Pain associated with abdominal surgery may result in physiological and behavioural alterations leading to delayed recovery and return to normal activity when analgesia is inadequate (Brioschi et al., 2023). Advances in veterinary anaesthesia over the past decades have emphasized the importance of multimodal analgesia with reduced dependence on opioids (Lemke, 2004). Multimodal perioperative analgesia combining systemic analgesics with local anaesthetic techniques has also been investigated in veterinary patients in India, including intraperitoneal administration of local anaesthetics and their combination with analgesic adjuncts (Gokulraj et al., 2022; Debnath et al., 2022).

Intraperitoneal administration of local anaesthetics is considered a simple, safe and economical technique for perioperative pain management in small animals undergoing abdominal surgeries (Korkmaz et al., 2019). Quadratus lumborum block (QLB) is an ultrasound-guided locoregional anaesthetic technique in which local anaesthetic is deposited within the interfascial plane adjacent to the quadratus lumborum muscle. The technique has gained considerable importance in modern regional anaesthesia because of its ability to provide both somatic and visceral analgesia (Elsharkawy et al., 2019). Initially described in human medicine as a variation of the transversus abdominis plane block (Blanco 2007), QLB has subsequently been investigated in canine cadaveric and clinical studies (Garbin et al., 2020).

Although studies evaluating intraperitoneal analgesia and QLB in dogs are available (Marchina-Gonçalves et al., 2023; Alonso et al., 2026), reports describing their comparative clinical efficacy under Indian veterinary practice conditions remain scarce. In particular, limited information is available regarding the use of ultrasound-guided QLB as a component of multimodal perioperative analgesia in dogs undergoing ovariohysterectomy in the Indian clinical setting. Therefore, the present study was undertaken to compare the analgesic efficacy of ultrasound-guided QLB and intraperitoneal ropivacaine for perioperative pain management in dogs undergoing ovariohysterectomy.

Experimental animals
 
Twenty-four client-owned female dogs of various breeds, ages and body condition scores presented for elective ovariohysterectomy were enrolled. Only clinically healthy dogs classified as ASA physical status I were selected. Dogs exhibiting aggressive or nervous behaviour, those older than six years, dogs with ASA status ≥II and those with a history of abdominal surgery were excluded.

The study was approved by the Institutional Animal Ethics Committee (Approval No. CVSC/CAU/IAEC/23-24/P-26.1) and written owner consent was obtained before enrolment. All procedures were conducted in accordance with institutional guidelines for the care and use of animals in research. All dogs underwent pre-anaesthetic physical, haematological and biochemical evaluation. Food and water were withheld for 12 h and 4 h, respectively.

Sample size was determined based on the availability of eligible client-owned dogs, ethical considerations and feasibility of repeated perioperative and postoperative assessments. Dogs were randomly assigned to treatment groups before anaesthetic induction using simple randomization in order to minimize selection bias. Standardized assessment criteria were used throughout the study. All observations were recorded by the same investigator to minimize inter-observer variation. Complete blinding was not feasible because of the clinical nature of the study and visible treatment differences.
 
Experimental design and anaesthetic protocol
 
Dogs were randomly assigned into three groups (n=8 each). Group M served as the control and received pre-emptive meloxicam only, Group RP received intraperitoneal ropivacaine and Group RQ received ultrasound-guided bilateral quadratus lumborum block (QLB).

All dogs were premedicated with glycopyrrolate (0.01 mg kg^-1 IM) and meloxicam (0.2 mg kg^-1 IM). Ten minutes later, diazepam (1 mg kg^-1 IV) was administered, followed by induction with propofol (3-5 mg kg^-1 IV to effect) and endotracheal intubation. Anaesthesia was maintained with propofol continuous rate infusion (0.2-0.5 mg kg^-1 min^-1 IV). Owing to its limited intrinsic analgesic effect, propofol allowed assessment of treatment-related analgesia with minimal masking of pain responses.

During anaesthesia, rectal temperature (RT), heart rate (HR), respiratory rate (RR), systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and peripheral oxygen saturation (SpO₂) were monitored using a multiparameter monitor.
 
Ultrasound-guided quadratus lumborum block
 
The thoracolumbar and flank regions bilaterally were aseptically prepared in Group RQ. Following induction, dogs were positioned in lateral recumbency with the side to be blocked uppermost. Ultrasound-guided bilateral interfascial quadratus lumborum block (QLB) was performed as described by Garbin et al., (2020); Viscasillas et al., (2021b) using ultrasound machine equipped with a microconvex transducer (5-8 MHz). The block was performed by an experienced anaesthetist familiar with ultrasound-guided regional anaesthetic techniques.

