Labor is one of the most intense and painful conditions requiring analgesia.1 Neuraxial anesthesia is the gold standard to provide effective, safe and reliable pain relief during labor and delivery.2 Numerous neuraxial techniques exist such as spinal anesthesia, traditional epidural (EPL), combined spinal-epidural (CSE) and dural puncture epidural (DPE).3 Over time, various refinements have been made to optimize the efficacy of the traditional labor epidural. Modifications include the type of neuraxial technique chosen, local anesthetic (LA) concentration and volume, varying strategies for initiation and maintenance of analgesia with different pump delivery systems and addition of adjuncts to LA (most commonly lipophilic opioids).4
The simplest but likely least used technique is spinal anesthesia. This single shot technique is used when rapid onset of analgesia is required, and delivery is expected to occur within an hour (of administration).3 Although quick and effective, there is no means to supplement analgesia once the spinal effect wears off and in the event that anesthesia is required a repeat single shot spinal, epidural or general aesthesia may be necessary.3
Lumbar epidural is the gold standard against which other pain relief measures are evaluated for labor analgesia. 2 The epidural space is identified with the loss of resistance technique and a catheter is inserted into the epidural space. Local anesthetic (with or without adjuvants) is delivered to the epidural space via the catheter.3 Epidural medication can be administered in various ways: manual boluses by the physician, continuous infusion (CEI), patient controlled epidural anesthesia (PCEA), programmed intermittent epidural boluses (PIEB) or a combination of these.4 Although safe and reliable, time to onset of analgesia is relatively slow.5 There may be limited sacral spread of medication, resulting in inadequate analgesia in the second stage of labor. Repeated epidural top-ups may result in large volumes of local anesthetic being given which increases the risk of motor blockade.6 7
In the CSE technique, the dura is intentionally punctured to allow administration of intrathecal medication. The epidural space is located with the loss of resistance technique. Thereafter, a small gauge spinal needle is used to puncture the dura in a needle-through-needle technique. Free flow of cerebrospinal fluid (CSF) confirms correct identification of both the spinal and epidural spaces and accurate midline placement. Intrathecal medication is administered before insertion of the epidural catheter. Maintenance analgesia is provided via the catheter. CSE has a much faster onset time and provides a reliable sacral block due to intrathecal medication when compared to EPL.8 The rate of unilateral and inadequate blocks is lower and fewer physician top-ups are required. This is possibly due to translocation of epidural medication to the intrathecal space via the dural puncture.3 Although CSE allows for rapid pain relief, the sudden decrease in maternal catecholamines may result in uterine hypertonus and fetal bradycardia.9 Other side effects such as maternal hypotension and pruritis may also occur.10 Due to the intrathecal medication, the epidural catheter cannot be immediately tested to exclude intrathecal, intravascular or malpositioned catheters.
The DPE was first described by Suzuki et al .11 in a cohort of abdominal surgery patients. As with CSE, the epidural space is located with the loss of resistance technique. The dura is then punctured with a small gauge spinal needle, but no intrathecal medication is administered. It is hypothesised that medication administered in the epidural space will move via the dural puncture into the intrathecal space allowing for faster onset of analgesia, better sacral spread, less unilateral block and lower rate of motor block compared to EPL.6 As no intrathecal medication is given the unwanted side effects such as uterine hypertonus, fetal bradycardia, maternal hypotension and pruritis are minimized.9 12 As the dura is punctured and CSF visualised, confirmation of midline placement is made and a test dose can be administered to rule out an intrathecal or intravascular catheter if desired.13
Thus, the DPE technique proposed to offer the ‘best of both worlds’ providing most of the benefits of the CSE technique without the unwanted side effects, but a faster and more reliable block when compared to EPL. However, the benefits have not consistently been confirmed in the literature when DPE is compared to EPL or CSE due to heterogenous results.
