2. LABOR ANALGESIA
Dr. Abbas Moallemy

3. HISTORICAL NOTES
Childbirth pain is arguably the most severe pain most women will endure in their lifetimes.
The modern era of childbirth analgesia began in 1847 when Dr. James Young Simpson administered ether to a woman in childbirth and later, in the same year, chloroform.
The use of analgesia for childbirth aroused violent opposition from some physicians, the public, and the clergy.
Simpson was labeled a heretic, blasphemer, and an agent of the devil.
The furor died down somewhat in 1853, when John Snow successfully administered chloroform to Queen Victoria for the birth of her eighth child.

4. PAIN OF CHILDBIRTH
Although it is a common observation that parturients vary in the amount of pain and suffering associated with labor and vaginal delivery, few well-designed studies on the prevalence, intensity, and quality of labor pain have been performed.
Melzack et al.used the McGill Pain Questionnaire to assess childbirth pain. The mean total pain rating index (PRI) was 34 for nulliparous and 30 for parous women.

6. Childbirth Pain Mechanisms and Pathways
Most data support the concept that the pain of the first stage of
labor originates predominantly in the cervix and the lower uterine segment, rather than the body of the uterus.
Dilation of the cervix and lower uterine segment results in distension, stretching, and tearing of tissues.
During the late first stage and second stage of labor, the descent of the fetus and intense stretching and tearing
of the tissues of the vagina and perineum become additional
sources of pain.

7. Typical of pain arising from viscera, the pain of the first stage
of labor is often referred to the Tl0 through L1 derma tomes.
Second stage pain from descent of the fetus in the birth canal is primarily somatic in nature and is transmitted through sacral nerves to the S2 through S4 segments of the spinal cord.

8. Factors That Affect the Pain of Childbirth
In addition to physiologic, the amount or degree of pain and suffering associated with childbirth is influenced by physical, psychologic, emotional, and motivational factors.
Physical factors that are associated with the severity and duration of childbirth pain include age, parity, history of previous pain or dysmenorrhea, fatigue, the condition of the cervix at the onset of labor, and the relationship between the size and position of the fetus to the size of the birth canal.
Generally, an older nullipara experiences longer and more painful labor than a younger nullipara.

9. Pain is greater in the presence of dystocia caused by contracted pelvis, a large baby, or abnormal presentation or position.
Psychologic factors, such as fear, apprehension, and anxiety,
also influence the degree of pain and suffering during childbirth.
The presence of family members or birthing companions during
labor and delivery may decrease anxiety and positively affect
the progress of labor.
Education, intense motivation, and cultural influences can influence the affective and behavioral dimensions of pain, although they probably minimally affect actual pain sensation.

10. NONPHARMACOLOGIC METHODS OF LABOR ANALGESIA
Nonpharmacologic methods to relieve the pain and suffering of
childbirth include childbirth education, emotional support, massage,
aroma therapy, audiotherapy, and therapeutic use of hot and cold.
More specialized techniques that require specialized training or equipment include hydrotherapy, intradermal water injections, biofeedback, transcutaneous electrical nerve stimulation (TENS), acupuncture or acupressure, and hypnosis.
Many of these techniques are inadequately studied in that study quality is poor and sample size is small, and therefore, conclusions
about efficacy are not possible.

11. Labor Support
Emotional support is commonly provided by the parturient's husband or a friend.
"Continuous labor support" refers to the nonmedical support of the parturient by a trained person.
Prospective, controlled trials and several systematic analyses have concluded that women who receive continuous labor support have shorter labors, fewer operative deliveries, fewer analgesic interventions, and greater satisfaction.

12. Hydrotherapy
Hydrotherapy is the immersion of the parturient in warm water
(deep enough to cover the abdomen) during labor (not birth).
Systematic reviews of randomized controlled trials have concluded that women experience less pain and use less analgesia without change in the duration of labor, rate of operative delivery, or neonatal outcome.

13. Intradermal Water Injections
Intradermal water injection consists of the injection of 0.05 to
0.1 mL of sterile water, using an insulin or tuberculin syringe, at
4 sites on the lower back: over each posterior superior iliac crest,and 1 cm medial/3 cm caudad to these injections.
The technique is used to treat back pain during labor. The injections themselves are acutely painful for about 20 to 30 seconds, but as the injection pain fades, so does lower back pain.
Randomized controlled trials have found that the technique is effective in reducing severe back pain during labor without any known side effects to the mother and fetus, although the rate of use of other analgesic modalities does not appear different from control groups.

