this study was approved by the ethical committee of the university of padua ( prot . all anesthetic 
 procedures were performed by the same experienced operator , who was aware of the assigned technique . animals : inclusion criteria : dogs older than 6 months presenting to the clinic , from january 2014 to january 2015 , for various 
 scheduled surgical procedures involving the pelvic limbs , based on the american society of anesthesiologists ( asa ) physical status classification i or ii as 
 determined following clinical examination . anesthesia protocols : before induction of ga , catheterization of the cephalic vein was performed . general anesthesia was then induced by 
 administering fentanyl 2.5 g / kg intravenously ( iv ) and propofol to effect . after orotracheal intubation and inflation of the cuff , the dog was 
 connected to the breathing system . all patients included in this study received intermittent positive pressure ventilation ( cato , draeger , germany ) , and their 
 metatarsal artery was catheterized . the electrocardiogram , hr , invasive blood pressure , respiratory rate , arterial oxygen saturation , fraction of inspired oxygen 
 ( fio2 ) , end - tidal carbon dioxide concentration ( feco2 ) , end - tidal isoflurane concentration ( feiso ) and esophageal temperature were 
 monitored continuously ( ge datex ohmeda as ) . lactated ringer s solution ( ringer lattato ; fresenius kabi , isola della scala ( vr ) , italy ) was administered iv during 
 anesthesia in all of the dogs . once the plane of anesthesia was stable , the systolic pressure variation ( spv ) was measured with the dog in left lateral recumbency 
 in accordance with gouva & gouva . in brief , the  wedge pressure function in the monitor s invasive pressures 
 channel was applied to the systemic arterial curve : ( step 1 ) the arterial pressure curve was labeled pulmonary arterial pressure , and the scale was adjusted 
 accordingly ; ( step 2 ) the  wedge pressure menu was accessed ; ( step 3 ) the comwheel was pressed to confirm ; the screen freezes at this point , and a blue 
 horizontal line appears ; and ( step 4 ) the operator is free to move this line to the uppermost point of the curve and then move it down to the lowest systolic 
 pressure . the spv was calculated as the difference between the maximum and the minimum systolic pressure ( spmax and spmin , respectively ) over a single respiratory cycle 
 and was expressed as a percentage : spv-%=100  ( spmax spmin)/(spmax + spmin)/2 . the median value over three consecutive spv measurements was taken . if the dog 
 was not completely suited to mechanical ventilation , or there was a detectable hr variability , or the mean arterial pressure ( map ) was < 50 mmhg , spv 
 measurement was suspended . propofol ( 1 mg / kg ) was given and spv measurement was resumed 5 min later , if abnormalities in the ventilatory pattern were due to an 
 inadequate depth of anesthesia . dogs with an map < 50 mmhg , compatible with a deep plane of anesthesia , had their feiso decreased . subjects were excluded from 
 the study , if these abnormalities did not respond to the relevant interventions or if they required a vasopressor . every dog with an spv higher than 4.5% under a 
 peak inspiratory pressure of 8 cmh2o received 3 ml / kg of lactated ringer s solution intravenously at a rate of 999 
 ml / hr using an infusion pump . every dog with an spv higher than 4.5% not responder to fluid 
 administration were excluded . the body temperature was maintained above 35c during the perioperative period using an active heating system ( bair hugger warmer 
 model 505 , augustine biomedical design , eden prairie , mn , u.s.a . ) . general anesthesia was maintained in dogs assigned to group i with isoflurane and to group p 
 with a propofol - based tiva . median values of hr and abp were recorded before ( t0 ) and 12 min after intrathecal injection ( t1 ) . when 
