Development and verification of saphenous, tibial and common peroneal nerve block techniques for analgesia below the thigh in the nonchondrodystrophoid dog

Veterinary Anaesthesia and Analgesia, 2006, 33, 36–48

doi:10.1111/j.1467-2995.2005.00234.x

RESEARCH PAPER

Development and verification of saphenous, tibial and common peroneal nerve block techniques for analgesia below the thigh in the nonchondrodystrophoid dog Lara M Rasmussen*

DVM, MS, Diplomate ACVS,

Alan J Lipowitz 

DVM, MS, Diplomate ACVS

& Lynelle F Graham 

DVM

*College of Veterinary Medicine, Western University of Health Sciences, Pomona, CA, USA  College of Veterinary Medicine, University of Minnesota, St Paul, MN, USA

Correspondence: Lara Marie Rasmussen, Affiliated Emergency Veterinary Service, 7717 Flying Cloud Dr., Eden Prairie, MN 55344, USA. E-mail: [email protected]

Abstract Objective To document simple and reliable local, infiltrating nerve blocks for the saphenous, tibial and common peroneal nerves in the dog. Study design Laboratory technique development; in vivo blind, controlled, prospective study. Animals Twenty canine cadavers and 18 clinically normal, client-owned dogs. Methods A peripheral nerve blockade technique of the tibial, common peroneal, and saphenous nerves was perfected through anatomic dissection. Injections were planned in the caudal thigh for the tibial and common peroneal nerves, and in the medial thigh for the saphenous nerve. Cadaver limbs were injected with methylene blue dye and subsequently dissected to confirm successful dye placement. Clinically normal dogs undergoing general anesthesia for unrelated, elective procedures were randomly assigned to treatment (bupivacaine; n ¼ 8) or control (saline; n ¼ 8) nerve blocks of the nerves under study. Upon recovery from general anesthesia, skin sensation in selected dermatomes was evaluated for 24 hours. Results Cadaver tibial, common peroneal, and saphenous perineural infiltrations were successful in nonchondrodystrophoid dogs (100, 100, and 97%, respectively.) Intraneural injection was rare 36

(1%; 1/105; tibial nerve) in cadaver dogs. In the treatment group of normal dogs, duration of loss of cutaneous sensation in some dermatomes (saphenous, superficial and deep peroneal nerve) was significantly different than control dogs; the range of desensitization occurred for 1–20 hours. No clinical morbidity was detected. Conclusions This technique for local blockade of the tibial, common peroneal, and saphenous nerves just proximal to the stifle is easy to perform, requires minimal supplies and results in significant desensitization of the associated dermatomes in clinically normal, nonchondrodystrophoid dogs. Clinical relevance This technique may be an effective tool for post-operative analgesia to the femorotibial joint and distal pelvic limb. Other applications, using sustained-release drugs or methods, may include anesthesia/analgesia in high-risk patients or as a treatment for chronic pelvic limb pain or selfmutilation. Keywords canine, common peroneal nerve, pain management, peripheral nerve blockade, saphenous nerve, tibial nerve.

Introduction The goal of peri-operative pain management is to reduce pain and thus speed recovery (Kehlet 1989) while minimizing complications related to the

Nerve block techniques for analgesia LM Rasmussen et al.

method of pain management (Hellyer 1997; Sethna 1998). The theory of pre-emptive analgesia suggests that an antinociceptive or analgesic treatment that prevents the establishment of central hyperexcitability (Bennett 2000) will diminish or prevent amplification of post-operative pain (Woolf 1983; Woolf & Chong 1993). Studies in human beings and rats have supported this concept (Ringrose & Cross 1984; et92; Fletcher et al. 1996), though contradictory data exist as well (Kissin 1996). Local anesthetics have been used for decades for analgesia in human medicine and are generally considered safe and effective for topical (Alvi et al. 1998), infiltrative (Ejlersen et al. 1992), and regional use (Rygnestad et al. 1997) in human children and adults. In veterinary medicine, local anesthesia has been used similarly for therapeutic purposes in most species (Day & Skarda 1991) and for diagnostic purposes primarily in the equine species (Thurmon et al. 1996). Longer acting drugs such as bupivacaine now bring the effectiveness of these analgesic techniques into the extended postoperative period with few complications (Moore et al. 1978). A subset of regional analgesia/anesthesia techniques are the peripheral nerve blocks. These involve infiltration of the area immediately surrounding peripheral nerves with anesthetic agent, and include nerve plexus applications, e.g. brachial plexus blocks, as well as individual nerve application, e.g. femoral nerve blocks. As nociceptive stimuli are carried via peripheral nerves to the spinal cord and on to the brain for processing and recognition as pain, interruption of these pathways at the peripheral nerve will create analgesia and/or anesthesia. Local anesthetic, peripheral nerve blocks are effective at preventing propagation of nerve impulses to the spinal cord and brain (Wildsmith 1986). The theory of pre-emptive analgesia suggests that these techniques administered prior to surgical stimuli may allow for more effective or longer duration pain management than other analgesic methods. Human studies of peripheral nerve blocks with bupivacaine for post-operative pain management show efficacy (McLoughlin & Kelley 1989; Allen et al. 1998). These techniques are associated, in human beings, with very low and minor morbidity (Giaufre et al. 1996; Fanelli et al. 1999). Veterinary literature supporting similar use in companion animals is limited (Cox & Riedesel 1997). With the increase in ambulatory surgical practice and the continual demand to maintain lower costs, Ó 2006 Association of Veterinary Anaesthetists, 33, 36–48

