20526121, 2022, 2, Downloaded from https://bvajournals.onlinelibrary.wiley.com/doi/10.1002/vrc2.308 by Consorci De Serveis Universitaris De Catalunya, Wiley Online Library on [25/11/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Received: 11 May 2021 Revised: 29 October 2021 Accepted: 27 January 2022 DOI: 10.1002/vrc2.308 CASE REPORT Companion or pet animals Continuous mandibular nerve block as sole analgesia for postoperative pain management after a hemimandibulectomy in a French Bulldog Adrià Aguilar-Catalan Laura Fresno Bermejo Pamela J. Murison 1 Hospital Clínic Veterinari, Universitat Autònoma Abstract de Barcelona, Bellaterra, Barcelona, Spain A 12-year-old French Bulldog presented for a mandibulectomy due to a large ameloblas- 2 University of Glasgow School of Veterinary toma in the left rostral mandibular body. Preoperative pain management consisted of Medicine, Glasgow, UK methadone 0.2 mg/kg and a mandibular nerve block with ropivacaine 0.5%. Intraopera- Correspondence tively, an indwelling perineural catheter was placed through the mandibular canal, with Adrià Aguilar-Catalan, Hospital Clínic Veterinari, the tip placed in the mandibular foramen for postoperative ropivacaine administration. Universitat Autònoma de Barcelona, Campus Ropivacaine 0.2% was administered every 6 hours for the first 36 hours without need Bellaterra, 08193 Bellaterra, Barcelona, Spain. Email: adria.aguilar@uab.cat of any systemic analgesic administration, providing adequate analgesia and allowing for a rapid recovery. The dog was completely alert and responsive in the immediate post- operative period and started eating 12 hours after surgery without any sign of pain or discomfort. No complications were observed during the postoperative period. The per- ineural catheter was removed after 40 hours and the dog was administered metamizole every 8 hours for analgesia and was discharged 48 hours after surgery. BACKGROUND of pre-, intra- and postoperative analgesia because of their high analgesic efficacy.3,4 Opioids are usually combined with Brachycephalic dogs are predisposed to several conditions, NSAIDs, used to treat postoperative pain and inflammation such as upper airway obstruction, respiratory compromise, by inhibition of the cyclooxygenase (COX) enzymes 1 and 2.5 gastrointestinal abnormalities and ocular problems, that Peripheral nerve blocks, using local anaesthetics, have proven increase the anaesthetic-related complications both during a vital component of a multimodal analgesia approach. Single- the peri-anaesthetic management and in the postoperative shot peripheral nerve blocks may then be used for intraopera- period, increasing hospitalisation stays.1 In brachycephalic tive and immediate postoperative pain management in which breeds, it is crucial to achieve a fast recovery, avoiding exces- postoperative pain may not last longer that 12–24 hours.6,7 If sive sedation or muscle relaxation, which will allow the longer postoperative pain is expected, the use of continuous animal to maintain airway patency and protect against aspi- peripheral nerve blocks (cPNB) using a perineural catheter ration of gastric fluids.1 At the same time, it is vital to achieve is a highly recommended adjunct or substitute to systemic good pain control, as this can help minimise complications drugs to improve pain management.7 The mandibular nerve, by promoting earlier ambulation and normal physiological a branch of the trigeminal (fifth cranial nerve), provides sen- functions.1 Similarly, geriatric patients may have decreased sory fibres to the hard and soft tissues of the mandible and metabolic compensatory mechanisms, decreased respiratory motor fibres to the masticator and mylohyoid muscles.8 Vari- and cardiovascular function and altered body composition, ous local anaesthetic techniques involving different branches which may predispose them to a higher anaesthetic risk of the mandibular nerve have been described to achieve anal- and longer recovery times.2 Special considerations such as a gesia in specific locations of the mandible.6,8 However, to decreased gastrointestinal transit time, which may increase achieve complete desensitisation of the mandible, a proxi- the risk of regurgitation, decreased drug metabolism and mal mandibular nerve block, including the blockade of the increased risk of hypothermia and hypoxia, increases the