1 What are the most commonly used parenteral opioids for labor analgesia? Which side effects are of special concern to the parturient?

Table 60-1 summarizes commonly used parenteral opioids and their side effects. In general, intravenous medications help the parturient tolerate labor pain but do not provide complete analgesia. The incidence of side effects and efficacy of analgesia are dose dependent. Maternal sedation and nausea are common. Opioids easily cross the placenta and may cause a decrease in fetal heart rate variability. In addition, intravenous opioids may cause neonatal respiratory depression and neurobehavioral changes.

2 What advantages does PCA offer over conventional intermittent bolus dosing?

Patient-controlled analgesia (PCA) has been associated with greater patient satisfaction, less risk of maternal respiratory depression, less need for antiemetic use, and better pain relief despite lower drug doses. PCA is especially useful if epidural anesthesia is contraindicated or not available. The most experience has been gained with meperidine and fentanyl using the regimens noted in Table 60-1.

3 Discuss the benefits of epidural analgesia for labor and delivery

In most laboring women epidural analgesia provides the most effective pain relief and reduces maternal catecholamine levels, potentially improving uteroplacental perfusion. Epinephrine and norepinephrine secretion increase as a result of painful contractions and may prolong labor by decreasing uterine contractility through their β-agonist activity. Painful contractions may also lead to maternal hyperventilation and respiratory alkalosis, which in turn shifts the oxyhemoglobin dissociation curve to the left, decreasing delivery of oxygen to the fetus. Most important, the benefits of enhanced maternal well-being with adequate analgesia and the risk of posttraumatic stress symptoms caused by inadequate analgesia should not be underestimated.

4 What are the indications and contraindications for epidural analgesia during labor and delivery?

Relief of labor-induced pain is sufficient reason for placing an epidural catheter. Analgesia can be readily converted to anesthesia by increasing the local anesthetic concentration, thus facilitating forceps or cesarean delivery. Labor analgesia benefits patients with hypertension and some types of cardiac disease (e.g., mitral stenosis) because it blunts the hemodynamic effects that accompany uterine contractions (increased preload, tachycardia, increased systemic vascular resistance, hypertension, and hyperventilation). The contraindications to epidural anesthesia include patient refusal, coagulopathy, uncontrolled hemorrhage, and infection at the site of needle introduction. Relative contraindications include systemic maternal infection, elevated intracranial pressure, prior spinal instrumentation with hardware, and certain neurologic diseases.

5 Discuss the importance of a test dose and suggest an epidural test dose regimen. When and why is this regimen used?

The test dose is used to diagnose subarachnoid or intravenous placement of the epidural catheter, thereby preventing total spinal anesthesia or systemic toxicity from local anesthetics. A common test dose is 3 ml of 1.5% lidocaine (45 mg) with 1:200,000 epinephrine (15 mcg). If the test dose of local anesthetic is administered, subarachnoid, motor, and sensory block will appear within 3 to 5 minutes. If the test dose is injected intravenously (IV), tachycardia results within 45 seconds (increase in heart rate of 30 beats/min) because of the epinephrine additive. Every time an epidural catheter is injected, it is a test dose of sorts; always monitor for signs of possible intravenous or subarachnoid local anesthetic injection. Aspiration of the catheter may not be adequate to identify all intrathecal or intravascular catheters. If there is any doubt in the practitioner’s mind about the exact location of the epidural catheter, the catheter should be removed and replaced.

6 What are the characteristics of the ideal local anesthetic for use in labor? Discuss the three most common local anesthetics used in obstetric anesthesia. How does epinephrine affect the action of local anesthetics?

The ideal local anesthetic for labor would have rapid onset of action, minimal risk of toxicity, minimal motor blockade with effective sensory blockade, and a minor effect on uterine activity and placental perfusion. Bupivacaine and ropivacaine are most commonly used for obstetric epidural analgesia. Lidocaine and chloroprocaine are most commonly used for obstetric surgical anesthesia.

