Perspective Chapter: Epidural Administration – New Perspectives and Uses

Abstract

Neuraxial techniques are commonplace in labor analgesia. Techniques for labor analgesia range from intrathecal and epidural anesthesia to peripheral nerve blocks, nitrous oxide, intravenous infusions, and acupuncture. The epidural approach is the most popular as it allows for local anesthetics to diffuse into the intrathecal space along with repeated or continuous doses of medication for labor and primary anesthetic for surgeries. The epidural technique affects differing spinal nerves (i.e., pain, autonomic, sensory, and motor) with varied effects depending on the concentration and volume of LA used. Adverse effects do exist following these techniques with hypotension being a major concern. A multitude of anesthetic agents can be given in the epidural; opioids are the most frequently used local anesthetic adjuvants. Alpha 2 adrenoreceptor agonists are also used as local anesthetic adjuvants. Although not performed routinely, peripheral nerve blocks play a complementary and supplementary role in epidural analgesia and anesthesia. There are absolute and relative contraindications to epidural anesthesia. Alternatives to neuraxial anesthesia that can be offered include infusion of ultrashort acting opioids, nitrous oxide, opioid agonist-antagonists, ketamine, TENS, and acupuncture. Local Anesthetic Systemic Toxicity may be more prevalent in the pregnant.

1. Introduction

Spinal anesthesia is a neuraxial anesthesia technique in which local anesthetic (LA) is placed directly in the intrathecal (i.e., subarachnoid) space and blocks transmission of pain by the spinal nerves. The subarachnoid space houses sterile cerebrospinal fluid (CSF), the clear fluid that bathes the brain and spinal cord. Spinal anesthesia is only performed in the lumbar area, specifically the mid to low lumbar levels to avoid damage to the spinal cord and to prevent intrathecally injected medications from having any activity in the upper thoracic and cervical regions.

Epidural anesthesia is also a neuraxial technique. However, the LA is placed ‘epi’ or outside the intrathecal space. The LA (for the most part) then diffuses to the intrathecal space. This allows for potentially repeated doses via a catheter. It also can be placed in other regions (i.e., thoracic and cervical) of the neuraxis as well. The epidural thus has a larger breadth of applicability and can provide pain relief to a multitude of patients including those in labor, those for pain management, and those having a variety of surgeries.

New and exciting developments include ultrasound guidance to help with proper and more rapid placement of epidurals, newer equipment and devices to deliver medication in an improved manner, and recommended adjuvants to enhance the quality and the duration of the epidural. In addition to these developments, this chapter will explore adjunctive therapies such as regional blocks and acupuncture.

2. Outline

This chapter will cover basic anatomic considerations, basic general and obstetric physiology, basic epidural techniques and position, ultrasound use for epidural placement, pharmacological drugs used in epidurals, complimentary and supplementary regional blocks with epidurals, other remedies when epidurals are not viable or fail, and local anesthesia systemic toxicity (LAST).

3. Anatomy

From innermost to outermost layers, going toward the skin posteriorly, the spinal cord is surrounded by pia, arachnoid, and dura mater (see Figure 1) [1]. The epidural space is next, but it is only a potential fat-filled space that is formed between the dura mater of the spinal cord and the ligamentum flavum of the posterior vertebral column (see Figure 2). The posterior vertebral column is made up of bone (vertebrae) and the intervertebral space that has the ligamentum flavum, the interspinous ligament, and, finally, the supraspinous ligament. The vertebral pedicles and intervertebral foramina form the lateral limits of the epidural space. Longitudinally, the epidural space extends from the foramen magnum to the sacral hiatus. The vertebral column consists of 7 cervical, 12 thoracic, and 5 lumbar vertebrae and the corresponding intervertebral spaces and the sacrum and coccyx.

Figure 1.

Spinal needle punctures dura mater for injection.

Figure 2.

Cross section view of vertebral body.

In adults, the spinal cord terminates at the level of the 1st and 2nd lumbar (L1–L2) vertebrae (see Figure 3) and is tethered to the coccyx. The spinal cord originates at L3, but after 1 year of age, the spinal cord moves upward (still tethered to the coccyx), creating a dural sac with CSF ending at the 2nd sacral vertebrae (S2) with many spinal nerves called the cauda equina. For safety, the epidural is placed below the L1–L2 vertebral interspace and above the sacrum that has no interspaces. The top of the iliac crest conveniently correlates with the L4–L5 interspace, and the L3–L4 or L4–L5 are the most common levels for insertion of the epidural. Problems with insertion include patients having scoliosis, osteophytes, calcifications, and diminished disc space because of vertebral fractures, to name a few.

