Obstetrical Analgesia and Anesthesia
BS. Nguyễn Hồng Anh
Obstetrical anesthesia presents unique challenges. Labor begins without warning, and anesthesia may be required within minutes o a ull meal. Vomiting with aspiration o gastric contents is a constant threat. Te usual physiological adaptations o pregnancy require special consideration, especially with disorders such as preeclampsia, placental abruption, or sepsis. Obstetrical analgesia and anesthesia have become extraordinarily sae over the past 40 years (Hawkins, 2011). Anestheticrelated maternal mortality rates decreased more than 60 percent during this time, and rom 2007 to 2017, only 0.4 percent o 6765 maternal deaths were due to anesthesia complications (Petersen, 2019). Creanga and colleagues (2017) reported the contribution o anesthetics to pregnancy-associated deaths has declined markedly in the United States (Fig. 25-1). Approximately two thirds o deaths associated with general anesthesia were caused by induction problems or intubation ailures during cesarean delivery. Deaths associated with regional analgesia were caused by spinal or epidural blocks reaching higher than planned spinal levels—26 percent; respiratory ailure—19 percent; and drug reaction—19 percent. O actors contributing to improved obstetrical anesthesia saety, the increased use o regional analgesia or labor and delivery is the most signicant. For general anesthesia, the improved case-atality rate is especially notable considering that this method is now used or the highest-risk patients and or emergencies with decision-incision intervals <15 minutes (Bloom, 2005). In addition, the incidence o aspiration, hypoxia, or other respiratory events has declined during the past three decades.
Tis is likely due to use o dicult-airway algorithms, advanced airway equipment, and increased in-house anesthesia stang (Davies, 2017; Lim, 2018). Despite these encouraging results with general anesthesia, rising complications with regional analgesia techniques are now reported (Davies, 2017).
GENERAL PRINCIPLES
■ Obstetrical Anesthesia Services
Every obstetrician should be procient in local and pudendal analgesia or select circumstances. However, it is preerable or an anesthesiologist or anesthetist to provide rapid and reliable pain relie to allow the obstetrician to ocus attention on the laboring woman and her etus.
Te American College o Obstetricians and Gynecologists (2019b) and the American Society o Anesthesiologists (2016) have rearmed prior directives that a woman’s request or labor pain relie is sucient indication or its provision. Identication o any o the risk actors shown in Table 25-1 should prompt consultation and collaboration with anesthesia personnel. Te resulting plan should ideally minimize the need or emergency anesthesia in this high-risk group. Goals or optimizing obstetrical anesthesia services have been established by the American College o Obstetricians and Gynecologists (2019b) and the American Society o Anesthesiologists (2016). o achieve these goals, the ollowing is a partial list o requisites:
1. Availability o a licensed practitioner credentialed to administer an appropriate anesthetic whenever necessary and to maintain support o vital unctions in an obstetrical emergency
2. Availability o anesthesia personnel to permit the start o cesarean delivery within 30 minutes o the decision to per- orm the procedure (decision–incision time)
3. Anesthesia personnel immediately available to support an emergency cesarean delivery during the active labor o a woman attempting vaginal birth ater prior cesarean (Chap. 31, p. 578)
4. Appointment o a qualied anesthesiologist to be responsible or all anesthetics administered
5. Availability o a qualied physician with obstetrical privileges to perorm operative vaginal or cesarean delivery during anesthesia administration
6. Availability o equipment, acilities, and support personnel equal to that provided in a surgical suite
7. Immediate availability o personnel, other than the surgical team, to assume responsibility or resuscitation o a depressed newborn (Chap. 32, p. 586).
o meet these goals, 24-hour in-house anesthesia stang is usually necessary. Providing such service in smaller acilities is more challenging. Tis is underscored by the act that approximately 40 percent o all hospitals providing obstetrical care have ewer than 500 deliveries per year (American Academy o Pediatrics, 2017). Bell and coworkers (2000) calculated the nancial burden that may be incurred to provide 24/7 obstetrical anesthesia coverage. Tey concluded that such coverage could not operate protably at their tertiary reerral institution, given the average indemnity and Medicaid reimbursement or labor epidural analgesia. Compounding this burden, some third-party payers have denied reimbursement or epidural analgesia in the absence o a specic medical indication—an approach repudiated by the American College o Obstetricians and Gynecologists (2019b).
