• View in gallery
    Figure 1—

    Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 20 cm in a sedated standing cow. The experimental procedure involved epidural injection of 2% lidocaine hydrochloride (0.25 mg/kg) in the first intercoccygeal or the sacrococcygeal intervertebral space, after which a flexible endoscope was inserted through the dilation shaft of an introducer set into the epidural space. In this instance, expansion of the epidural space with air provided an optimal endoscopic view of the epidural space. In the upper portion of the image, the bluish structure represents the dura mater in the epidural space. Dorsal is toward the top of the image.

  • View in gallery
    Figure 2—

    Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 10 cm in a sedated standing cow. Epidural fat is visible as a glistening white structure, and a spinal nerve (left upper portion of the image) is localized dorsally in the epidural space. Dorsal is toward the top of the image.

  • View in gallery
    Figure 3—

    Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 15 cm in a sedated standing cow. Notice the white-bluish nerves in the epidural space (upper and right side of the image) that are accompanied by reddish vessels. Dorsal is toward the top of the image.

  • View in gallery
    Figure 4—

    Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 10 cm in a sedated standing cow. In this view, a large reddish vessel is visible free within the epidural space (lower right portion of the image). Dorsal is toward the top of the image.

  • View in gallery
    Figure 5—

    Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 29 cm in a sedated standing cow. Notice the bluish appearance of the spinal dura mater in the ventral part of the epidural space. Dorsal is toward the top of the image.

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Use of endoscopy for examination of the sacral epidural space in standing cattle

Sonja FranzClinic for Ruminants, Department for Farm Animals and Herd Management, University of Veterinary Medicine, Veterinaerplatz 1, A-1210 Vienna, Austria.

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Agnes M. DadakInstitute of Pharmacology and Toxicology, Department of Basic Sciences, University of Veterinary Medicine, Veterinaerplatz 1, A-1210 Vienna, Austria.

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Yves MoensClinic for Anesthesiology and Perioperative Intensive Care, Department of Small Animals and Horses, University of Veterinary Medicine, Veterinaerplatz 1, A-1210 Vienna, Austria.

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Walter BaumgartnerClinic for Ruminants, Department for Farm Animals and Herd Management, University of Veterinary Medicine, Veterinaerplatz 1, A-1210 Vienna, Austria.

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Isabelle IffClinic for Anesthesiology and Perioperative Intensive Care, Department of Small Animals and Horses, University of Veterinary Medicine, Veterinaerplatz 1, A-1210 Vienna, Austria.

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Abstract

Objective—To develop an epiduroscopic technique for use in standing cattle and describe the endoscopically visible anatomic structures of the epidural space in the sacrococcygeal area.

Animals—6 healthy nonlactating, nonpregnant cows (mean ± SD age, 60 ± 18.5 months; mean weight, 599.7 ± 63.87 kg) and 3 bovine cadavers.

Procedures—Cadavers were used to allow familiarization with the equipment and refinement of the technique. Following these experiences, procedures were performed in live animals. Each cow was restrained in a stock. After sedation with xylazine (0.03 mg/kg, IV), 2% lidocaine hydrochloride (0.25 mg/kg) was injected epidurally in the first intercoccygeal or the sacrococcygeal intervertebral space. By use of an introducer set (guidewire and dilation trocar and shaft), a flexible endoscope (length, 75 cm; diameter, 2.3 mm) was inserted through the dilation shaft into the epidural space. To obtain an optimal view, small amounts of air were insufflated into the epidural space through the working channel of the endoscope via a syringe with special filter.

Results—Anatomic structures of the epidural space that were viewed by means of the endoscopic procedure included blood vessels, connective tissue, fat, nerves, and the spinal dura mater. No adverse events were detected during epiduroscopy, and it was tolerated well by all 6 cows.

Conclusions and Clinical Relevance—In ruminants, epidural structures can be viewed via endoscopy. Such epiduroscopic procedures may be useful in anatomic studies as well as for the diagnosis of disease or therapeutic interventions in ruminants.

Abstract

Objective—To develop an epiduroscopic technique for use in standing cattle and describe the endoscopically visible anatomic structures of the epidural space in the sacrococcygeal area.

Animals—6 healthy nonlactating, nonpregnant cows (mean ± SD age, 60 ± 18.5 months; mean weight, 599.7 ± 63.87 kg) and 3 bovine cadavers.

