Superior Cavopulmonary Anastomoses
Introduction
The superior cavopulmonary anastomosis is usually performed as an intermediate
palliation in patients with a functional single ventricle. The operation is typically
performed at about age 6 months, at which time pulmonary vascular resistance is
sufficiently low to unload the volume-loaded condition associated with shunt-dependent
pulmonary circulation, yet probably too elevated for a total cavopulmonary connection
(Fontan physiology). The superior cavopulmonary anastomosis can also be used as a source
of pulmonary blood flow in conjunction with the Damus-Kaye-Stansel anastomosis in patients
with double inlet left ventricle.
The superior cavopulmonary anastomosis is physiologically well-tolerated. This is
because the functional single ventricle with a superior cavopulmonary anastomosis is not
volume-loaded, and the distribution of cardiac output results in a Qp:Qs of about 0.5:1.
This volume-unloaded ventricle comes at the expense of cyanosis, typically with SaO2 of
about 75%. Because it is physiologically well tolerated, it is often an opportune time to
address any significant hemodynamic lesions that may increase the risk of a total
cavopulmonary anastomosis. Hence, any pulmonary angioplasties or valve repair or
replacements are often done at the time of the superior cavopulmonary anastomosis.
The superior cavopulmonary anastomosis is not appropriate for older children, as
exercise is very poorly tolerated in the upright individual. With exercise, significant
venous desaturation occurs from the muscles of the lower extremities, which is returned to
the inferior vena cava. It is the inferior caval blood which bypasses the pulmonary
circulation and is returned to the ventricle to be re-ejected into the systemic
circulation. Hence, systemic saturation drops significantly with exercise in the upright
individual, so that by about age 2 or 3 years, most children with a superior cavopulmonary
anastomosis should be converted to a total cavopulmonary connection. At this age,
pulmonary vascular resistance should be sufficiently to allow for a total cavopulmonary
connection, in the absence of other hemodynamic risk factors.
The hemi-Fontan operation is done with a period of circulatory arrest in order to
perform the cavo-atrial to pulmonary artery anastomosis, as it would be virtually
impossible to perform this anastomosis with a superior vena caval cannula in place.
Conversely, the bi-directional Glenn anastomosis can be performed with an superior vena
cava cannula in place, as the anastomosis is performed below the cannulation site.
No lines should be placed in the upper great veins as these may lead to thrombosis of
the cavopulmonary anastomosis or pulmonary artery. Standard procedures for re-do
sternotomy are performed. Single aortic and single atrial cannulae are placed and the
patient cooled to 20 C for circulatory arrest. The single
right atrium cannula needs to be placed low (towards the inferior vena cava) on the right
atrium in order not to interfere with the cavo-atrial junction. Any systemic-to-pulmonary
shunts are isolated, ligated, and divided as soon as cardiopulmonary bypass is started.
The pulmonary artery, aorta, superior vena cava, and right atrium are completely
dissected. This is often the most difficult (and dangerous) step of the operation,
especially following a Norwood type of operation in which the neo-aorta is firmly adherent
to the branch pulmonary arteries. The branch pulmonary arteries are entirely freed from
the take-off of the right upper-lobe branch to that of the left upper-lobe branch.
Dissection is usually started from the right of the superior vena cava,
particularly in re-do cases, and carried out well to the left of the aorta. The aorta is
mobilized, and encircle with one or two umbilical tapes, to be used for retraction. In
very difficult cases, it can be helpful to divide the aorta in order to gain further
exposure of the branch pulmonary arteries. If the neo-aorta appears to obstruct or stenose
the branch pulmonary arteries in any way, an aortopexy to reduce the circumference of the
aorta at the site of the pulmonary arteries can be performed. The aorta is then repaired
in standard fashion. The superior vena cava is mobilized. The azygous vein is isolated,
doubly ligated, and divided. A left superior vena cava, if present, should also be
dissected free, as its presence will necessitate a left superior cavopulmonary
anastomosis. The main pulmonary artery is ligated and divided if present. The cardiac end
(proximal stump) is oversewn with interrupted pledgeted sutures, as this area can lead to
especially troublesome bleeding if great care is not taken at this time to control it.