Figure 3.

Side view of lumbosacral spine.

4. Physiology

The epidural technique involves numbing different spinal nerves (i.e., pain, autonomic, sensory, and motor) with varied effects depending on the concentration and volume of LA used. Regardless of which nerves are blocked, there is a physiologic consequence to blocking these nerves. In particular, hypotension is the major potential problem due to blocking the sensitive sympathetic fibers and causing vasodilation [2, 3]. This hypotension, if severe enough, may lead to decreased organ perfusion and in the extreme organ dysfunction.

Another problem is the level of spread of LA. If the spread is too high (i.e., rostral), the intercostal muscles may be blocked, leading to an uncomfortable feeling of not being able to take a deep breath. If the spread is too low (i.e., caudal), the urinary muscles may be blocked leading to difficulty in urinating. Thus, targeting the right level is important. This is especially so in the parturient population.

Parturients in labor are the largest group of patients receiving an epidural. Knowing the stages of labor gives more insight into the level of epidural analgesia required. The first stage of labor includes cervical dilation and uterine contractions. The neural signaling via the sympathetic chain will enter the spinal cord at T10 –L1 (Figure 4), causing visceral pain to the parturient. If the epidural is placed at the L3–L4 or L4–L5 interspace, a bolus of 10–15 ml of LA would be necessary to affect the appropriate level.

Figure 4.

Sensory innervation from lumbosacral plexus.

In the second stage of labor, the fetal head descends, and the pain becomes more somatic in nature, with vaginal and perineal stretching as the pain is transmitted through the pudendal nerves at S2–S4 (see Figure 4). If the epidural is placed at the L3–L4 or L4–L5 interspace, a bolus of 20–25 ml of LA would be necessary to affect the appropriate level.

5. Epidural techniques and position

As stated in the introduction, the epidural is used because a catheter can be placed in the epidural space, allowing redosing. There are at least two alternatives to the classic epidural. One involves the placement of an epidural catheter combined with a spinal block and is called a combined spinal epidural (CSE). The intrathecal dose is administered before the catheter is placed. In the other, an epidural catheter is again placed after a spinal puncture, but no actual intrathecal dose is given, and this is called a dural puncture technique (DPT).

The classic epidural involves the placement of a catheter in the epidural space, a bolus dose of medication, and continuous medication infused into the epidural space through a pump. The bolus dose may take a bit of time to work as it has to diffuse into the intrathecal space.

The CSE offers a quicker onset of pain relief with the continued advantage of analgesia from the epidural infusion. In addition, confirming the CSF through the spinal needle allows the provider to feel confident that he or she is in the correct spot when placing the epidural. This confirms that the loss of resistance is not false (discussed later). While there is a small chance of post dural puncture headache (PDPH) with the dural puncture, the use of a very small gauge needle for the spinal puncture will decrease the chance to almost negligible. The quicker onset of the CSE may lead to unwanted hypotension, though. This hypotension can be mitigated by adding fluids and the use of vasopressors like phenylephrine and ephedrine.

The DPT is a compromise between the classic epidural and the CSE and is quicker than the classic epidural but has less hypotension than the CSE.

