Management of Pain in Obstetrics 2

By Dr. Chathura Ratnayake

Inhalational analgesia

     Several inhalational agents, both gaseous and volatile, have been used successfully in labor. Analgesia during labor can be provided by the inhalational anesthetic agents in subanesthetic concentrations thus relieving pain whilst maintaining maternal consciousness and avoiding regurgitation or aspiration of stomach contents. The efficacy of inhalational analgesia depends on the analgesic strength of the agent and on how quickly it reaches analgesic concentration after the start of inspiration. A rapid offset with complete elimination between contractions can avoid accumulation completely.

     Nitrous oxide is the commonly used gas in current practice. Various portable machines exist for administration of nitrous oxide blended with oxygen through an on-demand valve. Nitrous oxide concentrations can be varied from 0 to 75% in oxygen. For self-administration, a concentration above 50% nitrous oxide should not be allowed. Entonox, which is a mixture of 50% nitrous oxide and 50% oxygen, is the most commonly used preparation.

 

Systemic opioid analgesia

     Opioids have been used for anesthesia in labor for hundreds of years. However, it was not until the early twentieth century those techniques deliberately employing the analgesic effects of the opioids gained major attention. Unfortunately, the dosage and the effectiveness are limited by maternal and neonatal side-effects, so that only moderate pain relief could be obtained with these drugs.

A. Pethidine

     Pethidine has become the most commonly used and widely investigated systemic opioid in labor. It is principally a mu agonist but of a low potency. Administered as hydrochloride in a dose of 75-100mg intramuscularly, it reduces labor pain by about 25%.

     Delayed gastric emptying is a prominent feature. Respiratory depression is not usually observed in women who receive pethidine, because contractions continue to be painful and provoke hyperventilation. However, hypoxic episodes have been observed probably associated with significant under ventilation between contractions. The major metabolite, norpethidine, is itself active, and has convulsant properties. It is advisable to avoid pethidine in fulminating preeclampsia or eclampsia, particularly in repeated doses.

B. Fentanyl

     Fentanyl is a synthetic opioid. It primarily acts on mu-receptors and is approximately 80-100 times as potent as morphine. It has a rapid onset and shorter duration of action. The peak analgesic effect occurs within 5 minutes and the duration of effect is about 30 minutes after 1 mcg/kg administered intravenously. Fentanyl is principally bound to albumin which favors its transplacental transfer. For analgesia in labor 50-100mcg/hour is required, given in increments of 10mcg IV.

C. Tramadol

     Tramadol is a synthetic opioid.  It is a weak mu-agonist that has been prescribed in labor in doses of 50-100mg 4 hourly. The incidence of nausea is more common with tramadol than with pethidine or morphine.

 

Regional analgesic techniques

A. Epidural and subarachnoid administration of local anesthesia

     Epidural is the most effective form of pain relief technique for labor. Local anesthetics alone were used for many years, but are now generally administered in lower concentrations in combination with opioids like fentanyl. Combining opioid with local anesthetic provides effective, synergistic analgesia whilst reducing some of the unwanted side effects of local anesthetics, such as motor block.

Local anesthetics used in epidural analgesia

     Bupivacaine has high protein binding and a long duration of effect. It is the most frequently used local anesthetic for obstetric epidural analgesia. 10 ml of 0.25% bupivacaine (25mg) epidurally will normally provide good analgesia for approximately 90-120 minutes although repeated boluses may produce an increasing motor block. A spinal bolus of 2.5mg bupivacaine (1 ml of 0.25% bupivacaine, often diluted with 1 ml of 0.9% saline) will produce rapid onset of good analgesia for labor but this may only last 30 to 60 minutes. Lignocaine has a relatively short duration of action due to low lipid-solubility and is not used commonly.

Opioids used for epidural analgesia

     Good analgesia can be achieved in labor with low doses of a combination of opioid and local anesthetic. Side effects from neuraxial opioid administration include nausea, pruritus, urinary retention and respiratory depression. The respiratory depression may be delayed, particularly when less lipid soluble opioids are used such as diamorphine. Close observation of women who have received neuraxial opioids is important. A spinal dose of 15mcg of fentanyl added to local anesthetic will improve the quality of analgesia. An epidural loading dose of 50mcg fentanyl will similarly enhance the effect of local anesthetic. Continuous epidural infusion of up to 12ml per hour of 0.1% bupivacaine with 2mcg fentanyl per ml generally provides excellent pain relief in labor.

