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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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300
Key Questions in CONGENITAL CARDIAC SURGERY
JET can occur after any cardiac surgery, and recognised risk factors
•
include:
a) younger infants and neonates;
b) low body weight for age;
c) longer cardiopulmonary bypass or aortic cross-clamp times;
d) use of deep hypothermic circulatory arrest;
e) complex surgery;
f) anatomical location of intracardiac surgery — such as tetralogy
of Fallot or AVSD;
g) patients with genetic syndromes;
h) electrolyte disturbances;
i) acidosis;
j) use of inotropes.
JET causes haemodynamic compromise because:
•
a) tachycardia reduces diastolic filling time;
b) loss of atrioventricular synchrony;
c) increased myocardial oxygen consumption resulting in
worsening ventricular function.
JET can be recognised at the bedside with some characteristic
•
features, including:
a) tachycardia (usually over 170bpm);
b) change in the central venous pressure (CVP) waveform (canon
waves);
c) haemodynamic instability — such as hypotension;
d) features of low cardiac output status.
The only way to diagnose JET formally is with a 12-lead ECG,
•
including an atrial ECG using the epicardial pacing wires. The ECG
features include (Figure 7):
a) non-sinus tachycardia;
b) QRS morphology — which is usually similar to that seen in
sinus rhythm;
c) atrioventricular dissociation — where the ventricular QRS rate
is faster than the atrial P wave;
d) difficulty in identifying P waves, which are often lost within the
QRS complex, unless using an atrial ECG;
8 Paediatric cardiac intensive care
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Figure 7. Typical electrocardiographic rhythm strip of a patient with
junctional ectopic tachycardia.
e) regular QRS complexes with a fixed R-R interval, although the
occasional sinus beat can occur, making the rhythm appear
irregular.
As JET cannot be cardioverted, management is oriented towards
•
heart rate control and restoration of AV synchrony by:
a) providing adequate sedation and muscle relaxation to reduce
metabolic demand and intrinsic catecholamine release;
b) optimising electrolytes, especially magnesium, potassium and
calcium;
c) correcting acidosis;
d) reducing body temperature, initially aiming for normothermia
and then cooling down further as needed, which can be
achieved with antipyretics, environmental measures or cooling
devices. Generally, moderate hypothermia is reached (around
35°C);
e) reducing inotropes, especially dopamine, if possible, to reduce
any catecholamine-induced tachycardia and myocardial
oxygen consumption. A balance needs to be achieved in order
to counteract ventricular dysfunction and low cardiac output
which require inotropic support. The use of vasopressors may
be helpful in patients with systemic inflammatory response and
good ventricular function to allow weaning of inotropes;
f) administering antiarrhythmic drugs, including:
i) alpha agonists (such as clonidine and dexmedetomidine)
— which are used to reduce the intrinsic heart rate. Both
of these medications additionally provide excellent
sedation and display less complications than other
available sedative agents;
301
302
Key Questions in CONGENITAL CARDIAC SURGERY
ii) amiodarone — which can be used to provide rate control
by prolonging the duration of the myocardial action
potential and refractory period. It does, however, have a
demonstrated negative inotropic effect;
iii) beta-blockers (such as esmolol) — which are used to
provide rate control by increasing the atrioventricular
delay. As they have a powerful negative inotropic effect,
they are mainly used prior to consideration of
extracorporeal life support;
g) overdriving with epicardial pacing — which can be considered
when the JET rate is controlled. The use of overdrive pacing
(either AAI or DDD, depending on the situation) is set at
approximately 10-15 beats above the intrinsic JET rate and can
promote the return of AV synchrony;
h) extracorporeal life support (ECLS). ECMO may be indicated if
the JET is refractory to the management strategies described
above and the child remains in a low cardiac output state with
inadequate oxygen delivery to tissues. ECMO supports the
cardiac output until the JET resolves spontaneously.
15 What are the principles for renal replacement therapy
post-cardiotomy?
Acute kidney injury after congenital cardiac surgery is reported to
•
occur in 20-60% of cases, but is more common with:
a) younger age patients;
b) low body weight;
c) complex surgery (higher RACHS-1 category);
d) univentricular or cyanotic defects;
e) longer cardiopulmonary bypass and aortic cross-clamp times;
f) pre-operative pulmonary hypertension;
g) known chronic kidney disease;
h) patients who have required pre-operative ventilation, inotropes
or PICU admission.