effective pain management techniques allowing early release from the hospital without associated morbidity is desirable. The purpose of this study was to develop a reliable and simple percutaneous peripheral nerve block technique for the primary nerves of the canine pelvic limb. Materials and methods The study design was approved by the institutional ethical review committee. Laboratory assessment of perineural infiltration technique Twenty random breed canine cadavers were procured (average mass ¼ 30 kg; range 7–40 kg) that had died or been killed due to terminal illness. Chondrodystrophic animals were distinguished from nonchondrodystrophic animals based on short-limbed stature and established breed characteristics. Anatomic dissection of the course of the femoral and sciatic nerves (Figs 1 & 2) was conducted to identify palpable landmarks, fascial planes, and associated structures. A percutaneous, perineural injection technique was developed and applied to the saphenous, tibial, and common peroneal nerves of 35 limbs using a volume of methylene blue dye equivalent to 2 mg kg)1 of bupivacaine 0.5%, which was the projected clinical dose to be evaluated in vivo. Percutaneous, perineural injections (see technique that follows) were made with a 6.35 or 8.89 cm 20 SWG short-beveled, spinal needle with stylet (BD spinal needle with Quincke type point; Becton Dickinson & Co., Franklin Lakes, NJ, USA). Each nerve was then immediately dissected, and a record made of whether dye was coating the nerve grossly or not, and whether there was gross evidence of a needle puncture and associated dye within the nerve trunk. Injection technique The total dose (equivalent to 0.4 mL kg)1 bupivacaine 0.5%) for methylene blue dye was divided into two syringes: two-thirds dose in one syringe (tibial and common peroneal nerves) and one-third dose in the other (saphenous nerve) (Fig. 3). For the tibial and common peroneal combined perineural injections, the mid-region of the caudal thigh was clipped. The animal was placed in lateral recumbency with the treatment leg uppermost. 37

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Figure 1 Gross anatomy of the saphenous nerve and associated injection technique landmarks. Right thigh, medial view with the superficial and deep fascia removed.

Figure 2 Gross anatomy of the tibial and common peroneal nerves and associated injection technique landmarks. Left thigh, lateral view with the biceps femoris muscle reflected distally.

From the lateral aspect of the thigh, with the thumb of the nondominant hand located caudally in the groove between the biceps femoris and semimembranosus/semitendinosus muscles and fingers at the 38

cranial edge of the biceps femoris muscle, the body of the biceps femoris muscle at the midpoint between the patella and the greater trochanter was grasped and lifted. The thumb was advanced Ó 2006 Association of Veterinary Anaesthetists, 33, 36–48

Nerve block techniques for analgesia LM Rasmussen et al.

Figure 3 Injection technique for percutaneous administration of local anesthetic around the (a) tibial and common peroneal nerves and (b) saphenous nerve.

deeply into the groove in the caudal-to-cranial direction until the caudal aspect of the femur was felt. The spinal needle was positioned perpendicular to the long axis of the femur and parallel to the table surface and advanced caudally to cranially through the skin immediately adjacent to the thumb. The needle was advanced until the caudal aspect of the femur was contacted; the needle was withdrawn approximately 1 cm, the stylet was removed, and the drug syringe was attached. The distance from the needle tip to the skin was divided into approximate 10ths. The syringe was aspirated to evaluate for blood; if none was seen then one-tenth of the dose was injected; the needle was withdrawn onetenth the calculated distance and aspiration and injection were repeated. The grip on the biceps femoris muscle was slowly relaxed and injections continued until the entire dose was administered. If vascular penetration was suspected, on the basis of a sanguinous aspirate, the needle was redirected, re-aspirated and administration was continued. Ó 2006 Association of Veterinary Anaesthetists, 33, 36–48

Deep digital pressure was applied for 5 minutes following the procedure if blood had been aspirated. No attempt was made to contact or stimulate the nerve. For the saphenous perineural injections, the midregion of the medial thigh was clipped. The animal was placed in lateral recumbency with the treatment leg uppermost. An assistant held the thigh abducted and perpendicular to the table. The injection site was located at the midpoint between the pectineus muscle and the medial epicondyle of the femoro-tibial joint. A subtle groove between the sartorius and gracilis muscles, where the saphenous neurovascular bundle lies, was chosen as the penetration site. The spinal needle with syringe attached was held approximately 5° off the long axis of the femur, with the needle directed proximally and along the long axis of the femur. The needle was advanced approximately 1–2 cm through the skin and the dense, superficial fascia overlying the neurovascular bundle where, typically, a distinct 39

Nerve block techniques for analgesia LM Rasmussen et al.