■ Principles of Pain Relief
Labor pain caused by uterine contractions and cervical dilation is transmitted through visceral aerent sympathetic nerves entering the spinal cord rom 10 through L1. Later, perineal stretching transmits painul stimuli through the pudendal nerve and sacral nerves rom S2 through S4. Cortical responses to pain and anxiety are complex and may be infuenced by multiple actors.
Labor pain is a highly individual response to variable stimuli that are uniquely received and interpreted (Hawkins, 2010). Tese stimuli are modied by emotional, motivational, cognitive, social, and cultural circumstances. Specic modiers are maternal expectations or her childbirth experience, age, antepartum labor education, and quality o emotional support. Major causes o dissatisaction with pain relie are perceived labor pain and delay in ameliorating the pain (Yurashevich, 2019).
A mother’s physiological responses to labor pain may infuence maternal and etal well-being and labor progress. First, a higher metabolic rate leads to more oxygen consumption and the resultant hyperventilation may induce hypocarbia. Second, the sympathetic nervous system response to pain leads to elevated circulating catecholamine levels. Tese in turn raise cardiac output and vascular resistance, which may raise maternal blood pressure. Catecholamines also directly can adversely aect uterine activity and uteroplacental blood fow. Last, pain, stress, and anxiety cause release o stress hormones such as cortisol and endorphins. Eective analgesia attenuates or eliminates these responses.
ANALGESIA AND SEDATION DURING LABOR
I uterine contractions cause discomort, pain relie with a narcotic such as meperidine, plus an antiemetic tranquilizer such as promethazine, is appropriate. With a successul program o analgesia and sedation, discomort usually is elt at the acme o a uterine contraction, and the mother can rest quietly between contractions. Appropriate drug selection and administration rom the medications shown in Table 25-2 saely accomplishes these objectives.
■ Parenteral Agents
Meperidine and Promethazine
Meperidine, 50 to 100 mg, with promethazine, 25 mg, may be administered intramuscularly (IM) at intervals o 2 to 4 hours. Analgesia is maximal 30 to 45 minutes ater an IM injection. An almost immediate eect is achieved by giving meperidine intravenously (IV) in doses o 25 to 50 mg every 1 to 2 hours. In an earlier study, meperidine was ound to be the most common opioid used worldwide or pain relie in labor (Bricker, 2002). sui and associates (2004) ound meperidine to be superior to placebo or pain relie in the rst stage o labor. In a randomized investigation at Parkland Hospital, IV patient-controlled analgesia (PCA) with meperidine was ound to be an inexpensive and reasonably eective method or labor analgesia (Sharma, 1997). Women received 50-mg meperidine with 25-mg promethazine IV as an initial bolus. Tereater, an inusion pump was set to deliver 15 mg o meperidine every 10 minutes as needed until delivery. Neonatal sedation, as measured by need or naloxone treatment in the delivery room, was identied in 3 percent o newborns.
Meperidine readily crosses the placenta, and its depressant eect in the etus closely ollows peak maternal analgesia. Te active metabolite o meperidine, normeperidine, has a hal-lie o approximately 72 hours in the neonate. Tereore, other opioids discussed below are avored or labor analgesia. (American College o Obstetricians and Gynecologists, 2019b).
Butorphanol
Tis synthetic opioid-receptor agonist-antagonist narcotic, given in 1- to 2-mg IV doses every 4 hours as needed, compares avorably with meperidine or labor analgesia. Its major side eects are somnolence, dizziness, and dysphoria. Neonatal respiratory depression is less than with meperidine. Importantly, the two drugs are not given contiguously because butorphanol antagonizes the narcotic eects o meperidine. Hatjis and Meis (1986) described a transient sinusoidal etal heart rate pattern ollowing butorphanol administration, but no short-term maternal or neonatal adverse sequelae were noted (Chap. 24, p. 451).
