Introduction

Labor pain is considered to be one of the most severe pain in women’s life. Although it is not life threatening to healthy puerpera, the pain stress may increase the incidence of postnatal depression [1] and hemodynamic changes can probably have adverse effects on delivery process and fetus [2]. At present, neuraxial analgesia is widely accepted to be the gold standard to alleviate the labor pain. Labor neuraxial analgesia was initially maintained by manual intermittent boluses. Then, CEI, which is a technique using a catheter to provide continuous infusion to the epidural space with or without PCEA, became popular [3]. It was more stable and could reduce supplemental epidural dosage for breakthrough pain [4]. PIEB as a newly emerging technique has been proved by many studies that it resulted in less motor block and higher maternal satisfaction scores [5,6,7]. This review will examine the effect of PIEB compared with other techniques on labor outcomes, elaborate the latest research progress of the optimum PIEB time interval, epidural catheter type, flow rate, and concentration of local anesthetic, and discuss some concerns when implementing PIEB.

Method

The study was based on an extended literature search performed in the PubMed, Web of Science, and Cochrane Database of Systematic Reviews. Available articles were included from January 2010 and June 2022. The keywords used for the search were programmed intermittent epidural bolus, PIEB, automated mandatory bolus, AMB, labor analgesia, and labor analgesia as well as various combinations of these words. The publications were selected in accordance with the following inclusion criteria: The object of study were women receiving PIEB in maintenance for labor analgesia. The results of the study should include maternal and neonatal outcomes. The exclusion criteria were non-English studies and studies that did not use automated administration of bolus doses. This study primarily employs a literature review methodology, and as such, specific considerations for potential selection bias are not applicable.

Of the 263 publications identified in the search, 27 met the inclusion criteria for this review, including 15 randomized controlled trials, 2 cohort studies, 4 sequential allocation trials, 2 in vitro studies, 2 systematic reviews, and 2 meta-analyses.

PIEB and other techniques in maintenance of epidural labor analgesia

Labor neuraxial analgesia is usually maintained by CEI, PIEB, or PCEA. Among the three, CEI with or without PCEA is the most widely used method, PIEB became increasingly popular in recent years, and PCEA is usually accompanied with CEI or PIEB, but still some institutions use PCEA without a background infusion [8]. In this section, we will review some studies (Table 1) to compare PIEB, CEI, and PCEA in terms of the quality of analgesia, incidence of motor block, narcotic consumption, mode of delivery, labor process, and Apgar score, and different neuraxial procedures with PIEB make a difference in the maintenance of epidural labor analgesia on labor outcomes.

Table 1 Clinical trials comparing PIEB with CEI or PCEA
Full size table

PIEB vs CEI

Quality of analgesia

There are many indicators to evaluate the quality of analgesia. Commonly used are verbal analogue scale (VAS), maternal satisfaction, PCEA consumption per hour, number of PCEA bolus, and the incidence of breakthrough pain. Ferrer et al. [9] recruited recorded mean VAS score, maternal satisfaction, and percentage of women with breakthrough pain. The results showed no significant difference among the three indicators, but PIEB group demonstrated a trend of lower mean VAS score at each time after epidural and lower incidence of breakthrough pain. Two other randomized trials got the same results in maternal satisfaction [10, 11]. There are also some different conclusions. Riazanova et al. [12] found that at the active labor phase and the active pushing phase, compared with the CEI group, VAS scores in PIEB group declined significantly, and Fan et al. [13] got the similar results. Besides, they also found that the maternal satisfaction score in PIEB group was lower than the CEI group. A 2018 Cochrane [3] and a systematic review [14] approved that PIEB could reduce the incidence of breakthrough pain and the latter indicated that the rate of PCEA usage in PIEB + PCEA group was significant lower than that in CEI + PCEA group (OR, 0.30; 95% CI, 0.16–0.56). Another meta-analysis of randomized controlled trials [15] also found that the VAS score at 30 min, 2 h, 4 h, and 5 h, the rate of breakthrough pain (OR = 0.47, 95% CI: 0.28–0.80, I2 = 47%) and numbers of patients who require PCEA bolus (OR = 0.27, 95% CI: 0.14–0.51, I2 = 65%) were lower in PIEB group, besides the satisfaction score of patient was higher compared with the CEI group (WMD = 0.91, 95% CI: 0.42–1.39, I2 = 98%). In conclusion, compared with CEI, the effect on the quality of analgesia of PIEB may have some advantages, especially in VAS score, incidence of breakthrough pain and PCEA demand. Although some researches did not find significant difference between the two groups, the systematic reviews have the similar results.

