• 1

    Jones RS. Epidural analgesia in the dog and cat. Vet J 2001; 161: 123131.

  • 2

    Wetmore LA, Glowaski MM. Epidural analgesia in veterinary critical care. Clin Tech Small Anim Pract 2000; 15: 177188.

  • 3

    Klide AM, Soma LR. Epidural analgesia in the dog and cat. J Am Vet Med Assoc 1968; 153: 165173.

  • 4

    Bromage PR. Spread of analgesic solutions in the epidural space and their site of action: a statistical study. Br J Anaesth 1962; 34: 161178.

  • 5

    Strande A. Epidural anaesthesia in young pigs, dosage in relation to the length of the vertebral column. Acta Vet Scand 1968; 9: 4149.

  • 6

    Harthoorn AM, Brass W. Some practical aspects of epidural anaesthesia in the dog. Vet Rec 1954; 66: 117120.

  • 7

    Pascoe P. Local and regional anesthesia and analgesia. Semin Vet Med Surg (Small Anim) 1997; 12: 94105.

  • 8

    Lund EM, Armstrong PJ, Kirk CA, et al.Health status and population characteristics of dogs and cats examined at private veterinary practices in the United States. J Am Vet Med Assoc 1999; 214: 13361341.

    • Search Google Scholar
    • Export Citation
  • 9

    Lee I, Yamagishi N, Oboshi K, et al.Distribution of new methylene blue injected into the lumbosacral epidural space in cats. Vet Anaesth Analg 2004; 31: 190194.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10

    Johnson RA, Lopez MJ, Hendrickson DA, et al.Cephalad distribution of three differing volumes of new methylene blue injected into the epidural space in adult goats. Vet Surg 1996; 25: 448451.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Lee I, Soehartono RH, Yamagishi N, et al.Distribution of new methylene blue injected into the dorsolumbar epidural space in cows. Vet Anaesth Analg 2001; 28: 140145.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12

    Lopez MJ, Johnson R, Hendrickson DA, et al.Craniad migration of differing doses of new methylene blue injected into the epidural space after death of calves and juvenile pigs. Am J Vet Res 1997; 58: 786790.

    • Search Google Scholar
    • Export Citation
  • 13

    Hendrickson DA, Lopez MJ, Johnson R, et al.Cranial migration of different volumes of new methylene blue after caudal epidural injection in the horse. Equine Pract 1998; 20: 1214.

    • Search Google Scholar
    • Export Citation
  • 14

    Apostolou GA, Zarmakoupis PK, Mastrokostopoulos GT. Spread of epidural anesthesia and the lateral position. Anesth Analg 1981; 60: 584586.

    • Search Google Scholar
    • Export Citation
  • 15

    Lee I, Yamagishi N, Oboshi K, et al.Multivariate regression analysis of epidural pressure in cattle. Am J Vet Res 2002; 63: 954957.

Advertisement

Effect of body position on cranial migration of epidurally injected methylene blue in recumbent dogs

View More View Less
  • 1 Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.
  • | 2 Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.
  • | 3 Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.
  • | 4 Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

Abstract

Objective—To determine the relationship between different body positions during recumbency on the cranial migration of epidurally injected methylene blue in canine cadavers.

Sample Population—21 fresh cadavers of clinically normal adult female mixed-breed dogs.

Procedure—Dogs were randomly assigned to the following 3 groups: dogs remaining in right lateral recumbency (n = 7), dogs rotated from left to right lateral recumbency (7), and dogs rotated from dorsal to right lateral recumbency (7). Each dog received an epidural injection of 0.05% methylene blue (0.1 mL/kg) at the lumbosacral space. A dorsal laminectomy of the vertebral column was made, and cranial extent of methylene blue in 4 quadrants (right lateral, left lateral, ventral, and dorsal) was determined by examining dura mater staining.

Results—No significant difference was found among groups in regard to body weight or body condition score. Epidural cranial migration of methylene blue in the right lateral quadrant was significantly greater in dogs that remained in right lateral recumbency than in dogs that were rotated from left to right lateral recumbency. No significant difference was found within groups for epidural cranial migration of methylene blue between each quadrant. No significant relationship was found between body weight or body condition score and epidural cranial migration of methylene blue.

Conclusions and Clinical Relevance—Body positioning and amount of recumbency time influence cranial migration of epidurally injected methylene blue. If greater cranial migration of an epidurally administered drug is desired, placing the patient in lateral recumbency with the surgical site on the dependent side may precede surgery.

Abstract

Objective—To determine the relationship between different body positions during recumbency on the cranial migration of epidurally injected methylene blue in canine cadavers.