Most practitioners find it easier to place the epidural in the sitting position. The patient’s midline can be easily determined in the sitting position. There are five layers that a practitioner must pass through from a midline position in order to get to the epidural space (see Figure 1). These layers are the skin, the subcutaneous fat, the supraspinous ligament, the interspinous ligament, and the ligamentum flavum. While sitting, spinal flexion and neutral rotation should be achieved to establish a straight path for needle insertion in the intervertebral space between the spinous processes. It is helpful to first feel the landmarks, which include the top of the iliac crests correlating to the L4–L5 interspace. Additionally, it helps to feel the spinous processes and trace them down from cervical to thoracic to lumbar to identify if the patient has any scoliosis or curvature, which may make the procedure more difficult. Once the interspace is identified, one can place a mark at the chosen location. It is important to clean the back well in a sterile fashion. Chlorhexidine has been found to be superior to betadine in recent studies and is recommended unless the patient has an allergy to chlorhexidine. Typically, chlorhexidine should be allowed to dry for at least three minutes. Next, the epidural kit should be set up while allowing the chlorhexidine to dry. The procedure starts with injecting LA liberally with a 3/8 inch 25-gauge needle in the skin and subcutaneous space to numb the area. A longer (i.e., 1 ½ inch) 25-gauge finder needle may be used to determine the location of the interspace past the subcutaneous tissue. The epidural needle, usually a 17-gauge blunt Tuohy needle with obturator in place, is advanced in the same plane as the finder needle and is seated in the interspinous ligament. The obturator is removed, and a glass saline-filled syringe is attached to the Tuohy needle, and the resistance of the ligament is felt, preventing any saline from being injected. The Tuohy needle–glass syringe assembly is advanced very slowly, feeling for resistance every 1–2 mm. When the ligamentum flavum is reached, there may be, but often not, a subtle change in resistance. After passing the ligamentum flavum, there is a sudden loss of resistance, and the saline can be easily injected.

After the loss of resistance is confirmed, the glass syringe is removed carefully, and an epidural catheter is threaded into the epidural space through the Tuohy needle. The epidural catheter is placed 4–6 cm beyond the Tuohy needle into the epidural space. After catheter placement, the Tuohy needle is removed with careful attention as to not remove the newly placed catheter.

There may be problems placing the epidural catheter. A false loss of resistance may be obtained if the resistance of the ligament is not very obvious because of patient characteristics and so on. The patient may have an altered or difficult anatomy preventing the midline approach. When a midline approach is difficult, a paramedian approach can be tried. In the paramedian approach, the needle should be inserted 1–2 cm lateral to the inferior tip of the posterior spinous process, corresponding to the vertebra above the desired interspace. The needle is then advanced horizontally until the lamina is reached and then redirected medially and cephalad to enter the epidural space [4].

While an intrathecal puncture with a very small gauge needle will usually not cause a PDPH, an intrathecal puncture with the large 17-gauge bore Tuohy needle will almost certainly cause a PDPH, which may result in exaggerated complications. An ultrasound device may be helpful in preventing this occurrence.

6. Use of ultrasound

The ultrasound is a helpful tool, as one can have direct vision while placing the epidural, or at least visualize the midline when it is not visible secondary to calcifications, spina bifida, or instrumentation. In cases of obese patients or patients with scoliosis, the ultrasound can be particularly useful.

Using the ultrasound, a practitioner may see the midline and the depth at which the loss of resistance should occur. This lessens the risks of false loss of resistance and incorrect placement in the obese patients and fewer unwanted dural punctures with the Tuohy needle and less chance of headache in the ultrathin patients. The ultrasound is a radiation-free technique and therefore may be safely used in the obstetric patients. In addition, Rivanna produces the Accuro, which is a handheld, portable ultrasound. The Accuro uses 3D as well as 2D technology to line up the intralaminar and the epidural space. The device allows for the depth of the epidural space to be noted, allowing easier epidural placement.

7. Medications

A multitude of anesthetic agents can be given in the epidural to provide analgesia or anesthesia for procedures or surgeries. LAs work by inhibiting conduction of nerve impulses, by binding to a subunit of the voltage-gated sodium channels and impairing nerve impulses. When the sodium ions are prevented from entering the cell, the nerve conduction is inhibited.

LAs are classified as either amides or esters [5]. Amides are more stable in solutions, whereas esters are less stable. The amino esters are hydrolyzed by pseudocholinesterase in plasma, while amides undergo enzymatic degradation by the liver and are excreted in the urine. Common amide Las include lidocaine, bupivacaine, and ropivacaine. Common ester anesthetics include procaine, chloropropane, and tetracaine. Esters generally cause a greater degree of allergic reactions, due to the metabolites of amino esters, like para-aminobenzoic acid, which can cause an immunological response.

LAs block different nerves depending on the concentration of the LAs and the size (i.e., sensitivity) of the nerve. The smallest nerves that are the most sensitive are the pain, temperature, and autonomic nerves. The medium nerves that are less sensitive are the sensory nerves. The large nerves that are fairly resistant are the motor nerves, and the largest and most resistant are the positional nerves. Epidural analgesia for labor usually requires a more dilute LA solution, while epidural anesthesia for cesarean section requires a more concentrated LA solution.