Fentanyl
Tis short-acting and potent synthetic opioid may be given in doses o 50 to 100 µg IV every hour. Its main disadvantage is a short duration o action, which requires requent dosing or use o a PCA pump. Atkinson and coworkers (1994) reported that butorphanol provided better initial analgesia than entanyl and was associated with ewer requests or additional medication or or epidural analgesia.
Remifentanil
Tis ultrashort-acting opioid can be given using a PCA pump (see able 25-2). Remientanil is administered through a dedicated IV cannula to avoid bolus dosing, which can lead to apnea. Both respiratory monitoring and 1:1 nursing-to-patient ratio help watch or apneic spells, which occur in 25 percent o treated women (Stocki, 2014). In the RemiPCA SAFE Network Study, moderate maternal hypoxia (SaO2 <94 percent) was documented in a ourth o women (Melber, 2019). A multicenter randomized study showed PCA-administered remientanil halved the proportion o women subsequently requesting epidural analgesia compared with IM meperidine (Wilson, 2018).
Parenteral Agent Safety
Parenteral sedation is not without risks. Hawkins and colleagues (1997) reported that 4 o 129 maternal anesthetic-related deaths were rom such sedation. One was rom aspiration, two rom inadequate ventilation, and one rom overdosage. Narcotics used during labor may cause newborn respiratory depression. Naloxone is a narcotic antagonist capable o reversing respiratory depression induced by opioid narcotics.
It acts by displacing the narcotic rom specic receptors in the central nervous system. Ater adequate ventilation has been established, naloxone may be given to a newborn whose mother received narcotics. Naloxone is contraindicated in a newborn o a narcotic-addicted mother because withdrawal symptoms may be precipitated (American Academy o Pediatrics, 2017).
■ Nitrous Oxide
A sel-administered mixture o 50-percent nitrous oxide (N2O) and oxygen may provide satisactory analgesia during labor (Zarova, 2018). Some preparations are premixed in a single cylinder (Entonox), and in others, a blender mixes the two gases rom separate tanks (Nitronox). Te gases are connected to a breathing circuit through a valve that opens only when the patient inspires.
Te use o intermittent nitrous oxide did not alter the rate o epidural analgesia but did improve birth experience satisaction rates (Bobb, 2016; Lim, 2018). Maternal side eects include nausea, vomiting, dizziness, and drowsiness. Neonatal Apgar scores or umbilical cord blood gas results did not dier in women using nitrous oxide compared with those selecting other pain management methods or no analgesia in labor (Likis, 2014).
NERVE BLOCKS
Various nerve blocks provide pain relie during labor and/or delivery. Tese include pudendal, paracervical, and neuraxial blocks such as spinal, epidural, dural-puncture epidural, and combined spinal-epidural techniques.
■ Anesthetic Agents
Commonly used nerve block anesthetics are summarized in Table 25-3. Te dose o each agent varies widely and is dependent on the particular nerve block and physical status o the woman. Te onset, duration, and quality o analgesia can be enhanced by increasing the anesthetic agent’s dose, concentration, and volume or by altering its delivery mode. With their use, saety tenets include incremental boluses o the agent and careully monitoring or early warning signs o adverse eects. Appropriate equipment and personnel to manage these reactions must be immediately available.
Local analgesic agents are manuactured in more than one concentration and ampule size, and this raises the potential or dosing errors. Most oten, serious toxicity ollows inadvertent intravenous, subarachnoid, or subdural injection. Systemic toxicity rom local anesthetics typically maniests in the central nervous and cardiovascular systems. For this reason, beore epidural analgesia is initiated, a mixture o a small amount o local anesthetic drug and epinephrine is given as a test dose.
