the prevalence in patients under cesarean section ( c / s ) is 80 - 90% .
hypotension causes unpleasant symptoms such as nausea , vomiting , unconsciousness , respiratory depression , and cardiac arrest in mothers . in severe and prolonged conditions
, it leads to the impairment of uterine perfusion and ultimately fetal acidosis and neonatal depression .
the required spinal block height for c / s is at t4 - 6 dermatome level . in order to avoid expanded sympathetic block and hypotension ,
the spread of local anesthetic in subarachnoid space should not be higher than the t4 dermatome level .
the most common local anesthetic for spinal anesthesia in patients under obstetric and non - obstetric surgery is bupivacaine that can be used as isobaric or hyperbaric solution .
isobar bupivacaine is not commonly used for spinal anesthesia , but could be a good alternative for obstetric patients due to lower complications than the hyperbaric solution .
besides to volume , the concentration and dose of local anesthetic , as well as the baricity of solution might affect spinal block profile .
a study by rofaeel et al . showed an earlier onset of analgesia and higher sensory block level with isobar compared to hyperbaric bupivacaine during combined spinal - epidural analgesia for vaginal delivery ; without statistically significant differences in the incidence of hypotension .
solakovic reported that the baricity of local anesthetic was effective on the height of spinal block for c / s and hyperbaric bupivacaine was associated with higher incidence of hypotension than the isobar solution .
in contrast , in a randomized study , hallworth et al . observed that the incidence of hypotension and ephedrine use were greater in the isobaric bupivacaine than the hyperbaric bupivacaine .
the specific influence of the baricity of local anesthetics on the efficacy of the spinal block is controversial . in the literature , additional studies
are recommended to determine the effect of baricity of spinal local anesthetic on the spinal block characteristics , especially in obstetric patients .
considering the scarcity of publications and conflicting results on this topic , this study was instigated to compare isobaric and hyperbaric bupivacaine 0.5% plus fentanyl on maternal hemodynamics after spinal anesthesia for c / s .
in this double - blind randomized clinical trial , 84 eligible parturients for elective cesarean section under spinal anesthesia were enrolled .
the study was conducted at al - zahra hospital ( tabriz , iran ) during april 2014 to november 2014 .
the inclusion criteria were healthy pregnant women with term singleton pregnancy , age range18 - 40 years , and non - emergency cesarean section .
the exclusion criteria were patients with systemic and psychological disorders , pre - eclampsia , placental disorders , emergency c / s , weight>85 kg , height<150 cm , any contraindications for spinal anesthesia , and allergy to local anesthetic .
ethical approval was obtained from the research vice chancellor of tabriz university of medical sciences and all participants gave their written informed consent .
we determined that an effective sample size of 84 ( 42 per group ) would be required to provide the statistical power of 80% ( two - tailed test , =0.05 ) , in order to detect a 15% difference in the incidence of hypotension between the two groups .
the patients fasted for 6 hours . in the operating theatre , routine standard monitoring with non - invasive blood pressure ( nibp ) , electrocardiogram ( ecg ) , and pulse oximeter
ringer solution at a rate of 10 - 20 ml / kg was administered to all patients before the induction of spinal anesthesia . under aseptic conditions , with the patient in sitting position , lumber puncture was performed at the l2 - 3 or l3 - 4 interspaces . in terms of the baricity of local anesthetics ,
the patients were randomly categorized into two groups using a coded and sealed envelope technique ( figure 1 ) .
the study group ( n=42 ) was given isobar ( bupivacaine mylan s.a.s,100 mg/20ml , cedex , france ) and the control group ( n=42 ) received hyperbaric ( marcaine 0.5% spinal heavy , astra zeneca , cenexi , france ) . using a 25 g quincke spinal needle ,
10 mg bupivacaine 0.5% plus 15 g fentanyl was injected within 5 - 10 seconds .
