INTRODUCTION
Epidural analgesia was once considered one of the most effective methods for postoperative pain control in abdominal and thoracic surgeries [1]. However, its role has diminished in recent years with the increasing adoption of minimally invasive surgical techniques and the implementation of Enhanced Recovery after Surgery (ERAS) protocols [2]. Concerns about motor blockade, delayed ambulation, urinary retention, and catheter-related complications have contributed to this decline, and epidural techniques are now used less frequently in the postoperative setting [2,3].
Despite this trend, epidural analgesia continues to be the gold standard for labor analgesia [4,5]. Advances in drug delivery methods, particularly the development of programmed intermittent epidural bolus (PIEB), have renewed interest in its potential value. PIEB involves the automated administration of intermittent, high-pressure boluses of local anesthetic at predetermined intervals rather than continuous low-flow infusion. This approach enhances the spread of epidural drugs and may reduce the risk of motor blockade, thereby achieving a favorable balance between sensory analgesia and motor preservation [6-8].
In obstetric anesthesia, these theoretical advantages have been consistently confirmed in clinical trials and meta-analyses, demonstrating improved analgesia, lower anesthetic consumption, and greater maternal satisfaction with PIEB than with continuous infusion [9,10]. However, its application outside the field of obstetrics remains limited and underexplored. With the current shift toward opioid-sparing and mobility-preserving analgesic strategies under ERAS protocols, reexamining the potential of PIEB in perioperative settings has become increasingly relevant.
Therefore, this narrative review aims to summarize the mechanism and principles of PIEB, provide an overview of clinical evidence from obstetric anesthesia, where its efficacy has been most clearly demonstrated, and discuss emerging data in postoperative and non-obstetric contexts. Finally, we propose directions for future research to define the role of PIEB in modern perioperative pain management.
MECHANICAL AND PHARMACODYNAMIC MECHANISMS OF PIEB
PIEB is a method of maintaining epidural analgesia in which predetermined boluses of local anesthetic are automatically delivered at fixed intervals by an infusion pump, rather than continuous infusion, as in conventional continuous epidural infusion (CEI). The practical applications of PIEB in clinical settings are illustrated in Fig. 1. This delivery pattern generates higher injection pressures with each bolus [11,12], promoting broader longitudinal and circumferential spread of the local anesthetic within the epidural space [13,14] and producing a denser and more uniform sensory block than CEI (Fig. 2) [15]. This wider segmental nerve involvement contributes to enhanced analgesia by covering more dermatomes, whereas the low concentration of local anesthetic administered in intermittent boluses ensures that the total amount entering each nerve fiber is insufficient to induce motor blockade [7,8]. With CEI, the local anesthetic concentration remains persistently higher in the extraneural space than within the nerve, creating a continuous diffusion gradient that favors the inward movement of drug molecules. Over time, this sustained gradient leads to the accumulation of local anesthetics within the motor fibers, predisposing patients to motor blocks. By contrast, intermittent bolus administration allows the extraneural concentration to decrease between boluses, interrupting this steady gradient and preventing significant intraneural accumulation.
Together, these findings provide physiological and clinical rationales for PIEB as a more efficient and motor-sparing approach for epidural drug delivery. The conceptual distinctions between PIEB and CEI, which underlie these mechanistic advantages, are summarized in Table 1.
CLINICAL EVIDENCE IN OBSTETRIC ANESTHESIA
The clinical benefits of PIEB compared with CEI have been most extensively investigated in obstetric anesthesia, where numerous randomized controlled trials and meta-analyses have demonstrated that PIEB provides superior analgesic efficacy, reduces the incidence of motor block, and improves maternal satisfaction. Accordingly, PIEB is increasingly being adopted worldwide as the preferred method of epidural maintenance, gradually replacing conventional CEI.