15. Hypnosis
Self-hypnosis for treatment of childbirth pain has been practiced
for several centuries. Hypnosis requires prenatal training of the
mother, and sometimes her partner, by a traine hypnotherapist.
A meta-analysis of five randomized controlled trials that included 749 women found the use of pharmacologic analgesia methods was decreased in the hypnosis compared to control groups

16. Transcutaneous Electrical Stimulation
TENS involves the application of low-intensity, high-frequency
electrical impulses to the skin of the lower back. The buzzing,
electrical current sensation caused by the TENS unit may reduce the mothers awareness of contraction pain.
Studies of TENS are inconsistent, but in general, labor pain does not appear to be lessened, nor is the use of other analgesic modalities.

17. Acupuncture and Acupressure
Acupuncture is a component of traditional Chinese medicine that has gained popularity in Western cultures in recent years.
In three randomized controlled trials conducted in Scandinavian countries,women randomized to acupuncture versus control (no or"false" acupuncture) reported modestly lower pain scores and
lower use of epidural and systemic opioid analgesia.

18. SYSTEMIC ANALGESIA
Inhalation analgesia for labor and vaginal delivery is unusual in the United States, but is more common in other countries.
The only inhaled anesthetic agent currently in common use is nitrous oxide.
It is available in the United Kingdom as Entonox (The Linde Group, Munich, Germany), a mixture of 50% nitrous oxide and 50% oxygen.
The mother must be taught to breathe the mixture correctly, so that peak brain nitrous oxide concentrations coincide with peak contraction pain.
The intermittent use of nitrous oxide, however, appears safe for
the fetus and neonate.

19. Volatile halogenated anesthetic agents have been used in the
past for labor analgesia. Analgesia, however, is incomplete, as
doses that provide significant analgesia are also associated with
significant maternal sedation.
In a small study, pain relief scores were significantly higher in women who received sevoflurane compared to nitrous oxide, and women preferred sevoflurane. Sedation scores, however, were also higher with sevoflurane, and whether or not volatile agents interfere with the progress of labor (they inhibit uterine contractility) remains to be determined.

20. Parenteral Opioid Analgesia
Systemic opioid analgesia, administered by the subcutaneous, intramuscular, or intravenous route , is widely used around the
world either as the sole analgesic modality or prior to the administration of regional labor analgesia.
There is a high incidence of side effects (e.g., sedation, nausea, and vomiting),and analgesia is incomplete, at best, during active labor.
Maternal side effects include nausea, vomiting, delayed gastric emptying,dysphoria, and respiratory depression.
All opioids cross the placenta.In utero, opioids may result in a slower fetal heart rate and decreased beat-to-beat variability. The likelihood of neonatal respiratory depression depends on the dose and timing of administration

21. Patient-Controlled Intravenous Analgesia
Patient-controlled intravenous analgesia (PCIA) has theoretical
advantages to nurse-administered opioid analgesia, including superior analgesia with smaller drug doses, resulting in a lower incidence of side effects.
PCIA studies have been reported using meperidine, nalbuphine, fentanyl, and more recently, remifentanil with and without a background infusion.
Remifentanil has the theoretical advantage of rapid onset and offset compared to the other opioids.
However, as with other systemic opioid techniques, it is unclear whether remifentanil PCIA can provide satisfactory analgesia without an unacceptably high incidence of side effects.

22. NEURAXIAL ANALGESIA
Neuraxial labor analgesia is the most effective method of pain relief during childbirth and the only method that provides complete analgesia without maternal or fetal sedation.
The use of neuraxial analgesia for childbirth has increased dramatically in the United States over the past 40 years.
The most common techniques are continuous lumbar epidural analgesia and combined spinal-epidural analgesia. Single-shot spinal, continuous spinal, and caudal analgesia are occasionally used.

23. Contraindications to neuraxial analgesia and anesthesia include
patient refusal, infection at the puncture site, pre-existing
coagulopathy, and lack of experienced anesthesia providers.
Relative contraindications include hemorrhage or other causes
of hypovolemia, untreated systemic infection,preload dependent disease states, and lumbar spine pathology.

24. Epidural Analgesia
Lumbar epidural analgesia has been the mainstay of regional
labor analgesia.
Placement of an epidural catheter allows analgesia to be maintained until after delivery. Additionally, it allows conversion to epidural anesthesia should cesarean delivery be necessary.
Neural blockade to the TI0 dermatome is necessary to relieve uterine and cervical pain, whereas blockade of the sacral dermatomes is necessary to block the pain of vaginal and perineal distention.