 hypotension and bradycardia were observed , according to the definition given below , the lowest value registered by the monitor was recorded in the results . in order to perform the regional technique , anesthetized dogs were positioned in lateral recumbency , and the skin over the l3-s1 vertebrae 
 was aseptically prepared after clipping the hair . a lack of cerebral spinal fluid ( csf ) outflow was considered a procedural failure in intrathecal anesthesia . the 
 intrathecal injection was administered using a paramedian approach at the level of the intervertebral space between l5 and l6 using a 
 75-mm - long 25 g quincke needle ( spinal needle ; pic , grandate ( co ) , italy ) . once the csf outflow became visible in the hub of the needle , the intrathecal solution 
 was injected over 20 sec . once the injection was complete , dogs were 
 maintained in lateral recumbency , with the pelvic limb to be operated on lowermost , for 12 min and were then placed in dorsal recumbency . the bupivacaine ( bupisen iperbarica 0.5% ; galenica senese , monteroni darbia ( si ) , italy ) dose calculations were based on body mass ( bm ) and spinal cord length 
 ( scl ) as suggested by sarotti et al . . bupivacaine 0.5% ( mg ) : 0.3 bm ( kg ) + 0.05 scl ( cm ) spinal cord length ( scl ) was recorded as the distance between the caudal part of the spinal process of l7 and the occipital bone . the 1% morphine dose was 0.3 mg in dogs less than 10 kg , 0.5 mg in dogs between 11 and 20 kg , and 1 mg in dogs over 20 kg ( sarotti et al . ) 
 . event definition and treatment : hypotension was defined as being when every map value was lower than 60 mmhg . when hypotension was noticed , the 
 anesthesia plane was lightened and spv was checked again . every dog with an spv higher than 4.5% under a peak inspiratory pressure of 8 cmh2o received 
 3 ml / kg of lactated ringer s solution intravenously at a rate of 999 ml / hr using an infusion pump . when these actions were not able to raise the map above 60 mmhg , a bolus of ephedrine was administered until a maximal total dose of 200 
 g / kg was reached . if the hypotension did not respond to these treatments , a noradrenaline infusion at 0.11 g / kg / min was 
 administered . when bradycardia was observed , atropine at 20 g / kg iv was administered . bradycardia ranging between 55 and 59 bpm as a consequence of ephedrine administration was not treated . an a / m episode was defined as any body movement or sign of lightening of the ga , such as spontaneous or rapid eye blinking , resistance towards the ventilator or 
 muscular tremors . when lightening of anesthesia was observed , 1 mg / kg iv propofol was administered . the tnai was defined as being the total number of measures taken by the anesthetist either to deepen the anesthetic plane or to treat hemodynamic depression 
 between stabilization of the anesthetic plane after induction of anesthesia and skin incision . statistical analysis : dogs were assigned to one of the two treatment groups according to a computer - generated randomization sequence after the 
 placement of a catheter in the metatarsal artery . the estimated sample size required to detect a difference in the primary endpoint ( difference in map between 
 groups ) with a power of 80% and an alpha error of 5% using a two independent groups study design has been calculated . the effect size ( d ) of 1.42 was obtained 
 assuming a map difference at t1 of 10 mmhg , with a standard deviation of 7 mmhg . categorical variables were reported as frequencies and percentages , and differences between groups were analyzed using the fisher s exact test . continuous 
 variables were checked for normal distribution by visual inspection of bar graphs and histograms , and by using the shapiro  wilk test . data not normally 
 distributed were reported as the median and the range ( minimum  maximum ) , and differences were analyzed using the mann - whitney u test . intrathecal injection in 5/42 ( 12% ) and the placement of a catheter into the dorsal metatarsal artery in 15/42 ( 36% ) 