mylohyoid, the lingual and the inferior alveolar nerves, is risk of intra- and postoperative complications.2 Whenever reported to be the best approach.6,8 In human medicine, possible, local and regional anaesthesia should be used in cPNB of the mandibular nerve in patients with orofacial can- these patients to allow for a fast anaesthetic recovery from cer pain or mandibular fractures has been described.9–11 In anaesthesia and increased hospital length stay.2 veterinary medicine, a continuous mandibular nerve block Postoperative analgesia is often based on the administration using an epidural catheter placed in the mandibular canal of opioids, non-steroidal anti-inflammatory drugs (NSAIDs) has been reported in an alpaca.12 Postoperative cPNB may and local anaesthetics. Opioids are considered a cornerstone then be used in an effort to reduce opioid use and decrease This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2022 The Authors. Veterinary Record Case Reports published by John Wiley & Sons Ltd on behalf of British Veterinary Association. Vet Rec Case Rep. 2022;10:e308. wileyonlinelibrary.com/journal/vrc2  of  https://doi.org/10.1002/vrc2.308 20526121, 2022, 2, Downloaded from https://bvajournals.onlinelibrary.wiley.com/doi/10.1002/vrc2.308 by Consorci De Serveis Universitaris De Catalunya, Wiley Online Library on [25/11/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License  of  Veterinary Record Case Reports or exclude opioid-associated adverse effects,12,13 especially in patients that may benefit from a rapid recovery. LEARNING POINTS/TAKE-HOME MESSAGES The present case report describes the postoperative pain management using a perineural indwelling catheter in the ∙ The use of a continuous peripheral nerve block mandibular canal as the only method for analgesia adminis- allowed for a rapid recovery after anaesthesia with tration in a rostral hemimandibulectomy in a geriatric French a rapid functional recuperation. Bulldog. ∙ Local anaesthetic administration through perineu- ral catheters may be used as a sole postoperative means of pain management in certain patients. CASE PRESENTATION ∙ Pain scoring is mandatory if a continuous periph- eral nerve block is used to avoid inadequate pain A 12 year-old, 14-kg, neutered, male French Bulldog presented control. to the surgery department in the Hospital Clínic Veterinari, ∙ No complications were observed due to the per- Universitat Autònoma de Barcelona, with a large mass in the ineural catheter or ropivacaine administration. left cranial mandibular body with occasional bleeding. The mass had been diagnosed previously by biopsy as an odon- togenic ameloblastoma. The dog presented with inappetence and weight loss. Previous medical history includes a hemil- aminectomy due to intervertebral disc disease at the age of 6 years. At the age of 9 years, the dog underwent an orchidec- tomy due to a seminoma. Additionally, when the animal was 11 years old, a urethrostomy was performed due to urinary obstruction. TREATMENT The dog was accepted for general anaesthesia, imaging inves- tigation and surgery. On the day of anaesthesia, the physical examination showed a poor body condition (body condition score of 3 out of 9) and referred upper airway stertor auscultated in all F I G U R E  Computed tomography image of the odontogenic lung fields. The dog was aggressive, and did not allow any ameloblastoma manipulation without sedation. Haematology revealed a mild decrease in haematocrit (33%), a decrease in erythrocytes liative approach. After owner’s consent, the animal was pre- count (5.3 M/μl) and a decrease in haemoglobin concentration pared for surgery. (12.1 g/dl) with an increase in the platelet count (576,000/μl). Before surgery, a 22 G arterial catheter was placed in the The biochemistry was normal. right dorsal pedal artery for invasive arterial blood pressure The dog received omeprazole (1 mg/kg) and maropitant monitoring. (1 mg/kg) the day before surgery. Once clipped and aseptically prepared, a proximal Preanaesthetic medication consisted of acepromazine mandibular nerve block using a nerve locator was performed.6 (0.025 mg/kg) and methadone (0.3 mg/kg) intramuscularly Anatomic landmarks for the nerve location were the caudo- (IM). Twenty minutes after preanaesthetic medication, the ventral aspect of the zygomatic arch and the temporo- sedation was