When a cesarean delivery is necessary in a parturient with a labor epidural catheter in situ, cesarean delivery anesthesia is commonly initiated by injecting local anesthetic, commonly combined with a lipid-soluble opioid, through the existing catheter. This process is often referred to as epidural conversion. Although the ability to convert epidural labor analgesia to surgical anesthesia required for cesarean delivery anesthesia is frequently cited as a secondary reason for initiation of epidural analgesia, epidural conversion is not always successful.1–3 The reported failure rate depends on many factors, including accuracy of reporting and the definition of “failure.” The conversion failure rate may be used as a quality measure. For example, the Royal College of Anesthetists in the United Kingdom recommends a threshold of <1% conversion of neuraxial anesthesia to general anesthesia in elective cesarean deliveries and a threshold of <5% for emergency deliveries.4 Appreciation of the reasons for epidural conversion failure may help prevent the need for additional modes of surgical anesthesia.
Epidural conversion failure may necessitate induction of general anesthesia. There are many reasons why general anesthesia is not desirable, including a higher incidence of maternal mortality, the potential for pulmonary aspiration, difficult tracheal intubation, neonatal depression, unintentional intraoperative maternal awareness, uterine relaxation from volatile anesthetics, and postoperative pain, nausea, and sedation.5–12 Maternal dissatisfaction and pain are leading causes of litigation for obstetric anesthesia.13,14 For these reasons, successful epidural conversion is critically important.
INCIDENCE OF EPIDURAL CONVERSION FAILURE
The findings described in this section are based on a literature search in OvidSP and PubMed of studies that addressed failed epidural conversion; these are summarized in Table 1. Most of the articles reviewed were observational trials, although 1 meta-analysis and 1 randomized controlled trial are included.23,24 The definitions of epidural conversion failure are inconsistent. The majority of authors define failure as conversion to general anesthesia.11,15–18,25 Other authors define failure as conversion to another form of anesthesia.1–3,19 In these studies, epidural conversion failure ranged from 0% to 21%.2,3,17,19–21 A 2012 systematic review and meta-analysis found that the incidence of general anesthesia in women with preexisting epidural labor analgesia was approximately 5% and the need for a second anesthetic (spinal or repeat epidural techniques), without general anesthesia, was 2.7%.23 The reason for the wide variation in the reported incidence of failed epidural conversion is likely because of different definitions of failure, type of neuraxial labor analgesia (ie, epidural versus combined spinal-epidural [CSE] analgesia), study methodology, labor epidural infusion and bolus protocols, drugs used to initiate surgical anesthesia, methods used to test success of neuraxial blockade, care by a specialist, urgency of cesarean delivery, and surgical approaches.
FACTORS ASSOCIATED WITH EPIDURAL CONVERSION FAILURE
Reported factors associated with epidural conversion failure include the number of bolus doses for treatment of breakthrough pain during epidural labor analgesia, prolonged duration of analgesia, initiation of neuraxial analgesia using a traditional epidural technique compared with CSE labor analgesia, tall compared with short stature, epidural catheter placement by a nonspecialist, and urgency of cesarean delivery (Table 2).1–3,17–21 Most of the studies describing these associations are observational retrospective studies; they are therefore subject to many confounders, such as selection bias.
