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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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Key Questions in CONGENITAL CARDIAC SURGERY
Table 1 continued. Common monitoring tools used in the paediatric
intensive care unit.
End-tidal CO2(ETCO2)
ETCO2is mandatory monitoring for any ventilated patient
on the ICU. It measures the CO
of expiration (normally 35-45mmHg or 4.6-5.9kPa) and this
approximately correlates to the PaCO
difference due to alveolar dead space). Therefore, ETCO
is helpful in: (1) monitoring the effectiveness of gas
exchange and adequacy of mechanical ventilation; (2)
confirming and monitoring endotracheal tube position; (3)
assessment of cardiac output by monitoring for pulmonary
blood flow; and (4) monitoring of metabolic demand.
concentration at the end
2
(there is a slight
2
2
280
Near-infrared
spectroscopy (NIRS)
Amplitude integrated
electroencephalography
(aEEG)
Bispectral index (BIS)
NIRS monitoring is a method of monitoring regional tissue
oxygenation using infrared probes placed over the tissue of
interest. Typically NIRS is measured on both cerebral
hemispheres to ensure adequate cerebral oxygenation. This
is particularly helpful if on VA ECMO the carotid artery is
cannulated. The NIRS probe can also be placed on the
kidney giving a cerebral-renal NIRS difference and can be
helpful to ensure adequate cardiac output and detect falling
cardiac output.
Cerebral function monitors exist to measure a reduced
number of EEG channels. This data is then processed,
filtered and presented on a semi-logarithmic scale as an
aEEG, with one trace for each cerebral hemisphere. This
allows the bedside team to monitor for changes in
electrocortical activity, for example, with seizures or
encephalopathy.
BIS monitors are used to assess for the depth of sedation
or anaesthesia. The lower the number the more sedated
the patient.
3 Describe the principles of stabilising a neonate with a
duct-dependent systemic circulation
Lesions that require the ductus arteriosus (‘duct’) to supply the
•
systemic circulation include critical aortic stenosis, interrupted aortic
arch, coarctation of the aorta and hypoplastic left heart syndrome.
Whilst many of these can be diagnosed antenatally, some do not
•
present clinically until the duct has closed, at around day 5 to 14 of
life.
8 Paediatric cardiac intensive care
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As the duct closes, the systemic cardiac output, and therefore tissue
•
oxygen delivery, is critically impaired.
These neonates present in various degrees of cardiogenic shock
•
with poor peripheral pulses, a heart murmur, hepatomegaly,
respiratory distress, acidosis, lacticaemia and multiorgan failure.
Monitoring can show a difference between the pre-ductal (right arm)
•
and post-ductal (lower limb) blood pressures and pulse oximetry,
depending on the site of the lesion. During resuscitation, it is the
pre-ductal blood pressure/pulse oximetry that is of interest as this is
measuring the perfusion to the coronary arteries and brain.
The mainstay of management is to restore systemic perfusion by
•
reopening the duct and allowing the end-organ perfusion to improve
prior to undergoing relevant cardiac surgery.
The key intervention to reopen the duct is the use of prostaglandin.
•
The effect of prostaglandin is dose-dependent, with low doses (510ng/kg/min) used to maintain an open duct and higher doses (2050ng/kg/min) needed to reopen a closing duct. In some
circumstances, doses up to 100ng/kg/min are needed for a short
period of time to re-establish systemic flow, which can be confirmed
by return of peripheral pulses and resolution of shock.
The main side effects of prostaglandin are dose-dependent and
•
include apnoea, pyrexia and vasodilatation (which may lead to
hypotension).
Other interventions needed to support the neonate include, but are
•
not limited to:
281
a) intubation with ventilation and appropriate ongoing sedation;
b) full monitoring with adequate venous and arterial access;
c) inotropic support (often in the form of adrenaline or dopamine);
d) correction of electrolyte disturbances;
e) support of end-organ function, such as with renal replacement
therapy;
f) consideration of neurological injury, depending on the clinical
state that the neonate presented;
g) assessing for associated pathologies, such as sepsis and
genetic syndromes.
These interventions facilitate further assessment and organ recovery
•
prior to surgery.
The duct will almost always reopen and provides the intensive care
•
team time to optimise the neonate’s physiology before surgery. If the
282
Key Questions in CONGENITAL CARDIAC SURGERY
duct cannot be reopened, however, then urgent surgery may be
indicated.