Epinephrine with its associated tachycardia is used as a marker to help identiy incorrect placement i it occurs. A sudden signicant elevation in the maternal heart rate or blood pressure within 1 to 2 minutes ater administration suggests intravenous catheter placement. A block extending over wider than expected spinal levels and/or dense motor blockade indicate inadvertent catheter placement into the subarachnoid or into the subdural space.
Central Nervous System Toxicity
Early symptoms are those o stimulation, but as serum levels rise, depression ollows. Symptoms may include lightheadedness, dizziness, tinnitus, metallic taste, and numbness o the tongue and mouth. Patients may also show bizarre behavior, slurred speech, and muscle asciculation and excitation. Ultimately, generalized convulsions and loss o consciousness could result.
For neural and cardiac toxicity treatment, a rapid IV inusion o 20-percent intralipids eectively disassociates anesthetic drugs rom neural and myocardial cell membranes. For patients weighing >70 kg, a 100-mL bolus dose o lipid emulsion is given. Boluses can be repeated once or twice every 5 minutes or persistent cardiac instability. Te initial bolus is ollowed by a 200-mL inusion over 15 minutes (Neal, 2018).
For convulsions, an airway is established, and oxygen delivered. o halt seizures, lorazepam, 4 mg IV slowly, is administered and may be repeated once ater 10 to 15 minutes. Alternatively, diazepam, 5 to 10 mg IV every 10 to 15 minutes up to a total dose o 30 mg, can be used. Succinylcholine abolishes the peripheral maniestations o the convulsions and allows tracheal intubation. Magnesium sulate, administered according to the regimen or eclampsia, also controls convulsions (Chap. 41, p. 719).
Abnormal etal heart rate patterns such as late decelerations or persistent bradycardia may develop rom maternal hypoxia and lactic acidosis. With arrest o convulsions, oxygen administration, and other supportive measures, the etus usually recovers more quickly in utero than ollowing immediate cesarean delivery. Moreover, the mother is better served i delivery is delayed until the intensity o hypoxia and metabolic acidosis has diminished.
Cardiovascular Toxicity
Tese maniestations generally develop later than those rom cerebral toxicity, and they may not develop at all because they are induced by higher serum drug levels. Te exception is bupivacaine, which is associated with the development o neurotoxicity and cardiotoxicity at virtually identical levels (Catterall, 2018). Fortunately, bupivacaine is mostly used in dilute epidural solutions, and use o 0.75-percent solution is limited to a small dose or spinal analgesia. Similar to neurotoxicity, cardiovascular toxicity is characterized rst by stimulation and then by depression. Accordingly, hypertension and tachycardia are soon ollowed by hypotension, cardiac arrhythmias, and impaired uteroplacental perusion. As beore, 20-percent intralipids serve as the rescue.
Hypotension is managed initially by turning the woman onto either side to avoid aortocaval compression. A crystalloid solution is inused rapidly along with vasopressors. Emergency bedside cesarean delivery is considered i maternal vital signs have not been restored within 4 minutes o cardiac arrest, and the goal is delivery within 5 minutes (Chap. 50, p. 897). However, as with convulsions, the etus is likely to recover more quickly in utero once maternal cardiac output is reestablished.
■ Pudendal Block
Pain with vaginal delivery arises rom stimuli rom the lower genital tract. Tese are transmitted primarily through the pudendal nerve, the peripheral branches o which provide sensory innervation to the perineum, anus, vulva, and clitoris (Chap. 2, p. 21). Te pudendal nerve passes beneath the posterior surace o the sacrospinous ligament just as the ligament attaches to the ischial spine.
