Research Article | Open Access
The Effect of Acepromazine Alone or in Combination with Methadone, Morphine, or Tramadol on Sedation and Selected Cardiopulmonary Variables in Sheep
The sedative and selected cardiopulmonary effects of acepromazine alone or in combination with methadone, morphine, or tramadol were compared in sheep. Six ewes were randomly assigned to treatments: A (0.05 mg/kg acepromazine), AM (A plus 0.5 mg/kg methadone), AMO (A plus 0.5 mg/kg morphine), and AT (A plus 5 mg/kg tramadol). Parameters were assessed before sedative drug administration (baseline) and every 15 minutes thereafter, for two hours. Treatments A and AM were associated with increases in sedation score for 60 minutes and treatments AMO and AT for 30 minutes; however, there were no significant differences between treatments. There was a decrease in mean arterial pressure compared to baseline values in treatment A at 15, 45, 60, and 90 minutes, in treatment AM at 15 minutes, and in treatment AT from 45 to 120 minutes. Arterial blood carbon dioxide pressure increased at all time points in all treatments. Arterial oxygen pressure decreased in treatment AMO at 15, 30, and 120 minutes and in treatment AT at 15–45, 105, and 120 minutes, compared to baseline. Acepromazine alone causes a level of sedation similar to that observed when it is coadministered with opioids methadone, morphine, and tramadol. These combinations did not cause clinical cardiopulmonary changes.
Acepromazine is the most commonly used phenothiazine in veterinary medicine . In ruminants, acepromazine causes sedation and mild skeletal muscle relaxation even in low doses; however, it does not possess antinociceptive properties . Clinical dosing in goats (0.05 mg/kg) has minimal effect on cardiopulmonary function . In dogs, higher intravenous bolus may lead to bradycardia and long-lasting hypotension .
A combination of sedatives, such as acepromazine and opioids, is used routinely in dogs in order to potentiate the sedative effects and provide analgesia . Information regarding the effects of such associations in the ovine species in the current literature is sparse. Thus, the purpose of this study was to assess the sedative cardiorespiratory effects of acepromazine alone or in combination with different opioid agents. It was hypothesized that sedation would be superior following the administration of these combinations compared with administration of acepromazine alone.
2. Materials and Methods
All procedures involving the use of animals were carried out following approval by the Institutional Animal Welfare Ethics Committee (protocol #038/12).
Six nonpregnant Santa Inês ewes (mean age, months; mean body weight, kg) were used in the study. The animals were confined in 12 m2 paddocks, receiving Tifton grass, commercial formulation of ration for sheep, mineral supplementation, and water ad libitum. All animals were clinically healthy upon physical examination, complete blood count, evaluation of renal and hepatic functions, and coproparasitological test. The ewes were acclimated to their surroundings for 20 days prior to the beginning of the study and were accustomed to the presence of the researchers and underwent mild physical restraint daily. Before treatments, the animals were fasted for 24 h and the areas of the right jugular vein and auricular arteries were clipped. The skin in the areas used for vessel catheterization was aseptically prepared. A catheter (18 G) was introduced into the right jugular vein, and a second catheter (20 G) was introduced into an auricular artery with the sheep restrained in a standing position. The study was performed at about 1040 meters above sea level.
2.2. Experimental Design
The ewes were randomly assigned (by drawing of lots) to treatments, in a crossover study. All ewes received all treatments, and a seven-day washout period was allowed between treatments. The treatments were as follows: A, acepromazine (0.05 mg/kg, Acepran™ 0.2%, Vetnil, São Paulo, SP, Brazil); AM, A and methadone (0.5 mg/kg, Mytadom™ 10 mg per mL, Cristália, Itapira, SP, Brazil); AMO, A and morphine (0.5 mg/kg, Dimorf™ 10 per mL; Cristália, Itapira, SP, Brazil); and AT, A and tramadol (5 mg/kg, Tramadon™ 50 per mL; Cristália, Itapira, SP, Brazil). Drug combinations were mixed in one syringe and the final volume was adjusted to 5 mL (facilitated blinding), using normal saline solution, and administered via the jugular catheter over 30 seconds.
Data were collected at baseline (time 0, immediately before drug injections) and at 15-minute intervals for 120 minutes following administration of treatments.
