A woman is in the second stage of labor and has a spinal block in place for pain management

Caudal analgesia

Caudal anesthesia is an epidural block performed by entering the caudal space via the sacral hiatus. This is the most inferior access point to the epidural space and is found at the junction of the coccyx and sacrum. It can provide selective sacral block for the second stage of labor; however, it is rarely used now because of complications specific to the obstetric patient. The descent of the fetal head against the perineum, in addition to the normal sacral edema of pregnancy, obscures the landmarks of the sacral hiatus. This makes the caudal procedure technically challenging, and reports of transfixing the rectum and fetal skull puncture with the epidural needle have led many anesthesiologists to avoid this technique. Lumbar epidural anesthesia is considered a safer approach to the epidural space.

Spinal analgesia

Spinal anesthesia is used for both cesarean surgery and specific situations during labor. Medication is deposited into the cerebrospinal fluid (CSF)–filled intrathecal space as a single shot using pencil point spinal needles of very small dimension (see image below).

Advantages of spinal analgesia include rapid onset of analgesia, the potential for minimal motor block, little or no risk of systemic local anesthetic toxicity, minimal drug transfer to the fetus, and modest anesthesiologist staffing requirements. The dose and concentration of the local anesthetic can be tailored to the situation, with small doses of local anesthetic and opiate mixtures providing 1-3 hours of labor analgesia and larger doses producing surgical blocks suitable for cesarean section or other surgery.

The major limitation of spinal analgesia during labor is its limited duration, since it is typically a single-injection technique. If labor outlasts the duration of the spinal analgesic, it must be repeated or followed with systemic anesthesia. Efforts to overcome this fundamental limitation involve using either larger doses of the spinal drugs or agents with longer duration. Both approaches carry risks: larger doses may lead to more side effects, and the use of drugs with longer duration may result in effects that far outlast labor and delivery.

The most common agents used for spinal analgesia during labor are long-acting local anesthetics, lipophilic opioids, and adjuvant drugs such as epinephrine. Drugs are almost always used in combination to gain rapid onset, sufficient duration, and additive or synergistic analgesic effects. Synergy between spinally administered local anesthetic and opioid is most potent for the visceral pain of the first stage of labor and less so for the somatic pain of the second stage. Clinically, this translates into excellent to good analgesia during the first stage of labor, and fair to poor analgesia during the second stage.

Bupivacaine, a long-acting local anesthetic, is the most common local anesthetic used for spinal labor analgesia. Low doses are used to minimize motor block and maternal hypotension. Opioids are also frequently used, usually in combination with bupivacaine. Fentanyl or sufentanil provides a rapid analgesic effect with approximately 90-minute duration. Higher doses of sufentanil were once routinely used but were associated with a higher incidence of fetal bradycardia and occasional maternal respiratory depression. When delivery is not expected for more than 2 hours, morphine may be used.

Intrathecal morphine has been associated with delayed maternal respiratory depression up to 18 hours after injection and with recurrence of oral herpes lesions. Urinary retention, pruritus, and nausea/vomiting are all significantly more common with this drug than with fentanyl or sufentanil. Some practitioners administer continuous infusions of low-dose naloxone or oral naltrexone after delivery to diminish the side effect profile of intrathecal morphine.

The inclusion of epinephrine increases analgesic duration by as much as 45 minutes with some drug combinations. However, the incidence of nausea and motor block are also increased. Although a number of dosing combinations of local anesthetic and narcotic are used for spinal labor analgesia, the most common mixture is 1 mL of 0.25% bupivacaine with 25 µg of fentanyl as a single-shot intrathecal dose. A surgical block for cesarean surgery requires 1.4-1.6 mL of 0.75% bupivacaine with fentanyl or sufentanil added.

Complications

Numerous complications can arise from spinal anesthesia. The most common is the postdural puncture headache (PDPH), also known as a “spinal headache,” which develop from minutes to days after a dural puncture. Its hallmark is its positional nature: it is markedly worse while sitting up or standing than while supine. Spinal headaches occur in 1%-2% of spinal punctures with a 25-gauge Whitaker spinal needle. This is a dramatic improvement from the 25% incidence seen with the 22-gauge Quincke needle, [6] which had impeded spinal use in pregnancy prior to 1990.

Therapy for PDPH includes recumbent position, hydration, oral analgesia, and, in severe cases, epidural injection of 10-20 mL of the patient's fresh blood to "seal" the defect (known as a “blood patch”). The need for a blood patch is influenced by patient age, patient sex, and the size and type of needle. Women of childbearing age have a greater likelihood of developing PDPH; however, the design of pencil-point needles has reduced the incidence of headache to 1%-2%. As importantly, PLPH caused by these needles resolves quickly and rarely requires blood patch therapy.

After placement of the spinal block, the anesthesiologist must monitor the patient for evidence of dermatomal spread of anesthesia. A block below T10 is insufficient to control uterine pain, and a high thoracic level may produce hypotension that will require treatment.