The transducer was placed transversely, immediately caudal and parallel to the last rib (Fig 1), to obtain a transverse view of the cranial lumbar region. The identified landmarks included the external oblique, internal oblique, transversus abdominis, erector spinae, quadratus lumborum and psoas muscles, along with the transverse process and vertebral body of L1 (Fig 2).





A 23-gauge, 88 mm Quincke spinal needle was advanced under real-time ultrasound guidance using an in-plane ventrolateral-to-dorsomedial approach until the tip was positioned in the interfascial plane between the quadratus lumborum and psoas muscles. Following negative aspiration, 0.5% ropivacaine (1.5 mg kg^-1 per side) was injected. Correct placement was confirmed by ultrasonographic visualization of interfascial hydrodissection. The procedure was repeated on the contralateral side.
 
Intraperitoneal analgesia
 
Dogs in Group RP received intraperitoneal 0.5% ropivacaine (3 mg kg^-1), diluted with an equal volume of normal saline, immediately after laparotomy. Ovariohysterectomy was commenced 5 min after ropivacaine administration.
 
Clinical and physiological observations
 
Intraoperative analgesia was assessed using cumulative pain scores at skin incision (TI), right ovarian pedicle traction (TR), left ovarian pedicle traction (TL), cervix ligation (TC) and skin closure (TS). Scores were calculated from percentage changes in HR and RR, with values >10 indicating inadequate analgesia.

Depth of anaesthesia was evaluated by palpebral reflex monitoring. Recovery time was recorded from anaesthetic discontinuation until unassisted walking and expressed in minutes. Recovery quality was assessed according to the method of Sams et al. (2008).

Postoperative pain was assessed using the short-form Glasgow Composite Measure Pain Scale (SF-GCPS) at recovery (0 h) and at 6, 12 and 24 h. These intervals were selected to evaluate perioperative and early postoperative analgesia during the period of greatest pain following ovariohysterectomy and to assess analgesic adequacy and rescue analgesic requirements.

Physiological parameters (RT, HR, RR, SAP, DAP and SpO₂) were recorded before premedication (0 min), 30 min after induction and 1 h after laparotomy incision.
 
Serum cortisol and blood glucose
 
Blood samples were collected before premedication (0 min) and at 1 h and 24 h after laparotomy for serum cortisol estimation. Samples were collected in clot activator vials, centrifuged at 3500-4000 rpm for 5 min and analysed using a canine cortisol ELISA kit and microplate spectrophotometer. Blood glucose concentration was measured at the same time points using a glucometer.
 
Statistical analysis
 
Data were analysed using SPSS version 27.0. One-way and two-way ANOVA with fisher’s least significant difference test were used to evaluate group and time effects. Duncan’s multiple range test was applied for mean comparisons when significant differences were detected. Non-parametric data were analysed using the independent samples kruskal-wallis test. Results were expressed as mean±SE, with significance set at P<0.05.

Intraoperative analgesia
 
Mean intraoperative pain scores differed significantly among groups at various surgical stages (Table 1). In Group M, pain scores were significantly higher (P<0.01) during ovarian pedicle traction and cervix ligation than during skin incision and closure. Group RQ showed significantly lower (P<0.05) pain scores at all intraoperative stages compared to Groups RP and M, while Group RP had lower scores than Group M during ovarian pedicle traction and cervix ligation.



The superior analgesia in Group RQ may be attributed to deposition of ropivacaine adjacent to the quadratus lumborum muscle, producing somatic and visceral nociceptive blockade through spread along the thoracolumbar fascia and paravertebral space (Li et al., 2022; Paolini et al., 2024). Cadaveric studies demonstrated injectate spread to ventral spinal nerve branches (L1-L3) and the sympathetic trunk (T13-L3), providing effective somatic and visceral analgesia during abdominal surgery (Viscasillas et al., 2021a; Alaman et al., 2022).

The present findings agree with previous reports demonstrating improved perioperative analgesia and reduced nociceptive responses following ultrasound-guided regional anaesthetic techniques in dogs undergoing abdominal surgery.

Dogs receiving intraperitoneal ropivacaine also had lower intraoperative pain scores than the control group supporting Costa et al., (2019). Similar analgesic benefits of intraperitoneal ropivacaine have been reported in veterinary surgical patients (Gokulraj et al., 2022). This effect may result from blockade of peritoneal nociceptors via inhibition of voltage-gated sodium channels, together with systemic absorption and anti-inflammatory actions of ropivacaine (Wu et al., 2019).

Although meloxicam alone provided acceptable analgesia in Group M, pain scores were higher than in Groups RP and RQ. Previous studies have shown enhanced analgesia when NSAIDs are combined with local anaesthetics and other adjuncts in multimodal protocols (Herrera-Becerra et al., 2022). These findings further support combining systemic analgesics with locoregional techniques to improve perioperative pain control during ovariohysterectomy. No intraoperative rescue analgesia was required, as cumulative pain scores remained below 10.
 
