Ultrasound-guided sciatic nerve block in Wistar rat cadavers: Relevant anatomy and injection distribution

OBJECTIVE

To investigate the feasibility of an ultrasound-guided sciatic nerve block by describing the sonoanatomy and comparing the distribution of two volumes of bupivacaine dye solution for nerve staining.

STUDY DESIGN

Randomized, experimental, assessor-blinded cadaveric study.

ANIMALS

A total of 40 adult female Wistar rat cadavers.

METHODS

After studying the sonoanatomy of the sciatic nerve and adjacent structures using a high-resolution linear transducer (19-5 MHz), rat cadavers were randomly divided into two groups that were administered either 0.1 mL (group 0.1) or 0.2 mL (group 0.2) of bupivacaine dye solution per nerve, delivered via an in-plane technique. The extent of nerve staining was subsequently evaluated following dissection. Statistical analysis consisted of assessing data distribution using the Shapiro-Wilk test, followed by paired t-tests for continuous data, Mann-Whitney U test and McNemar's test for categorical data. Statistical significance was defined as p < 0.05.

RESULTS

The sciatic nerve was identified bilaterally as a double ellipsoid-shaped image, surrounded by a hyperechoic fascia separating the biceps femoris from the adductor muscle. The hypoechoic structure formed by the bupivacaine dye solution around the nerve was effectively visualized using ultrasound imaging. Sciatic nerve staining was successfully achieved in all pelvic limbs, with dye spread of 4.82 ± 1.55 mm and 5.47 ± 2.18 mm in groups 0.1 and 0.2, respectively (p = 0.128).

CONCLUSIONS AND CLINICAL RELEVANCE

This study achieved a detailed understanding of the sonoanatomy of the sciatic nerve and its adjacent structures, highlighting the feasibility of the ultrasound-guided technique for injection in Wistar rats. Furthermore, the results show a comparable distribution of dye solution in both groups. Use of the ultrasound-guided sciatic nerve block technique in rats not only exhibits substantial potential for regional anesthesia but also opens avenues for translational studies.

Regional anesthesia for dentistry and oral surgery

Pain is a perception that results from activation of a specific set of receptors by noxious stimuli. Processing by the central nervous system results in the stimulus to be perceived as pain. Thermal receptors respond to temperature changes, mechanoreceptors respond to pressure, tension, stretch, and chemoreceptors respond to substances released during the inflammatory process such as prostaglandins, histamine, serotonin, and bradykinin. The current standard of veterinary medical practice is adequate pain management for all patients. Regional anesthesia is one component of overall pain management of the oral surgery/dental patient and is described step-by-step.

Local and regional anesthetic and analgesic techniques in the dog and cat: Part II, Infiltration and nerve blocks

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Regional anesthesia of the infraorbital and inferior alveolar nerves during noninvasive tooth pulp stimulation in halothane-anesthetized cats

OBJECTIVE

To determine whether anesthesia of the infraorbital and inferior alveolar nerves abolishes reflex-evoked muscle action potentials (REMP) during tooth-pulp stimulation in halothane-anesthetized cats.

ANIMALS

8 healthy adult cats.

PROCEDURE

In halothane-anesthetized cats, an anodal electrode was attached to the tooth to be stimulated and a platinum needle cathodal electrode was inserted in adjacent gingival mucosa. Cathodal and anodal electrodes were moved to the upper and lower canine, upper fourth premolar, and lower first molar teeth for stimulation; baseline REMP was recorded. A 25-gauge 1-cm needle was inserted 0.5 cm into the infraorbital canal. A 25-gauge 1-cm needle was inserted 1 cm rostral to the angular process of the ramus, and advanced 0.5 cm along the medial aspect. Chloroprocaine was injected at each site. Each tooth was stimulated every 10 minutes for 90 minutes.

RESULTS

REMP was abolished within 10 minutes for all upper teeth, except for the upper canine tooth in 1 cat, and abolished within 10 minutes for lower teeth in 4 cats. In 1 cat, REMP was not abolished in the lower first molar tooth. In 3 cats, REMP was not abolished in the lower canine and first molar teeth. At 90 minutes, REMP was restored for all teeth except the lower canine tooth in 1 cat, for which REMP was restored at 120 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Regional anesthesia of the infraorbital and inferior alveolar nerves may provide dental analgesia in cats.

