Paravertebral block with lignocaine-bupivacaine mixture in goats

Loco-regional anaesthesia and sedation protocols are becoming more popular in ruminant. This research compared some effects of xylazine or acepromazine in combination with lignocaine-bupivacaine mixture for paravertebral nerve block in goats. Twenty adult, apparently healthy West African Dwarf goats were randomly allocated to two groups (five males and five females each). Each group received either xylazine (0.05 mg/kg) + 2 % lignocaine (2mg/kg) – 0.5 % bupivacaine (0.95 mg/kg) mixture (XLB) or acepromazine (0.05 mg/kg) + lignocaine-bupivacaine mixture (ALB). Clinical parameters were recorded immediately (0 minutes) and at 10-minute intervals for an hour and 24 hours. Venipuncture was carried out via jugular vein for haematology before administration of drug (B0), 30 minutes (B30), 60 minutes (B60) and 24 hours (B24). Data was analyzed using descriptive statistics and presented as mean and standard deviation at a significance level of 0.05. The onset of deep sedation following administration of acepromazine was 31.5 ± 0.97, while it was 2.90 ± 0.57 for xylazine. Acepromazine significantly (P < 0.05) reduced the rectal temperatures (RT) of the goats within the first 20 minutes and significantly reduced the respiratory rates of the goats when compared to xylazine. None of the drugs significantly altered the heart rate of the goats. None of the changes in haematological parameters was statistically significant across the sampling time frame. However, red cell parameters (Packed cell volume, red blood cell count, and haemoglobin concentration) and Lymphocyte count were significantly depressed after XLB administration. All the haematological changes were restored to pre-anaesthetic values after 24hours. This study demonstrates that xylazine can be a beneficial alternative and desirable for emergencies in minor ruminant sedation.


Introduction
The use of anaesthesia in Veterinary medicine is essential for providing pain management and enabling safe and humane surgical procedures.Ruminants, such as cattle, sheep, and goats, are unique species in Veterinary medicine, with their unique anatomy, physiology, and behaviour (Abrahamsen, 2013).General anaesthesia uses in ruminants such as cattle, sheep, and goats are limited due to several unique challenges (Galatos, 2011;Abrahamsen, 2013).These challenges include anatomical and physiological differences, the risk of ruminal stasis, the risk of inhaling ruminal contents, difficulty in intubation, and economic factors (Abrahamsen, 2013).
Given these challenges, regional anaesthesia, local anaesthesia, and chemical restraint are often used in ruminants instead of general anaesthesia (Clarke & Trim, 2013).Regional anaesthesia involves the injection of a local anaesthetic agent directly into the tissue or nerve supplying the area to be operated (Clarke & Trim, 2013).The benefits of local anaesthesia include rapid onset and effective pain relief, as well as allowing the animal to remain awake, alert, and cooperative (Edmondson, 2014).Several types of local techniques are used in regional anaesthesia, each with its own benefits and drawbacks.The most commonly used blockages in veterinary medicine include peripheral nerve blocks, epidural anaesthesia, and spinal anaesthesia (Garcia-Pereira, 2018).
Paravertebral nerve block, also known as a paravertebral injection, is a type of regional anaesthesia that involves the injection of local anaesthetic agents into the paravertebral space adjacent to the spinal cord (D'Ercole et al., 2018).This block type is commonly used in veterinary medicine to relieve pain during thoracic or lumbar surgery and other procedures in these regions (Olaifa et al., 2009).The paravertebral space is a fibro-fatty tissue surrounding the spinal cord and the spinal nerves.By injecting local anaesthetic agents into this space, it is possible to block the pain signals from the thoracic or lumbar spinal nerves and provide effective pain relief (Pawa et al., 2019).For this block, the spinal nerves T13, L1, and L2 are blocked (Kramer et al., 2014).The dorsal and ventral rami of the spinal nerves T13, L1, and L2 near the distal extremities of the transverse processes of L1, L2, and L4, respectively, are desensitized by the distal paravertebral nerve block (Edmondson, 2014).
Consequently, a more substantial block is produced.The goat will bend to the opposite side when the block is in operation since the muscles are relaxed, and associated vasodilation will also cause the flank to become warmer (Ames, 2014).This is particularly useful for debilitated animals with a compromised airway or for procedures that do not require the animal to be completely unconscious while standing (Imani et al., 2022).In addition, paravertebral nerve blocks are relatively simple and quick to perform and have a lower risk of adverse reactions than other forms of anaesthesia (Pawa et al., 2019).
Local anaesthesia alone is insufficient to achieve struggle-free procedure in minor ruminant humane handling (Oguntoye & Adetunji, 2009).Sedation and loco-regional protocols are desirable to ensure the best possible humane handling of goats for various clinical/surgical procedures.Studies on various sedatives such as xylazine and acepromazine in combination with loco-regional techniques such as distal paravertebral block have yet to be thoroughly researched.This study aimed to compare the effects of xylazine and acepromazine sedation on distal paravertebral nerve block with lignocaine-bupivacaine mixture in West African Dwarf (WAD) goats.

