Comparison of Clinical and Hemodynamic Effects of Isoflurane and Sevoflurane Anesthesia in Calves

Background : Inhalation anesthesia is the preferred method for use on many animal species, including ruminants, due to its superiority over the injectable anesthetics. The most commonly used inhalation anesthetics are isoflurane and sevoflurane The aim of the study was to investigate the effects of isoflurane and sevoflurane anesthesia on the cardiovascular system of calves. Materials, Methods & Results : A total of 20 calves (11 male, 9 female) between 1 and 6 months in age and 50 to 85 kg in body weight were used. The calves were divided randomly into two groups of 10 each, with one group being administered isoflurane and the other sevoflurane. An intramuscular dosage of 0.1 mg/kg of xylazine was administered to the calves as premedication. Induction was performed 10 min after calves were given an intramuscular dosage of 4 mg/kg of ketamine. Inhalation anesthesia was maintained with isoflurane or sevoflurane in 100% oxygen saturation. Before anesthesia, after induction and at intervals of 5, 10, 15, 20, 25, 30, 45, and 60 min of anesthesia, the body temperature, heart rate, and respiratory rate of the calves were recorded. Additionally, before anesthesia, after induction and


INTRODUCTION
Inhalation anesthesia is the preferred method for use on many animal species, including ruminants, due to its superiority over the injectable anesthetics [3,4,36].The most commonly used inhalation anesthetics are isoflurane and sevoflurane [28].Isoflurane is a clear, colorless, stable liquid inhalation anesthetic.Induction of and recovery from isoflurane anesthesia are rapid due to the low blood/gas partition coefficient [17,30].Sevoflurane is a colorless, liquid, nonirritant, nonflammable and nonexplosive volatile anesthetic agent with a slightly etheric odor.Induction of, recovery from and the control of intraoperative awareness of sevoflurane anesthesia is faster than isoflurane anesthesia, but its cost is quite high [17,30].
This aim of the present study was to investigate the effects of isoflurane and sevoflurane anesthesia on the cardiovascular system of calves.

Animals
Twenty calves undergoing general anesthesia for variety of clinical reasons in Adnan Menderes University Veterinary Faculty Surgery Department were enrolled in the study A total of 20 calves (11 male, 9 female) between 1 and 6 months (isoflurane average 3.2 ± 0.45, sevoflurane average 2.55 ± 0.39) in age and 50 to 85 kg in body weight (isoflurane average 64.5 ± 2.63, sevoflurane average 64.30± 2.80) were used.The calves were divided randomly into two groups of 10 each, with one group being administered isoflurane and the other sevoflurane.The calves were premedicated with an intramuscular dosage of 0.1 mg/kg of xylazine (Alfazyne ® ) 1 , and induction was performed 10 min later via an intramuscular dosage of 4 mg/kg ketamine (Alfamine ® ) 1 .Inhalation anesthesia was maintained with either isoflurane (Isoflurane ® ) 2 or sevoflurane (Sevorane Likit ® ) 3 in 100% oxygen saturation.

Analysis
Serum electrolyte [sodium (Na ++ ), ionized calcium (Ca ++ ), potassium (K + ), magnesium (Mg ++ )] and blood gases [arterial pH (pH), arterial carbon dioxide pressure (pCO 2 ), arterial oxygen pressure (pO 2 ), bicarbonate concentration (HCO 3-), total carbon dioxide (TCO 2 ), hematocrit(HCT), and oxyhemoglobin saturation (O 2 Sat)] were evaluated in the blood samples taken before and after induction and at intervals of 15, 30, 45, and 60 min of anesthesia.The second derivation, durations and amplitudes of the P and T waves, durations and amplitudes of the QRS complex, and durations of PQ and QT intervals were evaluated on the electrocardiography (ECG) recorded before anesthesia, after induction and during anesthesia.Following anesthesia termination, extubation time and the time it took for the straightening of the head and standing up were recorded.

Statistical analysis
The results were analyzed through descriptive statistics using the Statistical Package for Social Sciences (SPSS, IBM) 19.0.All data are presented as the arithmetic mean ( x ) and the standard error of the mean (S x ).Distribution and fitness of the data were evaluated by the Shapiro-Wilks test.Statistical tests were performed via two-way variance analysis in repeated measures, and multiple comparisons were corrected with the post-hoc Generalized Linear Model (GLM).Differences were considered statistically significant if P < 0.05.

