this study was approved by the animal care and use committee at gyeongsang national university ( approval number : gnu-140128-e0006 ) . these birds were hospitalized in the wildlife center in the province of gyeongsangnam - do , republic of korea , due to 
 various orthopedic injuries and had received appropriate medical treatments to recover their health . all vultures in this study were suspected of being between 
 1 and 2 years of age . body weights and lengths of the birds were ranged from 7.5 to 9.0 kg ( mean  sd of body weight , 8.27  0.40 kg ) and from 98 to 104 cm 
 ( mean  sd of body length , 100.9  2.0 cm ) , respectively . although these cinereous vultures were recovered to normal health , they had not been released because 
 of disability . the health status of ten cinereous vultures was assessed by physical examination , diagnostic imaging , cbc and serum biochemical analyses . in 
 addition , no clinical diseases were verified other than their disability caused by the previous orthopedic injuries . after recovering to normal health 
 conditions , the birds were acclimated to the rehabilitation program for at least 7 days prior to the study . the birds were then transferred to temporary 
 individual housing units , and food was withheld for 12 hr prior to anesthesia , although they were allowed access to water ad libitum . the experimental protocol was modified based on dose - related effects obtained from a previous study by naganobu and hagio . differences based on gender were not investigated , because cinereous vultures do not show sexual dimorphism . seoul , korea ) of an isoflurane vaporizer ( multiplus , royal medical co. , ltd . , pyeongtaek , korea ) setting in 100% 
 oxygen ( 3 l / min ) delivered via a mask . a non - rebreathing anesthetic circuit ( modified jackson rees anesthesia circuit ) was used in this study . 
 when voluntary movement of the nictitating membrane was absent for 30 sec , the trachea was intubated with an uncuffed endotracheal tube . the endotracheal tubes 
 with internal diameter of 8.0 mm ( n=8 ) and 7.5 mm ( n=2 ) were chosen to prevent leakage of the anesthetic agent according to the size of cinereous vultures . each 
 bird was restrained in dorsal recumbency to minimize the impairment of sternal motion . after endotracheal intubation , anesthesia was maintained by spontaneous 
 ventilation with isoflurane in 100% oxygen ( 3 l / min ) . the end tidal co2 partial pressure ( petco2 ) and the 
 inspired and end - tidal isoflurane concentrations ( etiso ) and respiratory rate ( rr ) were monitored with a calibrated multigas monitor ( as3 , 
 datex - ohmeda division instrumentarium corp . , helsinki , finland ) . initial anesthesia was maintained at 1.0% etiso . to measure the systolic arterial blood 
 pressure ( sap ) , diastolic arterial blood pressure ( dap ) , and mean arterial blood pressure ( map ) and obtain arterial blood samples for the blood gases and 
 acid - base analysis , a sterile 24-gauge catheter ( angiocath plus , becton dickinson , sandy , ut , u.s.a . ) was inserted aseptically through a small cut - down incision 
 into the superficial ulnar artery . the arterial catheter was connected to a blood pressure transducer ( transpac iv monitoring kit , abbott critical 
 care systems , north chicago , il , u.s.a . ) and a pressure line filled with saline , which was connected to the monitor for heart rate ( hr ) and direct blood 
 pressure ( bp ) monitoring . the values of the blood pressure were zeroed to the atmospheric pressure at the level of the chest . a lead ii electrocardiogram ( ecg ) was monitored using the monitor described above during the procedure . body 
 temperature ( bt ) was also recorded with an oral probe linked to the monitor . throughout the procedure , the bt was maintained at 3940c with a circulating water 
 blanket ( medi - therm , gaymer industries inc . , ochard park , ny , u.s.a . ) and a forced warm air blanket ( warm air hyperthermia system , 
 cincinnati sub - zero products inc . , ansan , korea ) was administered via an 
