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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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260
Key Questions in CONGENITAL CARDIAC SURGERY
In addition to systemic blood pressure, both right and left atrial
•
pressure should be monitored post-bypass.
Pulmonary hypertension may persist post-bypass but may be
•
managed by ventilation and pulmonary vasodilators, such as
milrinone and nitric oxide. If these fail, atrial fenestration allows
decompression through a right-left shunt.
Delayed sternal closure may be required to improve right ventricular
•
function.
Special care is necessary during any transfers.
•
18 Describe how the risk of anaesthesia can be minimised
in a patient with Eisenmenger syndrome
Anaesthesia in a patient with Eisenmenger syndrome carries
•
significant mortality and should not be performed unless essential.
Adequate venous return is crucial in pulmonary hypertension. Pre-
•
operative starvation should not exceed international
recommendations:
a) solid food and milk — 6 hours;
b) clear fluids — 1 hour.
Systemic arterial pressure fluctuates with variations in SVR and PVR.
•
When intracardiac communications are present, right-to-left shunting
•
and worsening cyanosis will be exacerbated by a:
a) fall in SVR, such as caused by anaesthesia;
b) rise in PVR, such as caused by hypoxia, hypercarbia or
inadequate anaesthesia/analgesia.
Similarly, left-to-right shunting, which occurs with RV dilatation,
•
further dysfunction and increased risk of arrhythmias, increases with
elevation in the SVR, such as caused by pain, anxiety or inadequate
anaesthesia.
Fluctuations in the heart rate and myocardial contractility should be
•
avoided. Effective communication between the surgeon and
anaesthetist allows responses to surgical stimuli to be minimised.
Oral anticoagulants should be converted to short-acting intravenous
•
agents peri-operatively, to avoid both thrombosis and excessive
bleeding.
7 Anaesthesia and congenital heart disease
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19 How does the presence of congenital heart disease
influence haemostasis?
Coagulation in congenital heart disease, especially cyanotic lesions
•
with polycythaemia, is modified by a number of factors, including:
a) thrombocytopaenia;
b) reduced fibrinogen levels;
c) increased fibrinolysis;
d) decreased levels of factors V and VIII, possibly secondary to
liver hypoperfusion.
Polycythaemia and hyperviscosity cause impaired flow, which is
•
implicated in thrombus formation.
Cardiopulmonary bypass causes haemodilution and exposes blood
•
to synthetic surfaces. Inflammatory and coagulation pathways are
activated, causing platelet dysfunction and coagulation abnormalities
independent of heparin.
20 What are the implications of congenital heart disease
for peri-operative blood transfusion?
Previous transfusions are common, increasing the risk of antibody
•
formation and making cross-matching more complex than usual.
Rapid, point-of-care testing including HemoCue®, SpHb and
•
thromboelastography®(TEG®) can guide the administration of blood
products and reduce the exposure to risk from excessive bleeding or
thromboembolic events, especially in complex redo procedures or
surgery for single-ventricle palliation.
Cyanotic patients with poor cardiac output may require an increased
•
haematocrit. Over-transfusion, however, causes hyperviscosity and
fluid overload, in addition to recognised risks, such as transfusionassociated lung injury (TRALI).
261
21 What are the anaesthetic considerations for
percutaneous device closure of an atrial septal
defect?
Although small ASDs may be closed percutaneously, the cardiac
•
catheterisation laboratory environment can be challenging for the
anaesthetist because:
a) access to the patient is limited by conflicting equipment
requirements;
262
Key Questions in CONGENITAL CARDIAC SURGERY
b) ambient light is low, to improve contrast on the display
screens;
c) temperature control is often not as effective as in the operating
theatre;
d) anaesthetic gas scavenging, gas supply and air-change rates
rarely reach operating theatre standards.
Vascular access sites and consent for transoesophageal
•
echocardiography (TOE) should be confirmed pre-procedure.
Blood loss from the puncture sites may be underestimated.
•
Device displacement or embolisation are rare complications, with a
•
reported rate of 0.55%, necessitating percutanous retrieval or open
surgery.
22 What strategies may be used to improve weaning from
cardiopulmonary bypass?
Weaning from cardiopulmonary bypass is one of the most critical
•
phases of the entire operation and must be managed with maximal
communication and clarity of action. The anaesthetist, surgeon and
perfusionist should operate according to one common strategy and
sequence of events.
One of the most important factors for a successful wean is achieving
•
an adequate repair. Residual lesions are generally poorly tolerated,
both from a haemodynamic balancing and myocardial function
standpoint.