RESULTS
The animals were anesthetized and operated on for the treatment of their respective conditions, which included 12 cases of umbilical hernia, 6 cases of omphalitis and 2 cases of omphalophlebitis (Table 1).Physiological parameters, electrolyte analysis results, blood gas values and electrocardiography (ECG) results are shown in Tables 2, 3, and 4, respectively.
During operations, the mean concentration of isoflurane was 2.3% (1.5-3) and 4.07% (2-5) for sevoflurane.The average operation time was 66.10 ± 5.13 min in the isoflurane group and 65.20 ± 9.35 min in the sevoflurane group.During the operations, 2 animals in the isoflurane group and 3 animals in the sevoflurane group urinated.Saliva, mucus, regurgitation, and defecation were not observed in either of the groups.Muscle relaxation was near normal in all groups.
Changes in the waves during anesthesia for the isoflurane and sevoflurane groups were not statistically significant (P > 0.05).Prior to anesthesia, there was no arrhythmia in any of the calves in the isoflurane group.During anesthesia, a second degree atrioventricular (AV) block was observed in one calf.For this arrhythmia, no intervention with medication was made, as the heart rate was within the physiological limits during the surgery, and the patient was followed up closely.In the sevoflurane group, there was no arrhythmia according to the ECGs taken before and during anesthesia.