Ethical clearance
This study was approved by the University of Ibadan Animal Care and Use Research Ethics Committee (UI-ACUREC).

Experimental animal
Twenty healthy male West African Dwarf (WAD) goats, aged between 1 and 1.5 years old and weighing an average of 10 ± 2 kg, were purchased from a local goat market in Ibadan, Oyo state, Nigeria.The animals were kept in a group of two communal pens at the faculty of veterinary medicine anim.al house teaching and research farm, University of Ibadan, Nigeria.The goats were fed forage (Cyanodon alaferensis), dry cassava peels, and supplemented with cereal-based concentrate.Fresh, clean water was provided, and bitumen was in the pen.In addition, salt lick was provided as a free choice in the pens.They were allowed to acclimatize for two weeks.Before the trials, the goats were judged to be generally healthy based on normal haemogram and complete examination findings.Drugs and other materials used for this study include 2 % Xylazine (XYLASED R , Bioveta, 683 23 IvaniocenaHane Czech Republic), acepromazine maleate, 2mg/ml (Kyron Prescriptions CC,21 New Goch Road, Benrose 2094), 2% Lidocaine HCL (MALVEN LIDOCAINE & ADRENALIN INJEC-TION R , Alpa Laboratories Ltd, Ijdamber-453446 Indore, India), bupivacaine hydrochloride (Marcain Astra Pharmaceuticals Ltd).

Study Design
Twenty adult, apparently healthy West African Dwarf goats were randomly allocated to two groups of ten animals: five males and five females.Each group received either xylazine (0.05mg/kg) + paravertebral block with 2 % lignocaine (2mg/kg)/ 0.5 % bupivacaine (0.95mg/kg) mixture (XLB) or Acepromazine (0.05mg/kg) + paravertebral block with lignocaine/bupivacaine mixture (ALB).Clinical parameters were recorded immediately after sedation/paravertebral block and at 10-minute intervals over a period of 60 minutes and 24 hours after the experiment.

Experimental Procedure
The goats were fasted for 12 hours before commencement of the clinical trials.Goats were tagged XLB 1-10 for xylazine + paravertebral block and ALB 1-10 for acepromazine + paravertebral block.After sedation of each group, as described by Clarke & Trim, (2013), the dorsolateral aspect of the caudal half of the left side of each goat was aseptically prepared by clipping the hair and cleaning with chlorhexidine and methylated spirit.The paravertebral block was achieved for either group with an injection of a mixture of 2 % Lignocaine (2 mg/kg) and 0.5 % Bupivacaine (0.95 mg/ kg) into the intervertebral spaces between T13 to L3 using a 10 ml syringe and 21G (gauge) needle.The drug was deposited around the spinal nerves as they emerged from the vertebral canal via the intervertebral foramina.

Sample collection
Blood samples (5 mls) each were collected from jugular venipuncture in EDTA bottles before administration of the drug (B0), at 30 minutes into analgesia (B30), immediately after the experiment (B60), and 24 hours (B24) after the experiment.Physiological parameters were taken manually (HR with a precordial stethoscope by auscultation, RR by counting the abdominal movements, and RT was recorded with an electronic thermometer) at 10-minute intervals over 60 minutes and 24 hours after the experiment.

Calculation
Time to recumbency (in minutes) was defined as the time interval between paravertebral injection of the local anesthetic mixture to analgesia of the area around the thoracic and abdominal wall, evidenced by the warmness of the area's nonresponse to pressure with artery forceps.The time to onset of analgesia was calculated (in minutes) from the time of paravertebral injection of the local anesthetic mixture to loss of reflex response to pinching with artery forceps.The return of response to pressure with artery forceps determined duration of analgesia (in minutes).Duration of recumbency (in minutes) was recorded from the time of the block to spontaneous movements of the hind limbs.

Data analysis
Statistical tools used for assumption testing were the Shapiro-Wilk test for normality and Levene's Test for Equality of Variances.The data generally did not fulfill normality and variance homogeneity; therefore, statistical analysis between paired groups was performed using the Mann-Whitney U-test, while the Kruskal-Wallis's test analyzed for n>2 groups.All data were presented as mean and standard deviation.The significance level employed was always at P < 0.05.