The literature reports an incidence of 2-7% of children requiring
•
renal replacement therapy (RRT) following congenital cardiac
surgery, which is associated with an increased mortality.
The indications for RRT include:
•
a) fluid overload;
b) acute kidney injury (if severe);
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c) oliguria or anuria;
d) profound acidosis;
e) hyperkalaemia;
f) acute on chronic renal failure.
The timing of initiation of RRT is often difficult, as it is important not
•
to start it too late, whilst minimising the time on RRT to avoid risks.
RRT can be delivered in two main ways:
•
a) peritoneal dialysis (PD) — which uses the child’s own
peritoneum as a filtration membrane with a glucose-based
dialysis fluid placed in the abdominal cavity. A temporary PD
catheter can be placed in the PICU. The dialysate is instilled
and left to allow dialysis across the peritoneum and then
drained out before the cycle is repeated. It works best in
neonates and smaller infants but becomes less effective with
increasing age. The advantages of peritoneal dialysis include:
i) being a relatively safe procedure (especially with the use
of ultrasound to guide catheter insertion);
ii) not requiring vascular access;
iii) not requiring anticoagulation;
iv) simple to operate equipment;
v) efficiency of fluid removal;
The disadvantages of peritoneal dialysis, however, include the:
i) limited control over clearance;
ii) haemodynamic instability with intermittent fluid shifts;
iii) limited use only in neonates and infants in the acute
setting;
iv) limited clearance of electrolytes and metabolic waste
products;
v) need to avoid if any gastrointestinal pathology is present;
b) continuous renal replacement therapy (CRRT, haemodialysis)
— which uses an extracorporeal circuit to drain venous blood
from the patient, pass it through a specialised membrane
which delivers filtration, dialysis or both, before returning the
blood (with the addition of replacement fluid) back to the
patient in the same venous line. The advantages of
haemodialysis include:
i) predetermined fluid removal;
ii) consistent clearance of electrolytes and metabolic waste
products;
iii) continuous and therefore less haemodynamic instability
once established;
iv) works well in all age groups;
303
304
Key Questions in CONGENITAL CARDIAC SURGERY
The disadvantages of haemodialysis, however, include the:
i) requirement for a large venous dialysis catheter;
ii) requirement for anticoagulation;
iii) potential for instability on initiation;
iv) more complex to prescribe and manage than PD;
v) possibility of ‘recirculating’ blood.
16 Describe the principles of managing an infant with a
postoperative chylothorax
Chylothorax represents the presence of lymphatic fluid in the pleural
•
cavity.
Although postoperative chylothorax in congenital cardiac surgery
•
remains a significant complication, its pathogenesis is complex and
not always clearly recognisable.
Although most post-surgical cases of chylothorax are ascribed to
•
surgical lesions of the lymphatic system within the mediastinum, this
is not always the case, as demonstrated by the good results obtained
with parietal pleural stripping.
It is, however, essential to differentiate between chylothorax and a
•
simple pleural effusion, given the very different clinical burden
associated with these conditions.
A postoperative chylothorax is associated with poor nutrition, longer
•
ICU and hospital length of stay, and a greater risk of thromboembolic
complications. Refractory chylothorax is associated with weight loss
and the need for interventions carry significant morbidity and
mortality.
Pleural chest drain losses are common post-cardiac surgery but if
•
they persist past 48 hours then the possibility of a chylothorax should
be considered.
Early enteral feeding is encouraged to allow early detection.
•
Definitive diagnosis is confirmed by analysis of pleural fluid
microscopy, which may demonstrate:
a) triglycerides >1.1mmol/L when enterally fed;
b) lymphocytes >80%;
c) chylomicrons.
A chylothorax can occur secondary to:
•
a) damage to the central lymphatic system (often the thoracic
duct), such as during aortic arch surgery;
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b) elevated systemic venous pressures, associated with the
Glenn or Fontan procedure, SVC obstruction or thrombosis,
or right ventricular failure;
c) congenital abnormalities in the lymphatic system.
The principles of managing a chylothorax include:
•
a) chest drain insertion to remove the effusion;
b) treating any reversible causes, such as SVC thrombosis;
c) monitoring of biochemical markers, serum proteins and
immunoglobulins;
d) nutritional management. If tolerated, continue with normal
enteral feed (especially breast milk) but if losses increase, then
change feed to medium chain triglyceride feed, which is not
absorbed via the lymphatic system. If drain losses continue to
be high, intravenous parenteral nutrition should be considered.
