| Backgroud:Density is one of the important factors which influences the intrathecal spread of local anesthetics, so it is very important getting the precision data about the the actual density of cerebrospinal fluid and local anesthetics,but we have hadn’t this information by far. In the first stage of this study we will firstly determine the density of cerebrospinal fluid (CSF) and local anesthetics, opioids commonly Used in China at37℃, which were measured by a highly accurate digital density meter and it’s precision is0.00005g/ml. Based on the results from clinical observation, limiting the dose of intrathecal bupivacaine for caesarean section can reduce the incidence of maternal hypotension, decreasing the baricity or the density of intrathecal bupivacaine solution for nonobstetric anesthesia can also reduce the height of cephalad sensory block and the incidence of hypotension and other side effects, but we have rare knowledge about the effect of the density (baricity) on the intrathecal spread of low-dose bupivacaine (<10mg) for caesarean section. We investigated the effect of density (glucose concentration) on the intrathecal spread of low-dose hyperbaric bupivacaine for caesarean section, especially on that of low-dose marginally hyperbaric bupivacaine. Materials and Methods:In first stage of this study the densities were measured by a density meter (DMA4500M, Anton Paar GmbH, Austria) at37℃。The simples of CSF were obtained from154patients scheduled for elective cesarean section and the44simples of local anesthetics and opioids were randomly taken from our hospital. The relation of the temperature and density of0.75%bupivacaine were also investigated. In the second stage of this study one hundred and twenty pregnant women scheduled for elective caesarean section under combined spinal-epidural anesthesia were randomly divided into four groups based on the different concentrations of glucose(8%,0.8%,0.5%,0.33%:group A-D respectively), contained in the local anesthetics solution. At37℃the mean(SD) density of these local anesthetics solution used in group A-D(7.2mg bupivacaine combined with2.0μg sufentanil:total volume was1.6ml) was1.02759±0.00003(conventionally hyperbaric),1.00255±0.00002(gently marginally hyperbaric),1.00122±0.00002(moderately marginally hyperbaric) and1.00084±0.00002(extremely marginally hyperbaric)respectively. Data collection included sensory block level, motor block, episodes of hypotension, effect of anesthesia and the incidence of shivering, nausea and other side effects. Results:The mean CSF densities in men (1.00060±0.00008g/ml),postmenopausal women (100065±0.00008g/ml), and nonpregnant premenopausal women (1.00047±0.00015g/ml) were greater than in term pregnant(1.00033±0.00008g/ml),(P<0.01). Except for meperidine the densities of all local anesthetics and opioids measured were lower than that of CSF. About0.75%bupivacaine, changes in temperature of1℃result in density changes of0.00020-0.00050g/ml. There was a downtrend in the mean(SD) maximum cephalad sensory block height, incidence of cervical block and hypotension accord with the decrease in density of local anesthetics solution. The mean(SD) maximum cephalad sensory block height in group A-D was C8, T2, T4and T6, respectively(P=0.000); The incidence of cervical block in group A-D was44.8%%,26.7%,3.3%and0.0%respectively(P<0.001); The incidence of hypotension in group A-D was48.3%,30.0%,13.3%and10.3%respectively(P=0.003). About maximum cephalad sensory block height, incidence of cervical block and hypotension, pairwise comparison suggest there was no significantly difference between group A and B(P>0.05), however, it was significantly higher in group A than in group C and D, it was also significantly higher in group B than in group D(P<0.05). The frequency of shivering, nausea and head discomfort was significantly different among groups and it was the lowest in group D. The assessment of the efficacy of the anesthesia and motor block to the lower limbs was similar among the groups. Multiple linear regression analysis showed there was a significant correlation between maximum cephalad sensory block height and density of local anesthetics solution(P<0.05) and no correlation with age, height,weight and body index(P>0.05). Conclusion:premenopausal women have slightly lower densities than do men and postmenopausal women and nonpregnant premenopausal women. All local anesthetics and opioids measured were hypobaric except meperidine. The density of0.75%bupivacaine was negtive correlation with temperature We conclude that about low-dose hyperbaric bupivacaine the effect of density on it’s intrathecal spread in caesarean section was similar to it’s in nonobstetric anesthesia, that is for caesarean section decreasing the density of low-dose intrathecal bupivacaine from conventionally hyperbaric solution(in glucose8%) to moderately marginally hyperbaric solution(in glucose0.5%) and extremely marginally hyperbaric solution(in glucose0.33%) can also reduce the height of cephalad sensory block and the incidence of hypotension and other side effects, but to gently marginally hyperbaric solution can’t do that. Low-dose extremely marginally hyperbaric bupivacaine combined with sufentanil can provide equal anesthesia to conventionally hyperbaric bupivacaine for caesarean section while with less adverse effect and deserves further assessment. |
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