Motor block

The high incidence of motor block, which is closely associated with increased use of instrumental delivery, is an important consideration that is widely concerned by obstetricians and anesthesiologists. Unfortunately, there is no consistent conclusion at present. Ojo et al. [10] involved 120 parturient and found that the Bromage score in the CEI group started to be significantly lower than PIEB in 4 h after the loading dose and the linear mixed-effect model demonstrated that the Bromage scores in CEI group were increasingly lower over time than the PIEB group. A prospective cohort study [16] assessed the prevalence of lower limb motor block (Bromage scale grade II-IV) every two hours and found that the prevalence in PIEB + PCEA group was significantly lower compared with the CEI group. However, Haidl and colleagues [11] found no statistical difference in the modified Bromage score at both 60 min and delivery. Ferrer et al. [9] compared the modified Bromage scale of PIEB with CEI at 15 min post-epidural and at every following hour until delivery. The results also showed no significant difference in motor unilateral block, while the incidence of motor blockade in CEI group at each time point was all higher than PIEB group. The conflicting evidence regarding the motor block might be related to the different end point of the studies. Although Ojo et al. [10] got the significant different results, the significant difference appeared 4 h after the loading dose while studies found no significant difference measured by the Bromage scores up to 3 h or at delivery (no clear time point). We can infer from these studies that there is no significant difference in the incidence of motor block between the two methods within 4 h and after 4 h, the prevalence of motor block using PIEB may be lower than using CEI.

Narcotic consumption

It is widely agreed that PIEB reduces the local narcotic consumption. Fan et al. [13] recruited 3000 parturients and the results indicated that the dosage of both ropivacaine and sufentanil in PIEB group decreased significantly. Several other randomized controlled studies and three systematic reviews found the similar results [3, 9, 12, 14,15,16,17]. Although Haidl et al. [11] found no difference in the total hourly consumption of the epidural solution between the two methods, PIEB group also had a tendency toward more bupivacaine rescue boluses. Moreover, the sample size of the study reflects the possibility that a larger sample size would have brought about a statistically difference.

The mode of delivery

The results from observational studies are contradictory. A cohort study conducted by Holgado et al. [18] compared CEI versus PIEB + PCEA and assessed the mode of delivery as the primary outcome found that the number of cesarean sections and instrumental deliveries in PIEB + PCEA group was significantly lower after correcting for confounders. In contrast, Bullingham et al. [16] found no significant difference in the mode of delivery. The results of randomized controlled trials are also inconsistent. Three randomized controlled trials did not found statistic difference in instrumental vaginal delivery rates and cesarean delivery rates between PIEB and CEI [9, 13, 17]. A Cochrane review [3] confirmed the results (risk of cesarean delivery: RR 0.92, 95% CI 0.70 to 1.21, I2 = 0% and risk of instrumental delivery: RR 0.75, 95% CI 0.54 to 1.06, I2 = 0%) However, Capogna et al. [6] and another systematic review [14] indicated a statistically lower incidence of instrumental delivery using PIEB (OR, 0.51; 95% CI, 0.30–0.84, I2 = 24%). As Bullingham et al. [16] put forward in the study that the rates of instrumental delivery observed in their study and previous randomized controlled trials (RCTs) demonstrated a consistent trend toward less incidence of instrumental delivery, we also find the same trend in the most of the above studies. Furthermore, the mode of delivery in all of these studies except Holgado et al. [18] was assessed as the secondary outcome. Therefore, more studies with the delivery mode as the primary outcome, confounders corrected and larger sample size should be conducted in future to determine the effects of PIEB and CEI on delivery mode, especially the incidence of instrumental delivery.