considered sufficient, and a 20 G over-the- mandibular joint. A 21-gauge, 40 mm stimulating needle needle catheter was placed in the left cephalic vein. As a was inserted rostral to the temporomandibular joint in a difficult intubation was suspected, the dog was preoxygenated caudo-rostral direction. The stimulating current was set at for 5 minutes before induction, which was accomplished 1 mA. The needle was advanced until the contraction of the with 2 mg/kg intravenous (IV) propofol. Intubation was digastricus, pterygoideus and the masseter muscles, as well as successfully performed with a 6-mm internal diameter cuffed movement of the jaw were elicited. The stimulating current endotracheal tube and the dog was connected to a circle was then reduced, and the local anaesthetic was delivered rebreathing system. Anaesthesia was maintained with isoflu- when no stimulation was elicited at 0.3 mA. The mandibular rane in 100% oxygen (0.7–1 L/min). Monitoring consisted of nerve block was accomplished with 0.5 mg/kg ropivacaine electrocardiography, capnography, oscillometric noninvasive 1% (0.7 ml) diluted with water for injection to a final con- blood pressure, pulse oximetry and oesophageal temperature. centration of ropivacaine 0.5% and a total volume of 1.4 ml. On the computed tomography (CT), a large mass was Cefazoline (25 mg/kg IV) was administered before surgery. observed occupying the mid to rostral part of the left Fluid therapy was started with lactated Ringer’s solution at mandibular body with severe osteolysis and bone destruc- 5 ml/kg/h. Surgery lasted for 120 minutes. Anaesthesia started tion (Figure 1). However, the caudal part of the mandible uneventfully, heart rate was between 130 and 140 beats per body appeared intact with no signs of mass infiltra- minute, respiratory rate was from 15 to 25 breaths per minute tion or osteolysis. As the tumour had defined margins and mean arterial blood pressure (MAP) was maintained and was not invading nearby structures, a left rostral between 65 and 75 mmHg. Fifty minutes after the start of hemimandibulectomy was considered rather than a more pal- surgery, blood pressure gradually decreased over 10 minutes 20526121, 2022, 2, Downloaded from https://bvajournals.onlinelibrary.wiley.com/doi/10.1002/vrc2.308 by Consorci De Serveis Universitaris De Catalunya, Wiley Online Library on [25/11/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Veterinary Record Case Reports  of  scoring was then performed by the first author (AdriàAguilar- Catalan) 2 hours postoperatively, and again every 4 hours after for the first 12 hours. All scores were between 1 and 2 out of 24 with no requirement for rescue analgesia during the first hours after surgery. All physical examinations were normal, and the dog remained comfortable with no signs of pain or discomfort during the night. Moreover, the dog’s behaviour improved, allowing surgical site palpation and wound clean- ing with no signs of aggression. OUTCOME AND FOLLOW-UP Twelve hours after the end of surgery, the dog started eating. Pain scoring was continued every 12 hours, with no increase in the pain scoring at any evaluation time. The cephalic IV F I G U R E  Computed tomography image of the catheter placed after catheter was removed 16 hours after surgery as the dog was the rostral hemimandibulectomy. (a) Diffusion catheter entering the eating and drinking, with no signs of discomfort. Metami- mandibular canal. (b) Entrance of the mandibular canal in the mandibular remnant. (c) Mandibular ramus zole (25 mg/kg PO every 8 hours) was started 24 hours after surgery. All physical examinations remained normal during the first day. from a MAP of 68 to 54 mmHg, and heart rate increased Ropivacaine instillation was stopped 32 hours after surgery. to 146 beats per minute. As haemorrhage was deemed Pain scoring was performed at 8:00 AM (40 hours after significant, blood loss was estimated to be 340 ml at that surgery) with a score of 1/24. Omeprazole and maropitant time and a crystalloid bolus (20 ml/kg administered over were stopped and metamizole (25 mg/kg PO) was continued 20 minutes) together with hypertonic saline (2 ml/kg bolus every 8 hours. As pain scores were low, the perineural catheter in 15 minutes) were administered. This resolved hypotension, was removed and the dog was discharged in the afternoon, increasing MAP to pretreatment