Spinal anesthesia produces hypotension in 10%-20% of cases, which presents risks to both mother and fetus. This is a result of arterial and venous vasodilation within the dermatomes that receive a sensory block. If high thoracic dermatomes (T1-T5) are anesthetized by the spinal injection, alteration of the cardiac sympathetic innervation slows the heart rate and reduces cardiac contractility. Epinephrine secretion by the adrenal medulla is also depressed. Concomitantly, the unopposed parasympathetic effect of cardiac slowing alters vagal stimulations.

As a result of these and related changes, shock follows promptly, particularly in hypotensive or hypovolemic patients. This is why essential elements of obstetric anesthesia include adequate intravenous hydration prior to administration of spinal anesthesia and frequent monitoring of maternal blood pressure after anesthesia is given. Any decrease in maternal blood pressure is rapidly corrected with intravenous fluids or a vasopressor.

Rarely, significant complications can develop following a dural puncture. Infection in the form of an epidural abscess or bleeding in the form of an epidural hematoma can lead to pressure on the spinal cord (cauda-equina syndrome) and cause nerve damage that may become permanent.

Epidural analgesia

Epidural techniques are common and effective methods of providing analgesia during labor and anesthesia for cesarean delivery.

An epidural involves placement of an indwelling catheter into the epidural space. The epidural catheter can then be used to deliver a continuous epidural infusion (CEI) of analgesic medication via a programmable pump. This technique allows rapid initiation of analgesia, minimal motor block, flexibility for varying clinical situations that evolve, and longer duration of effect than spinal anesthesia since an epidural catheter can be left in place for hours and possibly days, if necessary.

Often, the infusion system can incorporate patient autonomy. Patient-controlled epidural analgesia (PCEA) still involves a programmable pump to infuse the medication at a constant basal rate. Additionally, the parturient is given a button attached to the pump and instructed to press it if she becomes uncomfortable. This triggers the pump to give an additional bolus dose. Patients typically consume less total drug with PCEA compared to CEI, require fewer anesthetic personnel interventions, have no increased side effects, and have very high satisfaction. Compared with intravenous analgesia, patients with PCEA have lower pain scores, higher satisfaction levels, and less need for neonatal resuscitation.

While the second stage of labor is prolonged by epidural anesthesia, the duration of the first stage is unaffected. The use of outlet forceps is increased, but cesarean section rates are unchanged.

Epidural analgesia and anesthesia using local anesthetics have been in widespread use for decades. Historically, practitioners tended to use high concentrations of local anesthetic alone, which afforded excellent pain relief but often came at the expense of significant motor blockade and hypotension. Today, it is recognized that initiating analgesia with minimal motor block can be accomplished with low-concentration, high-volume epidural solutions. The analgesic synergy of a local anesthetic in combination with an opioid allows for very dilute concentrations of local anesthetic.

Complications

The most common risks associated with epidural analgesia during labor result from the consequences of sympathetic blockade or the unrecognized misplacement of the epidural catheter into an epidural vein or the intrathecal space. Hypotension after initiation of epidural or combined spinal-epidural analgesia (CSE) techniques occurs in approximately 10% of cases and typically is most pronounced at 15-20 minutes after initiation of neural blockade. Uterine blood flow is directly proportional to uterine arterial pressure, so maternal hypotension can lead to inadequate fetal-placental perfusion.

After initiation of labor analgesia, patients can be placed in a full or partial lateral position to prevent aortocaval compression by the gravid uterus, which may dramatically impede venous return and contribute to hypotension. Hypovolemia can be corrected by using intravenous hydration prior to placing the block. An intravenous bolus of crystalloid solution modestly reduces the incidence of significant hypotension following initiation of either spinal or epidural analgesia. If the maternal blood pressure falls in excess of 20% of the preblock level or any new fetal heart rate abnormalities appear, small doses of an intravenous vasopressor can be used to correct the hypotension.

Placement of the epidural catheter into an epidural vein occurs in approximately 5% of obstetric patients. This is much higher than in the nonobstetric population owing to epidural vein engorgement caused by compression of the vena cava by the gravid uterus. If intravenous catheter placement goes unrecognized, systemic local anesthetic toxicity (manifested by events as severe as seizures or cardiac toxicity) may result, although this is rare. Intravenous placement typically occurs with initial epidural catheter placement but may develop hours later, likely due to catheter movement as the patient changes position. If venous cannulation occurs, blood often spontaneously appears in the epidural catheter. Gentle aspiration of the catheter may also reveal blood. It is important to keep in mind that an epidural catheter may be intravenous even when no blood is seen during aspiration through the catheter.

