Ultrasound-guided quadratus lumborum block vs lumbosacral epidural anesthesia in cats undergoing ovariohysterectomy: a randomized pilot clinical trial

Abstract

Objectives

The aim of the present study was to compare analgesic and cardiopulmonary effects after bilateral ultrasound-guided quadratus lumborum block (QLB) and lumbosacral epidural (LsE) with levobupivacaine in cats undergoing ovariohysterectomy (OVH).

Methods

A prospective, randomized, blinded clinical trial was conducted. A total of 20 healthy female cats were allocated (1:1) to the LsE group (0.4 ml/kg 0.25% levobupivacaine) or the QLB group (0.3 ml/kg 0.25% levobupivacaine per hemiabdomen). Cats were premedicated with dexmedetomidine 3 µg/kg and meloxicam 0.1 mg/kg. Anesthesia was performed using propofol variable rate infusion (adjusted to clinical depth). Heart rate, respiratory rate, hemoglobin oxygen saturation, end-tidal carbon dioxide and systolic, mean and diastolic arterial pressures were recorded at seven standardized surgical time points. Postoperative pain (UNESP-Botucatu multidimensional composite pain scale) and sedation were assessed up to 6 h after surgery; methadone (0.25 mg/kg IM) was administered as rescue analgesia when indicated. Recovery milestones and mean propofol infusion rates were also compared. Data were analyzed using repeated measures ANOVA, unpaired t-tests or non-parametric tests, as appropriate (P <0.05).

Results

No significant between-group differences were detected for any cardiopulmonary variable (P >0.05), and no intraoperative rescue analgesia was required. Mean propofol infusion rates were similar (LsE 0.36 ± 0.07 vs QLB 0.39 ± 0.02 mg/kg/min; P = 0.0863). Postoperative pain scores did nor differ between groups. Only one cat in the QLB group required methadone at 6 h. Recovery milestones (extubation to standing: LsE 73 mins, QLB 79 mins; P = 0.4182) and sedation scores were comparable. No block-related complications or adverse events were observed.

Conclusions and relevance

Bilateral ultrasound-guided QLB with 0.25% levobupivacaine provided cardiopulmonary stability and early perioperative analgesic performance comparable to lumbosacral epidural anesthesia in cats premedicated with dexmedetomidine and meloxicam undergoing OVH, supporting its use as a clinical alternative, particularly when epidural access is contraindicated.

Keywords

Quadratus lumborum block epidural analgesia regional anesthesia levobupivacaine ovariohysterectomy

Introduction

Locoregional anesthetic and analgesic techniques continue to advance in veterinary anesthesiology. When integrated into multimodal protocols, they reduce anesthetic and analgesic requirements, provide antinociception, enhance cardiopulmonary stability and improve recovery quality, including earlier return to feeding and hospital discharge.^1,2

Epidural anesthesia-analgesia is a technique employed commonly in human anesthesia to provide optimum conditions for invasive orthopedic and soft tissue surgery. Its current use in small animals is comparatively less frequent.³ In small animals, the lumbosacral approach is considered more common than the sacrococcygeal approach,³ providing anesthesia, analgesia and motor block, with cranial spread proportional to the injected volume.^3–5 However, contraindications such as infection at the puncture site, sepsis, coagulopathy, pelvic malformations and hypovolemia may limit its use.^3,6

Ultrasound-guided locoregional anesthesia has enabled new peripheral nerve blocks as alternatives to epidural anesthesia.^7–9 Quadratus lumborum muscle block (QLB) involves the deposition of local anesthetic around the quadratus lumborum muscle, aiming to provide abdominal wall and visceral analgesia.^10–12 In human medicine, QLB is applied in procedures such as laparoscopy, intestinal resection, herniorrhaphy, cesarean section, nephrectomy, hip arthroplasty and hysterectomy.¹⁰ The small animal literature has expanded in recent years with studies involving QLB in various contexts, notably trials in cadaveric models.^12–17 In cats, a cadaveric study showed that ultrasound-guided injection of 0.4 ml/kg methylene blue in the quadratus lumborum plane stained the first to third lumbar (L1–L3) ventral roots, the sympathetic trunk from the 13th thoracic to the third lumbar vertebrae (T13–L3), the greater and lesser splanchnic nerves, the celiac ganglion and interfascial planes.¹⁶