 dogs failed , and two cases were excluded because their spv was higher than 4.5% despite the administration of a bolus of fluid . the remaining 20 dogs , which had 
 complied with the inclusion criteria , were divided evenly into two groups and analyzed . two dogs in group i and one in group p received a bolus of fluid before 
 the intrathecal injection , because their spv was higher than 4.5% under a peak inspiratory pressure constantly maintained at 8 cmh2o . the demographic 
 data ( breed , age , bm , scl and asa category ) of both groups can be found in appendix table a1 
 table a1.demographic data of dogs [ median ( range ) ] that met the inclusion criteria for groups i and pgroup p ( n=10)group i ( n=10)p - valuebreed ( n)7 mongrels5 mongrelsnot evaluated1 labrador4 labrador1 golden retriever1 pointer1 german shepherdage ( years)5.5 ( 1.514)7.5 ( 0.912.5)0.8bm ( kg)19.5 ( 735)31.5 ( 2.740)0.24scl ( cm)57.5 ( 4475)72.5 ( 3080)0.16asa category ( n)asa i ( 8)asa i ( 9)1asa ii ( 2)asa ii ( 1)bm : body mass ; scl : spine cord length ; asa , american society of anesthesiologists .. procedural data concerning the median local anesthetic dose used for neuraxial blockade , the median dose of morphine , the median dose of propofol 
 used for induction of anesthesia , the median dose of propofol per kilogram of body weight per hour and the median value of feiso in the first hour are reported 
 in table 1table 1.procedural data [ median ( range ) ] for groups i and pgroup p ( n=10)group i ( n=10)p - valuebupivacaine dose ( mg)8.7 ( 414.9)13.5 ( 2.3116)0.21bupivacaine dose related to bm ( mg / kg ) 0.42 ( 0.400.59)0.45 ( 0.40.85)0.32bupivacaine dose related to scl ( mg / cm ) 0.15 ( 0.10.19)0.18 ( 0.070.18)0.32morphine dose ( mg)1 ( 0.31)1 ( 0.31)0.81morphine dose related to bm ( mg / kg ) 0.03 ( 0.0270.07)0.03 ( 0.0250.11)0.28propofol induction bolus ( mg / kg ) 5 ( 46)5 ( 47)0.56mean propofol rate infusion in the first hours ( mg / kg / h ) versus mean et isoflurane ( % ) in the first hour25 ( 2035)1 ( 0.81.2)not evaluatedbm : body mass ; scl : spinal cord length ; et : end-tidal.table 2.hemodynamic data [ median ( range ) ] for groups i and p before intrathecal injection ( t0 ) and 12 min later ( t1)group p ( n=10)group i ( n=10)p - valuesap t0 ( mmhg)115 ( 94143)94 ( 75134)0.0005map t0 ( mmhg)79 ( 6695)67.5 ( 5073)0.0005dap t0 ( mmhg)63.5 ( 5976)55 ( 3360)0.0007hr t0 ( bt / min)87 ( 76150)92 ( 74135)0.56sap t1 ( mmhg)102.5 ( 86129)87 ( 74104)0.041map t1 ( mmhg)65 ( 5986)57 ( 5366)0.006dap t1 ( mmhg)51.5 ( 4569)47 ( 4153)0.034hr t1 ( bt / min)76.5 ( 60100)75 ( 54130)0.61hr : heart rate ; sap : systolic arterial pressure ; map : mean arterial pressure ; dap : diastolic arterial pressure.table 3.pre-surgical period : hypotension , vasoactive consumption , arousal / movement ( a / m ) , propofol consumption due to a / m , bradycardia , atropine consumption 
 and the total number of anesthetic interventions ( tnai ) in groups p and igroup p ( n=10)group i ( n=10)p - valuehypotension ( % ) 3/10 ( 30%)6/10 ( 60%)0.37total ephedrine consumption ( g / kg ) [ median ( range)]0 ( 050)75 ( 0200)0.016total noradrenalin consumption ( g / kg ) [ median ( range)]00>0.05a / m ( % ) 1/10 ( 10%)5/10 ( 50%)0.07total propofol consumption due to a / m ( mg / kg ) [ median ( range)]0 ( 01)1.5 ( 03)0.019bradycardia ( % ) 0/10 ( 0%)2/10 ( 20%)0.47total atropine consumption ( g / kg ) [ median ( range)]00 ( 020)>0.05tnai ( n ) [ median ( range)]0 ( 02)2 ( 05)0.022table 4.intra-surgical period : hypotension , vasoactive consumption , arousal / movement ( a / m ) , propofol consumption due to a / m , bradycardia , atropine consunption 
 and the total number of anesthetic interventions ( tnai ) in groups p and igroup p ( n= 10)group i ( n=10)p - valuehypotension ( % ) 1/10 ( 10%)0/10 ( 0%)>0.05total ephedrine consumption ( g / kg ) [ median ( range)]0 ( 025)0>0.05total noradrenaline comsumption ( g / kg ) [ median ( range)]00>0.05a / m ( % ) 01/10 ( 10%)>0.05total propofol consumption due to a / m ( mg / kg ) [ median ( range)]00 ( 01)>0.05bradycardia ( % ) 0/10 ( 0%)1/10 ( 10%)>0.05total atropine comsumption ( g / kg ) [ median ( range)]00 ( 020)>0.05tnai ( n)[median ( range)]0 ( 01)0 ( 01)>0.05 . the map at t0 and at t1 was higher in group p , as is shown in fig . 1.box plots of the mean arterial pressure ( map ) before ( t0 ) and 12 min after intrathecal injection ( t1 ) in groups p and i. map is 
