Accepted Manuscript

Description of a regional anesthesia technique for the dorsal cranium in the dog: a
cadaveric study

Yishai Kushnir, Gal S. Marwitz, Yael Shilo-Benjamini, Joshua Milgram

PII: S1467-2987(18)30134-X
DOI: 10.1016/j.vaa.2018.05.006
Reference: VAA 276

To appear in: Veterinary Anaesthesia and Analgesia

Received Date: 25 September 2017

Revised Date: 14 April 2018
Accepted Date: 2 May 2018

Please cite this article as: Kushnir Y, Marwitz GS, Shilo-Benjamini Y, Milgram J, Description of
a regional anesthesia technique for the dorsal cranium in the dog: a cadaveric study, Veterinary
Anaesthesia and Analgesia (2018), doi: 10.1016/j.vaa.2018.05.006.

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 ACCEPTED MANUSCRIPT

RESEARCH PAPER

Running head (Authors): Y Kushnir et al.

Running head (short title): Dorsal cranium nerve block in dogs

Description of a regional anesthesia technique for the dorsal cranium in the dog: a

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cadaveric study

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Yishai Kushnir, Gal S Marwitz, Yael Shilo-Benjamini & Joshua Milgram

Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and

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Environment, The Hebrew University of Jerusalem, Rehovot, Israel

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Correspondence: Yishai Kushnir, Koret School of Veterinary Medicine, The Robert H. Smith
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Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P. O. Box

12, Rehovot 7610001, Israel. E-mail: kushniry@yahoo.com

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Abstract

Objective To identify landmarks and to describe a technique for nerve blockade of the dorsal
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cranium in dogs.

Study design Anatomic cadaveric study.

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Animals A total of 39 dog cadavers, weighing 18.0 kg ± 9.7 kg, mean ± standard deviation.
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Methods The study was performed in three parts. In the initial part, cadavers were dissected to

determine the location of the frontal, zygomaticotemporal and major occipital nerves, and to

identify prominent landmarks for their blockade. In the second part, one technique was

developed to block each of the frontal and zygomaticotemporal nerves and two techniques,
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rostral and caudal, were developed to block the major occipital nerve. Injection solution was

0.05% methylene blue in 0.5% bupivacaine. In the third part, cadavers were used to test the

techniques developed in the second part with 0.04 mL kg−1 of the same injectate administered at

each site (maximal volume 0.5 mL per site). The length of nerve stained was measured, with a

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length ≥ 6 mm considered successful. Confidence intervals (CI) were calculated using Fisher’s

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exact test.

Results Success rates (95% CI) for the frontal, zygomaticotemporal, and rostral and caudal

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locations for the major occipital nerve were 94% (80–99%), 91% (76–98%), 74% (58–86%) and

77% (59–89%), respectively. With a combination of both locations, the success rate for the

major occipital nerve was 100% (90–100%).

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Conclusion and clinical relevance This study describes a simple regional anesthesia technique

using palpable anatomical landmarks that may provide analgesia for dogs undergoing
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craniotomy.
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Keywords dogs, dorsal cranium nerve block, frontal nerve, major occipital nerve, regional

anesthesia, zygomaticotemporal nerve.

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Introduction

Craniotomy is indicated in veterinary medicine for treatment of intracranial neoplasia, subdural

hemorrhage, traumatic brain injury and for introducing a shunt for therapy of hydrocephalus

(Glass et al. 2000; Armitage-Chan et al. 2007). Anesthetic management of patients with brain

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lesions is complicated and requires care in selection of anesthetic drugs. Some opioids which are

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primarily used for analgesia in these cases may cause vomiting and hypoventilation, which may

increase intracranial pressure (ICP), as well as sedation which may interfere in patient evaluation

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(Lefebvre et al. 1981; Armitage-Chan et al. 2007).

Local anesthetic agents prevent conduction of sensation and pain from the periphery to

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the spinal cord and brain as well as motor signals from the spinal cord to the periphery, provided
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that three or more Node’s of Ranvier of a peripheral nerve are blocked (Raymond et al. 1989).

Nerve blocks are a commonly used technique of locoregional anesthesia, which provide
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analgesia and decrease anesthetic and opioid requirements for a variety of surgical procedures
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(Wenger et al. 2005; Snyder & Snyder 2013; Boscan & Wennogle 2016). Other studies have
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shown that general anesthetic requirement using regional techniques are comparable to

systemically administered opioids (Lewis et al. 2014). However, dogs administered fentanyl had
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higher plasma cortisol and glucose levels and worse recovery scores than dogs that were

administered regional anesthesia (Romano et al. 2016). Increased plasma glucose may be
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detrimental to patients with increased ICP, as hyperglycemia is a poor prognostic indicator in

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humans following traumatic brain injury (Jeremitsky et al. 2005).