 intravenous 24-gauge catheter ( angiocath plus , becton dickinson ) placed in the ulnar vein during the procedure at a rate of 10 ml / kg / hr . the 
 environmental temperatures of the operating room were adjusted to between 20c and 23c , by the facilities and plants engineering department of the wildlife 
 center . after instrumentation , each bird was held initially at 1.0 , 1.5 , 2.0 , 2.5 and 3.0% etiso and then at 1.0% etiso for an equilibration period of 15 min in the 
 given order . at the end of the equilibration period , the direct bp , hr , rr and petco2 were recorded , and 0.4 ml arterial 
 blood was collected for ph , partial pressure of arterial oxygen ( pao2 ) , partial pressure of arterial carbon dioxide ( paco2 ) , bicarbonate 
 ( hco3 ) and base excess ( be ) analyses . blood gas analysis ( vetstat , idexx laboratories , inc . , westbrook , me , u.s.a . ) was 
 performed using a 1 ml heparin washed syringe immediately after the blood was sampled . when arrhythmia or respiratory instabilities occurred 
 during the procedure , the anesthetic concentration was immediately decreased to 1.0% etiso . after the procedure , the arterial catheter was removed , hemostasis 
 was performed by manual compression , and the skin was sutured . the vaporizer was then turned off , and the birds were allowed to breathe 100% oxygen until 
 extubation , which was performed when the presence of a swallowing or cough response was observed . time to induction and extubation , and total anesthesia time 
 were recorded for each anesthetic procedure . time to induction was defined as the time from the beginning of isoflurane inhalation to intubation . time to 
 extubation was defined as the time from the cessation of isoflurane administration to extubation . total anesthesia time was defined as the time from the 
 intubation to the cessation of isoflurane administration . all statistical analyses were performed using spss statistics 21 ( ibm corp . , armonk , ny , u.s.a . ) . repeated measures analysis of variance ( anova ) 
 and the bonferroni correction technique for multiple comparisons were used to compare the hr , rr , direct bp , petco2 , bt and blood gas data 
 at each designated anesthetic concentration . this study was approved by the animal care and use committee at gyeongsang national university ( approval number : gnu-140128-e0006 ) . these birds were hospitalized in the wildlife center in the province of gyeongsangnam - do , republic of korea , due to 
 various orthopedic injuries and had received appropriate medical treatments to recover their health . all vultures in this study were suspected of being between 
 1 and 2 years of age . body weights and lengths of the birds were ranged from 7.5 to 9.0 kg ( mean  sd of body weight , 8.27  0.40 kg ) and from 98 to 104 cm 
 ( mean  sd of body length , 100.9  2.0 cm ) , respectively . although these cinereous vultures were recovered to normal health , they had not been released because 
 of disability . the health status of ten cinereous vultures was assessed by physical examination , diagnostic imaging , cbc and serum biochemical analyses . in 
 addition , no clinical diseases were verified other than their disability caused by the previous orthopedic injuries . after recovering to normal health 
 conditions , the birds were acclimated to the rehabilitation program for at least 7 days prior to the study . the birds were then transferred to temporary 
 individual housing units , and food was withheld for 12 hr prior to anesthesia , although they were allowed access to water ad libitum . the experimental protocol was modified based on dose - related effects obtained from a previous study by naganobu and hagio . differences based on gender were not investigated , because cinereous vultures do not show sexual dimorphism . seoul , korea ) of an isoflurane vaporizer ( multiplus , royal medical co. , ltd . , pyeongtaek , korea ) setting in 100% 
 oxygen ( 3 l / min ) delivered via a mask . a non - rebreathing anesthetic circuit ( modified jackson rees anesthesia circuit ) was used in this study . 
