Evaluation of sevoflurane and isoflurane as maintenance agent in buffaloes after glycopyrrolate-xylazine-butorphanol-propofol anaesthesia 

Diaphragmatic hernia (DH) is a serious digestive disorder of recently parturited or pregnant buffaloes causing huge economic losses to farmers and livestock owners. Surgical correction of DH in buffaloes is a two stage procedure (Krshnamurthy et al., 1985). Laparo-rumenotomy through left flank under paravertebral block is followed by diaphragmatic herniorrhaphy under general anaesthesia. The buffaloes reported for diaphragmatic herniorrhaphy usually belong to category III or IV of ASA (American Society of Anaesthesiologists). Also, supine position in buffaloes during trans-abdominal approach for diaphragmatic herniorrhaphy results in a “low pressure-low flow” circulatory state which is aggravated during pregnancy (Peshin et al., 1987). So, an anaesthetic protocol having least depression on the cardiopulmonary system is highly desired. Balanced anaesthetic combination of glycopyrrolate-xylazine-butorphanol-Propofol produces smooth and rapid anaesthesia followed by quiet and excitement free recovery in buffalo calves for short duration (Potaliya et al., 2015). For longer duration surgeries continuous infusion or repeated top up doses of propofol are required (Hall and Peshin, 1996). The metabolism and elimination of propofol increase the stress on already compromised liver (Cagnardi et al., 2009); whereas isoflurane and sevoflurane have very little metabolism inside the body (Steffy et al., 2015). At present, isoflurane is the most widely used inhalant agent in veterinary anaesthesia but sevoflurane, a non-irritant inhalant, is gaining popularity due to its even lesser blood gas partition coefficient which provides more rapid induction and recovery from anaesthesia and a rapid alteration of anaesthetic depth (Kazama and Ikeda, 1988; Seller et al., 2013). Also, sevoflurane appears to offer a more stable heart rate profile in animals (Ebert et al., 1995). Isoflurane has been used as a safe and effective maintenance agent in water buffalo in experimental (Singh et al., 2013) as well as clinical studies (Bodh et al., 2015) but no information is available on the use of sevoflurane in water buffaloes. So, the present investigation was planned to compare the efficacy and safety of sevoflurane and isoflurane in clinical cases of buffaloes undergoing diaphragmatic herniorrhaphy.

The study was conducted on 12 clinical cases of DH in buffaloes aged 2-6 years and weighing 220Kg to 470Kg. These animals were randomly assigned in two groups of six animals each. All the buffaloes were premedicated with glycopyrrolate (0.01 mg/kg, IM) followed by xylazine (0.05 mg/kg, IM) and then butorphanol (0.03mg/kg, IV) at intervals of 10 minutes (Potaliya et al., 2015).  At the onset of ataxia, animals were restrained in lateral recumbency on a padded operation table and intubated after induction with propofol (1.3mg/kg, IV). Endotracheal tube was connected to the large animal anaesthesia machine for maintenance of general anaesthesia using isoflurane (group PI) or sevoflurane (group PS) in oxygen through an agent specific vaporizer and partial rebreathing system. Concentrations of these agents in inhalant mixtures were regulated to maintain adequate depth of anaesthesia by monitoring body reflexes and animal’s response to surgical stimulation. Inhalation of anaesthetic agent was discontinued after the last skin suture. All the animals were administered Ringer’s lactate and normal saline throughout the period of surgery.
        
The clinical and behavioral observations were recorded using blindfold method. The physiological parameters were recorded before rumenotomy, next day before premedication, at 5 min of induction, at 15 min and 30 min of start of inhalation, at recovery and at 24 hours of recovery. Blood samples were also collected in triplicate from the jugular vein at every designated interval of clinical observation for haematology, biochemistry and glucose estimation in EDTA, heparin and sodium fluoride, respectively. Haematology including haemoglobin (Hb), packed cell volume (PCV), total leucocytes count (TLC) and differential leucocytes count (DLC) were estimated in haematology analyzer 1MS4 from blood in EDTA vials. Plasma was harvested from remaining vials by centrifugation at 3000 rpm for 20 min and then stored at -20°C. Blood biochemical parameters viz. glucose, triglycerides, cholesterol, lactate dehydrogenase (LDH), alanine amino transferase (ALT), aspartate amino transferase (AST), alkaline phosphatase (ALP), gamma glutamyl transferase (GGT), direct bilirubin, plasma urea, creatinine, total plasma proteins and albumin were analyzed with ²EM 200™ chemistry analyzer using commercially available ₃Transasia XL kits while sodium, potassium, chloride and calcium were analyzed by automatic electrolyte analyser ⁴Easylyte^TM.
        
