Physiological and Behavioral Effects of Continuous Remifentanil-Xylazine Administration in Donkeys

Physiological and Behavioral Effects of Continuous Remifentanil-Xylazine 1 Administration in Donkeys 2 Kássia Fernanda Araújo Damascenoa, Andressa Nunes Moutaa, Larissa de Sant’Ana Alvesa, 3 Kathryn Nóbrega Arcoverdea, Herbert Reis Aragãoa, Jerson Marques Cavalcantea, Valéria 4 Veras de Paulaa 5 6 a Department of Animal Science, Universidade Federal Rural do Semi-Árido (UFERSA), 7 BR110 Km 47 s/n, P.O. Box 137, Presidente Costa e Silva, Mossoró – RN, Brazil, 59625-900. 8 9 ABSTRACT 10 Background: Remifentanil and xylazine are drugs that can allow standing equine surgery when 11 in continuous infusion. The literature presents no reports of this association in donkeys. 12 Objectives: To evaluate the behavioral, sedative, and cardiorespiratory effects of continuous 13 intravenous infusion of remifentanil and xylazine in donkeys. Study design: Experimental, 14 prospective, non-blinded study. Methods: 10 donkeys were sedated with an intravenous bolus 15 of xylazine (0.8 mg/kg). After 3 minutes, continuous infusions of xylazine (0.65 mg/kg/h) and 16 remifentanil (6 µg/kg/h) were administered for 60 minutes. Cardiorespiratory physiological 17 parameters, rectal temperature, gastrointestinal motility, and sedation and ataxia scores were 18 evaluated by a simple descriptive scale at M0 (baseline) and every 5 minutes, up to M60 (60 19 min), with scores 0-3. Head height concerning the ground was also evaluated. Dunnett and 20 Friedman statistical tests (p < 0.05) were used. Results: Heart rate (p = 0.049) and respiratory 21 rate (p = 0.001) decreased significantly at M10 and M5, respectively, compared to M0. There 22 was a significant decrease in systolic (p = 0.04), mean (p = 0.02), and diastolic (p = 0.03) blood 23 pressure at M15 compared to M0. The capillary refill time at M20 was statistically different (p 24 = 0.001) from M0. The head height in relation to the ground reduced significantly from M5 (p 25 = 0.001) to M60. Satisfactory sedation was obtained from M15 to M60. After stopping the 26 infusion, all donkeys recovered successfully (7.1 ± 2.4 minutes). No adverse effects were 27 observed during and after the infusion. Primary limitations: No painful stimulus or surgical 28 procedure was performed. Conclusions: Combining remifentanil and xylazine at the doses used 29 caused adequate sedation and short recovery time. Remifentanil did not cause excitation in the 30 donkeys. Future studies are necessary to test the protocol with painful stimuli. 31 Keywords: Asinine; Equine; Remifentanil; Sedation. 32 15 1 Introduction 33 Donkeys (Equus asinus) are rustic animals whose importance is often neglected due to 34 their specific characteristics, both in morphophysiological and pharmacological perspectives, 35 as well as their temperament.1 Thus, some studies have evaluated the effects of drugs on 36 donkeys2,3. However, protocols for this species are still scarce. 37 It is common to associate drugs to chemically contain equines, avoiding the 38 complications and costs of general anesthesia. The adrenergic alpha2-agonist drugs produce 39 sedation, analgesia, and muscle relaxation despite their adverse effects.4-6 Among adrenergic 40 alpha2-agonists, xylazine is the shortest acting and may result in insufficient analgesia for some 41 surgical or outpatient procedures in monotherapy. In these circumstances, they are administered 42 in association with opioids or with local blocking techniques to improve analgesia.7 43 Opioids are useful in anesthesiology because of their ability to decrease sympathetic and 44 somatic responses to