Labor process

Studies that have investigated this parameter have conflicting results. The Cochrane review and four RCTs [3, 6, 9, 10, 12] discussed the whole labor process, Fan et al. [13] studied the first stage of labor, and a RCT [17] considered the first and second stage of labor had no significant difference between PIEB and CEI. In contrast, in the meta-analysis by Xu et al. [14], the length of total and first and second stage of labor were all shorter using PIEB compared with CEI (15, 11, and 3 min), but the differences were hardly clinically significant. Liu et al. [19] and Wang et al. [15] got the similar findings with the former’s difference of total and first and second stage of labor 21.46, 13.41, and 4.98 min, respectively, and the difference of the first and second stage of the latter was 10.52 and 1.48 min, respectively. For the subgroup analysis of the meta-analysis [3], the results of subgroup that utilized PCEA showed that PIEB probably reduced the duration of labor analgesia (MD − 13.24 min, 95% CI − 20.71 to − 5.76, I2 = 0%) compared with CEI, while the subgroup that did not utilize PCEA found little or no difference in the duration of labor analgesia between the two methods (MD − 48.65 min, 95% CI − 129.92 to 32.62, I2 = 73%). The subgroups analysis of Liu et al. [19] indicated that the significant difference found in first and second stage of labor was mainly detected in parturients who received PCEA, while the results of total duration of labor remained irrespective of PCEA status. Considering that most institutions use PIEB or CEI together with PCEA for labor analgesia, PIEB can reduce the labor process, but there is little clinical significance.

Apgar score

In the four studies that reported Apgar scores [9, 12, 13, 17], one reported Apgar scores at 1, 5, and 10 min and three studies reported Apgar scores at both 1 and 5 min. None of the studies showed any significant difference in Apgar scores between the two techniques. These findings were confirmed in the meta-analysis by Sng et al. [3] and Xu et al. [14]. However, a meta-analysis that involved 15 studies [15] found that the Apgar score at 1 and 5 min in PIEB group was significantly higher than that of CEI group (WMD = 0.07, 95% CI: 0.02 to 0.12, I2 = 49%) (WMD = -0.08, 95% CI: −0.12 to −0.05, I2 = 21%). In these three meta-analyses, Wang et al. [15] had the highest number of included studies, while the other two studies only reviewed the data qualitatively due to high heterogeneity. The Apgar score has been typically compared as the secondary outcome, and the small sample size may be the reason why previous studies did not find statistically significant differences.

Epidural distribution

Current thinking suggested that better analgesic effect and lower total consumption of local anesthetic using PIEB might be associated with a wider sensory block and better homogeneous distribution compared with CEI. Hogan [20] studied three human bodies by injecting ink through epidural catheters inserted by standard techniques. After freezing and microtome sectioning, they found that rather than as a unified advancing front, the spread of solution is directed among paths between structures according to pressures by which they are compressed. This indicated that when large volumes and correspondingly high injectate pressure near the site of injection engage numerous channels, spread is most uniform. Mowat et al. [21] injected aqueous dye (1 ml) into the epidural catheter as a bolus or as an infusion over 30 min in seven anaesthetized pigs and compared the extent of dye spread. The results showed that bolus injection in a porcine model provided greater spread within the epidural space than delivery by infusion (15.2 ± 2.7 cm vs 8.9 ± 2.6 cm). This could result from the greater injection pressures. Many clinical trials agreed the above conclusions [10, 12, 17, 22].

PIEB vs PCEA

To our knowledge, few articles have been published to compare PIEB with PCEA without a background infusion. A two-center, double-blind, randomized study [23] compared the effect of PIEB and PCEA on labor analgesia. They randomized 130 nulliparous to PIEB group and PCEA group. Both groups used ropivacaine 0.12% with sufentanil 0.75 µg/ml and the same potential maximum volume per hour. The results showed that patients in PIEB group had reduced frequent breakthrough pain, fewer motor block, and greater local narcotic consumption with fewer PCEA boluses. Bourges et al. [24] also compared PCEA and PIEB. The maintenance solution levobupivacaine 0.625 mg/mL, sufentanil 0.25 mg/mL, and clonidine 0.375 mg/mL. They found that PCEA-only resulted in lower hourly consumption of local anesthetic, but the difference was not clinically relevant. Yet it is worth noting that, in both studies, the PIEB group also had on-demand patient-controlled epidural analgesia boluses instead of using PIEB-only. In Roofthooft et al. [23] study, the lockout interval of PCEA regimen in PIEB group was 20 min, longer than PCEA group with a 12 min lockout interval, while Bourges et al. used the same PCEA regimen in the two groups.