Local and regional anesthesia

Local anesthetics have the unique ability to produce complete blockade of sensory nerve fibers and prevent or pre-empt the development of secondary (central) sensitization to pain. For this reason, local and regional anesthetic techniques are often used with opioids, alpha 2-receptor agonists, dissociatives, and anti-inflammatory drugs as part of a multimodal strategy to manage pain. Lidocaine and bupivacaine are the local anesthetics used most commonly in dogs and cats. Lidocaine has a fast onset (10-15 min) and an intermediate duration of action (60-120 min), and is used for short diagnostic and surgical procedures. Bupivacaine has a slow onset (20-30 min) and a long duration of action (240-360 min), and is used to control pain both preoperatively and postoperatively. Local anesthetics are relatively safe if they are administered correctly. Administration of an excessive dose and accidental intravenous administration are probably the most common causes of systemic toxicity in small animals. Doses of local anesthetics, especially those for cats and small dogs, should always be calculated carefully. In many animals, the most simple and elegant way to control pain perioperatively is to perform a local or regional anesthetic block. Veterinarians should not hesitate to incorporate local and regional anesthetic techniques into their pain management strategies for dogs and cats.

Intravenous regional anesthesia (Bier block) in a dog

Intravenous regional anesthesia was used in an adult dog as part of a balanced approach to general anesthesia for amputation of the 4th digit of its right hind limb. It allowed the concentration of isoflurane to be reduced to 0.5%.

Regional anesthesia of the infraorbital and inferior alveolar nerves during noninvasive tooth pulp stimulation in halothane-anesthetized dogs

OBJECTIVE

To document that regional anesthesia of the infraorbital and inferior alveolar nerves would abolish reflex-evoked muscle action potentials (REMP) in the digastricus muscle during noninvasive stimulation of tooth pulp in halothane-anesthetized dogs.

DESIGN

Prospective study.

ANIMALS

9 healthy female dogs between 2 and 6 years old.

PROCEDURE

Dogs were anesthetized using halothane. An alligator clip anodal electrode was attached to the tooth to be stimulated, and a platinum needle cathodal electrode was inserted in adjacent gingival mucosa. The cathodal and anodal electrodes were moved to the left upper and lower canine, fourth premolar, and first molar teeth for sequential stimulation. Baseline recording of REMP was made for each tooth. Catheters were inserted percutaneously in the infraorbital and mandibular canals. Saline (0.9% NaCl) solution was injected at each catheterized site in 3 control dogs, and chloroprocaine hydrochloride was injected at each catheterized site in 6 test dogs. Each tooth was stimulated every 10 minutes for 90 minutes (test dogs) or every 10 minutes for 30 minutes and at 90 minutes (control dogs), and REMP was recorded.

RESULTS

REMP was abolished within 10 minutes in all test dogs, except during stimulation of the lower first molar in 1 dog. In 4 dogs, duration of blockade was less than 90 minutes. The REMP was not restored within 90 minutes for the upper teeth in 1 dog and within 2 hours for all teeth in another dog. At 24 hours, REMP was restored for all teeth except the lower left canine in 1 dog. The REMP was restored for the lower left canine in that dog at 96 hours. The REMP was not abolished at any time in control dogs.

CLINICAL IMPLICATIONS

Regional anesthesia of the infraorbital and inferior alveolar nerves may effectively provide analgesia for dental procedures in dogs.

Local and regional anesthesia and analgesia

Many benefits can be obtained from the use of drugs applied locally or regionally when treating dogs and cats that are in pain or will be in pain because of surgical trauma. These techniques often use less medication than for systemic administration with a reduction in the likelihood of toxic effects from these compounds. Complete relief of pain can be achieved by blocking nerves originating from the site of injury by using local anesthetics, but this may entail loss of all sensation and motor paralysis. Other drugs, such as the opioids, may decrease the nociceptive input with minimal effect on motor activity. This report discusses the use of local anesthetics and other drugs for analgesia of the skin, mucous membranes, joints, pleura, and peritoneum, and the application of these drugs for regional blocks of peripheral nerves and epidural/intrathecal injection.

Local and regional anesthesia in ruminants and swine

This article reviews the use of popular local and regional anesthetic and analgesic techniques for surgical anesthesia and postoperative analgesia in cattle, sheep, goats, and pigs. The emphasis is on proper technique, the use of a 2% lidocaine hydrochloride solution, and the epidural administration of alpha 2-adrenoceptor agonists and opioids for producing intra- and postoperative analgesia in ruminants and swine while preserving consciousness and minimizing side effects.

Innervation and anesthesia of the antler pedicle in wapiti and fallow deer

The heads from 6 mature male wapiti and 8 mature male fallow deer were dissected to provide a description of the nerves supplying the antler pedicles. Innervation in both species was found to resemble that of the red deer, with major contributions coming from the infratrochlear and zygomaticotemporal nerves. All heads displayed a dorsal branch from the auriculopalpebral nerve, but in only 2 wapiti and 3 fallow deer heads was this branch observed travelling to the pedicle. The dorsal branches of the 2nd cervical nerve were isolated in each head but could not be traced to the pedicles. Failure to induce anesthesia of the antler employing specific nerve blocks on the infratrochlear and zygomaticotemporal nerves can occur if the dorsal branch of the auriculopalpebral nerve is not blocked.

