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Implementation of Programmed Intermittent Epidural Bolus for the Maintenance of Labor Analgesia

Carvalho, Brendan MBBCh, FRCA, MDCH; George, Ronald B. MD, FRCPC; Cobb, Benjamin; McKenzie, Christine MD; Riley, Edward T. MD

doi: 10.1213/ANE.0000000000001407
Obstetric Anesthesiology: Special Article
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Programmed intermittent epidural bolus (PIEB) is an exciting new technology that has the potential to improve the maintenance of epidural labor analgesia. PIEB compared with a continuous epidural infusion (CEI) has the potential advantage of greater spread within the epidural space and therefore better sensory blockade. Studies have demonstrated a local anesthetic–sparing effect, fewer instrumental vaginal deliveries, less motor blockade, and improvements in maternal satisfaction with PIEB compared with CEI. However, the optimal PIEB regimen and pump settings remain unknown, and there are a number of logistical issues and practical considerations that should be considered when implementing PIEB. The PIEB bolus size and interval, PIEB start time delay period, and patient-controlled epidural analgesia bolus size and lockout time can influence the efficacy of PIEB used for epidural labor analgesia. Educating all members of the health care team is critical to the success of the technique. This review summarizes the role of PIEB for the maintenance of labor analgesia, outlines implementation strategies, suggests optimal settings, and presents potential limitations of the technique.

Supplemental Digital Content is available in the text.Published ahead of print July 26, 2016.

From the *Department of Anesthesia, Stanford University School of Medicine, Stanford, CA; and Department of Women’s & Obstetric Anesthesia, IWK Health Centre, Dalhousie University, Halifax, Nova Scotia, Canada.

Published ahead of print July 26, 2016.

Benjamin Cobb, MD, is currently affiliated with Department of Anesthesiology, University of North Carolina, Chapel Hill, North Carolina.

Christine McKenzie, MD, is currently affiliated with Department of Anesthesiology, University of North Carolina, Chapel Hill, North Carolina.

Accepted for publication April 11, 2016.

Funding: None.

Conflict of Interest: See Disclosures at the end of the article.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

Reprints will not be available from the authors.

Address correspondence to Ronald B. George, MD, FRCPC, Department of Women’s & Obstetric Anesthesia, IWK Health Centre, 5980 University Ave, Halifax, Nova Scotia, Canada B3K 6R8. Address e-mail to rbgeorge@dal.ca.

Patient-controlled epidural analgesia (PCEA) with a continuous epidural infusion (CEI) has been the optimal technique for delivering epidural labor analgesia for the past decade.1 Programmed intermittent epidural bolus (PIEB) delivery of epidural analgesia represents the next stage in the evolution of labor analgesia. When epidural catheters were first introduced, analgesia was provided by manual intermittent boluses of local anesthetic administered by midwives or anesthesia care providers on patient request. This technique was largely superseded by automated pumps that provide a CEI. Maintenance of analgesia with CEI results in 2 frequent outcomes: the need for rescue boluses to treat breakthrough pain when low infusion rates are used, or greater motor block when higher infusion rates are used in an attempt to decrease the need for rescue boluses.2

PCEA with or without CEI (ie, background infusion) for labor analgesia was introduced in 19883 and is now the most frequently used technique in North America.4 The addition of PCEA to CEI is associated with lower local anesthetic consumption, less motor block, and greater patient satisfaction and may decrease the need for clinician’s rescue bolus interventions.5–7 However, even when PCEA is combined with CEI, some patients still experience breakthrough pain requiring the attention of an anesthesia provider. The incidence is likely dependent on the patient’s understanding and appropriate use of PCEA, as well as the PCEA/CEI settings (ie, local anesthetic and opioid concentration, background infusion rate, PCEA bolus volume, and lockout interval).

Delivering the background local anesthetic/opioid solution as regularly spaced intermittent boluses rather than continuously may lead to a more extensive spread of the anesthetic solution in the epidural space. PIEB is an automated method of administering epidural local anesthetic solution (with or without opioids) boluses at fixed, scheduled time intervals. PIEB is used as an alternative to CEI alone or as part of a background local anesthetic infusion during a PCEA technique for labor analgesia. It has been proposed that delivery of the same dose of local anesthetic as an intermittent bolus is a more effective method for maintaining labor analgesia than CEI. We will review the potential for PIEB to improve maintenance of labor analgesia, describe the evidence for improved labor outcomes with PIEB, and discuss logistical considerations when implementing PIEB into clinical practice.