DISCUSSION
Although it is inexpensive but operationally limited, inhalation anesthesia is a more preferred method to that of injectable anesthesia for small ruminants, especially those that are weak, pregnant, very young or older, and in operations that last longer than an hour or in complicated surgical applications.Other important advantages of inhalation anesthesia are its manageable anesthetic depth and fast awakening from it.This study aimed to investigate the effects of isoflurane and sevoflurane anesthesia on the cardiovascular system of calves.
In ruminants, isoflurane has an induction concentration of 3-5% and an anesthetic concentration of 1.5-3% [7], while sevoflurane has an induction concentration of 4-6% and an anesthetic concentration of 2.5-4% [14,31].In this study, the concentration of isoflurane was 2.3% (2-5) and that of sevoflurane was 4.07% (3-5) for surgery.The calves were premedicated with a 0.1 mg/kg intramuscular dosage of xylazine, induction was performed with a 4 mg/kg intramuscular dosage of ketamine, and orotracheal anesthesia was maintained with either isoflurane or sevoflurane inhalation.In the isoflurane group, extubation, straightening of the head and standing up times were 12.40 ± 3.77 min, 20.4 ± 1.57 min, and 30.80 ± 1.89 min, respectively.In the sevoflurane group, extubation, straightening of the head and standing up times 13.40 4.99, 19.2 ± 1.49, and 28.0 ± 1.83 min, respectively.Although the calves in the isoflurane group were extubated earlier than those of the sevoflurane group, the time elapsed for straightening of the head and standing up were longer than that of the sevoflurane group.The anesthesia protocol provided a smooth anesthetic administration, general anesthesia and awakening.
Common complications during inhalation anesthesia in small ruminants include hypersalivation, regurgitation, tympani, apnea urination, defecation, and muscle tremors.In order to prevent these complications, it is recommended that animals be restricted from consuming food, 12-18 h, and water, 2-6 h, before anesthesia [17,26,31].In compliance with this recommendation, the animals in this study were prevented from food intake 12 h before and from water intake 6 h before anesthesia.During the operations, two animals in the isoflurane group and three animals in the sevoflurane group urinated.No other complications were encountered.Some authors [2,9,13,14,41] have reported that in many animal species, reduction in body temperature after inhalation anesthesia is due to impaired thermoregulation from inhibition of the limbic-hypothalamic center on account of the applied drugs and to the decrease of the metabolic activity and muscle activities of the organism resulting from deterioration of the hemostasis of the body heat.In the present study, a decrease in body temperature was observed, but these parameters remained within the normal limits for each group, despite the decrease being statistically significant in both groups.In particular, the decrease in the isoflurane group was significant from the 5th min of the anesthesia, compared to the baseline value, whereas it was significant from the 10th min of the anesthesia in the sevoflurane group.These findings were similar to previous studies, where body temperature was reported to decrease in buffalos [6], dogs [9], goats [22] and camels [2] after isoflurane anesthesia, and in dogs [9], cattle [14] and goats [22] after sevoflurane anesthesia.In the current study, regarding body temperature, there were no significant differences between isoflurane and sevoflurane anesthesia.
It has been reported that the effects of isoflurane and sevoflurane on the cardiovascular system are similar, and that depending on dosage, both anesthetics decrease arterial blood pressure, cardiac efficiency and systemic vascular resistance [1,11,20,28,40].The effect of isoflurane anesthesia on heart rate has been stated to vary among different species of animals and according to age.For example, an increased heart rate has been reported in dogs [12], horses [39], bulls [15], and cattle [35], and a decreased heart rate in lambs [5], sheep [13], and pigs [32].In dogs, the heart rate either rises or remains stable [38] by increasing the alveolar concentration in the inhalation anesthetic, or it drops by an increase in anesthetic depth due to increasing vagal tonus [17].In the current study, the heart rate decreased in both the isoflurane and sevoflurane groups.This decrease was statistically significant at premedication, induction and at the 5th, 10th, 15th, and 20th min intervals of anesthesia in the isoflurane group (P < 0.05; P < 0.01).In the sevoflurane group, the decrease in heart rate was statistically significant at premedication, induction and during anesthesia (P < 0.01; P < 0.001).There was no statistically significant difference in heart rate between the two groups (P > 0.05).The heart rate remained within the normal limits for each group in all time periods.The concentration of the anesthetic gases released was kept constant during anesthesia, and the operation was performed while the animal was under surgical anesthesia.A decreased heart rate in the anesthetized animals was expected to be related with the increased depth of the isoflurane and sevoflurane anesthesia.When both groups were compared in terms of heart rate, there was no statistically significant difference, the results of which support the idea that the reduced number of heart beats was in fact caused by the depth of the anesthesia.
It has been reported that, like other inhalation anesthetics, sevoflurane and isoflurane cause dosagerelated respiratory depression in many animal species, and that the effects of the two anesthetic agents on the respiratory system are similar.As the dose increases, depression deepens in spontaneous ventilation [9,21].Studies have reported that sevoflurane anesthesia induces respiratory depression in cattle [35], cats [21], and dogs [10], and that isoflurane induces respiratory depression in cattle [35] in a dose dependent manner.In the present study, the respiratory rate decreased after premedication and increased after induction and during anesthesia for both groups.This increase was statistically significant for the isoflurane group but not in the sevoflurane group.However, there was no statistical difference between the two groups.The findings obtained in this study differ from those reported by Hikasa et al. [21] and Doi et al. [10], where it was stated that the increase in respiratory rate was possibly caused by anesthesia or pain.In some steps of the operations, after the depth of anesthesia was changed, the respiratory rate was found to be normal.The difference between the findings from this study and those from the afore mentioned two studies could be attributed to an ineffective anesthetic level during operations.Furthermore, certain studies have emphasized that the increase in respiratory rate may be caused by the increase in the amount of pCO 2 resulting from the induction of the central and peripheral chemoreceptors [8,18,24,29,42].
Isoflurane has been reported to cause respiratory depression depending on dosage,and in the general anesthesia with spontaneous respiration, an increase in the amount of CO 2 in the blood and a decrease in arterial pH occur [8,18,24,29,42].In this study, the decrease in the pH level of the isoflurane group during administration of anesthesia at the 15th (P < 0.01), 30th (P < 0.001), 45th (P < 0.001), and 60th (P < 0.001) min compared to the baseline value was statistically significant.The decrease in the pH level of the sevoflurane group, after induction (P < 0.05) and during administration of anesthesia at the 15th (P < 0.01), 30 (P < 0.01), 45th (P < 0.001) and 60th (P < 0.001) min compared to the baseline value was statistically significant.In the isoflurane group, pCO 2 was determined to be 45.46 ± 1.67 at the beginning, 52.83 ± 2.14 after induction, 59.10 ± 1.82 at the 15th min, 61.16 ± 1.83 at the 30th min, 67.47 ± 0.76 at the 45th min, and 68.14 ± 1.12 at the 60th min.At these time points, the increase from the baseline value was statistically significant.In the sevoflurane group, pCO 2 was determined to be 48.04 ± 1.13 at the beginning, 55.96 ± 2.05 after induction, 61.42 ± 3.08 at the 15th min, 64.45 ± 2.91 at the 30th min, 68.03 ± 2.79 at the 45th min, and 69.80 ± 2.83 at the 60th min.At these time points, the increase from the baseline value was statistically significant.However, there was no statistically significant difference in pCO 2 levels between the two groups.Additionally, respiratory acidosis developed in both groups due to the increase of pCO 2 value and decrease of pH.These results showed similarity with the findings of Hikasa et al. [18].The increase in the levels of pCO 2 during isoflurane and sevoflurane anesthesia was reported to be higher in dogs [37] than in cats [19] and humans [10].Schulze et al. [33], in their study, stated that the increase in pCO 2 in animals under isoflurane anesthesia was associated with hypoventilation and pressure on the lungs during dorsal recumbency of the animal.In this study, the increase in pCO 2 and the cause of respiratory acidosis were attributed to the animals'recumbent position.
The present study found that there was a decrease in the HCT values in the isoflurane and sevoflurane groups compared to baseline values.While this decrease was not statistically significant in the isoflurane group, it was statistically significant at the 30th (P < 0.05), 45th (P < 0.05) and 60th (P < 0.05) min in the sevoflurane group.However, there was no significant difference in HCT values between the two groups, and although the HCT values decreased, they were still within the physiological limits.The decrease in the HCT levels during anesthesia could have been the result of fluid leaks from the capillary membranes or the effect of the sampling methods.
Changes in the O 2 Sat, Na ++ , Ca ++ and K + levels in both the isoflurane and sevoflurane groups were not statistically significant compared to the baseline values, and there was no statistical difference between the groups.Similar findings have been reported in goats [18] and buffalos [6].
Preanesthetics and anesthetics may cause clinically different forms of arrhythmia due to the alterations in heart rate they precipitate [23,34].Although these arrhythmias are able to be simply assessed by palpation of the heart beat auscultation or femoral pulse, electrocardiography is necessary for definitive diagnosis of arrhythmia and to determine the appropriate treatment.For this reason, it is important to include an ECG to the monitoring parameters in all patients under anesthesia.Normal sinus rhythm was detected in the ECGs of all the animals used in this study.Güzel and Perk [16] reported the formation of an atrioventricular junctional rhythm in one of the 24 patients taking isoflurane anesthesia.Similarly, in our study, a second degree AV block was formed on a calf in the isoflurane anesthesia group.In agreement with Miller et al. [25], who stated that intervention was not necessary so long as the arrhythmia did not progress, no intervention was made for the calf; however, it was closely followed, and after a short time, the rhythm returned to a normal level.On the other hand, in the sevoflurane group, no arrhythmia was observed in ECGs taken before and during anesthesia.