Different neuraxial procedures with PIEB

The dural puncture epidural (DPE) technique is a relatively new method for neuraxial labor analgesia. Due to its advantages such as fast onset, better sacral spread and fewer side effects compared to traditional epidural and combined spinal epidural techniques, it has received increasing attention in recent years. At present, there is relatively little research on the combination of DPE and PIEB. Song et al. [25] randomized 116 women to receive EP + CEI, DPE + CEI, and DPE + PIEB for labor analgesia. The result demonstrated that compared with EP/DPE + CEI, the use of DPE + PIEB achieved a greater anesthetic drug-sparing effect and superior analgesia quality without increasing maternal or neonatal side effects. This indicated that DPE + PIEB is a superior option for future labor analgesia. Epidural analgesia (EP) and combined spinal epidural (CSE) analgesia are currently mature and widely used neuraxial procedures. As mentioned earlier in our text, whether EP or CSE is used, the labor outcome of PIEB is better than that of CEI. We did not find studies compared EP, CEI or DPE when using PIEB as maintenance of epidural labor analgesia.

Implementation strategies

The time interval of PIEB

Since one of the biggest differences between PIEB and CEI is that the local anesthetic solution of PIEB is automatically administered at a fixed time interval, time interval is a noticeable parameter in PIEB regimen strategies. The optimal PIEB regimen is still unclear, and the implementation strategies vary among institutions and studies. In the institutions that implement PIEB, the time interval is generally 30–60 min, of which 60 min is the most common. To determine how PIEB interval and volume influence the labor outcome, some institutions conducted relevant researches (Table 2). Wong et al. [26] randomized 190 healthy nulliparous women to 1 of 3 maintenance regimens of PIEB: 10 mL every 60 min (10/60), 5 mL every 30 min (5/30), or 2.5 mL every 15 min (2.5/15). The epidural maintenance solution was bupivacaine 0.625 mg/ml and fentanyl 1.95 μg/ml. The primary outcome, median (interquartile range) adjusted bupivacaine consumption per hour of labor was 8.8 mg in group 10/60 compared with 10.0 mg in group 5/30 and 10.4 mg in group 2.5/15, and no difference was found in the pain scores at delivery, number of manual bolus doses for breakthrough pain, PCEA requests or administrations, time to first PCEA, and patient satisfaction.