Sensory nerve bers o the pudendal nerve are derived rom ventral branches o the S2 through S4 nerves. Te pudendal nerve block is a relatively sae, simple method o analgesia or vaginal delivery (Sultan, 2021). As shown in Figure 25-2, a tubular introducer is used to sheath and guide a 15-cm, 22-gauge needle into position near the pudendal nerve. Te end o the introducer is placed against the vaginal mucosa just beneath the tip o the ischial spine. Te introducer allows 1.0 to 1.5 cm o needle to protrude beyond its tip, and the needle is pushed beyond the introducer tip into the mucosa. A mucosal wheal is made with 1 mL o 1-percent lidocaine solution or an equivalent dose o another local anesthetic (see able 25-3). o guard against intravascular inusion, aspiration is attempted beore this and all subsequent injections. Te needle is then advanced until it touches the sacrospinous ligament, which is inltrated with 3 mL o lidocaine. Te procedure is repeated on the other side.
Within 3 to 4 minutes o injection, the successul pudendal block will allow pinching o the lower vagina and posterior vulva without pain. I delivery occurs beore the pudendal block becomes eective and an episiotomy is indicated, the ourchette, perineum, and adjacent vagina can be inltrated with 5 to 10 mL o 1-percent lidocaine solution directly at the planned episiotomy site. Te pudendal block usually has become eective by the time o repair.
Te maximum recommended total dose o lidocaine is 4.5 mg/kg and not to exceed 300 mg (see able 25-3). For a 50-kg woman, this would equal 225 mg (4.5 mg/kg × 50 kg). Tus, i 1-percent lidocaine is used, the calculated allowed amount would be: 225 mg ÷ 10 mg/mL = 22.5 mL. O note, or any drug solution, 1 percent = 10 mg/mL.
Pudendal block usually does not provide adequate analgesia when delivery requires extensive obstetrical manipulation. Parenteral or neuraxial anesthesia is usually necessary when complete visualization o the cervix and upper vagina or manual exploration o the uterine cavity is indicated. Inrequently, complications may ollow this block. As previously described, intravascular injection o a local anesthetic agent may cause serious systemic toxicity. Hematoma ormation rom peroration o a blood vessel is most likely when there is a coagulopathy (Lee, 2004). Te addition o a corticosteroid injected along with the local anesthetic did not decrease the incidence o pudendal neuralgia at 3 months (Labat, 2017).
Rarely, severe inection may originate at the injection site. Te inection may spread posteriorly to the hip joint, into the gluteal musculature, or into the retropsoas space (Svancarek, 1977).
■ Paracervical Block
Te cervix, vagina, and uterus are richly supplied by nerves o the uterovaginal plexus (Fig. 2-12, p. 25). Tis plexus lies within the connective tissue lateral to the uterosacral ligaments. Tus, injections are most eective i placed immediately lateral to the insertion o the uterosacral ligaments into the uterus (Rogers, 1998). For paracervical blockade, usually 1-percent lidocaine or 3-percent chloroprocaine, 5 to 10 mL, is injected into the cervix laterally at 4 and 8 o’clock positions.
Tis block usually provides satisactory pain relie during rststage labor. However, because the pudendal nerves are not blocked, additional analgesia is required or delivery. Te block may have to be repeated during labor because these anesthetics are relatively short acting.
Fetal bradycardia is a worrisome complication that develops in approximately 15 percent o these blocks (Rosen, 2002). Bradycardia usually develops within 10 minutes and may last up to 30 minutes. Doppler studies have shown an increase in the pulsatility index o the uterine arteries ollowing paracervical blockade (Chap. 14, p. 262). Tese observations support the hypothesis o drug-induced arterial vasospasm as a cause o etal bradycardia (Manninen, 2000). Tus, paracervical block should not be used in situations o potential etal compromise. For all o these reasons, we do not use this block at Parkland Hospital.
NEURAXIAL ANALGESIA
■ Neuraxial Regional Blocks
Epidural, spinal, dural-puncture epidural, or combined spinal-epidural techniques are the most common methods used or relie o pain during labor and/or delivery in the United States. Nearly 75 percent o mothers receive neuraxial anesthesia or pain relie (Butwick, 2018a). Among rst births, 68 percent o women who delivered vaginally received neuraxial pain relie compared with 57 percent o women delivering their second or higher number child. Antepartum education programs improve the understanding o labor analgesia and increase its use by 30 percent in Hispanic women who traditionally choose labor epidural analgesia less oten (ogioka, 2019). Butwick and associates (2018b) showed women are more likely to receive neuraxial analgesia with higher class o obesity—class I, 72 percent; class II, 73 percent; and class III, 76 percent.