Bupivacaine, an amide, is the most commonly used local anesthetic for obstetric analgesia. Pain relief after epidural injection is first noted by the patient after 10 minutes; 20 minutes is required to achieve peak effect. Analgesia usually lasts approximately 2 hours. Dilute solutions provide excellent sensory analgesia with minimal motor blockade. During early labor 0.125% bupivacaine or even lower concentrations is often adequate, whereas a 0.25% concentration may be required during the active phase of labor. Because bupivacaine is highly protein bound, its transplacental transfer is limited. Addition of epinephrine (1:200,000) to bupivacaine speeds its onset and lengthens its duration of action but also increases the intensity of motor blockade (which is not desirable in laboring patients).

Lidocaine is also an amide local anesthetic used in concentrations of 0.75% to 1.5% for sensory analgesia, but it crosses the placenta more readily than bupivacaine and produces more motor block than bupivacaine; thus it is rarely used outside the operating room. Analgesia lasts approximately 45 to 90 minutes and is usually apparent within 10 minutes.

2-Chloroprocaine is an ester local anesthetic. Onset of analgesia is rapid and lasts approximately 40 minutes; this short duration limits its usefulness in labor. Chloroprocaine 3% is frequently used to increase the anesthetic level quickly for cesarean section or instrumental vaginal delivery. Chloroprocaine has a very short half-life in maternal and fetal blood because it is metabolized by plasma esterase; thus it may be the safest of the commonly used local anesthetics.

7 Describe the properties and benefits of ropivacaine in obstetric anesthesia

Ropivacaine is slightly less potent than bupivacaine; therefore concentrations of 0.1% to 0.2% are used during labor. Onset, duration, and sensory block are similar to equipotent doses of bupivacaine. Motor blockade is slightly less than bupivacaine and may be an advantage. It has less cardiotoxicity (if inadvertently injected intravenously) because it binds less avidly to sodium channels of cardiac conduction tissue. Ropivacaine costs significantly more than bupivacaine.

8 Name three methods for administering epidural analgesia. State the concerns associated with each

Intermittent injection requires that the catheter be checked for migration into the subarachnoid space or a blood vessel via aspiration and a repeat test dose. After multiple injections the patient may develop intense motor blockade.

Epidural analgesia may also be maintained by continuous infusion of dilute local anesthetic (with or without added opioid). The benefits of this method include:

Maintenance of a stable level of analgesia

Stable maternal hemodynamics

Improved patient satisfaction

The patient should be assessed regularly for adequacy of analgesia and lack of motor blockade. The infusion pump should be different from that of intravenous infusion lines, and infusion tubing should be free of side ports to minimize the chance of accidental injection of other substances into the epidural space.

With patient-controlled epidural anesthesia (PCEA), the patient may deliver small incremental doses in addition to a programmed background infusion to control the level of analgesia. PCEA usually results in greater patient satisfaction and less total dosage of drug than other techniques. As with a continuous infusion, the patient should be checked frequently for degree of analgesia and motor blockade.

9 Discuss the complications of epidural anesthesia and their treatments

Hypotension (a decrease in systolic pressure of 20% to 30% from baseline) may accompany epidural local anesthetic administration and result in decreased uteroplacental perfusion and fetal distress. Hypotension results from sympathetic blockade, peripheral venodilation, and decreased venous return to the heart. Treatment includes volume expansion and placement of the mother in the full lateral position. Phenylephrine (50 to 100 mcg) or ephedrine (5 to 10 mg intravenously) should be administered if blood pressure does not promptly return to normal. In the absence of evidence of uteroplacental insufficiency, phenylephrine is currently the favored choice for many.

Limited spread or patchy blocks may occur as a result of septa within the epidural space, or the catheter may pass into spinal nerve foramina, similarly limiting spread.

Intravenous local anesthetic injection may produce dizziness, restlessness, tinnitus, seizures, and loss of consciousness. Cardiovascular (CV) collapse may follow central nervous system (CNS) symptoms. Bupivacaine CV toxicity secondary to large intravenous doses is especially severe and may be fatal. To treat local anesthetic toxicity:

Give the patient 100% oxygen and intubate if necessary (to oxygenate, hyperventilate, and protect the airway).

