The wide range of options available for pain relief during labor are summarized in Table 36-3.
TABLE 36-3:OPTIONS FOR PAIN MANAGEMENT ||Download (.pdf) TABLE 36-3: OPTIONS FOR PAIN MANAGEMENT
|Psychological support (birthing coach, partner, other family members) |
|Behavioral modification (Lamaze) |
|Hypnotherapy (relaxation exercises practiced before presentation to birthing unit) |
|Education (prenatal classes) |
|Massage, walking, various birthing positions |
|Nitrous oxide (Entonox) |
|Opioid analgesics |
|Epidural analgesia |
|Spinal anesthesia |
|Combined spinal and epidural anesthesia |
|Local infiltration |
|Pudendal block |
|Paracervical block |
Opioid analgesia includes intravenous (IV) and intramuscular (IM) techniques. Advantages include ease of use and patient acceptance. It is useful for those who prefer less invasive techniques and when regional anesthetics are contraindicated or unavailable.
Although sedatives and tranquilizers have been used in the past, the increasing availability of regional anesthesia has largely replaced their use. However, opioids are still used in many cases either as the sole agent for labor analgesia or in early labor as a temporizing measure until regional anesthesia is available. There is a risk of maternal and neonatal depression with their use. All parenteral opioids readily cross the placenta and cause neonatal central nervous system and respiratory depression. The choice of drug, timing of administration, and method of administration must be carefully considered. Side effects common to all opioids include respiratory depression, orthostatic hypotension, delayed gastric emptying, nausea, and vomiting.
The dose used is approximately 0.1 mg/kg maternal body weight every 3 to 4 hours. Peak effect is seen 1 to 2 hours after IM injection and 20 minutes after an IV injection, with a duration of action of 4 to 6 hours. The effect on the fetus depends on the time relationship of administration to delivery. If given within 3 hours of delivery, the risk of fetal narcosis is high.
The dose is 1 mg/kg every 3 to 4 hours. Peak effect is 40-50 minutes after an IM injection and 5 to 10 minutes after an IV injection. The duration of action is 3 to 4 hours. Maternal effect is similar to morphine. It is quickly transferred across the placenta, but peak levels are reached in the fetus 2 to 3 hours after administration. Infants born 2 to 3 hours after administration are most susceptible to opioid-induced respiratory depression. Elimination may take 2 to 3 days, and this manifests as lower APGAR scores and impaired neurobehavioral scores for the first 3 days of life. Normeperidine, an active metabolite, may be responsible for these changes.
A mixed agonist antagonist, provides good pain relief without respiratory depression and may be a better choice. Doses of 10 to 20 mg IM every 4 to 6 hours usually provide adequate analgesia.
This is a synthetic opioid. It has been used to provide pain relief in labor, but because of its short duration of action, it must be administered IV, usually through a patient-controlled analgesia (PCA) pump. Remifentanil is an ultra-short-acting synthetic opioid that has been used as an alternative to fentanyl in PCA pumps. Remifentanil has a half-life of 2 minutes and is rapidly metabolized by the fetus, so there should be minimal neonatal depression. Use of remifentanil PCA requires one-to-one nursing because of the risk of maternal hypoventilation Narcotic effects in the newborn are best antagonized with naloxone, 5 to 10 mcg/kg.
Nitrous oxide is a weak analgesic and amnesic. It is relatively insoluble in blood, so induction and recovery are both rapid. For labor analgesia, it is offered in a 50:50 mixture in oxygen (Entonox) to decrease the chances of maternal hypoxemia. Advantages are ease of use, the safety profile for the mother and infant, rapidity of onset of effect (50 seconds), and widespread availability. It is relatively simple to use because the patient self-administers it using a handheld face mask. To be effective, there must be adequate analgesic concentrations of nitrous oxide present in the blood and the brain at the peak of uterine contractions. This requires maternal cooperation, with deep inhalation as soon as the woman is aware of the onset of a contraction. Some patients may become drowsy. However, this effect is short lived after discontinuation of the agent. Common side effects include dizziness, nausea, dysphoria, and a sense of claustrophobia.
