Page 207 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

Complications flow through a previously occluded ductus) is considered a
technical complication that can be avoided. As previously
Haemorrhage most commonly occurs during dissection of mentioned, to reduce the risk of recanalization or limit its
VetBooks.ir experienced haemorrhage as the ligatures were being tied effect, the author commonly places a third ligature of poly-
the craniomedial ductus, although the author has also
propylene between the two traditional silk ligatures so that
after apparently uneventful dissection. Care must be taken
if the silk ligatures fail over time, the ductus will remain con-
not to continue the dissection too ‘deep’ in relation to the
ductus because the right pulmonary arterial branch is strained by the polypropylene and will, therefore, be unable
to ‘reopen’. Alternatively, poly propylene could be used as
vulnerable in this position. Similarly, a ‘shallow’ dissection
the primary ligation suture. The use of polypropylene
can lead the instrument directly into the medial ductus means that even if some flow returns as a result of silk liga-
wall. Occasionally, when haemorrhage is minimal, a ture failure, or following atrophy of additional connective
change in the direction of dissection (i.e. changing from
tissue inadvertently included in the original ligatures, the
cranial–caudal to caudal–cranial) will allow completion of flow through the duct should be permanently limited to a
the dissection. If haemorrhage is more brisk, the duct can
haemodynamically insignif cant volume.
i
be clamped. As previously mentioned, the author prefers
straight (ductus) clamps placed in a caudal to cranial
direction following elevation of the descending aorta using
the noose that was placed previously. In over 25 years per- Vascular ring anomalies
forming PDA surgery, the author has had to use TCOO only
once but has clamped and oversewn the ductus in more Vascular ring anomalies are secondary to abnormalities of
than six animals, including one cat. embryogenesis of the great vessels that result in encircle-
With ductus clamps in place and haemorrhage under ment of the oesophagus and the trachea by abnormally
control (see Figure 15.2), it is important to create enough positioned vascular structures. These conditions are rare.
room to transect the ductus and oversew the cut ends Different configurations have been described, including:
(hopefully incorporating the iatrogenic tear). This can be persistent right aortic arch (PRAA); double aorta; aberrant
achieved either by carefully repositioning the clamps or by left subclavian; aberrant right subclavian; and persistent
placing additional clamps alongside the initial haemostatic right ductus/ligamentum with a left aortic arch. PRAA
clamps, further away from the intended division site, to accounts for approximately 95% of all ‘vascular ring’ ana-
create enough room once the primary clamps are removed. tomical variants and often occurs along with an aberrant
The ductus ends can be closed using fine polypropylene left subclavian artery. The encircled oesophagus has a
suture material (1.5 metric (4/0 USP) to 0.7 metric (6/0 USP), focally narrowed lumen secondary to external vascular
depending on the size of the animal) either in two overlap- compression, which limits the size of particles of ingesta
ping rows of simple continuous sutures or one continuous that can pass. Food accumulates in the oesophagus
horizontal mattress suture oversewn by a simple continu- cranial to the constriction, creating dilatation and reducing
ous suture. Secure knots must be tied at each end and effective peristalsis.
these knots should be augmented by expanded polytetro-
fluroethylene (ePTFE) pledgets in large dogs. Additional
suture material should be ready prior to the removal of the Clinical features
vascular clamps. If haemorrhage is seen once the clamp is Affected animals are often presented because of regurgita-
removed, the leak can be sutured either immediately or tion of food and an associated failure to thrive. The clinical
following replacement of the clamp. It is common to see a signs are often most obvious once an affected animal is
small amount of leakage adjacent to the suture, through weaned from a liquid diet on to more solid foods. Frequent
suture needle holes, but application of a topical haemo- bouts of regurgitation will increase the risk of aspiration
®
static agent (e.g. cellulose: Surgicel , Ethicon) usually facili- pneumonia in affected animals, which, despite their condi-
tates the formation of blood clots that stop this bleeding. tion, usually remain bright with a ravenous appetite. Plain
Once the duct is ligated, the stay sutures are removed thoracic radiographs will often reveal a dilatated oesoph-
and the pericardial incision repaired. The chest is closed in agus containing particulate ingesta, cranial to the base of
a routine way, over a thoracostomy tube. the heart. Good-quality dorsoventral thoracic radiographs
may reveal an abrupt deviation in the caudal trachea as it is
Postoperative care pushed to the left side of the thorax by the abnormal right
aortic arch (Figure 15.5). The latter finding is pathogno-
The thoracostomy tube is maintained until the thorax is monic for PRAA. A barium oesophagogram will confirm
completely evacuated, then it is removed. Routine post- the presence of cranial thoracic megaoesophagus, identify
thoracotomy care is recommended. Ideally, cessation of the site of narrowing and provide information about the
flow across the ductus should be demonstrated by cardiac function of the caudal thoracic oesophagus, especially if
ultrasonography prior to discharge from the hospital. fluoroscopy can be used (Figure 15.6). Thoracic radio-
Depending on the severity of left heart enlargement, a graphs will also help determine the presence or absence of
mitral murmur (secondary to mitral annular dilatation) may pulmonary infiltrates, suggestive of aspiration pneumonia.
persist for some time, but reassessment 1–2 months later Angiographic studies using fluoroscopy or computed
should demonstrate some reverse remodelling of the myo- tomographic angiography can be an invaluable aid to
cardium along with reduction in intensity, if not complete understanding the vascular configuration and planning
abolition, of the murmur. surgical therapy, especially for non-PRAA vascular rings.

Outcome of ductus ligation Stabilization
In experienced hands, ligation of PDA is a very safe and If an affected animal has aspiration pneumonia, antibiotic
successful procedure. For animals that survive the surgery, therapy based on culture and sensitivity testing of
residual flow or ‘recanalization’ (defined as return of blood bronchoalveolar lavage samples should be initiated. If the

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