Indian Journal of Pain

REVIEW ARTICLE
Year
: 2014  |  Volume : 28  |  Issue : 2  |  Page : 71--81

Labor epidural analgesia: Past, present and future


Reena, Kasturi H. Bandyopadhyay, Mumtaz Afzal, Amiya K. Mishra, Abhijit Paul 
 Department of Anaesthesiology, Perioperative Care and Pain Services, Medica Superspeciality Hospital, Mukundapur, Kolkata, West Bengal, India

Correspondence Address:
Abhijit Paul
Department of Anaesthesiology, Perioperative Care and Pain Services, Medica Superspeciality Hospital, 127 Mukundapur, EM Bypass, Kolkata-700 099, West Bengal
India

Abstract

One of the most severe pains experienced by a woman is that of childbirth. Providing analgesia for labor has always been a challenge more so because of the myths and controversies surrounding labor. It is imperative to understand the pain transmission during various stages of labor in order to select a proper technique for providing labor analgesia. The adverse effects of labor pain are numerous and affect both the mother as well as the fetus. Currently lumbar epidural is considered to be the gold standard technique for labor analgesia. Local anaesthetics like bupivacaine and ropivacaine are commonly used and adjuvants like clonidine, fentanyl and neostigmine have been extensively studied. However, despite being so popular, epidural analgesia is not without complications, with hypotension being the most common. Other complications include accidental dural puncture, infection, intravascular placement, high block and epidural hematoma. Other neuraxial techniques include continuous caudal analgesia, and combined spinal epidural analgesia. The numerous studies investigating the various aspects of this method have also served to dispel various myths surrounding epidural analgesia like increased incidence of cesarean section and instrumental delivery, prolongation of labor and future back pain. The future of labor analgesia lies in the incorporation of ultrasound in identifying the epidural space helping in proper catheter placement. The keywords «DQ»labor epidural«DQ» in the PUBMED revealed a total of 5018 articles with 574 review articles and 969 clinical trials. The relevant articles along with their references were extensively studied.



How to cite this article:
Reena, Bandyopadhyay KH, Afzal M, Mishra AK, Paul A. Labor epidural analgesia: Past, present and future.Indian J Pain 2014;28:71-81


How to cite this URL:
Reena, Bandyopadhyay KH, Afzal M, Mishra AK, Paul A. Labor epidural analgesia: Past, present and future. Indian J Pain [serial online] 2014 [cited 2019 Sep 18 ];28:71-81
Available from: http://www.indianjpain.org/text.asp?2014/28/2/71/132843


Full Text

 Introduction



The pain of childbirth is arguably the most severe pain most women will endure in their lifetime. Since pain relief in labor has always been surrounded with myths and controversies, providing effective and safe analgesia during labor have remained an ongoing challenge. Neuraxial techniques are accepted as the gold standard for intrapartum labor analgesia. Multiple randomized controlled trials comparing epidural analgesia with systemic opioids, nitrous oxide, or both have demonstrated lower maternal pain scores and higher maternal satisfaction with neuraxial analgesia. [1],[2],[3],[4]

Pathways of labor pain: Basis for labor analgesia [Figure 1]

First stage of labor{Figure 1}

Begins from onset of regular uterine contractions and ends at complete cervical dilatation. Pain is caused by stretching of the lower uterine segment (LUS) and cervix, which stimulates the mechanoreceptors. Noxious impulses are carried by sensory nerve fibers (Aδ and C), which accompany sympathetic nerve endings, travel through paracervical ganglion and hypogastric plexus to the lumbar sympathetic chain which enter the spinal cord at T10, T11, T12 and L1 spinal segments. Pain is visceral in nature i.e. transmitted slowly, poorly localized, primarily in the lower abdomen, also referred to lumbosacral area, gluteal region and thighs.

Second stage of labor

Begins from complete cervical dilatation and terminates with the delivery of the baby. Pain is caused by distension of pelvic structures and perineum due to descent of the presenting part, ischemia and frank injury and is carried by somatic afferent nerve fibers that transmit impulses through pudendal nerve to the spinal cord at S2, S3, and S4 levels. Typical of somatic pain, it is sharp and well-localized.

However, Pain of 1 st stage does not end with the beginning of 2 nd stage but is superseded by pain of 2 nd stage.