Accumulation is negligible, and neonatal depression is rare.
Disadvantages are that if it is not administered correctly, peak analgesic effect may be delayed until after the contraction. Studies on its effectiveness have shown mixed results. It may be ineffective in up to half of parturients. Specialized equipment is required for its administration. Efficient scavenging is difficult, resulting in environmental pollution. It is unclear what, if any, the effects of long-term exposure to subanesthetic concentrations of nitrous oxide are.
Continuous lumbar epidural analgesia is the gold standard of labor analgesia. Its use has increased in the last 10 years with 57.8 percent of Canadian women using this technique during labor. It is the most effective way to block the pain of labor and can provide effective pain relief throughout all stages of labor and delivery.
It involves the injection of a dilute local anesthetic, usually combined with an opioid analgesic, into the lumbar epidural space. The drugs diffuse across the dura into the subarachnoid space, where they act on the spinal nerve roots to provide analgesia. Various combinations of drugs have been used as either intermittent boluses or by continuous infusion.
Placement of an epidural catheter allows analgesia to be maintained until after delivery. If a cesarean delivery is deemed necessary, conversion to epidural anesthesia can be completed rapidly, avoiding the need for general anesthesia in most cases.
Epidural analgesia produces a segmental and sensory nerve block with the onset of pain relief. Blood pressure may normalize because of vasodilatation and may lower in some instances. This may be beneficial in patients with pre-eclampsia. There may be a significant improvement in uteroplacental blood flow, both in healthy patients and those with hypertensive disorders of pregnancy. This is because of a reduction in vascular resistance as long as blood pressure is maintained.
Patient-controlled epidural analgesia (PCEA) has become increasingly popular. A low baseline infusion is given and the patient has the ability to “top up” with bolus doses of the same mixture. Alternatively, there is no background infusion, and the patient gives herself bolus doses on demand only. There is high satisfaction with this method and overall less medication is given than by the conventional infusion technique.
Another alternative to continuous infusion is programmed intermittent epidural bolus (PEIB). The pump will deliver a bolus dose at specific intervals (e.g., 8 mL every 45 minutes). This technique allows for greater spread of local anesthetic in the epidural space when compared to a continuous infusion. It can be used with PCEA. There is better analgesia, enhanced maternal satisfaction, less motor block, and reduced local anesthetic consumption when compared with a continuous infusion.
Contraindications to Epidurals
Absolute contraindications include patient refusal or inability to cooperate, uncorrected coagulopathy, sepsis or infection at the puncture site, uncorrected hypovolemia, and raised intracranial pressure. Any preexisting neurologic disease should be carefully documented before initiation of the epidural.
Technique of Epidural Analgesia
Before the initiation of the epidural, several steps must be taken. The anesthetist must review the patient’s obstetric history; review her medical and anesthetic history; and perform a focused physical examination, including the vital signs, airway, heart, lungs, and back. Emergency resuscitation equipment, drugs, and supplies must be readily available. An IV catheter, preferably 18 gauge, should be placed. Many anesthesia providers administer a 500-mL bolus of crystalloid, although the ASA Taskforce on Obstetric Anesthesia has stated that a fixed volume of IV fluid is not required before placement of a labor epidural. With the use of more dilute local anesthetics for epidural analgesia, severe hypotension is rarely seen.
After obtaining informed consent, the patient is either seated or placed in the lateral decubitus position. The lumbar area is prepped with an antiseptic solution. In the authors’ institution, 2 percent chlorhexidine in 70 percent isopropyl alcohol is the agent of choice. A sterile drape is placed over the prepped area. In the second or third lumbar interspace, the skin is infiltrated with 1 or 2 percent lidocaine. Either a paramedian or midline technique with a 16- or 17-gauge Tuohy needle is used, using loss of resistance to saline or air. The epidural space is identified, and a 20-gauge polyurethane multiorifice catheter is threaded 3 to 5 cm into the epidural space through the Tuohy needle, which is then withdrawn. The catheter is secured to the mothers’ back with an adhesive dressing and tape.