25. Compared to spinal analgesic techniques, the onset of epidural
analgesia is significantly slower (15-20 minutes compared to 2-5
minutes), particularly the onset of sacral analgesia.
It may take several hours of lumbar epidural infusion, or several bolus injections of local anesthetic into the lumbar epidural space, to achieve sacral analgesia. This is particularly disadvantageous in a rapidly laboring parturient who requires rapid onset of sacral analgesia for the late first and second stages of labor.
In addition, epidural compared to spinal analgesia requires significantly more drug(s) to attain comparable analgesia, thus increasing the risk of systemic toxicity

26. Finally, there is significantly more systemic absorption of anesthetic agents, and therefore, maternal and fetal plasma drug concentrations are higher with epidural compared to spinal analgesia.
Lumbar epidural analgesia is initiated in either the sitting or lateral position. The epidural space is identified with a 17- or 18-gauge epidural needle, usually using a loss-of-resistance to air of saline technique. A flexible catheter is passed through the needle approximately 4 to 5 cm into the epidural space, the epidural needle is removed, and the catheter is secured. A test dose is frequently administered to rule out intrathecal or intravascular catheter placement.

27. No matter whether a test dose is injected, drugs should be injected incrementally into the epidural space, as no test is 100% sensitive and catheters may migrate during use.
Pregnant women are very difficult to resuscitate from local anesthetic cardiac toxicity.
Analgesia is initiated by bolus injection of anesthetic(s) through the epidural needle, catheter, or both. Analgesia is maintained
with intermittent bolus injections or a continuous infusion.
The catheter is removed after delivery when there is no further
need for analgesia/anesthesia.

28. TYPICAL DRUGS FOR INITIATION OF EPIDURAL LABOR ANALGESIA
Drug Concentration Local anesthetics Dose (Volume) Bupivacaine mg/mL mL Ropivacaine mg/mL mL Opioidst Dose (Mass) Fentanyl µg Sufentanil 5-10 µg Adjuvants Epinephrine µg/mL Clonidine 60-75µg

29. Drugs for Initiation of Epidural Analgesia
Local anesthetics, primarily bupivacaine, have been the mainstay of epidural analgesia for many years.
The amount of epidural local anesthetic required for satisfactory analgesia increases as labor progresses. Low bupivacaine concentrations (<1.25 mg/mL) provide excellent analgesia with minimal motor block.
Bupivacaine is highly protein bound with minimal placental Transfer, and duration of analgesia is approximately 2 hours. Onset to peak effect is approximately 20 minutes.
Lidocaine and 2-chloroprocaine have shorter latency, but their duration of analgesia is shorter, limiting their usefulness for routine labor analgesia. In addition, lidocaine is less protein bound than bupivacaine and therefore has a higher umbilical vein/maternal vein ratio.

30. Ropivacaine is a homologue of bupivacaine, formulated as a single levorotatory enantiomer. Its onset and duration of action
are similar to bupivacaine, but it has less potential for cardiac
toxicity.
However, ropivacaine may be associated with less motor blockade than equipotent doses of bupivacaine.
Levobupivacaine, the S-enantiomer of bupivacaine, is not available in the United States. Similar to ropivacaine and bupivacaine in its onset and duration of action, it is less cardiotoxic than bupivacaine and is associated with less motor blockade compared to bupivacaine.

31. Opioids, particularly the lipid-soluble opioids, fentanyl and
sufentanil, are commonly added to local anesthetics for epidural
analgesia.
Epidural opioids and local anesthetics interact synergistically to provide analgesia.The addition of opioids shortens latency, allows for decreased concentration of local anesthetic, thus decreasing motor block, and prolongs analgesia.
While epidural opioids alone can provide moderate analgesia for
early labor, analgesia is incomplete, and the necessary dose is
accompanied by bothersome side effects (e.g., pruritus,nausea,
vomiting, maternal sedation, neonatal respiratory depression).

32. Combining local anesthetics with opioids allows for effective analgesia while minimizing the side effects of both drugs.
Fentanyl and sufentanil are ideal for labor analgesia because
of their rapid onset (5 to 10 minutes). Their short duration of
action (60 to 90 minutes) is overcome by maintaining analgesia
with a continuous epidural infusion.
Doses commonly used for epidural analgesia initiation and maintenance have been shown to be safe for both the mother and neonate.
Morphine has a much slower onset (30 to 60 minutes) and longer duration of action (12 to 24 hours) than fentanyl or sufentanil.

33. The long duration of action is not beneficial, as the bothersome side effects of morphine (pruritus, nausea, and vomiting) continue to be present after delivery.
Adjuvants for epidural labor analgesia include epinephrine and clonidine. Epidural epinephrine may contribute to analgesia by decreasing the uptake of local anesthetics and opioids from the epidural space secondary to vasoconstriction, and by binding to spinal cord α2-adrenergic receptors.
Clonidine also binds to α2-adrenergic receptors and has been shown to supplement epidural labor analgesia. It is not approved for use in obstetric patients in the United States, however, because of the risks of sedation and hypotension.