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Bolus Administration, Pressure Generation, and the Epidural Space

Epidural injections provide analgesia by the spread of local anesthetic through the noncontiguous epidural space surrounding the dural sac and nerve roots exiting the spinal canal. The effectiveness of epidural analgesia requires adequate spread of the anesthetic solution to produce sensory blockade of the necessary dermatomes. Multiple studies have attempted to characterize the spread of local anesthetic solution in the epidural space. Hogan8 studied the distribution of injected ink through epidural catheters in 3 nonembalmed adult cadavers by cryomicrotome section. He showed that the distribution of injected solutions in the epidural space is not uniform; spread is directed into multiple parallel passages according to the applied pressures by which the various structures are compressed. The most uniform spread occurred when large volumes, and correspondingly high injectate pressures near the site of injection, were administered.8

Kaynar and Shankar9 compared the spread of solution through a multiorifice epidural catheter administered by a bolus and infusion. A dye solution was infused continuously (10.5 mL/h) or by bolus administration (3.5 mL delivered over 1 minute every 20 minutes) onto a piece of white semiabsorbent paper over 60 minutes. The 10.5 mL/h infusion had very little flow through the distal orifice, whereas with the 3.5 mL boluses, the dye solution flowed through all 3 orifices. The dye distribution with the continuous infusion was only 0.3 in2 compared with 1.2 in2 after bolus administration. This finding implies that bolus administration compared with continuous infusion generates greater pressures and facilitates more uniform spread of anesthetic solution within the epidural space. A clinical study in gynecological patients confirmed improved spread; authors found that epidural ropivacaine 0.75% administered as 1 mL boluses every 20 minutes compared with a 3 mL/h continuous infusion resulted in a more extensive dermatomal spread as measured by loss of sensation to pinprick.10

The concept of PIEB is to combine the improved local anesthetic spread inherent in manual or PCEA bolus techniques with automated ongoing analgesia inherent in CEI. Programmed intermittent boluses rather than pain-triggered PCEA boluses have the potential benefit of providing a consistent level of analgesia and minimizing anesthesia care provider rescue bolus workload.1,5

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Is PIEB the Next Paradigm Shift for the Maintenance of Labor Analgesia?

Since 2004, multiple studies compared mandatory/automated/programmed intermittent epidural boluses to CEI with and without PCEA for labor analgesia (Table 1). Outcomes analyzed include pain scores, local anesthetic consumption, motor blockade, duration of labor, mode of delivery, and maternal satisfaction. George et al11 published a systematic review in 2013, which included 9 randomized control trials12–20 with 694 patients. Despite heterogeneous methodology among studies investigating PIEB for maintenance of labor analgesia, the vast majority of studies with PIEB were associated with decreased local anesthetic consumption, improved maternal satisfaction scores, and a decreased duration of the second stage of labor (Table 2). No statistically significant differences in mode of delivery or anesthesia interventions were found between PIEB and CEI; however, the meta-analyses were underpowered for these outcomes.11

Table 1

Table 1

Table 2

Table 2

Capogna et al20 reported decreased motor block and instrumental vaginal delivery rates with PIEB compared with CEI. This is the only PIEB labor analgesia study with these findings, and it is also the only study powered to identify a difference in instrumental delivery rate. A possible explanation for the findings of Capogna et al20 is that different local anesthetic concentrations were used for the PIEB and PCEA pumps (0.0625% and 0.125% levobupivacaine, respectively), and the high incidence of motor block and assisted delivery with CEI limits the generalizability of their findings.20 In a retrospective impact study performed at Stanford University, there was no increase in the spontaneous vaginal delivery rate after the introduction of PIEB (94% with CEI versus 90% with PIEB).21 Further studies are required to determine the potential benefit of PIEB in reducing the risk of instrumental vaginal delivery.