Three reviews conducted in 2018 and 2019 by Layera et al.14, Gunaydin et al.15 and Heesen et al.13 were unable to provide clear evidence of benefit when DPE was compared to EPL. However, some helpful conclusions could be drawn. DPE offered a more reliable benefit if a 25 gauge(G) spinal needle was used as opposed to the smaller 26G and 27G needles. This was shown by Cappiello et al.6 and Chau et al.16 with significantly decreased onset times, improved sacral block, decreased unilateral block and decreased top-ups in the DPE groups. A 27G needle for the dural puncture was used in two trials. Firstly, Thomas et al.12 found no difference in quality of analgesia evidenced by no difference in catheter manipulation rates, sacral root sparing, unilateral block, peak block level, number of top-up doses and LA consumption. A higher incidence of dry taps also occurred. In contrast, Yadav et al.17 observed some benefits noting lower visual analogue scale (VAS) scores at 5 and 10 minutes (p<0.008), faster onset time and improved analgesia quality (p<0.05). However, there was no difference in the time to first top up request, LA consumption and duration of labor.17 Wilson et al.5 used a 26G needle for dural puncture. They found although time to VAS <10 was shorter in the DPE group, the percentage of patients with adequate labor analgesia at 10 minutes did not differ between groups.5 No differences in complications or post dural puncture headaches (PDPH) were noted in any studies, however due to small sample sizes, complications occurring less frequently may not have been identified.14 All trials used varying types, concentrations and volumes of LA which made comparison of results challenging.14
Three additional randomized control trials have been conducted since these reviews, but again heterogenous results were found. Two of the trials have incorporated the use of PIEB delivery systems found to be more effective18 and possibly better suited for use with DPB. The proposed mechanism is that during the administration of a LA bolus, pressure within the epidural space will increase thus facilitating movement of medication into the intrathecal space.
Song et al.19 compared 3 groups: DPE combined with PIEB, EPL combined with CEI and EPL combined with PIEB including a total of 116 patients. A 25G needle was used for dural puncture. The primary outcome was time to adequate analgesia. As hypothesized, faster onset of analgesia and lower LA consumption was noted in the DPE + PIEB group. Reliable sacral block was also achieved. The incidence of side effects including pruritis, PDPH and maternal hypotension were comparable in all groups. Despite these findings, no difference in maternal satisfaction was found. Unfortunately, due to the lack of a fourth group (EPL and PIEB) in this study, the effect of the PIEB itself is unclear. The extent to which the DPE alone contributed to the favourable outcomes cannot be isolated from the possible effect of the PIEB.20
Bakhet21conducted a study comparing EPL, DPE and CSE combined with a loading dose followed by PCEA in 120 parturients. A 25G needle was used for dural puncture. Primary outcome was mean hourly LA consumption. CSE outperformed both DPE and EPL with regards to LA consumption, time to onset of analgesia, numeric pain rating scale (NPRS) and time to achieve T10 block. There were no significant differences between the DPE and EPL for these observations. Occurrence of motor blockade, side effects and maternal satisfaction were comparable amongst all three groups Most recently, Tan et al.22 has reported results from a double-blinded randomized controlled trial comparing DPE to EPL in 132 obese parturients. They suggested that the DPE technique may be useful in this patient population as the dural puncture would confirm midline placement resulting in a lower failed epidural rate. Dural puncture was made with a 25G spinal needle and after an initial loading dose, PIEB with a PCEA function provided maintenance analgesia. The primary outcome was a composite of: (1) asymmetrical block, (2) epidural top-ups, (3) catheter adjustments, (4) catheter replacement and (5) failed conversion to regional anesthesia for cesarean section. No significant difference was found for the primary composite outcome between the two groups. However, the authors acknowledge that the confidence intervals were wide and contained potentially clinically relevant differences. There were also no differences in the secondary outcomes including motor block, LA consumption, top-ups, side effects and maternal satisfaction.
One possible explanation for continued conflicting results may be that the mechanisms determining flux through the meninges rely on multiple factors. The size of the dural hole is an important determinant as shown by Bernards et al.23, where more morphine and lidocaine crossed the dural orifice when the dura was pierced with an 18G versus 24G needle. This would explain why less favourable results were seen in some studies with 26G and 27G spinal needles.5 12 Other important factors include: total epidural drug mass and inherent rate of drug transfer through intact meninges.14 23 24 25 A greater effect is seen with medications with an inherently slow diffusion rate. Studies using lower volumes and concentrations of LA also had less favourable outcomes.12 22 Higher injectate pressures generated by PIEB may promote drug transfer across the dural puncture as suggested by the results by Song et al.19 However this was not seen when PIEB was used by Tan et al.22 in the obese parturient.
Thus, despite further randomized trials also incorporating new pump delivery systems, the suggested theoretical benefits of DPE have not consistently been documented. It is unclear why contrasting results have been found. In addition to this, in an editorial by Segal and Pan4, some concerns have been raised regarding the methodology of a number the trials showing favourable results. At this time, although benefits have been identified, they have not shown to be significant or consistent. However, studies have been limited by small sample sizes and use of varying needle sizes and LA regimes. It is suggested that a larger, multi-centre, double blinded and randomized study should be conducted. This should employ the use of a 25G needles, modern pump delivery systems and commonly used LA regimes. A larger sample size would also allow identification of side effects that do not occur commonly such as PDPH.
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