Analgesic effect
Women receiving PIEB generally report lower pain scores [9,10,16,17], fewer episodes of breakthrough pain [9,10], and a reduced need for additional rescue boluses [8-10,17-20]. Notably, PIEB is also associated with a lower frequency of clinician interventions, reflecting a more stable baseline analgesic effect [19,21]. This reduction in clinician intervention may have practical implications such as decreasing staff workload and contributing to higher maternal satisfaction, an outcome that has clinical and operational significance [19]. However, several randomized controlled trials have reported no significant differences in pain scores [18,20], which appears to be attributable to differences in the timing of epidural initiation and pain assessment, dose of local anesthetic, and parity among the study populations. Nevertheless, most meta-analyses have demonstrated consistent results favoring PIEB, confirming its superiority in maintaining stable analgesia throughout labor. In addition to improved analgesic efficacy, PIEB is associated with a reduced total local anesthetic consumption [8,10,17,19,21], which may lower the risks of systemic toxicity and maternal hypotension.
Motor block
Another valuable advantage of PIEB is its motor-sparing effect [8,10,16,17,20]. Studies have demonstrated a lower incidence of motor block among women receiving PIEB than among those maintained on CEI, even when pain relief is superior. Although some studies have reported no significant differences in motor-sparing effects [18], these results may be explained by the short observation duration, as motor function is often assessed within approximately 4 h after the initiation of epidural analgesia [22]. Motor block with CEI tends to increase over time, leading to a time-dependent divergence in the incidence between CEI and PIEB as the duration of epidural maintenance lengthens [8]. Accordingly, studies with longer observation periods have shown a clearer distinction in the incidence of motor block between the two techniques [23,24]. The clinical relevance of this feature is substantial; preservation of motor function allows greater maternal mobility during labor, may contribute to a shorter labor duration, and has been associated with a lower incidence of instrumental vaginal delivery [8,10,17].
Maternal satisfaction
Previous reports have confirmed that PIEB improves maternal satisfaction with analgesic experiences [9,10,16,21]. Although maternal satisfaction is multifactorial and not solely dependent on the quality of analgesia [17], most studies reporting higher maternal satisfaction with PIEB have also observed lower pain scores, fewer episodes of breakthrough pain, and a reduced need for additional rescue boluses [9,10,16]. Taken together, these findings suggest that consistent analgesic levels, a lower incidence of motor blockade, and fewer clinician interventions contribute to an enhanced overall labor experience.
Obstetric and neonatal outcome
Obstetric outcomes appear to be unaffected or slightly improved with the use of PIEB compared with CEI. Several randomized controlled trials and meta-analyses have shown no increase in the duration of the first or second stages of labor and no increase in the rates of instrumental vaginal delivery [21] or cesarean section [10]. However, most studies suggest that the preservation of motor function and improved maternal cooperation associated with PIEB contribute to a shorter second stage of labor [5,10,16,17] and reduced instrumental vaginal delivery or cesarean section [8,10,16,17]. These findings indicate that PIEB provides effective analgesia without compromising the normal labor progress.
Regarding neonatal outcomes, no significant differences have been reported in Apgar scores [9,18,21] or fetal heart rates [9] between the PIEB and CEI groups.
However, these obstetric and neonatal parameters are generally evaluated as secondary outcomes in most studies, and their relatively low incidence, combined with limited sample sizes, may reduce the statistical power to detect meaningful differences. Therefore, the findings should be interpreted with caution. No increase in adverse maternal or neonatal outcomes has been observed with PIEB, supporting its favorable safety profile.
Collectively, the accumulated evidence suggests that PIEB not only enhances maternal analgesic experiences but also maintains a favorable obstetric and neonatal safety profile comparable to or potentially superior to conventional CEI.