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Optimizing PIEB Settings

Infusion pumps are available on the market that will deliver PIEB; however, the CADD Solis Ambulatory Infusion Pump (Smiths Medical, St. Paul, MN) is the first pump available in North America that can simultaneously deliver PIEB and PCEA. The standard flow rates for the CADD pump are 0 to 175 mL/h; however, rates up to 500 mL/h can be delivered. Several parameters must be programmed into the epidural pump software program. The PIEB bolus interval is the amount of time that elapses from the beginning of one intermittent bolus to the beginning of the next bolus (Figure A). The time to the first PIEB bolus after starting the pump is programmed as part of the initial setup. Specific to the CADD pump setup, this is referred to as the “NEXT bolus” interval and should be equal to or less than PIEB bolus interval to avoid the risk of analgesia wearing off before the first programmed dose (Supplemental Digital Content, http://links.lww.com/AA/B441). The PCEA bolus and lockout interval are similar to other pumps currently in use (Figure B). Specific to the CADD pump are 2 variations of the bolus interval type that defines the interaction between PCEA doses and PIEB. If the bolus interval type is set to “PCEA lockout,” a delivered PCEA dose delays the beginning of the next PIEB by the PCEA lockout time (Figure C). If the bolus interval type is set to “bolus interval,” a delivered PCEA dose delays the beginning of the next PIEB by the PIEB bolus interval time (Figure D). Both Stanford and the IWK Health Centre initially chose the former option, “PCEA lockout,” because of concerns of prolonged PIEB lockouts with repetitive PCEA uses with the “bolus interval” setting (Figure E).

Figure

Figure

Although studies generally demonstrate lower local anesthetic consumption with PIEB compared with CEI, this outcome may be an artifact of pump start times. A CEI regimen is usually initiated immediately after block initiation, and the first PIEB is generally given after an increment (eg, 60 minutes after initiation of neuraxial analgesia). Even if both PIEB and CEI are set at the same hourly dose, the PIEB group will appear to have lower local anesthetic consumption when the study stop time is short of the completed hour in any analysis that does not account for this (Supplemental Digital Content A, http://links.lww.com/AA/B441). If the first PIEB dose is instead initiated 30 minutes after initiation of neuraxial analgesia (Supplemental Digital Content B, http://links.lww.com/AA/B441), then for the 0- to 30-minute period the CEI local anesthetic use will be in advance of the PIEB, but will be behind for the 31- to 60-minute period. On average, local anesthetic use in this second scenario will be better matched over the hour period. However, censoring the data before the end of the full hour period, which may naturally occur with delivery, will still artificially favor the PIEB technique’s local anesthetic consumption in studies not accounting for this. Initiating the PIEB immediately (Supplemental Digital Content C, http://links.lww.com/AA/B441) after initiation of neuraxial analgesia is the only scenario that will artificially favor less local anesthetic delivery in the CEI technique if data are censored before the full hour. Wong et al16 accounted for this potential methodological confounder and included an adjusted value of local anesthetic consumption.16 However, in the meta-analysis by George et al11, final projections of drug sparing in the PIEB group reflect the unadjusted value.

The optimal PIEB bolus volume(s) and lockout period(s) are not known and vary significantly among studies investigating PIEB for maintenance of labor analgesia (Table 1). Wong et al22 studied 190 nulliparous women in spontaneous labor randomly assigned to 1 of 3 PIEB dose regimens: group 2.5/15 (received 2.5 mL every 15 minutes), group 5/30 (received 5 mL every 30 minutes), and group 10/60 (received 10 mL every 60 minutes) using a solution of bupivacaine 0.0625% with fentanyl. They showed a trend toward local anesthetic sparing without a sacrifice in analgesia by increasing the volume and time between scheduled intermittent boluses. Group 10/60 consumed less total bupivacaine than women in groups 2.5/15 and 5/30. However, there were little differences in pain scores, PCEA requests or administrations, number of manual bolus doses, time to first PCEA request, or patient satisfaction with labor analgesia between groups. Clearly, additional studies are needed to clarify the optimal settings for PIEB administration, and the relative ratio of local anesthetic administered via PIEB and PCEA. Groups initiating PIEB pumps into their practice should use this opportunity to build consensus for managing labor analgesia. The pumps can be custom programmed for each case; however, this is labor intensive; planning a consensus of preferred protocols and protocol deviations is likely in the best interest of patient safety.

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The Clinical Experience Implementing PIEB

In November 2012 and January 2014, Health Canada and the US Food and Drug Administration, respectively, approved PIEB combined with PCEA (CADD Solis Epidural Pump, Smiths Medical, St. Paul, MN) for clinical use. In the autumn of 2014, our 2 institutions, Stanford and Dalhousie Universities, began using PIEB labor analgesia. Table 3 outlines the solutions and settings used at our respective institutions. Neuraxial analgesia is initiated with either a combined spinal–epidural (CSE) or an epidural technique (approximately equipotent). Both institutions use a CSE technique in a portion of their patients. The CEI and PCEA dosing at the IWK Health Centre was approximately half that at Stanford before the switch to PIEB. The PIEB protocol chosen at the IWK Health Centre and the current PIEB dosing at Stanford are remarkably similar.