Table 2 Clinical trials on implementation strategies
Full size table

Investigators from Mount Sinai Hospital, University of Toronto, performed three biased-coin up-and-down sequential allocation trials [27,28,29] to obtain the effective interval 90% for the PIEB regimen (EI90) to find the optimal interval time. Their first study [27] involved 40 nulliparous women who underwent spontaneous or induced labor. The 0.0625% bupivacaine plus sufentanil citrate solution 2 μg/ml was used as the maintenance solution. In all subjects, the PIEB dose was fixed at 10 mL. The PIEB interval for the first patient was set at 60 min, and the subsequent patients’ PIEB intervals were set at different intervals (60, 50, 40, and 30 min; 60, 50, 40 and 30 groups, respectively). The results demonstrated that the optimal time interval was approximately 40 min, nearly 70% of the patients in group 30 had sensory block above T6, while in groups 40, 50, and 60, the percentage was 44%, 22%, and 11%, respectively. The bupivacaine solution used this study is similar to Wong et al., and the main difference between the two studies is the total volume of bupivacaine solution in each group and whether PCEA or manual bolus was used to prevent breakthrough pain. Since 44% of women in the first study experienced upper sensory block to ice above the T6 level, which suggested that the spread of the epidural mixture was exaggerated and unnecessary, they designed another research to discuss during the first stage of labor, the effective PIEB time interval between 5 mL boluses of bupivacaine 0.125% with fentanyl 2 μg/ml. The second study [28] used the same method and found that the EI90 was approximately 35 min, 20/40 women had an upper sensory block above T6, no motor block appeared in 34/40 women, and no hypotension treatment was required. They then conducted a third study [29] to determine the EI90 for the PIEB boluses of 2.5 mL of 0.25% bupivacaine plus fentanyl 8 μg/ml. The results demonstrated that the estimated EI90 was 20 min, beyond their estimated hypothesis which was 30–60 min. Another result contrary to their assumption was that the consumption of local anesthetic with this regimen was higher than in their previous studies. Zhou et al. [30] also adopted the same method as the above two articles to investigate the optimal duration with 10 ml of ropivacaine 0.08% and sufentanil 0.3 mg/mL which is the standard treatment for labor pain in China. The optimal PIEB interval was about 42 min, and the incidence of maximum sensory block level above T6 was 20%, 5.3%, 0%, and 0% of parturients in groups 30, 40, 50, and 60, respectively. They compared their study with Epsztein et al. [27] which used the same duration of time intervals and bolus volumes and found that the incidence of motor blockade decreased statistically.

Li et al. [31] studied the relationship of body temperature between PIEB at different intervals combined with PCEA. They randomly divided 170 primiparous women into group A (5 ml/30 min) and group B (10 ml/60 min). The maintenance dose was 0.075% ropivacaine and 0.5 μg/ml sufentanil. Maternal temperature in group A was higher than that in group B at the time of cervix being completely dilated and 2 h after delivery. The incidence of intrapartum fever, VAS score, serum TNF-α, IL-6, CRP levels and epidural analgesic dosage at two hours after delivery in group A were all higher than those in group B.

From these studies, the body temperature and incidence of postpartum fever was lower with fewer anesthetics used at intervals of 60 min than at intervals of 30 min or less in PIEB + PCEA mode. The optimal interval of 10 mL of bupivacaine 0.0625% with fentanyl 2 μg/mL, 5 mL boluses of bupivacaine 0.125% with fentanyl 2 μg/ml, 10 ml of ropivacaine 0.08% and 0.3 mg/mL sufentanil, and 2.5 mL of 0.25% bupivacaine plus fentanyl 8 μg/ml in PIEB is 40, 35, 42, and 20 min, respectively. With the above-discussed results, we refer that when the deliver bolus is 10 ml, the optimal intervals are similar, around 40 min, regardless of the kind of the drugs. When the single bolus becomes smaller, the optimal interval gets shorter. Since the commonly used drug concentration is about 0.1% and the commonly used single dose is 5 ml or 10 ml, we recommend that the optimal interval can be between 35–40 min. However, since all of these studies only included nulliparous women and first stage of labor, more studies should be done to clarify whether the results are available for the whole process of labor and all parturients.

Epidural catheter type and bolus infusion rate

The bolus infusion rate and catheter type are the possible factors that affect the analgesic effect in PIEB regimen as well. The common infusion rate is 100-400 ml/h, and the catheter type also varied among institutions. Since the presumed advantages of PIEB compared with CEI result from larger volumes and more uniform distribution of solution in the epidural space [20], two in vitro studies [32, 33] (Table 3) discussed the relationship between delivery speeds, catheter type and bolus injection pressure.

Table 3 In vitro studies
Full size table

The first one [32] performed 660 measurements to evaluate the pressure and flow characteristics of 11 commonly used epidural catheters according to the PIEB regimen. They measured the pressure at flow rates of 100, 250, and 400 ml/h with a bolus volume of 10 ml. The results demonstrated that the pressure increased 1.31, 1.65, and 2.00 mmHg for 18G, 19G, and 20G catheters, respectively, per 1 ml/h of increased flow rate. Analyses contained wire-reinforced catheters which indicated that the pressure of 18G, 19G and 20G catheters increased by 1.16 mmHg, 1.76 mmHg, and 2.36 mmHg, respectively, for each additional 1 ml/h flow rate. These findings indicate that higher gauged catheters, higher flow rates, and wire-reinforced catheters generate higher pressures. The equipment may also influence the maximum pressure since different infusion pumps have different threshold for occlusion alarms. In addition, the combination of a high flow rate and increased catheter gauge may trigger the occlusion alarm. The study only tested multi-orifice epidural catheters.