Knowledge of the anatomic basis of the transmission of labor pain [Figure 1] underlies the current treatment of labor pain using regional techniques. Pain of the first stage of labor can be treated with bilateral paracervical plexus or lumbar sympathetic blockade [Figure 2]. Sacral somatic pain of the second stage can be prevented with bilateral pudendal nerve blockade. Epidural and intrathecal blockade (neuraxial blockade) provides complete analgesia for both the first and second stages of labor.{Figure 2}

Painful labor produces several adverse changes in maternal physiology, which have important implications for the fetus too [Figure 3]. [Table 1] lists the adverse effects of labor pain and the benefits offered by labor epidural analgesia.{Figure 3}{Table 1}

Melzack and colleagues used the McGill Pain Questionnaire to measure the pain during labor and delivery [Figure 4]. [5] They found that nulliparous women had a higher total mean pain-rating index (PRI) than parous women. The PRI represents the sum of the rank values for all words chosen from 20 sets of pain descriptions. The PRI scores of laboring women were 8 to 10 points higher than those associated with cancer pain, phantom limb pain, and post-herpetic neuralgia. Of the 28 parturient, who were given successful epidural analgesia, the PRI score decreased from a mean of 28 before the block to a mean of 8.0 and 7.6 at 30 and 60 minutes, respectively, after induction of analgesia.

Characteristics of the ideal labor-analgesic drugs

Safe for both mother and fetusEase of administration Consistent and predictable with rapid onset of actionMaintains maternal composure and co-operation during both the 1st and 2nd stages of laborHigh technical success ratesAnalgesia through all stages of labor Devoid of motor blockadeRetains maternal expulsive efforts Facilitates the delivery of anesthesia for cesarean section

Neuraxial labor analgesia

It is the only technique that can completely relieve the pain during labor. Though it is considered the gold standard for labor analgesia, the technique is not without its own inherent complications.

History

Neuraxial analgesia into obstetric practice was introduced at the end of the 19th century, an year after August Bier, a German surgeon, described six lower extremity operations rendered painless by means of "cocainisation of the spinal cord". [10] Oskar Kreis, a Swiss obstetrician, described total anesthesia of the lower body in six laboring parturient after subarachnoid injection of cocaine. [11] Subsequent milestones in the development of labor epidural analgesia are mentioned in [Table 2].{Table 2}

Indications for neuraxial analgesia

Maternal request Hypertensive disorders of pregnancy Pre-existing medical disease Multiple pregnanciesPrevious cesarean section Prolonged laborDeterioration in fetal well-being.

Contraindications for neuraxial analgesia

Maternal refusal Coagulopathy and thrombocytopenia Local or systemic infection Inadequate staffing or facilities Increased intracranial pressure Uncorrected maternal hypovolemia.

Techniques of neuraxial analgesia

1. Continuous caudal analgesia : Caudal analgesia was the first form of regional analgesia used during labor. [34] However, it is not the technique of choice for labor analgesia due to following disadvantages:

Requires larger amounts of local anesthetics (L.A.) in the first stage.Difficult to perform as more anatomical anomalies are seen in the sacrum than in the lumbar vertebrae, thereby increasing failure rates. [35]Risk of puncturing the rectum and fetal head, if the procedure is carried out during the later part of second stage of labor. [36]

2. Lumbar epidural analgesia: Epidural analgesia is appropriate at virtually any time of labor when the parturient experiences painful contractions, provided there are no contraindications. In the past, epidural analgesia was withheld until parturient was in the active phase of labor (cervix 4 to 6 cms dilated). Presently, with the use of low concentration of L.A. along with opioids, we can start the epidural even in the latent phase of labor.

Present methods and drug regimen followed

Epidural catheter positioned and placement verified Initial block-Bupivacaine 0.125% or ropivacaine 0.125% to 0.2% (10-15 ml) with fentanyl 2 μg/mlMaintenance of analgesia-

1. Intermittent bolus injections: In spite of better and uniform spread of the L.A. in the epidural space with superior quality of analgesia, breakthrough pain is the greatest disadvantage of this method.

2. Continuous infusion of the analgesic: Continuous epidural infusion (CEI) of a dilute solution of L.A. is a popular technique for the maintenance of epidural analgesia during labor. Benefits include-

Maintenance of a stable level of analgesiaDiminished risk of maternal hypotensionChances of systemic L.A. toxicity reduces due to less requirement of bolus dosingSatisfactory perineal analgesiaDecreased workload for anesthesiologist For points 1) and 2) the regimes are mentioned in [Table 3]{Table 3}

3. Patient Controlled Epidural Analgesia (PCEA): Regimes are discussed in [Table 4] Advantages in comparison with intermittent top ups and CEI are: [37],[38],[39]{Table 4}

Less maternal hypotension and motor blockTotal amount of L.A. used is reducedGives many parturient, a feeling of empowerment and control

4. Combined Spinal Epidural Analgesia (CSE): Combined spinal epidural (CSE) technique combines the rapid, reliable onset of profound analgesia resulting from intrathecal injection along with the flexibility and longer duration of analgesia due to epidural administration of the L.A. [53] Moreover, for cesarean sections, the same catheter can be used for providing anesthesia.