 when voluntary movement of the nictitating membrane was absent for 30 sec , the trachea was intubated with an uncuffed endotracheal tube . the endotracheal tubes 
 with internal diameter of 8.0 mm ( n=8 ) and 7.5 mm ( n=2 ) were chosen to prevent leakage of the anesthetic agent according to the size of cinereous vultures . each 
 bird was restrained in dorsal recumbency to minimize the impairment of sternal motion . after endotracheal intubation , anesthesia was maintained by spontaneous 
 ventilation with isoflurane in 100% oxygen ( 3 l / min ) . the end tidal co2 partial pressure ( petco2 ) and the 
 inspired and end - tidal isoflurane concentrations ( etiso ) and respiratory rate ( rr ) were monitored with a calibrated multigas monitor ( as3 , 
 datex - ohmeda division instrumentarium corp . , initial anesthesia was maintained at 1.0% etiso . to measure the systolic arterial blood 
 pressure ( sap ) , diastolic arterial blood pressure ( dap ) , and mean arterial blood pressure ( map ) and obtain arterial blood samples for the blood gases and 
 acid - base analysis , a sterile 24-gauge catheter ( angiocath plus , becton dickinson , sandy , ut , u.s.a . ) was inserted aseptically through a small cut - down incision 
 into the superficial ulnar artery . the arterial catheter was connected to a blood pressure transducer ( transpac iv monitoring kit , abbott critical 
 care systems , north chicago , il , u.s.a . ) and a pressure line filled with saline , which was connected to the monitor for heart rate ( hr ) and direct blood 
 pressure ( bp ) monitoring . the values of the blood pressure were zeroed to the atmospheric pressure at the level of the chest . a lead ii electrocardiogram ( ecg ) was monitored using the monitor described above during the procedure . body 
 temperature ( bt ) was also recorded with an oral probe linked to the monitor . throughout the procedure , the bt was maintained at 3940c with a circulating water 
 blanket ( medi - therm , gaymer industries inc . , ochard park , ny , u.s.a . ) and a forced warm air blanket ( warm air hyperthermia system , 
 cincinnati sub - zero products inc . ansan , korea ) was administered via an 
 intravenous 24-gauge catheter ( angiocath plus , becton dickinson ) placed in the ulnar vein during the procedure at a rate of 10 ml / kg / hr . the 
 environmental temperatures of the operating room were adjusted to between 20c and 23c , by the facilities and plants engineering department of the wildlife 
 center . after instrumentation , each bird was held initially at 1.0 , 1.5 , 2.0 , 2.5 and 3.0% etiso and then at 1.0% etiso for an equilibration period of 15 min in the 
 given order . at the end of the equilibration period , the direct bp , hr , rr and petco2 were recorded , and 0.4 ml arterial 
 blood was collected for ph , partial pressure of arterial oxygen ( pao2 ) , partial pressure of arterial carbon dioxide ( paco2 ) , bicarbonate 
 ( hco3 ) and base excess ( be ) analyses . blood gas analysis ( vetstat , idexx laboratories , inc . , westbrook , me , u.s.a . ) was 
 performed using a 1 ml heparin washed syringe immediately after the blood was sampled . when arrhythmia or respiratory instabilities occurred 
 during the procedure , the anesthetic concentration was immediately decreased to 1.0% etiso . after the procedure , the arterial catheter was removed , hemostasis 
 was performed by manual compression , and the skin was sutured . the vaporizer was then turned off , and the birds were allowed to breathe 100% oxygen until 
 extubation , which was performed when the presence of a swallowing or cough response was observed . time to induction and extubation , and total anesthesia time 
 were recorded for each anesthetic procedure . time to induction was defined as the time from the beginning of isoflurane inhalation to intubation . time to 
 extubation was defined as the time from the cessation of isoflurane administration to extubation . total anesthesia time was defined as the time from the 
 intubation to the cessation of isoflurane administration . all statistical analyses were performed using spss statistics 21 ( ibm corp . , armonk , ny , u.s.a . ) . repeated measures analysis of variance ( anova ) 
 and the bonferroni correction technique for multiple comparisons were used to compare the hr , rr , direct bp , petco2 , bt and blood gas data 
 at each designated anesthetic concentration . mean  sd induction and extubation time were 297.2  33.9 sec and 308.1  37.8 sec , respectively . three of 