Stop convulsions with a barbiturate or a benzodiazepine.

Support blood pressure (intravenous fluids and pressors).

Use cardiopulmonary resuscitation and advanced cardiac life support protocols as necessary.

Treat bradycardia with atropine.

Treat ventricular tachycardia with amiodarone.

Treat ventricular fibrillation with vasopressin, epinephrine, and defibrillation.

Consider administration of intralipid to act as a lipid “sink” to bind the local anesthetic and remove it from the maternal circulation.

Deliver the fetus if an effective rhythm is not restored within 5 minutes so more effective cardiopulmonary resuscitation can be provided to the mother.

The incidence of unintentional dural puncture is about 1% to 8%. If cerebrospinal fluid (CSF) is noted, the needle may be removed, and the epidural catheter placed at an alternate interspace. Local anesthetic subsequently injected epidurally may pass into the subarachnoid space and result in a block that is unexpectedly high or dense. Alternatively the epidural catheter can be threaded through the dural hole at the time of puncture, and a continuous spinal anesthetic can be provided. Leaving the spinal catheter in place for 24 hours may decrease the incidence of headache.

The incidence of an unexpected high block or total spinal block is approximately 1 in 4500 lumbar epidurals during labor. Risk is minimized by aspirating the catheter and giving a test dose each time the catheter is bolused. The signs and symptoms of a total spinal block include hypotension, dyspnea, inability to speak, and loss of consciousness. Treatment includes intubation, oxygen administration, ventilation, and support of maternal circulation with pressors.

10 Explain the mechanism of action of intrathecal and epidural opioids. What effect do they have on pain perception, sympathetic tone, sensation, and movement?

Opioids administered intrathecally or epidurally provide excellent analgesia without appreciably affecting sympathetic tone, sensation, or voluntary motor function. Opioids given via these routes bind to presynaptic and postsynaptic receptor sites in the dorsal horn of the spinal cord (Rexed’s laminae I, II, and V), altering nociceptive transmission. Some of the effects of lipid-soluble opioids may be caused by their systemic absorption.

11 What opioids are used to provide spinal and epidural analgesia during labor? Name their most common side effects. Do they provide adequate analgesia for labor and delivery when used alone?

The most commonly used neuraxial (spinal and epidural) opioids are fentanyl and sufentanil (Table 60-2). Pruritus, nausea, and vomiting are the most common side effects; delayed respiratory depression is the most serious complication, although very uncommon in this population. Intrathecal or epidural opioids alone may provide adequate relief for the early stages of labor, but they are unreliable in producing adequate analgesia for the active phase of labor. Very high doses of epidural opioids are required, which leads to excessive side effects. Concurrent administration of local anesthetic is necessary for late cervical dilation and delivery of the infant.

TABLE 60-2 Opioids used to Provide Intrathecal (Spinal) Analgesia During Labor

12 Is there a cause-and-effect relationship between epidural anesthesia and prolonged labor or operative delivery?

No. This issue was highly controversial. It has been reported that epidural analgesia is associated with prolonged labor and increased operative delivery, but recent studies do not support this assertion. Although epidural labor analgesia may prolong the second stage by about 30 minutes, there appears to be no harm to mother or fetus, and the American College of Obstetricians and Gynecologists (ACOG) recommends allowing an extra hour of pushing for mothers with an epidural block in place. ACOG has stated that: “Neuraxial analgesia techniques are the most effective and least depressant treatments for labor pain … more recent studies have shown that epidural analgesia does not increase the risks of cesarean delivery.”

13 Relate the advantages and disadvantages of spinal anesthesia for cesarean section. Which drugs are frequently used in the technique?

Spinal anesthesia produces a dense neural blockade; it is relatively easy to perform, has a rapid onset, and carries no risk of local anesthetic toxicity. The development of small-gauge, noncutting needles has significantly reduced the incidence of postdural-puncture headache (PDPH) to 1% or less. Hypotension can be treated by rapid hydration (1 L colloid or 1 to 2 L crystalloid), positioning to avoid aortocaval compression, and use of phenylephrine (50 to 100 mcg) or ephedrine (5 to 10 mg IV) if blood pressure does not improve with these measures. Commonly used drugs for spinal anesthesia are summarized in Table 60-3.