It is important to ensure that a dietician is involved;
e) IV octreotide, if the losses are persistently high;
f) surgical options — which are used in recurring chylothorax and
include:
i) thoracic duct ligation;
ii) pleurodesis;
iii) pleurectomy.
305
17 What are the principles of intensive care unit
postoperative management for a neonate with
biventricular anatomy following a palliative operation?
Pulmonary artery (PA) banding is a procedure used to limit
•
pulmonary blood flow and is often performed to protect the
pulmonary vascular bed from high flow in patients with a large left-toright shunt, until the child is large enough for a full correction of their
original lesion.
Upon return to the PICU, the management strategy will depend on
•
the degree of obstruction produced by the band.
Loose PA bands, producing mild to moderate obstruction to
•
pulmonary blood flow, are accepted if planned for a long period of
time. This will allow the child to grow and with the subsequent
increase of cardiac output result in a progressively tighter band. The
immediate postoperative management is therefore generally
orientated to minimising the left-to-right shunt and reducing
pulmonary oedema. If unresponsive, surgical recalibration may be
required.
306
Key Questions in CONGENITAL CARDIAC SURGERY
PA bands producing moderate to severe obstruction may result in
•
right ventricular failure, hypoxia and low cardiac output, especially in
the post-bypass setting, associated with myocardial stunning. They
may require PVR reducing interventions to increase pulmonary blood
flow, inotropic support, and if unresponsive, surgical recalibration.
Infants following isolated PA banding can generally be extubated
•
quickly, although it is useful to allow a period of time to assess the
band’s clinical effect.
Aortopulmonary shunts, such as a modified BT shunt, can be used
•
to provide pulmonary blood flow in situations when a full biventricular
repair cannot take place immediately. A key question for the
intensivist to determine is whether the BT shunt provides the only
source of pulmonary blood flow. It is important to assess shunt
dependency, as the consequence of shunt failure would lead to no
pulmonary blood flow and rapid arrest.
Management of the infant post-BT shunt includes:
•
a) appropriate anticoagulation with heparin, which is then
converted to aspirin;
b) balancing of the circulations;
c) rapid extubation, if this was the only procedure performed;
d) support nutrition and promote growth prior to the child’s
definitive surgery.
18 What are the principles of intensive care unit
management for a neonate or infant following surgical
repair of transposition of the great arteries?
An arterial switch is performed in neonates with ventriculo-arterial
•
discordance but the operation may also include a VSD closure,
repair of the atrial septum or PDA closure.
The two key aspects to consider for PICU management are:
•
a) a neonate undergoing cardiopulmonary bypass;
b) reimplantation of the coronary arteries.
The postoperative complications that can be seen following an
•
arterial switch include:
a) standard complications of cardiopulmonary bypass;
b) low cardiac output, which typically occurs 6-12 hours post-
bypass;
c) coronary artery complications;
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d) arrhythmia;
e) pulmonary hypertension.
The management of these infants requires appropriate knowledge of
•
the coronary artery perfusion pressure. During systole, the left
coronary artery is almost occluded, and most perfusion occurs during
diastole. In normal health, the right ventricle is perfused in both systole
and diastole due to the lower force of contraction. If the RV pressure
is elevated, however, such as with pulmonary hypertension, then the
perfusion is only in diastole. Coronary artery perfusion pressure
(CAPP) can be approximately calculated using this formula:
Left or right CAPP =
Aortic diastolic BP – Left or right ventricular end-diastolic pressure
In the absence of mitral lesions, LVEDP can be assumed to be equal
to the left atrial pressure, which is measured with a direct left atrial
áå=ëáíì
line that is inserted in theatre and left
In the absence of tricuspid lesions, the RVEDP can be assumed to
be equal to the CVP, measured by the internal jugular central venous
line.
for PICU care.
307
Left CAPP = Aortic diastolic BP – Left atrial pressure
Right CAPP = Aortic diastolic BP – Central venous pressure
Coronary artery problems are more likely in infants with single
•
coronary systems or coronary arteries with an intramural course.