 ten vultures developed adverse cardiorespiratory effects as the isoflurane concentration was increased from 2.5% to 3.0% etiso . specifically , sinus arrhythmia 
 occurred in one vulture , and two vultures showed difficulty breathing . as soon as symptoms were observed , the anesthetic concentration was immediately decreased 
 to 1.0% etiso , at which time their arrhythmias and dyspnea disappeared . following the procedure , all vultures recovered from the anesthesia uneventfully , and no 
 more cardiorespiratory problems all of the vultures tested in this experiment were treated and put through the 
 rehabilitation program . the mean hr , rr , arterial bp ( sap , map and dap ) and petco2 of cinereous vultures at various concentrations of isoflurane are summarized 
 in table 1table 1.dose-response effects on temperature , cardiovascular and respiratory parameters following isoflurane anesthesia with spontaneous ventilation in 
 cinereous vultures ( aegypius monachus)variables1.0% etiso ( first)1.5% etiso2.0% etiso2.5% etiso3.0% etiso1.0% etiso ( second)(n=10)(n=10)(n=10)(n=10)(n=7)(n=10)hr ( beats / min)99  23124  35170  54198  60199  49100  22rr ( breaths / min)17  1213  1012 413  514  511  5sap ( mmhg)157  22154  21148  18138  15127  7156  15map ( mmhg)130  18124  21117  20106  1597  8122  13dap ( mmhg)109  20103  2496  2584  1971  1092  15petco2 ( mmhg)41  846  854  758  962  1148  5bt ( c ) 39.8  0.639.7  0.539.7  0.539.7  0.439.8  0.439.7  0.4a ) values are presented as the mean  sd . abbreviations : hr , heart rate ; rr , respiratory rate ; sap , systolic arterial blood pressure ; map , mean arterial 
 blood pressure ; dap , diastolic arterial blood pressure ; petco2 , end tidal carbon dioxide partial pressure ; bt , body temperature . b ) 
 p<0.01 , significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , 
 significant difference compared with the values at the first application of 1.0% etiso . e ) p<0.05 , significant difference compared with the values of 1.5% etiso .. the bt remained constant throughout the procedures . the mean hr , arterial bp and petco2 changed significantly with changes 
 in isoflurane concentration . when the vultures were subjected to 2.0 , 2.5 and 3.0% etiso , the hr and petco2 increased significantly 
 relative to the value obtained at the first application of 1.0% etiso . in addition , there were significant increases in hr and petco2 from 
 2.0 to 2.5% and from 2.5 to 3.0% etiso . when the vultures were subjected to 3.0% of etiso , the arterial bp decreased significantly compared to the value 
 obtained at the first application of 1.0% etiso . abbreviations : hr , heart rate ; rr , respiratory rate ; sap , systolic arterial blood pressure ; map , mean arterial 
 blood pressure ; dap , diastolic arterial blood pressure ; petco2 , end tidal carbon dioxide partial pressure ; bt , body temperature . b ) 
 p<0.01 , significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , 
 significant difference compared with the values at the first application of 1.0% etiso . the mean arterial blood gas and acid - base changes of cinereous vultures at various isoflurane concentrations are summarized in table 2table 2.dose-response effects on arterial blood gas and acid - base balance following isoflurane anesthesia with spontaneous ventilation in cinereous vultures 
 ( aegypius monachus)variables1.0% etiso ( first)1.5% etiso2.0% etiso2.5% etiso3.0% etiso1.0% etiso ( second)(n=10)(n=10)(n=10)(n=10)(n=7)(n=10)ph7.50  0.057.46  0.057.41  0.067.33  0.067.24  0.067.48  0.05pao2 ( mmhg)518  31522  26512  20502  18457  88527  19paco2 ( mmhg)38  741  648  960  1276  1539  6hco3 ( mmol / l)26.8  3.626.9  2.727.8  2.728.8  2.929.8  3.426.0  2.7be ( mmol / l)4.3  2.93.5  2.22.7  1.71.5  1.90.1  2.83.1  2.3a ) values are presented as the mean  sd . abbreviations : pao2 , partial pressure of arterial oxygen ; paco2 , partial pressure of 
 arterial carbon dioxide ; hco3 , calculated bicarbonate concentration ; be , calculated base excess . b ) p<0.01 , 
 significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , significant difference compared 
 with the values at the first application of 1.0% etiso . g ) p<0.05 , significant difference compared with the values of 2.5% etiso .. the mean arterial ph , pao2 and paco2 changed significantly with changes in the isoflurane concentration . when the vultures 
 were subjected to 2.0 , 2.5 and 3.0% etiso , the arterial ph decreased significantly compared to the value obtained at the first application of 1.0% etiso . in 
 addition , there were significant decreases in arterial ph from 2.0 to 2.5% and from 2.5 to 3.0% etiso . when vultures were subjected to 3.0% etiso , the arterial 