The second one [33] used four epidural catheters (2 single hole and 2 multi hole) to test the pressure generated by normal saline delivery at 100, 175, 300, and 400 ml/h. No matter used single-orifice or multi-orifice catheters, the peak pressure increased with the increase in the infusion speed and at all infusion speeds, the peak pressure of multi-hole catheters was higher than that of single-orifice catheters, although the difference was small.

To confirm how the bolus delivery rates influence the quality of analgesia in human, Lange et al. [34] (Table 2) conducted a RCT to find how does the infusion bolus delivery rate affect labor analgesia. They recruited 108 nulliparous women and randomized them to the low-rate (100 ml/h) and the high-rate (300 ml/h) group. The maintenance epidural solution was bupivacaine 0.625 mg/ml with fentanyl 1.95 μg/ml, with the 60 min interval each bolus (10 ml). The results showed no significant difference in the hourly bupivacaine consumption and patient requested/delivered epidural bolus ratio between groups which indicated that epidural bolus delivery rates were not related to labor analgesia quality. Another RCT [35] (Table 2) involved 90 nulliparous women and randomized them to receive PIEB delivered at 250 mL/h (G250) or 125 mL/h (G125). Analgesia was sustained using a mixture of 0.0625% bupivacaine and 2 μg/ml fentanyl, with the PCEA boluses administered at 10 mL intervals every 40 min. The results of the study also demonstrated that different infusion rates of PCEA provided comparable analgesic effect. Furthermore, the researchers observed that women in the G125 group had a lower incidence of hypotension (11.1% vs 33.3%; P = 0.01). It is worth noting that, in both studies, the median bupivacaine consumption decreased approximately 0.9 mg/h although it is not statistically different and it suggests a potential advantage of employing a higher infusion rate; larger sample size may obtain different results. Considering the results of the two studies and higher rates of infusion (greater than 250 ml/h) require a high-flow tubing to achieve optimal flow dynamics with PIEB which may increase the cost, a lower infusion rate may be preferable. However, there is still relatively little research on this topic. The infusion rates compared in the two articles were different, and the patients involved in the above studies were nulliparous women and warrant further investigation.

From these studies, the higher flow rate, higher gauged catheters, and wire-reinforced catheters can generate higher pressure. Multi-orifice catheter can also result in higher pressure compared with single-orifice catheter, and the equipment may influence the maximum pressure. However, the above conclusions are obtained in vitro condition where the pressure, volume and compliance are different from the epidural space but may have an impact on the distribution of solution, and the safe peak pressure in the human epidural space remains unknown. Current clinical studies have not found that the increased infusion rate can improve the quality of labor analgesia. Despite the result of the clinical study and in view of the common speculation, we consider that higher gauged, wire-reinforced and multi-orifice catheters are better. For the flow rate, considering the cost, the bolus delivery rates lower than 250 ml/h may be appropriate. Further studies are required to figure out the relationship between bolus infusion rate, catheter type, pressure generated during PIEB injection, and analgesic effect and set the optimal value.