It is paramount that attention is placed at identifying any early signs
•
of myocardial dysfunction and circulatory imbalance. Ventilation and
pulmonary function need to be optimised prior to initiating the
weaning procedures.
Most groups adopt agreed weaning protocols, to eliminate
•
misunderstandings and adverse events.
The effects of residual lesions are numerous and can be severe,
•
including:
a) pressure overload — in the presence of residual stenoses,
such as RVOT obstruction, mitral stenosis or LVOT
obstruction; this will worsen the oxygen supply-demand
balance, leading to right ventricular failure, left ventricular
failure or biventricular failure, which can have catastrophic
consequences;
b) volume overload — in the presence of a residual VSD,
significant atrioventricular valve regurgitation or an untreated
7 Anaesthesia and congenital heart disease
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large PDA; this will reduce systemic cardiac output and/or
result in pulmonary overflow at the expense of systemic
perfusion, leading to both cerebral and myocardial
hypoperfusion, and early ventricular failure.
Early signs of myocardial dysfunction may be identified by:
•
a) poor systemic blood pressure in the presence of a normal
afterload and adequate preload;
b) high venous pressures (including left atrial pressure when
indicated) and inadequate systemic pressure;
c) poor pulmonary blood flow as indicated by low end-tidal CO
d) decreasing arterial oxygen saturation;
e) direct observation of a poorly contracting heart, mottled
epicardium, distended ventricles and ensuing bradycardia;
f) TOE or epicardial echocardiographic evidence.
Arrhythmias have a significant impact on cardiac function, including:
•
a) bradycardia — which causes a linear reduction in cardiac
output in children;
b) tachyarrhythmias — which reduce diastolic filling time and
coronary perfusion, and increase myocardial work;
c) epicardial pacing — which may be required to achieve optimal
rate and rhythm.
;
2
263
Filling pressures should be optimised. As PVR varies more in
•
children, right atrial pressure (RAP) may not reflect left-sided filling
pressures, and hence it may be necessary to directly monitor left
atrial pressure (LAP).
Calcium handling in the neonatal myocardium is immature and
•
extracellular calcium has a more significant role. Ionised calcium
levels must be targeted to optimise contractility.
Inotropes may be required, with the choice of agent depending on
•
the underlying pathology. In view of the relative hypertrophy of the RV
and reactive pulmonary vasculature, milrinone is commonly used in
infants.
Temperature and adequate rewarming procedures are paramount to
•
maintain control of vascular tone, ventricular afterload and enzymatic
function, especially for the coagulation system.
Failure to respond to pharmacological measures may necessitate the
•
use of mechanical assist devices, usually extracorporeal membrane
oxygenation (ECMO) or ventricular assist devices (VAD).
264
Key Questions in CONGENITAL CARDIAC SURGERY
23 Describe the monitoring used for anaesthesia on
patients with congenital heart disease
Minimum monitoring standards are set for all patients undergoing
•
general anaesthesia (including transfer) and are shown in italics
below. They ensure both safety and lack of awareness and pain
(Figure 10).
•
•
Figure 10. Standard anaesthetic monitoring with many
physiological parameters easily viewed, including
electrocardiogram (white), invasive blood pressure
(red), right atrial pressure (yellow), oxygen saturations
(blue), anaesthetic gases (purple), respiratory gases
(green), temperature and near-infrared spectroscopy
(bottom right corner).
Airway:
a)
~бкп~у=йкЙллмкЙI=ЗблЕзееЙЕнбзе=~д~кгл
b)
ЙсйбкЙЗ= Е~кДзе= ЗбзсбЗЙ= ЕзеЕЙенк~нбзе
endotracheal tube is placed in the trachea).
Breathing:
a)
ймдлЙ=зсбгЙнку
b)
нбЗ~д=оздмгЙл=~еЗ=~бкп~у=йкЙллмкЙ
c)
кЙлйбк~нзку=к~нЙ
;
;
;
(confirming that the
;
7 Anaesthesia and congenital heart disease
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d)
белйбкЙЗ=зсуЦЙе=ЕзеЕЙенк~нбзе
e)
озд~нбдЙ=~е~ЙлнЬЙнбЕ=~ЦЙен=ЕзеЕЙенк~нбзе
Circulation:
•
a)
b`d
;
b)
_дззЗ= йкЙллмкЙ
needed);
c) Filling pressure (right internal jugular line +/- left atrial line post-
bypass). Pulmonary artery catheters are rarely used due to the
added risks;
d) TOE, if indicated.
Neurological function:
•
a) near-infrared spectroscopy (NIRS) — which assesses cerebral
oxygenation;
b) bispectral index (BIS) — which provides information on the
depth of anaesthesia;
c)
еЙкоЙ= лнбгмд~нзкл
when muscle relaxants are administered.