In the past, a test dose of 3 mL of lidocaine 1.5 percent with epinephrine 1:200,000 was injected at this point to rule out intrathecal or intravascular catheter placement. If the dose was injected intravascularly, the patient would experience tinnitus, a metallic taste, and dizziness. Tachycardia would be seen because of the beta-adrenergic effects of the epinephrine. However, because of the wide variations in heart rate that occur with contractions, this effect may be masked. It is recommended that the traditional test dose should be given immediately after a contraction to maximize sensitivity.
The use of a traditional test dose is controversial. Epinephrine may reduce placental blood flow by producing uterine artery constriction. It is relatively contraindicated in cases such as diabetes mellitus or preeclampsia, where there may be decreased uteroplacental blood flow. An undesirable side effect of the traditional test dose is that it produces motor block. There may be maternal hypotension caused by block of sympathetic nerves.
Today, the anesthetist may elect to “test” the epidural with a more dilute solution that will be used for infusion. The epidural is loaded with 3- to 5-mL increments of the epidural solution. Examples are 0.0625 to 0.1 percent bupivacaine with fentanyl 2 mcg/mL or 0.08 to 0.125 percent ropivacaine with fentanyl 2 mcg/mL. A total of 15 to 20 mL of these solutions can be used to incrementally load the epidural while watching the vital signs.
Effects on Labor and Delivery
Many studies have attempted to identify factors associated with cesarean delivery. In the past, observational studies have suggested that epidural analgesia, particularly when administered in early labor, is associated with an increased risk of cesarean delivery. Studies are difficult to perform because it is not ethical to assign women to a placebo group with no analgesia. A recent Cochrane Database Systemic Review from 2018 compared epidural analgesia to nonepidural or no analgesia in labor. In trials of singleton, uncomplicated pregnancies conducted since 2005, epidural analgesia does not increase the proportion of women who have an assisted vaginal delivery. It is felt that changes in administration of epidural analgesia such as the use of low dose local anesthetics and opioid account for this.
Historically, multiple observational studies have found that early initiation of epidural analgesia (cervical dilatation 3-5 cm) is associated with a higher risk of cesarean delivery. Randomized controlled trials have not shown this to be true. In 2006, the American College of Obstetricians and Gynecologists (ACOG) rescinded their recommendation to delay epidural placement until mothers were in active labor. Epidurals can be safely placed at any stage of labor, including the second stage.
Studies have attempted to address whether or not neuraxial analgesia prolongs the duration of the first and second stages of labor. Studies are conflicting regarding the effect on the first stage of labor. If it does prolong it, it is to a minor degree. The bulk of evidence suggests that neuraxial analgesia does prolong the second stage of labor to a small degree. However, neonatal outcomes do not appear to be affected.
Risks of Epidural Analgesia
Risks of epidural analgesia and anesthesia should be disclosed to the patient. Studies looking at informed consent have shown that patients want to be informed of significant material risks even if the incidence is low.
Common side effects include pruritus, nausea and vomiting, urinary retention, and fever. There is a failure rate of up to 12 percent in labor epidurals. The risk of postdural puncture headache (PDPH) is quoted at 1 percent, but this incidence is increased with new trainees and is reduced with experience. It is common to have localized pain or backache at the site of skin entry, especially if there are multiple passes with the Tuohy needle. This may last for up to several weeks. There is no evidence to suggest that epidural analgesia causes long-term backache.
Infection at the site of insertion is rare, as is meningitis. It has been reported in the literature. Meticulous sterile technique during insertion and during top ups of the epidural must be observed.
Traumatic injury to a vessel in the epidural space leading to an epidural hematoma is rare. If a patient has back pain or a worrisome neurologic examination, then imaging should be obtained urgently. Surgical decompression should be performed urgently or paralysis may result.