Radiological appearance of air introduced during equine regional limb anaesthesia

Twelve horses were injected intra-articularly into the metacarpophalangeal joint and extra-articularly in the region of the lateral palmar digital nerve with 1 ml air and local anaesthetic to simulate gas accidentally introduced during regional anaesthesia. Half the horses underwent limited exercise after which all horses were radiographed at 15 and 45 min and then every 24 h until all evidence of gas had disappeared. Intra-articular gas appeared as gas capped radiolucencies (GCR) in the proximal aspect of the joint. Extra-articular gas appeared as linear radiolucencies (LR) which initially tended to migrate proximally. There was no significant difference in gas resorption in exercised and nonexercised horses. All gas was resorbed within 96 h with most of the gas already gone at 48 h.

[Blood serum and milk serum levels of sodium benzylpenicillin after intravenous regional antibiosis in surgery of the claw area in cattle]

An intravenous regional antibiosis using 10 Mega I.U. Sodium-Benzylpenicillin was carried out during surgery in 14 dairy cows affected with spontaneous occurring digital diseases. Blood serum and milk serum levels were determined over a period of 48 hours by means of a micro agar diffusion method using Sarcina lutea Stamm BGA Berlin as a test germ. Even before opening of the rubber tourniquet, penicillin traces were detectable in the blood serum of 6 cows. Maximal concentrations ranging from 0.43 mcg/ml to 8.63 mcg/ml were determined after 45 minutes to 4 hours. 24 hours after intravenous regional antibiosis no levels above the limit of detectability were determined. Significant lower maximal concentrations were found in claw amputation cases as compared with claw preserving surgical interventions. Milk serum levels showed delayed and lower maximal concentrations, ranging between 2.09 and 0.09 mcg/ml. In 5 animals no positive levels were detected. After 48 hours, penicillin levels were below the limit of detectability in the milk of all examined animals.

Perineural and spinal anesthesia

Local and regional anesthetic techniques are useful tools for the equine practitioner. These techniques allow surgery to be performed without the risk and cost of general anesthesia. There are, however, risks associated with the local and regional techniques. Neurotoxicity, although rare, may occur when 200 mL or more of a local anesthetic are infiltrated in a short period of time to a 450-kg horse. More likely, horses may become ataxic after nerve blockade in the limbs. This ataxia may lead to self trauma because the horse may not know where the limbs are actually being placed. Although local and regional anesthesia may not always be easy to achieve, persistence and practice will result in consistent nerve blockade.

Standing surgical procedures of the foot

Several surgical conditions affecting the foot can be successfully managed with the horse standing. Many factors affect the clinician's choice of whether to perform surgery with the horse standing or anesthetized. Temperament or pregnancy of the horse and economics may influence the decision to perform surgery with the horse standing. This article discusses several foot conditions that can be treated successfully in the ambulatory horse.

Standing laser surgery of the head and neck

The use of carbon dioxide and Nd:YAG lasers has expanded the capabilities of equine surgeons. These lasers are used to incise, vaporize, and coagulate tissue with minimal hemorrhage and reduced morbidity to the patient. In this article, practical fundamentals of laser surgery are briefly reviewed, and selected standing laser procedures of the head and neck are discussed.

Ophthalmic procedures and surgery in the standing horse

Although many ophthalmic procedures can be performed on the standing horse, the decision to perform a procedure under sedation rather than general anesthesia must be made on the basis of the temperament of the horse, severity of the injury, and skill of the veterinarian. For example, veterinarians who are not comfortable with small suture material may find accurate repair of an eyelid laceration easier after general anesthesia rather than attempting to handle this suture in a moving patient. Correct use of nerve blocks and topical anesthesia will greatly facilitate examination, diagnosis, and treatment, and, in addition, will serve to prevent further damage to the eye during these procedures.