Given the growing adoption of the QLB in veterinary medicine and the still limited, albeit increasing, body of in vivo clinical evidence in cats, it is essential to determine, in a standardized setting, how this technique compares with the traditional reference. Accordingly, this study aimed to compare bilateral ultrasound-guided QLB and lumbosacral epidural anesthesia (LsE) in female cats undergoing elective ovariohysterectomy (OVH) under propofol anesthesia, focusing on intraoperative cardiopulmonary variables and perioperative early analgesic performance. We hypothesized that ultrasound-guided QLB would provide cardiopulmonary stability and perioperative analgesic performance comparable to those achieved with LsE, without significant adverse effects.

Materials and methods

Animals and study groups

The protocol for this randomized, prospective, blinded pilot study was approved by the Ethics Committee of the School of Veterinary Medicine and Zootechny of the Federal University of Bahia (reference number 31/2024) and conducted at a university veterinary hospital between September 2023 and February 2024. The manuscript was prepared in accordance with Consolidated Standards of Reporting Trials (CONSORT) guidelines for randomized trials.¹⁸ Because directly comparable feline data for bilateral QLB and LsE using the same concentration of levobupivacaine were limited, a formal hypothesis-driven power calculation was not considered sufficiently justified. Therefore, a sample size of 10 cats per group was adopted as a pragmatic sample size for this pilot study, which was intended to provide preliminary estimates of variability and effect size for future confirmatory trials.

Before enrolment, eight animals were used for operator training and standardization of the QLB technique. Subsequently, 20 healthy adult female cats of unspecified breed were included in the study after written informed owner consent had been obtained. Cats were considered healthy based on clinical history, physical examination, complete blood count and serum biochemical profile. Exclusion criteria included indocile behavior, clinical signs of pain during preoperative assessment, pregnancy, age under 6 months or any health condition.

Each cat included in the clinical trial was assigned a number (1–20) according to the order of admission. Based on this number, the patient was assigned to one of the two groups, with a 1:1 ratio: LsE or QLB group, with 10 cats each. The randomization list was generated using a randomization plan generator (Research Randomizer, http://www.randomizer.org/). The cats were fasted on food and water for 8 h and 2 h, respectively. On the day of the experimental trial, the animals were transported to an air-conditioned preoperative room in individual cages, where they remained for at least 2 h, following cat-friendly guidelines for handling and manipulation.

Anesthetic protocol

All animals were premedicated with dexmedetomidine at a dose of 3 µg/kg (100 µg/ml IM, dexmedetomidine hydrochloride; Cristália) and meloxicam at a dose of 0.1 mg/kg (20 mg/ml SC, Maxicam; Ourofino). Once a satisfactory level of sedation had been achieved, the lumbosacral, ventral and lateral abdominal regions of all cats were clipped to ensure study masking, as well as the right cephalic vein, which was cannulated after local antisepsis. Fluid therapy was then started with lactated Ringer’s solution (Fresenius Kabi Brasil) at a rate of 5 ml/kg/h IV, using an infusion pump (Infusion Pump SK 600 IB; Mindray).

After 20 mins of sedation, the animals were pre-oxygenated for 2 mins and then induced into anesthesia with propofol (Propovan 10 mg/ml; Cristália) at a dose of 1 mg/kg every 10 s until satisfactory mandibular relaxation.¹⁹ Then 0.2 ml of lidocaine (Xylestesin 20 mg/ml; Cristália) was applied to the larynx. Subsequently, tracheal intubation was performed using an appropriate size endotracheal tube. Anesthesia was maintained with propofol variable rate infusion (initial rate 0.4 mg/kg/min) delivered by an infusion pump (Injectomat MC Agilia; Fresenius Kabi). Cats received 100% oxygen at a flow rate of 200 ml/kg/min via a respiratory system without gas rebreathing and were permitted to breathe spontaneously.