values and decreasing heart 48 hours after surgery. Ambulatory treatment consisted of rate to 115 beats per minute. From that point, anaesthesia prednisone 1 mg/kg PO every 24 hours for 2 days, followed by was uneventful. During surgery, the dog received methyl- a decreasing dose protocol, metamizole (25 mg/kg PO every prednisolone (1 mg/kg IV), and a second dose of cefazoline 12 hours) was continued for 2 days and amoxicillin-clavulanic (25 mg/kg). acid (22 mg/kg PO every 12 hours) was continued up to 10 days After the mandibulectomy, a perineural diffusion catheter postoperatively. was introduced through the mandibular canal. A 16 G, 30 cm long polyurethane catheter was used, with a 10 cm dispersion area with micropores. The mandibular canal was identified DISCUSSION by the surgeon at the rostral end of the mandibular remnant and the catheter was introduced through it in a rostro-caudal The present case report describes the use of a perineural dif- direction. The catheter was advanced until the tip was sensed fusion catheter placed in the mandibular canal during surgery by palpation exiting through the mandibular foramen in the for postoperative pain control. To the authors’ knowledge, this mandibular ramus. The 10 cm dispersion area was observed is the first report of a perineural catheter as the sole postoper- to be all within the mandibular canal. Once in place, the ros- ative analgesia after a mandibulectomy in a dog. tral end of the catheter was tunnelled subcutaneously to the Mandibulectomies are considered severely painful surgi- ventral and rostral remaining part of the mandible. The exter- cal procedures, which often need high doses of systemic nal part of the diffusion catheter was then turned caudally, analgesics, such as pure μ agonist opioids, increasing the and its distal end was sutured to the skin of the neck with a risk of side effects associated with these drugs. The use Roman sandal tie, allowing for local anaesthesia to be admin- of local and regional anaesthesia produces numerous ben- istered safely during the postoperative period. After the per- efits, such as reduced opioid use, fewer opioid-related side ineural catheter placement, the surgical incision was closed. A effects, reduced length of hospital stay, faster rehabilitation postoperative CT was performed to confirm the catheter posi- and patient satisfaction in human beings.7,14 Local anaesthet- tion passing through the mandibular canal, emerging from ics reversibly block voltage-gated sodium channels in the neu- the mandibular foramen (Figure 2). An Elizabethan collar was rons to reduce excitability. The transmission of noxious stim- used as the animal was aggressive, and to avoid dislodging or uli to the spinal cord and brain is prevented, thus providing accidentally distracting the perineural catheter. analgesia.15 Mandibular nerve block can be used to improve Anaesthetic recovery was uneventful. Postoperative treat- pain management and increase quality of life in patients with ment consisted of methylprednisolone (1 mg/kg IV every mandibular fractures or tumours.6,9–12 24 hours), amoxicillin-clavulanic acid (22 mg/kg IV every The animal described in this case report was a brachy- 8 hours), maropitant (1 mg/kg SC every 24 hours) and cephalic geriatric dog with inappetence and weight loss. Due omeprazole (1 mg/kg IV every 12 hours). Analgesia was to the dog’s condition, our main objective was to enhance accomplished with 0.3 mg/kg of ropivacaine 0.2% (0.15 ml/kg the recovery and promote a fast return to normal function and a total volume of 2.1 ml) through the catheter every by providing adequate pain management and avoiding exces- 6 hours. Once recovered, the dog was pain scored using the sive postoperative sedation. cPNBs using indwelling perineu- Glasgow Composite Pain Scale - Short Form (GCPS-SF). Pain ral catheters for pain management in mandibular fractures 20526121, 2022, 2, Downloaded from https://bvajournals.onlinelibrary.wiley.com/doi/10.1002/vrc2.308 by Consorci De Serveis Universitaris De Catalunya, Wiley Online Library on [25/11/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License  of  Veterinary Record Case Reports and cancer pain have been described in human medicine with lodgement, leakage, disconnection, irritation or allergic reac- good results.9–11 In veterinary medicine, Stathopoulou et al. tions, as