controlled closed water circuits
(isolated from the patient) to two heat exchangers incorporated in the
cardioplegia circuit and oxygenator circuits.
371
Figure 9. Heater cooler unit attached to the cardiopulmonary bypass
circuit (red arrows), with the heat exchange mat (zigzag lines) that
separates heater-cooler water flow from patient blood flow.
Monitoring venous and arterial blood temperatures detects any
•
thermal gradient. It is important to maintain this gradient <10°C to
avoid microbubble formation during rewarming.
As children lose heat more readily than adults due to a relatively large
•
body surface area in relation to their body mass, smaller gradients
between the core and peripheral temperatures are used, as infants on
372
Key Questions in CONGENITAL CARDIAC SURGERY
CPB regulate body temperature ineffectively. Large gradients result in
rapid heat loss from the core compartment to the peripheral tissues.
Children more often have shunts or collateral vessels, requiring deep
•
hypothermic circulatory arrest (DHCA) to provide a clear surgical field.
21 What measures are used by the perfusionist to optimise
cerebral protection during surgery for congenital
cardiac disease?
Brain O2supply (delivery) should be optimised and demand reduced,
•
which is particularly important in children, with their higher O
Oxygen delivery = Cardiac output (CO) x Oxygen content
where: CO = Stroke volume (SV) x Heart rate (HR)
Oxygen content = (Hb x 1.34 x SpO2) + (PaO2x 0.03)
Optimising oxygen delivery pre- and post-surgery may be achieved
•
by maintaining:
demand.
2
a) adequate haemoglobin (Hb) levels with transfusion triggers
varying with age (children Hb 90g/L, adults 80g/L) and
disease (cyanotic disease Hb 120g/L). This can also be aided
by minimising CPB circuit volumes;
b) adequate arterial oxygen saturations;
c) cerebral blood flow — by increasing CPB flow or CO2levels
(with resultant vasodilatation).
Reduced oxygen demand can be achieved with:
•
a) reduced temperature (ice packs are more useful in infants
where the fontanelles are unfused);
b) effective sedation/analgesia.
Tissue oxygenation can be monitored using:
•
a) internal jugular venous saturation — where levels >95%
suggest minimal cerebral O2extraction;
b) near-infrared spectrophotometry (NIRS) — which provides
continuous transcranial arterial saturation levels.
Although the evidence of their effects on long-term outcomes is
•
uncertain, a number of drugs have also been used to aid cerebral
protection, including:
10 Cardiopulmonary bypass
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
a) corticosteroids — which potentially reduce inflammation but
may increase infection risk;
b) mannitol — which can reduce fluid overload but may affect
intracellular neuronal volume with severely damaging effects.
Antegrade or retrograde cerebral perfusion can also be used to
•
reduce brain injury (Figure 10).
RA cannula
Ao root cannula
Clamp for antegrade
coronary perfusion
Clamp for antegrade
cerebral perfusion
RBCA cannula
Figure 10. Operative image demonstrating the set-up for deep
hypothermic circulatory arrest and regional antegrade perfusion to the
brain and heart. Flow to the circle of Willis is delivered by the distal arm
of the arterial line to the right brachiocephalic artery (via an interposition
graft) which has been clamped proximally. Flow to the coronaries is
delivered by the proximal arm of the arterial line to the aortic root, which
has been clamped distal to the cannula. The left common carotid artery
(LCCA) and left subclavian artery (LSCA) have been individually snared
(not shown). The arch is now accessible beyond the isthmus while on
beating heart and brain perfusion. RBCA = right brachiocephalic artery;
Ao = aorta; RA = right atrium.
University Hospital Southampton, UK.