POTENTIAL ROLE OF PIEB IN PERIOPERATIVE PAIN MANAGEMENT
Although the analgesic efficacy of PIEB has been most clearly demonstrated in obstetric anesthesia, its theoretical rationale suggests that similar benefits extend to perioperative pain management. Modern surgical practices increasingly emphasize minimally invasive techniques and multimodal analgesia, with the overarching goals of enhanced recovery and reduced opioid use. Despite its proven efficacy for pain control, epidural analgesia has been criticized for its invasive nature and adverse effects such as motor weakness, delayed mobilization, and urinary retention, which have contributed to its declining use in abdominal surgery over the past few decades [2,3]. The motor-sparing characteristics of PIEB may help address these concerns, allowing epidural analgesia to be reconsidered as a component of modern multimodal pain strategies. In the earlier decades, CEI was the predominant method of epidural drug delivery. More recently, PIEB has emerged as an alternative approach that offers a distinct mode of administration. However, its applicability in the context of enhanced recovery protocols has not yet been adequately evaluated.
Evidence from post-cesarean populations supports this possibility, showing that PIEB provides effective relief from incision and uterine contraction pain with less motor blockade and superior analgesia than CEI [23,24]. These findings suggest that intermittent bolus delivery maintains a robust sensory blockade while facilitating early mobilization and recovery after cesarean section.
In non-obstetric surgery, the available evidence remains limited and mixed. In open gynecologic procedures, a randomized controlled trial reported that PIEB produced lower pain scores and reduced ropivacaine consumption than CEI, suggesting that PIEB provides more consistent analgesia [25]. However, other randomized studies of major abdominal surgeries found no significant differences between PIEB and CEI in terms of pain control, opioid consumption, or patient satisfaction [26,27]. The lack of a clear benefit in these two studies may be attributable to the relatively small bolus volumes of 2-6 ml used, which were likely insufficient to provide adequate epidural spread and analgesic coverage for the extensive surgical fields involved in major abdominal procedures. Notably, one of these studies reported a substantial reduction in total local anesthetic consumption in the PIEB group, indicating a potential improvement in analgesic efficiency, even in the absence of overt differences in pain intensity [26].
Within perioperative ERAS pathways, the relevance of PIEB becomes clearer when its key characteristics are considered in relation to specific recovery goals. First, more effective analgesia with PIEB may support opioid-sparing multimodal analgesia, which is a key ERAS priority [28]. Second, the lower incidence of motor blocks observed with PIEB has potential implications for early mobilization, which is often hindered by motor weakness during CEI [29]. Third, reduced cumulative exposure to local anesthetics suggests the possibility of more stable hemodynamics, which is a crucial factor influencing early recovery after major surgery [29,30]. Together, these features indicate that PIEB contributes to enhanced functional recovery, an overarching objective emphasized throughout ERAS protocols [31].The current data indicate that PIEB offers a feasible alternative for postoperative epidural maintenance and is conceptually compatible with ERAS-based perioperative care. Nevertheless, these findings remain preliminary, and further research is needed to confirm its role and define the optimal parameters for integrating PIEB into perioperative multimodal analgesia strategies.
LIMITATIONS AND FUTURE DIRECTIONS
In Korea, CEI with patient-controlled epidural analgesia (PCEA) remains the predominant background regimen for labor analgesia. Although accumulating evidence suggests the advantages of PIEB, several limitations and practical challenges remain before it can be widely implemented.
Uncertainty in optimal PIEB regimens
The optimal PIEB regimen, including bolus volume, concentration, dosing interval, and delivery speed and pressure, remains uncertain, as protocols vary considerably across studies and institutions. Breakthrough pain may occur when bolus intervals are excessively long or bolus volumes are insufficient, resulting in a greater reliance on patient-controlled boluses and fluctuations in analgesia. Therefore, establishing an optimal combination of bolus volume and dosing interval is essential to balance analgesic stability and motor preservation.
Previous investigations have primarily focused on the relationship between bolus volume and dosing intervals. Because these findings depend heavily on the specific local anesthetic, its concentration, and the adjuvant opioid used, the applicability of one regimen to another remains limited. Generally, when the same regimen is used, larger bolus volumes (approximately 10 ml) tend to provide superior analgesic efficacy compared with smaller volumes of 5-6 ml [32-34].