‘pop’ was appreciated. The needle was advanced an additional 2–3 cm within this fascial plane. The syringe was aspirated to evaluate for blood; if none was seen the test substance was injected as the needle was slowly withdrawn. Digital pressure was applied for 5 minutes if the needle accidentally penetrated a blood vessel. In vivo assessment of perineural infiltration technique Sixteen healthy, large breed dogs undergoing general anesthesia for routine, elective procedures unrelated to the pelvic limbs e.g. dental prophylaxis, surgical sterilization, etc. were randomly assigned, following informed owner consent, to treatment (bupivacaine 0.5%, 0.4 mL kg)1; Sensorcaine 0.5%; Astra USA, Inc., Westborough, MA, USA) or control (sterile, preservative-free saline, 0.4 mL kg)1) groups. The dogs were premedicated with acepromazine maleate (0.02 mg kg)1, IM; Phoenex Pharmaceutical, Inc., St Joseph, MO, USA) and oxymorphone hydrochloride (0.05 mg kg)1, IM; Numorphan; DuPont Pharma Ltd, Manati, Puerto Rico) 30 minutes prior to induction with thiopental (10–15 mg kg)1, IV to effect; Pentothal; Abbott Laboratories, Chicago, IL, USA). Dogs’ trachae were intubated and maintained on halothane (Halocarbon Laboratories, River Edge, NJ, USA) or isoflurane (IsoFlo; Abbott Laboratories) in 100% oxygen delivered via a semiclosed circle system for the duration of the elective procedures (30–45 minutes). Immediately following induction, the study leg was randomly chosen, and the nerve block technique (treatment or control) was performed with a 20 SWG short-beveled, spinal needle with stylet, by an investigator unaware of group assignments (LMR) (see injection technique). Following tracheal extubation, five dermatome test sites (Fig. 4) were evaluated in random order for cutaneous sensation every hour for 12 hours by an investigator who was unaware of test group designation, then every 4 hours for 12 hours or until sensation returned. The skin of the test site was grasped with hemostatic forceps; an abrupt pinch was applied and recognition by the dog was monitored. A positive skin sensation was recorded if the dog turned toward or vocalized during the stimulus. The lateral cutaneous femoral test site served as the positive control site. Motor function was evaluated at 24 hours by observing the walk40

ing gait for evidence of inappropriate placing, toe dragging or lameness. Statistical analysis Multivariate analysis of variance and Student’s t-test were used to compare in vivo desensitization times. Bonferroni adjustment was applied post hoc in an effort to control for type 1 error associated with multiple t-tests; p < 0.01 was considered significant. Results Laboratory assessment of perineural infiltration technique Grossly normal pelvic limbs from 18 canine cadavers with an estimated body mass range of 10–25 kg and that had died or been killed due to natural causes, were used in the development of the techniques. Fifteen cadavers were of normal stature; three cadavers were of a chondrodystrophoid body conformation. Perineural infiltration was successful in 83–89% of injection sites in 35 cadaver limbs, and in 97–100% of injection sites in the 30 nonchondrodystrophoid cadaver limbs (Table 1). Presumptive morbidity was defined as dye within the body of the nerve and was seen in 1% (1/105) of test sites (tibial nerve; nonchondrodystrophoid limb). Percutaneous perineural infiltration was unsuccessful, i.e. no dye was found within 1 cm of nerve sheath in at least one of three sites in 80– 100% of chondrodystrophoid breeds (n ¼ 5). In vivo assessment of perineural infiltration technique Sixteen healthy, large breed dogs (age range 0.5– 10 years; body mass 20–45 kg) participated in the study. Desensitization of cutaneous zones innervated by the saphenous, tibial, and common peroneal nerves occurred for up to 20 hours following perineural infiltration with bupivacaine (Table 2). Perceived desensitization of control dogs’ test sites ranged from 1 to 4 hours; the control site in these subjects, e.g. lateral cutaneous femoral, had a similar range of desensitization. Multivariate analysis of variance permitted us to test whether the four sites that were expected to be affected by bupivacaine responded in a uniform, statistically significant manner. This primary data analysis strategy permitted us to test all four sites at the same time, Ó 2006 Association of Veterinary Anaesthetists, 33, 36–48

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Figure 4 Testing sites for the dermatomes for the lateral cutaneous femoral, superficial peroneal, deep peroneal, tibial, and saphenous nerves.

Table 1 Positive percutaneous perineural infiltration of new methylene blue around the saphenous, tibial, and common peroneal nerves in canine cadaver limbs

Sample population

Saphenous

All cadaver limbs (n ¼ 35) 29/35 (83) Non-chondrodystrophoid limbs (n ¼ 30) 29/30 (97) Chondrodystrophoid (n ¼ 5) 0/5 (0)

Tibial

Common peroneal

31/35 (89) 30/30 (100) 1/5 (20)

31/35 (89) 30/30 (100) 1/5 (20)

Values are expressed as n (%).