Lidocaine is the archetypical LA. At a concentration of 0.5%, a bolus of lidocaine will block transmission to the pain, temperature, and autonomic fibers. At a concentration of 1.0%, a bolus of lidocaine will block sensory fibers. At a concentration of 2.0%, a bolus of lidocaine will block motor fibers. However, there is an overlap, and at 0.5%, the bolus may affect some sensory fibers, and at 1%, the bolus may affect some motor fibers. An infusion of LA requires a lesser concentration for the same effect on the nerves and may be given continuously. An infusion of 0.25, 0.5, and 1% lidocaine will block the smaller, medium, and large nerves, respectively.

Lidocaine is of medium onset and lasts a medium duration of time. Bupivacaine is of slower onset but lasts much longer, while chloroprocaine is of fast onset but lasts a short time. 0.125, 0.25, and 0.5% bupivacaine boluses and 1, 2, and 3% chloroprocaine boluses correspond to lidocaine boluses. A 0.0625, 0.125, and 0.25% bupivacaine infusion and a 0.5, 1, and 2% chloroprocaine infusion correspond to a lidocaine infusion. Ropivacaine and levobupivacaine are the only commercially available single-enantiomer local anesthetics, these were initially developed as less cardiotoxic alternatives to bupivacaine [6].

The concentration and volume of LAs determine LAST (discussed later). A lesser concentration and hence safer mixture of LAs may be used if other drugs (namely, adjuvants) are added to the mix. Some adjuvants (i.e., bicarbonate) decrease the onset time; some adjuvants (i.e., epinephrine) prolong the duration of block; some adjuvants (i.e., opioids) enhance the analgesia.

By adding these adjuvants, it is possible to give such a dilute mixture of LAs that will allow the patient to ambulate and be pain-free with few side effects. This is known as a ‘walking’ epidural. There are many combinations of these mixtures. One such combination is ropivacaine 0.025% with fentanyl 3 mcg/ml and epinephrine 0.5 mcg/ml [7].

Also, not all infusions are the same. Rather than using the traditional continuous infusion techniques for labor, the new programmed intermittent epidural boluses (PIEBs) are thought to provide better analgesia and lower anesthesia requirements overall. The PIEB allows for the patient to get a spray of epidural medications, covering more dermatomes and adding to analgesic satisfaction and less motor block. Unlike the traditional continuous epidural infusions that deposit medication in the same location, the PIEB allows the epidural infusion to be spread over a greater area [8]. PIEB labor analgesia has a higher threshold for motor blockade because the intraneural concentration is reduced as local anesthetic diffuses out of the nerve between boluses.

Properties: Local anesthetics that have an increased lipid solubility are associated with enhanced diffusion through neuronal coverings and lower milligram dosage and hence higher potency. In contrast, those local anesthetics which are lipid-insoluble are more highly protein bound in the blood and have a longer duration [9]. The baricity of a local anesthesia is used to determine where the local anesthetic will spread in the intrathecal space. Dissociation constant determines the portion of the drug that stays in the lipid soluble tertiary molecular state (lower PKa) and hastens onset.

Opioids are the most frequently used local anesthetic adjuvants, and their use in neuraxial blocks has evolved over the last 50 years. The dose, site of injection, lipophilicity, and the acid-base milieu of the site of drug deposition determine the extent of efficacy of the block. They can be given intrathecally or epidurally. Typically, the epidural dose is 5–10 times the intrathecal dose as the epidurally placed drug must diffuse to the intrathecal space to work. The opioids used as adjuvants have differing properties. Morphine must be prepared as a preservative-free solution. The hydrophilic nature of neuraxial morphine results in cephalad spread, thereby increasing the area and duration of analgesia. However, the adverse effect of its use in neuraxial blocks includes respiratory depression (early and late), nausea, vomiting, pruritus, and urinary retention. Fentanyl has been shown to have a lesser prolongation of block compared with neuraxial morphine with a more favorable adverse effect profile. The addition of epinephrine to the fentanyl results in a slightly further prolongation with still better adverse-effect profile, especially less nausea. The use of epinephrine 1:1000 or 1:10000 along with lidocaine and fentanyl in spinal anesthesia in women candidates for C-section produced no statistically significant difference in the hemodynamic, post-operative nausea and vomiting and post-operative paralysis and pain relief [10, 11].