each ampoule contained 5 mg / ml solution ( 0.5% ) and 80 mg dextrose ( 8% ) .
the solutions were freshly prepared in numerically labeled syringes at the beginning of each spinal anesthesia by an anesthesiologist who was not involved in the study variables record .
a nurse anesthetist , who was also blind to the medication , administered the solution .
patients were immediately positioned in supine , kept at 15 degrees left lateral tilt , and slight ( 10 degrees ) leg - up position until the delivery of neonate .
patients were given oxygen at the flow rate of 4 - 6 l / min by face mask .
maternal hemodynamic parameters ( systolic blood pressure(sbp ) , diastolic blood pressure ( dbp ) , mean arterial pressure ( map ) , and heart rate ( hr ) ) were recorded every 2 minutes up to the delivery of the neonate and then every 5 minutes until the end of surgery .
sbp<100 mmhg or a decrease beyond 25% from the baseline levels was treated by incremental i.v .
doses of ephedrine 5 mg or phenylephrine 50 g . if bradycardia ( hr<60/min ) occurred , atropine 0.5 mg was injected .
the highest level of sensory block , motor block scale ( by bromage et al .
scoring ) , vasopressor requirements , total amount of fluid administered , incidence of side effects ( nausea , vomiting , agitation , respiratory depression , and loss of consciousness ) , neonatal apgar scores at 1 and 5 minutes , and duration of sensory and motor block were recorded .
intravenous metoclopramide 5 mg and midazolam 1 mg were administered to treat vomiting and agitation , respectively .
patients were treated with assisted ventilation if they had respiratory depression or loss of consciousness .
two anesthesiologists ; one for preparing the study solutions and management of anesthesia , and the other with a medical student ( unaware of the study group ) were in charge of recording patients data .
data are presented as meansd , median ( range ) , and counts ( number ) .
the mean was analyzed using the student s t - test and median by the mann - whitney u - test , fisher s exact test , and chi - square test .
all analyses were performed using the spss statistical software , version 15 ( spss inc . ,
as shown in table 1 , the groups were comparable in terms of age , weight , height , c / s causes , parity , and duration of operation .
the majority of patients ( 95.2% in the isobaric and 85.7% in the hyperbaric groups ) had level t5 sensory block ( p=0.26 ) .
sensory block of t3 level was seen in 2 ( 4.8% ) and 7 ( 16.16 % ) patients of the study and control groups , respectively ( p=0.03 ) .
demographic data between the groups data are presented as meansd , median ( interquartile range ) , and number ( % ) .
cpd : cephalopelvic disproportion hemodynamic variables are shown in table 2 . there were no significant differences in terms of baseline hr , sbp , dbp , map and spo2 between the two groups .
the incidence of hypotension in the hyperbaric group was higher than the isobar group , although not statistically significant .
the time to first hypotensive episode and the lowest sbp were not significantly different between the two groups .
the duration of hypotension in the hyperbaric group was significantly greater than the isobar group .
hemodynamic variables between the groups data are presented as meansd and number ( % ) .
sbp : systolic blood pressure , dbp : diastolic blood pressure , map : mean arterial pressure , spo2 : peripheral capillary oxygen saturation .
the most common complication was sustained hypotension that occurred in 16.6% of patients in the hyperbaric group .
the prevalence of bradycardia , nausea , vomiting , and agitation was equal in both groups .
none of the neonates had apgar score7 at 5 minutes of delivery ( table 3 ) .
the duration of sensory ( 63.487.31 min vs. 67.125.7 min , p=0.01 ) and motor block ( 69.027.1 min vs. 77.05.3 min , p=0.01 ) were shorter in the study group .
maternal complications and neonatal variables between the groups data are presented as meansd and number ( % ) .
the results of this study showed that when spinal anesthesia was performed with 10 mg isobaric bupivacaine plus fentanyl , it produced greater hemodynamic stability than the same dose of hyperbaric solution in patients undergoing c / s .