 

B. Patient-controlled analgesia

     Patient-controlled analgesia with intravenous administration of opioid analgesics was assessed for control of obstetric pain as early as in 1970. The patient's ability to control the analgesic administration may produce pharmacological as well as psychological benefits.

C. Patient-controlled epidural analgesia

     Patient-controlled epidural analgesia (PCEA) allows immediate access to more epidural solution, and creates flexibility allowing self-titration of solution to acceptable analgesic endpoint throughout labor. Reduces staff workload and reduced drug delivery might minimize side-effects and risks.

     Disadvantages are delayed feedback loop associated with the slow onset of epidural solution, concerns about equipment, safety, monitoring, need for proper training and education of staff.

 

D. Combined spinal-epidural analgesia (CSEA) in labor

     Combined spinal-epidural analgesia (CSEA) has evolved in an attempt to optimize the advantages of each separate technique.

     Advantages are more rapid onset of pain relief, good perineal analgesia despite much smaller drug doses, motor block and its unwanted sequelae are reduced, thus improving maternal satisfaction. Disadvantages are increased risk of complications due to two procedures as opposed to one.

 

E. Effect of epidural analgesia on labor

     Epidural block induced prior to well-established labor may be followed by desultory labor. During the second stage of labor, epidural analgesia that provides effective pain relief is likely to reduce appreciably maternal expulsive efforts. As a consequence, an epidural block could lead to:

· Delay or, less frequently, failure of descent of the presenting part and,

· Spontaneous rotation to the occiput anterior position, which will lead to an increased incidence of operative vaginal delivery as well as caesarean delivery.

     However, mothers with high-risk, prolonged or difficult labors are more likely to request epidural analgesia. It is therefore difficult to prove whether the increased rate of interventional delivery seen in mothers with epidurals is the result of causation rather than association.

 

F. Other local anesthetic techniques

     Perineal infiltration with local anesthetic solution is of no value for analgesia during labor, but is employed prior to episiotomy just before delivery of the baby.

     Pudendal block is a relatively simple, safe and effective method of providing analgesia for spontaneous delivery, normally performed by the obstetrician. Pudendal block may not provide adequate analgesia for forceps delivery or when delivery requires extensive manipulation. 10ml of local anesthetic solution (lignocaine 10mg/ml) containing adrenaline is injected, after appropriate aspiration.

     Paracervical block serves to relieve the pain of uterine contractions, but because the pudendal nerves are not blocked, additional analgesia is required for delivery. Usually lignocaine is injected at 3 and 9 o'clock position. Because these anesthetics are relatively short acting, paracervical block may have to be repeated during labor. This technique has fallen out of favor because of the high incidence of fetal bradycardia and neonatal depression.

 

Pain After Delivery

     Abdominal pain is a common symptom in women after vaginal delivery. A pain intensity of ‘moderate’ and ‘severe’ is twice as frequent in multiparous (58%) than nulliparous (30%) women. It is exacerbated by breast feeding in most women (96% nulliparous and 81% multiparous). Pain relief is obtained from standard therapies   in only half of these women. The abdominal pain has a temporal relation with uterine contractions and significantly increases in severity with parity and with the duration of the uterine contraction.

 

The Evidence Basis for Pain Management During Labor

     The COCHRANE evidence based reports have   researched factors that may influence pain relief in labor and are summarized below.

· Continuous support from a partner or caregiver can reduce the frequency of use of epidural analgesia and the amount of other analgesia administered to a mother

· Water immersion during labor reduces pain intensity and analgesic use

· Complementary and alternative therapies such as: Self-hypnosis and acupuncture decrease the amount of pain relief  required during labor

· Epidural analgesia compared with no epidural analgesia or no pain relief provides better pain relief and maternal satisfaction with no increased risk for CS, fetal depression or long term backache

· Adoption of the upright position in the second stage of labor can reduce the amount of severe pain experienced

· Combined spinal epidural analgesia when used in labor induces pain relief about 5 minutes  faster than epidural analgesia but it causes more pruritis

· Opioids given intramuscularly for pain relief during labor have not been found to be effective

 

Summary

     Pain during pregnancy and labor is due to multitude of factors. Its management involves preparing and educating the pregnant mother for the pregnancy and delivery as well as providing effective analgesia during labor and delivery process. Post natal pain relief also needs to be attended as it’s very easy to get neglected. The attitude of the care givers towards pain in obstetric practice determines the successful and fulfilling outcomes for women.

 

References

Charlton JE, editor. Core Curriculum for Professional Education in Pain. IASP Press;        2005.

Russell R, editor. Anesthesia for Obstetrics and Gynecology. BMJ Press; 2000.