(arterial line if beat-to-beat measurement is
— which monitor neuromuscular function
;
.
265
Renal perfusion:
•
a) urinary catheter;
b) NIRS — which can be applied to the flank overlying the kidney.
Metabolism:
•
a)
qЙгйЙк~нмкЙ
b) Blood gases (arterial and central venous).
Monitoring lines may also be used to provide treatment options, such
•
as:
a) central lines — which may be used to administer drugs;
b) urinary catheters — which may be used to administer cold
fluids if extra cooling is required.
(central and peripheral);
24 What are the principles behind cerebral oximetry
monitoring in congenital cardiac surgery?
Unlike haemoglobin, bone and tissue are largely transparent to near-
•
infrared (IR) light.
266
Key Questions in CONGENITAL CARDIAC SURGERY
Oxyhaemoglobin and deoxyhaemoglobin absorb different
•
wavelengths of IR light maximally (Figure 11). The relative absorption
of IR light at 730nm and 810nm by oxygenated and deoxygenated
haemoglobin is estimated from the proportion of reflected light.
Figure 11. Oxygenated and deoxygenated haemoglobin absorbs IR
light to different extents at different wavelengths. The relative proportions
of each can therefore be measured.
Unlike conventional pulse oximtery, cerebral oximetry does not
•
require pulsatile flow. It can therefore be used during
cardiopulmonary bypass
Regional oxygen saturation is measured by placing a light-emitting
•
source and a photo-detector over adjacent portions of skin. With the
oximeter on the forehead, cerebral cortex oxygenation can be
estimated (Figure 12).
Cerebral oxygenation can be used as a marker of cerebral perfusion.
•
Manipulation of systemic blood flow, cerebral vascular tone and
haematocrit aids optimisation.
7 Anaesthesia and congenital heart disease
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Figure 12. The display of the INVOS™ machine
(Medtronic, Watford, UK), which is used to measure
tissue oxygenation. There are four possible channels,
potentially allowing monitoring of both cerebral
hemispheres and intra-abdominal viscera bilaterally.
267
25 What are the risks with central venous access in a
patient with congenital heart disease (Figure 13)?
Although rare, complications may be fatal and must be considered
•
prior to line placement. The frequency of complications is inversely
proportional to the patient’s weight.
Immediate risks include:
•
a) trauma to vessels (aberrant anatomy increases risk);
b) arterial cannulation;
c) arrhythmias — particularly if lines or wires enter the atrium;
d) air embolus — which may become paradoxical in the presence
of shunts, especially in spontaneously ventilated patients;
e) embolisation of catheter or guidewire parts, if multiple lines are
inserted.
Early risks include:
•
a) blood loss — which may be concealed under the drapes;
b) pneumothorax, haemothorax or hydrothorax — especially when
internal jugular or subclavian vessels are cannulated.
Key Questions in CONGENITAL CARDIAC SURGERY
268
Figure 13. A 5.5Fr, 8cm triple-lumen catheter (Arrow
USA). The blue-coloured tip is made from very pliable material that
minimises vessel trauma. Insertion is performed over a ‘J’ tip guidewire
using the Seldinger technique.
Medium-term risks include:
•
a) infection;
b) venous thrombosis — especially with subclavian lines.
Long-term risks include:
•
a) vessel occlusion — which may result in problems for future
catheterisation or surgery;
b) vessel stenosis — which is particularly important in passive
circulations where venous return (and therefore cardiac
output) may be impaired.
Risks can be reduced by simple manoeuvres, including:
•
a) ultrasound — which reduces the risk of mechanical
complications;
b) Trendelenburg position — which minimises the chance of air
embolus;
®
, Teleflex, NC,
7 Anaesthesia and congenital heart disease
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c) sterile precautions during line insertion and subsequent use, as
per ‘Matching Michigan’;
d) leaving lines
áå=ëáíì
for the shortest possible time.
26 What are the indications and risks associated with
transoesophageal echocardiography?
TOE allows dynamic imaging of the heart and great vessels. Probes
•
are available for children heavier than 3.5kg (Figure 14).
269
Figure 14. A 7mm paediatric TOE probe. The close-up shows the
articulated scanning tip, which allows movement through a wide range
of angles.
The indications are wide ranging and include:
•
a) assessment of anatomy when transthoracic echocardiography
(TTE) is non-diagnostic, or impossible due to patient
compliance, surgical access or poor windows;
b) diagnosing pathology, including endocarditis or thrombus,
prior to cardioversion;
c) immediate evaluation of surgical results in theatre;
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