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160 Section III: Spinal Procedures

Hemorrhage
Significant hemorrhage can occur during the surgical approach if the
patient is rotated or the midline is not identified correctly and muscle
dissection is done at the level of the transverse processes, thus damag-
ing branches of the vertebral artery. Extensive lateral retraction of the
longus colli muscles can also lead to hemorrhage between the mus-
cles and vertebral bodies from branches of the vertebral artery [2].
Hemorrhage caused by damage to the vertebral venous plexus is
very common; in most cases it can be controlled and does not lead to
major complications. However, death has been reported secondary
to hemorrhage of the vertebral venous plexus [10,13]. In a case series
of 112 dogs that underwent ventral slot, significant hemorrhage was
reported in 26.7% of the cases. Hemorrhage can be worse in dogs
receiving aspirin or with deficiency of von Willebrand factor. Testing
for deficiency of von Willebrand factor by measuring the concentra-
tion of von Willebrand factor or by performing a buccal mucosal
bleeding time should be routinely performed in Doberman Pinschers
and Rottweilers. All hemorrhage should be controlled before clo-
sure, as there is a large potential space for hematoma formation.

Respiratory Complications
Two main types of respiratory complications can occur in patients
Figure 17.5 Transverse view of an inverted cone ventral slot. The decom-
pression window resembles an inverted cone in which the base of the cone undergoing surgery for cervical spinal disorders. Some patients
lies adjacent to the ventral vertebral canal allowing maximal surgical access may experience ventilatory failure associated with neurological
cranially, caudally and laterally. This modification of the traditional ventral dysfunction leading to paralysis or paresis of the respiratory mus-
slot minimizes the risk of hemorrhage and subluxation. Source: Reproduced culature [14]. In contrast, some patients are able to ventilate nor-
with the permission of The Ohio State University. mally, but have abnormal pulmonary gas exchange because of lung
pathology such as pneumonia or atelectasis associated with recum-
bency and prolonged anesthesia [3,13,14].
In dogs, the neurons of the medullary respiratory center enter the
The disadvantages are the limited visualization offered by the
slanted slot and the possibility of extending the slot too far cranially spinal cord via the reticulospinal tracts and give rise to the phrenic
and damaging the vertebral venous plexus. nerve through segments 5–7 of the cervical spinal cord [14]. The
reticulospinal tracts also give rise to the neurons that innervate the
intercostal muscles via the segmental intercostal nerves. Most dogs
Video‐assisted Ventral Slot
Minimally invasive spinal surgery has been used in humans for with ventilatory compromise have lesions located between C2 and
many years. This technique has been used in cervical spinal sur- C4 spinal cord segments, therefore cranial to the origins of the
gery in dogs by Leperlier et al. [11]. The authors used an endo- phrenic nerve [14]. A study evaluated 263 dogs that underwent cer-
scopic device designed for spinal surgery in humans without vical spine surgery and found that 4.9% developed ventilatory fail-
fluoroscopic guidance as described in humans. A skin incision of ure and required positive‐pressure ventilation postoperatively.
2.5–5 cm was performed over the targeted disc space. Careful Most dogs were weaned off the ventilator (mean 4.5 days) and
study of the vertebral landmarks is paramount as the approach is recovered [14]. Pneumonia has also been reported as a complica-
limited. When the technique was applied in clinical patients, a tion of ventral slot leading to death [15].
midline approach was first used to drill the ventral cortex and
cancellous bone without video assistance. Video‐assisted endos- Cardiac Dysrhythmias and Hypotension
copy was then used to drill the inner (dorsal) cortex and for disc The risk of cardiac dysrhythmias is greater with ventral slot surgery
removal. The slot was performed in the correct disc space in all than with thoracolumbar intervertebral disc decompression sur-
dogs and no major complications were observed. Purported gery [16]. This is most likely associated with retraction of the
advantages of this technique are the limited invasiveness and carotid arteries, vagal nerve, and sympathetic trunks and anatomi-
faster recovery. The preliminary experience suggests it is a safe cal disruption of the sympathetic tectotegmental tracts of the spinal
technique if one uses the proper instrumentation and carefully cord [13,16]. Stimulation of the vagus nerve or the carotid bodies
respects the local surgical anatomy. may cause bradycardia, and manipulation of the sympathetic trunks
may cause premature ventricular contractions. A study evaluated
52 dogs that underwent ventral slot and found severe bradycardia
and hypotension leading to death in three dogs (5.7%) [13].
Complications Hypotension may develop secondary to cardiac dysrhythmias,
Several complications have been reported with the ventral slot pro- prolonged anesthesia, and blood loss, factors regularly seen in dogs
cedure. Complications range from minor hemorrhage, probably the undergoing ventral slot surgeries. Systolic blood pressure was eval-
most common complication, to death. The incidence of significant uated in 75 dogs undergoing ventral slot and 16.5% were found to
complications following ventral slot in the largest retrospective develop intraoperative hypotension (<70 mmHg) [12]. It is also
study published to date (112 dogs were studied) was 14.9%, with possible that the incidence of hypotension is even higher than
6.3% of deaths associated with the procedure [12]. described because the few studies specifically evaluating intraoper-