The study was approved by the Review Board for Animals Care of the the University of Messina. Procedures were performed in accordance with Italian law (D.M. 116192), Europe law (O.J. of E.C. L 358/1 12/18/1986), and USA laws (Animal Welfare Assurance No A5594-01, Department of Health and Human Services, USA). Prior to the cats enrolment in the study, the owners provided informed consent.
thirty female cat and ten males of 3,5 ± 0,5 kg ,were admitted to our hospital for the following ophthalmic surgeries: penetrating corneal ulcers (n = 32) and cataract (n = 8). The patients were chosen for their docile temperament and they were randomly divided into four groups of treatment of ten subjects each (L, LC, GC, and C group) by drawing a ticket. All cats were sedated using butorphanol 0.2 mg kg− 1 (Dolorex 1%; Intervet, Aprilia Italy), dexmedetomidine 15 µg kg− 1 (Dexdomitor 0.5%, Pfizer Animal Health, Roma Italy) and midazolam 0.2 mg kg− 1 (Ipnovel 0,5% Roche, Basilea Switzerland) combined and administered intramuscurarly. Following sedation, a 0.64 × 19-mm, 24-G venous (DELTA VEN, Deltamed Italy) catheter was inserted in the cephalic vein for medication and fluid administration. Artificial tear eye drops were applied on corneal surface every thirty minutes until the start of surgery (Artelac splash; Baush & Lomb, Italy). Anaesthesia was induced with propofol (Proposure 1%, Merial Italy) at effect intravenously. All cats received 2 mg kg-1 of lidocaine (Lidocaina 2%, Zoetis, Roma Italy) sprayed on the glottis and the endotracheal intubation was performed with a cuffed tube. Anaesthesia was maintained with isoflurane (ESTEVE; Barcelona, Spain) delivered in 100% oxygen via a non-rebreathing circle system (Mapleson B in parallel of Lack). Controlled respiration was supported by intermittent positive pressure ventilation. The mechanical ventilator (Servoventilator 900 C, Siemens Elema Sweden) was set using the following parameters: respiratory rate 20 breaths min− 1,volume 1.5 L min− 1, tidal volume of ∼ 18 mL kg− 1, inspiratory/expiratory ratio (I:E) 1:2, and airway pressure 20 cmH2O.
Then, all the cats were administered peribulbar sub-Tenon’s anaesthesia in the eye to be operated using a 0.4 × 13 mm 27 G sterile needle (Latex Free Benefis®Italy). The anaesthetic mixture was applied both in the inferior temporal corner and in the upper nasal corner by inserting the needle between orbit and eyeball (Davis et al, 1986). The L group received L-bupivacaine 1.25 mg kg− 1 (0.75% Chirocaina; Abbott, USA); LC group received 1.25 mg Kg− 1 of L-bupivacaine combined with cisatracurium 0.01 mg kg− 1 (0.2% Nimbex; Glaxo, Smithkline spa Italy); C group received 0.01 mg kg− 1 of cisatracurium; GC group received 0.01 mg kg− 1 of cisatracurium intravenously. All peribulbar anaesthesia were performed with the same volume of drug (1 ml), with the addition of saline solution 0,9%. If ineffective block occurred, additional local anaesthetic peribulbar block with L-bupivacaine was administered. A single observer, blinded to treatment, recorded the following parameters: heart rate (HR – beats min− 1), respiratory rate (RR – breaths min− 1, end-tidal carbon dioxide tension (EtCO2 - mmHg), arterial haemoglobin oxygen saturation (SpO2 - %), non-invasive blood pressure (NIBP - mmHg) by placing a cuff around the base of the tail, and the concentration of inspired and expired isofluorane (IT/ET isofluorane) using a multiparameter model (AMI s.r.l., Leonardo model Italy).
The evaluation of neuromuscular transmission was performed by detecting the TOF (Train of four) using a machine (TOF-Watch® SX; Organon, Italy) set automatically before each use at 50 mA and 1-0.1 Hz. The stimulating electrodes were applied at the medial part of the elbow (at the level of the ulnar nerve), whereas the recording of potentials was obtained by applying the electrodes above the carpus muscles. All parameters were measured immediately before sedation (time 0), after sedation (S), except TOF, SpO2, and EtCO2,, and at 5, 10, 15, 20, 25 and 30 minutes after anaesthesia.
The intraocular pressure (IOP - mmHg) was measured with Tono-Pen Vet (Reichert Italy). The IOP baseline value was recorded after instillation of one drop of oxybuprocaine (0.4% Novesina; Novartis Italy) in awake animals. Afterward, the IOP was measured after sedation, at 5 and 10 minutes after peribulbar anaesthesia, and before the start of surgery with cats in sternal recumbency. The degree of mydriasis was evaluated by measuring the horizontal pupil diameter (mm) with Jameson calipers (E2410 Storz®, Italy) in awake animals, after sedation, at 5 and 10 minutes after anaesthesia, and before the start of surgery. The horizontal pupil diameter was measured (mm) by a single observer in the same room, lit with a 40W lamp. After sedation, eyeball centralization (akinesia) was evaluated by three independent observers that recorded if the eye was rotated or centrally positioned. Any deviation of the eye from central position was considered as rotated.1− 4 Onset and duration of akinesia (minutes) of extraocular muscles were recorded by a single observer.
All cats after full recovery have been discharged from hospital.
Statistical analysis was performed using SPSS 15.0 IBM software for Windows. A Kendall’s test of concordance Shapiro-Wilk test and a power calculation of sample were performed. The data, expressed with median and range, were compared using Friedman test to evaluate changes along the time line and compared differences among groups. Statistical significance was set at p < 0.05.