harmful stimulation.8 Combinations of an alpha2-agonist with an opioid 45 in single or repeated administrations, or even as part of a peri anesthetic protocol, can provide 46 synergistic analgesic effects and good sedation. This association reduces the potential for 47 excitation at the level of the central nervous system.9 48 Remifentanil is an opioid derivative of phenylpiperidine, supplied as remifentanil 49 hydrochloride, a lyophilized powder. Animal studies indicate that the pharmacological 50 properties of remifentanil are similar to those of other potent μ-opioid receptor agonists, such 51 as alfentanil.10 Characterized as a potent opioid of ultra-short duration, its use has been 52 described in studies conducted in different species, where it was shown to be a safe drug, 53 producing minimal hemodynamic changes, in addition to its onset of action and rapid recovery 54 after cessation of use, regardless of the duration of its administration. Therefore, remifentanil 55 16 appears to be a highly titratable opioid, providing profound analgesia for very brief periods in 56 which analgesia is necessary or for prolonged periods without the concern of prolonged 57 recovery.8,12 Some studies describe its use in horses5,6,12. However, the literature has no 58 information on the systemic effects of remifentanil in donkeys. 59 In this context, this study aimed to evaluate the physiological and sedative effects of 60 continuous intravenous infusion of remifentanil and xylazine in donkeys from the northeastern 61 region of Brazil. We hypothesized that adverse effects would be insignificant when associating 62 the drugs in low doses and continuous infusion, and the sedation protocol can be considered for 63 seasonal surgical procedures. 64 65 2 Material and Methods 66 67 2.1 Animals 68 69 The study conditions were submitted to and approved by the Animal Use Ethics 70 Committee (CEUA/UFERSA) under protocol number No. 42/22. Ten adult donkeys from the 71 northeastern region of Brazil, seven males and three females, aged 5.3 ± 2.2 years and weighing 72 120.4 ± 21.4 kg, were used. The animals were classified as healthy after clinical and laboratory 73 examination (blood count, urea, creatinine, aspartate aminotransferase, alanine 74 aminotransferase, and total proteins) for the inclusion criteria. A sample calculation was 75 performed based on a pilot study with three animals using the dose presented in the study with 76 horses6. The calculation was done using GPower 3.1.9.7. This calculation and the mean and 77 standard deviation of sedation of M5, alpha 0.05, and Power 0.8 were compared with the 78 constant 0 of M0. The animals were dewormed with ivermectin (Ivomec®, Boehringer 79 17 Ingelheim), associated with trichlorfon and mebendazole (Trichlorsil paste®, Vansil), and 80 vaccinated against rabies four weeks prior to the start of the study. The animals were housed in 81 groups of five, in pickets of 10 x 7 m in the open air, with shade, and fed with voluminous grass 82 (Pennisetum purpureum) and concentrate (ground corn, soybean meal, wheat bran, common 83 salt, and calcitic limestone) twice a day, with water ad libitum. The acclimatization to the new 84 environment took four weeks. 85 86 2.2 Experimental study 87 88 One day before the procedure, the animals were transferred to individual stalls. Prior to 89 the experiment, they were subjected to a 12-hour fast from solid food and had access to water 90 ad libitum. 