The use of a scalp block is common in humans. Anesthesia of the greater and lesser

occipital nerves, the supratrochlear and supraorbital nerves, the auriculotemporal nerve and the

zygomaticotemporal nerve, provide sufficient analgesia to reduce sympathetic response to

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surgery and maintain hemodynamic stability (Lee et al. 2006; Guilfoyle et al. 2013). This allows

surgery to be performed without anesthesia in human patients (termed awake craniotomy) for

procedures in which it is necessary to maintain consciousness to facilitate location of lesions and

to avoid damage of important functional centers (Papangelou et al. 2013).

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Although locoregional anesthesia may be a very useful tool in a balanced protocol for

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craniotomy in dogs, to the best of our knowledge it has not been previously described. A

neuroanatomic study showed that the cranium in dogs is innervated mainly by the major occipital

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nerve, the frontal nerve and the zygomaticotemporal nerve (Whalen & Kitchell 1983). The aims

of this study were to define prominent landmarks that could be used for nerve blocks of the

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frontal, zygomaticotemporal and major occipital nerves in normocephalic dogs and to evaluate
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these landmarks in brachycephalic dogs. Our hypothesis was that external landmarks could be

used for application of the frontal, zygomaticotemporal and major occipital nerve blocks, and
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that landmarks could be easily identified and in both normocephalic and brachycephalic breeds
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and nerve blockade success would not be different between the two groups.
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Materials and methods

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This study was performed on 39 dog cadavers weighing 18.0 ± 9.7 kg [mean ± standard

deviation (SD)]. A total of five cadavers were used in part I, 17 in part II, and 21 in part III. Four
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of these cadavers were used both in part II to develop one technique and concurrently in part III
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to evaluate the other techniques, and are therefore counted twice. The numbers used are

elaborated further in the description of each part of the study. All dogs used were euthanized for

reasons unrelated to the study and donated to this study with signed owner consent.
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Part I

The area of interest was based on the surgical approach used to perform a rostrotentorial or

caudotentorial craniotomy, which enable surgical access to many cerebral structures and the

cranial cerebellum (Seim 2007). The rostral border of the area of interest was a line connecting

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the medial canthus of each eye, the caudal border was a line between the caudal aspect of the

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base of the ears, and the lateral borders were lines between the lateral aspect of the base of the

ears and the lateral canthi of the eyes. Five canine cadavers were used to identify the

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macroscopic cutaneous nerves located in the area of interest, and to dissect the paths of the

nerves until a consistent prominent landmark along the path of each nerve was identified. The

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area of interest was first marked on the skin with permanent marker. Then the skin in the median
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plane was incised with a scalpel from the rostral border to the level of the third cervical vertebra.

The macroscopic cutaneous nerve branches innervating the skin in the area of interest were
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identified, isolated and followed to the point at which they exited the deep tissues. Thus the
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origins of the cutaneous nerves were identified.

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The optimal injection site was located where the nerves exited the deep tissues and

defined by proximity to prominent landmarks. One injection site was identified for each of the
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frontal and the zygomaticotemporal nerves, and two injection sites (rostral and caudal) were

defined for the major occipital nerve.

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Part II

An injection technique was developed for each of the defined locations. Various methods and

modifications were employed in an effort to identify the best technique. Six canine cadavers

were used to develop the injection technique for the frontal and zygomaticotemporal nerves. A
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total of 13 and 17 canine cadavers were required to develop the injection techniques for the

rostral and caudal injection sites for the major occipital nerve, respectively.

A solution of 1 mL of 1% methylene blue diluted in 20 mL bupivacaine (Kamacaine:

0.5% Bupivacaine-HCl; Kamada Ltd, Israel) was used (0.04 mL kg−1 at each injection site). A

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total of 0.5 mL was defined as the maximum volume administered per site. Immediately after

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injection, the relevant nerve was approached by a skin incision and a combination of blunt and

sharp dissection of the subcutaneous tissue. The coloration of the nerve was subjectively

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assessed as successful or unsuccessful. Small alterations in the technique were made depending

on outcome of each attempt, using trial and error, in order to increase the success of each

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technique. The results of this part of the study were not included in the statistical analysis.
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Part III
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Techniques developed in the first two parts of the study were tested for accuracy of injection
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intended to block the frontal and zygomaticotemporal nerves (17 dog cadavers). Two techniques
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were developed to block the major occipital nerve; the major occipital rostral injection technique

(MORIT; 21 dogs) and the major occipital caudal injection technique (MOCIT; 17 dogs).
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MOCIT was modified after Part III had commenced for the other nerves. An additional four

cadavers were added to test MORIT and MOCIT only.

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The composition and volumes of the injectate were identical to use in Part II. All the sites
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on one side of the cadaver were first injected and then immediately dissected. The length of

nerve stained was measured with a ruler and recorded, and a colored nerve segment of ≥6 mm

was defined as a successful block (Viscasillas et al. 2013; Langton & Walker 2017). These

procedures were then duplicated on the other side of the head. A total of 34 nerve injections were
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evaluated for frontal and zygomaticotemporal nerves and MOCIT, and 42 injections for MORIT.

