Comparative evaluation of ropivacaine, ropivacaine- dexmedetomidine and ropivacaine – clonidine combinations for epidural analgesia in cattle

Epidural analgesia is one of the most popular, reliable and safe techniques in animals that can provide analgesia for a variety of surgical procedures. Epidural anaesthesia has been shown to cause less cardiopulmonary and other systemic side effects than general anaesthesia in ruminants (Hall et al., 2001). Local anaesthetics are usually used for these procedures and for postoperative analgesia. However, because local anaesthetics cause both sensory and motor blockage, ataxia can develop in the hind legs, causing the animal to lie down. Alpha 2 adrenergic agonists become popular because of their sedative, analgesic, antihy- pertensive, antiemetic actions in addition to reducing the anaesthetic drug requirements. Alpha 2 adrenergic agonists have been tried either alone or in combination with other drugs to prolong the duration of anaesthesia (Swami et al., 2012) for epidural administration. Ropivacaine is a new long acting amide local anaesthetic with structural and pharmaco- dynamics similarly to bupivacaine. However, ropivacaine has a lower central nervous system and cardiotoxic potential than bupivacaine. Ropivacaine has been used as epidural analgesia in buffaloes (Kamble et al., 2016) and cattle (Araujo et al., 2012). Dexmedetomidine is a potent and highly selective α 2 adrenoceptor agonist with sympatholytic, sedative, amnestic and analgesic properties. It reduces the dose requirements of opioids and anaesthetic agents and attenuates the haemodynamic response to tracheal intubation and surgical stimuli. Clonidine, a partial α 2 adrenergic agonist has analgesic properties and potentiates local anaesthetic effects, increases the intensity and duration of analgesia. It is known to have sedative properties and the side effects are hypotension and bradycardia. The present study was carried out to study physiological and pulseoximetric changes after epidural administration of  ropivacaine, ropivacaine- dexmedetomidine and  ropivacaine – clonidine combinations in cattle.

Cattle of either sex aged between 1 yr to 6yrs, presented to the college clinic with various surgical problems were randomly selected and routine clinical and haematological examinations were carried out. Among those, eighteen animals of either sex with surgical conditions like tail injuries (4), urolithiasis (4),anal tumours(4), perineal tumours(4) and extensive lacerations of hind limbs (2) were selected and used for present study. The animals were randomly divided into three groups of six animals each. Group I animals were given ropivacaine hydrochloride (0.75%) at 0.25 mg/kg body weight, Group II animals were administered with ropivacaine hydrochloride (0.75%) at 0.25 mg/kg body weight and dexmedetomidine at 5 µg/kg b.wt and Group II animals were administered with ropivacaine hydrochloride (0.75%) at 0.25 mg/kg body weight and clonidine at 2 µg/kg b.wt in the sacrococcygeal site. In all the animals, parameters like time of sedation, analgesic effect, muscular relaxation, reflexes and recovery time after epidural administration of ropivacaine alone and in combination with dexmedetomidine and clonidine were recorded.
        
Physiological parameters like respiratory rate, rectal temperature, pulse rate and heart rate were recorded at 0, 5, 10, 15, 30 and 60 minutes time intervals. Blood samples were collected to estimate haematological and serum biochemical changes like PCV, Hb, ALT (IU/ml), AST (IU/ml), ALP (IU/ml), blood glucose(mg/dl) and serum cortisol (ng/ml) at 0, 30, 60 and 120 minutes time intervals after epidural analgesia.

In our study onset of analgesia differed significantly between the groups. The fastest onset of analgesia was produced by ropivacaine-dexmedetomidine combination followed by ropivacaine-clonidine combination and slowest onset was recorded with ropivacaine in all the animals. Similar trends for onset of analgesia with ropivacaine-dexmedetomidine combination were reported by Aksoy et al., (2012) in cows.Regarding the depth and spread of analgesia, statistically significant difference was noticed between the groups throughout the study. The spread of analgesia was more cephalic with ropivacaine-dexmede- tomidine epidural analgesia. Profound analgesia was observed in animals during ropivacaine-dexmedetomidine epidural injection followed by group III and group I. There was severe ataxic in the animals of group II and they became recumbent within 10 minutes.
        
In the present study disappearance and reappearance of the various reflexes were recorded to assess the effect of anaesthetics in cattle (Table 1). Animals in group II showed rapid abolition and prolonged reappearance of all  reflexes followed by group III and I animals. There was significant difference between the groups in reflex scores at any recorded intervals. This might be attributed to the fact that α 2 adrenoreceptor agonists significantly elevate the nociceptive threshold mediated by α 2 adrenoceptors located in the dorsal horn of the spinal cord (Rafee et al., 2016).
 

        
The combination of ropivacaine-dexmedetomidine produced deeper and prolonged analgesia followed by ropivacaine-clonidine and ropivacaine alone. The prolongation of the motor block of ropivacaine-dexme- detomidine can be explained by the binding of α 2 adrenoreptor agonists to motor neurons in the dorsal horn and the synergism between local anesthetic and α 2 adreno- ceptor agonists as reported by Kumari et al., (2017) in goats.
        