Epinephrine is a potent vasoconstrictor that decreases absorption into the vasculature. This results in an increase of duration of block and an increase in the systemic safety profile. It by itself may also add some analgesia.

Adding epinephrine to an LA with or without opioids allows for a more dilute LA solution, and in the extreme, the dilute concentration of an LA together with a dilute concentration of opioid allows a parturient to have pain relief (especially during the first stage of labor) with virtually no effect on the motor nerves. A ‘walking’ epidural can be sometimes be achieved with a solution of 0.0625% bupivacaine 2 mcg/ml of fentanyl and 5 mcg/ml of epinephrine.

Alpha 2 adrenoreceptor agonists (Clonidine, Dexmedetomidine) are also used as local anesthetic adjuvants. They act on postjunctional alpha-2 adrenoreceptor in the dorsal horn of spinal cord.

Neuraxially, they have a local effect on the blockage of sympathetic outflow, while peripherally, they prolong the duration of analgesia by hyperpolarization of cation channels [12]. Epidural clonidine in doses of 25–50 mcg/h has been found to have fewer side effects. Intrathecal administration of clonidine has evolved in terms of dosing from the initial phases of higher doses (i.e., 150 mcg) to routine use of lesser doses (i.e., 15–40 mcg) in present-day practice to avoid its cardiovascular adverse effects.

Dexmedetomidine is a 7-times more selective alpha-2 receptor agonist in comparison to clonidine and has a similar mechanism of blocking hyperpolarization activated cation channels. Intrathecal (5–10 mcg) and epidural dexmedetomidine (1 mcg/kg) as an adjuvant to isobaric bupivacaine or in combination with the commonly used LA has been investigated for its analgesic efficacy in various patient subsets. Its use has been associated with prolonged duration of block and improved postoperative analgesia without any associated hypotension or other adverse events, especially when used at doses less than 5 mcg. However, it is often associated with a higher incidence of bradycardia. Comparative evaluation of dexmedetomidine and clonidine has revealed the superiority of dexmedetomidine when used as an adjuvant for epidural or intrathecal administration.

Dexamethasone is a potent steroidal anti-inflammatory agent and can be used as an adjuvant. There is evidence to suggest that dexamethasone has analgesic properties in addition to increasing the duration of LA action.

8. Peripheral nerve blocks

Although not performed routinely, peripheral nerve blocks (PNBs) play a complementary and supplementary role in epidural analgesia and anesthesia.

The lumbar paravertebral block (PVB) is placed outside the dura mater by the paraspinal space and is used when a standard epidural is not or cannot be used. The typical dermatomal spread for a single-level block with an injected volume of 5 mL is four dermatomal levels. A bilateral PVB at the T12–L1 level is used for a cesarean section. In addition, visceral pain can be treated with a paravertebral sympathetic block (PSB) that prevents pain from uterine innervation via the preganglionic and postganglionic sympathetic fibers of the superior and inferior hypogastric plexus (branches of the hypogastric nerve).

The major advantage of paravertebral nerve blocks is that analgesia can be provided in patients for whom neuraxial analgesia could be complicated, such as neuraxial anatomical abnormalities or spine surgery with instrumentation. The duration of analgesia with typical agents is 9–12 h.

The transversus abdominis plane (TAP) block is a field block of the thoracolumbar nerves that run in the fascial plane between the internal oblique muscle and the transversus abdominis muscles (Figure 5), the anterior primary rami course between the internal oblique and the transversus abdominis muscles, and, subsequently, branch into the lateral and anterior cutaneous nerves at approximately the midaxillary line. It is used to complement a neuraxial block. The major disadvantage is that it does not provide visceral analgesia. This omission explains why many studies have failed to show the superiority of TAP or give mixed results when compared with standard multimodal analgesia.

Figure 5.

Illustration of transversus abdominis plane (TAP) block.

The quadratus lumborum block (QLB) is also a field block of the thoracolumbar nerves but is placed more laterally (Figure 6). Its posterior spread into the paravertebral space can potentially affect the sympathetic chain, conferring some visceral as well as somatic analgesia. The QLB seems to have a greater dermatomal spread than the TAP block.