Methods used to perform a CSE block

Epidural catheter insertion followed by spinal needle placement at a lower interspace Epidural needle is inserted beside the spinal needle at the same interspace In the most commonly used "needle-through-needle" technique, epidural space is identified with an epidural needle in the standard fashion; the needle then functions as an introducer for a long, small-gauge (25-to 27-gauge) pencil-point spinal needle.

Drug regimens: Epidural regime can be followed as mentioned in [Table 3]. Initial bolus options through spinal route are:Opioids onlyàOpioids with low dose L.A.à opioids combined with 2.5 mg of isobaric bupivacaine (hyperbaric bupivacaine settles too low in the sacrum and does not reliably provide analgesia of similar quality) [54] or 2-4 mg of ropivacaine (more expensive L.A. and offers no clinical advantage over bupivacaine when given intrathecally). [55]Disadvantages of CSE technique:

Dural puncture is required, albeit with a small-gauge needle. However, the risk of post-dural puncture headache (PDPH) does not seem to be increased with CSE compared with epidural analgesia. [56]The incidence of pruritus is higher [Table 5] with intrathecal versus epidural opioids. [57]Following the initiation of CSE analgesia, it remains unclear for 1 to 2 hours whether the epidural catheter is functional or not (e.g. properly sited in the epidural space). Therefore, CSE analgesia may not be the technique of choice if a functioning epidural catheter is critical to the safety of the patient (e.g. in the presence of a non-reassuring fetal heart rate [FHR] pattern, or an anticipated difficult airway).An increased frequency of non-reassuring FHR tracings and fetal bradycardia occurs with CSE. The etiology may be related to an acute reduction in circulating maternal catecholamines specially epinephrine which is a tocolytic, resulting in uterine hyper tonicity. [58]

Recent Advances:

a. Computer Integrated Patient Controlled Epidural Analgesia (CI-PCEA): PCEA is safe and effective method for maintaining epidural analgesia for the patients in labor. However, the optimal regimen is still a subject of debate. [59] A PCEA regimen with a background infusion appears to be more effective in lowering pain scores of parturient compared with the demand-only PCEA without increasing the total amount of L.A. used. [60]

A novel epidural drug delivery system has been developed in which,{Figure 4}

A laptop computer with a programed algorithm is connected to a standard epidural pump [Figure 5]The computer program automatically adjusts the background infusion rate based on the analysis of patient's L.A. requirement in the last one hour [Figure 6]. It has been found that women on CI-PCEA technique had similar LA consumption compared with demand-only PCEA. But CI-PCEA was associated with lesser incidence of breakthrough pain and increased maternal satisfaction. [61],[62]

b. Programmed intermittent epidural boluses (PIEB): In PIEB, the hourly total amount of L.A. solution normally used in a CEI is administered as intermittent boluses. Studies have shown that PIEB resulted in similar analgesia, higher maternal satisfaction, less need for unscheduled rescue boluses and a reduced consumption of L.A. when compared with CEI. [63] Some reasons may explain these findings:

The high-driving pressure generated to inject a bolus may result in a more uniform spread of the solution in the epidural space. [64]With the use of multi-orifice epidural catheters, solutions injected as a bolus exit the catheter through all the orifices resulting in a wider spread, as opposed to solutions injected as infusion, which exit only through the proximal orifice. [65]

6. Adjuvants: Different adjuvant drugs have been used in neuraxial labor analgesia:

a. Opioids- dosages of various opioids have already been discussed. The advantages of neuraxial opioids are:

Reduces the time of onset and prolongs the duration of epidural analgesiaReduces L.A. consumption [66]Decreases the incidence of insufficient analgesia [67]Reduced incidence of troublesome motor block Problems are:PruritusNausea-vomitingMaternal respiratory depressionFHR abnormalitiesUrinary retention

b. Epinephrine-Epidurally administered epinephrine reduces the minimum L.A. concentration (MLAC) of bupivacaine in laboring patients and improves the quality of analgesia. [68] These effects are mediated through its vasoconstrictive and spinal α2-adrenergic action. Problems are:

