Intercostal block in a rabbit undergoing exploratory thoracotomy - case reportABSTRACT
Rabbits stand out in challenging anesthesia, due to their smaller size and different anatomy. Thoracic surgery is challenging due to the mandatory tracheal intubation to maintain positive ventilation and its high level of pain. The intercostal block aims to control pain during the trans-operative and post-operative period, thus making it possible to maintain acceptable pain levels, reducing the use of general analgesics and providing a better quality of anesthetic recovery. The study aims to report a case of a rabbit, where for diagnosis and possible treatment she underwent exploratory thoracotomy and pain control was achieved through intercostal block with 2 mg/kg of lidocaine and 1 mg/kg of bupivacaine. The technique used was based on companion animals, where through palpation of the intercostal space, a needle is inserted, and the anesthetic is injected between the pleura and the intercostal muscle caudal to the rib. It proved to be effective in controlling trans-surgical and post-operative pain, as during evaluations and monitoring the animal showed no signs of pain.
Keywords:
anesthesia; surgery; pain; lagomorphs
RESUMO
Os coelhos se destacam em anestesias desafiadoras, devido ao seu menor tamanho e à sua anatomia diferente. A cirurgia torácica é desafiadora em razão da intubação traqueal obrigatória para manter a ventilação positiva e de seu alto nível de dor. O bloqueio intercostal visa controlar a dor durante os períodos transoperatório e pós-operatório, possibilitando, assim, a manutenção de níveis aceitáveis de dor, bem como reduzindo o uso de analgésicos gerais e proporcionando uma melhor qualidade de recuperação anestésica. Este estudo tem como objetivo relatar um caso de uma coelha, a qual, para diagnóstico e possível tratamento, foi submetida à toracotomia exploradora, e o controle da dor foi obtido por meio do bloqueio intercostal com 2mg/kg de lidocaína e 1mg/kg de bupivacaína. Trata-se de uma técnica utilizada baseada em animais de companhia, nos quais, por meio da palpação do espaço intercostal, uma agulha é inserida e o anestésico é injetado entre a pleura e o músculo intercostal caudal à costela. A técnica mostrou-se eficaz no controle da dor transcirúrgica e pós-operatória, pois, durante as avaliações e o monitoramento, o animal não apresentou sinais de dor.
Palavras-chave:
anestesia; cirurgia; dor; lagomorfos
INTRODUCTION
Among unconventional pets, rabbits, rodents, and other mammals have shown growth in Brazil, increasing from 2.6 million individuals in 2021 to 2.7 million in 2022, representing a 3.8% increase in just one year (ABINPET, 2024). Thus, the demand for specialized professionals to care for these animals has become necessary, as owners' lack of knowledge can lead to clinical complications, and issues considered mild in other species may pose potential life risks in rabbits (Szabo et al., 2016).
Rabbits have the same indications for anesthesia as dogs and cats, such as for imaging diagnostics, spaying/neutering, and surgical resections. Pre-anesthetic preparation requires laboratory tests, and when necessary, imaging exams that can identify subclinical changes, leading to the need for patient stabilization before the procedure (Longley, 2008; Szabo et al., 2016).
Pain is a process that must be evaluated. Behavioral changes may be associated with pain and chronic diseases, underscoring the need to understand species-specific behavior to identify pain. Surgeries are particularly traumatic procedures that generate high levels of pain, necessitating the use of analgesics in the anesthetic protocol (Johnston, 2005).
Sedation is a method for reducing stress during physical restraint, with ketamine being used for this purpose. Ketamine can serve as an adjunct to reduce the amount of general anesthetic used and modulate pain by antagonizing NMDA receptors, reducing the need for opioids, and offering an anti-hyperalgesic effect (Barter, 2011).
Ketamine doses can be adjusted depending on the procedure and the patient's temperament. Some doses reported in the literature range from 5-10mg/kg of ketamine combined with midazolam at 0.5-1mg/kg. Additionally, doses of 7-10mg/kg combined with midazolam are used for mild sedation, and 20 mg/kg intramuscularly for anesthetic induction and maintenance (Longley, 2008; Carpenter and Harms, 2022).