Blocking techniques

All animals were stabilized on a light anesthetic plane (presence of anal reflex and digit pinching). Cats in the LsE group were placed in the sternal decubitus position, with the pelvic limbs extended cranially. After antisepsis, the lumbosacral epidural space was punctured with a 22 G spinal needle (Tuohy Unilever; Unisis) inserted slowly at a 90° angle to the skin in midline and advanced until the ligamentum flavum.^5,20 Then 0.25% levobupivacaine, without vasoconstrictor (NOVabupi 2.5 mg/ml; Cristália), was administered in a dose of 1 mg/kg (0.4 ml/kg) for 45 s. The correct location of the epidural space was confirmed by the absence of reflux of the cerebrospinal fluid and resistance to injection, sequential relaxation of the anal sphincter, and the absence of reflex responses in the perineal region and pelvic limbs.²⁰ After injecting the local anesthetic, the animal was kept in the sternal decubitus position for 20 mins.

The animals in the QLB group were placed in the right lateral decubitus position. For the ultrasound-guided QLB, a 10 MHz linear transducer (5–12 MHz/ L746; SonoScape) from a veterinary ultrasound system (SonoScape A5V; SonoScape) was positioned perpendicular to the spine, under the space of the transverse process of second lumbar vertebra (L2).¹⁷ A 22 G, 80 mm echogenic needle (Unilever; Unisis) was introduced into the interfascial plane between the quadratus lumborum and psoas minor muscles at the level of the L2 with ventrodorsal needling. Then 0.75 mg/kg (0.3 ml/kg) of 0.25% levobupivacaine (NOVabupi 2.5 mg/ml; Cristália) was administered and the sonographic hydrodissection of the interfacial plane was visualized in real time, confirming the correct deposition of local anesthetic. An interval of 10 mins was observed to establish the blockade. The animal was then placed in the left lateral decubitus position and the same procedure was performed in the contralateral hemiabdomen.

A total average time of 30 mins was established for the performance of epidural anesthesia (LsE) and bilateral QLBs.

If signs of correct epidural analgesia or adequate hydrodissection were not observed during execution of the LsE and QLB techniques, the animals were excluded from the study.

Surgery and intraoperative monitoring

The animals were placed in dorsal decubitus on an active thermal mattress and subjected to elective OVH. The rate of continuous propofol infusion was adjusted during the intraoperative period to allow for an adequate anesthetic-surgical plan, according to an assessment of reflexes and physiological variables.¹⁹ After any change, the same infusion rate was maintained for 10 mins before further adjustments.

Cardiopulmonary parameters were monitored continuously using a multiparameter monitor (Lifewindow LW9xVet; Digicare Animal Health). Recorded variables included heart rate (HR), respiratory rate (ƒ_R), end-tidal carbon dioxide (Pe’CO₂), hemoglobin oxygen saturation (SpO₂) and oscillometric arterial blood pressures (systolic [SAP], diastolic [DAP] and mean [MAP]). Data were specifically documented at seven time points: immediately before skin incision (T1); at the end of celiotomy (T2); after clamping the right (T3) and left (T4) ovarian pedicles; after uterine cervix clamping (T5); and at the start of muscle (T6) and skin (T7) sutures.

During surgery, if necessary, 2.5 µg/kg of fentanyl (Fentanest 0.05 mg/ml; Cristália) was given as rescue analgesia in the event of an increase in ƒ_R, HR and MAP above 20% in relation to T1 values, accompanied by an absence of eyelid reflex, absence of mandibular tone or purposeful movement.⁷ Throughout the procedure, the temperature of the animals was kept between 37°C and 38°C. The same team performed all anesthetic and surgical procedures. At this stage, the two surgeons and the single anesthesiologist involved in intraoperative procedures were blinded to the allocated treatment protocol.

Postoperative assessment

The anesthesia recovery time was defined as the interval between the end of the anesthesia supply and extubation (TA), the first head movement (TB), sternal positioning (TC) and quadrupedal positioning (TD), expressed in minutes.

Animals were assessed for pain using the UNESP-Botucatu multidimensional composite pain scale (MCPS),²¹ in which scores are in the range of 0–27, with higher scores indicating greater pain intensity. The scale is based on the evaluation of specific behaviors, posture, attitude and responses to physical contact. Owing to the difficulty of measuring blood pressure in non-anesthetized and/or sedated cats,²² this parameter was not included in the postoperative assessment (subscale 3 – physiological variables). Each cat was initially observed inside the cage without disturbance. Assessments were then performed in the following order: respiratory rate (breaths/min), determined by observing thoracic wall movements; and after opening the cage, heart rate (beats/min) was measured by thoracic auscultation using a stethoscope. Thereafter, the animal was gently handled, offered a small amount of food, and its behavior and posture were evaluated to assign the UNESP-Botucatu MCPS score. Animals with a pain score greater than 6/27 at each assessment time point received methadone (0.25 mg/kg IM, MYTedom 10 mg/ml; Cristália) as rescue analgesia.