Acid-base management is important as a reduction in temperature
•
produces an increased solubility of CO2(Boyle’s law), reduced
pCO2and a higher pH (i.e. metabolic alkalosis). During hypothermia,
Image courtesy of Mr. Antonio Ravaglioli,
373
374
Key Questions in CONGENITAL CARDIAC SURGERY
two different methods can be used to maintain homeostasis,
including:
a) alpha stat strategy — which allows the pCO2to drift as
dictated by solubility, hence as the patient cools, the blood
becomes more alkalotic. The potential advantages of this
strategy include maintenance of the:
i) autoregulatory capacity of the cerebral arteries — which
couples cerebral blood flow to O2demand. Hence, the
reduced flow may minimise damage caused by
microemboli;
ii) buffering capacity of the alpha imidazole group of
histidine and more normal protein function;
iii) intracellular electromechanical neutrality — which is
essential for normal cellular function;
b) pH stat strategy — which maintains pCO
of 7.4 at the patient’s temperature, by the addition of CO2. The
potential advantages of this strategy include:
i) increased flow to the cerebral vessels — which results
in improved cerebral cooling, at a cost of increased
embolic load;
ii) minimising the left shift of the O2dissociation curve that
occurs with hypothermia, hence O2can more easily be
unloaded to the tissues.
at 5.3kPa and a pH
2
The best strategy is unclear, with pH stat maybe better with DHCA,
•
as cerebral vasodilation and increased blood flow provides more O
during cerebral cooling. There is some evidence of an advantage in
paediatric patients but less so in adults. Alpha stat is used for
rewarming.
22 What are the indications for deep hypothermic
circulatory arrest in congenital cardiac surgery?
The use of deep hypothermic circulatory arrest in congenital cardiac
•
surgery is uncommon and it is generally limited to certain operations,
including:
a) aortic arch surgery — where regional perfusion of carotid
and/or coronary arteries can be used to minimise injury, such
as:
i) coarctation of the aorta with hypoplasia of the aortic arch
requiring full arch reconstruction;
2
10 Cardiopulmonary bypass
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
ii) interrupted aortic arch requiring complex reconstruction
(as in cases of long segments of interruption);
iii) Norwood procedure;
iv) rare aneurysms of the aorta (PHACES complex);
v) descending aortic surgery, such as redo-repair of
coarctation of the aorta or its complications to protect
the spinal cord against ischaemia and paraplegia;
b) complex neonatal and paediatric surgery — where multiple
systemic-pulmonary collaterals return blood to the left side of
the heart and/or pulmonary arteries;
c) difficult cases of obstructed total anomalous pulmonary venous
connection;
d) unifocalisation of major aortopulmonary collateral arteries
(MAPCAs).
23 What are the principles of deep hypothermic
circulatory arrest?
During total DHCA, no tissues are perfused and O2debt is
•
inevitable, despite the reduced basal metabolic rate.
As cerebral metabolism decreases 6-7% for every 1°C fall in
•
temperature, the patient is usually cooled to 15-20°C before initiating
circulatory arrest.
The risks of DHCA include:
•
375
a) impaired microcirculation due to increased plasma viscosity,
vasoconstriction and reduced erythrocyte plasticity. This can
be minimised by haemodilution by bringing the haematocrit to
20% at 20°C but at the risk of inadequate O2delivery during
rewarming;
b) neurological injury and reduced postoperative neurocognitive
function;
c) coagulopathy and platelet dysfunction;
d) systemic inflammatory response syndrome (SIRS) with
associated capillary leak, oedema and organ dysfunction.
Safety is both time- and temperature-dependent (Table 1), with major
•
changes in mortality, such as low mortality at 18°C for 45 minutes of
DHCA whereas 90 minutes of DHCA is associated with 90% mortality.
Selective cerebral perfusion enhances brain protection and can be
•
achieved with:
a) antegrade flow — by cannulating the right axillary or subclavian
arteries and clamping the brachiocephalic artery, thereby
376
Key Questions in CONGENITAL CARDIAC SURGERY
Table 1. Safe duration of deep hypothermic circulatory arrest at
different temperatures.
qЙгйЙк~нмкЙ=Eш`F =====================Ъp~СЙЫ=ae`^=нбгЙ=EгбемнЙлF
36 1
32 5
28 10
24 20
20 30-40
16 45-60
directing flow to the right common carotid artery. An additional
cannula can be placed in the left common carotid artery.
Recommended flows range between 10-30mL/kg/min with a
perfusion pressure 30-70mmHg (Figure 11);
Figure 11. Antegrade cerebral perfusion circuit with blood returned to
the patient via the left common carotid artery and the right common
carotid artery (via the right subclavian artery).