4 Describe the principles of stabilising a neonate with a
duct-dependent pulmonary circulation
The most common lesions that require the duct to supply the
•
pulmonary circulation include critical pulmonary stenosis, pulmonary
atresia (with or without a ventricular septal defect) and tetralogy of
Fallot with severe right ventricular outflow tract obstruction.
Whilst many of these can be diagnosed antenatally, some do not
•
present until the duct has closed at around day 5 to 14 of life.
As the duct closes, there is reduced blood flow to the pulmonary
•
artery and lungs, causing inadequate oxygenation of the blood, and
a right-to-left shunt, ultimately causing cyanosis.
These neonates present with varying degrees of cyanosis, usually
•
identified by pulse oximetry. Many are not in physiological distress.
These neonates tend to fail the so called ‘hyperoxia test’. High O
•
concentration ventilation is used to gauge the response in
saturations. There may be a small improvement in oxygen saturation
levels due to the reduction of pulmonary artery pressures, or any
associated V/Q mismatch, but the neonate remains cyanotic.
As the duct closes, or with increasing degrees of obstruction to the
•
right ventricular outflow tract, there will be increasing cyanosis. Often
the systemic cardiac output is maintained but with increasing hypoxia
there is impaired tissue oxygenation delivery and acidosis causing
the child to deteriorate (Figure 1).
The aim of management is to restore pulmonary perfusion by
•
reopening the duct. Although this will not normalise the oxygen
saturation levels, it will ensure adequate pulmonary blood flow and
mixing.
As for systemic duct-dependent circulations, the key intervention is
•
the use of prostaglandin to reopen the duct.
Although many neonates will tolerate the hypoxia, intubation and
•
ventilation is indicated if the patient demonstrates:
2
a) signs of shock;
b) acidosis and lacticaemia;
c) profound cyanosis;
d) apnoea, as a side effect of the prostaglandin.
Other interventions needed to support the neonate include good
•
general intensive care measures and organ support.
8 Paediatric cardiac intensive care
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283
Figure 1. Characteristics and aetiology of systemic and pulmonary
duct-dependent circulations.
The duct will usually reopen, which provides the intensive care team
•
time to optimise the neonate’s physiology before surgery. If the duct
cannot be reopened, however, then urgent surgery may be indicated
with fully corrective surgery or a systemic to pulmonary shunt, such
as a modified Blalock-Taussig (BT) shunt, to temporarily improve
pulmonary blood flow.
Other conditions can cause cyanosis, without being solely
•
dependent on the duct, such as transposition physiology or common
mixing defects.
5 How can persistent pulmonary hypertension of the
newborn be differentiated from cyanotic congenital
heart disease?
Persistent pulmonary hypertension of the newborn (PPHN) is a
•
common problem for neonatologists that reflects the failure of the
foetal circulation to transition to the postnatal circulation.
It results in elevated pulmonary artery pressures, an ongoing right-to-
•
left shunt through the duct and foramen ovale with persistent
284
Key Questions in CONGENITAL CARDIAC SURGERY
hypoxia, causing further worsening of the pulmonary pressure and
right heart failure.
PPHN can be an isolated phenomenon but it is also associated with:
•
a) congenital diaphragmatic hernia;
b) cystic congenital adenomatoid malformation (CCAM) of the
lung;
c) pulmonary hypoplasia;
d) meconium aspiration syndrome;
e) sepsis/congenital infections;
f) birth asphyxia;
g) many other pathologies.
Unlike primary and secondary pulmonary hypertension seen outside
•
the neonatal period, no absolute value of pulmonary artery pressure
defines PPHN.
It can be challenging to distinguish PPHN from cyanotic congenital
•
heart disease in the acute setting when there is no obvious cause for
PPHN (Table 2).
Table 2. Differentiating persistent pulmonary hypertension of the newborn
from cyanotic congenital heart disease.
cÉ~íìêÉ
Response to 100% oxygen
PaO
2
Response to inhaled nitric
oxide (iNO)
Response to reducing
PaCO
2
The fundamental criterion in use is the exclusion of congenital heart
•
disease using echocardiography as the gold standard diagnostic
tool. Unless carried out by an expert sonographer, however, it is
mЙклблнЙен=ймдгзе~ку
ЬуйЙкнЙелбзе=зС=нЬЙ
еЙпДзке=EmmekF
Minor response
Variable: occasionally
normal or high PaO
Usually a good response
Improved oxygenation
2
`у~езнбЕ=ЕзеЦЙебн~д
ЬЙ~кн=ЗблЙ~лЙ
No response
Never has normal
PaO
2
No or minimal
response
No response
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possible to miss important and treatable causes of PPHN, such as
obstructed total anomalous pulmonary venous connection (TAPVC).
