From labor to surgery: expanding the role of programmed intermittent epidural bolus beyond obstetric

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.

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.