The Norwood Operation
Introduction
The Norwood operation, which converts the morphologic right ventricle into the systemic
ventricle, was developed for palliation for hypoplastic left heart syndrome (HLHS). More
recently, the Norwood operation has gain popularity as a meas of palliating many lesions
in which the morphologic left ventricle may be inadequate to maintain systemic
circulation, as may occur in many forms or atrioventricular
and ventriculoarterial malconnections.
Preparation for circulatory arrest
Aprotinin, Solu-Medrol, Regitine, Phenobarbital and antibiotics are given
preoperatively, PGE1 is discontinued and the room temperature is lowered as much as
possible to start surface cooling. A sternotomy is performed, the thymus excised in total,
the heart suspended in a pericardial cradle, and the patient is systemically heparinized.
The right pulmonary artery is dissected free and snared down with a silk suture in
order to better control pulmonary run-off. An aortic purse string is placed on the very
proximal pulmonary artery, just above the sinuses of Valsalva. A single venous purse
string is placed around the right atrial appendage, one that is large enough to later
enable atrial septectomy directly through the purse string.
The patient is cannulated, placed on cardiopulmonary bypass, and cooled to 18 - 20°C.
The left pulmonary artery is mobilized and snared down with a silk suture. The head is
packed in ice, and once half-flows are achieved, the ventilator is turned off.
The dissection
The aorta, pulmonary artery, ductus arteriosus, the descending thoracic aorta, and head
vessels are widely mobilized. Dissection begins by mobilizing the aorta away from the
pulmonary artery. The first-assistant picks up the large pulmonary artery to retract
against the diminutive aorta which is dissected away from the pulmonary artery using
electrocautery. The aorta is dissected completely from its root to the head vessels. The
head vessels will need to be completely mobilized. The innominate artery is dissected
above the innominate vein, and both the right subclavian and right carotid arteries are
mobilized and encircled with snares.
The pulmonary artery and large arterial duct are dissected free. The assistant pulls
back on the pulmonary artery to expose the arterial duct, which is dissected on both its
left and right sides well beyond the insertion of the ductus into the aorta. More
dissection than appears necessary is done. Care is taken not to injure the recurrent
laryngeal nerve. It is usually during this part of the dissection that the left carotid
and subclavian arteries are completely mobilized. Snares and tourniquets are placed around
each of the four head vessels, and a snare alone is placed around the arterial duct.
The homograft is prepared for later insertion prior to instituting circulatory arrest.
It is cut from a pulmonary homograft, one that is chosen to be large and to have at least
one long branch. The inlet portion and the valve of the homograft are discarded. The
widest portion of the homograft is at the inlet end, which tapers with a nice curve
towards the longest and best of the two branch pulmonary arteries. It is best not to make
the homograft too wide. The Prolene stitch that is used to sew the homograft in place can
be placed at this time, or saved for later.
Protection of the heart and brain
A period of 20 minutes of core cooling to 18 - 20°C with the head packed in ice is
considered minimum cerebral protection. The pump is turned off, the patient drained into
the reservoir through the venous line, the head vessels are snared down, and the arterial
cannula is removed. A spoon-shaped clamp is placed on the descending aorta past the
arterial duct, and 20 cc/kg of cold-blood potassium cardioplegia is administered via a
catheter placed through the aortic purse string. Following administration of cardioplegia,
the field is cleared as much as possible for the palliation: the spoon-shaped clamp is
removed and the branch pulmonary artery snares are released. Generally, the stitch is left
around both branch pulmonary arteries as these will aid later exposure when working on
pulmonary blood flow. The arterial duct is tied off, and the venous cannula is removed.
The Palliation
The septum primum is resected. This is generally first attempted through the venous
purse-string. If the atrial septum is deviated far posteriorly so that its exposure is
difficult, then a small atriotomy can be made along the right atrioventricular groove, and
the septum resected through the atriotomy. The coronary sinus may be cut back into the
left atrium at this time.