Epidural analgesia rarely causes neurologic complications. In fact, most postpartum neurologic complications are obstetric palsies from nerve compression by the fetal head. Nerves may also be stretched with positioning in labor. A detailed neurological exam and imaging may be required to determine the cause.
Systemic toxicity is related to high plasma levels of local anesthetics and is extremely rare. Most commonly, it is caused by accidental IV injection. Initial signs and symptoms include tinnitus and disorientation and ultimately seizures and cardiovascular collapse. It is more likely to be seen after epidural than after spinal because the doses are higher for epidurals, especially when dosing epidurals for cesarean sections. The risk of toxicity is reduced by dosing incrementally and by aspirating the catheter before injecting.
If signs of central nervous system toxicity occur, the injection should be stopped. Seizures should be treated with benzodiazepines (midazolam 2-5 mg) or barbiturates (thiopental 50-100 mg). The airway should be secured and supplemental oxygen provided.
If cardiovascular toxicity develops, advanced cardiac life support protocols should be followed. The airway should be secured. When performing chest compressions, the uterus must be displaced leftward after 20 weeks’ gestational age so that the major vessels are not compressed by the enlarged uterus. If spontaneous circulation has not returned, the current recommendation is to deliver the baby within 5 minutes after cardiac arrest.
Early administration of lipid emulsion (20% intralipid) is recommended for local anesthetic toxicity. After the airway has been secured, a bolus of 1.5 mL/kg is administered IV over 1 minute followed by an infusion of 0.25 mL/kg/min for at least 10 minutes after return of spontaneous circulation. The bolus may be repeated. Total dose should not exceed 10 mg/kg over 30 minutes.
The definition of a failed block is inadequate analgesia or anesthesia after an epidural. Failed blocks may be caused by inadequate dosing of drugs, patient factors, or technical issues related to the placement of the epidural. If inadequate amounts of drugs are injected, then the required spinal segments will not be blocked and analgesia will not be achieved. Scar tissue or other anatomical features in patients may rarely cause epidural failure. Another factor to consider is that the Tuohy needle or the catheter may not be sited within the epidural space. The catheter may migrate after being positioned, either out through an intervertebral foramen or back out through the skin. With multiorifice catheters, one or more of the orifices may not be in the epidural space. The catheter may be positioned more to one side, causing a unilateral block. Ideally, the catheter should be placed 3 to 5 cm within the epidural space to avoid migration of the catheter.
Spinal Anesthesia and Combined Spinal Epidural
Spinal anesthesia is not often used alone for labor analgesia because of the finite duration of action of the agents used. However, it may be combined with epidural analgesia for rapid onset of pain relief. Anesthesia is initiated with a subarachnoid injection of opioid and local anesthetic, then maintained via the epidural catheter. This can be done in several ways. The most popular is with a needle through needle technique, where the Tuohy needle is inserted into the epidural space and then serves as an introducer for the spinal needle. The spinal needle passes though the Tuohy needle and punctures the dura. Small doses of local anesthetic combined with opioids, such as bupivacaine 2 mg and fentanyl 10 to 15 mcg, are injected intrathecally, the spinal needle is removed and the epidural catheter is threaded. Alternatively, two different interspaces can be utilized, with the epidural placed first then the spinal performed at a lower level sequentially.
The duration of analgesia is about 90 minutes. If the patient has not delivered within that time period, the epidural catheter can be activated. The author starts the epidural infusion immediately rather than waiting for patient request so that there is uninterrupted analgesia. In this situation, the epidural test dose is omitted.
The needle through needle technique does require the use of a long spinal needle, which must protrude 12 to 17 mm beyond the tip of the epidural needle when the two needles are fully engaged. To reduce the risk of PDPH, a small (25 or 27 gauge) noncutting spinal needle is preferred.
The combined spinal–epidural (CSE) technique does result in a greater incidence of fetal bradycardia compared with epidural techniques. The mechanism is believed to be attributable to a transient imbalance in epinephrine compared with norepinephrine levels. Epinephrine has a tocolytic effect and causes uterine relaxation. With rapid onset of analgesia, circulating epinephrine levels drop. This results in a relative increase in uterine tone and may lead to a prolonged tetanic contraction. This is usually short lived and does not result in increased cesarean delivery rates.