As a brie review, the epidural space lies just outside the dural sac. Te dura mater encases the subarachnoid space, which contains the cauda equina o the spinal cord and cerebrospinal fuid (CSF) (Fig. 25-3). Spinal and intrathecal anesthesia are synonymous, and agents are injected into the subarachnoid space. Epidural analgesia via a catheter in the epidural space is typically used or relie o labor pain, although it can also be used or anesthesia during operative vaginal and cesarean delivery.
Spinal analgesia is typically given as a single intrathecal injection o a local anesthetic at the time o operative vaginal or cesarean delivery. Variations o these two basic approaches are described in the subsequent sections.
■ Spinal (Subarachnoid) Block
Introduction o a local anesthetic into the subarachnoid space to eect analgesia oers a short procedural time, rapid blockade onset, and high success rate o inducing analgesia. Te subarachnoid space is smaller during pregnancy likely because o internal vertebral venous plexus engorgement (see Fig. 25-3A). As a result, compared with nonpregnant women, the same amount o anesthetic agent in the same volume o solution produces a higher-level blockade in parturients.
Vaginal Delivery
Spinal analgesia involving only lower spinal levels can be used or operative vaginal delivery. Te level o analgesia should extend to the 10 dermatome, which corresponds to the level o the umbilicus. Blockade to this level provides excellent relie rom the pain o uterine contractions. Te spinal block provides also excellent analgesia to the lower uterine segment, vagina, and perineum.
Several local anesthetic agents have been used or spinal analgesia (see able 25-3). Addition o dextrose to any o these agents creates a hyperbaric solution, which is heavier and denser than CSF. A sitting position causes a hyperbaric solution to settle caudally, whereas a lateral position will have a greater eect on the dependent side. Lidocaine given in a hyperbaric solution produces excellent analgesia and has the advantage o a rapid onset and relatively short duration. Isobaric bupivacaine provides satisactory analgesia or more than 1 hour. Singledose spinal analgesia is usually administered when the cervix is ully dilated, and all other criteria or sae operative vaginal delivery have been ullled (Chap. 29, p. 533). Preanalgesic IV hydration with 1 L o crystalloid solution will prevent or minimize hypotension in many cases.
Cesarean Delivery
A level o sensory blockade extending to the 4 dermatome is desired or cesarean delivery. A dose o 10 to 12 mg o bupivacaine in a hyperbaric solution is administered. Te addition o 20 to 25 µg o entanyl improves the quality and prolongs the duration o the spinal block, reduces shivering, and minimizes reerred pain. In addition, 0.1 to 0.2 mg o intrathecal morphine can be added or pain control postoperatively.
With intrathecal morphine, the risk or respiratory depression should be considered. Te Society o Obstetric Anesthesia and Perinatology recommends postoperative respiratory monitoring based on dose, patient risk actors, and perioperative risk actors. A low-dose regimen, dened as >50 µg and ≤150 µg, in women with no risk actors requires respiratory rate and sedation checks postoperatively or the rst 12 hours. In women with additional risk actors, these saeguards are conducted postoperatively or the rst 24 hours, and additional monitoring with pulse oximetry or capnography is considered. Last, this monitoring method is also recommended in all women receiving doses >150 µg (Bauchat, 2019).
Complications
Shown in Table 25-4 are some o the more common complications associated with neuraxial analgesia. Hypotension. Tis common complication may develop soon ater injection o the local anesthetic agent. It stems rom vasodilation caused by sympathetic blockade and is compounded by obstructed venous return due to uterine compression o the vena cava. In the supine position, even in the absence o maternal hypotension, placental blood fow may still be signicantly diminished. reatment includes uterine displacement by let lateral patient positioning, rapid IV crystalloid inusion, and IV vasopressors.