Variation in Haematological parameters after administration of either XLB or ALB.
There was a slight and transient drop in PCV of the goats following xylazine administration, while there was a slight and transient rise in PCV level following Acepromazine administration (Table 1, Figure 1, Figure 2).There was also a slight transient drop in Platelets count following either Xylazine or Acepromazine administration (Table 1, Figure 3, Figure 4).None of the changes in haematological parameters was statistically significant across the sampling time frame.However, the red cell parameters (PCV, RBC, and HB) as well as Lymphocyte count were all significantly depressed (P < 0.05) after Xylazine administration when compared to post-Acepromazine administration (Table 2).Conversely, Xylazine administration significantly elevated Eosinophil counts (P < 0.05).All the haematological chang-es were restored to pre-anaesthetic values after 24 hours.Generally, male animals had higher red cell parameters (PCV, RBC, and HB) compared to females, but this was not statistically significant (Table 2).However, all other blood parameters measured were significantly higher (P < 0.05) in females than in males.Neutrophil count was the only exception where males had a significantly higher (P < 0.05) value than females, and Platelets count did not significantly differ across sexes.Acepromazine significantly (P < 0.05) reduced the rectal temperatures (RT) of the goats within the first 20 minutes of administration, but beyond 20 minutes, there was no significant deviation of the rectal temperature of the goats irrespective of the type of drug administered (Table 3, Figure 3 and 4).It was also observed that Acepromazine administration significantly (P < 0.05) reduced the respiratory rates of the goats when compared to the Xylazine effect (Figure 5).None of the drugs significantly (P > 0.05) altered the heart rate of the goats.

Anaesthetic Indices
The average time to onset of deep sedation following administration of Acepromazine was 31.5 ± 0.97, while that of Xylazine was 2.90 ± 0.57.There was no significant sexual difference in the duration of onset of either drug.