Procedures—Cadavers were used to allow familiarization with the equipment and refinement of the technique. Following these experiences, procedures were performed in live animals. Each cow was restrained in a stock. After sedation with xylazine (0.03 mg/kg, IV), 2% lidocaine hydrochloride (0.25 mg/kg) was injected epidurally in the first intercoccygeal or the sacrococcygeal intervertebral space. By use of an introducer set (guidewire and dilation trocar and shaft), a flexible endoscope (length, 75 cm; diameter, 2.3 mm) was inserted through the dilation shaft into the epidural space. To obtain an optimal view, small amounts of air were insufflated into the epidural space through the working channel of the endoscope via a syringe with special filter.

Results—Anatomic structures of the epidural space that were viewed by means of the endoscopic procedure included blood vessels, connective tissue, fat, nerves, and the spinal dura mater. No adverse events were detected during epiduroscopy, and it was tolerated well by all 6 cows.

Conclusions and Clinical Relevance—In ruminants, epidural structures can be viewed via endoscopy. Such epiduroscopic procedures may be useful in anatomic studies as well as for the diagnosis of disease or therapeutic interventions in ruminants.

Endoscopy is a minimally invasive percutaneous examination technique that can be used for colorauthentic visualization of the epidural space located inside the vertebral canal.1 The epidural space is a potential space that surrounds the spinal cord between the dura mater and the endosteum, which covers the inside of the bony structure of the vertebral canal.2

In the human medical literature, visualization of the spinal cord by use of a rigid endoscope was first reported by Burman3 in the 1930s, who examined human cadavers and named the procedure myeloscopy. In 1938, myeloscopy was first performed in living humans4 from which a detailed description of the anatomic structures of the epidural space was obtained. The technical development of fiber optics represented important progress in endoscopic procedures1,5 and was important for clinical application of endoscopy of the epidural space in human patients.6–12 Since 1996, such epiduroscopy has been used for the diagnosis and treatment of disease in humans.5,10

Current indications for epiduroscopy in human medicine are differential diagnosis of chronic low-back pain and removal of foreign bodies and neoplastic lesions.1,5 Pathologic changes, such as adhesions, fibrosis, and lumbar spinal stenosis as well as nerve root compression, can be diagnosed on the basis of epiduroscopic findings.1,13

In veterinary medicine, epiduroscopy has not been used for diagnostic or therapeutic purposes in living animals, to our knowledge. Epiduroscopy has been performed in cadavers of rabbits under experimental conditions6; the procedure has also been performed in dog cadavers with the objective of describing anatomic features and technical details.14 The purpose of the study reported here was to develop a suitable epiduroscopic technique for use in standing cattle and describe the endoscopically visible anatomic structures of the epidural space in the sacrococcygeal area.

Materials and Methods

The study procedure was approved by the Institutional Ethics Committee of the University of Veterinary Medicine of Vienna and had governmental approval (BMBWK-68.205/0,020-BrGT/2007).

Initial procedures—To allow familiarization with the introduction of the introducer assembly and the handling of the endoscope, procedures were conducted in 3 bovine cadavers (animals that had been euthanatized for reasons unrelated to this study). The cadavers were positioned in a sternal or ventrolateral position, and the endoscope was introduced between the first and second coccygeal vertebrae or at the sacrococcygeal junction. For expansion of the epidural space, insufflation of air (35 mL; 1 cadaver) or instillation of physiologic saline (0.9% NaCl) solution (40 mL; 2 cadavers) through the working channel of the epiduroscope was performed.

Experimental procedures—The experimental portion of the study was performed in 6 healthy nonpregnant, nonlactating cows (designated as cows 1 through 6). The breeds of cows included Brown Swiss (n = 4), Simmental (1), and Holstein-Friesian (1). The cows were 33 to 86 months old (mean ± SD age, 60 ± 18.5 months) and weighed 522 to 700 kg (mean weight, 599.7 ± 63.87 kg). Body condition was scored on a scale of 1.00 to 5.00 for each cow according to a reported method15; values ranged from 2.10 to 2.71. The distance from the occipital bone to the first coccygeal vertebra was measured in each cow; mean body length was 191.2 ± 10.87 cm.