The patient is exsanguinated into the venous reservoir, the venous cannula removed, and
the head packed in ice. The right atrium is opened away from the area of the cavo-atrial
junction where the anticipated cavo-atrial to pulmonary artery anastomosis will be made.
The main pulmonary artery is opened on its anterior surface starting centrally at the main
pulmonary artery and extended the incision leftwards towards the take-off of the left
upper-lobe branch. This same incision is extended rightwards to a point directly
underneath the superior vena cava. The superior vena cavo-atrial junction is opened after
verifying its position through the right atriotomy. The cavo-atrial incision is extended
into the superior vena cava with a gentle posterior spiral to a point directly opposite
the rightward extension of the right pulmonary artery incision. This same incision is then
extended onto the right atrium itself to align with the leftward extension of the left
pulmonary artery incision. An adequate atrial septal defect is ensured at this time by
looking through the incised cavo-atrial junction. If necessary, more septum primum is
excised, with or without cutting back on the coronary sinus towards the left atrium. The
posterior row of the anastomosis between the incised edge of the cavo-atrial junction and
the posterior edge of the divided pulmonary artery is placed using a running suture of 7-0
Maxon. An intra-atrial septation patch of GoreTex or homograft is placed through the
cavo-atrial incision in order to direct superior vena cava flow into the right atrium, and
inferior vena cava flow into the atrioventricular valve. A left superior vena cava, if
present, in anastomosed to end-to-side to the left pulmonary artery with a running suture
of 7-0 Maxon at this time. As the systemic circulation is now excluded from the open
operative field, the venous cannula is replaced and full-flow or reduced-flow
cardiopulmonary bypass resumed. The anterior row of the anastomosis is completed by
augmenting the roof of the anastomosis with a triangular patch of homograft, GoreTex, or
pericardium. The atriotomy is closed with running Prolene suture.
With suction being applied both to the aortic root, and while the coronary arteries are
being temporarily occluded, the aortic cross-clamp is removed. Ventilation is resumed.
Pleural tubes and pacing leads are placed and secured. Following full rewarming, the
patient is weaned from cardiopulmonary bypass. The inferior vena cava cannula is removed.
The heparin is reversed with protamine. Diagnostic pressures of the aortic root and the
superior vena cava are performed. Pulse oximetry is followed. Transesophageal
echocardiography is performed. The pump blood is slowly returned to the patient. The
aortic cannula is removed. Hemostasis and sternal closure is performed.
- Attention is directed to cerebral protection and perfusion:
- The superior vena cava should invariably be cannulated when reduced-flow cardiopulmonary
bypass is used, as would be done for a bi-directional Glenn operation. This is done to
decrease cerebral venous pressure and hence increase cerebral perfusion pressure. This is
of particular importance when coming of cardiopulmonary bypass, at which time there may be
relative systemic hypotension in the presence of elevated central venous pressure.
- The presence of aorto-pulmonary collaterals can pose a significant risk to cerebral
protection, by ‘stealing’ blood away from the brain to the lungs. In such
circumstances, low systemic perfusion pressures may result while on cardiopulmonary bypass
due run-off of blood into pulmonary circulation, further contributing to cerebral
ischemia. hyperventilation in such circumstances promotes all of the above
pathophysiological mechanisms, and should be avoided at all times. Circulatory arrest is
best avoided, if possible, under such circumstances, although the technical portion of the
operation becomes significantly more difficult under such circumstances.
- In cases in which circulatory arrest is used, the head is packed in ice prior to turning
off the pump. The patient is exsanguinated into the venous reservoir.