Figure 6.

Quadratus lumborum block.

The disadvantage of the block is that it is more difficult than a TAP block, and it has greater systemic absorption through the highly vascularized muscle bed, potentially causing local systemic anesthetic toxicity.

An erector spinae plane block (ESPB) involves truncal deposition of LA in the plane anterior to the erector spinae muscles and superficial to the transverse processes of thoracic or lumbar vertebrae, resulting in considerable spread in both cephalo-caudad and medial-lateral directions. This is a complementary block for neuraxial anesthesia after cesarean section.

The disadvantage of this block is that it is difficult to place.

A paracervical block is a supplementary block for the first stage of labor when a neuraxial block is inadequate. It can be placed by the obstetric team especially if a neuraxial block team is unavailable (Figure 7).

Figure 7.

Illustration of paracervical block.

The disadvantage of the paracervical block is that it has a high incidence of fetal bradycardia, and it does not help with the second stage of labor.

A pudendal nerve block is a supplementary block for the second stage of labor when a neuraxial block is inadequate. It too can be placed by the obstetric team especially if a neuraxial block team is unavailable.

The disadvantage of the pudendal block is that it alone does not provide reliable analgesia for the second stage of labor as both the cervical and pudendal nerves must be blocked. However, the block is useful for episiotomy and repair (Figure 8).

Figure 8.

Illustration of pudendal nerve block.

Liposomal bupivacaine may also be used for the peripheral nerve blocks. Liposomal bupivacaine is a prolonged-release (up to 72 h) formulation of bupivacaine approved by the US Federal Drug Administration for postoperative analgesia by single-dose infiltration. It is expensive to use, and not many centers approve its use (Figure 9).

Figure 9.

Different block levels for labor analgesia.

9. When you need something besides an epidural

There are both absolute and relative contraindications to epidural anesthesia. The absolute contraindications include patient refusal, localized sepsis in the area where the neuraxial anesthesia is to be performed, an allergy to the medications used [13, 14], and severe coagulopathy such as disseminated intravascular coagulation.

Thrombocytopenia has previously been considered a contraindication for neuraxial anesthesia; however, recently, the consensus regarding platelets has been changing. Rather than looking at an absolute number, the overall platelet trend can help to determine if a patient is a good candidate for neuraxial anesthesia. In 2016, the ASA practice guidelines for obstetric anesthesia stated that it is unnecessary to have a routine platelet count for a healthy parturient [9]. Coagulation profile is also not recommended unless the parturient has a history of coagulopathy, preeclampsia, or HELLP syndrome. While there is no minimum platelet count, 70,000 platelet count has been an acceptable number [15, 16].

Relative contraindications include generalized fever or infection, spina bifida, multiple sclerosis, anticoagulation, central nervous system disorders and preload dependent states (i.e., aortic stenosis), previous back surgery or instrumentation, placement in anesthetized adults, and needle placement through a tattoo [17].

An ultrashort acting opioid such as remifentanil may be used. Remifentanil is rapidly metabolized by serum and tissue cholinesterases and consequently has an acceptable level of maternal side effects with minimal or no fetal side effects.

Nitrous oxide (N2O) may also be used especially in countries where neuraxial analgesia is unavailable. Remifentanil may offer better pain relief than nitrous oxide with fewer side effects. However, N2O can still be used.

N2O is a nonflammable, tasteless, and odorless gas. N2O is always delivered with oxygen in a 50:50 mixture. It can be used for the first and second stages of labor as well as during postdelivery procedures such as laceration repair, manual removal of the placenta, and uterine curettage. It may also facilitate the initiation of epidural analgesia. N2O is self-administered and has a rapid onset of 30 to 50 seconds. N2O administration is intermittent and delivered via face mask. The patient’s inhalation triggers the opening of a negative pressure demand valve and is timed by the patient to coincide with uterine contractions. Anecdotal reports have noted the patient report of greatest relief when the woman begins inhalation approximately 30 seconds prior to the start of her contraction. This pattern of inhalation allows for peak serum levels of N2O to coincide with the peak of the uterine contraction. Offset is rapid, with elimination of the N2O by exhalation occurring within a few minutes of discontinuation. It is important that the N2O be administered by the patient herself using a handheld face mask; no straps or other devices should be used to secure the mask to the patient’s face that could lead to excessive drowsiness. Learning the correct technique by practicing with the first few contractions is important in order to maximize results. Patient satisfaction and success with therapy can be enhanced by thorough teaching with a focus on the timing of breathing. Pain relief is less effective than with neuraxial analgesia utilizing local anesthetics.