Concentration of local anesthetic

Previous studies suggested that low concentrations of local anesthetics (≤ 0.1% bupivacaine, 0.1% levobupivacaine, or ≤ 0.17% ropivacaine) had some advantages compared with high concentrations of local anesthetics. A meta-analysis published by Sultan et al. [36] showed that low concentrations were associated with a lower incidence of assisted vaginal delivery (OR = 0.70; 95% CI 0.56 to 0.86; I2 = 0%), less motor block (OR 3.9; 95% CI 1.59 to 9.55; I2 = 55%) and a shorter second stage of labor (WMD-14.03; 95% CI-27.52 to-0.55; I2 = 93%). Another systematic review identified nine RCTs [37] that found no differences in the risks of assisted vaginal delivery (OR = 1.18; 95% CI, 0.93–1.49, I2 = 0%) but lower incidence of motor block (OR = 4.05; 95% CI, 2.19–7.48, I2 = 60%) and pruritus (OR = 0.07; 95% CI, 0.03–0.16, I2 = 2%) in low concentration groups. Nevertheless, the methods in maintenance of epidural labor analgesia in these studies are CEI with PCEA methods, and unfortunately, we do not find studies available on this topic relate to PIEB techniques. The results of Shatalin et al. [29] demonstrated no advantage in using concentrated solutions in PIEB because of increased consumption of local anesthetic; however, they just compared their results with their previous studies so the conclusion was not convincing enough.

The risk and practical concern with PIEB

The main concern of the implementation of PIEB is that the optimal regimen of PIEB remains unknown. In addition, different institutions use different types and concentrations of drugs, and each patient has their own conditions (such as weight, height, progression of labor, and the condition of the epidural space). Therefore, adjustments to the PIEB plan must be made for each individual patient. Due to the larger boluses and longer interval of PIEB administration compared with CEI, complications such as subarachnoid blockage, drug entry into the bloodstream, and catheter obstruction are difficult to detect in a timely manner. Therefore, right after the placement of the epidural catheter, experimental doses should be administered and attention should be paid to observe the blood pressure, heart rate and pain relief of the parturient after administering the loading dose. The administration plan also should be adjusted promptly according to these conditions. After the loading dose is administered, patients typically experience significant pain relief, reduced release of catecholamines, and increased uterine contractions. However, this may result in fetal head compression and bradycardia. Therefore, continuous fetal heart monitoring is necessary too. During labor analgesia, blood pressure, heart rate, and fetal heart rate should be continuously monitored to ensure safety and relevant personnel should always be nearby to promptly identify potential risks and improve patient discomfort.

The adjustment of PIEB parameters should be within the safe range, higher dose may increase the incidence of motor block and hypotension, short intervals may increase drug consumption and affect the setting of PCEA lockout time, and high flow rates may increase the incidence of high-pressure alarms. Thus, several parameters should be adjusted together rather than adjusting a single parameter.

Due to the shortage of anesthesiologists in China, they cannot always stay with the parturient. Therefore, training should also be provided to midwives and obstetricians, so that they can timely detect patients’ discomfort or problems with the analgesic pump and inform the anesthesiologist in a timely manner. The price is also a factor that needs to be considered. As far as we know, the cost of PIEB pump is similar to that of CEI pump. Of course, institutions can also purchase pumps combined with PCEA or CEI to provide different choices for economically capable parturients.

Conclusion

PIEB as a new technique in maintenance of labor analgesia is advantageous and promising. From the current studies, it has the potential to improve analgesic quality and reduce consumption of narcotic compared with CEI and reduce the occurrence of breakthrough pain, motor block but increase the drug consumption compared with PCEA. Meanwhile, the incidence of side effects does not increase. The advantages of PIEB compared with CEI might be associated with a wider sensory block and better homogeneous distribution. The optimal regimen is still unclear. Anesthesiologists still need to formulate the implementation strategies according to the specific conditions of patients, medical institutions and the existing research results. The recent researches indicate that longer interval may decrease the body temperature and the incidence of postpartum fever with fewer anesthetics is used. Higher flow rate, higher gauged catheters, and wire-reinforced and multi-orifice catheters can generate higher pressure in vitro condition. Equipment may also affect analgesia by influencing the maximum pressure. In current clinical studies, no difference has found between the flow rate and analgesic quality. Lower concentrations of local anesthetics may have some benefits, but this still needs to be confirmed by the future studies. From the existing results, we think that using lower concentration anesthetic with the time interval in the range of 35–40 min, higher gauged, wire-reinforced, and multi-orifice catheters, lower than 250 ml/h flow rate can be a reference regimen. Besides, during the whole process, blood pressure, heart rate, and fetal heart rate should be continuously monitored and administration plan also needs to be adjusted promptly according to patient’s condition.