Discussion
The result of this investigation showed that the mixture of lignocaine and bupivacaine provided a rapid onset of action and longer duration of analgesia from each study, respectively.In addition, it corroborates the report by Oguntoye & Adetunji (2009) and Rostami & Vesal (2011).There was no restriction on the type of goat used, which is one of the reasons paravertebral nerve block procedures were used, as it is a safe and effective technique that provides localized anaesthesia and pain management in pregnant, obese, and old goats while minimizing the risks associated with general anaesthesia (Rush & Stockler, 2022).In this study, Goats were fasted before administration of the sedatives and local anesthetics to ensure a reduced amount of food and liquid in the forestomach, thereby lowering the possibility of regurgitation and aspiration of stomach contents into the lungs (Hendrickson, 2013).When stomach contents get into the lungs, a dangerous condition called aspiration pneumonia can develop.Consequently, sepsis, respiratory distress, and even death can result (Longo et al., 2019).
Additionally, fasting aids in abdominal clearing and enhances vision during the procedure, making it more straightforward to locate and access the desired nerve roots (Niehaus & Mora, 2022).Hypoglycaemia, hypotension, and bradycardia are risks that can be decreased by fasting before and after a paravertebral nerve block (Sullivan & Wall, 2012).In addition, xylazine effects can impair gastrointestinal motility, which raises the danger of aspirating stomach contents and regurgitating them (Seddighi & Doherty, 2016), reducing the amount of food and rumen contents in the digestive tract to promote drug absorption assist boosting the effectiveness of the drug and shorten onset of action (Riebold, 2015), Additionally, since the presence of food and rumen contents in the digestive tract can exacerbate the adverse of xylazine, such as hypotension or respiratory depression, fasting can help lower the risk of these side effects (Lin, 2015).The body weight of a goat determines how much medication is required; however, if food and rumen contents are not taken into account, the dosage may be incorrect (Riebold, 2015).The results of this investigation, which showed that lignocaine and bupivacaine were fully miscible, are in tandem with an earlier report from a study published by Oguntoye & Adetunji (2009) on goats.The practice of mixing short-and long-lasting local anaesthetic agents is based on the assumption that there is no drug-drug interaction and that both agents behave as if the other agent were not present.The miscibility may be explained by the Pkas of lidocaine and bupivacaine, which are somewhat similar, aside from the fact that both local anaesthetics are aminoamides (de Araújo et al., 2019;Lawan et al., 2019).Because their serum concentrations fall within the same range as those of the component drugs present when injected, pharmacokinetic studies of such mixtures have proven safe (de Araújo et al., 2019;Lawan et al., 2019).Loco-regional anesthesia is preferably paired with sedation to offer humane, stress-free pharmacological immobilization of the animal patient for the planned surgery in veterinary practice (Lawan et al., 2019).Sedatives frequently used in small ruminants include xylazine, acepromazine, and diazepam (Hall et al., 2000;Lawan et al., 2019).Additionally, Oguntoye & Adetunji (2009) reported the need for sedatives and local anesthetics to achieve proper surgical anaesthesia.However, it also induces significant cardiorespiratory depression and osmotic dieresis in ruminants (Kalhoro, 2006;Molaei et al., 2010).Acepromazine, a phenothiazine tranquilizer, only has a minor sedative effect, has no analgesic effects, and causes peripheral vasodilation and moderate hypotension (Hall et al., 2000;Lawan et al., 2019).Although there are numerous sedatives available, xylazine and acepromazine were used in this study because they are highly potent sedatives known to provide profound drowsiness and relaxation that can last for a considerable period (Dzikiti et al., 2009;Vesal et al., 2011).This is significant when extended sedation is necessary, such as during a surgical procedure (Seddighi & Doherty, 2016).Also, when compared to other sedatives, xylazine and acepromazine are relatively affordable (Bednarski, 2015).
The slight and transient decrease in PCV seen in this study after xylazine injection demonstrates that it is risky to administer xylazine to animals with lower PCV because the sedative effect can have negative consequences on goats with low packed cell volume (PCV), making them more vulnerable to those effects (Potter et al., 2022).Blood pressure and pulse rate may drop due to xylazine, which may result in less oxygen reaching tissues in the body, including the brain, heart, and other vital organs like the lungs (Rankin, 2015).The effects of hypoxia may be exacerbated in goats with low PCV as a result of this, which can further reduce the ability of the blood to carry oxygen, as reported by Jones & Allison (2007).The slight decrease in the rectal temperature after 20 minutes of acepromazine administration recorded in this study can be due to environmental temperature, dehydration of the goats, or the animal health status, corroborating the report by Potter et al. (2022).Acepromazine has the propensity to promote mild vasodilation and increase blood flow to peripheral tissues; platelets may have been temporarily sequestered in the spleen and other organs, resulting in a minor transitory reduction in platelets (Rubio et al., 2022).Xylazine is capable of promoting vasoconstriction and reduces blood supply to peripheral tissues, which results in platelet sequestration in the spleen and other organs in goats; decreased platelet count recorded in this study occurred after injection of the xylazine (Sutil et al., 2017).Goats with thrombocytopenia, which is a condition that increases the risk of bleeding, may be more susceptible to the adverse effects of sedatives like acepromazine and xylazine (Posner, 2018).Haemoglobin concentration, haematocrit, and RBC count in goats are three RBC characteristics that can decrease following xylazine administration to goats (Ukwueze et al., 2023), this causes vasoconstriction, which reduces blood flow to peripheral tissues and increases RBC sequestration in the spleen and other organs (Sutil et al., 2017).The significant elevation of eosinophils post-xylazine administration observed in this study may be connected to how the drug affects the sympathetic nervous system, which also determines how quickly immune cells are released from the bone marrow into the bloodstream (Nance & Sanders, 2007).Other blood parameters recorded in this study were considerably higher in females than in males, which may be related to hormonal differences; oestrogen has been proven to have vasodilatory effects, which may result in increased blood flow and higher blood pa-rameters in females (Samir et al., 2020).The sexual dimorphism of mammalian haemograms is naturally reflected in the variation in red cell characteristics between male and female goats (Underwood et al., 2015;Samir et al., 2020).Within the first 20 minutes after administration of acepromazine in this study, there was a considerable drop in the rectal temperature, heart rate, and respiratory rate; thisthe vasodilatory effect of the drug may have caused this decrease, lowered metabolic rate, altered thermoregulation, and decreased physical activity (Posner, 2018).
Despite the fact that many anesthetists steer clear from using xylazine and other alpha-two agonists due to the established sensitivity of ruminants to these drugs, the rapid and smooth onset of the sedative effect of xylazine is beneficial for emergency scenarios (Ewing, 1990;West et al., 2014;Dugdale et al., 2020).This observation from this study, which pointed to the risk of hypothermia in goats using acepromazine, has been previously reported (Dzikiti et al., 2009).This study may not accurately reflect the results that might be obtained across the various goat breeds and age groups since it only used a small number of goats from a single breed and a specific age range (one to two years).

Conclusions
In conclusion, this work should encourage more investigation into small ruminant anaesthesia.Specifically, this study shows that xylazine can be an excellent substitute for sedating small ruminants in combination with the distal paravertebral technique.

Table 1
Haematolgical parameters of goats at different sampling intervals after administration of either XLB or ALB

Table 2
Blood parameters of goats according to gender after administration of either XLB or ALB

Table 3
Physiological parameters of goats at different sampling intervals after administration of either XLB or ALB *Different superscripts represent statistically significant differences (P < 0.05)