The degree of sedation was assessed and scored as follows: fully alert and able to walk (0); alert but ataxic and unable to walk (1); drowsy, occasionally agitated (2); and drowsy (3).²³ Evaluation time points were 0.5, 1, 1.5, 2, 3, 4 and 6 h postoperatively. At this stage, pain assessment was performed by two evaluators trained in the UNESP-Botucatu MCPS, both of whom were blinded to the allocated treatment protocols. At the end of the experimental period, all animals were treated with dipyrone (25 mg/kg IM, Novalgina 500 mg/ml; Sanofi-Aventis). Animals that did not receive rescue analgesia were also treated with tramadol hydrochloride (2 mg/kg IM, Tramadon 50 mg/ml; Cristália).^24,25

Throughout the experiment, the animals were monitored for possible complications associated with the lumbosacral epidural technique, including failed or insufficient block, inadvertent vascular puncture, local anesthetic toxicity, hypotension, urinary retention and respiratory depression. Animals were also monitored for possible complications related to the QLB, including failed or insufficient block, inadvertent vascular puncture, local anesthetic toxicity, hematoma formation and direct needle trauma to adjacent soft tissues or abdominal structures.^3,5

Statistical analysis

Statistical analysis was performed using GraphPad Prism version 8 software. The Shapiro–Wilk test was used to assess the normality of the variables. Variations over time and between groups were analyzed using two-way repeated measures ANOVA, followed by the Bonferroni post-hoc test for multiple comparisons at each time point. The unpaired t-test was used for parametric variables between groups at single time points, while the Mann–Whitney U-test was used for non-parametric variables. Results with normal distribution were presented as mean ± SD, while sedation scores were presented as median and interquartile range. Postoperative pain scores were presented as mean ± SD. The occurrence of intraoperative or postoperative rescue analgesia and adverse events was assessed descriptively. The level of statistical significance was set at P <0.05.

Results

A total of 32 cats were previously selected. Of these, four were excluded because of indocile behavior and inability to be handled by the veterinarian team. Eight animals were considered pilots for the training curve to standardize the anesthetic volume and perform the QLB technique. Therefore, the final study population consisted of 20 cats distributed in two groups of equal numbers (Figure 1).

Age, animal weight, and average surgical and anesthetic times did not differ between treatments. The rate of propofol did not vary with time and the mean propofol infusion rate was not affected by treatment (Table 1).

Table 1

Comparison of the results of perioperative data between cats that underwent ovariohysterectomy with lumbosacral epidural anesthesia (LsE) or quadratus lumborum block (QLB)

Perioperative data	LsE	QLB	P value
Age (months)	8.5 ± 2.7	8.4 ± 2.0	0.5845
Weight (kg)	2.71 ± 0.4	3.0 ± 0.5	0.1768
Duration of surgery (mins)	27.2 ± 3.3	23.7 ± 4.3	0.2288
Duration of anesthesia (mins)	61.7 ± 7.4	59.6 ± 9.43	0.3741
Mean propofol infusion rate (mg/kg/min)	0.36 ± 0.07	0.39 ± 0.02	0.0863

Data are mean ± SD

All the LsE and QLB injections were successful. No complications related to the techniques and local anesthetic were observed in either group.

Table 2 shows the evolution of the cardiopulmonary variables for each treatment. There were no significant differences in HR, SAP, MAP, DAP, ƒ_R, SpO₂ and Pe’CO₂ between the LsE and QLB groups (P >0.05). None of the LsE and QLB animals required rescue analgesia during intraoperative intervals.