A non significant decrease in rectal temperature was recorded in group I and group III animals till the entire period of observation. Whereas, group II animals showed non significant decrease in rectal temperature after 10 minutes and reached base value after 60 minutes (Table 2). In the present study non significant decrease in RT after the onset of effect might be due to decrease in heat production due to decreased muscular activity and due to reduced metabolic rate. Similar findings were reported in buffalo calves (Amarpal et al., 2007) and goats (Singh et al., 2015). On the contrary Araujo et al., (2012) reported a significant increase in RT following epidural analgesia in cattle.
 

        
In group I, there was a non significant increase in RR from 5 min after epidural analgesia and reaching maximum of 36.17±5.13 at 60 min. A significant increase in RR following epidural administration of ropivacaine was observed in cattle (Araujo et al., 2012). This is in  contrary with the findings of Singh et al., (2005) in caprine, Amarpal et al., (2007) in buffalo calves and Khajuria et al., (2014) in goats, who noticed non significant change in RR during epidural ropivacaine analgesia. Group II animals showed a non significant fall up to 30 minutes reaching a minimum of 19.50 ± 2.99. A non significant increase in RR was observed in group III animals throughout the period of study (Table1).  Respiratory depression associated with dexmedetomidine might be secondary to the CNS depression produced by α 2 adrenoceptor stimulation. Similar findings were recorded by various workers like Ahmad et al., (2013), Kumar et al., (2016) and Rafee et al., (2016) following premedication with dexmedetomidine in combination with midazolam, ketamine anaesthesia in dogs.
        
In group I, there was a non significant increase in PR from 5 min after epidural analgesia. Group II animals showed a non significant increase in PR after15 min. A non significant increase in PR was observed in group III animals throughout the period of study (Table 2). Aksoy et al., (2012) recorded no change in PR following epidural analgesia with dexmedetomidine and ropivacaine in calves.
          
 In group I, there was a non significant increase in HR from 15 min after epidural analgesia (Singh et al., (2005) in caprines, Amarpal et al. (2007) in buffalo calves. Group II animals showed a non significant decrease in HR after 5 min and reaching a minimum of 56.17±2.29 at 30 min interval. A non significant decrease in HR was observed in group III animals throughout the period of study.  There was a significant difference (p<0.05) between the groups in entire period of observation (Table 2). Ahmad et al., (2013) recorded decrease in HR following intramuscular administration of dexmedetomidine alone or in combination with ketamine, midazolam in dogs. This non significant decrease in HR was due to central sedative, autonomic and peripheral vascular effects of α 2 adrenoceptor agonists. Inhibition of sympathetic tone due to reduction in norepinephrine release from the CNS, vagal activity in response to α  2 agonists induced vasoconstriction and direct increase in the release of acetylcholine from parasympathetic nerves in the heart, have been reported as the possible mechanisms by which α 2 agonists induced bradycardia.
        
In group I non significant increase in SpO₂   was recorded from 10 min after epidural analgesia. However, Amarpal et al., (2007) in buffalo claves, observed no significant change in SpO₂ following epidural analgesia with ropivacaine. Group II animals showed a non significant decrease in SpO₂ after 5 min and reaching a minimum of 84.67 ± 2.39 at 30 min interval. A non significant decrease in SpO₂ was observed in group III animals throughout the period of study. A non significant decrease in SpO₂ might be due to a certain degree of respiratory depression by the anaesthetics as mentioned by Khattri et al., (2013).
        
ECG findings of animals during epidural ropivacaine analgesia showed non significant increase in the heart rate throughout period of observation. Sinus arrhythmia was observed in four animals of this group 30 min after epidural injection. One animal has developed atrial pre mature complex along with sinus arrhythmia 20 min after epidural analgesia. Sinus arrhythmia and hyperkalemia was noticed in one animal after 20 min of analgesia (Fig 1). On the contrary, Amarpal et al., (2007) recorded no change ECG after epidural administration of ropivacaine in buffalo calves.
 

        
ECG findings of group II animals showed non significant decrease in the heart rate throughout period of observation. Sinus arrhythmia was evident in all animals of this group after 15 min of epidural injection (Fig 2). Whereas Aksoy et al., (2012) observed sinus rhythm and no arrhythmias following ropivacaine-dexmedetomidine epidural analgesia.
 

 
ECG findings of animals during epidural ropivacaine - clonidine analgesia showed non significant decrease in the heart rate throughout period of observation. Sinus arrhythmia was observed in four animals of this group after 30 min of epidural injection (Fig 3). One animal has developed atrial fibrillation along with sinus arrhythmia 20 min after epidural analgesia. Sinus arrhythmia and decreased QRS complex was noticed in one animal after 20 min of analgesia.
 