Each cow was restrained in a stock and sedated with xylazinea (0.03 mg/kg, IV). The epidural injection site was identified by lifting and lowering the tail and simultaneous palpation of the first intercoccygeal or the sacrococcygeal intervertebral space. The area was aseptically prepared. A small stab incision was made in the skin with a scalpel. Subsequently, an epidural puncture was performed in the caudocranial direction by use of an 18-gaugeb Tuohy needle inserted into the epidural space according to a standard technique. Correct needle placement was confirmed by use of an acoustic device.16,c In brief, the acoustic device was attached to the Tuohy needle via a nondistensible pressure line, which was also connected to a volumetric pumpd that delivered 100 mL of physiologic saline solution/h and to a pressure transducer via a 3-way stopcock. The signal from the pressure transducer was relayed via a pressure amplifier to a microprocessor. The frequency from the microprocessor output was adjusted by use of a transistor associated with a loudspeaker. Pressure changes associated with the differing resistances of tissues encountered at the tip of the Tuohy needle resulted in different acoustic signals. A higher tone was generated by increasing pressure; the decrease in pressure on entering the epidural space generated a lower sound.

For each epiduroscopic procedure, insertion depth and angle of insertion to the horizontal of the Tuohy needle were recorded. The authors used the term flat angle for an insertion angle ≤ 45° (to the horizontal plane) and the term steep for an insertion angle > 60°. If no blood appeared in the needle hub, 2% lidocaine hydrochloridee (0.25 mg/kg) was administered epidurally during a 90-second period. After 3 minutes, correct epidural needle placement and epidural injection of lidocaine were confirmed by observation of loss of tail tone and lack of reaction to needle stab stimuli on the tail and the perianal region.

Epiduroscopy was performed by use of a flexible endoscopef (length, 75 cm; diameter, 2.3 mm). The endoscope had a working channel and a navigation system that allowed the tip of the endoscope to be moved in 2 directions (dorsally, 120°; ventrally, 170°). For recording purposes, the endoscope was connected with a camera,f which transmitted the endoscopic images to a monitor. An image-archiving software systemf was used for digital recording. A xenon light sourcef completed the endoscopic equipment.

To allow insertion of the endoscope into the epidural space, a purpose-builtg introducer and guidewire assembly was used with the Seldinger technique.17,18 The length of a J-wire (approx 30 cm) was introduced through the Tuohy needle, and the latter was then withdrawn. Subsequently, a 15-cm-long dilator was inserted and withdrawn to facilitate the placement of a 9-F, 6-cm introducer canula. The guidewire was withdrawn, and the epiduroscopic examination through the introducer canula was commenced.

To obtain an optimal endoscopic view, air was insufflated into the epidural space via a syringe with a bacterial filter.h The total amount of air and the insertion length of the endoscope were recorded. Endoscopically visible structures, such as fat, connective tissue, nerves, and vessels, were recorded as well as the patency of the epidural space and vessel pulsation.

The maximal insertion length of the endoscope was measured when the spinal dura mater was visible. Any signs of discomfort of the animal during epiduroscopy were recorded. As each cow was guided from the stock back to the stable, ataxia (present or absent) was recorded. Five hours after epiduroscopy, a complete physical examination was performed; for 1 month after the procedure, any development of adverse effects was entered in a hospital-based software program.

Results

Data regarding the epidural injection site and insertion depth and angle of the Tuohy needle for each cow were recorded (Table 1). The mean insertion depth of the Tuohy needle was 44.16 ± 12 mm. In cow 2, the insertion angle between the Tuohy needle and the horizontal plane was severely steep (80°); this caused difficulty in placement as well as deformation of the shaft, and the flexible epiduroscope could not be inserted. The shaft was removed, and the sacrococcygeal junction was chosen for epidural injection. The epiduroscopic procedure was subsequently successful.

Table 1—

Details of a technique of endoscopy of the epidural space in the sacrococcygeal area applied in 6 standing cows. Cows received an IV injection of xylazine (0.03 mg/kg, IV) and an epidural injection of 2% lidocaine hydrochloride (0.25 mg/kg) prior to endoscopy.

CowInsertion site of endoscopeInsertion depth of Tuohy needle (mm)Insertion angle of Tuohy needle (with reference to the horizontal plane [degree])Insufflation of air(mL)Distance that the endpscope had to be inserted before the dura mater was observed (cm)
1SCJ553540Not visible
2SCJ35803025
3FICIS35451020
4SCJ55402029
5FICIS304020Not visible
6SCJ55303020

SCJ = Sacrococcygeal junction. FICIS = First intercoccygeal intervertebral space.