- The heart is arrested with an infusion of cold blood-potassium cardioplegia. This is
done after as much of the dissection (below) is done with the heart being perfused.
Dissection
- The pulmonary artery, aorta, superior vena cava, and right atrium are completely
dissected. This is often the most difficult (and dangerous) step of the operation,
especially following a Norwood type of operation in which the neo-aorta is firmly adherent
to the branch pulmonary arteries.
- The branch pulmonary arteries are dissected.
- For the hemi-Fontan operation, the branch pulmonary arteries are entirely freed from the
take-off of the right upper-lobe branch to that of the left upper-lobe branch. Dissection
is usually started from the right of the superior vena cava, particularly in re-do
cases, and carried out well to the left of the aorta. For the bi-directional Glenn
operation, a less extensive dissection is performed, and if the dissection for a planned
hemi-Fontan operation is unusually difficult, then a less extensive dissection and
bi-directional Glenn anastomosis should be performed.
- The aorta is mobilized, and encircle with one or two umbilical tapes, to be used for
retraction.
- In very difficult cases, it is occasionally helpful to divide the aorta in order to gain
further exposure of the branch pulmonary arteries. If the neo-aorta appears to obstruct or
stenose the branch pulmonary arteries in any way, an aortopexy to reduce the circumference
of the aorta at the site of the pulmonary arteries can be performed. The aorta is then
repaired in standard fashion.
- The superior vena cava is mobilized. The azygous vein is isolated, doubly ligated, and
divided.
- A left superior vena cava, if present, should also be dissected free, as in its presence
a left superior cavopulmonary anastomosis will need to be performed.
- The main pulmonary artery is ligated and divided if present. The cardiac end (proximal
stump) is oversewn with interrupted pledgeted sutures, as this area can lead to especially
troublesome bleeding if great care is not taken at this time to control it.
- The right atrium is opened towards the inferior vena cava end.
- An adequate atrial septal defect is ensured at this time. If necessary, more septum
primum can be excised, or the coronary sinus can be cut back into the left atrium.
- The superior vena cava is divided above the area of the sinus node over its course with
the right pulmonary artery.
- The right pulmonary artery is incised both on its superior and inferior aspect, for
anastomosis to the cephalic and cardiac ends of the divided superior vena cava,
respectively.
- The cephalic end of the superior vena cava is anastomosed to the superior incision on
the right pulmonary artery, and the cardiac end to the inferior incision, using 7-0 Maxon.
- A large intra-atrial septation patch is placed through the right atrial incision while
the patient is being fully rewarmed. The patch is placed in order to direct superior vena
cava flow into the right atrium, and inferior vena cava flow into the atrioventricular
valve. The patch should be as large as possible, and can be made of GoreTex or homograft.
- A left superior vena cava, if present, is divided and anastomosed in end-to-side fashion
to the left pulmonary artery with, using a running suture of 7-0 Maxon.
- The atriotomy is closed with a running Prolene suture.
Completing the operation
- With suction being applied both to the aortic root and the left ventricular vent, and
while the coronary arteries are being temporarily occluded, the aortic cross-clamp is
removed.
- The superior and inferior caval snares are released.
- The superior venal cava cannula is removed. The site of cannulation is repaired with
interrupted 6-0 Prolene suture if there is any distortion.
- Ventilation is resumed
- The left ventricular vent is removed while a Valsalva is being performed.
- A left atrial line is placed while ventilation is temporarily held.
- Pleural tubes and pacing leads are placed and secured.
- Following full rewarming, the patient is weaned from cardiopulmonary bypass.
- The inferior vena cava cannula is removed
- The heparin is reversed with protamine
- Diagnostic pressures of the aortic root and the superior vena cava are performed. Pulse
oximetry is followed. Transesophageal echocardiography is performed.
- The pump blood is slowly returned to the patient.
- The aortic cannula is removed.
- Hemostasis and sternal closure is performed.
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