A total of 34 nerves were evaluated for MORIT and MOCIT concurrently. In these nerves, if

either technique was successful, this was considered as a successful major occipital nerve block

(MONB). Success of staining for all examined techniques was compared between

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brachycephalic skulls and all other cadavers.

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Statistical analysis

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Only the results from Part III of the study were used in the statistical analysis. Normal

distribution of nerve length was assessed using the Shapiro-Wilk test. Normal data are presented

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as mean ± SD. Fisher's exact test was used to calculate confidence intervals for the probability of
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achieving a successful injection. A two-tailed Fischer’s exact test was used to compare success

rates between brachycephalic and other dogs. Success rate probabilities are presented as percent,
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and 95% confidence interval. Statistical analysis was performed using WinPepi software,
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Version 11.42 (Brixtonhealth.com). Significance was set at p ≤ 0.05.

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Results
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Parts I and II

The location of the frontal nerve for injection was where the nerve traverses/exits the dorsal
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aspect of the orbit (Fig. 1). On the margo orbitalis of the frontal bone a small indentation is
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palpable at its most dorsal point. A 25 gauge, 1.6 cm hypodermic needle (medharmony; DYN

Medical Equipment Ltd, Israel) was inserted at this point perpendicular to the skin and advanced

to its full length, ventral to the dorsal rim of the orbit and directed dorsally within the orbit and
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away from the globe. Half the volume of the injectate was deposited at the maximal depth and

the remainder was injected as the needle was retracted.

The zygomaticotemporal nerve was located by introducing a 25 gauge, 1.5 cm

hypodermic needle through the skin caudal to the orbital ligament and ventral to its attachment

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on the zygomatic process of the frontal bone (Fig. 2). The border between the ligament and bone

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is easily palpable. The needle was then advanced ventrally, rostrally and medially towards the

nasal planum so that the tip was at the caudomedial aspect of the ligament. Half the volume of

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injectate was administered at this location with the remainder injected after the needle was

retracted and advanced dorsally in the same plane.

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The injections for the major occipital nerve were performed with the head and neck in
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ventroflexion (Fig. 3). To perform the MORIT, a 23 gauge, 2.5 cm hypodermic needle (KDL,

Shanghai KDL MED. CO., China) was inserted medial to the caudomedial edge of the scutiform
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cartilage and directed towards the cranial aspect of the spinous process of the axis. Injections
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were performed at three levels, within the subcutaneous tissue, within the cutaneous muscle and
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deep to the cutaneous muscle. A volume of 0.04 mL kg−1 was injected at each depth, therefore a

total volume of 0.12 mL kg−1 was administered for this technique. Half the volume at each site
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was injected with the needle fully inserted with the rest injected during needle extraction (Fig. 3).

To perform the MOCIT an identical needle was inserted lateral (1 cm in a 20 kg dog) to

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the caudal edge of the dorsal spinous process of the axis, in the indentation between the caudal
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oblique muscle of the head and the biventer cervicis muscle (Fig. 3). The biventer cervicis

muscle can be identified as it slips under the fingers when deep palpation is performed from the

midline laterally. The needle was inserted until it penetrated the tissues deep to the cutaneous

muscle (0.5 cm at a 20o angle) and then advanced cranially, parallel to the dorsal spinous process
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of the axis, to the cranial edge of the spinous process of the axis. At this point the major occipital

nerve is superficial to the splenius muscle. Half the volume of injectate was deposited at this

point and the remainder as the needle was extracted.

The total volume used for these four techniques, administered on both sides of the head,

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was 4.8 mL kg−1 (0.04 mL kg−1 for FNB, ZTNB and MOCIT, and 0.12 mL kg−1 for MORIT on

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each side). This equals a total dose of 2.4 mg kg−1 bupivacaine.

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Part III

A total of 32 out of 34 [94% (80–99%)] injections for the frontal nerve were successful (Table

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1). In both failures the stain was observed in a vessel, one in a branch of the rostral deep
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temporal artery running parallel to the nerve, and the other in a small vein adjacent to the nerve.

Overall, the frontal nerves were stained 18.6 ± 6.0 mm and the length of stain exceeded 20 mm
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in 19 of 34 [56% (38–73%)] nerves.

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A total of 31 out of 34 [91% (76–98%)] attempts to locate the zygomaticotemporal nerve

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were successful (Table 1). Overall staining of the nerve was 16.4 ± 7.3 mm and the length of

stain exceeded 20 mm in 13 [38% (22–56%)] nerves. The success rate of the MORIT was 31 of
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42 [74% (58–86%)]. Mean length of stain was 16.1 ± 11.1 mm. In 19 [45% (30–61%)] nerves

length of stain exceeded 20 mm. A total of 26 out of 34 MOCIT attempts were successful, [77%
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(59–89%)]. Mean length of stain was 14.4 ± 9.1 mm. In 11 [32% (17–51%)] nerves length of
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stain exceeded 20 mm. Unsuccessful injections (<6 mm of staining) for the zygomaticotemporal

and major occipital nerves were characterized by spread of solution in the adjacent tissue and no

intravascular injections.
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For the 17 cadavers in which both the MORIT and MOCIT were performed concurrently

on the same nerve (MONB), a successful stain by at least one technique was observed in 34 / 34

[100% (90–100%)] nerves. In 23 of 34 [68% (50–83%)] nerves the length of nerve stained

exceeded 20 mm.