 pao2 decreased significantly relative to the value obtained at the first application of 1.0% etiso . when the vultures were subjected to 2.5 and 
 3.0% etiso , the arterial paco2 increased significantly relative to the value obtained at the first application of 1.0% etiso . in addition , there were 
 significant increases in arterial paco2 as the etiso increased from 2.5 to 3.0% . the mean be values changed significantly at 3.0% etiso relative to 
 the value obtained at the first application of 1.0% etiso . however , the mean hco3 values did not change significantly with changes in 
 isoflurane concentration . abbreviations : pao2 , partial pressure of arterial oxygen ; paco2 , partial pressure of 
 arterial carbon dioxide ; hco3 , calculated bicarbonate concentration ; be , calculated base excess . b ) p<0.01 , 
 significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , significant difference compared 
 with the values at the first application of 1.0% etiso . the mean hr , rr , arterial bp ( sap , map and dap ) and petco2 of cinereous vultures at various concentrations of isoflurane are summarized 
 in table 1table 1.dose-response effects on temperature , cardiovascular and respiratory parameters following isoflurane anesthesia with spontaneous ventilation in 
 cinereous vultures ( aegypius monachus)variables1.0% etiso ( first)1.5% etiso2.0% etiso2.5% etiso3.0% etiso1.0% etiso ( second)(n=10)(n=10)(n=10)(n=10)(n=7)(n=10)hr ( beats / min)99  23124  35170  54198  60199  49100  22rr ( breaths / min)17  1213  1012 413  514  511  5sap ( mmhg)157  22154  21148  18138  15127  7156  15map ( mmhg)130  18124  21117  20106  1597  8122  13dap ( mmhg)109  20103  2496  2584  1971  1092  15petco2 ( mmhg)41  846  854  758  962  1148  5bt ( c ) 39.8  0.639.7  0.539.7  0.539.7  0.439.8  0.439.7  0.4a ) values are presented as the mean  sd . abbreviations : hr , heart rate ; rr , respiratory rate ; sap , systolic arterial blood pressure ; map , mean arterial 
 blood pressure ; dap , diastolic arterial blood pressure ; petco2 , end tidal carbon dioxide partial pressure ; bt , body temperature . b ) 
 p<0.01 , significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , 
 significant difference compared with the values at the first application of 1.0% etiso . e ) p<0.05 , significant difference compared with the values of 1.5% etiso .. the bt remained constant throughout the procedures . the mean hr , arterial bp and petco2 changed significantly with changes 
 in isoflurane concentration . when the vultures were subjected to 2.0 , 2.5 and 3.0% etiso , the hr and petco2 increased significantly 
 relative to the value obtained at the first application of 1.0% etiso . in addition , there were significant increases in hr and petco2 from 
 2.0 to 2.5% and from 2.5 to 3.0% etiso . when the vultures were subjected to 3.0% of etiso , the arterial bp decreased significantly compared to the value 
 obtained at the first application of 1.0% etiso . abbreviations : hr , heart rate ; rr , respiratory rate ; sap , systolic arterial blood pressure ; map , mean arterial 
 blood pressure ; dap , diastolic arterial blood pressure ; petco2 , end tidal carbon dioxide partial pressure ; bt , body temperature . b ) 
 p<0.01 , significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , 
 significant difference compared with the values at the first application of 1.0% etiso . the mean arterial blood gas and acid - base changes of cinereous vultures at various isoflurane concentrations are summarized in table 2table 2.dose-response effects on arterial blood gas and acid - base balance following isoflurane anesthesia with spontaneous ventilation in cinereous vultures 
 ( aegypius monachus)variables1.0% etiso ( first)1.5% etiso2.0% etiso2.5% etiso3.0% etiso1.0% etiso ( second)(n=10)(n=10)(n=10)(n=10)(n=7)(n=10)ph7.50  0.057.46  0.057.41  0.067.33  0.067.24  0.067.48  0.05pao2 ( mmhg)518  31522  26512  20502  18457  88527  19paco2 ( mmhg)38  741  648  960  1276  1539  6hco3 ( mmol / l)26.8  3.626.9  2.727.8  2.728.8  2.929.8  3.426.0  2.7be ( mmol / l)4.3  2.93.5  2.22.7  1.71.5  1.90.1  2.83.1  2.3a ) values are presented as the mean  sd . abbreviations : pao2 , partial pressure of arterial oxygen ; paco2 , partial pressure of 
 arterial carbon dioxide ; hco3 , calculated bicarbonate concentration ; be , calculated base excess . b ) p<0.01 , 
 significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , significant difference compared 