In all cows, puncture of the epidural space was successfully achieved as verified by use of the acoustic device. The distinct decrease in pressure when entering the epidural space resulted in a clear lowering of sound frequency in all the cows of the present study. Before epiduroscopy was attempted, correct epidural needle placement was confirmed by detection of local anesthetic effects of lidocaine in all cows.

After insertion of the Tuohy needle and the shaft, mild bleeding (blood vessel trauma) was evident in 1 of the 6 cows. In that cow, the endoscopic view was impaired and the endoscope had to be pulled back several times to clean the lens at the tip of the endoscope with physiologic saline solution.i

As the endoscope was inserted through the shaft in all cows, the epidural space was viewed as a canal-like structure (Figure 1) . However, during advancement of the epiduroscope, the view was occasionally obstructed by fat. Air was injected through the working channel until a canal-like structure was visible again. The amount of air needed for visualization of a patent canal varied widely among the cows (Table 1). There was no resistance when moving the endoscope cranially or caudally in the epidural space, nor did that movement interfere with the quality of the images.

Figure 1—
Figure 1—

Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 20 cm in a sedated standing cow. The experimental procedure involved epidural injection of 2% lidocaine hydrochloride (0.25 mg/kg) in the first intercoccygeal or the sacrococcygeal intervertebral space, after which a flexible endoscope was inserted through the dilation shaft of an introducer set into the epidural space. In this instance, expansion of the epidural space with air provided an optimal endoscopic view of the epidural space. In the upper portion of the image, the bluish structure represents the dura mater in the epidural space. Dorsal is toward the top of the image.

Citation: American Journal of Veterinary Research 69, 7; 10.2460/ajvr.69.7.894

Epidural fat was easily recognized; fat deposits had a white-yellow foamy appearance with a shiny surface (Figure 2) . The amount of endoscopically visible epidural fat varied considerably among the cows. In all cows, white fibrous tissue was variably distributed throughout the epidural space. Connective tissue could also be seen in strand-like structures. Nerves were identified as white structures, mostly accompanied by small red vessels (Figure 3) . A variable number of larger vessels traversed the epidural space, but no pulsation within those vessels was detected (Figure 4) .

Figure 2—
Figure 2—

Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 10 cm in a sedated standing cow. Epidural fat is visible as a glistening white structure, and a spinal nerve (left upper portion of the image) is localized dorsally in the epidural space. Dorsal is toward the top of the image.

Citation: American Journal of Veterinary Research 69, 7; 10.2460/ajvr.69.7.894

Figure 3—
Figure 3—

Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 15 cm in a sedated standing cow. Notice the white-bluish nerves in the epidural space (upper and right side of the image) that are accompanied by reddish vessels. Dorsal is toward the top of the image.

Citation: American Journal of Veterinary Research 69, 7; 10.2460/ajvr.69.7.894

Figure 4—
Figure 4—

Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 10 cm in a sedated standing cow. In this view, a large reddish vessel is visible free within the epidural space (lower right portion of the image). Dorsal is toward the top of the image.

Citation: American Journal of Veterinary Research 69, 7; 10.2460/ajvr.69.7.894

In 4 of 6 cows, the spinal dura mater was viewed endoscopically (Figure 5). It appeared as a bluish shiny structure in 3 cows and had a more gray-colored surface in 1 cow. This structure was localized in the dorsal part (n = 2 cows) or in the ventral part (2) of the endoscopic view. In these 4 cows, the endoscope was inserted to a length of 20 to 29 cm when the spinal dura mater was observed. In 2 of the 6 cows, the spinal dura mater was not visible by use of the study technique.

Figure 5—
Figure 5—

Endoscopic view of the epidural space at the level of an insertion length of the endoscope of 29 cm in a sedated standing cow. Notice the bluish appearance of the spinal dura mater in the ventral part of the epidural space. Dorsal is toward the top of the image.

Citation: American Journal of Veterinary Research 69, 7; 10.2460/ajvr.69.7.894

Iatrogenic injury during epiduroscopy involved mild bleeding because of needle insertion in 1 cow. During endoscopic examination, 3 cows reacted with slight back arching (1, 3, and 5 times for cows 1, 4, and 5, respectively), but no aversive behavior was observed. When cows were moved back to the stable after the epidural anesthesia and the endoscopic examination, each had signs of ataxia of the hind limbs. However, a complete physical examination 5 hours after epiduroscopy revealed no deviation from physiologic findings, including apparently normal gait. During the month after completion of the study, no abnormalities were detected via daily physical examination in any of the cows.

