The Effect Of Epidural Catheter Design On Labor Analgesia During Programmed Intermittent Epidural Boluses

BackgroundsLabor analgesia is increasing concerns of the government.Optimizing labor analgesia strategies and making them easy to implement and popularize are research focuses for anesthesiologists.Since programmed intermittent epidural bolus(PIEB)was applied to labor analgesia,it has been gaining greater popularity.Different from the traditional continuous epidural infusion(CEI),PIEB releases anesthetic drugs rapidly and intermittently into the epidural cavity at a preset time interval.PIEB demonstrates certain advantages over CEI and has been widely used in labor analgesia.However,shortcomings of PIEB are also found in clinic.The high pressure generated by the rapid pumping of PIEB often sets off an occlusion alarm,and then stops the infusion,hindering the popularization of its application.Through previous research,our team found that the epidural catheter design was an important factor affecting occlusion alarm.At present,there is no relevant research on how to select the different types of epidural catheters to achieve the optimal analgesic effect during PIEB.To this end,our subject first plans to test the delivery rates and catheter parameters,plot a dose-effect curve and determine optimal delivery rates and catheter designs which should produce the best diffusion range in vitro.Then,according to the in vitro test results,a clinical case-control study is carried out to further verify the appropriate delivery rate of PIEB and the adaptive catheters,and formulate an optimized new scheme of PIEB for labor analgesia.1.Effect of Epidural Catheter parameters and delivery rates on Injectate Pressure:in VitroAim: To investigate the effect of epidural catheter parameters and delivery rates on pressure generated by bolus administration.Methods: The pressure was measured at five delivery rates(120,240,360,480,and 600 m L/h)through twelve representative epidural catheters.Student t test was applied for comparison among catheter groups.Pearson’s correlation coefficients were used to assess the relationship between the delivery rate and pressure.Results: 60 combinations of different epidural catheters and delivery rates were generated,and 180 pressure tests were performed.The mean pressure in 900mm(length)catheters was higher than in 800 mm catheters(P<0.05,all delivery rates);The mean pressure in a 20 gauge catheter was significantly higher than in 19 gauge catheters(P<0.01,all delivery rates),and the peak pressure in the 20 gauge catheter reached the alarm threshold when the delivery rate exceeded 360 m L/h;The mean pressure in the three-lateral ports catheter was higher than in the one-lateral port catheter(P<0.05,delivery rates of 120,240,360 and 480 m L/h);The mean pressure in the close-ended catheters was significantly higher than in the open-ended catheters(P<0.01,all delivery rates);The mean pressure in the open-ended wire-reinforced catheters was lower than in the non-reinforced catheters(P<0.01,all delivery rates).The pressures were correlated with delivery rates(r>0.8,P<0.05,12catheters).Conclusion: There is a strong positive correlation between pressure and delivery rates.Catheters with long length,large gauge,close-ended and multiple-lateral ports will increase the pressure.The reinforced catheters will not significantly increase the pressure and can be applied to PIEB mode.In order to reduce the risk of triggering occlusion alarms,small gauged catheters were recommended to PIEB(when delivery rate exceeded 360 m L/h).2.Selection of Optimal Parameters of Wire-reinforced Epidural Catheter:in Vitro Aim: Wire-reinforced epidural catheters provide advantages in labor analgesia with a low risk of epidural hemorrhage and misplacement.To find the optimal parameters of wire-reinforced epidural catheters,we conducted this in vitro study and identified the association between delivery rates,catheter tips and dye diffusion.Methods: The pressure and dye diffusion distance and area were measured at five delivery rates of 120,240,360,480 and 600 m L/h through three wire-reinforced epidural catheters(open-ended,three lateral ports,OE-3;close-ended,three lateral ports;open-ended,uniport,OE-0).One-way ANOVA analysis and Bonferroni post-hoc test were used to compare the mean pressure,dye diffusion distance and area.Pearson’s correlation coefficients were used to evaluate the relationship between mean pressure and dye diffusion.Results: A total of 30 pressure tests and 30 dye diffusion measurements were performed.The diffusion distance of CE-3 was significantly shorter than that of OE-3 and OE-0 at all delivery rates(P<0.05);The diffusion distance of OE-3 was shorter than that of CE-0 at the rate of 480 m L/h and 600 ml L/h(P=0.001 and P=0.032);At the rate of 240 m L/h,the diffusion area of CE-3 and OE-3 was larger than that of OE-0(CE-3 vs OE-0,P=0.003,OE-3 vs OE-0,P=0.014),but there was no significant difference when the rate reached or exceeded 360 m L/h(all P>0.05);The pressure was correlated with the dye diffusion distance and area in the open-ended catheters(r>0.8,P<0.001),but only with the diffusion area in the close-ended catheter(r=0.8359,P<0.001).Conclusion: At high rate(>360m L/h),the multiport catheters had no advantages over uniport catheters in diffusion area,while uniport catheters significantly increased the diffudion distance.The open-ended uniport reinforced catheters combined with high rate is more conducive to drug diffusion in epidural cavity.3.Comparison Between Uniport and Multiport Wire-reinforced Catheters for Labor Analgesia During Programmed Intermittent Epidural Boluses: A Randomized Controlled Clinical Trial Aim: The vitro study found that the uniport wire-reinforced catheter was conducive to drug diffusion at high rate.We conducted the clinical study to compare the effect of uniport and multiport wire-reinforced catheters on labor analgesia with PIEB,and preliminarily explore the advantages of uniport wire-reinforced catheters.Methods: 182 nulliparous and healthy women with a singleton pregnancy at a cervical dilation between 2 and 5 cm at request for neuraxial analgesia were eligible for this trial,and were randomized to receive either uniport or multiport catheters.Epidural analgesia was initiated and maintained with a solution of 0.1% ropivacaine with 0.3μg/m L of sufentanil.The programmed intermittent epidural bolus volume was 10 m L administered every 45 minutes at a delivery rate of 480 m L/h after test dose.All pumps were programmed an 8m L patient-controlled epidural(PCEA)bolus and a 10-minute lockout interval configured between PCEA or PIEB/PCEA boluses.The primary outcome was the percentage of participants with a NRS score ≤3 during two consecutive uterine contractions 20 minutes after the initial epidural bolus.Secondary outcomes included the time to achieve adequate analgesia,sacral 2 sensory block level,requirement for PCEA or provider-administered boluses,ropivacaine consumption,mode of delivery,adverse effects and maternal satisfaction.Results: 169 parturients finished the trial(unpiport catheter group n=85,multiport catheter group n=84).The percentage of parturients with adequate analgesia 20 minutes after initial bolus was higher with the uniport catheters than with the multiport catheters(71.8% vs 56.0%,OR=2.00,95%CI: 1.18-2.53,P=0.032).The median times(interquartile range)to adequate analgesia were 12(9-15)min and 20(16-24)min with uniport and multiport catherters.S2 sensory blockade levels were more frequently observed in the uniport catheter group at 20 minutes(P<0.05).Parturients with multiport catheters reported significantly higher NRS score at 10-cm cervical dilation(P<0.001).The percentage of parturients requiring patient-controlled epidural analgesia and the hourly consumption of ropivacaine were lower with the uniport catheters compared to the multiport catheters(all P<0.05).There were no differences in the incidence of unilateral block,side effects,cesarean delivery,duration of labor and maternal satisfaction between the two groups.Conclusion: Uniport catheters with a 480 m L/h delivery rate for epidural labor analgesia had improved analgesic efficacy compared with multiport catheters.