Anesthetic management in a free-ranging crab-eating fox (Cerdocyon thous) with splenic rupture - case reportABSTRACT
The crab-eating fox (Cerdocyon thous) is a medium-sized mammal found throughout South America, known for its adaptability to diverse environments and a varied diet. Recently, habitat loss and increased encounters with roadways have led to a rise in road traffic accidents involving this species, resulting in significant trauma such as splenic rupture. This report details the anesthetic management of a free-ranging crab-eating fox with splenic rupture following a road traffic accident. The patient, an adult male weighing 6.6 kg, presented with hypotension and pale mucous membranes. Initial chemical restraint was administered using tiletamine-zolazepam and morphine. An abdominal ultrasound revealed splenic rupture with active hemorrhage and a systolic arterial pressure (SAP) of 60 mmHg. Immediate fluid resuscitation was initiated, but the patient remained hypotensive. A transversus abdominis plane (TAP) block was performed with bupivacaine and lidocaine, which significantly reduced the need for isoflurane. The splenorrhaphy was performed, and the patient's condition improved with fluid therapy, dobutamine infusion, and reduced isoflurane concentration. Postoperatively, SAP stabilized, and urinary output was within normal ranges, indicating no acute renal injury. This case highlights the TAP block's effectiveness in managing pain and stabilizing hemodynamics, underscoring the need for tailored anesthetic approaches in wildlife trauma.
Keywords:
hypotension; splenorrhaphy; trauma; hemorrhagic shock; transversus abdominis plane block
RESUMO
O cachorro-do-mato (Cerdocyon thous) é um mamífero de médio porte da América do Sul, conhecido por sua adaptabilidade e dieta variada. Com o aumento dos acidentes de trânsito devido à perda de habitat, traumas como a ruptura esplênica tornaram-se comuns. Este relatório descreve o manejo anestésico de um cachorro-do-mato livre com ruptura esplênica após um acidente. O paciente, um macho adulto de 6,6kg, apresentou hipotensão e mucosas pálidas. Foi realizada contenção química com tiletamina-zolazepam e morfina, e a ultrassonografia revelou ruptura esplênica com hemorragia ativa e PAS de 60mmHg. A ressuscitação volêmica foi iniciada, mas a hipotensão persistiu. Um bloqueio do plano transverso do abdome (TAP) com bupivacaína e lidocaína reduziu a necessidade de isoflurano. A esplenorrafia foi realizada, e a condição do paciente melhorou com fluidos, infusão de dobutamina e redução de isoflurano. No pós-operatório, a PAS estabilizou e a produção urinária estava normal, sem lesão renal aguda. O caso demonstra a eficácia do bloqueio TAP na dor e na estabilização hemodinâmica, enfatizando a necessidade de abordagens anestésicas adaptadas para a vida selvagem.
Palavras-chave:
hipotensão; esplenorrafia; trauma; choque hemorrágico; bloqueio do plano do transverso abdominal
INTRODUCTION
The crab-eating fox (Cerdocyon thous) is a medium-sized mammal belonging to the Canidae family, characterized by dense fur with coloration ranging from gray to brown (Ramos Jr et al., 2003). It is found in various regions of South America and is known for its adaptability to different environments, including dense forests, open areas, and savannas (Courtney and Maffei, 2004). Its diet is varied, including fruits, insects, small vertebrates, and carrion, reflecting its generalist habits (Pedó et al., 2006).
In recent years, habitat loss due to agricultural expansion, deforestation, and urbanization has forced these animals to encroach increasingly upon urban areas and roadways, resulting in a significant rise in road traffic accidents involving this species (Forman et al., 2003). The study by Navas-Suarez et al. demonstrated that the crab-eating fox ranks second among species most frequently involved in road traffic accidents. Generally, road traffic accidents are responsible for a high incidence of trauma in wildlife, with splenic rupture being a common injury in such events (Navas-Suárez et al., 2022).
Splenic rupture can lead to severe consequences, including hypotension due to blood loss, acute kidney injury from hypoperfusion, and hemorrhagic shock, which can result in death if not properly managed (Edwards et al., 2021). Hypotension, or low blood pressure, compromises the perfusion of vital organs, while acute kidney injury can progress to renal failure, impairing the kidneys' ability to eliminate bodily waste (Davis et al., 2022).
Anesthetic management for splenorrhaphy in wildlife requires a meticulous approach to maintain hemodynamic stability. The transversus abdominis plane (TAP) block has proven effective for analgesia in abdominal surgeries, reducing the need for general anesthetics such as isoflurane, especially in cases of trauma that compromise circulation (Turan et al., 2022). This is the first report describing the application of the TAP block in a crab-eating fox, highlighting its potential benefit for analgesia and anesthetic management in this species.