CONCLUSIONS
In conclusion, the effects of isoflurane and sevoflurane anesthesia on the cardiovascular and respiratory system were similar, and although the changes that emerged during anesthesia were statistically significant, it was nonetheless found that the changes were within the physiological limits.As the results showed there to be no statistical difference between the groups, both of the anesthetics can be safely used on calves.Though with that said, it is believed that isoflurane would be economically preferable to sevoflurane, as the latter is more expensive.In evaluating all these findings collectively, it can be concluded that using isoflurane is more advantageous for use on calves.Acknowledgements.The authors would like to acknowledge the assistance of the surgery departement staff and veterinary students of the University of Adnan Menderes in data collection and the Adnan Menderes University Scientific Research Foundation for financial support.The authors do not have potential conflicts of interest to declare.

Ethical approval.
The ethical approval of the study was provided by the University's Institutional Animal Care and Use Committee (approval number: 2012/080).Each calve owner consented to the anesthetic procedure.

Declaration of interest.
The authors report no conflicts of interest.The authors alone are responsible for the content and writing of paper.

Table 1 .
Operation time, extubation time, head straightening, time to standing up of groups.

Table 2 .
Effects of different anesthesia groups on body temperature, respiatory rate, heart rate over time.

Table 3 .
Blood gas and electrolyte values of calves under isoflurane and sevoflurane anesthesia procedures.

Table 4 .
Electrocardiographic parameters of calves under isoflurane and sevoflurane anesthesia procedures.