Discussion

To the authors' knowledge, this is the first description of in vivo endoscopic examination of the epidural space in cows. The procedure enabled observation of anatomic structures in the bovine epidural space, including the spinal dura mater, nerves, vessels, and connective tissue.

Although it was developed for the use in humans, the endoscopic equipment used in our study was suitable for performance of epiduroscopy in cattle. In human medicine, flexible endoscopes with diameters as large as 3.5 mm and working channel diameters as large as 1.5 mm have been successfully used1; a working channel is necessary for insertion of additional instruments such as biopsy forceps as well as for irrigation and insufflation.

In the study of this report, the endoscopic examination of the epidural space was performed in standing cows. This might be an advantage because of the ease of positioning a trocar or needle in the epidural space. In a study14 of dog cadavers, ventral recumbency with the hind limbs directed cranially (adjacent to the trunk) was used; in human medicine, the patients are placed in prone position with the legs extended.1

For the epiduroscopic procedure, cows in our study were sedated and administered an anesthetic agent epidurally. Moreover, the technique for epidural anesthesia and the subsequent procedure for insertion of the epiduroscope were combined. The insertion angle of the Tuohy needle and the shaft for introduction of the epiduroscope ranged from 30° to 80° (with respect to the horizontal plane). However, in 1 cow, the angle insertion of the epiduroscope was steep (80°); because of associated difficulties in completing the procedure, the insertion had to be repeated at a flatter angle. For caudal epidural injection in cattle, an angle of 80° (with respect to the horizontal plane) is recommended by some authors,19 whereas others recommend an angle of 45° to 60°.20 We suggest that a flat angle between 30° and 45° is useful when performing epiduroscopy in cows. Because epidural puncture at a flat angle was assumed to be difficult, an acoustic device was used to correctly identify the epidural space. The use of an acoustic device to correctly identify the epidural space in humans16 and horsesc has been described.

In our study, the use of a Tuohy needle and introducer set (introducer and guidewire) intended for human epiduroscopy1 allowed a safe and easy insertion of the endoscope into the epidural space, and damage to the endoscope was avoided. The introducer shaft with the length of 6 cm was ideal for introducing the endoscope because the Tuohy needle was inserted to a depth of 3 to 5.5 cm when penetrating the epidural space.

Under physiologic conditions, the epidural space is a virtual space. So that epiduroscopic procedures are safe, obtaining a clear visual field is essential. To obtain good endoscopic visualization of the epidural structures, the epidural space needs to be expanded by fluid or air injection.1,13,21–23 The influence of epidural fluid or air injections on epidural pressure is known.1,24 To avoid excessive epidural pressure and potential damage to the nerves and spinal cord, the volume and speed of the infusion must be monitored.1,24,25

For epiduroscopy in humans, small injections of air have been used with good results and no adverse effects.23 In 1 study,21 however, the epidural space was distended by use of air injections with difficulty and remained open only temporarily. In the study of this report, the epidural space was expanded via insufflation of air. No procedure-associated complications developed in any cow, nor was the quality of the endoscopic images considered inadequate. Recently, in humans, a continuous flush of sterile saline solution during epiduroscopy has been used with good results.1,13 This method was also successfully used in canine cadavers.14 However, there is a report23 in which injection of physiologic saline solution into the epidural space did not enable clear endoscopic views22 and a reduced visual field persisted in humans. Similar problems were encountered by the authors of this report during the pilot study involving bovine cadavers, wherein both techniques (use of physiologic saline solution or air injections) were used to expand the epidural space.

In the cows of this report, it was possible to steer the optic portion of the endoscope straight toward the epidural space via gentle rotation and dorsoventral movements without any visible damage to the epidural structures. The fact that the spinal dura mater was observed ventrally as well as dorsally in certain epiduroscopic views suggests that the ventral and dorsal portions of epidural space were entered in some cows. In our study, deliberate switching of views from the dorsal to the ventral part of the epidural space was not attempted.