Table 3

Table 3

Although a 60-minute PIEB interval has been used frequently (Table 1), both institutions were concerned that 60 minutes was too long between dosing intervals and reduced the PIEB interval times. At both institutions, the currently used flow rate of the PIEB is 250 mL/min with standard disposables for the epidural pump (CADD Yellow-Striped Administration Set).

After initiating PIEB at Stanford University, reports of subtherapeutic labor analgesia by the nursing staff were received, which led to setting changes. The PIEB bolus was increased to 9 mL, and the initial PIEB start bolus interval decreased to 30 minutes after initiation of analgesia (Table 3). Because of the linkage between PIEB and PCEA bolus described above, the PCEA lockout interval was reduced from 15 to 10 minutes (Table 3). The epidural pump bolus infusion rate was increased from 250 to 400 mL/min. Higher pressure manual boluses are associated with much higher catheter flow rates.23 To accommodate the higher flow rate, the pump tubing was changed from the standard epidural pump tubing (CADD Yellow-Striped Administration Set) that permitted a 250 mL/h infusion rate, to high-volume, 500 mL/h, tubing (CADD Yellow-Striped High Volume Administration Set). The higher flow rate may optimize PIEB function by increasing local anesthetic spread in the epidural space. Higher flow rates may improve diffusion throughout the epidural space; however, the gauge of the epidural catheter may be the limiting factor, therefore limiting the possible increased efficacy of a higher programmed flow rate. The CADD Solis Epidural Pump is equipped with an upstream occlusion sensor (on/off option) and downstream sensor (low-/high-sensitivity modulator). Stanford has subsequently changed back to 250 mL/min rate using the standard infusion tubing because of frequent downstream alarms with the higher flow rate. The downstream alarms were likely due to the resistance of the epidural catheter magnified by a high flow rate.

At the IWK Health Centre, the initial PIEB settings were guided by an assumption that with intermittent bolus administration, blockade of motor fibers may be less likely. Analgesia and motor blockade are produced by local anesthetic moving from the extraneural space into the nerve. When given in intermittent boluses, the amount of local anesthetic penetrating the nerve does not reach the threshold for motor blockade as its intraneural concentration is reduced as local anesthetic diffuses out of the nerve between boluses.24 Quality improvement processes including nursing feedback and data downloads from the CADD pumps suggested increased motor block and reduced PCEA use. To address these concerns, the PIEB interval was increased from 30 to 45 minutes and the bolus volumes increased correspondingly (Table 3). Further quality improvement inquiries may shape more setting changes in the future.

Although our limited quality improvement evaluations at each institution suggest the changes outlined above were preferable, randomized studies are required to determine the optimal PIEB settings for maintenance of epidural labor analgesia. In addition, because of the number and variability of changes instituted simultaneously, we are unable to determine which specific PIEB setting change made an impact.

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Practical and Safety Concerns With PIEB Implementation

A number of practical issues warrant consideration when introducing PIEB for epidural labor analgesia. Above all other considerations, when considering a change to PIEB, patient safety must be at the forefront of the implementation team. As previously discussed, the optimal regimen for effectiveness and safety of PIEB remains unknown. Modifications to the PIEB settings are to be expected and preferably should not be made all at once so the impact of each change can be evaluated. Based on our experience, we suggest maintaining current hourly local anesthetic dosing when transitioning from CEI to PIEB if your current protocols deliver an hourly dose similar to the final protocols listed in Table 3.21 If current hourly CEI doses are greater than those suggested in Table 3, then initiation of the PIEB protocol with an appropriate reduction (eg, 10%–25%) in the hourly dose may reduce the incidence of hypotension and higher sensory blockade potentially associated with PIEB delivery. Reductions in dosing can be implemented after the transition, as indicated. It is important to appreciate that the PCEA lockout and PIEB interval times are linked. High flow rates may increase PIEB and PCEA bolus spread within the epidural space; however, this may increase the incidence of high pressure alarms.