Depth of anaesthesia, recovery time and quality of recovery
 
Depth of anaesthesia and and recovery times (Table 2) did not differ significantly among the groups. However, recovery quality was significantly better (P<0.05) in Group RQ. The improved recovery quality in Group RQ may be attributed to superior perioperative analgesia provided by QLB (Viscasillas et al., 2022). Reduced nociception, decreased central sensitization and lower postoperative discomfort may contribute to smoother recovery. No hindlimb weakness or motor blockade was observed after QLB.


 
Postoperative analgesia
 
SF-GCPS pain scores differed significantly (P<0.01) among groups and time intervals (Table 3). In Group M, pain scores increased progressively and were highest at 24 h. Groups RP and RQ showed lower scores at 0 and 6 h, followed by gradual increases at 12 and 24 h. Group RQ had the lowest postoperative pain scores, followed by Groups RP and M.



The lower pain scores in Groups RQ and RP may be attributed to QLB and intraperitoneal ropivacaine, respectively. The superior analgesia in Group RQ agrees with previous studies reporting prolonged abdominal analgesia and reduced postoperative pain after QLB in dogs. Similar analgesia-enhancing effects of truncal nerve blocks have been reported in small animal surgery (Lazzarini et al., 2024). The gradual rise in pain scores likely reflected declining analgesic effects of ropivacaine and meloxicam, which provide analgesia for approximately 6-8 h and 20-24 h, respectively (Morgaz et al., 2021). Rescue analgesia was required earliest in Group M, followed by Groups RP and RQ, further supporting the prolonged analgesic efficacy of QLB.
 
Physiological parameters
 
Rectal temperature decreased significantly (P<0.01) from baseline to 1 h in all groups but remained within physiological limits, with no significant intergroup differences (Table 4).



Heart rate increased non-significantly at 30 min and returned towards baseline by 1 h in all groups. Although intergroup differences were not significant, HR was comparatively lower in Groups RQ and RP than in Group M. Respiratory rate and SpO₂ showed a non-significant decrease at 30 min followed by a slight increase at 1 h, without significant group differences.

Systolic and diastolic arterial pressures decreased non-significantly at 30 min and approached baseline values by 1 h in all groups. The comparatively lower SAP and DAP in Groups RQ and RP may reflect improved intraoperative analgesic stability. Similar evaluation of cardiopulmonary responses under different anaesthetic protocols has been reported in dogs (Bayan et al., 2024).

All physiological parameters remained within normal ranges, indicating adequate cardiopulmonary stability. The lower HR and blood pressure values in Groups RQ and RP were likely associated with improved analgesia. Although severe hypotension following QLB has been reported in humans due to extensive sympathetic blockade (Sá et al., 2018), no such complications occurred in the present study.
 
Serum cortisol and blood glucose
 
Serum cortisol and blood glucose concentrations increased significantly (P<0.05) at 1 h after surgery in all groups and declined by 24 h (Table 5). Group RQ showed significantly lower cortisol and glucose concentrations at 1 h than Groups RP and M. Elevation in serum cortisol and blood glucose may be attributed to activation of the hypothalamic-pituitary-adrenal axis associated with surgical trauma and anaesthetic stress. Previous studies in dogs have also evaluated the effects of propofol- and ketamine-based anaesthetic protocols on haematobiochemical responses (Bayan et al., 2021). Elevated cortisol promotes insulin-resistant gluconeogenesis, resulting in hyperglycaemia (Rubio et al., 2022). The lower cortisol and glucose concentrations in Groups RQ and RP indicate superior visceral analgesia and attenuation of the surgical stress response following QLB and intraperitoneal ropivacaine administration. Similar findings have been reported with locoregional and intraperitoneal analgesic techniques (Debnath et al., 2022; Li et al., 2022).



The study supports the use of ultrasound-guided QLB as an opioid-sparing component of multimodal analgesia for canine ovariohysterectomy under Indian veterinary conditions and adds to the limited indigenous literature on this technique.

Both ultrasound-guided quadratus lumborum block (QLB) and intraperitoneal ropivacaine provided effective perioperative analgesia in dogs undergoing ovariohysterectomy, with physiological parameters remaining within normal limits. However, QLB produced superior intraoperative and early postoperative analgesia compared with intraperitoneal ropivacaine and meloxicam alone. Therefore, QLB may be considered a promising multimodal analgesic technique for pain management in dogs undergoing ovariohysterectomy.

The present study was supported by College of Veterinary Sciences and Animal Husbandry, Central Agricultural University (Imphal), Selesih, Mizoram, India.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
All animal procedures for experiments were approved by the Committee of Experimental Animal care and handling techniques were approved by the University of Animal Care Committee.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.