Sample Population—21 fresh cadavers of clinically normal adult female mixed-breed dogs.

Procedure—Dogs were randomly assigned to the following 3 groups: dogs remaining in right lateral recumbency (n = 7), dogs rotated from left to right lateral recumbency (7), and dogs rotated from dorsal to right lateral recumbency (7). Each dog received an epidural injection of 0.05% methylene blue (0.1 mL/kg) at the lumbosacral space. A dorsal laminectomy of the vertebral column was made, and cranial extent of methylene blue in 4 quadrants (right lateral, left lateral, ventral, and dorsal) was determined by examining dura mater staining.

Results—No significant difference was found among groups in regard to body weight or body condition score. Epidural cranial migration of methylene blue in the right lateral quadrant was significantly greater in dogs that remained in right lateral recumbency than in dogs that were rotated from left to right lateral recumbency. No significant difference was found within groups for epidural cranial migration of methylene blue between each quadrant. No significant relationship was found between body weight or body condition score and epidural cranial migration of methylene blue.

Conclusions and Clinical Relevance—Body positioning and amount of recumbency time influence cranial migration of epidurally injected methylene blue. If greater cranial migration of an epidurally administered drug is desired, placing the patient in lateral recumbency with the surgical site on the dependent side may precede surgery.

Epidural anesthesia and analgesia are used in dogs for a number of reasons. They can provide anesthesia of caudally located dermatomes and analgesia that extends to the forelimbs.1,2 The epidural space is located between the vertebral column and the dura mater. The technique of epidural injection in dogs is almost invariably performed at the lumbosacral epidural space, although, in larger dogs, it may occasionally be performed at the sacrococcygeal epidural space.1-3 Some factors that influence the cranial migration of material injected into the epidural space include injectate volume, rate of infusion, patency of intervertebral foramina, posture, gravity, baricity, and vascular absorption.4 The volume of epidural injectate required to reach a specific spinal cord level on the basis of body length has been evaluated in pigs and dogs by use of radio-opaque solutions and dermatome analgesia.5,6 The discovery of spinal opioid receptors spawned the practice of providing analgesia by epidural administration of opioids. Small amounts provide substantial analgesia with minimal systemic effects.7

It has been recommended that animals be positioned in sternal recumbency and kept in that position following injection to provide bilateral analgesia or in lateral recumbency with the surgical site as the dependent side until the block has taken effect.7 To our knowledge, no studies exist that support the effects of positioning on the distribution of epidurally injected material in dogs. The purpose of the study reported here was to determine whether the body position during recumbency has an effect on cranial migration of epidurally administered methylene blue in cadavers of clinically normal dogs.

Materials and Methods

Sample population—Twenty-one fresh cadavers of mixed-breed sexually intact female dogs of indeterminate age were used. Cadavers were obtained within 30 minutes of euthanasia. Dogs had been euthanatized for reasons unrelated to this study.

Procedures—Body condition score (on a 9-point scale) was assessed by use of a previously described method.8 Each dog received an epidural injection of 0.05% methylene bluea

(0.1 mL/kg) while in sternal recumbency. Epidural injections were made into the lumbosacral epidural space with a 22gauge, 6.4-cm (2.5-in) spinal needle,b with the needle bevel directed cranially. All injections were made by the same investigator (EHH) at 30 to 40 minutes after euthanasia. To ensure the accuracy of all epidural injections, dissection to the level of the ligamentum flavum was performed.

The 21 dogs were randomly assigned to 1 of the following 3 groups: dogs that remained in right lateral recumbency (n = 7), dogs that were rotated from left to right lateral recumbency (7), and dogs that were rotated from dorsal to right lateral recumbency (7). After epidural injection, each dog was immediately placed in the appropriate recumbency position (right, left, or dorsal) on the basis of group assignment. Ten minutes were allowed to elapse, and then, each dog was turned to or allowed to remain in right lateral recumbency. Necropsy was performed approximately 40 minutes after epidural injections by other investigators who were blinded to the dogs’ group assignments. At necropsy, dorsal laminae of each vertebra were removed and the extent of cranial migration of the methylene blue within the epidural space was measured from the lumbosacral intervertebral disk to the most cranial aspect of staining of the dura mater. Measurements were obtained from the left, right, ventral, and dorsal aspects of the spinal cord. All measurements were done by the same investigator (AAG).