 higher in dogs in the group p compared with those in group i at t0 ( p=0.0005 ) and t1 ( p=0.006 ) the whiskers show the range values , the width of the box shows the interquartile range , and the bar in the box is 
 the median value . hypotension , vasoactive consumption , a / m , propofol consumption due to a / m , bradycardia , atropine consumption and tnai in groups 
 p and i in pre - surgery and intra - surgical periods are reported , respectively , in tables 3 and 4 . in pre - surgery period , 2.box plots of the total number of anesthetic interventions to deepen the anesthetic plane or to treat hemodynamic depression in the pre - surgical period is 
 higher in group i than in group p ( p=0.022 ) . the whiskers show the range values , the width of 
 the box shows the interquartile range , and the bar in the box is the median value . ( p=0.022 ) , while in intraoperative period , tnai was not different between groups ( p>0.05 ) . in pre - surgery period , ephedrine consumption was higher in group i ( p=0.016 ) , while in intraoperative period , ephedrine consumption was not different between groups 
 ( p>0.05 ) . bm : body mass ; scl : spine cord length ; asa , american society of anesthesiologists . bm : body mass ; scl : spinal cord length ; et : end - tidal . hr : heart rate ; sap : systolic arterial pressure ; map : mean arterial pressure ; dap : diastolic arterial pressure . box plots of the mean arterial pressure ( map ) before ( t0 ) and 12 min after intrathecal injection ( t1 ) in groups p and i. map is 
 higher in dogs in the group p compared with those in group i at t0 ( p=0.0005 ) and t1 ( p=0.006 ) the whiskers show the range values , the width of the box shows the interquartile range , and the bar in the box is 
 the median value . box plots of the total number of anesthetic interventions to deepen the anesthetic plane or to treat hemodynamic depression in the pre - surgical period is 
 higher in group i than in group p ( p=0.022 ) . the whiskers show the range values , the width of 
 the box shows the interquartile range , and the bar in the box is the median value . this study shows that the ga protocol can have a relevant impact on the total number of interventions performed by the anesthetist in the pre - surgical period of 
 anesthesia , to treat cardiovascular depression or arousal / movement episodes in dogs receiving intrathecal anesthesia . this aspect of combined anesthesia has not been investigated in the veterinary literature , even though such anesthesia is very frequently used in veterinary 
 practice . according to this study , dogs , undergoing neuraxial anesthesia , which was maintained under anesthesia using a propofol - based tiva , required less 
 interventions to control cardiovascular depression or involuntary movements compared with dogs maintained under isoflurane - induced anesthesia . this can be an 
 important feature when deciding on an anesthetic protocol in a busy veterinary practice , where maintaining an elevated surgical patient flow is important . there 
 is no published work examining the relationship between workload and anesthetic safety in veterinary care . in a survey of the medical sector regional anesthesia techniques can only 
 contribute significantly to the quality and efficiency of the perioperative care of veterinary patients when complications , possibly arising from these 
 procedures , are minimized . in fact , in the authors experience , when performing a regional anesthesia technique using a volatile anesthetic , it is more difficult 
 to resolve the conflicting requirements of having an adequate and stable hypnotic level while limiting hypotension and cardiovascular depression in dogs . in 