To achieve the ideal anesthetic plane for surgery, induction with halogenated anesthetics using an oxygen vaporizing mask becomes an easily performed technique in rabbits, unlike injectable anesthetics that must be carefully calculated for a safe dose. Propofol is one of the injectable drugs used for anesthetic induction, with a reported dose of 3mg/kg in the literature. Anesthesia maintenance can then be done with volatile or injectable anesthetics in continuous infusion (Longley, 2008; Mendes et al., 2022).
The use of local blocks has become popular for their effects in reducing the dose of general anesthetics, maintaining hemodynamic stability, and enhancing postoperative recovery quality. Local anesthetics work by interrupting nerve conduction through sodium channel blockades along the axonal neuron (D'Ovidio and Adami, 2019). An example is bupivacaine, indicated at a dose of 2mg/kg diluted in saline solution for thoracic analgesia, which can be delivered through a thoracic drain previously established to aid treatment (Szabo et al., 2016).
Thoracic surgeries in rabbits are more challenging than in dogs and cats, as rabbits have a smaller thorax and more delicate organs, requiring precise movements by the surgeon. The most common reasons for thoracotomies in rabbits include resection of neoplastic masses such as thymomas, pulmonary abscesses, lobectomies, and correction of lung lobe torsion. In these procedures, the loss of negative thoracic pressure during thoracotomy necessitates mechanical or assisted positive ventilation, along with tracheal intubation (Szabo et al., 2016, Aguilar et al., 2025).
To anesthetize the thoracic wall region where the surgical incision will be made, intercostal nerves can be blocked. The intercostal nerve is located between the parietal pleura and the intercostal muscle, and after exiting the paravertebral space, it divides into four motor and sensory branches. To block this nerve, a local anesthetic should be applied caudal to the rib, at a depth adequate to reach the space between the pleura and the intercostal muscle, as shown in Fig. 1. A nerve locator can be used as an auxiliary tool (Otero and Portela, 2017).
Anatomical representation of the thoracic wall, showing the location of the intercostal nerve and its cutaneous branches. Source: Otero and Portela, 2017.
Due to the lack of reports on intercostal blocks in rabbits, as well as anesthesia for thoracotomy, this study aims to report on the intercostal nerve block performed on a domestic Lion Head rabbit undergoing exploratory thoracotomy at the Veterinary Teaching Clinic of the State University of Central-West.
CASE REPORT
On July 19, 2023, a spayed female Lion Head rabbit, approximately nine years old and weighing 2.3kg, was brought in for treatment with a history of occasional sneezing and coughing. During the anamnesis, the owner reported that the rabbit lived with another male of the same species, both having free access to a yard with a garden during the day and kept in an outdoor enclosure at night. No changes were reported in the other animal.
During the physical examination, sensitivity was observed upon palpation of the initial portion of the esophagus/trachea, as well as respiratory muffling during thoracic auscultation on the left side. Radiography was recommended for a more precise assessment, but due to the cost, the owner opted for a trial of medicinal treatment without a definitive diagnosis. Thus, malt paste was prescribed to aid in eliminating hairballs and preventing trichobezoar formation, with a follow-up scheduled in 15 days.
At the follow-up visit, the owner reported complete improvement in sneezing after one week of treatment, but the physical evaluation showed worsening in lung sounds and respiratory effort, prompting another recommendation for radiography. This time, the owner agreed to the exam, which revealed a rightward displacement of the cardiac silhouette within the thoracic cavity, loss of cardiac silhouette contours, dorsal displacement of the trachea with preserved lumen, and marked increase in pulmonary parenchyma radiopacity in an alveolar pattern, most prominent in the left cranial lobe. The radiographic findings suggested left lung lobe torsion, with neoplasia as a differential diagnosis. Exploratory thoracotomy was recommended for diagnostic support.
The exploratory thoracotomy took place on August 16. During the pre-anesthetic physical exam, the patient presented a calm demeanor, heart rate (HR) around 200 bpm (beats per minute), respiratory rate (RR) of 60 rpm (respirations per minute), pale mucous membranes, and a capillary refill time (CRT) of 2.5 seconds. A blood sample was collected for lab tests, though only a small amount could be obtained, prioritizing hematocrit (30%) and total plasma proteins (7.9g/dL). The patient was classified as ASA IV regarding anesthetic risk.