91 Initially, the physiological parameters of respiratory rate (RR) by inspection of the costal 92 grid, capillary refill time (CRT), heart rate (HR) by cardiac auscultation, rectal temperature 93 (RT), mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure 94 (DBP) through a multiparametric monitor (multiparametric monitor, touch screen, Delta Life, 95 model DL1000), and gastrointestinal motility by auscultation, assessing intestinal borborygmus 96 in the dorsal and ventral quadrants of the right and left side, were evaluated at baseline (M0). 97 After M0, trichotomy and antisepsis of the jugular vein were performed for catheterization, 98 using a 16-gauge catheter coupled to a 3-way stopcock. 99 Subsequently, the animals received a 0.8 mg·kg-1 bolus of xylazine (xylazine 100 hydrochloride 2%, Syntec®) administered within 60 seconds by infusion pump (RS700 VET, 101 RZVET®) and, after 3 minutes, continuous infusions of xylazine and remifentanil (remifentanil 102 hydrochloride, Eurofarma®) were initiated at the rates 0.65 mg/kg/h and 6 µg/kg/h, 103 18 respectively, and discontinued over 60 minutes after three minutes of the initial xylazine bolus 104 (Figure 1). 105 106 XYLAZINE BOLUS 3 MIN AFTER XYLAZINE BOLUS 63 MIN AFTER XYLAZINE BOLUS BEGINNING OF CI XYLAZINE AND REMIFENTANIL END OF CI XYLAZINE AND REMIFENTANIL Figure 1. Linear representation of the beginning and end of xylazine and remifentanil infusions in donkeys. Adapted from Palarrols et al., 2020. The same physiological parameters evaluated at M0 (HR, RR, CRT, RT, MAP, SBP, 107 and DBP) were monitored every 5 minutes until 60 minutes after drug administration (M60). 108 Gastrointestinal motility was evaluated 15 min, 1h, 4h, 8h, and 24h after the infusions (M60). 109 The head height above the ground was measured using a tape measure graduated in 110 centimeters from 0 to 160 cm, which was fixed to the lateral bar of the physical containment 111 trunk to evaluate sedation. The distance between the ground and the mandibular symphysis was 112 measured before beginning the instrumentation, in an environment free of external stimuli, 113 considering the head height of the animal at M0. Sedation was also evaluated using a simple 114 descriptive scale, assessing the level of sedation and ataxia,5,13 with scores from 0 to 3 for both 115 items (Table 1). 116 19 Table 1: Simple descriptive scale (SDS) scoring system for sedation and ataxia (FUNCIA et al., 2016)5. SEDATION SCORE SIGNS 0 No sedation. The animal is alert, with normal posture and response to contact with the evaluator. Normal objection to intervention. 1 Light sedation. Head lowered, facial muscles relaxed, and lower lip hanging. Some response to intervention. 2 Moderate sedation. Head lowered towards the floor and swinging the hind legs. Slight response to intervention. 3 Marked sedation. Tries or becomes recumbent. No response to intervention. ATAXIA SCORE SIGNS 0 No ataxia. The animal stands and walks normally; can rotate with force. 1 Mild Ataxia. The animal can walk, but with some lack of limb control. 2 Moderate ataxia. The animal can only walk with support, staggers, but avoids falling. 3 Marked ataxia. The animal cannot walk without danger of falling, staggers, falls, turns over. 117 The patient's quality and total recovery time were evaluated from the end of the 118 infusions to the time the patient presented with a score of zero for sedation and minimal ataxia. 119 The sedation score was assessed every two minutes after stopping the continuous infusion of 120 xylazine and remifentanil. 121 Any need for more drugs for sedation, decreased administration, or any unexpected 122 effect would be reported from the first xylazine bolus until recovery. 