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Five brachycephalic dogs were included in Part III, two Boxers and one French Bulldog,

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Pekingese and an American Staffordshire Bull Terrier crossbred. No anatomic variations in the

routes of the nerves were noted during dissections. Injections for the frontal, zygomaticotemporal

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and major occipital nerves (caudal technique) were performed bilaterally on three brachycephalic

dog cadavers (total of 6 injections for each nerve), and MORIT on four cadavers (total 8 sites). A

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significant difference was found only for the MORIT success rate between brachycephalic (3 of
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8; 38%) and other dogs (27 of 34; 79%) (p = 0.031; Table 2). However MONB was successful in

100% of brachycephalic dogs.

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Discussion
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In this study high success rate of nerve staining was observed for the frontal,

zygomaticotemporal and major occipital nerves (both blocks combined), which suggests that this
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technique may provide analgesia for craniotomy in the dog. The frontal nerve branches off the

ophthalmic nerve [cranial nerve (CN) V1], one of the three branches of the trigeminal nerve (CN
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V). The frontal nerve provides sensory innervation to the skin of the lateral two thirds of the
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upper eyelid, to the dorsal midline of the head (Giuliano & Walsh 2013). Frontal nerve blocks

were described for horses and ruminants (Carpenter & Byron 2015; Valverde & Sinclair 2015),

and are used for procedures involving the eye and horn. However a technique for frontal nerve

block has not been described in dogs (Giuliano & Walsh 2013).
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The dorsal ophthalmic vein and lateral dorsal palpebral artery are in close proximity to

the frontal nerve as it passes over the orbital rim. Deeper within the orbit the route of the frontal

nerve is parallel to that of the rostral deep temporal artery (Evans & Kitchell 1993). In two out of

34 injections of the frontal nerve the dye was injected into a vessel. Intravascular injection is a

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common technical complication in locoregional anesthesia. Its prevalence can be decreased by

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using careful needle insertion technique and aspiration prior to injection, or using ultrasound

guidance (Campoy & Schroeder 2013; El-Boghdadly & Chin 2016). Since aspiration prior to

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injection in a cadaver is impossible, this complication could not have been avoided in this study.

Staining of other nerves in proximity to the frontal and zygomaticotemporal nerves were not

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observed during the study. However we did not specifically look for other nerves during
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dissections in part III.

The zygomaticotemporal nerve is a branch of the zygomatic nerve, which diverges from
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the maxillary nerve (CN V2), a branch of the trigeminal nerve (CN V). The zygomaticotemporal
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nerve provides sensory innervation to the skin dorsal to the zygomatic arch, over the temporalis
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muscle and cranial to the ear. This area overlaps the frontal nerve on the lateral canthus of the

eye (Evans & Kitchell 1993). Zygomatic nerve blocks have been described in the dog, where
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local anesthetic is administered near the orbital fissure (foramen orbitorotundum), and also

blocks the trochlear, lacrimal, abducent and oculomotor nerves, resulting in ocular akinesia and
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pupillary dilation (Giuliano & Walsh 2013). A similar approach in cows may also result in
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maxillary nerve blockade (Valverde & Sinclair 2015). In horses a zygomatic nerve block from

the ventral aspect of the orbit has been described, avoiding blockade of other nerves (Carpenter

& Byron 2015). Zygomaticotemporal nerve block was described in cows and goats using a

similar approach to the one described in this study, caudal to the zygomatic process of the frontal
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bone (Valverde & Sinclair 2015), however it was not reported in the dog. The use of

zygomaticotemporal and frontal nerve blocks may also be indicated for some ophthalmic

surgeries, and therefore their application may extend further than solely for craniotomies

(Giuliano & Walsh 2013).

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The major occipital nerve arises from the dorsal ramus of the second cervical nerve. It

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supplies muscular branches to the semispinalis capitis and splenius muscles. As it proceeds

rostrally, passing through the splenius, cervicoauricularis profundus and cervicoauricularis

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superficialis muscles, it becomes superficial and gives off cutaneous branches to the skin near

the scutiform cartilage. The major occipital nerve innervates the skin from the caudal aspect of