TABLE 60-3 Drugs used for Spinal Anesthesia for Cesarean Section

14 What are the advantages and disadvantages of cesarean section with epidural anesthesia vs. spinal anesthesia? What are the most commonly used local anesthetics?

If epidural analgesia is used for pain relief during labor and delivery, higher concentrations of local anesthetics can provide surgical anesthesia. The local anesthetic should be given in increments, titrating to the desired sensory level. Titration of local anesthetic results in more controlled sympathetic blockade; thus the risk of hypotension and reduced uteroplacental flow may be decreased. Typically epidural anesthesia produces less intense motor and sensory blockade than spinal anesthesia.

Disadvantages of epidural anesthesia include slower onset, larger local anesthetic dose requirement, occasional patchy block unsuitable for surgery, and the risk of total spinal anesthesia or systemic toxicity if the epidural catheter migrates subarachnoid or intravascular. Unintentional dural puncture may occur, and 50% to 85% of such patients experience headache. Drugs commonly used for cesarean section are 0.5% bupivacaine, 0.75% ropivacaine, 2% lidocaine, or 3% chloroprocaine. Epinephrine (1:200,000) may be added to prolong the duration of the block, decrease vascular absorption of the local anesthetic, and improve the quality of the block. The addition of epinephrine to a local anesthetic does not appear to affect uterine blood flow adversely, and it decreases the risk of maternal toxicity. Opioids enhance intraoperative analgesia and provide postoperative pain relief.

15 How is combined spinal/epidural anesthesia performed? What are its advantages?

The practitioner first finds the epidural space by loss-of-resistance technique with a Touhy needle. Subsequently a long (120 mm), small-gauge (24 to 27 G), noncutting spinal needle is advanced through the epidural needle until the dura is punctured and clear CSF is noted. A spinal dose of local anesthetic (plus narcotic, if desired) is injected into the subarachnoid space, and the spinal needle is removed. The epidural catheter is subsequently threaded into the epidural space. Small doses of spinal local anesthetics and opioids provide rapid and reliable analgesia for much of stage 1 labor. Epidural infusion of dilute local anesthetic and opioid will maintain analgesia. This technique does not increase the risk of PDPH over epidural analgesia alone.

16 List the indications for general anesthesia for cesarean section

Extreme fetal distress (in the absence of a functioning epidural catheter)

Significant coagulopathy

Inadequate regional anesthesia

Acute maternal hypovolemia/hemorrhage

Patient refusal of regional anesthesia

17 What concerns the practitioner when administering general anesthesia for cesarean section? How is it performed?

The obstetric population is at greater risk for difficult intubation, rapid oxygen desaturation, and aspiration of gastric contents. The goal is to minimize maternal risk and neonatal depression. This goal is accomplished by following certain guidelines. After monitors are placed, while the patient is being preoxygenated, the abdomen is prepared and draped. When the obstetricians are scrubbed in and ready to make their skin incision, rapid-sequence induction with cricoid pressure is performed, and incision occurs after correct endotracheal tube placement is verified. Frequently used induction agents include thiopental, ketamine, propofol, or etomidate. Succinylcholine is the muscle relaxant of choice for most patients (1 to 1.5 mg/kg). To prevent maternal awareness until the neonate is delivered, a combination of 50% nitrous oxide in oxygen is used with a low end-tidal concentration of a halogenated agent (0.5 minimum alveolar concentration). Larger concentrations of a volatile agent may cause relaxation of the uterus and excessive bleeding.

After delivery of the child, the concentration of nitrous oxide is increased, and opioids are administered. Benzodiazepines and muscle relaxants may also be used at the practitioner’s discretion. The concentration of the volatile agent is decreased if uterine atony appears to be a problem. Oxytocin (Pitocin) is also administered to facilitate uterine contraction. At the conclusion of the procedure the patient is extubated after thorough orogastric and airway suctioning and after the patient has demonstrated return of strength and mentation.