The general management strategy of neonates following an arterial
•
switch operation include:
a) managing general cardiopulmonary bypass complications;
b) monitoring for cardiac ischaemia by assessing ST segments
on serial ECGs and regional wall motion on echocardiography;
c) managing low cardiac output by:
i) milrinone with adrenaline and/or dopamine;
ii) reducing metabolic demand with ventilation, sedation
and normothermia;
iii) consideration of mechanical support, such as ECMO;
d) maintaining coronary perfusion pressure by:
i) adding a low-dose vasopressor (such as
noradrenaline/vasopressin) to prevent diastolic
hypotension;
308
Key Questions in CONGENITAL CARDIAC SURGERY
ii) avoiding fast or large fluid boluses, as they will increase
the left atrial pressure and central venous pressure,
thereby reducing coronary perfusion;
e) managing arrhythmias;
f) administering diuretics, restricting fluid input and consideration
of renal replacement therapy;
g) consideration of cardiac catheterisation for coronary angiography
if clinical deterioration or ventricular arrhythmias ensue.
19 What are the principles of intensive care unit
management for a neonate with total anomalous
pulmonary venous drainage?
Abnormal connections of all four pulmonary veins usually presents in
•
the neonatal age and may present to the PICU prior to surgery.
The appropriate assessment of the pre-operative clinical status
•
needs to include the presence and severity of possible obstruction to
blood drainage from the lungs. This can present at the level of the
pulmonary veins, veno-atrial connection or interatrial communication,
and will result in pulmonary venous hypertension, pulmonary arterial
hypertension, pulmonary oedema, hypoxia and shock.
In the presence of no or minimal obstruction, there may be increased
•
pulmonary blood flow or signs of congestive cardiac failure.
Obstructed TAPVC is a true paediatric cardiac surgical emergency,
•
which requires immediate surgical correction, as medical
management is only a temporising measure. Non-obstructed TAPVC
can be managed with conventional heart failure treatment until
surgery.
Following TAPVC repair surgery, the common problems seen
•
include:
a) standard complications of cardiopulmonary bypass;
b) pulmonary hypertension crisis;
c) persistent residual pulmonary venous obstruction;
d) pleural effusion or chylothorax;
e) arrhythmias.
Management strategies for TAPVC repair patients may include:
•
a) managing the general complications of cardiopulmonary bypass;
b) careful monitoring and treatment of pulmonary hypertension;
c) managing arrhythmias;
d) administration of diuretics, fluid restriction or renal replacement
therapy;
e) managing low cardiac output state.
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20 What are the principles of intensive care unit
management for a neonate or infant following surgical
repair of an anomalous left coronary artery from the
pulmonary artery?
The anomalous origin of the left main coronary artery produces a
•
state of chronic ischaemia during gestation, as the myocardium is
perfused with poorly oxygenated blood. The left ventricle can appear
dilated and poorly contracting at birth.
Although elevated PVR immediately after birth can prevent or limit
•
coronary flow steal into the pulmonary circulation, when PVR does
drop, the myocardium is not only poorly oxygenated but is also poorly
perfused.
This often leads to acute myocardial ischaemia or infarction, with a
•
dilated poorly functioning left ventricle and mitral regurgitation, either
physiological or due to papillary muscle infarction.
Many of these children may already be on the PICU pre-operatively
•
due to their poor clinical status. This makes them a high-risk group
of patients.
The postoperative issues that can be seen include:
•
309
a) general complications of cardiopulmonary bypass;
b) low cardiac output — which may be related due to the poor LV
function pre-operatively, as well as the effect of
cardiopulmonary bypass;
c) coronary artery spasm or anatomical issues with the
reimplantation;
d) mitral valve regurgitation;
e) arrhythmia — which are often atrial or nodal rhythms. If VF or
VT ensure, it is important to ensure that there are no underlying
coronary perfusion problems.
The general management strategy of neonates following surgical
•
repair of an anomalous coronary artery include:
a) managing the general complications of cardiopulmonary bypass;
b) monitoring for cardiac ischaemia by assessing ST segments
on serial ECGs and regional wall motion on echocardiography;
c) managing low cardiac output by:
i) milrinone with adrenaline and/or dopamine;
ii) reducing metabolic demand with ventilation, sedation
and normothermia;
iii) consideration of mechanical support, such as ECMO;
d) maintaining coronary perfusion pressure;
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