The PIEB technique requires nursing, midwife, physician (obstetrician and anesthesiologist), and patient education before and at the time of implementation. Although nursing staff does not manage the epidural infusion settings in our institutions, they are primarily responsible for monitoring the patient’s comfort during labor, assisting with PCEA education, calling physicians to provide rescue boluses, and stopping epidural pumps. We noted significant misunderstanding of the technique, particularly the timing of PCEA dosing and lockout times surrounding PIEB. PIEB should be treated as a “background dose” and the PIEB schedule should not influence attempted PCEA bolus administration (ie, clinicians should not advise patients to coordinate PCEA bolus dose administration with PIEB bolus dose administration). The pump settings should prioritize safety, and attempts to time the PCEA requests to the PIEB settings will likely lead to delays in treating breakthrough pain and impact efficiency.

To date, there does not appear to be any additional risk associated with PIEB versus CEI + PCEA delivery; however, as PIEB becomes adopted by more labor units, safety concerns may become evident. A potential logistical issue with PIEB is that pump occlusion or unintentional intrathecal catheter placement would only become apparent when the first PIEB bolus is initiated. With the use of a CEI technique, the infusion is usually initiated immediately after the catheter is placed; thus, errors may be apparent before the anesthesia care provider has left the room. As a hypothetical example, if a CSE technique is used to initiate analgesia and no pharmacological epidural test dose is administered via the epidural catheter, the PIEB pump will be initiated using an untested epidural catheter. If there is an unrecognized intrathecal catheter, a 10-mL bolus of 0.0625% bupivacaine would deliver 6.25 mg bupivacaine into the intrathecal space. This dose is unlikely to cause a total spinal but would induce a motor block in most patients. In addition, even if the boluses are deposited in the epidural space, PIEB may be associated with more abrupt physiological changes (eg, hypotension, motor block) compared with CEI especially if more concentrated epidural solutions are used. Until we have more safety data on the technique, there should be increased vigilance with regard to monitoring blood pressure, sensory/motor block, and fetal heart rate. In addition, patient ambulation (“walking epidurals”) in the setting of PIEB maintenance analgesia has not been studied and should be avoided until we understand the different dynamics associated with bolus versus continuous delivery of local anesthetic into the epidural space.

Institutions will also need to factor in the cost of purchasing additional equipment, software, and/or disposables when considering PIEB implementation for labor analgesia. However, if epidural pumps are required to be purchased or upgraded, we encourage obtaining pumps capable of providing PIEB with PCEA. Epidural pumps that have the option of both CEI and PIEB with or without PCEA are preferable. There may be clinical settings in which CEI is preferable; for example, patient with significant cardiac disease in whom a slow epidural infusion may be preferable to a bolus technique.

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CONCLUSIONS

PIEB has the potential advantage of greater spread of local anesthetic solution within the epidural space and therefore better sensory blockade compared with CEI. Studies have demonstrated a local anesthetic–sparing effect (fewer instrumental vaginal deliveries, less motor blockade, and shorter duration of labor) and improvement in maternal satisfaction with PIEB compared with CEI for labor analgesia maintenance. The optimal PIEB regimen and pump settings remain unknown. Our 2 institutions have identified settings that are currently working well and better than our previously used CEI with PCEA techniques. PIEB is exciting new technology that has the potential to improve the maintenance of epidural labor analgesia; however, an implementation educational strategy and a continuous quality improvement framework should occur concurrently to guide initiation and ongoing efforts to optimize analgesic efficacy and maternal safety. The analgesic and labor outcome improvement with using PIEB compared with CEI as a background to a labor PCEA technique is incremental, and a number of logistical and practical considerations need to be addressed to optimize the potential benefits of this labor epidural technique.

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DISCLOSURES

Name: Brendan Carvalho, MBBCh, FRCA, MDCH.

Contribution: This author helped develop the review article and write the manuscript.

Conflicts of Interest: Brendan Carvalho has received funding for research from Covidien LP and is a Smiths Medical pain advisory panel member.

Name: Ronald B. George, MD, FRCPC.

Contribution: This author helped develop the review article and write the manuscript.

Conflicts of Interest: Ronald B. George reported no conflicts of interest.

Name: Benjamin Cobb, MD.

Contribution: This author helped develop the review article and write the manuscript.

Conflicts of Interest: Benjamin Cobb reported no conflicts of interest.

Name: Christine McKenzie, MD.

Contribution: This author helped develop the review article and write the manuscript.

Conflicts of Interest: Christine McKenzie reported no conflicts of interest.

Name: Edward T. Riley, MD.

Contribution: This author helped develop the review article and write the manuscript.

Conflicts of Interest: Edward T. Riley reported no conflicts of interest.

This manuscript was handled by: Cynthia A. Wong, MD.

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