Increased incidence of maternal motor deficitProlonged labor duration by ß-agonist effects (tocolytic), especially on higher epidural doses. [69]

c. Clonidine-acts through α2-receptors located in the dorsal horn to produce labor analgesia. Pre-synaptic stimulation of α2-receptors inhibits neurotransmitter release and post-synaptic stimulation prevents neuronal transmission through hyper polarization. When administered epidurally it prolongs analgesia, reduces L.A. consumption as well as epidural top-ups for breakthrough pain without increasing side effects. [70] However, doses above 100 μg induce maternal hypotension, bradycardia and sedation and new onset FHR changes. [71]

d. Neostigmine-Neuraxial administration results in increased concentration of acetylcholine in the synapses, which acts as an important neurotransmitter in the descending inhibitory pathway. Intrathecal administration of neostigmine produces analgesia, but also cause motor block, dizziness, bradycardia, nausea or vomiting. [72] Several trials evaluated the effects of epidural neostigmine showing it to be a promising adjuvant drug for labor analgesia. [73],[74]

7. Walking epidural: The term was first coined for the low dose CSE opioid analgesia, as the mother's ability to ambulate is retained. In the last decade, the concentration of L.A. used to maintain labor epidural analgesia has markedly reduced (0.0625%-0.125%) in contrast to the traditional high concentrations used in past.

Primary advantage of ambulation in labor include parturient freedom of mobility, autonomy and self-control in labor, increased uterine activity and intensity of contractions, decreased frequency of contractions, decreased pain and duration of the first stage of labor, less incidence of foetal heart rate abnormalities and decreased incidence of operative and/or assisted deliveries. [75] There are, however, few reliable data to determine if ambulation in labor is harmful, helpful, or has no effect on the progress of labor and feto-maternal outcome as discussed in [Table 6].{Table 5}{Table 6}

8. Double catheter technique: A lumbar epidural catheter placed at the first- or second-lumbar interspace can be used to provide analgesia during the first stage of labor, followed by the use of a caudal epidural catheter to provide analgesia during the second stage. This increases the likelihood of providing a true segmental block. This technique is most useful in cases in which an extensive sympathectomy must be avoided (e.g., aortic stenosis, primary pulmonary hypertension).

Future of labor analgesia

a. Ultrasound-guided neuraxial technique: Ultrasound imaging is becoming an increasingly popular aid for performing neuraxial blockade due to the following advantages:

It helps to identify the midline, localize the epidural space, measure the skin-to-epidural space distance and estimate the angle of needle insertionFacilitates the placement of epidural needles not only in healthy parturient but also in obese pregnant women and patients with scoliosis [84]Can be used as a teaching tool, improves the epidural placement learning curve

However, problems with ultrasound-guided neuraxial techniques are increased procedural time, increased cost of the procedure and need of expertise.

b. Novel LOR (loss of resistance) methods: The loss of resistance technique is most frequently used to detect the epidural space. [85] As LOR is a subjective feeling, higher failure rates occur with inexperienced anesthesiologists. Various methods have been developed to facilitate epidural space detection of which the following are worth mentioning:

a. EPIDRUM®: This is a recently developed air operated, LOR device for identifying epidural space. It is placed between the epidural needle and the syringe and has a thin diaphragm on the top. The diaphragm deflates once the needle tip enters the epidural space [Figure 7]. [86]

b. EPISURE® AutoDetect syringe: The Episure syringe™ is a unique spring-loaded LOR syringe. It has a coaxial compression spring within a Portex Pulsator™ LOR syringe. This syringe supplies a constant pressure while the operator is advancing the Tuohy epidural needle [Figure 8]. [87]

Advantages of novel LOR methods

Enables the anesthesiologist to control the Tuohy needle with both hands, and therefore passage through ligamentum flavum can be controlled better.Visual observation of LOR overcomes operator subjectivity and variability, thus, their use might offer a more precise end point compared with the standard LOR syringe.

c. Novel epidural needles: Needle-shaped Ultrasound probe: This is simply an optically guided insertion of epidural needle. Three optical fibers are embedded in Tuohy needle shaft, one emits light; two absorb light and the optical spectra are analyzed to identify the various tissue planes [Figure 9]. [88]

d. Smart pumps: Highly sophisticated infusion technology [Figure 10] can be used with both epidural as well as intravenous infusions. They are called "smart" because they incorporate multiple comprehensive libraries of drugs, usual concentrations, dosing units and dose limits, to avoid medication errors. [89]{Figure 5}{Figure 6}{Figure 7}{Figure 8}{Figure 9}{Figure 10}

 Conclusion



Epidural analgesia compared with other techniques, provides the most effective form of analgesia. Recent innovations in drug combinations and delivery systems meet the needs of most parturient in a safe and effective manner. The use of low concentrations of L.A. combined with lipid-soluble opioids does not impede the progress of labor or depress the newborn. The newer technologies may be incorporated to enhance the success rate of the procedure.

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