Epidural catheters can also be unknowingly placed in the intrathecal (or spinal) space. The local anesthetic dose required for typical spinal anesthesia is approximately 15% of the dose required for epidural anesthesia; therefore, if a typical epidural dose is unintentionally administered spinally, a rapid spinal block involving the phrenic nerve, all sympathetic nerve fibers, and the brainstem will occur. This is clinically termed total spinal anesthesia. Prevention of total spinal anesthesia is similar to the previous discussion of intravascular epidural catheters. Spontaneous flow of CSF can sometimes be observed from either the epidural needle or catheter. Epidural catheters can also be aspirated prior to administering medication, with the appearance of clear to blood-tinged fluid suggesting intrathecal placement.

Many clinicians use an initial test dose to identify intrathecal or intravenous placement. This test dose contains an amount of local anesthetic, which would provide a recognizable and safe spinal anesthetic if injected intrathecally, as well as epinephrine, which would signal intravenous placement through increased heart rate and blood pressure. Owing to the large differences in dose requirements, this dose of local anesthetic should be insufficient to cause a significant epidural block. A rapid rise in maternal heart rate suggests an intravascular catheter, while a significant sensory block developing 2-5 minutes after the test dose administration suggests an intrathecal catheter.

Epidural blocks that seem unusually high or “dense” also suggest unintentional spinal placement. As maternal heart rate also increases during active contractions, some clinicians recommend timing the test dose injection with the end of the previous contraction.

Even with this approach, interpretation of epinephrine test doses in the parturient can be challenging. Clinicians may choose to fractionate local anesthetic boluses given via the epidural catheter, dividing the intended dose into 3-4 smaller doses administered over 5-10 minutes in hopes of detecting improper catheter placement. Any previously functioning epidural catheter that suddenly becomes ineffective should be suspected of having migrated into an epidural vein.

As mentioned in Spinal anesthesia, accidental puncture of the dura with an epidural needle or intentional puncture of the dura during CSE can lead to a spinal headache. Epidural abscess, hematoma, and nerve damage are also rare but possible complications.

Combined spinal-epidural analgesia

It is possible to combine the advantages of spinal analgesia (fast onset of analgesia, profound potency of opioids delivered intrathecally) with the duration and flexibility of an epidural catheter. This is known as combined spinal-epidural analgesia (CSE). The technique adds the placement of intrathecal local anesthetic and opiate at the same time as the placement of the epidural catheter.

Most commonly, after the epidural needle has been advanced into the epidural space, as illustrated above, a spinal needle is advanced through the epidural needle into the intrathecal space, and a small amount of medication is injected. The spinal needle is removed, and an epidural catheter can then be threaded via the epidural needle, which still remains in the epidural space. Once the catheter is in place, the epidural needle is removed. The intrathecal medication provides immediate sacral analgesia, which is appropriate for parturients entering the second stage of labor. The epidural catheter can be used to as part of a PCEA, as described in Epidural analgesia.

Additional benefits of this option include decreased total neuraxial drug consumption due to minimal need for epidural medications in the first 2 hours after the spinal injection, an increased effectiveness of epidural medications after use of the CSE technique (presumably from facilitated epidural drug entry into the CSF via the dural opening produced during spinal placement), and a decreased unintentional dural puncture (“wet-tap”) rate with the epidural needle.

Several other favorable outcomes have been noted in relation to CSE. CSE labor analgesia is associated with faster cervical dilation than conventional epidural labor analgesia, perhaps owing to the minimal local anesthetic motor block that accompanies most CSEs. CSE techniques have a lower rate of epidural catheter replacement during labor than conventional epidural catheter placement. This outcome is probably consequent to confirmation of epidural needle location by obtaining CSF via the long spinal needle. Finally, failure of an epidural to provide adequate anesthesia for cesarean delivery is more likely after conventional epidural catheter placement than CSE.

Some disadvantages of CSE labor analgesia are apparent. It impairs the ability to evaluate the subsequent epidural dosing for unintended intrathecal spread. One of the major reasons to give an epidural test dose is to identify intrathecal placement of the epidural catheter. This test dose is usually accomplished by a small local anesthetic dose via the catheter and observing the patient for rapid development of spinal anesthesia.

Critics of CSE believe that, because the initial CSE dose is usually administered prior to placing the epidural catheter and results in rapid spinal analgesia, it is difficult to exclude the possibility of unintentional intrathecal placement of the epidural catheter. No clinical studies have been conducted to confirm or refute this critique. Another criticism of CSE analgesia is that ineffective epidural catheters are not discovered until the initial intrathecal block has dissipated, which is approximately 90 minutes after initiation of CSE labor analgesia. This is a clinical trade-off; there are fewer epidural block failures with CSE, but those that do occur are not immediately apparent.

Because of these drawbacks to the CSE technique, CSE has become the default procedure for labor analgesia in only 8% of US obstetric units. It is now largely reserved for situations in which a multiparous patient is near full dilation at the time of block placement. In this situation, the intrathecal drug produces sacral blockade and relieves the perineal pain caused by fetal head descent. These sacral dermatomes are not anesthetized in the early phase of epidural anesthesia.

Which are the causes of somatic pain in a client who is in the second phase of labor?

What interventions does the nurse perform to provide emotional support?

Which characteristic is associated with false labor contraction?