Neuraxial labor analgesia is commonly initiated using an epidural technique in which there is no dural puncture, or a CSE technique in which the dura is punctured with a small-gauge spinal needle. There is evidence that labor analgesia initiated with a CSE technique is more reliable and fails less frequently than analgesia initiated with an epidural technique.2,26,27 In a retrospective study of 1025 parturients, epidural compared with CSE catheters were associated with higher epidural conversion failure (odds ratio [OR], 5.5; 95% confidence interval [CI], 2.0–14.9; P = .001).20 This study was unusual, in that CSE analgesia was used much more frequently than epidural and had a low failure rate (CSE, 10/895 [1.1%]; 95% CI, 0.4–1.8; epidural, 7/113 [6.2%]; 95% CI, 1.8–10.6). Other investigators were not able to demonstrate a difference between the 2 techniques. In a randomized trial in a private practice setting (all procedures were performed by experienced anesthesiologists), Gambling et al24 found no difference in epidural conversion failure in CSE compared with epidural analgesia (CSE, 0/63; epidural, 2/56 [3.6%]; 95% CI, −1.3 to 8.4; P = .21); however, the study was underpowered to detect epidural conversion failure. Two observational studies also showed inconclusive results. Riley and Papasin19 were unable to demonstrate a benefit with CSE (CSE, 3/41 [7.3%]; 95% CI, 0.6%–15.3%; epidural, 17/199 [7.3%]; 95% CI, 4.7%–12.4%; P = .54). Similarly, Norris et al28 were unable to demonstrate a benefit with CSE (CSE, 8/133 [6.0%]; 95% CI, 2.0%–10.1%; epidural, 7/186 [3.8%]; 95% CI, 1.0%–6.5%; P = .25). None of these studies had sufficient power to demonstrate superiority of 1 technique compared with the other. Although CSE analgesia may be more reliable for labor analgesia, there are currently insufficient data to conclude that epidural catheters placed as part of CSE labor analgesia are superior to catheters placed as part of a traditional epidural technique to prevent epidural conversion failure.
Several studies suggest that initiation of neuraxial labor analgesia by obstetric anesthesiologists decreases the incidence of epidural conversion failure. A nonspecialist refers to an attending anesthesiologist who spends the majority of time covering nonobstetric services. One institutional study showed that when epidural labor analgesia was initiated by specialists, the catheter failed in 2 of 70 cases compared with 20 of 170 cases for nonspecialists (2.9% vs 11.8%; OR, 4.5; 95% CI, 1.0–19.9).19 In another single-institution study, the incidence of induction of general anesthesia for nonspecialist and obstetric anesthesiologists was 5.5% and 1.2%, respectively (OR, 4.8; 95% CI, 1.5–15.6).21 A meta-analysis based on these retrospective studies found that the epidural conversion failure rate for nonspecialist anesthesiologists was 7.2% compared with 1.6% for obstetric anesthesiologists (OR, 4.6; 95% CI, 1.8–11.5).23,24
One possible explanation for this difference is that obstetric anesthesiologists are more willing to manipulate the epidural catheter. Campbell and Tran21 demonstrated that 85% of failed epidural catheters can be successfully converted to surgical anesthesia by withdrawing the catheter by 1 cm. However, while 58.3% of specialists employ this technique, only 5.9% of nonspecialist anesthesiologists did so (OR, 22.1; 95% CI, 7.2–67.8).
The finding that overall epidural catheter failure rate is lower among specialist anesthesiologists is supported by the results of a randomized controlled trial of CSE compared with epidural labor analgesia from a large private practice with many specialist obstetric anesthesiologists.18 The labor epidural catheter replacement rate was very low (<2%) as was the epidural conversion failure (<1%).24
On the basis of these 2 relatively homogeneous retrospective studies, the weight of evidence suggests that epidural conversion failure occurs less commonly when obstetric anesthesiologists provide care rather than generalists.6,18
A number of studies have reported that the need for additional epidural boluses during labor for the treatment of breakthrough pain is associated with higher epidural conversion failure rates.3–7 Even a single unscheduled bolus increases the odds of epidural conversion failure (OR, 2.37; 95% CI, 1.6–3.5).21 In 1 prospective study, patients with adequate epidural anesthesia required a mean (±SD) of 0.6 (±1.1) boluses, whereas those with failed epidural conversion required 1.7 (±1.6) boluses. The authors concluded that the number of boluses was the best predictor of epidural anesthesia failure (OR, 4.4; 95% CI, 1.6–12.2; P = .0004).17
Some authors used a cutoff threshold of 2 boluses to study prediction of epidural conversion failure. One retrospective study that compared patients who received ≥2 boluses with those who received 0 or 1 bolus found that increased boluses were highly associated with epidural conversion failure (OR, 6.6; 95% CI, 2.5–17.9; P < .001).4 In a prospective study, >1 bolus was associated with epidural conversion failure compared with 1 or no boluses (OR, 1.6; 95% CI, 1.1–2.4; P = .016).3
A meta-analysis based on these studies determined that the rate of epidural conversion failure increased 3-fold in parturients who required additional boluses in labor (16.4% compared with 4.6%; OR, 3.2; 95% CI, 1.8–5.5).23 Although there is some heterogeneity among these studies (particularly concerning the number of boluses), the results all support the premise that the need for supplemental epidural labor analgesia is strongly predictive of epidural conversion failure.