Management of PPHN is similar to the management of pulmonary
•
hypertension. Isolated PPHN may be an indication for extracorporeal
life support, as it is a reversible pathology.
6 What are the principles of pre-operative management
of a neonate with single-ventricle physiology?
The majority of patients with functionally single-ventricle anatomy are
•
most often diagnosed antenatally. At that point, counselling and
planning for postnatal management, including a suitable site of
delivery, can take place.
Diagnosis is rarely made postnatally, but in such cases, children are
•
likely to present with cardiogenic shock and/or cyanosis.
The aim of care is to ensure a suitable balance between pulmonary
•
perfusion and systemic perfusion (Qp:Qs = 0.7-1:1), which is usually
monitored by oxygen saturation levels. Levels of approximately 7580% with good clinical signs of systemic perfusion are ideal.
To ensure a balanced Qp:Qs, there must be:
•
285
a) an unrestrictive interatrial communication, secundum atrial
septal defect or patent foramen ovale;
b) a patent duct of adequate size for the body surface area;
c) a balance between pulmonary vascular resistance (PVR) and
systemic vascular resistance (SVR) (Figure 2).
For the majority of neonates, during the period of high PVR,
•
maintaining duct patency with prostaglandin E2and careful
monitoring to ensure a balanced Qp:Qs is sufficient and additional
medical intervention can potentially worsen the imbalance.
Upon the fall of PVR in the following days after birth, excessive
•
pulmonary blood flow with a subsequent fall in systemic blood flow
(elevated Qp:Qs) can occur. This is demonstrated by high oxygen
saturation levels, respiratory distress (due to pulmonary oedema),
poor peripheral perfusion with a lacticaemia and low central venous
saturation. This imbalance is further worsened if the SVR also rises
(Figure 3). If this scenario occurs, intervention is required.
ICU interventions are designed to rebalance the Qp:Qs to 1:1 or
•
slightly lower. It is important to ensure that the atrial septum is nonrestrictive, which may require an urgent balloon atrial septostomy.
286
Key Questions in CONGENITAL CARDIAC SURGERY
Figure 2. Single-ventricle physiology with hypoplastic left heart
syndrome (HLHS) and a balanced Qp:Qs. SVC = superior vena cava; IVC
= inferior vena cava; SVR = systemic vascular resistance; PVR =
pulmonary vascular resistance; size of arrows = volume of flow; SaO
arterial oxygen saturation levels; SvO
= venous oxygen saturation levels;
2
Qs = systemic blood flow; Qp = pulmonary blood flow.
2
=
Figure 3. Single-ventricle physiology with hypoplastic left heart
syndrome (HLHS) and high pulmonary blood flow. SVC = superior vena
cava; IVC = inferior vena cava; SVR = systemic vascular resistance; PVR
= pulmonary vascular resistance; size of arrows = volume of flow; SaO
arterial oxygen saturation levels; SvO
= venous oxygen saturation levels;
2
Qs = systemic blood flow; Qp = pulmonary blood flow.
2
=
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If the Qp:Qs ratio is high, associated with excessive pulmonary blood
•
flow, management includes:
a) increasing the PVR by:
i) ventilating to a higher PaCO2, which acts as a pulmonary
vasoconstrictor;
ii) avoiding oxygen, which is a pulmonary vasodilator;
iii) reducing the prostaglandin infusion, if possible, whilst
ensuring the duct stays open;
b) decreasing the SVR by:
i) administering adequate sedation and analgesia;
ii) ensuring normothermia;
iii) reducing the afterload reduction, such as using
milrinone.
If the Qp:Qs ratio is low with reduced pulmonary blood flow, it would
•
suggest that the duct is closing or has closed, or that the PVR is very
high. This scenario is rare pre-operatively but more commonly seen
after the Norwood operation.
Calculating the exact Qp:Qs in these children can be difficult without
•
full monitoring or a diagnostic cardiac catheter. Qp:Qs can be
calculated at the bedside of the patient on the PICU using:
287
Qp:Qs = Aortic saturations – Mixed venous saturations
Pulmonary venous saturations – Pulmonary artery saturations
Aortic saturations are measured directly from the arterial blood gas.