2.3. Cardiopulmonary Parameters and Rectal Temperature
Heart rate (HR, beats per minute [bpm]) was measured for one minute using a transthoracic stethoscope, on the fifth intercostal space with the point of a flexed elbow used as landmark. Mean arterial pressure (MAP, mmHg) was recorded using the invasive approach, following percutaneous catheterization of the left or right median auricular artery and coupling the catheter connected to a system filled with heparin solution (50 UI/mL) and a calibrated aneroid manometer. The system was zeroed using the air-saline junction at the point of the shoulder in standing and sternally recumbent animals and the xiphoid process in laterally recumbent animals as reference points. Rectal temperature (RT, Celsius degree: °C) was assessed using a transrectal thermometer. Respiratory rate (RR, breaths per minute) was obtained by observation of the thoracic costal movements during a 1-minute period. Arterial blood samples (0.5 mL) were collected from the auricular artery catheter into a heparinized syringe, for assessment of blood pH (pHa), partial pressure of carbon dioxide (PaCO2, mmHg), partial pressure of oxygen (PaO2, mmHg), bicarbonate (, mmol/L), and base excess (BE, mmol/L). Blood samples were immediately analyzed following sampling using blood pH and gas analyzer (Cobas b121 Roche®, Basel, Switzerland). Corrections were performed based on the values of body temperature. All data were obtained by a single evaluator.
2.4. Sedation Assessment
Sedation was assessed using a noninteractive behavioral scale, ranging from 0 to 10 points  (Appendix 1, in Supplementary Material available online at https://doi.org/10.1155/2017/7507616), with zero indicating no sedation and 10 maximum sedation. Sedation was scored by three observers who were blinded to the treatments. All of the observers performed the sedation assessment independently and the final score was the arithmetic mean of the three scores.
2.5. Statistical Analysis
Data are presented in tables as means, medians, standard deviation, and maximum and minimum values. All parameters were submitted to the Shapiro-Wilk normality test using the software R, followed by analysis using the GraphPad PRISM 5 software. Variables presenting normal distribution were compared among time points using repeated measures one-way ANOVA, followed by Dunnett’s posttest; for comparison among treatments, the two-way ANOVA was used, followed by Bonferroni’s posttest. Variables presenting nonnormal distribution were compared using Friedman’s test, followed by Dunn’s posttest for comparison in pairs. Significance level used for all tests was 5%.
3.1. Cardiopulmonary Parameters and Rectal Temperature
Observations on HR, MAP, and RT at time points according to treatment are shown on Table 1. Posttreatment HR did not differ () from baseline values in any of the treatments, and there was no difference () in HR among treatments at any time points.
|Significantly different from time 0 within the same treatment ().|
There was a decrease in MAP in treatment A relative to baseline values at 15 (), 45, 60, and 90 minutes (), in treatment AMO at 15 minutes (), and in AT from 45 to 120 minutes (). There was no significant difference () among treatments at any time points.
A decrease () in rectal temperature was observed in animals in treatment A at 45 and 60 minutes and at all time points in AM (); however, there was no difference () among treatments.
3.2. Arterial Blood Gas Analysis
Results of RR, pHa, PaCO2, PaO2, , and BD at time points according to treatment are shown on Table 2. Respiratory rate decreased () in comparison to the baseline values at all time points in treatments A and AMO and at 15 and 90 minutes in treatment AM (). However, there was no significant difference () among treatments at any time point.
|Significantly different from time 0 within the same treatment (). Significantly different from other treatments at the same time point ().|
The pHa increased in treatment AMO at 90 minutes () and from 60 to 120 minutes in AT (). There was an increase () in PaCO2 in all treatments at all time points, but there was no difference () among treatments.
PaO2 decreased, in comparison to baseline values, in treatment AMO at 15, 30, and 120 minutes () and at 15, 30, 45, 105, and 120 minutes () in treatment AT. Comparison among treatments revealed a decrease () in PaO2 at 15 and 30 minutes in treatments AT and AM.
An increase () was observed in in comparison to baseline values at all time points in all treatments. Regarding BE, an increase () was seen at 15–120 minutes in treatments A, AM; AMO at 15–105; and at 30–120 minutes in AT, compared to baseline values.
3.3. Sedation Score
Signs of excitation of the central nervous system were observed, especially in the animals receiving acepromazine-tramadol, such as sialorrhea, bruxism, vocalization, and increased sensitivity to touch; resolution of these signs occurred within 30 minutes. Animals treatments AM and AMO exhibited the most profound sedation. Two animals in the AM treatment became sternally recumbent (score 6) 30 minutes after premedication and one ewe after 45 minutes. Score 6 was also verified in one animal after treatment AMO at 15 and 60 minutes.
Posttreatment scores differed () from baseline values at 15–60 minutes in animals in treatment A, at 15 (), 30–45 (), and 60 minutes () in treatment AM, and at 15 () and 30 minutes () in treatments AM and AT (Table 3). There was no significant difference () among treatments at any time point.
|Statistically different from baseline within treatment ;|