 particular , subjects undergoing neuraxial anesthesia are exposed to a high risk of hypotension , which is mainly due to 
 sympathetic nerve supply blockade and bradycardia . the degree to which this occurs depends on the balance between sympathetic and parasympathetic activities , the 
 extent of the sympathetic block , the degree of cardiac filling and the adequacy of cardiac function . additionally , the 
 concurrent administration of systemic anesthetic drugs , such as isoflurane or propofol anesthetics , can impair the compensatory hemodynamic response 
 ( vasoconstriction in unblocked areas of the body ) to neuraxial administration of local anesthetics [ 16 , 25 ] . an experimental study in vagotomized cats found that the baroreceptor reflex is significantly better maintained with 
 propofol than with isoflurane at equipotent doses . isoflurane and propofol administration causes hypotension mainly 
 through a combination of three mechanisms : myocardial contractility impairment , a decrease in systemic vascular resistance and an increase in venous capacitance 
 [ 14 , 18 , 24 , 29 ] . however , a lower risk of hypotension has been found when propofol was compared with isoflurane to maintain anesthesia in dogs undergoing 
 various surgical and diagnostic procedures . a similar finding has been reported in cats when general anesthesia was 
 maintained with propofol , but it differs from humans in that propofol does not seem to provide clear advantages over 
 inhalation anesthetics in terms of reducing ioh [ 5 , 15 ] . in our study , the incidence 
 of hypotension in the group i was double than in the group p , however , the sample size of the study was not adequate to reach a statistically significant 
 difference on this aspect . nevertheless , the amount of ephedrine consumed in the group i was significantly higher than in the group p in the pre - surgery period 
 ( p=0.016 ) . compared with isoflurane , propofol better preserves aortic pressure and increases aortic compliance and goodchild & serrao , in an experimental study , proved that cardiac output and arterial pressure are well preserved at propofol blood concentrations commonly used during 
 maintenance in dogs if the preload is maintained . these authors also found that the preload reduction by a veno - dilator effect is the main mechanism that causes a 
 decrease in cardiac output when using propofol in this species . cephalad spread of local anesthetic increases the likelihood of bradycardia via 
 two postulated mechanisms : the blockade of sympathetic cardiac accelerator fibers that arise at t1-t4   and decreased 
 venous return . even though in this study , a low incidence of bradycardia was found , post - intrathecal injection 
 lowering of blood pressure was not apparently compensated by a rise in hr . this may have been determined by the above - described mechanisms related to intrathecal 
 anesthesia . in the current study , the decrease in hr due to intrathecal injection did not differ between the two groups . which concludes that hr did not differ between isoflurane and propofol 
 anesthesia , whereas aortic pressure was higher in dogs anesthetized with propofol . group i subjects received a significantly higher amount of propofol to treat a / m episodes ( p=0.019 ) . immobility is a fundamental requirement 
 when a neuraxial block is carried out , as movement can increase risks ranging from nerve block failure to causing spinal cord damage . many subjects in group i had 
 a mean blood pressure close to 60 mmhg in the pre - block period , and the dogs may have been kept at a lighter anesthesia plane in an attempt to avoid hypotension , 
 which thus favored a / m episodes . however , an increased risk of awareness has been reported in pediatric patients maintained under anesthesia with volatile 
 anesthetic agents compared with using tiva ( awareness rate 5% vs 0.2% ) . dogs enrolled in the current study underwent volemic assessment by measuring spv after having reached a stable plane of anesthesia . spv is a dynamic index of 