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the skull to the base of the external occipital crest as well as the rostral aspect of the dorsal pinna,
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and the skin from the rostral tip of pinna to the midline. There is some overlap between the major

occipital nerve and the zygomaticotemporal nerve (Evans & Kitchell 1993).
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In the preliminary part of the study it was noticed that the cutaneous branch of the major
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occipital nerve runs cranially in the subcutaneous tissue only branching extensively as it enters
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the skin of the head. In one of the dogs in the preliminary study, however, a large branch

diverged from the main trunk of the nerve, three cm caudal to the scutiform cartilage, and
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continued cranially to innervate the skin of the head. This branch was subsequently seen in all

but one other dog, leading us to conclude that this is common but inconsistent branch of the
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major occipital nerve. This variability in anatomy may be the cause for the lower success rates
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for the MORIT (71%). This unnamed branch of the major occipital nerve runs cranially under

the cutaneous muscle, which it penetrates to reach the subcutaneous tissue where it continues to

run cranially, finally branching and innervating the skin over the caudal aspect of the temporal

muscle. The branch follows a tortuous route and the location at which it penetrates the cutaneous
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muscle varied among individuals complicating our attempts to describe an ideal location to block

it. The variable nature in the location of this nerve is also reflected in the modest success rate of

only 76% with the MOCIT. MORIT requires injecting at three different depths and MOCIT

requires tactile feedback to assess the depth of the needle. Although the muscles are easily

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palpable, addition of ultrasound guidance to image the relevant structures may prove to be

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superior to a blind technique for these nerve blocks. Combining both blocks provided 100%

success and based on this finding it would appear that performing both MOCIT and MORIT

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concurrently would substantially increase the chance of a successful MONB. The clinical

importance of this finding is beyond the scope of this study, however, and caution is advised in

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trying to extrapolate these findings to clinical cases. The MONB has been described in humans
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where it is performed along the superior nuchal line half-way between the occipital protuberance

and the mastoid process (Gazoni et al. 2008). A similar approach was attempted in this study but
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it was abandoned as it failed to stain the major occipital nerve.

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Both MONB injections were performed with the head in a flexed position. Patients
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should be positioned with care while performing these blocks, since an occlusion of the jugular

vein may cause an increase in ICP (Armitage-Chan et al. 2007). In addition, ventroflexion can
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result in a kink of the endotracheal tube, leading to increased arterial partial pressure of carbon

dioxide (which also increases intracranial pressure) or suffocation.

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Local anesthetics bind to sodium channels and prevent sodium influx, thus they prevent
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formation of the action potential and block nerve conduction. Cessation of the action potential

only occurs after a complete block of ionic efflux for approximately 6 mm of nerve, which

correlates to the length of nerve spanning three Nodes of Ranvier in a large mammalian nerve

(Arbuthnott et al. 1980; Raymond et al. 1989). If however only a partial block occurs, owing to
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lower concentration of local anesthetic, up to 20 mm of nerve must be exposed to local

anesthetic to block conduction of the action potential (Raymond et al. 1989). A length of stain

greater than 6 mm is usually considered sufficient for a nerve block to be successful and has

been used in other studies (Viscasillas et al. 2013; Langton & Walker 2017). Some studies state

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whether the nerve was stained or not without specifying the length of staining (Rasmussen et al.

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2006; Echeverry et al. 2010), whereas others use 20 mm as their criteria (Campoy et al. 2010). In

the present study, a nerve stained 6 mm and longer was defined as a success. This should be

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sufficient particularly for the frontal and zygomaticotemporal nerve blocks, as there is very little

soft tissue surrounding these nerves to dilute the concentration of local anesthetic. However, we

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reported the length of stain and the percentage of nerves that were stained ≥ 20 mm, as this may
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have clinical relevance, especially for the major occipital nerve which has a variable route

through soft tissue.

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The success rates reported in this study of 94%, 91% and 100% for successfully staining
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the frontal, zygomaticotemporal and major occipital nerves, respectively, are similar or better
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than those described in previous studies evaluating commonly used nerve blocks. Successful

staining of the maxillary nerve in dogs was reported to be 27% using a percutaneous approach
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and 64% using an infraorbital approach (Viscasillas et al. 2013). Another study reported success

rates of 82% and 89% for the percutaneous and transorbital approaches to the maxillary nerve,
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respectively (Langton & Walker 2017). In a separate study the percutaneous approach was
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clinically effective in dogs (Cremer et al. 2013). An anatomic study using electrolocation and

ultrasound guidance and a stricter criterion of 20 mm staining, reported success in 100% of

femoral and 88% of sciatic nerve blocks (Campoy et al. 2010). Later studies showed that

applying these blocks provides clinically effective analgesia (Campoy et al. 2012; Bartel et al.
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2016). Based on these reports and follow up clinical studies, the success rate of nerve staining

found in the present study suggests that these nerve blocks may be clinically effective. However,

the clinical effectiveness and safety of these blocks are beyond the scope of this study and will

have to be evaluated in clinical patients.

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The dogs used in this study varied in both size and conformation. Brachycephalic dogs

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were included in this study although the anatomy of the head in these breeds may differ. Some

brachycephalic breeds are more susceptible to primary intracranial tumors (Song et al. 2013),

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and may be more likely to be subjected to craniotomy. Therefore, it was important to assess

brachycephalic breeds as well. No anatomical variation was observed in the location of the

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nerves in these breeds. Although success rates for MORIT were lower, the major occipital nerve
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was stained in a similar fashion in all dogs, as were the frontal and zygomaticotemporal nerves.

