Page 149 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

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

infection or self-mutilation) or the thoracostomy tube damage to the lungs and heart during the sternal osteotomy
(leakage from either the stoma or the seals between the by limiting penetration of the saw blade. Once a segment of
VetBooks.ir mediastinum is most commonly seen as a result of baro- can be inserted into the thorax to protect the intrathoracic
thoracostomy tube and three-way stopcock). Pneumo-
the sternotomy has been completed, a malle able retractor
structures during completion of the remainder of the
trauma causing marginal alveolar rupture. Re-expansion
pulmonary oedema can occur following forcible or exces-
preserved if possible, but occasionally a complete median
sive re-expansion of chronically collapsed lung lobes. The sternotomy. The manubrium and/or xiphoid should be
pathogenesis is complex and multifactorial, with proposed sternotomy is required, such as when excising a large
mechanisms including mechanical disruption of vessels cranial mediastinal mass. Some surgeons have expressed
during re-expansion of collapsed lung lobes, surfactant concerns that complete median sternotomy results in
abnormalities, changes in pulmonary artery pressures as a sternal instability and an increased risk of postoperative
result of lung re-expansion, release of free radicals and a complications, but these are not supported by the findings
direct effect of hypoxia on vascular permeability. To mini- of other investigators provided that the median sternotomy
mize the risk of re-expansion pulmonary oedema, chroni- is closed appropriately (Burton and White, 1996). The edges
cally atelectatic lungs should be reinflated with gradual of the sternotomy incision should be protected with mois-
re-expansion and airway pressure should not exceed tened laparotomy sponges, and Finochietto rib retractors
15 cmH 2O, or the lungs should be allowed to re-expand are recommended to maintain retraction and maximize
with normal respiration during recovery (Worth and exposure of the thoracic cavity (Figure 11.5d).
Machon, 2006). Following completion of the surgical procedure, a thora-
costomy tube should be inserted into one or both hemi-
thoraces. The thoracostomy tube should be kept open to
Median sternotomy the atmosphere during closure to prevent tension pneumo-
A median sternotomy is the only approach that provides thorax. Once an airtight closure is achieved, air and fluid are
exposure to the entire thoracic cavity and is recom- evacuated from the pleural space, subatmospheric intra-
mended for diseases involving both hemithoraces (e.g. thoracic pressure is re-established and the thoracostomy
cranial mediastinal tumours, pyothorax and penetrating tube is then closed. Stable closure of the median stern-
thoracic injuries) and for exploratory thoracotomies (e.g. otomy is imperative to avoid postoperative pain, pneumo-
spontaneous pneumothorax). Access to structures in the thorax and sternal non-union. A figure-of-eight technique
dorsal thoracic cavity, such as the great vessels and over the sternal synchondrosis is preferred, using heavy-
bronchial hilus, can be difficult, particularly in deep- gauge suture material (Figure 11.5e), sternal wire or ortho-
chested dogs. If required, a median sternotomy can be paedic wire (Figure 11.5fg) passed around each sternebra
combined with a ventral midline cervical incision, coeli- so that each costosternal junction is incorporated in the
otomy or lateral thoracotomy. closure. Sternal wire can be more convenient to place as it
has greater malleability than orthopaedic wire and is manu-
Surgical technique factured with swaged-on needles. A figure-of-eight pattern
can be performed with orthopaedic wire using either one
Animals are positioned in dorsal recumbency. The skin and twist (i.e. one wire in a figure-of-eight pattern around the
subcutaneous tissues are incised along the ventral midline sternal synchondrosis) or two twists (i.e. one wire each
over the sternum (Figure 11.5a). The pectoral muscles are side of the sternal synchondrosis and the wires twisted
sharply incised along the sternal midline (Figure 11.5b). together). One- and two-twist figure-of-eight orthopaedic
Some surgeons bluntly elevate the pectoral muscles from wire closure of the median sternotomy is significantly less
the sternebrae, whilst others prefer to incise but not elevate likely to fail than one or two cerclage wires around the body
the muscles. A sternotomy is then performed along the mid- of each sternebra (Davis et al., 2006). Figure-of-eight
line with an oscillating saw (Figure 11.5c), although patterns will re-inforce abaxial sternal segments and also
an osteotome and mallet, Lebsche sternum knife or No. 10 prevent direct perpendicular shearing forces being exerted
scalpel blade can also be used, depending on the size of by the orthopaedic wire (Burton and White, 1996; Davis
the animal. Care should be taken to avoid iatrogenic et al., 2006).

(a) (b)
The steps involved in performing a median sternotomy. (a) A skin incision is made along the ventral midline over the length of the sternum.
11.5
The incision is continued through the subcutaneous tissues to expose the pectoral muscles (PM). (b) The pectoral muscles (PM) are sharply
incised along the ventral midline. (continues)

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