 volemia validated in dogs undergoing graded exsanguination   and was recently characterized as a predictor of fluid 
 responsiveness in the same species . fluids were administered when spv ( calculated as a percentage ) was equal to or 
 higher than 4.5% in an anesthetized dog under a peak inspiratory pressure constantly maintained at 8 cmh2o . there is a high probability that the 
 subject would have hemodynamically benefited from a bolus of fluid . in the authors opinion , volemia assessment can be particularly important when comparing 
 hemodynamic events after neuraxial anesthesia in order to avoid jeopardizing results , because hypovolemia is well known to worsen post - puncture hypotension in 
 subjects undergoing neuraxial anesthesia . even though , the importance of the volemic assessment in clinical practice , as 
 well as during hemodynamic experimental studies , can not be underestimated , anesthesia was 
 maintained with isoflurane , in the original study on the clinical use of spv , and 4.5% has not been confirmed by any 
 study as being the best threshold for fluid responsiveness when propofol is used to maintain anesthesia . this study compares isoflurane with propofol in the 
 maintenance of anesthesia in the intraoperative period . this can be considered a limitation , because 
 recovery can be a period when complications can call for anesthetist involvement , and therefore , can contribute to the anesthetist s workload . , when comparing dogs recovery from anesthesia maintained with isoflurane or propofol , found that the 
 isoflurane - maintained group stood more quickly than the propofol - maintained group ( mean time 27.7 vs. 34.5 min ) , even though the incidence of adverse effects was 
 not different . in order to maximize the advantages in performing a regional anesthetic technique , the anesthesia protocol should be carefully planned . the use of different 
 protocols can affect the number of complications arising during the anesthetic period when a regional anesthetic block is performed . when intrathecal anesthesia 
 is planned , maintaining anesthesia with propofol - based tiva in dogs can guarantee better cardiovascular parameters , less a / m episodes and fewer interventions by 
 the anesthetist than using volatile anesthetics in the pre - surgical period .
the aim of this prospective , randomized clinical trial was to compare the total number of anesthetic interventions ( tnai ) performed by the anesthetist to treat 
 cardiovascular depression or arousal / movement episodes in dogs receiving intrathecal and general anesthesia ( ga ) , maintained using propofol - based tiva ( group p ) 
 or isoflurane ( group i ) . 
 mean arterial pressure ( map ) before ( t0 ) and 12 min after intrathecal anesthesia ( t1 ) and intraoperative 
 vasoactive consumption were also compared . 
 the tnai to deepen the anesthetic plane or to treat hemodynamic depression in the pre - surgical and intra - surgical 
 period was calculated in forty - two client - owned dogs randomly assigned to group p or i. ten dogs for each group complied with the inclusion criteria and were 
 analyzed . in pre - surgical period , 
 the tnai was higher in group i [ 2 ( 05 ) ] than group p [ 0 ( 02 ) ] ( p=0.022 ) , and ephedrine consumption was also 
 higher in group i [ 75 ( 0200 ) g / kg ) ] than group p [ ( 0 ( 050 ) ] ( p=0.016 ) . 
 map ( mmhg ) in group p was 79 ( 6695 ) at 
 t0 and 65 ( 5986 ) at t1 and 67.5 ( 5073 ) and 57 ( 5366 ) in group i , respectively . at t0 and t1 , map was higher in 
 group p ( p=0.005 and p=0.006 , respectively ) . 
 no differences were found between the two groups in the intrasurgical period 
 ( p>0.05 ) . 
 this study shows that the ga protocol can have a relevant impact on the tnai performed by the anesthetist in the pre - surgical 
 period of anesthesia , to treat cardiovascular depression or arousal / movement episodes in dogs receving intrathecal anesthesia .