well as inaccurate tip placement, infections, cardio- reported the management of a mandibular body fracture in vascular and central nervous system local anaesthetic toxicity an alpaca with cPNB.12 In that case report, an alpaca pre- and neurological complications such as nerve injury.14 Specific sented with a mandibular body fracture due to a dental root mandibular block complications include diplopia, tempo- abscess. Pain was not controlled with the use of buprenor- rary loss of vision, ophthalmoplegia, ptosis, mydriasis and phine and meloxicam according to the alpaca’s clinical appear- periorbital blanching.12 However, in the present case, no com- ance. To improve pain management, an epidural catheter was plications were observed neither during placement nor during placed under CT guidance for an inferior alveolar nerve block. the postoperative management of the perineural catheter. The epidural catheter was introduced through the mandibu- Ropivacaine was chosen as the local anaesthetic agent in lar foramen in a caudo-rostral direction until the tip of the this case. Several reasons were considered when choosing catheter lay in the mandibular canal. One millilitre of ropi- ropivacaine as the analgesic agent. Ropivacaine has a long vacaine 0.75% was administered every 6 hours and systemic duration of action, longer than lidocaine and similar to bupi- analgesics were discontinued. After catheter placement and vacaine, ranging from 180 to 480 minutes in the dog. How- ropivacaine administration, the alpaca seemed brighter and ever, ropivacaine analgesia has been reported to last up to more responsive, and started eating. The catheter was left in 10 hours in a mandibular block in a dog, so a longer interval place for 10 days and no complications due to the catheter between administrations may be possible.7 Ropivacaine also placement were observed. However, after sedation for wound shows increased cardiovascular and nervous system safety debridement, the alpaca became distressed and dysphagic, profile with less accumulation.22,23 This feature is especially and an aspiration pneumonia was suspected. Euthanasia was important in cPNB as repeated doses of the drug are adminis- performed due to the guarded prognosis of the case.12 There- tered over time so increased plasma concentrations of the drug fore, although euthanasia was performed due to the poor may reach toxic concentrations. Finally, ropivacaine shows a prognosis and continuing disease processes, the placement of greater degree of differential block than other local anaesthet- a perineural indwelling catheter in the mandibular canal for ics due to its decreased lipophilicity when compared to other the intermittent administration of local anaesthetic was con- local anaesthetics. Ropivacaine is less likely to penetrate, and sidered an excellent way to provide analgesia, avoiding sys- therefore to block, large, myelinated fibres such as motor Aβ temic analgesia administration. fibres. This may be beneficial in the case of nerves with sensory Benefits of cPNB include a direct analgesic effect by and motor fibres such as the mandibular nerve,22,23 which is blocking the transmission of pain from the affected area, important in masticatory muscle movement. allowing for a dramatic decrease in supplemental opioid Local anaesthetic administration may cause nerve injury, therapy and a decrease in opioid-related side effects as well via mechanical, ischaemic or chemical factors. Nerve injury as enhanced postoperative recovery.12,14 Opioids have been may lead to neurological deficits that tend to be transient. associated with multiple adverse effects, such as sedation, Mechanical or ischemic damage could occur with pressure on nausea, vomiting, respiratory depression and urinary reten- nerves or on the blood vessels supplying those nerves. Direct tion as well as opioid-induced hyperalgesia, in both human neurotoxicity is thought to be related to the physicochemi- and veterinary medicine,16,17 and may prolong recovery and cal properties of local anaesthetics, composition, the concen- return to normal function in patients with previous physio- tration of local anaesthetic administered and the duration of logical decline in organ functions or in their mechanisms of the administration; however, the cellular mechanisms lead- compensation.2,18 Therefore, in this brachycephalic