With the use of pencil point or atraumatic spinal needles for this technique, the risk of PDPH is not significantly increased.
Dural puncture epidural anesthesia is another technique that is identical to CSE anesthesia other than there is no drug injection intrathecally. The intent is to allow for augmented transfer of epidural injected drugs into the subarachnoid space, which possibly results in faster onset of analgesia.
Postdural Puncture Headache
Headache is one of the most common symptoms seen in the postpartum period. When the dura is breached by a 16-gauge Tuohy needle, a PDPH will develop in up to 88 percent of parturients. The headache is believed to be caused by leakage of cerebrospinal fluid through the rent in the dura, which causes intracranial hypotension. When standing, there is traction on pain-sensitive structures. Cerebral vasodilatation is also believed to play a role. This headache has a strong postural component with relief of symptoms when supine. The International Headache Society has defined PDPH as a bilateral headache that develops within 7 days after lumbar puncture and disappears within 14 days after the lumbar puncture. The headache worsens within 15 minutes of assuming the upright position and disappears or improves within 30 minutes of resuming the recumbent position.
The headache is usually described as occurring in the frontal and/or occipital areas, but may also involve the neck and upper shoulders. The usual onset of symptoms is within 48 hours of the dural puncture, but in 25 percent of cases, it presents later than 3 days. Nausea, vomiting, nuchal rigidity, hearing loss, and diplopia may be seen.
This headache can be debilitating and may significantly impair the mother’s ability to care for herself and her infant. The natural history is that symptoms will resolve over 10 days, but there have been case reports of persistent headaches for weeks to months. The duration of headache is usually related to the gauge of the needle that breached the dura.
Management of the second stage may affect the incidence of headache after accidental dural puncture. One study of 33 patients who had accidental dural puncture showed that the incidence of headache was 10 percent (1 in 10) in those who went on to have cesarean section compared to 74 percent (17 of 23) in those who pushed.
Many treatments have been proposed for treatment of PDPH including caffeine infusions, ACTH injections, and more recently sphenopalantine ganglion nerve block. However, epidural blood patch remains the definitive treatment for severe headache. Treatment of PDPH usually begins with conservative measures such as bed rest and analgesics. This delay increases the success rate of the blood patch, which has a failure rate of up to 71 percent if performed within the first 24 hours of dural puncture versus a failure rate of 4 percent if performed later than 24 hours after dural puncture. The optimal volume of autologous blood to be injected is believed to be 20 mL. Success rates vary from 75 to 93 percent and a second blood patch may be required in some cases.
This method is now rarely used in North America for labor analgesia because there has been a high incidence of complications with its use, specifically fetal asphyxia and poor neonatal outcome, especially with the use of bupivacaine. However, it is an easily performed method of achieving pain relief during the first stage of labor. It is ineffective for the second stage of labor. Its main advantage is that the block can be performed by the obstetrician, and the attendance of an anesthetist is not required. It is more commonly used to provide analgesia for other gynecologic procedures.
The injection is made transvaginally into the posterolateral fornices, thus blocking the sensory pathways at the junction of the uterosacral ligaments with the cervix. The procedure can be carried out in the patient’s bed or the delivery table. The block is instituted during the active phase of labor with the cervix at least 3 to 4 cm dilated.
Equipment consists of a 20-gauge needle, 13 to 18 cm long, with a sheath or needle guide of such length that 1.5 cm of the tip of the needle protrudes when it is inserted up to its hub. The needle sheath is guided by the fingers into the vagina and placed in the fornix just lateral to the cervix at a tangent to the presenting part. The needle (with the attached syringe) is introduced through the guide until the point rests against the mucosa. With quick, slight pressure, the needle is pushed through the mucosa to a depth of 6 to 12 mm. Aspiration is performed to guard against direct intravascular injection. If no blood returns, the desired amount of anesthetic agent is used. It is advisable to wait for a few minutes after the injection of one side. Fetal heart auscultation is performed, and if it is normal, the other side is injected. If fetal bradycardia occurs, the procedure should be discontinued. Mepivacaine, lidocaine, and procaine in 1 percent concentrations are effective. Bupivacaine is not recommended because of a high incidence of fetal bradycardia.