Table 2

Intraoperative values of heart rate (HR), systolic arterial pressure (SAP), mean arterial pressure (MAP) and diastolic arterial pressure (DAP), respiratory rate (ƒ_R), oxyhemoglobin saturation (SpO₂) and end-tidal carbon dioxide (Pe’CO₂) of cats treated with lumbosacral epidural anesthesia (LsE) or quadratus lumborum block (QLB), under propofol anesthesia, at intraoperative time points (T1–T7*)

Variables	Groups	T1	T2	T3	T4	T5	T6	T7	P value
HR (beats/min)	QLB	128 ± 16	134 ± 21	151 ± 20	158 ± 21	154 ± 21	150 ± 18	144 ± 22	0.6331
HR (beats/min)	LsE	122 ± 13	133 ± 26	156 ± 17	162 ± 20	154 ± 19	155 ± 14	155 ± 18	0.6331
SAP (mmHg)	QLB	136 ± 15	109 ± 19	132 ± 29	138 ± 25	144 ± 16	134 ± 15	127 ± 13	0.8583
SAP (mmHg)	LsE	132 ± 12	109 ± 16	141 ± 27	145 ± 24	140 ± 18	135 ± 16	135 ± 15	0.8583
MAP (mmHg)	QLB	114 ± 11	89 ± 12	101 ± 15	103 ± 16	105 ± 10	101 ± 11	97 ± 7	0.5439
MAP (mmHg)	LsE	109 ± 15	88 ± 22	114 ± 30	117 ± 29	115 ± 25	113 ± 19	111 ± 16	0.5439
DAP (mmHg)	QLB	93 ± 10	69 ± 8	83 ± 13	83 ± 14	81 ± 9	74 ± 7	72 ± 6	0.7684
DAP (mmHg)	LsE	90 ± 12	64 ± 13	81 ± 16	82 ± 12	77 ± 9	75 ± 10	73 ± 11	0.7684
f_R (breaths/min)	QLB	34 ± 8	22 ± 9	29 ± 8	27 ± 9	25 ± 9	24 ± 8	22 ± 7	0.2512
f_R (breaths/min)	LsE	32 ± 9	19 ± 5	23 ± 5	24 ± 5	25 ± 7	25 ± 8	26 ± 8	0.2512
SpO₂ (%)	QLB	99 ± 1	100 ± 1	99 ± 1	99 ± 1	99 ± 1	99 ± 1	99 ± 1	0.4998
SpO₂ (%)	LsE	100 ± 1	99 ± 1	99 ± 1	99 ± 1	99 ± 1	99 ± 1	99 ± 1	0.4998
Pe’CO₂ (mmHg)	QLB	35 ± 5	37 ± 7	37 ± 3	39 ± 5	39 ± 5	39 ± 6	39 ± 6	0.7487
Pe’CO₂ (mmHg)	LsE	34 ± 5	37 ± 5	38 ± 4	38 ± 5	37 ± 4	38 ± 5	37 ± 6	0.7487

Data are mean ± SD. No significant differences were observed (P >0.05)

T1 = immediately before the skin incision; T2 = at the end of the celiotomy; T3 = after clamping the right ovarian pedicle; T4 = after clamping the left ovarian pedicle; T5 = after clamping the uterine cervix; T6 = at the beginning of the muscle suture; T7 = at the beginning of the skin suture

In the postoperative evaluation, there were no significant differences between the treatments for the time elapsed between the end of anesthetic supply and extubation, the first head movement, and the establishment of the sternal and quadrupedal positions (Table 3).

Table 3

Times (in mins) to extubation, first head movement, and attainment of sternal and standing quadrupedal of cats receiving lumbosacral epidural anesthesia (LsE) or quadratus lumborum block (QLB)

Recovery times	LsE	QLB	P value
TA	17.7 ± 13.1	23.7 ± 14.1	0.5012
TB	40.1 ± 11.6	39.9 ± 20.4	0.6764
TC	58.8 ± 6.9	66.7 ± 25.8	0.3627
TD	73 ± 13.1	79 ± 37.9	0.4182

Data are mean ± SD. No significant differences were observed (P >0.05)

TA = extubation; TB = first head movement; TC = attainment of sternal; TD = standing quadrupedal quadratus

No significant differences were detected in the degree of sedation (P = 0.2211) and pain scores (P = 0.6206) between the groups (Figures 2 and 3; Tables S1 and S2 in the supplementary material). No adverse events were recorded during recovery. During the 6-h postoperative observation period, only one animal in the QLB group required rescue analgesia, with a pain score of 10 at 6 h after surgery.