previous studies have shown that the incidence of hypotension after spinal anesthesia was 40 - 100% .
the overall incidence of hypotension was 51.1% , meaning that the prevalence of hypotension is still high . in our study , hypotension was developed in 40.47% and 61.90% of patients in isobaric or hyperbaric bupivacaine group , respectively .
we could not prevent hypotension completely ; however , we were able to reduce its incidence by about 20% in the isobaric group compared with the hyperbaric group .
the ephedrine requirement was reduced in patients given isobaric bupivacaine , and their systolic and diastolic blood pressures remained more stable with respect to baseline blood pressures compared with patients in the other group .
the main reasons for hypotension after spinal anesthesia are rapid blockage of sympathetic nerves and aortocaval compression leading to decreased systemic vascular resistance ( svr ) , decreased venous return because of blood pooling in the peripheral veins , and reduced cardiac output .
the decrease in sympathetic efferent activity after spinal anesthesia is related to the dose of bupivacaine , and intrathecal fentanyl does not lead to further depression in the sympathetic efferent activity .
studies have indicated that when the intrathecaly given dose of local anesthetic is reduced by adding the opioids , it reduces the incidence of hypotension after spinal anesthesia .
the reason for the lower incidence of hypotension in our study could be related to adequate preloading of patients and particularly the use of low - dose and low - volume intrathecal solution .
low doses of the isobar or hyperbaric local anesthetic block fewer segments and likely limit the spread of sympathetic blockade . in the present study , the incidence and duration of hypotension were high in the hyperbaric group . additionally , the onset of hypotension in the control group was more rapid compared with the study group , although not statistically significant . in a randomized clinical trial , rofaeel et al
. observed that the incidence of hypotension was greater in women undergoing labor analgesia , who were randomly assigned to receive isobaric bupivacaine combined with fentanyl as the spinal component of a combined spinal - epidural analgesia in the sitting position , compared with that of the hyperbaric bupivacaine .
critchly et al . observed that the use of heavy solutions of bupivacaine ( hyperbaric solution ) for subarachnoid block was associated with an increased incidence and more rapid onset of hypotension and heart rate changes , a decrease in central venous pressure ( cvp ) , and a greater need for early corrective treatment of hypotension by vasopressor agents during the initial phase of subarachnoid block .
they also found that the cardiovascular effects of spinal block seemed to be related to more rapid sensory blockade ; a parameter that we did not evaluate .
other studies have shown that hypotension after spinal anesthesia is due to higher level block and assigned sympathetic denervation path .
hussain et al . , in a randomized clinical trial in patients undergoing endoscopic urologic surgery under spinal anesthesia with hyperbaric or isobaric bupivacaine and low dose fentanyl , reported that isobaric bupivacaine can provide a dense block for surgery with minimum hemodynamic effects . in the present study , hemodynamic changes were higher in the hyperbaric group such that the number with arterial hypotension and requiring vasopressors intraoperatively was higher ; a fact attributed to the higher density of bupivacaine .
since the doses of bupivacaine were the same in both groups , other confounding factors in the occurrence of hypotension ( e.g. oxytocin infusion ) were similar .
research studies have reported that the baricity of local anesthetic solution affects the level of spinal block .
the sensory block of t3 level was seen to be higher in patients of the control than the study groups .
these findings indicate that sensory block in the isobaric group was in the healthy range and suitable for caesarean section .
when spinal anesthesia is performed in sitting position and then the patient is immediately positioned in supine state , hyperbaric solution moves to cephalad .
the isobaric solution is intended to remain at injection level , but hyperbaric solution is intended to move the dependent site of supine with normal spinal anatomy .
therefore , hyperbaric solution causes anesthesia upon higher than t4 level . in the present study ,
more patients of the hyperbaric group had sensory block level at t3 than the study group .
because the block does not extend into the upper thoracic level , it leads to little sympathetic block .