For clinical observations, a fixed criterion as per Bodh et al., (2015) was followed for evaluation of quality of anaesthesia. Scoring was done to assign numerical values starting from 1 to 4 (1-poor, 2-fair, 3-good, 4-excellent) for premedication quality, induction quality, maintenance quality and recovery quality. Qualitative and subjective effects (sedation, analgesia, muscle relaxation) of the drugs were judged by observing physical response of the animal to surgical stimulation during herniorrhaphy. Numerical values starting from 0 to 3 (0-no effect, 1-mild effect, 2-moderate effect, 3-deep effect) were used for scoring sedation, analgesia and muscle relaxation during maintenance of anaesthesia. For behavioral observations, body reflexes in relation to time were recorded. Physiological parameters like rectal temperature along with ambient temperature, heart rate and respiratory rate were also recorded at each designated interval. The statistical analysis of data was done by one-way-analysis of variance and Duncan’s multiple range test (DMRT).

The animals included in the study were off feed, mostly having recurrent tympany, poor body condition, scanty to no faecal output since many days and few had regurgitation. During surgery severe adhesions were present between reticulum, diaphragm, thoracic cavity and adjoining viscera posing severe threat to life. The average duration of illness, body weight of animals and the quality of anaesthesia during herniorrhaphy are presented in Table 1 and the behavioral parameters are in Table 2.
 

 

        
Preanaesthetic drugs were administered to minimize pain, remove apprehension, facilitate handling of animal,  and to minimize undesirable sympathetic and parasym- pathetic reflex activity. Glycopyrrolate stimulates cardiac reflex and blocks vagus reflex. It has a powerful and prolonged antisialogogue activity than atropine and has fewer tendencies for unwanted CNS side effects than atropine (Proakis and Harris, 1978). Administration of glycopyrrolate before xylazine, reduces salivation and maintains heart rate near normal in compromised animals. Xylazine provides sedation or, in higher doses, restraint (recumbency and light planes of general anaesthesia) in cattle (Carroll and Hartsfield, 1996). Butorphanol in combination with xylazine reduces the dose and duration of sedation than xylazine alone (Lin and Riddell, 2003). A synergism between alpha₂-agonist and opioid analgesic has also been reported in goats (Carroll et al., 1998).
        
Analgesia and sedation scores were significantly high in group PI than in PS (Table 1). Elcock and Sweeny (2002) also reported lower analgesia in human for knee artheroscopy maintained on sevoflurane after propofol-fentanyl anesthesia than on isoflurane. However, the propofol-sevoflurane combination has also been used in cats (Selmi et al., 2005), dogs (Luis et al., 2009) and goats (Setoyama et al., 2003) but without any report of poor analgesia. Induction scores in both the groups were high as propofol is an ultrashort acting anaesthetic agent which has high serum protein binding (Dawidowicz et al., 2006). The lower dose of propofol (@1.3 mg/kg) was sufficient for induction and intubation in buffaloes due to synergism of premedicants, butorphanol with xylazine, as reported in goats (Carroll et al., 1998).The maintenance score and muscle relaxation were similar in both the groups.  The lower blood gas partition coefficients of isoflurane (1.46) and sevoflurane (0.68) helped in maintaining adequate plane of surgical anaesthesia rapidly by adjusting the concentration. Cardiopulmonary functions were well preserved in all the animals maintained on either isoflurane or sevoflurane. Singh et al., (2013) and Bodh et al., (2015) also reported isoflurane to be suitable agent for maintenance of general anaesthesia in buffaloes. Sevoflurane has been used in cattle (Seller et al., 2013) and goats (Setoyama et al., 2003) satisfactorily. It produces dose dependent CNS, cardiovascular and respiratory depressant effects that generally parallel those of isoflurane (Patel and Goa, 1996). Recovery scores were excellent in both the groups as it was rapid, smooth and excitement free. Rapid redistribution of propofol from brain to other tissues and low solubility of isoflurane and sevoflurane were responsible for quick recovery, once discontinued (Read et al., 2002; Seller et al., 2013). In all the animals after glycopyrrolate administration muzzle and nostrils became dry and after xylazine spontaneous activity decreased. Drooping of eyelids and loss of palpebral reflex occurred soon after intravenous administration of propofol. Corneal reflex was intact but sluggish. Intubation was performed after loss of swallowing reflexes and relaxation of jaw. For maintenance in PI group initially vaporizer was set at 3.5% and after 5 minutes maintained at 1.5%-2.5% during the herniorrhaphy,  however, in PS group it was 5% followed by 2.5% to 3.5% during maintenance as sevoflurane has higher minimum alveolar concentration (MAC) than isoflurane in different animals (Aida et al., 1996; Hikasa et al., 2000). With placement of the last skin suture vaporizer was shut off and only oxygen was given till regain of swallowing reflex.
        