The mixed venous saturations are assumed to be the same as the
central venous saturations, as measured from an internal jugular
central venous line.
The pulmonary venous saturations are assumed to be 100%, as
there is an assumption that the child has no parenchymal lung
disease. Some choose to select a lower number, such as 95-98%,
as often these children present with pulmonary oedema or V/Q
mismatch.
The pulmonary artery saturations are the same as the aortic
saturations, as it is the pulmonary artery that is supplying the
systemic circulation in a true single-ventricle system
Whatever the clinical status of these children, discussion should take
•
place with families to ensure that they understand the implications of
single-ventricle surgery and the overall prognosis.
Surgery is usually performed following the natural fall in the PVR,
•
usually around 7 to 14 days.
Key Questions in CONGENITAL CARDIAC SURGERY
7 What are the principles of pre-operative management
of an infant or child with heart failure due to a large
left-to-right shunt?
Large left-to-right shunts result in high pulmonary blood flow, left
•
ventricular volume loading and heart failure, and may be caused by a:
a) large ventricular septal defect (VSD);
b) atrioventricular septal defect (AVSD);
c) patent ductus arteriosus (PDA);
d) aortopulmonary (AP) window.
Atrial septal defects (ASD) do not usually lead to heart failure until
•
very late in life and almost never in infancy.
Children with ventricular shunts, PDA and AP window can present
•
with breathlessness, respiratory distress, failure to thrive,
hepatomegaly, cardiomegaly or a murmur. The deterioration is often
precipitated by:
288
a) falling PVR with increasing age;
b) intercurrent infections (typically bronchiolitis in the winter
months);
c) pulmonary hypertensive episodes, caused by pulmonary
pressure or volume overload, especially if there is a delay in
recognition or treatment.
Investigations may show cardiomegaly with signs of pulmonary
•
congestion on chest radiograph or pulmonary oedema on lung
ultrasound.
The management strategy for these patients will vary depending on
•
the severity of the clinical picture, with many of these children
managed medically prior to surgery, including:
a) treating any intercurrent illness;
b) reducing pulmonary oedema with:
i) diuretics;
ii) positive end-expiratory pressure (either non-invasive or
invasive ventilation);
c) reducing pulmonary blood flow (by increasing PVR) by:
i) reducing the minute ventilation to increase PaCO2;
ii) minimising oxygen usage;
d) promoting aortic forward flow and reducing the left-to-right
shunt by afterload reduction using:
i) angiotensin-converting enzyme (ACE) inhibitors;
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ii) inodilators, such as milrinone;
iii) positive pressure ventilation;
e) optimising nutrition and growth.
The timing for intervention can then be planned with options
•
including:
a) palliative surgery, such as pulmonary artery banding;
b) complete surgical or interventional correction.
8 What are the principles of pre-operative management
of an infant or child with cyanosis due to a right-to-left
shunt?
This group of children typically include tetralogy of Fallot and
•
pulmonary atresia with or without a ventricular septal defect.
The right-to-left shunt results in reduced pulmonary blood flow, with
•
systemic oxygen desaturation and a negative hyperoxia test.
The right-to-left shunt varies depending on the relationship between
•
the SVR and PVR and the degree of right ventricular outflow tract
obstruction. Children with tetralogy of Fallot can have hypercyanotic
episodes (‘spells’), where transiently the right-to-left shunt is
increased, often due to dynamic worsening of the RVOTO.
PICU care is required when pulmonary blood flow reaches a critical
•
level, resulting in significant cyanosis, impaired oxygen delivery to
tissues and possible neurological symptoms.
The main aim of PICU care is to improve pulmonary blood flow,
•
which can be achieved by:
289
a) reducing right-to-left shunt by:
i) reducing the PVR using oxygen therapy, sedation,
muscle relaxation, ventilation to a normal/lower PaCO
or with inhaled nitric oxide therapy;
ii) increasing the SVR using phenylephrine, noradrenaline
or vasopressin, or cooling to normothermia;
iii) reducing the RVOT obstruction to improve pulmonary
artery flow by avoiding acidosis, the use of beta-blockers
(such as esmolol), sedation or analgesia, and
administering adequate preload with fluids;
b) interventional cardiology, including:
i) stent insertion, in the RVOT or PDA;
ii) balloon valvuloplasty, such as in critical pulmonary
stenosis;
2
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