Sites of injection vary. Some inject at 3 and 9 o’clock, but others give several injections at 3, 4, 8, and 9 o’clock. In any case, 10 mL is given on each side in single or multiple doses.
Most parturients experience complete or partial relief from pain almost immediately with a duration of about 1 hour. If the cervix is not yet fully dilated, a second block may be required. Other forms of anesthesia are required for the actual delivery.
Transient numbness and paresthesias of one or both lower extremities occur commonly as a result of spread of the local anesthetic to the sciatic nerve or part of the lumbosacral plexus.
Rapid absorption or intravascular injection may cause symptoms of local anesthetic toxicity, including dizziness, anxiety, shaking, and occasional seizures and loss of consciousness. Occasionally, transient hypotension may occur. There is a risk of hematoma formation at the site of injection. There have been case reports of parametritis.
The main concern of paracervical block is the effect on the fetus. Changes in fetal heart rate (FHR) can be seen in up to 30 percent of cases with the majority being fetal bradycardia. In up to 20 percent of the cases when bradycardia is seen, it is sufficient to impair tissue perfusion, with acidosis and neonatal depression the ultimate result.
The etiology of the bradycardia is complex and likely occurs by several pathways:
Uterine artery vasoconstriction because of the proximity of the injection, leading to placental hypoperfusion and fetal asphyxia
Direct uterine artery injection
Direct intramyometrial injection
Diffusion of local anesthetic through the uterine arteries and deposition into the intervillous spaces with subsequent fetal uptake and direct fetal cardiotoxicity
Direct fetal injection
Changes in FHR are seen more frequently in primigravidas, in those with previous nonreassuring FHR patterns, and in very low birthweight infants (<2500 g). Onset is usually within 2 to 10 minutes after injection and may last 3 to 30 minutes. With prolonged bradycardia, fetal acidosis and neonatal depression may be seen, especially if delivery is within 30 minutes of injection.
Due to the high risk of complications, this technique should be avoided if the fetus is compromised, as in cases of placental insufficiency, prior fetal distress, and prematurity. Use only small doses of dilute local anesthetics. Avoid vasoconstrictors such as epinephrine. Do not perform this block if delivery is anticipated within 30 minutes. If the cervix is dilating rapidly, the chance of aberrant injection is increased, and the block should not be performed. The FHR should be monitored continuously during and after the block.
Do not use this block if there is a known sensitivity to local anesthetics or if there is vaginal bleeding or infection.
Direct Infiltration Anesthesia
The main purpose of perineal infiltration is to permit incision and repair of episiotomy, as well as suturing of lacerations.
Xylocaine 1 percent provides a rapid onset of action and profound anesthesia. Total volume of 30 to 50 mL is sufficient for most cases
Either the needle is inserted at the posterior fourchette and the injections are made lateral or the needle is inserted at a point halfway between the anus and the ischial tuberosity and the injections are made toward the midline
Using a 25- to 27-gauge needle, a wheal is made by injecting a small amount of the local anesthetic solution into the skin where the needle is to be inserted
The needle is then changed to a 22 or 20 gauge, which is inserted through the wheal. Multiple injections are made into the subcutaneous tissue, muscles, and fascia after aspiration to ensure that the needle is not intravascular
Adequate analgesia is achieved within 5 minutes
The technique is simple to perform, with no special anatomic knowledge necessary. The success rate is almost 100 percent. However, complete perineal anesthesia is not achieved because only the infiltrated areas are anesthetized.
