Page 205 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

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

shape of the different forms of PDA, and his analysis of Non-surgical occlusion of PDA with intravascular
the histology of the ductus wall, which suggested that the thrombogenic coils, the Amplatz ductal occluder or the
TM
VetBooks.ir were the cause of failure of the normal closure mechanism, using interventional radiology techniques, has become the
specifically designed Amplatz canine ductal occluder,
TM
eccentric distribution of muscular and elastic fibres therein
most common therapy used in referral practice. As non-
have proved to be definitive studies. These studies also
demonstrated that certain regions of the ductus and the
and delivery system design have meant that surgical liga-
section of the aortic wall through which the ductus surgical occlusion has evolved, refinements in occluder
courses (called the ‘ductus aneurysm’) were very thin in tion of PDA is only considered for either very small or
comparison with the normal aorta. This finding could very large animals, where non-surgical occlusion is not
explain, in part, the fragility of the ductus/aorta occasion- pos sible for technical reasons. As a consequence, even
ally experienced during dissection in some animals. In highly trained surgeons are not practised at the dissection
addition, certain anatomical types of ductus (very short required for successful surgical ligation of a PDA; in addi-
and wide) may be even more challenging to dissect free. tion, surgery is only ever required for the most challenging
These cases, it is suggested, would be better suited to patients. Although operative mortality rates of 0% have
clamping, division and oversewing of the cut ends of the been reported by individuals highly experienced in
ductus (Buchanan, 1967). cardiac surgery (Bureau et al., 2005), for most, lack of
familiarity with the procedure means that the risk of a
Clinical features fatal ‘technical’ complication is considerable. However, if
owners cannot afford referral for specialist treatment
Animals with left to right shunting of blood frequently have (surgery or minimally invasive occlusion) this operation
a palpable ‘thrill’ associated with a ‘machinery’ murmur can be successful in the hands of any practised surgeon
most easily heard at the left fourth intercostal space and familiar with intrathoracic surgery.
radiating cranially. This murmur is often identified during Several surgical techniques that allow the successful
routine pre-vaccination examination. Affected animals will placement of circumferential ductal ligatures have been
typically develop congestive left heart failure within the described in the peer-reviewed literature and surgical
first 12 months of life. Dogs with ‘balanced flow’ across texts. Broadly, these are: predominantly extrapericardial
the PDA and dogs with right to left shunting PDA will have dissection; predominantly intrapericardial dissection; and
minimal to no audible murmur and such animals may be an indirect approach to encircling the ductus by dissection
presented with a combination of exercise intolerance and around the aorta cranial and caudal to the ductus (Jackson
apparent lumbar pain, and will frequently sit down follow- and Henderson, 1979). The author of this chapter has no
ing modest exercise. Affected dogs will often have differ- personal experience with the last technique so it will not
ential cyanosis (i.e. pink mucus membranes cranially with be mentioned further. It is important, however, to select a
contemporaneous blue mucus membranes in the caudal technique and to practise that technique almost exclu-
body), reflecting the admixture of deoxygenated blood sively, since familiarity will bring better results. Both
with the left ventricular output ‘downstream’ to the site Buchanan (1967) and Eyster (1985) advocated performing
where the brachycephalic trunk and left subclavian arter- manoeuvres that would be useful in the event of ductal
ies leave the aorta. haemorrhage. Although rarely needed, these manoeuvres
Diagnosis of heart enlargement and the presence of have formed a routine part of the author’s preparation, in
pulmonary oedema can be made radiographically, so case intraoperative complications develop (see earlier
radio graphs should be obtained of any dog with such comments on TCOO). As previously mentioned (see also
a murmur and pulmonary ‘crackles’. Abnormal heart Chapter 1), prior to commencing any surgical procedure, it
chamber enlargement and the flow through a ductus can is critical that any contingency plans are made (blood
be confirmed using ultrasonography. products, familiarization with anatomy, equipment avail-
ability and team preparation). In the author’s team, the
Patient stabilization custom is to have ‘time out’ prior to initiating surgery to
ensure that everyone in the operating room is aware of
If pulmonary oedema is present, loop diuretics (furosemide) what is being done and is alert to any potential complica-
should be administered for a short period (a couple of days) tions and also prepared to take mitigating actions. Only
prior to anaesthesia for occlusion of the PDA. Animals with once the team is certain these are all ‘in place’ does the
‘balanced flow’ may benefit from pulmonary vasodilators, surgery begin.
such as sildenafil, prior to surgical intervention. Ductus dissection can be performed through the left
fourth intercostal space in most animals. Occasionally, a
PDA occlusion fifth intercostal incision is preferable in cats and some
dogs; the evaluation of the position of the ductus relative
Ductal occlusion is normally recommended for dogs and to the chest wall, based on preoperative radiographs, can
cats with left to right shunting PDA. Animals with ‘balanced assist in this decision. Once the chest is opened, the peri-
flow’ through a PDA and, therefore, concomitant pulmonary cardium is opened immediately ventral to the phrenic
hypertension, may also be considered candidates for PDA nerve, to provide access to the transverse pericardial
occlusion, but PDA occlusion is contraindicated in animals sinus, therefore facilitating the placement of a straight
with established pulmonary hypertension (presumed persis- vascular clamp across the ascending aorta and main
tent fetal pulmonary circulation) with permanent right to left pulmonary artery trunk, to allow temporary TCOO in the
shunting of blood. Although more complications are seen in event of haemorrhage (see Figure 15.2). The author
older dogs with PDA and dogs with more severe left heart prefers either extrapericardial dissection alone or com-
dilatation (causing severe mitral incompetence and/or atrial bined extra- and intrapericardial dissection (in very small
fibrillation), such complications are not usually of a ‘tech- patients), so no further intrapericardial manipulations are
nical’ surgical nature and these animals usually still benefit done at this stage. The phrenic nerve and the vagus nerve
haemodynamically from ductus occlusion (van Israël et al., are dissected free from the pericardium and retracted
2003; Bureau et al., 2005). ventrally using stay sutures or a silicone vessel loop. The

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