After physical restraint, pre-anesthetic medication (PAM) was administered, consisting of ketamine (Cetamin©, ketamine, Syntec, Brazil; 20mg/kg, IM), midazolam (Dormonid®, midazolam maleate, União química faracêutica nacional s/a, Brazil; 0.6mg/kg, IM), morphine (Dimorf®, morphine sulfate pentahydrate, Cristália, Brazil; 2 mg/kg, IM), and xylazine (Xilazin®, xylazine hydrochloride, Syntec, Brazil; 0.5mg/kg, IM). Five minutes post-PAM, the animal was in deep sedation.
At this point, the patient exhibited respiratory difficulty and intense cyanosis, leading to oxygen supplementation and induction with isoflurane (Isoforine®, isoflurane, Cristália, Brazil) via mask. Orotracheal intubation was subsequently performed using a "blind" technique with a 2.5mm (internal diameter) tube without a cuff, as shown in Fig. 2. In the "blind" technique, locating the trachea and passing the tube can be challenging; however, in this case, intubation was successfully achieved.
Anesthetized Lion Head rabbit, in right lateral decubitus, positioned for intercostal nerve block and surgical procedures. Physiological monitoring includes electrocardiographic, blood pressure measurement, oxygen saturation, and esophageal temperature assessment. Source: The author.
Anesthetic maintenance was conducted with isoflurane in a calibrated vaporizer, ranging between 2.5V% and 3V% in a Baraka-type anesthetic circuit, with an oxygen flow rate of 2L/min and assisted ventilation maintained throughout the procedure. After catheterizing the left cephalic vein, fluid therapy was administered with Lactated Ringer’s solution at an infusion rate of 5mL/kg/h.
The intercostal block was performed using bupivacaine (Neocaína®, bupivacaine hydrochloride, Cristália, Brazil; 1mg/kg) and lidocaine (Xylestesin®, lidocaine hydrochloride, Cristália, Brazil; 2mg/kg) with a hypodermic needle (13x4.5), extending from the 3rd to the 8th intercostal spaces, as the surgical incision was made in the 5th intercostal space (Fig. 3).
During anesthetic maintenance, the following parameters were monitored: oxygen saturation (SpO2), heart rate (HR), respiratory rate (RR), electrocardiogram, non-invasive blood pressure (oscillometric method), and esophageal temperature. Oxygen saturation remained at 99%, HR varied between a maximum of 145 bpm and a minimum of 130 bpm, RR ranged from 8 to 14 rpm, esophageal temperature ranged from 39ºC to 37.8ºC, and blood pressure measured by the oscillometric method averaged 70mmHg. Monitoring was performed with a (Delta Life-DL1000®) multiparametric monitor.
Intercostal nerve block performed on a 2.3kg Lion Head rabbit for exploratory intercostal thoracotomy. (A) Delimitation and palpation of the intercostal spaces, preparation of the anesthetic solution in a 1mL syringe, and use of a 13x4.5 mm hypodermic needle. (B) Needle insertion and dispersion of the local anesthetic within the intercostal space. Source: The author.
After an hour and a half of anesthesia, the patient showed slow recovery, with a high level of sedation and remained with the orotracheal tube for another 30 minutes after stopping isoflurane, requiring 100% oxygen post-extubating during hospitalization.
During the procedure, enrofloxacin (Zoletril®, enrofloxacin, União química faracêutica nacional s/a, Brazil; 15mg/kg, IM), metoclopramide (Nausetrat©, metoclopramide hydrochloride, UCBVET, Brazil; 0.5mg/kg, IM), and dexamethasone (Dexaflan©, dexamethasone, Brazil; 1mg/kg, IM) were administered to provide antimicrobial protection, maintain peristaltic movement, and exert an anti-inflammatory effect, respectively.
Regarding the surgical procedure, the patient showed no significant lesions or lung lobe torsion, and a sample was taken for histopathological examination.
For analgesic rescue, butorphanol (Butorfin®, butorphanol tartrate, Vetnil, Brazil) was administered at a dose of 1 mg/kg every four hours via the subcutaneous route. However, the patient's condition deteriorated, resulting in death 12 hours after the procedure.
A necropsy was performed, revealing an enlarged right lung lobe, causing compression and displacement of the heart to the left side, as shown in Fig. 4. Upon incision, the mass displayed characteristics of a caseous abscess. A sample of the material was sent for histopathological examination, with a diagnosis of marked, multifocal, fibrinosuppurative bronchointerstitial pneumonia associated with bronchiectasis, featuring areas of pronounced abscess formation. However, identification of the causative bacterial agent was not possible due to sample fixation in formaldehyde.