Discussion

The present findings indicate that QLB with 0.25% levobupivacaine can maintain cardiopulmonary stability and early analgesia comparable to epidural anesthesia with lumbosacral access in cats undergoing OVH. In a recent study, 0.25% bupivacaine was used to compare QLB (0.4 ml/kg/hemiabdomen) with sacrococcygeal epidural anesthesia (0.3 ml/kg) in cats anesthetized with isoflurane. According to the authors, the techniques tested provided perioperative analgesia compatible for ovariectomy.⁷ However, using the same criteria as in this study, intraoperative analgesic rescues were necessary in 12% of cats treated with sacrococcygeal epidural anesthesia and 20% of cats receiving QLB. Adequate QLB should include complete analgesic coverage of the abdominal wall and viscera by anesthetizing the ventral branches of the thoracolumbar nerves, sympathetic trunk, and celiac and mesenteric ganglia.^11–15 In this context, it was considered more prudent to compare the ultrasound-guided QLB technique with the epidural technique via lumbosacral neuroaxial access, which results in more cranial migration and analgesia coverage.³ The purpose of using a volume of 0.4 ml/kg administered for over 45 s was to disperse local anesthetic cranially, as smaller volumes are commonly used for sensory blockade of the pelvis, perineum and pelvic limbs.^3,4

The choice of levobupivacaine was considered because of its greater cardiovascular and neurotoxic safety than the racemic mixture, while providing a comparable sensory blockade.²⁶

Under the conditions of this study, the type of locoregional technique did not significantly affect propofol requirements. However, it should be noted that low mean infusion rates were required, both for animals treated with epidural anesthesia (0.36 ± 0.07 mg/kg/min) and for those that received QLB (0.39 ± 0.02 mg/kg/min) with 0.25% levobupivacaine. In female cats premedicated with dexmedetomidine and undergoing OVH, the mean requirement for propofol to maintain anesthesia was 0.5 ± 0.17 mg/kg/min, with a mean requirement for five analgesic rescue doses of fentanyl (2.5 µg/kg) per animal over 40 mins of surgery.¹⁹

Variable changes in HR, decreased cardiac contractility and f_R, hypoxia, hypercapnia and vasodilation are proportionally associated with the dose of propofol.^19,27 In this context, the observed cardiopulmonary stability is directly related to the low propofol infusion rates used. Once the potential physiological interferences of the locoregional blocks have been ruled out, it can be stated that both provided satisfactory intraoperative analgesia. This is evidenced by the absence of cardiopulmonary variations compatible with a sympathetic response to pain stimuli, which was consistent with the absence of intraoperative opioid rescue requirement.

The findings of this study lend support to the hypothesis that LsE or QLB with 0.25% levobupivacaine, administered as part of a multimodal anesthetic protocol, provides similar recovery milestones in cats undergoing elective OVH. The mean time to establish the quadrupedal positions was 79 and 73 mins for QLB and LsE, respectively. In female dogs treated with 0.25% levobupivacaine through the epidural route, motor blockade was observed for a mean period of 83 mins.²⁸ However, it is believed that the similarity in recovery times is related to the multimodal anesthetic protocol used, since there is no interference from the motor blocked in the QLB. The surgery times of 23 mins for LsE and 27 mins for QLB are consistent with the recovery times observed in cats under propofol anesthesia. Similarly, in cats anesthetized with propofol for a period of 30 mins, an average time to walking without ataxia of 74 mins was recorded.²⁹ Total intravenous anesthesia with propofol represents a growing alternative to inhalation anesthesia. Cats slowly metabolize phenolic compounds because of the lack of functional glucuronosyltransferase enzymes (UGT1A6). However, this should not have clinically relevant consequences after short infusion periods (up to 60 mins) in healthy cats.^29,30 Sedation scores recorded in this study were consistent with the recovery times observed. As no adverse events were recorded, we suggest that the prolonged time to assume the quadrupedal position was more likely attributable to the propofol infusion than to the local anesthetic technique.

Postoperative pain scores remained consistently low in both groups throughout the 6-h evaluation period, and only one (10%) cat in the QLB group required rescue analgesia. However, early postoperative scores should be interpreted cautiously, as residual sedation may have affected food intake, particularly between 0.5 and 1.5 h after surgery. Because sedation scores did not differ significantly between groups, this potential influence was likely comparable between treatments.