 with the values at the first application of 1.0% etiso . g ) p<0.05 , significant difference compared with the values of 2.5% etiso .. the mean arterial ph , pao2 and paco2 changed significantly with changes in the isoflurane concentration . when the vultures 
 were subjected to 2.0 , 2.5 and 3.0% etiso , the arterial ph decreased significantly compared to the value obtained at the first application of 1.0% etiso . in 
 addition , there were significant decreases in arterial ph from 2.0 to 2.5% and from 2.5 to 3.0% etiso . when vultures were subjected to 3.0% etiso , the arterial 
 pao2 decreased significantly relative to the value obtained at the first application of 1.0% etiso . when the vultures were subjected to 2.5 and 
 3.0% etiso , the arterial paco2 increased significantly relative to the value obtained at the first application of 1.0% etiso . in addition , there were 
 significant increases in arterial paco2 as the etiso increased from 2.5 to 3.0% . the mean be values changed significantly at 3.0% etiso relative to 
 the value obtained at the first application of 1.0% etiso . however , the mean hco3 values did not change significantly with changes in 
 isoflurane concentration . abbreviations : pao2 , partial pressure of arterial oxygen ; paco2 , partial pressure of 
 arterial carbon dioxide ; hco3 , calculated bicarbonate concentration ; be , calculated base excess . b ) p<0.01 , 
 significant difference compared with the values at the first application of 1.0% etiso . c ) p<0.05 , significant difference compared 
 with the values at the first application of 1.0% etiso . in raptors , the anesthesia with isoflurane resulted in rapid induction and recovery , and the anesthetic depth was easily controlled . even allowing for reported adverse cardiac effects of isoflurane in raptors , such as tachycardia , hypertension and arrhythmias , this anesthetic agent was considered as a reasonable selection to anesthetize the birds , because of its evident 
 cardiorespiratory stability . thus , the results of the present study indicate that it is possible to safely use isoflurane by controlling the anesthetic 
 concentration . etiso concentrations of 1.5 to 2.0% were considered adequate for anesthetic maintenance with minimal adverse effects in cinereous vultures . according to previous studies [ 17 , 18 , 23 ] , 
 although the minimum alveolar concentration ( mac ) is not appropriate as an index of potency for inhalant anesthetics in birds , the minimum anesthetic 
 concentration as a similar index has been used to determine the anesthetic dose . the minimum anesthetic concentration for isoflurane in ducks is 1.3% , while that for cockatoos is 1.44% , and for captive thick - billed parrots , it is 
 1.07% . factors that may influence the minimum anesthetic concentration include age , circadian rhythm , methodology used 
 to determine the minimum anesthetic concentration , severe hypercapnia , severe hypoxemia , changes in body temperature , severe hypotension and acidemia or alkalemia 
 [ 16 , 24 ] . accordingly , therefore , in the present study , the clinical etiso 
 concentration was used as an index for inhalant anesthetics dose . many previous studies [ 8 , 18 , 19 , 21 , 32 ] of avian anesthesia have not included measurement of awake cardiovascular 
 parameters . although comparison of the awake and anesthetized parameters is important to evaluate the significance of the adverse effects caused by the 
 anesthetics , birds can be extremely sensitive to the stress induced by handling . in birds that are restrained or 
 excited , the hr can be 184 to 401% higher than that of birds that are caged , free from excitement or at rest . in our 
 pilot study , although measurement of the cardiorespiratory parameter was attempted while the vultures were awake , it was not possible to maintain stable enough 
 conditions to collect the data normally . sinus arrhythmia is defined as a patterned , irregular sinus rhythm with alternate slowing and acceleration of the hr . in the current study , three of the 
 cinereous vultures developed cardiorespiratory problems ( sinus arrhythmia and respiratory instability ) , while attempting to increase the etiso from 2.5 to 3.0% . therefore , it can be assumed that the 
 anesthetic index is more than 2.5 . the sinus arrhythmia at 
 high hr identified via ecg was identified in a vulture of this study . the anesthesia of 3.5% etiso is associated with cardiac arrhythmia , such as second degree 
 atrioventricular block in bald eagles , probably because of an increase of vagal tone . premature ventricular contractions 