34. Combined Spinal-Epidural Analgesia
Combined spinal-epidural (CSE) analgesia has become increasingly popular in the past decade.
Onset of analgesia is significantly faster compared to epidural analgesia.
Complete analgesia for early labor can be accomplished with the intrathecal injection of lipid soluble opioids without the addition of local anesthetics, thus avoiding motor blockade and decreasing the risk of hypotension.
The effective opioid dose is significantly less than for systemic or epidural administration.Therefore, systemic drug absorption is minimal, as are direct fetal effects.

35. The addition of local anesthetic to a lipid soluble opioid results in sacral analgesia within several minutes.
This is a decided advantage compared to lumbar epidural analgesia ,as sacral analgesia is difficult to accomplish after a single lumbar epidural dose of local anesthetic.
CSE analgesia provides more complete analgesia for women in advanced stages of labor or women whose labor is progressing rapidly.
Finally, use of the CSE technique may decrease the incidence of failed epidural analgesia

36. There are several undesirable side effects of CSE analgesia: The incidence of pruritus is higher with intrathecal versus epidural Opioids.
Dural puncture is required to initiate CSE analgesia. The risk of postdural puncture headache (PDPH) may be minimally higher with the CSE compared to pure epidural technique (estimated excess rate of 3 in 1000).
Another potential drawback of CSE analgesia is that it will be unclear for 1 to 2 hours after initiation of analgesia as to whether the epidural catheter is properly sited in the epidural space.

37. Several techniques for CSE analgesia/anesthesia have been described, including using two skin punctures in two interspaces,
two punctures in one interspace, and the needle-through-needle
technique.

39. Drugs for Initiation of Combined Spinal-Epidural Analgesia
Drug(s) Opioid dose (µ.g) Bupivacaine dose (mg)
Fentanyl
Sufentanil
Bupivacaine
fentanyl
Bupivacaine
sufentanil
Bupivacaine Fentanyl
Fentanyl Morphine
Morphine

40. CSE labor analgesia is usually initiated with a lipid soluble opioid
(fentanyl or sufentanil) or a combination of opioid and local anesthetic.
Morphine is not commonly used because of its long latency and long duration of action (a disadvantage, as women usually deliver before regression of side effects). However, morphine has been successfully combined with intrathecal bupivacaine and fentanyl in order to shorten latency and increase duration of analgesia.
This combination of drugs may be particularly useful in settings where continuous epidural infusion techniques are impractical.

41. Meperidine is unique among the opioids in that it has weak local anesthetic properties. However,meperidine was associated with a significantly higher incidence of nausea and vomiting compared to combined fentanyl-bupivacaine.
Intrathecal opioids can provide complete analgesia early in labor when the pain stimuli are primarily visceral.
Onset of analgesia occurs within 5 minutes and lasts 70 to 100 minutes.
The relative potency ratio of intrathecal sufentanil to fentanyl for labor analgesia is 4.4:1
When administered at twice the EDso, the duration of sufentanil analgesia was 25 minutes longer than fentanyl, although the incidence of side effects was not different

42. The duration of action of intrathecal opioids is dose-related, although fentanyl doses greater than 25 µg do not increase duration of analgesia and are associated with a higher incidence of side effects.
In the late first stage and second stage of labor, local anesthetic
must be added to the opioid in order to block somatic stimuli
from the vagina and perineum.
The local anesthetic works synergistically with the opioid; thus, lower doses of both drugs can be used.
Bupivacaine is most commonly combined with fentanyl or sufentanil. Bupivacaine doses between 1.25 to 2.5 mg are commonly used.

43. Levobupivacaine and ropivacaine are not approved for intrathecal use in the United States. They are less potent than bupivacaine for intrathecal labor analgesia.
Bupivacaine without opioid is not commonly used for labor analgesia. Doses high enough to provide analgesia are associated
with significant motor blockade and lower doses either do not provide satisfactory analgesia or are associated with an unacceptably short duration of action.

44. Maintenance of Epidural Analgesia
Epidural analgesia may be maintained with intermittent bolus
injection, continuous epidural infusion, or patient controlled epidural analgesia (PCEA), with or without a background infusion.
Continuous epidural infusions result in less need for bolus injections and increased patient satisfaction, but higher total
drug dose compared to intermittent injections. However,the infusion of lower concentration-bupivacaine at a higher rate
may result in similar analgesia with less motor block and no
increase in total dose.