Urgency of cesarean delivery has been associated with epidural conversion failure. A prospective study reported a 25% epidural conversion failure when the indication for the cesarean delivery was an immediate threat to life, either fetal or maternal.1 A meta-analysis of 7 studies concluded that urgency was a risk factor for epidural conversion failure (OR, 40.4; 95% CI, 8.8–185.6).23 Unfortunately, this analysis is weakened by significant study heterogeneity. For example, many authors exclude urgent cesarean delivery from their analysis. Regardless, urgency is associated clearly with epidural conversion failure, given that the conversion of epidural labor analgesia to surgical anesthesia may not be accomplished in the few minutes allotted for an urgent cesarean delivery. It has been shown that general anesthesia can be initiated an average of 8 minutes faster than regional anesthesia.29 Beckman and Calderbank29 have shown increased neonatal morbidity associated with general anesthesia. However, it is unclear whether this reflects the danger inherent in the anesthetic itself or the underlying fetal comorbidities or the indication for cesarean delivery. In summary, the degree of urgency is highly predictive of epidural conversion failure; however, it is well recognized that general anesthesia is often preferable when time is of the essence.
A single study identified tall stature as an independent risk factor for epidural conversion failure.3 Patients with epidural conversion failure had a mean (±SD) height of 167 cm (±8), whereas those with successful conversion had a mean height of 163 cm (±7). The same study found no correlation between body mass index (BMI) and epidural conversion failure.
Studies have reported greater labor epidural catheter replacement rates in obese parturients, leading some authors to postulate that higher BMI is associated with epidural conversion failure.22,26,27 A meta-analysis combining 6 studies found that maternal weight was not associated with epidural conversion failure.23 Only 1 of the 6 studies was able to demonstrate an association between weight and epidural conversion failure.17 It is possible that the lack of association between maternal weight and epidural conversion failure represents the fact that the epidural labor analgesia replacement rate is higher in obese parturients and may have occurred before the decision to perform cesarean delivery. However, it should be noted that obese patients often have other comorbidities, which increase the likelihood of emergency cesarean delivery. For these reasons, they are often excluded from study populations and underrepresented in these studies, leading to heterogeneity in the meta-analysis.30
Five of the 6 studies were unable to find a significant correlation between the duration of epidural labor analgesia and the epidural conversion failure.3,17–21 The results of the remaining study were inconclusive. Despite adequate power, the meta-analysis shows no clear association between duration of epidural labor analgesia and the rate of epidural conversion failure. Two underpowered studies showed no association between cervical dilation at the time of initiation of labor epidural analgesia and epidural conversion failure.17,20
In summary, there is evidence that neuraxial block placement by a nonspecialist anesthesiologist, an increased number of manual boluses during labor, and the urgency of a cesarean delivery are all predictors of epidural conversion failure.
Given that some risk factors for epidural conversion failure have been identified, careful attention to epidural labor analgesia may help prevent epidural conversion failure. Early recognition of poorly functioning epidural labor analgesia provides the anesthesiologist time to manipulate or replace the epidural catheter. As discussed earlier, simple catheter manipulation (a common, but not evidence-based practice), such as pulling the catheter back by 1 cm, or administering additional local anesthetic, may improve labor epidural analgesia.21 Obstetrical anesthesiologists may have fewer epidural conversion failures than generalist anesthesiologists. Although it is not feasible to recommend that all obstetric patients are treated by specially trained obstetric anesthesiologists, it does seem prudent to improve the level of obstetric education for the generalist anesthesiologist.