10 Cardiopulmonary bypass
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
b) retrograde flow — by attaching the arterial line or a shunt to the
superior vena cava. Recommended flows range between 250400mL/min with a perfusion pressure of 25-40mmHg. The
presence of deoxygenated blood in the aortic arch is indicative
of cerebral O2uptake (Figure 12).
377
Figure 12. Retrograde cerebral perfusion circuit with blood returned to
the patient via the superior vena cava.
24 What are the principles of renal protection during
cardiopulmonary bypass?
The kidneys are particularly at risk of damage during periods of low
•
flow or low pressure, resulting in retention of excess fluid and
solutes, and loss of protein.
378
Key Questions in CONGENITAL CARDIAC SURGERY
Haemofiltration before, during or after CPB can remove excess
•
plasma water and solutes. The different techniques used during
cardiac surgery include:
a) continuous ultrafiltration (CUF) — where the whole circuit,
including the patient, is filtered during CPB;
b) zero-balance ultrafiltration (ZBUF) — where a high-volume
circuit ultrafiltration is performed during rewarming;
c) modified ultrafiltration (MUF) — where, following separation
from CPB, blood is removed from the arterial line, passed
through the haemofilter, and then returned to the patient via the
venous cannula. Careful volume management is required to
avoid hypotension consequent upon reduction in preload and
cardiac output.
Measuring DO2(oxygen delivery), with a target range of 270-
•
280mL/min/m2, has more recently been used as a goal-directed
perfusion strategy (with the addition of a high haematocrit) and has
been shown to significantly reduce the risk of postoperative acute
renal dysfunction.
25 What are the principles of anticoagulation reversal
following surgery for congenital cardiac disease?
Reversal of anticoagulation is typically performed with protamine,
•
which is a cation derived from salmon sperm. It is strongly alkaline
thereby attracting the strongly acidic heparin from its binding site on
anti-thrombin III. Inadequate doses of protamine leave free heparin
circulating.
Protamine reactions can be classified as:
•
a) Class 1 — which is characterised by hypotension triggered by
histamine. It is treated by fluid and vasopressors;
b) Class 2a — which is true anaphylaxis, triggered by IgE
antibodies. It is treated with immediate cessation of protamine,
and administration of adrenaline, hydrocortisone,
chlorphenamine and bronchodilators;
c) Class 2b/c — which are immediate (b) and delayed (c)
anaphylactoid reactions, mediated by the complement
cascade, and usually less severe than class 2a;
d) Class 3 — which is characterised by catastrophic pulmonary
vasoconstriction, caused by complement activation and
release of thromboxane A2 that results in pulmonary
10 Cardiopulmonary bypass
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
hypertension, RV failure, circulatory shock and severe
bronchospasm. It is treated with immediate cessation of
protamine, commencement of adrenaline and milrinone, and
often reinstitution of CPB (with heparin administered).
26 What are the main features of blood conservation and
bleeding in congenital cardiac surgery?
Paediatric patients pose a unique challenge to blood conservation
•
due to:
a) small blood volume;
b) requirements for a higher haematocrit (to deliver O
CPB;
c) increased rate of cyanotic heart disease;
d) immature coagulation system and association with congenital
deficiency of coagulation factors;
e) increased risk of platelet dysfunction;
f) profound hypothermia is used more commonly.
) during
2
379
Adult patients with congenital heart disease may be more prone to
•
bleeding due to:
a) redo operation — especially as pre-emptive femoral CPB may
be necessary, which is associated with prolonged mediastinal
dissection during anticoagulation and may result in significant
cumulative blood loss;
b) abnormal coagulation systems;
c) more challenging to cross-match blood due to antibody
production following previous transfusions.
In congenital patients with smaller blood volume, some techniques
•
are used to reduce the risk of requiring blood transfusion, including:
a) retrograde autologous priming (RAP) and antegrade
autologous priming to displace bypass prime with the patient's
own blood;
b) miniature circuits with vacuum-assisted venous drainage to
reduce haemodilution;
c) using whole blood (with high hematocrit) from the venous line,
which is given directly to the anaesthetist before protamine is
administered but after the completion of the modified
ultrafiltration process.
Соседние файлы в папке Библиотека им академика М.И. Перельмана