A similar regional nerve block technique is used in humans to anesthetize the

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zygomaticotemporal, major and lesser occipital, auriculotemporal and the terminal braches of the
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frontal nerve. This technique has been shown to provide analgesia for deeper layers, such as the
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temporalis muscle and its underlying bone, and decreases postsurgical headache (Pinosky et al.

1996; Guilfoyle et al. 2013). In the dog only the innervation of the skin of the dorsal cranium has
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been studied (Whalen & Kitchell 1983). We found no reference to the sensory innervation of the

deeper structures such as the temporalis muscle and bone in dogs.

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An incisional line block could be used as an alternative to the regional technique,

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however in humans an incisional block may fail to provide analgesia to the dorsal cranial bone

for cranial pinning and bone flap removal. For an incisional technique to be effective it must be

performed both superficially along the skin incision and deep along the line of the bone flap

(Hillman et al. 1987; Pinosky et al. 1996). Performing a deep incisional line block may be more
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difficult in dogs since the temporalis muscle is a large muscle in this species (Hermanson &

Evans 1993).

A possible technical failure associated with nerve blocks is intraneural injection, which is

associated with higher injection pressures and possible nerve damage (Hadzic et al. 2004). Use

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of hypodermic needles with a sharp angled tip, as described in this study, may increase the risk

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of intraneural injection (Selander et al. 1977). The prevalence of intraneural injection was not

assessed in this study and may be a possible complication of the technique described. Use of

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short bevel needles, careful insertion technique, use of ultrasound guidance and avoiding high-

pressure injections may decrease this risk (Hadzic et al. 2004; Campoy & Schroeder 2013).

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The limitations of this study are associated with the use of cadavers. It is possible that
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distribution of the injected substance will be different in live dogs. Furthermore, using cadavers

does not allow assessing the effectiveness and the safety of these techniques.
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In conclusion, this study describes a regional technique that may provide analgesia for
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craniotomy, by performing frontal, zygomaticotemporal, and rostral and caudal major occipital
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nerve blocks. Further investigation of the application of this technique in live dogs is warranted.
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Acknowledgements

The authors thank Elinor Malchi-Kushnir for creating the injection illustrations.
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Author contributions

YK: study design, data acquisition and analysis, drafted the manuscript; GSM and JM: study

design, data acquisition and analysis, reviewed the manuscript; YS-B: data interpretation,

reviewed the manuscript. All authors approved the final version.

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Conflict of interest statement

Authors declare no conflict of interest.

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References

Arbuthnott ER, Boyd IA, Kalu KU (1980) Ultrastructural dimensions of myelinated peripheral

nerve fibres in the cat and their relation to conduction velocity. J Physiol 308, 125–157.

Armitage-Chan EA, Wetmore LA, Chan DL (2007) Anesthetic management of the head trauma

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patient. J Vet Emerg Crit Care 17, 5–14.

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Bartel AK, Campoy L, Martin-Flores M et al. (2016) Comparison of bupivacaine and

dexmedetomidine femoral and sciatic nerve blocks with bupivacaine and buprenorphine

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epidural injection for stifle arthroplasty in dogs. Vet Anaesth Analg 43, 435–443.

Boscan P, Wennogle S (2016) Evaluating femoral-sciatic nerve blocks, epidural analgesia, and

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no use of regional analgesia in dogs undergoing tibia-plateau-leveling-osteotomy. J Am
AN
Anim Hosp Assoc 52, 102–108.

Campoy L, Schroeder K (2013) General considerations. In: Small Animal Regional Anesthesia
M

and Analgesia. Campoy L, Read MR (eds). Blackwell Publishing, USA. pp. 3–9.
D

Campoy L, Bezuidenhout AJ, Gleed RD et al. (2010) Ultrasound-guided approach for axillary
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brachial plexus, femoral nerve, and sciatic nerve blocks in dogs. Vet Anaesth Analg 37, 144–

153.
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Campoy L, Martin-Flores M, Ludders JW et al. (2012) Procedural sedation combined with

locoregional anesthesia for orthopedic surgery of the pelvic limb in 10 dogs: case series. Vet
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Anaesth Analg 39, 436–440.

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Carpenter RE, Byron CR (2015) Equine local anesthetic and analgesic techniques. In: Lumb &

Jones’ Veterinary Anesthesia and Analgesia (5th edn). Grimm KA, Lamont LA, Tranquilli

WJ et al. (eds). Wiley & Sons, USA. pp. 886–911.

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Cremer J, Sum SO, Braun C et al. (2013) Assessment of maxillary and infraorbital nerve

blockade for rhinoscopy in sevoflurane anesthetized dogs. Vet Anaesth Analg 40, 432–439.