Attention is directed towards reconstruction of the ventricular outflow tract. The
pulmonary trunk is divided at it’s bifurcation, the ductus arteriosus is doubly ligated
and divided, and all residual ductal tissue is removed from the aortic side. The
spoon-shaped clamp is replaced on the distal descending aorta, and the distal aorta is
incised 1 cm past the ductus insertion site. The underside of the transverse and ascending
arch are incised to the point where the aorta exactly meets the facing commissure of the
divided pulmonary artery. The reverse-bite Potts scissors are best for opening the
undersurface of the aorta. The incision starts distally at the ductus insertion site, and
proceeds proximally, The first-assistant gently retracts the divided lip of the aorta to
aid in exposure. It is of extreme importance not to spiral this incision. Once the
descending aorta is opened, it is best to pick up the exact point of where the pulmonary
artery meets the ascending aorta, and using the reverse-bite Potts, to make a straight
incision connecting the two points. In extremely small aortas, the root of the main
pulmonary artery can be opened for about 1 - 2 mm proximally, and the aortic incision
extended a bit farther. This will make for a larger coronary anastomosis.
The spoon-shaped clamp is now removed, and the coronary anastomosis is performed by
anastomosing the proximal aorta to the pulmonary artery. This is best done with
interrupted suture of 7-0 Prolene, with 3 - 4 sutures placed on either side of the point
where the aorta meets the commissure of the pulmonary artery. The spoon-shaped clamp is
replaced on the descending aorta, and stay stitches are placed on the upper lip of the
aortic incision to facilitate exposure. One is placed at the takeoff of the innominate
artery, and the other at the takeoff of the left subclavian artery. The homograft is sewn
into place, starting distally, and working proximally. The posterior row is placed first,
and the closure is done up to the innominate stay-stitch. Next, the anterior row is
placed, up to the left subclavian stay-stitch. At this point, any residual ductal shelf is
divided. The anterior row is then completed up to the innominate stay-stitch. The
spoon-shaped clamp can now be removed, as distal aortic exposure is no longer required.
The length of the homograft is assessed by gauging how long the homograft should be to
meet the divided proximal end of the main pulmonary artery. With the assistant holding the
homograft and the pulmonary artery together, the extra homograft tissue is removed from
the posterior row. Generally, all that is extra from the posterior row is removed, while
no extra tissue is generally removed from the anterior row. The posterior row is now
completed, going ‘around the horn’ of the neoaorta, and up to the coronary
anastomosis. The anterior row is completed, and the stitch tied and cut.
Cardiopulmonary bypass is reinstituted by filling the atrium and aortic root with cold
normal saline, and replacing the aortic and venous cannulas. Cardiopulmonary bypass is
started, and any air in the systemic circulation is allowed to flow down the aorta. The
head vessel snares are released and removed.
Restoration of pulmonary blood flow
The distal divided end of the pulmonary artery is patched with GoreTex or homograft.
The size of the shunt chosen is based on the weight of the patient, and the estimated
amount of pulmonary blood flow. For patients with normal or near-normal appearing chest
films and preoperative saturation greater than 80 percent, the size of the shunt in mm is
approximately the weight in kilograms, (e.g. for a 3.5 kg baby a 3.5 mm shunt is used).
The more congested the chest film is, the lower the saturation, and the greater the weight
of the baby, the larger the shunt. For premature babies less than 3.0 kg, a 3.0 mm shunt
is generally chosen.
The systemic arterial side of the shunt is performed first. The anastomosis is
performed on the posterior aspect of the innominate-subclavian artery junction in an
end-to-side fashion using polypropylene suture. The pulmonary side of the shunt is
performed next. The site of the anastomosis is chosen to lie close to the ductus insertion
site, which allows for equalization of flow into both left and right pulmonary arteries.
Following completion of the shunt, a clamp is applied to the shunt until weaning from
cardiopulmonary bypass is started. |