Statistical analysis—Analyses were performed in a blinded fashion. Normality was tested by use of the Kolmogorov-Smirnov test. Among-group comparison of cranial migration of epidurally injected methylene blue in each quadrant, within-group comparison of migration in the 4 quadrants, and among-group comparison of body weight and BCS were done by use of a 1-way ANOVA. Post hoc analysis was done by use of a Tukey multiple comparison test. Linear regression modeling was applied to compare body weight and BCS with cranial migration of epidurally injected methylene blue. Significance was defined as a value of P < 0.05.

Results

Dogs had body weights between 14.1 and 27.1 kg (mean ± SD, 21.06 ± 4.1 kg) and had a mean BCS of 4.6 ± 1.3. No significant difference was found among groups in regard to body weight or BCS. Epidural cranial migration of methylene blue in the right lateral quadrant was significantly greater in dogs that remained in right lateral recumbency than in dogs that were rotated from left to right lateral recumbency (Table 1). No significant difference was found among groups for epidural cranial migration in each of the other quadrants or for overall cranial migration. No significant difference was found within groups for epidural cranial migration of methylene blue in each of the quadrants. No significant relationship was found between body weight or BCS and epidural cranial migration of methylene blue.

Table 1—

Mean ± SD epidural cranial migration of methylene blue from the lumbosacral intervertebral disk space in 21 dogs.

VariableQuadrant of stained dura mater
Left lateral (cm)Right lateral (cm)Dorsal (cm)Ventral (cm)P values*
Left to right recumbency group (n = 7)13.1 ± 1.812.1 ± 3.013.1 ± 4.210.5 ± 2.80.35
Right lateral recumbency group (7)15.9 ± 8.320.3 ± 6.119.8 ± 7.713.1 ± 4.20.18
Dorsal to right recumbency group (7)14.8 ± 3.315.2 ± 2.417.7 ± 4.714.4 ± 3.10.31
P values0.590.010.120.12

Values of P < 0.05 indicate a significant within-group difference.

Values of P < 0.05 indicate a significant among-group difference.

Discussion

The meninges are membranous layers that surround and protect the spinal cord and the brain. The meninges are composed of the following 3 membranes: dura mater, arachnoid membrane, and pia mater. The capillary space between the dura mater and arachnoid membrane is the subdural cavity, which may contain a small amount of fluid. The epidural space is the space between the inner periosteum of the vertebral canal and dura mater and is filled with adipose and connective tissue.1

After epidural injection, drugs cross the spinal meninges to reach the dorsal horn of the spinal cord and exert their effects. Epidurally administered drugs probably exert their effects in many ways including diffusion through the dura to act on the nerve roots and spinal cord; leakage through intervertebral foramina, producing multiple paravertebral nerve blocks; or diffusion through dural nerve root sleeves, producing spinal root block.1,7 Other than the physical distribution, final effects of an epidurally administered drug are related to its lipid solubility, pKa (ie, pH at which the drug is 50% ionized), pH of the solution and the tissue, and binding capacity of the drug.1

Several studies9-13 have been published on distribution and cranial migration of methylene blue injected epidurally in cats, goats, pigs, calves, and horses. The main focus of these studies is the relationship between different volumes of epidurally injected methylene blue and cranial migration in different species. Results of these studies9-13 indicate that a linear relationship exists between the volume (mL/kg) of epidurally injected methylene blue and the cranial migration in the epidural space. The 4 major factors that influence the migration of anesthetic solution in the epidural space are as follows: physical characteristics of the species, technical factors, intrinsic anatomic factors such as the distribution of epidural adipose tissue and the structure of epidural veins, and epidural pressure.9,11 In our study, variations related to species characteristics and technical factors were minimized by use of the same species and similar technique performed by the same investigator.

It is common practice to place the patient in lateral recumbency with the surgical site on the dependent side to provide analgesia or in sternal recumbency to provide bilateral analgesia.7 This recommendation is predicated on the belief that a potential effect of gravity on solution distribution exists. It has been shown that epidural cranial migration may be affected by gravity because the caudally located thoracic and cranially located lumbar vertebrae, especially T13, are higher than other vertebrae when an animal is in sternal recumbency.2,7 Gravity may have an effect not only on epidural cranial migration but also on concentration of the local anesthetic at the site of interest, as indicated by faster onset and greater duration of action.14 The gravity effect may be used to influence the distribution of analgesia by placing the patient on the affected side for 15 to 20 minutes after the epidural injection.1,2,7 However, surgical procedures frequently require the affected leg to be on the nondependent side, forcing the patient to be turned after some time has passed and potentially affecting the migration of the epidural injectate.