Echeverry DF, Gil F, Laredo F et al. (2010) Ultrasound-guided block of the sciatic and femoral

nerves in dogs: a descriptive study. Vet J 186, 210–215.

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El-Boghdadly K, Chin KJ (2016) Local anesthetic systemic toxicity: continuing professional

RI
development. Can J Anaesth 63, 330–349.

Evans HE, Kitchell RL (1993) Cranial nerves and cutaneous innervation of the head. In: Miller’s

SC
Anatomy of the Dog (3rd edn). Evans HE (ed). W.B. Saunders, USA. pp. 953–987.

Gazoni FM, Pouratian N, Nemergut EC (2008) Effect of ropivacaine skull block on perioperative

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outcomes in patients with supratentorial brain tumors and comparison with remifentanil: a
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pilot study. J Neurosurg 109, 44–49.
M

Giuliano EA, Walsh K (2013) The eye. In: Small Animal Regional Anesthesia and Analgesia.

Campoy L, Read MR (eds). Blackwell publishing, USA. pp. 103–118.

D

Glass EN, Kapatkin A, Vite C, Steinberg SA (2000) A modified bilateral transfrontal sinus
TE

approach to the canine frontal lobe and olfactory bulb: surgical technique and 5 cases. J Am

Anim Hosp Assoc 36, 43–50.

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Guilfoyle MR, Helmy A, Duane D, Hutchinson PJ (2013) Regional scalp block for

postcraniotomy analgesia: a systematic review and meta-analysis. Anesth Analg 116, 1093–
C

1102.
AC

Hadzic A, Dilberovic F, Shah S et al. (2004) Combination of intraneural injection and high

injection pressure leads to fascicular injury and neurologic deficits in dogs. Reg Anesth Pain

Med. 29, 417–423.

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Hermanson JW, Evans HE (1993) The muscular system. In: Miller’s Anatomy of the Dog (3rd

edn). Evans HE (ed). W.B. Saunders, USA. pp. 258–384.

Hillman DR, Rung GW, Thompson WR, Davis NJ (1987) The effect of bupivacaine scalp

infiltration on the hemodynamic response to craniotomy under general anesthesia.

PT
Anesthesiology 67, 1001–1003.

RI
Jeremitsky E, Omert LA, Dunham CM et al. (2005) The impact of hyperglycemia on patients

with severe brain injury. J Trauma 58, 47–50.

SC
Langton SD, Walker JJA (2017) A transorbital approach to the maxillary nerve block in dogs: a

cadaver study. Vet Anaesth Analg 44, 173–177.

U
Lee EJ, Lee MY, Shyr MH et al. (2006) Adjuvant bupivacaine scalp block facilitates
AN
stabilization of hemodynamics in patients undergoing craniotomy with general anesthesia: a

preliminary report. J Clin Anesth 18, 490–494.

M

Lefebvre RA, Willems JL, Bogaert MG (1981) Gastric relaxation and vomiting by apomorphine,
D

morphine and fentanyl in the conscious dog. Eur J Pharmacol 69, 139–145.
TE

Lewis KA, Bednarski RM, Aarnes TK et al. (2014) Postoperative comparison of four

perioperative analgesia protocols in dogs undergoing stifle joint surgery. J Am Vet Med
EP

Assoc 244, 1041–1046.

Papangelou A, Radzik BR, Smith T et al. (2013) A review of scalp blockade for cranial surgery.
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J Clin Anesth 25, 150–159.

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Pinosky ML, Fishman RL, Reeves ST et al. (1996) The effect of bupivacaine skull block on the

hemodynamic response to craniotomy. Anesth Analg 83, 1256–1261.

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Rasmussen LM, Lipowitz AJ, Graham LF (2006) Development and verification of saphenous,

tibial and common peroneal nerve block techniques for analgesia below the thigh in the

nonchondrodystrophoid dog. Vet Anaesth Analg 33, 36–48.

Raymond SA, Steffensen SC, Gugino LD, Strichartz GR (1989). The role of length of nerve

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exposed to local anesthetics in impulse blocking action. Anesth Analg 68, 563–570.

RI
Romano M, Portela DA, Breghi G, Otero PE (2016) Stress-related biomarkers in dogs

administered regional anaesthesia or fentanyl for analgesia during stifle surgery. Vet Anaesth

SC
Analg 43, 44–54.

Seim HB (2007) Surgery of the brain. In: Small Animal Surgery (3rd edn). Fossum TW (ed).

Mosby-Elsevier, USA. pp. 1379–1401.

U
AN
Selander D, Dhunér KG, Lundborg G (1977) Peripheral nerve injury due to injection needles

used for regional anesthesia. An experimental study of the acute effects of needle point
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trauma. Acta Anaesthesiol Scand. 21, 182–188.

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Snyder CJ, Snyder LB (2013) Effect of mepivacaine in an infraorbital nerve block on minimum
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alveolar concentration of isoflurane in clinically normal anesthetized dogs undergoing a

modified form of dental dolorimetry. J Am Vet Med Assoc 242, 199–204.