Communication among the anesthesiologic, neonatologic, and obstetric teams is critically important for the management of parturients. If the obstetric team conveys that a patient is more likely to undergo a cesarean delivery, early initiation of neuraxial labor analgesia is endorsed. If the obstetrician expresses concern about the fetal heart rate tracing, the anesthesiologist should reevaluate how well the epidural catheter is functioning in anticipation of the need to convert to surgical anesthesia. The American Society of Anesthesiologists Task Force on Obstetric Anesthesia suggests that initiation of epidural labor analgesia before the onset of labor in certain patients, such as those with anticipated difficult airways, twin gestation, and obesity, should be considered.31
Once a decision for cesarean delivery is made for a parturient with labor epidural analgesia, conversion to surgical anesthesia does not need to be done in haste. It is important to visually assess the epidural catheter to ensure that it has not migrated since placement. Some anesthesiologists test the function of the catheter by administering just enough local anesthetic to determine whether epidural surgical anesthesia will likely function properly. Careful assessment of the level and density of neuroblockade after administration of approximately 5 to 10 mL of local anesthetic solution (one-quarter to one-third of the full dose) may alert the anesthesiologist to a nonfunctioning catheter before the entire dose has been administered. This small dose should result in a block that is bilateral and progressing cephalad.32 If there remains any question about the reliability of surgical anesthesia, alternative modes of neuraxial anesthesia should be considered early, before administering the entire planned local anesthetic dose.
When epidural conversion failure does occur, other options should be explored. A meta-analysis of 13 observational trials found that 7.7% of parturients who had labor epidural analgesia required a second anesthetic (spinal, epidural, or general anesthesia) for surgical anesthesia.23 Of note, in an analysis of 4 trials, 10.7% of women undergoing epidural anesthesia for cesarean delivery required some form of supplementation (intravenous, inhalational, or not specified).23
ALTERNATIVE ANESTHETIC TECHNIQUES
When neuraxial anesthesia is attempted, testing should reveal loss of touch perception at T6, pinprick sensation at T5, or ice sensation at T3.33–35 If surgical anesthesia cannot be achieved, an alternative neuraxial anesthetic technique may be required. A final alternative, general anesthesia will not be discussed in this review.
An option after failed epidural conversion is to place a new epidural catheter. However, epidural catheter replacement is time-consuming; administration of the local anesthetic to attain a surgical level must be titrated carefully.36 Injection of a second full dose of local anesthesia into the epidural space places the patient at risk for local anesthetic systemic toxicity (LAST).37 Placing an epidural catheter in a partially anesthetized patient can be challenging and perhaps unsafe, although the risk of neurologic injury is likely overstated.38
Single-Shot Spinal Anesthesia
The decision to initiate single-shot spinal anesthesia after neuraxial labor analgesia remains controversial and should be undertaken with caution. The single-shot spinal approach involves removing the epidural catheter and starting afresh with spinal anesthesia. Spinal anesthesia is preferred by some practitioners who believe that it may provide superior anesthesia compared with that offered by epidural surgical anesthesia.1,37,39 Traditionally, initiation of spinal anesthesia shortly after discontinuing labor epidural analgesia has been discouraged because of multiple reports of subsequent high or total spinal anesthesia (Table 3).40–45
Initiation of single-shot spinal anesthesia for cesarean delivery after labor epidural analgesia may be done electively or more often because of a poorly functioning epidural catheter used for labor analgesia, either before attempted epidural conversion or after failed epidural conversion. Because of the risk of high or total spinal anesthesia when spinal anesthesia is initiated shortly after failed epidural conversion, some experts recommend reducing the spinal dose or allowing greater time between the last epidural catheter drug administration and the single-shot spinal injection.44
Some anesthesiologists do not ever inject local anesthetic through a labor epidural analgesia catheters for surgical anesthesia, but instead always discontinue the epidural catheter and electively induce spinal anesthesia.45,46 Two studies did not find an increased incidence of total spinal anesthesia after single-shot spinal anesthesia following epidural labor analgesia. One of these studies described bolus-free epidural labor analgesia and the practice of discontinuing the epidural labor infusion when the patient reaches full dilation.45 The other study did not allow the administration of epidural catheter boluses for 30 minutes before placement of a single-shot spinal anesthesia and also decreased the intrathecal local anesthetic dose by 16% (from a usual dose 12.5–10.5 mg).46
The optimal spinal local anesthetic dose that should be administered after epidural labor analgesia is not known. Some studies suggest that decreasing the dose could adversely affect the duration of surgical anesthesia and increase the need for intravenous and inhalational supplementation and general anesthesia.36,53 Although high-spinal anesthesia is not common, and spinal anesthesia after epidural labor analgesia without a prior bolus might be safe,45,46 D’Angelo et al54 reported high-spinal anesthesia as a serious complication of neuraxial anesthesia. The Serious Complication Repository (SCORE) Project identified spinal anesthesia after a failed epidural as a common cause of high neuraxial block; >50% of the high-spinal blocks reported in the repository were associated with failed epidural conversion.54 It is important to be aware that high-spinal anesthesia has occurred in patients who have received recent large epidural boluses and in those without any prior bolus.