        
There was a non significant increase in haemoglobin and PCV values from 30 min after epidural analgesia in group I and group III animals (Table 3). On the contrary no significant change in Hb and PCV was reported after administration of ropivacaine in goats (Singh et al., 2005) and buffalo calves (Amarpal et al., 2007 and Kamble et al., 2016). Singh et al., (2015) observed decrease in Hb after epidural administration of ropivacaine in goats. Group II animals which were subjected to ropivacaine-dexme- detomidine analgesia showed a non significant decrease in haemoglobin  and PCV after 30 min (Table3). However, the fluctuations in the haemoglobin values were non significant between the groups. Similar findings were reported by Aksoy et al., (2012) in cows, Kamble et al., (2016) and Jaiswal et al., (2017) in buffalo calves and Kumari et al., (2017) in goats during ropivacaine-dexmedetomidine epidural analgesia. In the present study, decrease in HB and PCV might be attributed to the sequestration of blood cells in spleen resulting in to decrease in total erythrocyte count in circulation and simultaneous drop in the Hb and PCV  induced by the adrenolytic property of α 2 adrenoceptor drug (Kumar et al., 2016). The changes observed in haematological parameters in the present study were transitory and compensatory.
 

        
A non significant increase in AST, ALT was noticed in all groups throughout the period of observation but this increase was within the normal physiological limit (Table 4). The changes in AST and ALT might be explained by the fact that ropivacaine and dexmedetomidine undergo complete biotransformation by glucoronidation and by cytochrome P₄₅₀ mediated alphatic hydroxylation to inactive metabolites in the liver (Kumari et al., 2017). This is in agreement with the findings of Kumari et al., (2017) who evaluated ropivacaine, ropivacaine-dexmedetomidine epidural analgesia in goats.
 
  
 
In our study a non significant increase in ALP was noticed in group I and III animals during the entire period of observation and a non significant decrease in ALP was observed in animals during ropivacaine-dexmedetomidine epidural analgesia (Table 4). Ahmad et al., (2013) recorded significant increase in ALT and ALP during ropivacaine- xylazine epidural analgesia in goats. Jaiswal et al., (2017) observed non significant increase in ALP in buffalo claves following dexmedetomidine analgesia. On the contrary, Kumari et al., (2017) observed no change in ALP following epidural anaesthesia with ropivacaine and ropivacaine-dexmedetomidine in goats.
        
In group I, there was a non significant increase in glucose values at 30 min after epidural analgesia (Table 4). Kumari et al., (2017) also observed increase in blood glucose levels following administration of epidural ropivacaine in goats. Significant increase (p<0.05) in glucose values was observed in group II and III animals throughout the period of study animals following epidural administration of ropivacaine-dexmedetomidine and ropivacaine-clonidine. The variations in glucose values differ significantly (p<0.05) between the groups. Similar observations were reported by Ahmad et al., (2013), Kumari et al., (2017) in goats, Kamble et al., (2016), Jaiswal et al., (2017) in buffalo calves after epidural administration of different anaesthetics. Hyperglycemia was more and longer in animals following ropivacaine-dexmedetomidine injection and might be due to more depression of central nervous system, more stress to the animals induced inhibition of insulin release by stimulation of pancreatic B cells and to increased production of glucose in liver (Kumari et al., 2017).
        
In group I, there was a non significant increase in cortisol values at 120 min after epidural analgesia (Table 4). A significant decrease (p<0.05) in cortisol values were recorded in group II animals throughout the period of study.  In group III non significant increase in cortisol was observed up to 60 min. The changes in cortisol values were non significant between the groups.
        
Elevated glucose levels have been correlated with increase in cortisol level. Under stressful condition especially during anaesthetics there is an increased liberation of glucocorticoid, which could be responsible for the rise in glucose level (Kumar et al., 2016).  In our study, a non significant increase in cortisol was observed in animals subjected to ropivacaine, ropivacaine-clonidine analgesia. This increase in serum cortisol might be attributed due to increased level of stress of anaesthesia. Where as a significant decrease in cortisol was recorded in ropivacaine-dexmedetomidine group throughout the observation period. This is in agreement with the findings of Bishat et al., (2016) following dexmedetomidine-etomidate-sevoflurane anaesthesia in dogs.
        
The results of the study have shown that the addition of either dexmedetomidine or clonidine as adjuvant to epidural ropivacaine not only prolongs the duration of analgesia but also provides stable cardiovascular parameters. Dexmedetomidine has a visible edge over clonidine as it enables an earlier onset and establishment of sensory and motor block. Further, addition of these two adjuvants promotes faster onset compared to established time of onset of analgesia with ropivacaine alone.

It is concluded that all the three anaesthetics drug combinations can be used safely in cattle for epidural analgesia. However dexmedetomidine is a better adjuvant than clonidine in epidural analgesia as far as stable cardio-respiratory and haemato-biochemical parameters are concerned. Hence, ropivacaine along with dexmedetomidine produced better epidural analgesia with least effect on haematological and biochemical profiles and therefore, be recommended for epidural analgesia in cattle.