Given these data, it is imperative to deepen the understanding and refine the veterinary care techniques specific to this species, aiming to optimize prognosis and increase survival rates in cases of road traffic trauma. However, to date, there are no records in the literature documenting the anesthetic approach for splenic rupture in this species. In this context, the present work aims to report the anesthetic technique employed in a crab-eating fox with splenic rupture, contributing to the development of therapeutic strategies for wildlife victims of trauma.
CASUISTRY
A free-ranging crab-eating fox (Cerdocyon thous) was received at the Superintendence University Veterinary Hospital Unit of de Federal University of Fronteira Sul with a history of recent road traffic accident. The patient, an adult male weighing 6.6 kg, presented pale mucous membranes and a heart rate of 184 beats per minute (bpm). For evaluation and diagnostic testing, chemical restraint was administered using tiletamine-zolazepam (Zoletil® 50,Virbac, São Paulo, Brazil; 8mg/kg, IM) and morphine (Dimorf®, Cristália, São Paulo, Brazil; 0.4mg/kg, IM). Approximately 15 minutes post-administration, venous access was established in the cephalic vein.
An abdominal focused assessment with sonography for trauma (AFAST) was performed, revealing splenic rupture with active hemorrhage. Systolic arterial pressure (SAP), measured using a Doppler ultrasound device (DV 610, Medmega, São Paulo, Brazil) was 60 mmHg. To address hypotension, a fluid bolus of lactated Ringer's solution was administered at a rate of 10 mL/kg/hour for 10 minutes. Post-fluid bolus, the SAP increased to 65 mmHg, although the patient remained hypotensive.
The patient was promptly referred to the surgical center for splenorrhaphy and was classified as American Society of Anesthesiologists (ASA) physical status 4E. No additional doses of premedicates or anesthetic induction agents were required. Antibiotic prophylaxis was administered with cephalothin (Cefariston®, Blau, São Paulo, Brazil; 25mg/kg, IV). A laryngoscope was used for direct visualization during endotracheal intubation with a 5.5-mm internal diameter endotracheal tube. General anesthesia was maintained with isoflurane (Isoforine®, Cristália, São Paulo, Brazil) administered in oxygen via an out-of-circle precision vaporizer integrated with a circle-breathing system. Additionally, lactated Ringer's solution was administered at a rate of 5.0 mL/kg/hour (IV).
Physiological parameters were monitored using a multiparameter monitor (RMZ1200vet, RZVet, São Paulo, Brazil) to record peripheral oxygen saturation of hemoglobin, end-tidal carbon dioxide, isoflurane concentration, esophageal temperature, and electrocardiogram (ECG). Indirect systolic arterial pressure was assessed using Doppler sphygmomanometry.
Following the setup of monitoring equipment and abdominal antisepsis, an ultrasound-guided (M-TURBO; Sonosite Inc, Bothell, WA) transversus abdominis plane (TAP) block was performed using 0.2 mL/kg of bupivacaine and 0.2 mL/kg of lidocaine. A linear ultrasound transducer (HFL 36x/13-6 MHz) was positioned perpendicular to the longitudinal axis to enable visualization of the abdominal muscles.
A 20-gauge, 6.25-cm spinal needle was inserted into the muscular plane until reaching the fascia between the internal abdominal oblique and transversus abdominis muscles. The needle tip was positioned in the fascial plane at the midpoint between the lower edge of the last rib and the iliac crest. Hydrodissection of the fascial plane confirmed correct needle placement and the anesthetic was injected while monitoring drug spread (Fig. 1). The block was performed bilaterally.
Transversus abdominis plane block illustrating the hydrodissection of the facial plane between the internal oblique and transversus abdominis muscles in an adult male crab-eating fox (Cerdocyon thous) with splenic rupture, submitted to splenorrhaphy. EO = External oblique muscle. IO = Internal oblique muscle. TA = Transversus abdominis muscle. TAP = Transversus abdominis plane. LA = Local anesthetic.
Post-TAP block, the patient was positioned in dorsal recumbency for the surgical procedure. Splenorrhaphy was performed over a total surgical time of 40 minutes, successfully controlling the hemorrhage in 20 minutes. At this time, SAP was recorded at 60 mmHg, and the heart rate was 150 bpm.