 have been described in isoflurane anesthetized ducks , however , the arrhythmias resolved when isoflurane concentration was reduced , which might suggest that higher anesthetic concentrations can more easily induce arrhythmia in birds . in avian species , anesthetic dose - related changes in cardiorespiratory parameters have been reported during inhalational anesthesia . spectral doppler - derived 
 cardiac parameters , including hr and blood flow velocities , were found to decrease significantly in common buzzards anesthetized with isoflurane . in chickens [ 17 , 18 ] , dose - related decreases 
 in arterial bp were observed , but hr did not differ when the chickens were anesthetized with isoflurane or sevoflurane during controlled ventilation . when ducks 
 were anesthetized with isoflurane during spontaneous ventilation , there was no significant dose - dependent difference between the means of either hr or arterial bp 
 . however , another study   demonstrated that there was a significant 
 dose - dependent increase in hr when ducks were anesthetized with halothane during spontaneous ventilation . in this study , a dose - dependent increase in hr and 
 decrease in arterial bp were observed in cinereous vultures anesthetized with isoflurane during spontaneous ventilation . therefore , the patterns of the 
 dose - dependent changes in cardiorespiratory parameters may vary depending on the species of bird , type of inhalant anesthetic and ventilation conditions . in 
 addition , as reported in mammals , a decrease in systemic vascular resistance caused by inhalant anesthetics seems to 
 be the most probable cause of the hypotension observed in the current study . respiratory depression caused by anesthesia with isoflurane was investigated in different bird species during spontaneous ventilation [ 11 , 12 , 25 , 32 ] . species - dependent characteristics , such as the absence of a diaphragm , restriction of sternum excursions by dorsal recumbency and decreased responsiveness of 
 intrapulmonary chemoreceptors to co2 caused by inhalant anesthetics , make birds more sensitive to respiratory depression caused by inhalant anesthetic 
 [ 5 , 10 , 22 ] . in the present study , an 
 increase in petco2 and paco2 and decrease in ph were associated with the respiratory depression caused by anesthesia with 
 isoflurane . in a previous study , inhalant - induced hypoventilation resulted in increased petco2 , 
 paco2 and hco3 and decreased ph . an fio2 > 40% has been shown to lead to hypoventilation in ducks anesthetized 
 with isoflurane , likely due to depression of o2-sensitive chemoreceptors and a depressed ventilator drive . in addition , previous studies [ 11 , 18 , 19 , 26 ] reported respiratory acidosis in ducks anesthetized with isoflurane and chickens anesthetized with sevoflurane during spontaneous ventilation . 
 moreover , increased sympathetic activity and circulating concentration of catecholamines , peripheral vasodilation and myocardial depression were caused by 
 hypercapnia in humans . when the things above are taken into consideration , the respiratory and cardiovascular effects by 
 anesthesia with isoflurane seem to affect the cardiorespiratory system complexly . depression of the central nervous system 
 may be associated with a ph below 7.2 . moreover , the decreased ph may lead to organ damage and failed activity of some 
 enzymes , causing alterations in metabolism . dose - dependent decreases in arterial ph were observed during isoflurane 
 anesthesia in the present study . a non - rebreathing anesthetic circuit , such as the modified jackson rees anesthesia circuit used in this study , is considered to 
 be ideal for the use in birds , because it provides minimal resistance to patient ventilation . however , inhalant 
 anesthetics leading to respiratory depression seems to be much more significant in birds than mammals . this may justify the fact that the thoracic musculature in 
 birds plays significantly important roles in ventilation and that they relax these muscles during anesthesia . when 
 aerobic energy metabolism is degraded or there is a low hematocrit or lactic acidemia , a negative be is expected as an indicator of acid / base status . since the be was > 2 mmol / l in the present study , the disturbance in ph was more likely due to respiratory rather than 
 metabolic changes . a previous study investigated that saline administration results in dilutional acidosis . in the present study , 0.9% normal saline was administered during the procedure at a rate of 10 ml / kg / hr . 