indicating that the treatment group and control group significantly differed across the composite of the four sites [F(4,11) ¼ 8.91, p ¼ 0.002]. Secondary analyses using t-tests to examine each site separately indicated that while all sites responded in the predicted direction, the results were most dramatic for superficial peroneal and saphenous in comparison with deep peroneal and tibial (Table 2). Bonferroni post hoc adjustments confirmed this pattern. As predicted, this pattern of effective desensitization can be contrasted against the response of the control site, lateral cutaneous femoral, which did not show any significant differÓ 2006 Association of Veterinary Anaesthetists, 33, 36–48

ences between treatment and control groups. Motor control was normal in all dogs when evaluated at 24 hours post-injection. No inadvertent vascular penetration occurred during this study and no morbidity was seen or subsequently reported in study subjects. Discussion Cadaver dissections were beneficial to the establishment of landmarks for application of this technique. Universally known and easy to recognize landmarks were chosen: greater trochanter, patella, 41

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Table 2 Time (hours) of desensitization of cutaneous autonomous zones (lateral cutaneous femoral, superficial peroneal, deep peroneal, tibial, and saphenous) following percutaneous, perineural injections of bupivacaine (Tx) (0.5%; 0.4 mL kg)1) or saline (Ctrl) in normal dogs (n ¼ 16) Lateral cutaneous femoral

Patient data

Mean SD Range p-value

Superficial peroneal

Deep peroneal

Tibial

Saphenous

Tx

Ctrl

Tx

Ctrl

Tx

Ctrl

Tx

Ctrl

Tx

Ctrl

1 2 2 1 1 1 2 4 1.8 1.0 1–4 1

2 3 2 2 1 2 1 1 1.8 0.7 1–3

4 7 16 5 9 11 1 16 8.6 5.5 1–16 0.004*

2 4 2 2 1 2 1 1 1.9 1.0 1–4

1 5 16 5 11 6 1 2 5.9 5.2 1–16 0.05

2 4 2 2 1 2 1 1 1.9 1.0 1–4

2 8 7 6 11 1 1 1 4.6 3.9 1–11 0.07

2 4 2 2 1 2 1 1 1.9 1.0 1–4

2 5 5 5 11 16 20 5 8.6 6.4 2–20 0.01*

3 3 2 2 1 2 1 1 1.9 0.8 1–3

*Confirmed mean difference was significant using post hoc Bonferroni adjustment.

femur, biceps femoris muscle, semimembranosus/ semitendinosus muscles, pectineus muscle, medial femoral epicondyle, and the groove between caudal sartorius and gracilis muscles (Figs 1 & 2). Peripheral nerve block techniques rely on the concept of injecting local anesthetics into fascial compartments surrounding nerves (Winnie et al. 1973; Mansour 1995). In the cadaver portion of this study, the common peroneal and tibial nerves were found to lie in a fascial plane sandwiched between the biceps femoris and the semimembranosus/semitendinosus muscles. This compartment, the target for the block technique, was injected, thus bathing the nerves in dye (or local anesthetic agent). In both the cadaver and relaxed, anesthetized dogs, the biceps femoris muscle was easy to identify and grasp; when grasped, this fascial compartment was expanded, and a needle was easily directed into it. The saphenous nerve was found to run in a neurovascular bundle along the medial thigh. It was confined in a groove created by the borders of the caudal sartorius and gracilis muscles, and covered by deep medial femoral and crural fascia. These fascia created another compartment, this one quite superficial, which could be entered easily with a needle; dye (or local anesthetic drug) was injected here to bathe the saphenous nerve. The femoral nerve, composed of fibers from the fourth, fifth, and sixth lumbar spinal cord segments, 42

is formed in the body of the iliopsoas muscle; it then gives off the saphenous nerve at the level of the coxofemoral joint. The saphenous nerve may have both a muscular branch (to the sartorius muscle) and a cutaneous branch, though most commonly the muscular branch originates from the femoral nerve itself and the saphenous nerve is solely a cutaneous nerve. It innervates the skin of the medial thigh and femoro-tibial joint, the medial femorotibial joint capsule, femoro-tibial joint intraarticular structures, the skin of the dorsomedial tarsus, and the first digit and proximal aspect of the second digit of the pelvic limb (O’Connor & Woodbury 1982; Haghighi et al. 1991). The common peroneal, i.e. fibular, and tibial nerves are bundled together and termed the sciatic nerve as they exit the pelvic region. The sciatic nerve divides into these distinct nerves variably in the thigh between the coxofemoral and stifle joints. The common peroneal nerve, and its branches, innervate the caudolateral femoro-tibial joint capsule, the lateral meniscus, the flexors of the tarsus, the extensors of the digits, the skin of the dorsum of the tarsus/metatarsus, and the digits. The tibial nerve, and its branches, supply the caudal femorotibial joint capsule, the extensors of the tarsus, the flexors of the digits, and the plantar aspect of the tarsus and digits (Bennett & Vaughan 1976; Bennett 1976; Evans & Christensen 1979; O’Connor & Woodbury 1982). The proximal caudal cutaneous Ó 2006 Association of Veterinary Anaesthetists, 33, 36–48