123 20 2.3 Statistical Analysis 124 Data were expressed as mean ± standard deviation, median, minimum, and maximum 125 values using the SAS V8 statistical program (System for Windows - SAS Institute Cary, North 126 California; USA). After verifying the parametric assumptions, statistical differences between 127 the times studied (M0 – M60) were verified through analysis of a mixed-effects model for 128 repeated measures (Proc Mixed of the SAS program) for each variable studied, followed by the 129 Dunnett test. The baseline moment (T0) was used as the base comparison variable. 130 Nonparametric data were analyzed using the method described by Friedman. The significance 131 level considered was 5%. 132 133 3 Results 134 135 The sedation and ataxia obtained were satisfactory in all animals throughout the 136 procedure, soon after xylazine administration. After 20 minutes, moderate ataxia and sedation 137 were observed, with a median sedation and ataxia score of 2 for both parameters remaining 138 throughout the procedure. The height of the head in relation to the ground was significantly 139 lower (p = 0.001) at baseline during the entire infusion time (Table 2). 140 141 Table 2 - Mean ± standard deviation (SD) for sedation score, ataxia score, and head height of donkeys submitted to continuous infusion of remifentanil and xylazine for 60 minutes. Variables Measures M0 M5 M10 M15 M20 M30 M45 M60 Sedation score (0-3) Mean ± SD 0 ± 0 0.9 ± 0.6** 1.0 ± 0.5** 1.2 ± 0.4** 1.6 ± 0.2* 1.7 ± 0.5* 1.9 ± 0.3* 1.9 ± 0.3* Median 0 1 1 1 2 2 2 2 Min - max 0 - 0 0 - 2 0 - 2 1 - 2 1 - 2 1 - 2 1 - 2 1 - 2 21 Ataxia score (0-3) Mean ± SD 0 ± 0 0.8 ± 0.6** 1.0 ± 0.5** 1.1 ± 0.6** 1.6 ± 0.5* 1.7 ± 0.5* 1.8 ± 0.4* 1.9 ± 0.3* Median 0 1 1 1 2 2 2 2 Min - max 0 - 0 0 - 2 0 - 2 0 - 2 1 - 2 1 - 2 1 - 2 1 - 2 Head height (cm) Mean ± SD 83.0 ± 9.5* 28.7 ± 28.3** 28.78 ± 33.1** 18.11 ± 25.3** 16 ± 22.2** 17 ± 21.3** 16.56 ± 21.4** 14.44 ± 17.3** Median 82.5 15 15 5 5 10 5 10 Min - max 65 - 100 0 - 85 0 - 84 0 - 78 0 - 69 0 - 63 0 - 63 0 - 56 *, ** Different asterisks on the same line indicate statistically significant difference (p < 0.05 - Dunnett). HR decreased significantly (p = 0.049) ten minutes after xylazine administration and its 142 continuous infusion with remifentanil (M10), while RR decreased significantly (p = 0.001) after 143 5 minutes of the xylazine bolus (M5). MAP (p = 0.02), SBP (p = 0.04), and DBP (p = 0.03) 144 decreased significantly from M15, while RT remained stable throughout the procedure (Table 145 3). 146 147 Table 3 - Mean values ± standard deviation (SD) for heart rate (HR), respiratory rate (RR), systolic blood pressure (SBP), mean arterial pressure (MAP), diastolic pressure (DBP), capillary refill time (CRT), and rectal temperature (RT) of donkeys submitted to continuous infusion of remifentanil and xylazine in 60 minutes. Variables Measures M0¥ M5 M10 M15 M20 M30 M45 M60 HR (bpm) Mean ± SD 44.4 ±6.2* 40.9 ±6.1* 39.8 ±7.9** 39.3 ±7.1** 39.5 ±9 ** 37.1 ±8.4 ** 38 ±7.8 ** 41.5 ±13.6 ** RR (bpm) Mean ± SD 34.3 ±7.6 * 18.0 ±9.0** 15.3 ±7.8** 14.1 ±7.9** 13.8 ±6.5** 11 ±5.1** 9.8 ±5.7 ** 10.5±6.3** †SBP (mmHg) Mean ± SD 166.8 ±23.5 * 160.7 ±34.2 * 153.7 ±28.5 * 137.6 ±34.4 ** 136.3 ±28.3 ** 144.8 ±32.8** 147.3 ±39.9** 131.7 ±30.3** 28 16. Lawless SP, Cohen ND, Lawhon SD, Chamoun-Emanuelli AM, Wu J, Rivera-Vélez A, 285 Weeks BR, Whitfield-Cargile CM. Effect of gallium maltolate on a model of chronic, 286 infected equine distal limb wounds. PLoS One. 2020;15(6):e0235006. Doi: 287 10.1371/journal.pone.0235006 288 17. Taylor P. Veterinary anaesthesia and analgesia: from chloroform to designer drugs. Vet 289 Rec. 2014;174(13):318-21. Doi: 10.1136/vr.g2249 290 18. Kamerling S, Wood T, DeQuick D, Weckman TJ, Tai C, Blake JW, Tobin T. 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