On the basis of the findings in our study, a significantly greater migration was found on the right lateral quadrant in those dogs that were kept in right lateral recumbency versus those that were turned from left to right lateral recumbency. This suggests that if a gravity effect is desired, animals should be positioned with the surgery site on the dependent side and the epidural performed with no subsequent change in recumbency position. Results of previous studies9,11,15 indicate that a greater tendency exists for the dye to migrate in a cranial rather than dorsal or lateral direction. This probably happens because less resistance exists along this 9,11,15 Our results are in contradiction to the findings in these reports, as no significant difference was found between any of the quadrants within a group.

In conclusion, results of our study indicate that, when given enough time, positioning does have a significant influence over the cranial migration of epi durally injected methylene blue. No significant increase was found in the epidural cranial migration of methylene blue in the left or dorsal quadrants in dogs that were in left lateral or dorsal recumbency for 10 minutes before they were rotated to right lateral recumbency for about 30 minutes. In contrast, dogs that remained in right lateral recumbency for about 40 minutes had a significantly greater epidural cranial migration of methylene blue in the right quadrant, compared with dogs that were turned from left to right lateral recumbency. Keeping a patient in a certain body position this long before a procedure may not be clinically practical, and further studies are needed to evaluate the shortest amount of time required to achieve an increase in cranial migration of the epidural injectate in the gravity-dependent side. The epidural cranial migration of methylene blue in our study supports the common belief that epidural cranial migration is greater in the dependent side when the patient is in lateral recumbency, but only if the animal remains in that position for a long enough time.

BCS

Body condition score

a.

Methylene blue injection USP, Taylor Pharmaceuticals, Decatur, Ill.

b.

Monoject Sensi-Touch spinal needle, Sherwood Medica, St Louis, Mo.

References

  • 1

    Jones RS. Epidural analgesia in the dog and cat. Vet J 2001; 161: 123131.

  • 2

    Wetmore LA, Glowaski MM. Epidural analgesia in veterinary critical care. Clin Tech Small Anim Pract 2000; 15: 177188.

  • 3

    Klide AM, Soma LR. Epidural analgesia in the dog and cat. J Am Vet Med Assoc 1968; 153: 165173.

  • 4

    Bromage PR. Spread of analgesic solutions in the epidural space and their site of action: a statistical study. Br J Anaesth 1962; 34: 161178.

  • 5

    Strande A. Epidural anaesthesia in young pigs, dosage in relation to the length of the vertebral column. Acta Vet Scand 1968; 9: 4149.

  • 6

    Harthoorn AM, Brass W. Some practical aspects of epidural anaesthesia in the dog. Vet Rec 1954; 66: 117120.

  • 7

    Pascoe P. Local and regional anesthesia and analgesia. Semin Vet Med Surg (Small Anim) 1997; 12: 94105.

  • 8

    Lund EM, Armstrong PJ, Kirk CA, et al.Health status and population characteristics of dogs and cats examined at private veterinary practices in the United States. J Am Vet Med Assoc 1999; 214: 13361341.

    • Search Google Scholar
    • Export Citation
  • 9

    Lee I, Yamagishi N, Oboshi K, et al.Distribution of new methylene blue injected into the lumbosacral epidural space in cats. Vet Anaesth Analg 2004; 31: 190194.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10

    Johnson RA, Lopez MJ, Hendrickson DA, et al.Cephalad distribution of three differing volumes of new methylene blue injected into the epidural space in adult goats. Vet Surg 1996; 25: 448451.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Lee I, Soehartono RH, Yamagishi N, et al.Distribution of new methylene blue injected into the dorsolumbar epidural space in cows. Vet Anaesth Analg 2001; 28: 140145.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12

    Lopez MJ, Johnson R, Hendrickson DA, et al.Craniad migration of differing doses of new methylene blue injected into the epidural space after death of calves and juvenile pigs. Am J Vet Res 1997; 58: 786790.

    • Search Google Scholar
    • Export Citation
  • 13

    Hendrickson DA, Lopez MJ, Johnson R, et al.Cranial migration of different volumes of new methylene blue after caudal epidural injection in the horse. Equine Pract 1998; 20: 1214.

    • Search Google Scholar
    • Export Citation
  • 14

    Apostolou GA, Zarmakoupis PK, Mastrokostopoulos GT. Spread of epidural anesthesia and the lateral position. Anesth Analg 1981; 60: 584586.

    • Search Google Scholar
    • Export Citation
  • 15

    Lee I, Yamagishi N, Oboshi K, et al.Multivariate regression analysis of epidural pressure in cattle. Am J Vet Res 2002; 63: 954957.

Contributor Notes

Address correspondence to Dr. Gorgi.

Dr. Gorgi's present address is Department of Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.