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sural nerve exits the sciatic bundle at the level of the greater trochanter and is not likely affected by the technique described herein. This branch innervates the skin of the caudolateral aspect of the femorotibial joint region (Haghighi et al. 1991). The lateral cutaneous sural nerve exits the sciatic bundle variably in the thigh and may be affected by this technique. All lower sciatic branches (distal caudal cutaneous sural, tibial, and common peroneal nerves) are likely to be affected by this technique. The results of the perineural injections were not reliable in cadavers with a typical chondrodystrophic anatomy, i.e. short, angular limb conformation relative to body size. This was presumed to be due to a lack of consistent anatomy among nonchondrodystrophoid and chondrodystrophoid cadavers and between each chondrodystrophoid individual. Given the lack of initial success of this technique in cadavers with this body conformation, further in vivo studies were conducted only on dogs with a nonchondrodystrophoid conformation. For application of this technique to chondrodystrophoid breeds, a refinement of the technique would need to be made; the use of nerve stimulators would likely be of benefit for accurate and repeatable nerve location. The cadavers used in the first part of this study presented some unique characteristics which may have influenced the results. Given their slight dehydration and rigidity compared with a normal, anesthetized dog, the compartments for deposition of dye may have been more distinct and easier to reach with the needle. The choice of cadavers and the marking agent, new methylene blue dye, allowed immediate determination of dye location; it did not allow quantification of dye spread. Using magnetic resonance imaging (MRI) or ultrasound in clinical patients, researchers have been able to document the final location of deposited local anesthetic (Marhofer et al. 2000). In the clinical setting, these tools might be valuable for confirming proper drug placement and extent of change following placement for further comparative studies. When comparing dermatome sensitivity in vivo to a control site on the same patient, the presence of drug effect and its duration were relatively easy to determine. When comparing data from treated and control patients, it was clear that a treatment effect was present given the longer period of dermatome desensitization (Table 2). The ranges of desensitization for each nerve were quite wide (Table 2) but did indicate the potential for benefits to the periÓ 2006 Association of Veterinary Anaesthetists, 33, 36–48

operative time period. The potential reasons for this variation in duration are several. Duration of action of bupivacaine is determined by degree of protein binding, drug absorption by the nerve, systemic drug absorption, exposure of the nerve to the drug, and the nerve size (Ganley & Ganley 1987; PopitzBergez et al. 1995; Tetzlaff 2000). Systemic drug absorption varies by individual, given its dependence on blood flow and tissue pH for redistribution; this contributed to the variation in desensitization times between individuals. Drug type and concentration were kept constant in this study, but increasing the total drug volume might have increased the chance that the drug would contact the nerve, induce an effect, and produce desensitization. Injection technique determines the amount of drug deposited in close relationship to the target nerve; the wide range of desensitization (from none/ minimal to 20 hours) seen in this study might be due, in large part, to this variable. The common peroneal and tibial nerve blocking technique has more room for drug deposition error or inconsistency between subjects as the fascial compartment is more spacious and these nerves are deeper below the skin surface than the saphenous nerve. Dermatome sensitivity was similar for superficial and deep peroneal test sites; this was expected given that the parent nerve, the common peroneal, was blocked with this technique. The dermatome sensitivity of the tibial test site was expected to be similar to the superficial and deep peroneal test sites as one of the parent nerves, the sciatic, or the immediate crux of the common peroneal–tibial branching was blocked with this technique. It was apparent, based on comparison with the control test site in several subjects (see Table 2), that some nerves were not affected by the treatment. Poor drug placement is the most logical explanation for this finding. Confirmation of proper drug deposition with ultrasound, MRI, or nerve stimulators may maximize the effective duration of desensitization (Marhofer et al. 1998, 2000; Fanelli et al. 1999). The dermatomes chosen in this study correspond to the cutaneous areas innervated by the nerves that also supply innervation to the femoro-tibial joint and its surrounding structures. Cutaneous innervation of the pelvic limb in male dogs was determined by Haghighi et al. (1991) using electrophysiologic evaluations. The autonomous zone test sites, i.e. those skin locations that do not have crossover innervation by more than one major nerve, used for testing the saphenous, superficial 43

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and deep peroneal, tibial and lateral cutaneous femoral nerves are depicted in Fig. 4. These zones may be used as an evaluation tool for individual nerve sensory function. In the in vivo study, the treatment group (bupivacaine) had a longer duration of sensory deficit to the dermatomes supplied by the common peroneal, tibial, and saphenous nerves than those of the control group (saline). Whether the nociceptive fibers from the femorotibial joint and surrounding structures were included in these blocks, and thus whether these nerve blocks are appropriate for providing peri-operative pain control, remains to be determined. Morbidity associated with peripheral nerve block techniques is due to both physical disruption of nerve fibers when a nerve is punctured and to increased intraneural pressure when fluid is instilled within the relatively indistensible nerve structure itself (Selander et al. 1979; Maruyama 1997). Inadvertent, intraneural injection was confirmed as having a low incidence (1/105 injections) in the laboratory cadaver study. This may have been influenced by subtle cadaver dehydration and a resultant increase in tissue (nerve and sheath) resistance to penetration. The only noted morbidity in the in vivo normal dog study was a motor deficit to the flexors of the hock and the extensors of the digits in some treatment subjects; this was expected given the influence of local anesthetic drugs on both sensory and motor fibers of treated nerves. All subjects were fully ambulatory with the return of sensation confirmed prior to the end of the 24-hour study period. The control subjects with anesthesia of the skin test sites for up to an average of 4 hours post-injection may be explained by one of two possibilities. First, these subjects had similar durations of anesthesia in their control sites, e.g. lateral cutaneous femoral, so the testing impression of anesthesia at each skin site may have been due to centrally mediated analgesia, or sedation influences. Second, these subjects may have experienced varying degrees of technique-related nerve trauma. Subtle, persistent, sensory deficits are unlikely to be detected in the veterinary patient given the lack of objective criteria. Variable-term sensory and motor deficits and occasional severe paresthesias have been noted in human beings following various nerve block techniques (Derrick & Aun 1996; Kaufman et al. 2000; Atchabahian & Brown 2001). The use of a short-beveled needle appeared to allow advancement within a tissue plane, compared with deviation into adjoining planes, and minimized 44