The pudendal nerve originates from S2, S3, and S4. It exits the pelvis through the lower part of the greater sciatic foramen, curves around the ischial spine, crosses the sacrospinous ligament close to the attachment to the ischial spine and then reenters the pelvis alongside the internal pudendal artery at the lesser sciatic foramen. At this point, the pudendal nerve breaks up into the inferior hemorrhoidal (rectal) nerve, the perineal nerve, and the dorsal nerve of the clitoris. These nerves are best blocked at the ischial tuberosity. Additional innervation is received from the pudendal branch of the posterior femoral cutaneous nerve, which supplies the posterior labial portion of the perineum. A secondary innervation is provided by the ilioinguinal and genitofemoral nerves. These nerves must be blocked by supplemental infiltration to achieve thorough anesthesia of the anterior portions of the labia majora and mons pubis.
The timing of administration of this block is important to its success. In primigravidas, it is done when the cervix is fully dilated and the presenting part is at station +2. In multiparas, the block is administered at 7- to 8-cm dilatation. Pudendal anesthesia is sufficient for spontaneous delivery or low forceps extractions, breech delivery, and repair of episiotomy and lacerations. It may be combined with local infiltration. Before the widespread availability of epidurals, it was the preferred analgesic technique for delivery. It can be used when contraindications to neuraxial anesthesia exist or when low forceps delivery is required.
Either a transvaginal or transperineal approach may be used. The transvaginal approach is most commonly used.
The local anesthetic is injected around the pudendal nerve through a 15.2 cm needle with a .625 cm spacer. A commonly chosen agent is 1 percent lidocaine. Effective analgesia is achieved within 15 minutes. After an intradermal wheal has been raised, the needle is inserted through the skin midway between the anus and the ischial tuberosity. As the needle is advanced, small amounts of local anesthetic are injected. The index finger of the left hand is inserted into the vagina or rectum to palpate the tuberosity of the ischium. The needle is then directed toward the ischial spine. A number of injections are made:
Five to 10 mL is injected at the anterolateral aspect of the spine, as well as under the tuberosity, to block the inferior pudendal branch of the posterior cutaneous nerve. At this point, the syringe can be detached from the needle and refilled
The needle is then advanced to the medial aspect of the ischial spine, where another 5 to 10 mL is injected to block the branches of the pudendal nerve. Because the pudendal artery and vein run parallel to the nerve, intermittent aspiration to ensure the needle is not intravascular should be performed
Another 5 to 10 mL of the solution is injected as the needle is advanced 2.5 cm past the ischial tuberosity into the ischial fossa. This blocks the pudendal nerve in Alcock’s canal
The point of the needle is advanced posteriorly to the ischial spine. The finger can palpate the sacrospinous ligament, and it guides the needle in this direction until a “popping” sensation indicates that the needle has pierced the ligament. The needle is advanced another 0.5 cm, and 5 to 10 mL of solution is injected at this point to block the pudendal needle before it divided. The needle is withdrawn, and the other side is blocked
The final step is to infiltrate the area that lies 1.5 cm lateral and parallel to the labia majorum from the middle of the labium to the mons pubis. This effectively blocks the secondary innervation from the iliohypogastric, ilioinguinal, and genitofemoral nerves. This must be done bilaterally
A 10- or 20-mL syringe is attached to a 15.2 cm needle with a .625 cm spacer. The left pudendal nerve is blocked first. The index and middle fingers of the left hand are inserted into the vagina, and the ischial spine and sacrospinous ligament are palpated.
Holding the syringe in the right hand, the needle is placed in a specialized pudendal needle sheath, such as an Iowa trumpet with the sharp tip retracted into the sheath. Using the groove formed by the apposition of the index and middle fingers, the needle is inserted into the wall of the vagina toward the tip of the ischial spine. The needle is advanced 1.5 cm into the sacrospinous ligament, and 5 to 10 mL of local anesthetic solution is injected. The needle is then advanced until it “pops” through the sacrospinous ligament, and 5 to 10 mL of local anesthetic is injected with intermittent aspiration to ensure the needle is not intravascular. Supplementary infiltration of the area lateral to the labia majora is carried out as described in the section “Transperineal Approach.” The procedure is then repeated on the other side.