however , a study by rofaeel et al . showed that when intrathecal isobaric bupivacaine is used for delivery analgesia , it induces sensory block higher than the hyperbaric solution .
toptas et al . compared the effects of hyperbaric and isobaric bupivacaine spinal anesthesia on hemodynamics and heart rate variability in non - obstetric surgery .
they concluded that the incidence of hypotension was not different between the two groups , but hyperbaric bupivacaine caused significantly greater heart rate variability .
greater doses of ephedrine were used in the control group due to a higher incidence of hypotension .
the duration of sensory and motor block was prolonged in the hyperbaric group , indicating that the duration of block is related to baricity of spinal anesthesia .
however , punshi et al . found that sensory block level regression was delayed in the isobaric group and prolonged the duration of block .
srivastava et al . did not find any difference between the two groups with respect to duration of the block despite a difference in the baricity of local anesthetic solution .
they suggested that the spread of spinal solution is not dependent on the density of bupivacaine .
therefore , there was no difference in the onset time , highest level , and recovery of sensory block between the two groups of patients undergoing cesarean section under spinal anesthesia with hyperbaric or isobaric bupivacaine .
although the incidence of hypotension was significantly different between the two groups , it could easily be treated with vasopressors and did not cause adverse effects on the mother and fetus / neonate . in this study ,
in addition , helmi et al . showed that isobaric bupivacaine produced more rapid onset and longer duration when compared to hyperbaric bupivacaine .
they did not show significant differences in the incidence of hypotension between the two groups .
secondly , the temperature of local anesthetic has an important role in the spread of agents within the cerebrospinal fluid ( csf ) and thus influences the extent of spinal block . the temperature of the solution should equilibrate to the temperature of csf .
however , a bupivacaine that could be stored at room temperature was used in this study .
isobaric bupivacaine produces less incidence and duration of hypotension , lower use of vasopressors , and shorter sensory and motor block than the hyperbaric bupivacaine after spinal anesthesia for c / s .
 background : after spinal anesthesia , patients undergoing cesarean section are more likely to develop hemodynamic changes . 
 the baricity of local anesthetic has an important role on spinal blockade effects . 
 the aim of this study was to compare the isobar and hyperbaric bupivacaine 0.5% plus fentanyl on maternal hemodynamics after spinal anesthesia for c / s.methods : in this double - blind study , 84 healthy pregnant women undergoing c / s using bupivacaine 0.5% isobar ( study group , n=42 ) or hyperbaric ( control group , n=42 ) for spinal anesthesia were scheduled . 
 the study was conducted from 21 april 2014 to 21 november 2014 at al - zahra hospital , tabriz , iran . 
 parameters such as maternal hemodynamics , block characteristics , side effects , and neonatal apgar scores were recorded . 
 data were analyzed using the spss software by performing chi - square test , fisher s exact test , one - way anova , mann - whitney u - test , and student s t test.results:the incidence of hypotension in the isobar group was lower than the hyperbaric group , although it was not statistically significant ( 40.47% vs. 61.9% , p=0.08 ) . 
 the duration of hypotension was shorter in the study group ( 1.67.8 min vs. 7.412.5 min , p=0.004 ) . 
 the dose of ephedrine was lower in the study group ( 2.46.6 mg vs. 5.310.7 mg , p=0.006 ) . 
 the main maternal side effect is sustained hypotension that was seen in 0 patients of the isobar and 7 ( 16.66% ) of hyperbaric groups ( p=0.006 ) . 
 none of the neonates had apgar score7 at 5 min of delivery ( p=1.0 ) . 
 sensory and motor block duration was shorter in the study group ( p=0.01).conclusion : isobaric bupivacaine is associated with more hemodynamic stability and shorter sensory and motor blockade in mothers under spinal anesthesia for c / s . 
 trial registration number : irct201401287013n7 
Introduction
Patients and Methods
Results
Discussion
Conclusion