the likelihood of nerve penetration, i.e. the needle pushed the nerve out of its way. This speculation is supported by findings of nerves and nerve fascicles rolling away from short-beveled needles in comparison with long-beveled needles (Selander et al. 1977; Macias et al. 2000). Some questions have been raised as to the safety of short-beveled needles in regional anesthesia given the in vivo findings of less severe morbidity associated with long-beveled needles (Rice & McMahon 1992). Maruyama (1997) reported that long-tapered needles produced the least amount of axonal damage following nerve puncture (compared with short-tapered and undefined-beveled needles), but the author did not comment on ease of nerve penetration with this needle configuration. No clinical studies are available to compare morbidity associated with various needle configurations, so the question remains unanswered. Given the ‘blind’ nature of the technique herein described, i.e. no objective placement confirmation, the shortbeveled needle was chosen due to presumed lower risk of accidental nerve penetration. More sophisticated techniques that employ nerve stimulators or ultrasound to locate and/or avoid nerves may benefit from the use of long-beveled or long-tapered needles to minimize axonal trauma if accidental nerve puncture should occur. Bupivacaine, used in this study, is a preservativefree, isotonic solution of an amide-type local anesthetic with a pKa of 8.1. In comparison with its chemically similar relation, lidocaine, bupivacaine is protein bound to a greater extent and has a greater degree of lipid solubility. The mechanism of action of bupivacaine is similar to other local anesthetics; these substances block sodium and potassium channels and block the propagation of nerve impulses (Wildsmith 1986; Brau et al. 1995, 1998). Bupivacaine was chosen to confirm the success of the nerve block techniques in this study because of its potency, long duration of action, low morbidity, and sparing effect on motor fibers making it an ideal local anesthetic for the perioperative period (Moore et al. 1970, 1978; Ganley & Ganley 1987; Dyhre et al. 1997). The dose of bupivacaine chosen for this study (0.4 mL kg)1 of 0.5% bupivacaine or 2 mg kg)1) was extrapolated as a ‘safe’ dose from clinical studies in adult human beings (0.3–6 mg kg)1; various regional applications) (Moore et al. 1970, 1978) and human infants (2 mg kg)1; spinal), (Breschan et al. 1998) and nonclinical studies in sheep (3.5 mg kg)1; IV) (Kasten & Martin 1986), Ó 2006 Association of Veterinary Anaesthetists, 33, 36–48

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dogs (24 mg kg)1; IV) (Kasten & Martin 1986), and rats (0.3 mg kg)1; peripheral nerve block) (Dyhre et al. 1997). The LD50 in mice for intravenous administration of bupivacaine is 6–8 mg kg)1 and for subcutaneous administration is 38–54 mg kg)1. As species variation has been reported in the pharmacokinetics of bupivacaine (Coyle et al. 1984), the toxic arterial and venous serum concentrations need to be determined for the dog, for this application, to select an appropriate dose. The human medical field is replete with data supporting the use of peripheral nerve blocks for a variety of medical conditions. The therapeutic use of peripheral nerve blocks has been described for use in the human emergency room setting to provide pain relief in otherwise compromised patients, e.g. head, thoracic, or abdominal trauma patients and those unable to tolerate systemic analgesics (Brennan 1993). These uses have been modified to include indwelling catheter delivery of local anesthetic nerve blocks via constant rate infusions, intermittent ‘top-up’, or patient-controlled mechanisms (Hamid et al. 1992; Mackenzie & Pullinger 1997; Klein et al. 2000; Chelly et al. 2001). Morbidity with these indwelling delivery systems is low in human beings (Cuvillon et al. 2001) and in rats (The Local Anesthetics for Neuralgia Study Group 1994). With longer duration and patient-customized techniques, acute and chronic pain management can be implemented effectively with low morbidity. Intractable cancer pain and various chronic pain syndromes in human have been effectively controlled with these longer duration techniques (Fischer et al. 1996; Shulman et al. 1998). The pain associated with limb fractures in elderly human beings can be palliated in high-risk, inoperable patients, or total surgical anesthesia and post-operative analgesia can be delivered in highrisk elderly or juvenile patients for various limb procedures (Tobias 1994; de Visme 1998). Postsurgical/post-injury rehabilitation can be initiated sooner and to a higher degree with the use of these indwelling options (Capdevila et al. 1999). Pain associated with soft-tissue procedures, such as varicose vein stripping, vascular graft collection for cardiac bypass, skin graft collection and muscle biopsy, have been successfully managed in human beings with local anesthetic nerve blocks as well (Maccani et al. 1995; Griffith et al. 1996; Khan et al. 1998). Many of these indications occur in veterinary patients; the feasibility of peripheral nerve blocks for them needs to be assessed. SelfÓ 2006 Association of Veterinary Anaesthetists, 33, 36–48