 although each vulture was administered about 100150 ml of normal saline , the values of ph , paco2 and hco3 were 
 within the normal range during the anesthetic phase at the second application of 1.0% etiso . therefore , the present study indicates that the dilution associated 
 with saline administration at the rate of 10 ml / kg / hr did not affect ph of the birds . in the current study , the duration of anesthesia and the specific concentration of anesthetics may be significant factors influencing changes in 
 cardiorespiratory parameters . a previous study   investigated whether anesthesia with isoflurane did not cause a 
 significant change in the arterial bp of spontaneously ventilating anesthetized hispa - niolan amazon parrots . the same study reported that a decrease of hr was 
 noted only after 45 min of anesthesia . conversely , another study conducted by joyner et al .   reported 
 that the hr and rr significantly decreased over time , whereas the arterial bp significantly increased over time in bald eagles anesthetized with isoflurane during 
 spontaneous ventilation . however , since there was very limited information describing the correlation between the duration of anesthesia and changes in 
 cardiorespiratory parameters of birds , it is difficult to define exactly how the prolonged period of anesthesia would affect changes in cardiorespiratory 
 parameters of the birds . in the present study , while dose - dependent increases in petco2 and paco2 were measured , the rr taken at 
 the second application of 1.0% etiso appeared to be slightly lower than that taken at the first application of 1.0% etiso , but these differences were not 
 statistically significant . based on the results , although spirometry was not used to measure breathing capacity , respiratory depth was not able to be maintained 
 because of anesthetic induced muscle relaxation . although the duration of anesthesia had no significant effects on the cardiorespiratory parameters investigated 
 in the current study , it is difficult to be certain that the duration of anesthesia would not have any effects on the cardiorespiratory parameters of the 
 cinereous vulture under different clinical settings . in conclusion , when the isoflurane concentration was increased during spontaneous ventilation in cinereous vultures , a dose - dependent increase in hr and 
 petco2 with minimal changes in rr , a decrease in arterial bp and respiratory acidosis were observed . overall , isoflurane for anesthesia of 
 spontaneously breathing cinereous vultures is a suitable choice for diagnostic or surgical procedures . however , careful controls of anesthetic dose and 
 ventilation conditions are recommended for this species .
anesthesia is an inevitably important component of diagnosis and treatments examining the health condition of wild animals . 
 not only does anesthesia become an 
 essential tool in minimizing stress of the patients and providing an opportunity to deliver accurate and safe procedures , but it also ensures the safety of the 
 medical crew members . 
 this study was conducted to investigate the dose - response cardiorespiratory effects of isoflurane during spontaneous ventilation in ten 
 cinereous vultures . 
 each bird was administered isoflurane at initial concentration of 1.0 , 1.5 , 2.0 , 2.5 and 3.0 and then an end - tidal isoflurane concentrations 
 ( etiso ) of 1.0% for an equilibration period of 15 min in the given order . at the end of the equilibration period , 
 the direct blood pressure ( bp ) , heart rate 
 ( hr ) , respiratory rate ( rr ) and end tidal co2 partial pressure ( petco2 ) were recorded , and blood gas analysis was performed . 
 increasing isoflurane concentrations during spontaneous ventilation led to dose - dependent increases in hr and petco2 , with minimal changes 
 in rr , decreased arterial bp and respiratory acidosis . 
 overall , isoflurane for anesthesia of spontaneously breathing cinereous vultures is a suitable choice for 
 diagnostic or surgical procedures .