Post-mortem necropsy images of a 2.3kg Lion Head rabbit, 12 hours after exploratory intercostal thoracotomy. (A) Anatomical structures of the thoracic and abdominal cavities. White arrow: heart. Black arrow: lung abscess occupying almost the entire thoracic cavity. Blue arrow: abdominal cavity. (B) Incised thoracic caseous abscess. Source: The author.
RESULTS AND DISCUSSION
Dissociative anesthetics are widely used in rabbits, often combined with tranquilizers or centrally acting muscle relaxants such as α-2 agonists. The doses indicated by Pessoa (2014) are 20-40mg/kg of ketamine and 1-5mg/kg of diazepam, differing from Longley (2008), who suggests doses of 5-10mg/kg of ketamine and 0.5-1mg/kg of midazolam. The dosages recommended by the latter author were similar to those used in the patient in this case report, with the aim of combining drugs to reduce doses and minimize adverse effects.
It is well known that orotracheal intubation in rabbits is challenging due to anatomical differences that hinder visualization of the glottis. Several orotracheal intubation techniques are described in the literature. Falcão et al. (2011) describes the “blind” orotracheal intubation technique, after esophageal cannulation with a 3.5 tube (3.5mm ID), followed by intubation with a 2.5 tube (2.5mm ID). Twelve rabbits were used in this study, demonstrating this technique as highly successful and easy to perform. In this case report, the “blind” technique was used without esophageal cannulation, showing some difficulty in locating the trachea but allowing for successful tube placement.
For intra- and postoperative analgesia for thoracotomy, Otero and Portela (2017) state that the intercostal block is limited to the thoracic wall, reaching the sternum, and thus requires additional analgesic support for adequate intraoperative pain control. The authors also note that the paravertebral block can affect spinal nerves, providing not only thoracic wall desensitization but also visceral analgesia.
Lidocaine is considered by Grimm et al. (2017) to be the most versatile and widely used local anesthetic in veterinary medicine, due to its desirable effects of rapid onset and moderate duration. Johnston (2005) recommends a maximum dose of 1.5mg/kg of bupivacaine and 2mg/kg of lidocaine for rabbits, which justifies the doses used in this case report. Barter (2011), on the other hand, reports that doses of 2mg/kg of lidocaine and 1mg/kg of bupivacaine are sufficient for performing an infiltrative block.
Thoracic surgeries are among the indications for intercostal block. Otero and Portela (2017) also recommend its use for pain control in rib fractures, such as those resulting from trauma. Barter (2011) suggests the use of butorphanol to help control pain in rabbits at a dose of 0.2 to 0.5mg/kg every 2 hours. Carpenter and Harms (2022), however, recommend a dose of 0.1 to 1mg/kg every 2-6 hours. The animal in this case was monitored, and during assessments showed no signs of pain, indicating that the butorphanol dose and interval used were effective for pain management.
Some authors, such as Le Campion et al. (2022), describe locoregional transverse abdominal plane blocks with ultrasound guidance. Mendes et al. (2022) also report maxillary nerve blocks for tooth extractions, demonstrating effectiveness in inhibiting pain transmission. Aguilar et al. (2025) describe the technique and comparison of ultrasound-guided intercostal nerve injection, demonstrating greater accuracy and lower risk of accidental pleural perforation compared to the blind approach. Thus, we observe the importance of local blocks in this species, as they improve the quality of pain control and contribute to a smooth anesthetic recovery.
CONCLUSION
It is concluded that intercostal block is a fast and effective technique for thoracic analgesia in thoracotomy surgery. It requires anatomical knowledge to perform, but it is a low-cost technique, as it uses few materials and equipment. It does not require the use of systemic analgesics, since it does not provide visceral analgesia.
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ABINPET: Associação Brasileira da Indústria de Produtos para Animais de Estimação. São Paulo, SP. ABINPET: c2024. Disponível em: https://abinpet.org.br/wpcontent/uploads/2024/03/abinpet_folder_dados_mercado_2024_draft2_web.pdf Acesso em: maio 2025.
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Publication Dates
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Publication in this collection
14 July 2025 -
Date of issue
Jul-Aug 2025
History
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Received
02 Dec 2024 -
Accepted
17 Feb 2025