mutilation in the veterinary patient, as seen with some behavioral diseases or trauma, may be also managed effectively using nerve block techniques with longer acting agents such as lipid-emulsified or liposome-encapsulated local anesthetics (Boogaerts et al. 1995; Lazaro et al. 1999), local anesthetic combinations (Hassan et al. 1993) a2-agonists combined with local anesthetics (Reinhart et al. 1996), local anesthetic in polymer matrixes (Masters et al. 1993), locally applied ammonium sulfate or tricyclic antidepressants (Hertl et al. 1998; Gerner et al. 2001). Diagnostic nerve blocks have been used extensively in horses (Manning & St Clair 1976; Merriam & Finocchio 1981). Diagnostic and therapeutic use of nerve blocks in small animals has been limited (Hellyer 1997). The utility of peripheral nerve blocks has been well established in human beings, most commonly in conjunction with other drugs and techniques for a balanced, multimodal approach to surgical anesthesia (Casati et al. 2000; de Visme et al. 2000) and post-operative analgesia (Allen et al. 1998; Graf & Martin 2001). The cardiovascular, respiratory, urinary, and gastrointestinal side effects (Fanelli et al. 1998) of these other anesthetic/analgesic techniques may be reduced or eliminated through the incorporation of peripheral nerve block techniques in a multimodal approach. The veterinary profession will benefit from investigations into wider applications of peripheral nerve blocks in veterinary patients based on the human data supporting the use of these techniques. This study confirms the success of this novel technique in desensitizing dermatomes innervated by the tibial, common peroneal, and saphenous nerves in nonchondrodystrophoid dogs. References Allen HW, Liu SS, Ware PD et al. (1998) Peripheral nerve blocks improve analgesia after total knee replacement surgery. Anesth Analg 87, 93–97. Alvi R, Jones S, Burrows D et al. (1998) The safety of topical anaesthetic and analgesic agents in a gel when used to provide pain relief at split skin donor sites. Burns 24, 54–57. Atchabahian A, Brown AR (2001) Postoperative neuropathy following fascia iliaca compartment blockade. Anesthesiology 94, 534–536. Bennett D (1976) An anatomical and histological study of the sciatic nerve, relating to peripheral nerve injuries in the dog and cat. J Small Anim Pract 17, 379– 386. 45

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Ejlersen E, Andersen HB, Eliasen K et al. (1992) A comparison between preincisional and postincisional lidocaine infiltration and postoperative pain. Anesth Analg 74, 495–498. Evans HE, Christensen GC (1979) Miller’s Anatomy of the Dog (2nd edn). W.B. Saunders, Co., Philadelphia, PA, USA. Fanelli G, Casati A, Aldegheri G et al. (1998) Cardiovascular effects of two different regional anaesthetic techniques for unilateral leg surgery. Acta Anesthesiol Scand 42, 80–84. Fanelli G, Casati A, Garancini P et al. (1999) Nerve stimulator and multiple injection technique for upper and lower limb blockade: failure rate, patient acceptance, and neurologic complications. Study group on regional anesthesia. Anesth Analg 88, 847–852. Fischer HB, Peters TM, Fleming IM et al. (1996) Peripheral nerve catheterization in the management of terminal cancer pain. Reg Anesth 21, 482–485. Fletcher D, Kayser V, Guilbaud G (1996) Influence of timing of administration on the analgesic effect of bupivacaine infiltration in carrageenin-injected rats. Anesthesiology 84, 1129–1137. Ganley JV, Ganley TJ (1987) Peripheral nerve physiology and local anesthesia. J Am Podiatr Med Assoc 77, 329– 337. Gerner P, Mujtaba M, Sinnott CJ et al. (2001) Amitriptyline versus bupivacaine in rat sciatic nerve blockade. Anesthesiology 94, 661–667. Giaufre E, Dalens B, Gombert A (1996) Epidemiology and morbidity of regional anesthesia in children: a one-year prospective survey of the French-Language Society of Pediatric Anesthesiologists. Anesth Analg 83, 904– 912. Graf BM, Martin E (2001) Peripheral nerve block. An overview of new developments in an old technique. Anaesthesist 50, 312–322. Griffith JP, Whiteley S, Gough MJ (1996) Prospective randomized study of a new method of providing postoperative pain relief following femoropopliteal bypass. Br J Surg 83, 1735–1738. Haghighi SS, Kitchell RL, Johnson RD et al. (1991) Electrophysiologic studies of the cutaneous innervation of the pelvic limb of male dogs. Am J Vet Res 52, 352–362. Hamid SK, Scott NB, Sutcliffe NP et al. (1992) Continuous coeliac plexus blockade plus intermittent wound infiltration with bupivacaine following upper abdominal surgery: a double-blind randomised study. Acta Anaesthesiol Scand 36, 534–539. Hassan HG, Youssef H, Renck H (1993) Duration of experimental nerve block by combinations of local anaesthetic agents. Acta Anaesthesiol Scand 37, 70–74. Hellyer PW (1997) Management of acute and surgical pain. Semin Vet Med Surg (Small Anim) 12, 106–114. Hertl MC, Hagberg PK, Hunter DA et al. (1998) Intrafascicular injection of ammonium sulfate and bupivacaine