CSE anesthesia is an attractive option after epidural conversion failure, given that it provides fast onset, reliability, and the ability to extend the extent and duration of the block through the epidural catheter.53,55 In the sequential CSE technique, spinal anesthesia is initiated with an intentionally low dose of local anesthetic (eg, 6–9 mg of 0.75% hyperbaric bupivacaine), thus decreasing the risk of high-spinal anesthesia. If the resulting block is inadequate for surgical anesthesia, supplemental doses of local anesthetic and opioid can be injected through the newly sited epidural catheter.56 Epidural volume extension refers to the administration of epidural saline, after giving a small intrathecal local anesthetic dose to extend the cephalad level of neuroblockade.57
Some practitioners express concern about an untested epidural catheter when initiating cesarean delivery CSE anesthesia. One study on laboring patients found that if CSF was observed in the spinal needle, the need for epidural catheter replacement was significantly lower than in attempted CSE procedures without return of CSF through the spinal needle (4.1% vs 28.6%).58 The observation of CSF in the spinal needle serves as a positive predictor that the tip of the epidural needle is correctly located in the epidural space. After the administration of small doses of intrathecal local anesthetic, both the sequential technique and the epidural volume extension can raise the level of the anesthetic block.56,57 Alternatively, opioid alone may be injected intrathecally and surgical anesthesia can be established after the administration of epidural local anesthetic. There is some evidence that dural puncture with a spinal needle, without injecting medication, leads to more reliable epidural labor analgesia, and this may also apply to surgical anesthesia.59
Continuous Spinal Anesthesia
Continuous spinal anesthesia has long been advocated as an excellent form of anesthesia, especially for patients with cardiopulmonary disease in whom the dermatomal block level must be titrated carefully.60 Other patients who are candidates for continuous spinal anesthesia include those with previous spine surgery, morbidly obese patients, and those with anticipated difficult airways.61 However, the incidence of postdural puncture headache after dural puncture with an epidural needle remains high.62 Continuous spinal anesthesia also may be associated with failure and neurologic injury.63 For these reasons, continuous spinal anesthesia has been reserved primarily for patients who experience an unintentional dural puncture with an epidural needle. However, it may be an option for patients with failed epidural conversion; the local anesthetic dose is low (decreasing the risk for LAST) and the level of neuroblockade can be titrated, unlike a single-shot spinal anesthetic.
Local Anesthetic Infiltration
Local anesthetic infiltration has been used in the past when neuraxial anesthesia or general anesthesia was not an option. This anesthetic technique is not used currently, largely because of lack of training and expertise, the resulting poor anesthesia, potential for delay of care, and the risk of LAST. However, local anesthetic infiltration may be used in an emergency to supplement poorly functioning neuraxial anesthesia.37,64 Intravenous and inhalational supplementation with midazolam, fentanyl, ketamine, and nitrous oxide are also useful when a parturient with neuraxial anesthesia experiences intraoperative discomfort or anxiety. Up to 10.7% of patients with epidural conversion require supplementation.18,23,37,64
This review highlights some of the reasons for epidural conversion failure. Close multidisciplinary communication among anesthesiologists, obstetricians, neonatologists, and nursing staff is vitally important for good outcomes. The anesthesiologist should be regularly briefed about all parturients on the labor and delivery floor. Careful attention to intrapartum pain scores, breakthrough pain, and the need for manual epidural bolus doses, airway examinations, and the progress of labor will help to ensure successful epidural conversion. There is a need for additional high-quality studies to enhance our understanding of why epidural catheter conversion failure occurs.
Name: Suzanne K. W. Mankowitz MD.
Contribution: This author helped write the manuscript.
Name: Antonio Gonzalez Fiol, MD.
Contribution: This author helped write the manuscript.
Name: Richard Smiley, MD, PhD.
Contribution: This author helped write the manuscript.
This manuscript was handled by: Cynthia A. Wong, MD.
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