geriatric ing to the nerve damage are still not clear.15,24 A low con- dog, it was considered best to avoid potential opioid adverse centration of ropivacaine was used in the present case report, effects by using local anaesthetic perineural administra- as it is the usual ropivacaine concentration used by the first tion and to reserve opioid analgesics as rescue analgesia if author in postoperative nerve blocks. Low concentration of needed. Due to this dog’s temperament, it was considered local anaesthetics is thought to reduce local anaesthetic nerve that avoiding opioids would help in encouraging activity and damage.12 This low concentration was effective to provide avoiding ileus/decreased gut activity to allow a rapid return analgesia, probably due to the proximity of the catheter to the to normal function (in order to be able to discharge the dog mandibular nerve. In Stathopoulou et al., 1 ml of ropivacaine to the owner’s care). NSAIDs also provide good analgesia for 0.75% was administered every day for 10 days in an alpaca, postoperative inflammatory pain without sedation or delayed with no abnormal postmortem mandibular nerve histopatho- recovery, but they may increase the risk of gastrointestinal, logical findings observed.12 Thus, the lower ropivacaine con- renal or liver complications.5 Moreover, NSAIDs could not centrations and shorter duration of use in the present case be used in the present case as corticosteroids were being report are not expected to have caused any nerve damage. administered concurrently.5,19 Therefore, it was decided to Using a low concentration of drug enabled a larger volume administer 0.3 mg/kg ropivacaine 0.2% every 6 hours and of ropivacaine to be used, which may have been beneficial to to pain score the animal using GCPS-SF intermittently. No ensure adequate spread along the mandibular nerve. additional systemic analgesics were required during the first During surgery, hypotension developed, associated with 24 hours after surgery. Administration of metamizole, a COX active haemorrhage due to the mass resection. Bleeding was 3 inhibitor and endogenous opioid and endocannabinoid assessed by looking at the surgery drapes and swabs, as well system activator,20 was started before discharge to provide as the amount of blood in the suction container.25 The total ambulatory analgesia. The timing ensured adequate onset amount was considered to be 340 ml approximately, which before perineural catheter removal.20,21 accounted for nearly 30% of the dog’s estimated circulatory cPNB catheters are not without complications. The com- volume. Blood products were not available immediately, so plications reported in the literature include obstruction, dis- an initial bolus of crystalloids and hypertonic saline 7.5% 20526121, 2022, 2, Downloaded from https://bvajournals.onlinelibrary.wiley.com/doi/10.1002/vrc2.308 by Consorci De Serveis Universitaris De Catalunya, Wiley Online Library on [25/11/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Veterinary Record Case Reports  of  were administered. Hypertonic saline produces a greater 10. Hammond D, Olaore S, Mangesh S, Gallaway E. Catheter-based local volume expansion than the volume administered and has analgesia for the fractured mandible of a patient with history of heredi- tary angioedema. J Surg Case Rep. 2019;5:rjz126. been recommended in animals for initial management of 11. Singh B, Bhardwaj V. Continuous mandibular nerve block for pain relief. haemorrhage.26 In the present case, fluid therapy improved A report of two cases. Can J Anesth. 2002;49:951–3. cardiovascular variables and transfusion was withheld in 12. Stathopoulou T, Seymour C, McSloy A, Adams J, Viscasillas J. Pain man- case of further intraoperative blood loss or postoperative agement of a mandibular fracture in an alpaca (Vicugna pacos) via epidu- decreased blood volume were observed. ral catheter placement in the mandibular foramen. Vet Rec Case Rep. 2019;7:e000863. In conclusion, the administration of 0.3 mg/kg ropivacaine 13. Richman JM, Liu SS, Courpas G, Wong R, Rowlingson AJ, McGready 0.2% (total volume 2.1 ml) every 6 hours through a perineural J, et al. Does continuous peripheral nerve block provide superior indwelling catheter placed in the mandibular canal to block pain control to opioids? A meta-analysis. 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