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time of hernia repair for post-operative pain relief. Br J Clin Pract 43, 281–283. Merriam JG, Finocchio EJ (1981) Protocol for differential diagnosis of diseases of the equine foot. Vet Med Small Anim Clin 76, 89–93. Moore DC, Bridenbaugh D, Bridenbaugh PO et al. (1970) Bupivacaine for peripheral nerve block: a comparison with mepivacaine, lidocaine, and tetracaine. Anesthesiology 32, 460–463. Moore DC, Bridenbaugh LD, Thompson GE et al. (1978) Bupivacaine: a review of 11,080 cases. Anesth Analg 57, 42–53. O’Connor BL, Woodbury P (1982) The primary articular nerves to the dog knee. J Anat 134, 563–572. Popitz-Bergez FA, Leeson S, Strichartz GR et al. (1995) Relation between functional deficit and intraneural local anesthetic during peripheral nerve block. A study in the rat sciatic nerve. Anesthesiology 83, 583– 592. Reinhart DJ, Wang W, Stagg KS et al. (1996) Postoperative analgesia after peripheral nerve block for podiatric surgery: clinical efficacy and chemical stability of lidocaine alone versus lidocaine plus clonidine. Anesth Analg 83, 760–765. Rice ASC, McMahon SB (1992) Peripheral nerve injury caused by injection needles used in regional anaesthesia: influence of bevel configuration, studied in a rat model. Br J Anaesth 69, 433–438. Ringrose NH, Cross MJ (1984) Femoral nerve block in knee joint surgery. Am J Sports Med 12, 398–402. Rygnestad T, Borchgrevink PC, Eide E (1997) Postoperative epidural infusion of morphine and bupivacaine is safe on surgical wards. Organisation of the treatment, effects and side-effects in 2000 consecutive patients. Acta Anaesthesiol Scand 41, 868–876. Selander D, Dhuner K-G, Lundborg G (1977) Peripheral nerve injury due to injection needles used for regional anesthesia. Acta Anaesthesiol Scand 21, 182–188. Selander D, Brattsand R, Lundborg G et al. (1979) Local anesthetics: importance of mode of application, concentration and adrenaline for the appearance of nerve lesions. An experimental study of axonal degeneration and barrier damage after intrafascicular injection or topical application of bupivacaine (Marcain). Acta Anaesthesiol Scand 23, 127–136. Sethna N (1998) Regional anesthesia and analgesia. Semin Perinatol 22, 380–389. Shulman M, Lubenow TR, Nath HA et al. (1998) Nerve blocks with 5% butamben suspension for the treatment of chronic pain syndromes. Reg Anesth Pain Med 23, 395–401. Tetzlaff JE (2000) The pharmacology of local anesthetics. Anesthesiol Clin North America 18, 217–233. The Local Anesthetics for Neuralgia Study Group (1994) A surgically implantable nerve irrigation system for intermittent delivery of dissolved drugs: evaluation of

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long-term performance and histocompatibility in rats. J Pharmacol Toxicol Methods 31, 221–232. Thurmon JC, Tranquilli WJ, Benson GJ (eds) (1996) Lumb and Jones’ Veterinary Anesthesia (3rd edn). Lea & Febiger, Baltimore, MD, USA. Tobias JD (1994) Continuous femoral nerve block to provide analgesia following femur fracture in a paediatric ICU population. Anaesth Intensive Care 22, 616–618. de Visme V (1998) Peripheral blocks of the lower limb for repair of fractured neck of femur. Br J Anaesth 81, 483– 484. de Visme V, Picart F, Le Jouan R et al. (2000) Combined lumbar and sacral plexus block compared with plain bupivacaine spinal anesthesia for hip fractures in the elderly. Reg Anesth Pain Med 25, 158–162.

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Wildsmith JA (1986) Peripheral nerve and local anaesthetic drugs. Br J Anaesth 58, 692–700. Winnie AP, Ramamurthy S, Durrani Z (1973) The inguinal paravascular technic of lumbar plexus anesthesia: the 3-in-1 block. Anesth Analg 52, 989–996. Woolf CJ (1983) Evidence for a central component of postinjury pain hypersensitivity. Nature 308, 686–688. Woolf CJ, Chong MS (1993) Preemptive analgesia – treating postoperative pain by preventing the establishment of central sensitization. Anesth Analg 77, 362– 379. Received 25 July 2003; accepted 1 February 2004.

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