Studies on intravenous regional analgesia of the hind limb in the bovine

Twenty-five buffalo calves (age: 14 +/- 1.9 months; body weight: 102 +/- 9.4 kg) were subjected to intravenous regional analgesia (IRA) of the hind limb with 2% lignocaine HCl (4 mg/kg b.w.), infused through the dorsal digital vein. In control animals 15 ml of normal saline was infused. The effect of tourniquet release after 35 (8 calves) and 65 min (7 calves) on EEG, ECG, arterial and venous pressures, blood gases and pH, respiration and temperature were studied. A detectable concentration of lignocaine occurred before the release of tourniquet. The lignocaine concentration recorded in the systemic circulation did not produce any significant nervous or cardiovascular changes before or after release of tourniquet. Transient EEG and ECG changes were seen in six (tourniquet release after 35 min) and three (tourniquet release after 65 min) IRA animals, respectively. No significant changes were seen in heart rate, respiratory rate and rectal temperature, systolic, diastolic, mean arterial and central venous pressures. Arterial blood pH, PCO2 and HCO3- concentration showed no significant differences. Animals receiving IRA did not show hypoxaemia typical to postural changes.

Regional anesthesia

Organ toxicity from local anesthetic agents is rare. This makes these agents an attractive option in the high-risk patient. Complications associated with local anesthetics are related to overdosage. Overdosage with local anesthetic agents administered epidurally may cause motor paralysis and hind-limb weakness. Systemic signs of local anesthetic overdosage include changes in central nervous system activity (excitement or depression), muscle tremors, and hypotension. Because the dose required to produce these effects in the horse is high (12 mg/kg), this complication is uncommon. Few side effects and low cost justify the use of local anesthetic techniques in equine practice.

Problems associated with the interpretation of the results of regional and intra-articular anaesthesia in the horse

The difficulties associated with the interpretation of the results of regional and intra-articular anaesthesia are discussed with reference to eight lame horses. The clinical and radiographic features of each horse are described, together with the results of anaesthesia. One horse had clinical and radiographic signs consistent with navicular disease but it was not possible to relieve the lameness. Two horses had fractures of bones within the foot but lameness was not improved by palmar (abaxial sesamoid) nerve blocks. One horse had more than one cause of lameness. Four horses had joint pathology but none responded to intra-articular anaesthesia.

Observations following intravenous xylazine administration in steers

Xylazine was used on 84 occasions to anaesthetise 34 steers, (17 Herefords and 17 Friesians) between 10 and 24 months of age with bodyweights ranging from 209 to 563 kg. Xylazine as a 2 per cent solution was injected intravenously; the mean dose for the Hereford steers was 0.228 mg/kg and for the Friesian steers 0.274 mg/kg. On 21 occasions xylazine only was used. On the other occasions the xylazine was supplemented with local or regional analgesia. The Hereford steers became recumbent after injection of xylazine more readily than the Friesian steers and took longer to recover. In addition the Hereford steers showed fewer reactions to surgical stimulation than the Friesians. It is concluded that xylazine should be supplemented with some form of effective analgesia whenever a surgical operation is performed.

Anesthesia for cesarean section in the dog and cat

Anesthesia for cesarean section should ideally provide adequate muscle relaxation, analgesia, and narcosis or sedation for optimal operating conditions and safety to the dam. Since drugs that depress the dam must cross the blood-brain barrier, however, it is impossible to anesthetize the dam and not expose the fetuses to the anesthetic. No one agent or protocol is ideal for all dams, and satisfactory anesthesia for cesarean section can be induced in a number of ways. Cesarean section can be performed with either regional or general anesthesia.

Transpalpebral exenteration in cattle

Description of a simple and fast surgical method and the necessary regional anesthesia for treatment of extensive global and orbital affections is given. The results of this transpalpebral exenteration procedure were highly satisfactory.

Intravenous regional analgesia for surgery of the limbs in goats

Intravenous regional analgesia (IVRA) has been achieved in twelve West African Dwarf (WAD) goats in a total of 35 trials with 2 per cent lidocaine hydrochloride without any significant complications. Experimental analgesia was effected 25 times on the limbs of seven goats. Analgesia was also produced 10 times on the limbs of five goats and a major orthopaedic procedure (amputation) performed on the anaesthetized limbs and digits. The analgesia produced was found to be adequate for the procedure. The comparative values of this method of regional analgesia are discussed.

Lidocaine concentrations associated with intravenous regional anesthesia of the distal limb of cattle

Cannulation for injection of lidocaine HCl was done in 3 distal veins in the hindlimb of 5 young Friesian cattle maintained in a light plane of general anesthesia. The local and systemic plasma and tibiotarsal joint synovial fluid concentrations of lidocaine (British lignocaine) were estimated for 60 minutes after the drug (10 ml, 2% (w/v)) was injected into the veins distal to a tourniquet. The lidocaine concentration in the distal veins was high but variable initially, and fell markedly over the 60 minutes. The systemic circulation always had a low but measurable concentration of lidocaine that became slightly higher in the 5 minutes after tourniquet release. According to the concentrations found, the risk of toxicity of lidocaine by using this technique in clinical practice would appear negligible.