This was an assessor-blinded, randomized, clinical research study. All cases were enrolled over a 6 week period during the autumn of 2021 at Clinic of the Veterinary Hospital of the ‘Aldo Moro’ University of Bari. The same team of surgeon performed all the procedures.
Sixty male cats presented for castration, weighing 2, 5 – 4, 1 kg with a age < 1 years, were recruited to this study after obtaining informed owner consent and approval from the ‘Aldo Moro’ University of Bari ethical committee (Approval Number 15/2021). They were of good health, had no previous pathologies, and were allocated to the very low aesthetic risk class (ASA 1). Exclusion criteria were cats that had been treated with any analgesic, sedative or anesthetic drug in the previous 30 days, very agitated / aggressive, obese and with clinical signs of disease. Two days before surgery, patients underwent a comprehensive physical examination, hematological and serum biochemistry panel. The cats were randomly assigned to two groups: the R and C groups, using StatView statistical software.
In both groups, the cats were sedated using intramuscular injections of 3 mcg/kg dexmedetomidine (Dexdomitor®, Vetoquinol Italia SRL, Bertinoro, Italy) and 0.25 mg/kg methadone (Semfortan®, Eurovet Animal Health BV, Bladel, The Netherlands) mixed in the same syringe . The premedicants were administered into the lumbar epaxial muscles. After 20 min, a 24-G venous catheter was inserted to start a standard maintenance fluid therapy (NaCl 0.9%, 4 ml/Kg/h) . Propofol (Vetofol®, Esteve, Barcelona, Spain) at 1 mg/kg was administered intravenously to induce general anesthesia. Orotracheal intubation was promoted, while anaesthetic maintenance was performed with sevoflurane (EtSev 2,5%, SevoFlo®, Ecuphar Italia S.r.l., Milano, Italy) , vaporized in 100% oxygen, in an open anaesthesia system, always performed by the same anaesthesiologists. From this point throughout the surgery, an anesthetist blinded to the group monitored: plane of anesthesia, spontaneous ventilation, heart rate, respiratory rate, non-invasive blood pressure, oxygen hemoglobin saturation and body temperature (monitor GE-Datex Ohmeda B 450), ensuring a satisfactory anesthetic plan [15, 16].
UGF block (R group) and NaCl 0.9% injection (C group)
The UGF block was performed with the guidance of an ultrasound system (MyLab™ ClassC, Esaote Spa, Genua, Italy). The infiltration of ropivacaina (0.2 mL/kg at 0.5%) (Naropina®, Aspen Pharma Trading 69 Limited) was performed using a BD needle with a Quincke tip (22 G, 0.7 × 90 mm). The local anesthetic was infiltrated into the spermatic cord at the level of its emergence from the superficial inguinal ring (R group) . In C group the same volume of NaCl 0.9% was injected in the same way.
The same surgical team orchiectomized all 60 cats. All surgery were performed with a scrotal approach and lasted about 6 min (± 30 s). Before the procedure, the cardiorespiratory parameters of all animals (pre-incisional values of heart rate, respiratory rate, and blood pressure) were recorded to evaluation the eventual surgical increase . These parameters were registered at six moments during the procedure: first skin cutting of the scrotum (S1), traction on the first spermatic cord (S2), ligature of the spermatic cord (S3), second skin cutting of the scrotum (S4), traction of the second spermatic cord (S5) and ligature of the second spermatid cord (S6). In case of intraoperative increase of 30% of cardiorespiratory parameters respect the pre-incisional value, a bolus of fentanyl was administered i.v. (2 mcg/kg, Fentadon®, Eurovet Animal Health BV) . At the end of the surgery, 0.2 mg of Meloxicam® (Metacam, Boehringer Ingelheim Italia S.p.A.) was injected s.c. in all patients .
Postoperative pain evaluation
Postoperative evaluations began at the end of surgery (0 h) and were repeated at 1, 2, 3, 4, 5 and 6 h. In this period, a blind operator to the group the cat belonged, assigned a score from 0 (pain free) to 30 (unbearable pain), using the UNESP-Botucatu scale [10, 11]. Patients with 7 or higher scores received methadone hydrochloride (0.2 mg/kg im) as rescue analgesia [10, 11].
Data analysis was performed using Stata MP17 software and compiled forms were imputed into a dataset using an Excel spreadsheet. Continuous variables were described as mean ± standard deviation (SD) and range, and categorical variables as proportions. The skewness and kurtosis test was utilized to evaluate the normality of continuous variables; all the continuous variables were normally distributed. The t student test for independent data was used to confront continuous variables between groups, the ANOVA for repeated measures test was used to compare continuous variables between groups and detection time; the Fisher’s exact test were used to compare the proportions. To assess the determinants of rescue analgesia, a multivariate logistic regression model was used in which rescue analgesia was the outcome and group assignment (R vs. C), age (months) and weight (kg) were the determinants. The adjusted odds ratio (aOR) was calculated with the 95% confidence interval (95%CI). For all tests, a p-value < 0.05 was considered statistically significant.