Hypotension was observed upon the animal’s admission to the hospital. In addition to spleen hemorrhage, hypotension may have been exacerbated by sympathetic blockade. This sympathetic blockade is likely attributable to the use of isoflurane, an inhaled anesthetic known to cause vasodilation and reduce sympathetic outflow. Initially, a fluid bolus of lactated Ringer's solution was administered. During surgery, the animal remained hypotensive with a SAP of 50 mmHg. After controlling the hemorrhage, a dobutamine (Dobutamine Hydrochloride, Minas Gerais, Brazil) infusion was initiated at 5μg/kg/min and the vaporizer setting was reduced from 1.2% to 0.3%. SAP showed minimal improvement, reaching 60 mmHg after 15 minutes. The dobutamine infusion rate was then increased to 10μg/kg/min, and the vaporizer setting was reduced to 0%. A considerable increase in SAP was noted 5 minutes later, with a SAP of 80 mmHg.
During the postoperative period, Ringer's solution was administered at a rate of 5 mL/kg/hour. Urinary output (UO) was monitored periodically at 1-hour intervals, while systolic arterial pressure (SAP) and heart rate (HR) were monitored every 5 minutes until full recovery of physiological parameters and consciousness. In the first postoperative hour, UO was 1.1 mL/kg/hour, and SAP increased to 90 mmHg, leading to a reduction in the dobutamine infusion rate to 5 μg/kg/min. In the subsequent hour, SAP increased to 110 mmHg with a UO of 1.5 mL/kg/hour. During the third postoperative hour, SAP decreased to 90 mmHg, prompting an increase in the dobutamine infusion rate to 10 μg/kg/min, and UO was 1.06 mL/kg/hour. In the following hour, UO remained at 1.06 mL/kg/hour, and SAP increased to 110 mmHg. The dobutamine infusion rate was then reduced by 2μg/kg/min each hour, with continuous SAP monitoring, and discontinued 3 hours later when SAP reached 130 mmHg, coinciding with the patient's recovery of consciousness. Thereafter, SAP did not exhibit significant variations.
DISCUSSION
Hemorrhagic shock, characterized by significant blood loss, can lead to a drastic reduction in circulating blood volume, thereby decreasing cardiac output and systemic blood pressure. The clinical signs observed, including pale mucous membranes and low systolic arterial pressure (SAP), are consistent with hypovolemic shock secondary to severe hemorrhage (Edwards et al., 2021).
In this case, maintaining general anesthesia with isoflurane was essential to ensure an adequate surgical plane and may have contributed to the hypotensive state. Isoflurane causes dose-dependent cardiovascular depression, leading to hypotension. It decreases systemic vascular resistance and myocardial contractility, which can exacerbate preexisting hypotension in patients with significant blood loss (Picker et al., 2001).
The TAP block played a crucial role in managing the patient’s condition, providing effective regional anesthesia, which significantly reduced the need for inhalant anesthetics. This approach was beneficial in this case, as it allowed for a decrease in the isoflurane vaporizer setting, ultimately leading to an improvement in the patient's SAP. During the surgical procedure, the patient was maintained with minimal isoflurane, and at certain points, isoflurane was entirely discontinued, highlighting the efficacy of the TAP block in providing sufficient analgesia (Espadas-González et al., 2022).
During the postoperative period, systolic arterial pressure (SAP) was closely monitored to ensure adequate tissue perfusion. Administration of lactated Ringer's solution and frequent adjustments in the dobutamine infusion rate were essential for stabilizing the patient's condition. Urinary output (UO) was monitored to assess renal function and detect any potential acute kidney injury resulting from severe hypotension (Davis et al., 2022). Normal urinary output ranges from 1 to 2 mL/kg/hour; values lower than 0.08 mL/kg/hour indicate anuria, and oliguria is defined as urinary output below 0.27 mL/kg/hour (Shaw and Ihle, 1997). Since the UO consistently remained within the normal range throughout the monitoring period, it indicates that the patient did not sustain any renal injury due to the hypotension.
CONCLUSIONS
In conclusion, the hypotension observed in this crab-eating fox was primarily due to hemorrhagic hypovolemic shock from splenic rupture, compounded by the cardiovascular depressant effects of isoflurane. The implementation of a TAP block provided effective analgesia, allowing for a reduction in isoflurane concentration and contributing to hemodynamic stabilization. This case highlights the critical need for comprehensive anesthetic management strategies, including the use of regional anesthesia and vigilant monitoring, to optimize patient outcomes in veterinary trauma cases.
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Publication Dates
-
Publication in this collection
28 Apr 2025 -
Date of issue
May-Jun 2025
History
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Received
09 Sept 2024 -
Accepted
26 Nov 2024