To the best of our knowledge, we found only one in vivo study comparing epidural anesthesia with QLB in cats.⁷ This modality of block was compared with the sacrococcygeal epidural technique with 0.25% bupivacaine (0.3 ml/kg) in the animals undergoing ovariectomy. Similarly, the authors ruled out the use of postoperative rescue analgesia for 2 h after extubation and attributed good postoperative analgesic comfort to both techniques.⁷ In female dogs premedicated with medetomidine (20 µg/kg) and meloxicam (0.2 mg/kg) and that also underwent OVH, QLB performed bilaterally with 0.25% bupivacaine (0.4 ml/kg per hemiabdomen) promoted satisfactory analgesia for 4 h after surgery, with an increase in pain scores after this period.³¹ The QLB is effective in promoting perioperative analgesia in cats undergoing ovariectomy, significantly reducing the need for rescue opioid use, indicating visceral analgesia without significant adverse effects.^15,32,33 Applying larger volumes (0.5 ml/kg per hemiabdomen) instead of smaller volumes (0.3 ml/kg per hemiabdomen) in the QLB with 0.2% bupivacaine in cats undergoing ovariectomy demonstrated a significantly lower need for intraoperative rescue analgesia and lower postoperative pain scores, ruling out any clinical signs of bupivacaine toxicity or other QLB-related complications.³⁴ Regarding the use of the lumbosacral epidural route, a recent study in female cats undergoing OVH reported a postoperative analgesic duration of 1.5 h using 0.25% levobupivacaine.²⁰ The use of 1 mg/kg of 0.5% bupivacaine on the same route resulted in a mean analgesic duration of 79.4 ± 6.3 mins.³⁵

Among the methodological aspects that may have influenced postoperative comfort, premedication with meloxicam and dexmedetomidine likely contributed to attenuation of nociceptive responses during the early recovery period.^36,37 Even considering this potential influence, QLB and LsE with 0.25% levobupivacaine were associated with comparable cardiopulmonary stability and early perioperative analgesic performance. These preliminary findings support the hypothesis that QLB may represent a viable alternative to LsE in cats undergoing OVH.

Despite the promising results obtained in this study, some limitations should be considered for future research. The postoperative evaluation period was relatively short, and a longer follow-up would be necessary to better characterize the duration of analgesia and the timing of rescue analgesic requirements, especially for a fascial plane block used as part of a multimodal analgesic regimen. This limitation was associated with the refusal of most pet owners to keep their animals hospitalized for extended periods for evaluation.

A further limitation is the modest sample size (10 cats per group), which reduces the statistical power to detect small-to-moderate between‑group differences. Although no significant differences emerged for cardiopulmonary variables, propofol infusion rate showed a smaller trend (P = 0.0863), suggesting that a larger cohort might clarify whether a true sparing effect exists.

Conclusions

Bilateral ultrasound-guided QLB with 0.25% levobupivacaine was associated with cardiopulmonary stability and early perioperative analgesic performance comparable to that observed with LsE in cats undergoing OVH. These preliminary findings support QLB as a potential clinical alternative, although confirmatory studies with larger sample sizes and prolonged analgesic evaluation are recommended.

Supplemental Material

Table S1

Sedation scores in cats receiving LsE or QLB at postoperative time points (h).

Supplemental Material

Table S2

Pain scores in cats receiving LsE or QLB at postoperative time points (h).

Footnotes

Accepted: 25 May 2026

Supplementary material

The following files are available as supplementary material:

Table S1: Sedation scores in cats receiving LsE or QLB at postoperative time points (h).

Table S2: Pain scores in cats receiving LsE or QLB at postoperative time points (h).

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

We thank the Coordination for the Improvement of Higher Education Personnel–Brazil (CAPES) for the scholarship 88887.711127/2022-00. AE-L (Proc. 310248/2021-3) is supported by the research productivity and technological development fellowship of the National Council for Scientific and Technological Development (CNPq). The funders had no role in this study’s design, in the collection, analysis and interpretation of data, or the writing of the manuscript.

Ethical approval

The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognized high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS. Although not required, where ethical approval was still obtained, it is stated in the manuscript.

Informed consent

Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers, tissues and samples) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.

ORCID iD

Ravena O Mangabeira

Gabriel M Rodrigues

Clara L Moura

Vinícius J Moraes

Alice R de Oliveira

Vivian F Barbosa

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