Regarding the dosing interval, a study using 10 ml boluses suggested an optimal interval of approximately 40 min [35], while another study using 5 ml boluses reported a shorter interval of approximately 35 min [36]. Recent interval-finding studies further demonstrate that shorter intervals are required when smaller volumes are used [37-40] —for instance, 2.5 ml of bupivacaine 0.25% with fentanyl 8 µg•ml⁻¹ every 20 min [38], 8 ml of ropivacaine 0.1% with sufentanil 0.3 µg•ml⁻¹ every 41 min [39], and 10 ml of ropivacaine 0.08% with sufentanil 0.3 µg•ml⁻¹ every 42 min [40].
Recently, a mathematical modeling-based analysis explored the optimal PIEB settings using a solution of ropivacaine 0.2% combined with fentanyl 10 µg•ml⁻¹, suggesting that a bolus volume of 6.2 ml every 59.8 min optimizes patient-centered outcomes [41]. Although this finding provides a useful reference, further clinical data are required to establish universally applicable PIEB regimens and delivery parameters.
Safety and practical issues
There are concerns that the rapid administration of relatively large bolus volumes during PIEB may increase the systemic absorption of local anesthetics, thereby raising the potential risk of local anesthetic systemic toxicity. However, current evidence does not indicate a higher incidence of systemic toxicity compared with conventional CEI [6]. In obstetric settings, where maternal hemodynamics and fetal well-being are closely interrelated, heightened vigilance, including close monitoring of blood pressure, signs of systemic toxicity, and fetal heart rate, remains warranted until more robust safety data become available [6,22].
The implementation of PIEB is further limited by the requirement for specialized infusion pumps that are capable of programmed bolus delivery. Not all commercial devices are equipped with PIEB functionality, and their availability varies by region. Moreover, the technical performance of these systems differs: occlusion alarms can be triggered by high injection pressures or catheter resistance, which interrupt bolus delivery [6]. Standardization of device specifications and performance is essential to ensure safety and reproducibility in clinical practice. In Korea, Accumate 1200 (Woo Young Medical Co., Ltd.) is currently the only commercially available epidural infusion pump with PIEB functionality. This device provides both PIEB and PCEA modes and administers programmed bolus doses at a fixed delivery speed of approximately 120-240 ml/h, with the duration of bolus administration determined by the selected bolus volume. These device-specific characteristics, along with regional limitations in equipment availability, should be considered when interpreting PIEB-related outcomes or implementing institution-specific PIEB protocols.
Limited generalizability beyond obstetric settings
Most clinical evidence on PIEB originates from obstetric populations, and extrapolation to perioperative or postoperative settings should be approached with caution. The anatomical characteristics of the epidural space and pain profile after major surgery differ substantially from those during labor.
In the postoperative context, particularly following extensive abdominal procedures, the optimal bolus volume and interval required to achieve effective dermatomal coverage while maintaining motor and hemodynamic stability remain undefined. Most studies have used relatively small bolus volumes [26,27], which may not generate adequate epidural spread or pressure to fully exploit the mechanistic benefits of PIEB.
Furthermore, the clinical role of PIEB in ERAS and multimodal analgesic pathways remains unclear.
Future directions
Future research should focus on (1) defining optimal regimens for specific patient populations, (2) evaluating their role across diverse surgical populations, and (3) incorporating recovery-related and functional outcomes, such as ambulation, bowel function, opioid consumption, and hospital length of stay. Large-scale randomized controlled trials in non-obstetric settings are warranted to determine whether the benefits demonstrated in labor analgesia can be translated into broader perioperative practice.
CONCLUSION
PIEB represents a significant advancement in epidural anesthesia, providing improved pain relief with reduced motor block and anesthetic use in obstetric settings. Although the optimal dosing regimens remain under investigation, the benefits of PIEB are increasingly being explored in broader surgical populations. Further investigations should refine delivery parameters and evaluate the role of PIEB across diverse surgical populations.
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