45. DRUG SOLUTIONS FOR MAINTENANCE OF EPIDURAL LABOR ANALGESIA
Drug solution Local anesthetic Opioid
concentration concentration
(mg/mL) (µg/mL)
Bupivacaine-fentanyl
Bupivacaine-sufentanil
Ropivacaine-fentanyl
Ropivacaine
Continuous infusions rate: ml/hour. PCEA parameters: PCEA bolus
5-10 mL, lockout interval min, background infusion 0-15 ml/hour
(commonly 30%-50% of hourly dose requirement).

46. PCEA allows for both a continuous epidural infusion and patient-titrated bolus injections. PCEA resulted in greater patient Satisfaction and a lower average hourly dose of bupivacain(and therefore less motor block), and less need for physician intervention.
PCEA allows for both a continuous epidural infusion and patient-titrated bolus injections. PCEA resulted in greater patient satisfaction and a lower average hourly dose of bupivacaine (and therefore less motor block), and less need for physician intervention.

47. The protocols for PCEA vary widely, and it is unclear whether this affects analgesia and outcome.
At one extreme, most of the hourly dose is administered via a background infusion which the parturient may supplement with self-administered boluses.
At the other extreme, there is no background infusion and the entire dose is self-administered via intermittent boluses.
Bupivacaine consumption is higher with background infusions compared to a pure PCEA technique without a background infusion.

48. Although data are conflicting as to whether a backgroun infusion improves analgesia, it may be helpful in selected parturients (e.g., nulliparas with long labors).
The parturient administered bolus dose is 5 to 10 mL, the lock-out interval is 10 to 20 minutes, and the background infusion varies from 0 to 15 mL.
Commonly,30% to 50% of the hourly dose is administered as a background infusion.
The bolus administration of epidural anesthetic solution appears to result in improved analgesia with a lower total drug dose.

49. Investigators have recently demonstrated that timed (automated) intermittent boluses (5 to 10 mL every 30 to 60 minutes) administered via a programmable pump result in improved parturient satisfaction, less drug use, longer duration of analgesia, and less breakthrough pain compared to a continuous infusion of the same mass of drug per unit time.
There may be better distribution of anesthetic solution within the epidural space when large volumes are injected as a bolus compared to a slow infusion.

50. Single-Shot and Continuous Spinal Analgesia
In general, single-shot spinal analgesia is not useful for most laboring patients because of its limited duration of action.
It may be indicated in parturients who require analgesia/analgesia shortly before anticipated delivery or in settings where continuous epidural analgesia is not possible. Drugs for single-shot spinal analgesia mimic those used for the initiation of CSE analgesia .
Continuous spinal analgesia is currently not practical for most parturients. The available catheters (essentially epidural catheters) require a large gauge introducer needle and are therefore associated with an unacceptably high incidence of PDPH.

51. However,the placement of a continuous spinal catheter is a management option in patients with inadvertent dural puncture with an epidural needle or when rapid analgesia is necessary in an obese patient.
Continuous spinal labor analgesia is commonly maintained with the same solution used for epidural analgesia, but at a rate of 1 to 2 ml/hour.

52. Caudal Analgesia
Continuous caudal epidural analgesia is used infrequently in the practice of modern obstetric anesthesia. Large volumes of local anesthetic are required for first stage analgesia and result in higher maternal plasma concentrations of drug.
There is a risk of needle/catheter misplacement and direct injection into the fetus.
However,this technique is an option in patients in whom access to the lumbar spinal canal is not possible (e.g., fused lumbar spine).

53. Side Effects of Neuraxial Analgesia
Hypotension
Pruritus
Fetal Bradycardia
Maternal Hyperthermia

54. Complications of Neuraxial Analgesia
Inadvertent Dural Puncture
Respiratory Depression

55. OTHER REGIONAL ANALGESIC TECHNIQUES
Paracervical Block
Lumbar Sympathetic Block
Pudendal Block
Perineal Infiltration

56. EFFECTS OF ANALGESIA ON THE PROGRESS OF LABOR
Randomized controlled trials,however, uniformly demonstrated that early labor initiation of neuraxial compared to systemic opioid analgesia does not adversely affect the outcome of labor, and in fact, may result in faster labor.
Several groups of investigators have demonstrated that neuraxial analgesia with bupivacaine 2.5 mg/mL results in a higher instrumental vaginal delivery rate compared to low dose bupivacaine-opioid techniques.
Thus, it is the responsibility of the anesthesiologist to use a regional technique that minimizes motor block in order to decrease the risk of instrumental vaginal delivery.