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Song RB, Vite CH, Bradley CW, Cross JR (2013) Postmortem evaluation of 435 cases of

intracranial neoplasia in dogs and relationship of neoplasm with breed, age, and body weight.
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J Vet Intern Med 27, 1143–1152.

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Valverde A, Sinclair M (2015) Ruminant and swine local anesthetic and analgesic techniques.

In: Lumb & Jones’ Veterinary Anesthesia and Analgesia (5th edn). Grimm KA, Lamont LA,

Tranquilli WJ et al. (eds). Wiley & Sons, USA. pp. 941–959.

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Viscasillas J, Seymour CJ, Brodbelt DC (2013) A cadaver study comparing two approaches for

performing maxillary nerve block in dogs. Vet Anaesth Analg 40, 212–219.

Wenger S, Moens Y, Jäggin N, Schatzmann U (2005) Evaluation of the analgesic effect of

lidocaine and bupivacaine used to provide a brachial plexus block for forelimb surgery in 10

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dogs. Vet Rec 156, 639–642.

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Whalen LR, Kitchell RL (1983) Electrophysiologic studies of the cutaneous nerves of the head

of the dog. Am J Vet Res 44, 615–627.

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Table 1 Results of four techniques to deposit a solution of 0.05% methylene blue in 0.5%

bupivacaine over the frontal nerves (0.04 mL kg−1 per site), the zygomaticotemporal nerves (0.04

mL kg−1 per site) and the major occipital nerve (rostral and caudal techniques; 0.04 mL kg−1 for

MOCIT and 0.12 mL kg-−1 for MORIT) in canine cadavers. Staining of a nerve >6 mm was

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Nerves
Parameter
Frontal Zygomaticotemporal Major occipital

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(MORIT) (MOCIT)

Staining success 32/34 31/34 31/42 26/34

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Success rate 94% 91% 74% 77%

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(%) (95% CI) (80 to 99%) (76 to 98%) (58 to 86%) (59 to 89%)
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Length of nerve 18.6 ± 6.0 16.4 ± 7.3 16.1 ± 11.1 14.4 ± 9.1
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stained (mm)

MORIT, major occipital rostral injection technique; MOCIT, major occipital caudal injection
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Table 2 Comparison of results in brachycephalic and nonbrachycephalic canine cadavers of the

frequency of successful staining (>6 mm) after injection of a solution of 0.05% methylene blue

in 0.5% bupivacaine over the frontal nerves (0.04 mL kg−1 per site), the zygomaticotemporal

nerves (0.04 mL kg−1 per site) and the major occipital nerve (rostral and caudal techniques; 0.04

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mL kg−1 for MOCIT and 0.12 mL kg−1 for MORIT). Data are presented as the number of nerves

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successfully stained/number of sites injected (%).

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Skull shape Nerves

Frontal Zygomaticotemporal Major occipital

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Brachycephalic 6/6 (100%) 4/6 (67%) 3/8 (38%) 6/6 (100%)
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Not brachycephalic 26/28 (93%) 27/28 (96%) 27/34 (79%) 20/28 (71%)

p-value 1.000 0.074 0.031 0.297

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MORIT, major occipital rostral injection technique; MOCIT, major occipital caudal injection
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Figure 1 (a) Lateral and (b) dorsal view of the frontal nerve block technique. A 25 gauge, 1.6 cm

needle was inserted on the margo orbitalis of the frontal bone where a slight dorsal indentation is

palpable at its most dorsal point and advanced to its full length perpendicular to the skin, ventral

to the dorsal rim of the orbit and directed dorsally away from the globe.

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Figure 2 (a) Lateral and (b) dorsal view of the zygomaticotemporal nerve block technique. A 25

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gauge, 1.6 cm needle was inserted caudal to the orbital ligament, ventral to its attachment on the

zygomatic process of the frontal bone, and advanced ventrally, rostrally and medially towards

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the nasal planum (dotted line) until it reached the caudomedial aspect of the ligament. The
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injectate was divided between this location at A and at B after the needle was retracted and

advanced dorsally in the same plane.

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Figure 3 (a) Lateral and (b) dorsal view of the major occipital nerve block techniques. For the
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major occipital rostral injection technique (MORIT), a 23 gauge, 2.5 cm needle (A) was inserted

subcutaneously medial to the caudomedial edge of the scutiform cartilage and directed towards
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the cranial aspect of the spinous process of the axis. The injectate was administered at this point

(A). After the needle was retracted and advanced deeper in the same plane, injections were
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injection technique (MOCIT), the needle (D) was inserted lateral (1 cm in a 20 kg dog) to the

caudal edge of the dorsal spinous process of the axis until it penetrated the tissues deep to the

cutaneous muscle (D1) and then the needle angle to the skin was decreased so that the needle
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was parallel to the dorsal spinous process of the axis (D2), and the tip advanced to the cranial

edge of the spinous process of the axis.

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