In the present study, the endoscopically visible epidural structures included fat, connective tissue, vessels, and nerves. In humans, epidural fat is generally described as semifluid.26 Epidural fat of cattle has been typically described20 as yellowish, thin, flat, fat lobes, most of which are attached to the spinal dura mater; the lobes are joined by a reddish gelatinous tissue. The fluid component was not perceived by the authors during epiduroscopy in the cows of this study; however, introduction of air into the epidural space might have distorted the anatomic appearance of the epidural fat. The cows in our study had a variable amount of epidural fat. The amount of epidural fat is not correlated with the fat content of the whole body in living humans and dog cadavers.14,21

In the cows of the present study, a variable number of vessels were seen in the epidural space. Anatomically, a venous sinus is usually present on the base of the vertebral canal in humans.26 The nonpulsating large vessels observed in the epidural space of the cows may be veins, but they were not clearly identified in every cow.

The spinal cord in cattle usually ends at the middle of the sacrum. The spinal dura mater was observed at 20 to 29 cm from the epidural puncture site in 4 of the 6 cows in our study. This location was close to the middle of the sacrum. The fact that the spinal dura mater was not visible in 2 cows may be related to the presence of a large amount of fat or inadequate positioning of the endoscope relative to the dura mater. An approach via the lumbosacral space, performed as part of the study14 involving dog cadavers, may be feasible in cattle, thereby allowing visualization of more cranially located structures, such as the dural sac and spinal nerves. The sacral approach is commonly used in humans for diagnostic epiduroscopy.5,13 An atlanto-occipital approach might also be an option, but in the authors' opinion, it does not seem practicable in cows without general anesthesia because of the anatomic proximity of vital structures and the possibility of life-threatening iatrogenic damage.

When performing epiduroscopy in cattle, possible complications must be taken into consideration. Complications related to this type of procedure described in the human medical literature include hemorrhage, mechanical damage (eg, traumatic dural puncture), and infection.5 To avoid procedure-associated infections, sterile precautions must be taken. Performing epiduroscopy more caudally in the sacrococcygeal region may lessen the risk of spinal damage and even the risk of traumatic dural puncture. Further studies concerning safety of this procedure and possible complications in cows are necessary. In addition, studies are necessary to determine the anatomic features of the epidural space in bovids. Given that dissection disrupts the position of the spinal dura mater, the epidural veins, and the uniquely semifluid epidural fat,27 an in vivo diagnostic imaging technique such as epiduroscopy may be helpful in visualizing anatomic structures of the epidural space, which cannot be observed by use of other imaging techniques.1

Because of problems associated with anesthesia, epidural anesthesia in cattle is of particular clinical importance. It is a routine anesthetic technique that is mainly performed for surgical interventions in the region of the perineum, anus, vulva, and vagina.19 Various substances (eg, local anesthetic agents, α2-adrenoceptor agonists, and opioids) are administered in the sacrococcygeal, intercoccygeal, or lumbosacral region to provide anesthesia and analgesia.19 Among individual bovids, the variation in resultant anesthesia and analgesia is wide; that variation is thought to be attributable to differences in the distribution of solution injected into the epidural space.20,28–32

It is conceivable to use epiduroscopy to evaluate the impact of various epidurally administered drugs on the epidural structures. Furthermore, the technique could be applied to assess any damage associated with epidural anesthesia (administered with or without use of epidural catheters), which has been reported in the literature.33–35 Although this novel technique might be of limited clinical application in cattle, it is of great scientific interest to gain more insight into the anatomic structures of the epidural space in this species, both in the physiologically normal and pathologic states. On the basis of our experience with the technique, the application of epiduroscopy in other animal species could be explored.

a.

Gräub AG, Bern, Switzerland.

b.

Portex Tuohy needle 18G, Portex Inc, Keene, NH.

c.

Iff I, Mosing M, Lechner T, et al. The use of an acoustic device to identify the extradural space in standing horses (abstr), in Proceedings. Am Vet Anesth Cong 2007;41.

d.

Graseby 3300, Graseby Medical Ltd, Watford, Hertfordshire, England.

e.

Xylanaest purum 2%, Gebro Pharma, Fieberbrunn, Austria.

f.

Karl STORZ, Tuttlingen, Germany.

g.

Einführbesteck 9F, Smiths Medical Deutschland GmbH, Kirchesoon, Germany.

h.

Millex filter unit (25 mm), Millipore, Vienna, Austria.

i.

Kochsalz Braun 0.9%, B. Braun Melsungen AG, Melsungen, Germany.

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Contributor Notes

Dr. Iff's present address is Division of Anesthesia, Department of Veterinary Clinical Science, University of Liverpool, Leahurst CH64 7TE, England.

The authors thank Hütter Andreas and Karl STORZ, Austria, for providing the endoscopic equipment.

Address correspondence to Dr. Franz.