Initiation of recovery was manifested by regain of alar, corneal and palpebral reflexes, opening of eyelids and movement of ears. Extubation time in group PS was significantly lower than group PI (Table 2). The times for regain of muscle tone, head rightening reflex and returning to sternal recumbency were similar in both the groups, however, the times taken for standing with ataxia and for complete recovery were significantly less in buffaloes that were maintained on sevoflurane than on isoflurane. Previous studies also reported the duration from recovery to standing to be shorter with sevoflurane than with isoflurane in dogs (Kazama and Ikeda, 1988; Mutoh et al., 1997; Johnson et al., 1998).
        
A significant decrease in rectal temperature was recorded in both the groups. It might be attributed to decrease in the skeletal muscle tone, reduced metabolic rate, muscle relaxation, along with depression of thermoregulatory center and vasodilatation. The ambient temperatures between the two groups varied significantly but the patterns of observations within the group were similar. The effect of ambient temperature is evident in buffaloes of both groups on heart and respiration rate during pre and post anaesthetic period (Table 3). Heart rate increased significantly in both the groups at 15 min of glycopyrrolate as it stimulates cardiac reflex and blocks vagus reflex. Khan et al., (2007) also reported similar findings in buffaloes. The respiratory rate decreased more in groups maintained on isoflurane than on sevoflurane. Ebert et al., (1995) also found sevoflurane to offer a more stable cardiorespiratory profile in horses. Premedication with xylazine and butorphanol might also be associated with respiratory depression (Stoelting, 2011). Sevoflurane and isoflurane have been reported to cause dose dependent decrease in respiratory rate, blood pressure, cardiac output and systemic vascular resistance and an increase in PETCO₂ when maintained at one MAC in humans, dogs, horses, sheep and goats (Aida et al., 1996; Mutoh et al., 1997; Johnson et al., 1998; Hikasa et al., 2000; Galloway et al., 2004).
 

        
Hb, PCV and TLC decreased (Table 4) in both the groups during the anaesthetic period which might be due to pooling of circulating blood cells in the spleen or other reservoirs secondary to sympathetic activity (Gasthuys et al., 1987). Neutrophilia and lymphocytopenia in both the groups could be as a result of surgical trauma and stimulation of adrenal glands (Desborough, 2000).
 

        
Significant increase in plasma glucose levels (Table 5) was observed in both the groups which might be due to increased sympathetic stimulation and insulin inhibitory effect of xylazine and increased gluconeogenesis (Nunez et al., 2004). Injury of muscles by foreign bodies, during rumenotomy and herniorrhaphy as well as restraining for surgery might be the cause of rise in LDH level. There was slight rise in the triglycerides level at five minutes of propofol administration. No significant changes in the AST, ALT, GGT levels were observed between the groups. Total plasma proteins (TP) and A:G ratio revealed a significant decrease (P<0.05) during the period of anaesthesia (from premedication to recovery) in both the groups. The plasma urea and creatinine levels were raised at premedication to 24 hours of recovery than the pre-operative values in both  the groups as animals had no access to oral intake leading to poor state of hydration and compromised haemodynamics (Steffy et al., 1979). There was very little chance of compound A (pentafluoro-isopropenyl fluoromethyl ether) formation as the flow rate of oxygen was high and the circuit was partially open during the entire period of anaesthesia. The decrease in TP and A:G ratio in both groups might be attributed to expanded intravascular volume due to fluid therapy, shifting of fluid from extravascular compartment to intravascular compartment to maintain normal cardiac output (Brock, 1994) and the protein degradation caused by surgical stress and trauma.
 
  
 
Buffaloes of both the groups were deficient in plasma electrolytes (Na, K, Cl, Ca) preoperatively which improved post-operatively towards normal level without any significant difference (Table 4). These buffaloes were anorectic for many days and had reduced water intake. Also, all had inflammatory adhesions of reticulum with adjacent organs of abdominal cavity which adversely affected the rumeno-reticular motility and outflow of ingesta. Therefore, changes in the plasma concentration of electrolytes in such animals were expected (Behl et al., 1997). Fluid therapy during treatment, provision of common salt in drinking water and initiation of food intake after surgery caused increase in plasma concentration of these electrolytes.

Sevoflurane and isoflurane were clinically effective as well as a safe maintenance agent in balanced anaesthetic combination with glycopyrrolate-xylazine-butorphanol-Propofol in buffaloes undergoing diaphragmatic herniorr- haphy. The recovery form anaesthesia was faster and cardio-respiratory depression was lesser with sevoflurane than  isoflurane in buffaloes.