Environmental pollution can occur with the use of N2O, and a scavenger system is required. Increased access to N2O services in hospitals and birth centers has long been advocated by the midwifery profession. A position statement on Nitrous Oxide for Labor Analgesia issued by the American College of Nurse-Midwives in 2009 advocates for the availability of N2O to all laboring women and recommends that all certified nurse-midwives and certified midwives be trained “to administer and oversee safe use of N2O analgesia during labor” [18]. The American Society of Anesthesiology and the American Congress of Obstetricians and Gynecologists do not currently have any position statements regarding N2O use for labor analgesia.

Inability to obtain CSF, sometimes referred to as a ‘dry tap’, is one of the causes of failure of the intrathecal portion of a CSE or DPT. A failed lumbar puncture is usually because of poor positioning of the patient or incorrect needle insertion, both factors being within the control of the anesthetist. Abnormalities of the spine (kyphosis, scoliosis, calcification of ligaments, and consequences of osteoporosis), obesity, and patient anxiety make both positioning the patient and needle insertion more difficult. The appearance of clear fluid at the needle hub is usually the final confirmation that the subarachnoid space has been entered. Intrathecal spread is governed by the interplay between solution, physical characteristics, gravity, and the configuration of the vertebral canal. Anatomical abnormalities can lead to problems with spread. The curves of the vertebral column are integral to solution spread, and any obvious abnormality, kyphosis, or scoliosis may interfere with the process. The epidural should hopefully still work, but analgesia may be delayed.

Systemic medications may also be used if the epidural is inconvenient or has failed. Opioid agonist-antagonists, such as butorphanol and nalbuphine, have also been used for obstetric analgesia when an epidural is inconvenient or has failed. These analgesic drugs may have a lower incidence of nausea and vomiting [19]. Butorphanol is probably the most popular of the mixed agonist-antagonists. A disadvantage is a high incidence of maternal sedation. The recommended dose is 1–2 mg by IV or IM injection.

Nalbuphine 10 mg IV or IM is an alternative to butorphanol.

Ketamine is another analgesic drug that is often used specifically if the epidural is ‘patchy’ or incomplete. In low doses (0.2–0.4 mg/kg), ketamine provides analgesia without causing neonatal depression. However, ketamine has sedative and amnestic properties that may be troublesome for the parturient.

Alternate techniques such as TENS and acupuncture in labor have been tried, but the results are at best mixed. One controlled study comparing acupuncture to no treatment for labor pain concluded that acupuncture was not effective, but a non-controlled study (i.e., without a comparator) on a larger population concluded that acupuncture was effective [20]. Acupuncture has been shown to be helpful in alleviating anxiety even in laboring patients.

10. Local Anesthetic Systemic Toxicity (LAST)

For obstetric patients, LAST may be more prevalent than the nonpregnant population secondary to decreased protein binding, increased tissue blood flow, and vascular engorgement. Data suggest that up to 20 out of 10,000 peripheral nerve blocks and 4 out of 10,000 epidural blocks result in systemic local anesthetic toxicity [21].

The systemic toxicity initially manifests as central nervous system toxicity. The patient may feel lightheaded, dizzy, have ringing in the ears, and trouble focusing. As the systemic toxicity progresses, excitatory symptoms such as shivering, tremors, muscle twitching, and even seizures appear, resulting from an initial blockade of inhibitory pathways by the local anesthetic drugs [17]. As the toxicity progresses further, cardiac manifestations appear. This may result in severe hypotension, atrioventricular conduction delay, idioventricular rhythms, and, eventually, cardiovascular collapse [7].

Local anesthetic toxicity is difficult to treat, and lipid containing solutions to absorb the local anesthetic are used. In particular, Intralipid, a 20% fat emulsion, is used.

Also, the seizure threshold can be raised by giving a small dose of benzodiazepine such as midazolam, if CNS toxicity is suspected.