One systematic review concluded that vasopressors should be given only in the setting o hypotension (Fitzgerald, 2020). For treatment, phenylephrine is now the preerred drug to treat hypotension rom neuraxial analgesia. It is a pure alpha agonist and raises blood pressure solely through vasoconstriction. Maternal bradycardia develops more requently with phenylephrine than with ephedrine or norepinephrine (Sharkey, 2019; Veeser, 2012). Although ephedrine was believed to correct hypotension without reducing blood fow, phenylephrine is associated with better umbilical cord blood gases (Ngan Kee, 2017). A metaanalysis o 36 randomized trials also suggests that both agents have comparable ecacy but that phenylephrine yields a lower rate o etal acidosis (Xu, 2018). For administration, prophylactic inusions o phenylephrine are eective and may require less physician intervention compared with intermittent boluses (Ngan Kee, 2004). As another potential agent, norepinephrine may improve cardiac output with its beta-adrenergic eects but also is associated with a lower cord arterial pH compared with phenylephrine (Chen, 2021; Mohta, 2019).
High Spinal Blockade. Most oten, complete spinal blockade ollows administration o an excessive dose o local anesthetic. However, it can also develop with inadvertent delivery o a small amount o local anesthetic drugs into the subdural space. Tis small potential space lies between the dura mater and arachnoid mater and outside the subarachnoid space. Because o its limited capacity, even small volumes will reach higher spinal levels. Hypotension and apnea develop quickly and must be immediately treated to prevent cardiac arrest. In the undelivered woman: (1) the uterus is immediately displaced laterally to minimize aortocaval compression, (2) eective ventilation is established, preerably with tracheal intubation, and (3) IV fuids and vasopressors are given to correct hypotension.
Postdural Puncture Headache. Leakage o CSF rom the dural puncture site can lead to postdural puncture headache. Presumably, when the woman sits or stands, the diminished CSF volume creates traction on pain-sensitive central nervous system structures. An alternative mechanism is compensatory cerebral vasodilation in response to CSF loss—the Monro-Kellie hypothesis (Mokri, 2001).
Te incidence o obstetrical postdural puncture headache in women undergoing spinal analgesia ranges rom 0.2 to 1 percent (Maronge, 2012; Sprigge, 2008). Tis rate is similar to the overall occurrence o postdural puncture headaches, which approximates 1 headache per 200 blocks. A study o 567 postpartum hospital encounters showed that 40 percent o presentations or headache are due to neuraxial anesthesia, and these visits most oten occur within 7 days o delivery (Rodriguez, 2020).
Procedural preventive steps include using a small-gauge spinal needle and avoiding multiple punctures. In a prospective, randomized study o ve dierent spinal needles, Sprotte and Whitacre needles had the lowest risks o associated postdural puncture headaches (Vallejo 2000). Rates are high with inadvertent dural puncture during epidural analgesia and approximate 0.2 to 1 percent (Introna, 2012; Maronge, 2018). No strong evidence supports placing a woman fat on her back or providing vigorous hydration to prevent headache (Arevalo-Rodriguez, 2016). A prophylactic blood patch perormed within 24 hours o dural puncture does not diminish either the incidence o postdural puncture headache or the need or a subsequent therapeutic blood patch (Scavone, 2004).
I a headache develops, administration o caeine, which is a cerebral vasoconstrictor, has limited ecacy (Katz, 2017). With severe headache, an epidural blood patch is most eective and preerred treatment. Autologous blood is obtained aseptically by venipuncture, and 10 to 20 mL is injected into the epidural space at or below the site o dural puncture. Tis site is selected because the blood will spread more readily in the cephalad direction. Further CSF leakage is halted by either mass eect or clot ormation.
Relie is immediate, and complications are uncommon. I a headache does not have the pathognomonic postural characteristics or persists despite treatment with a repeat blood patch, other diagnoses should be considered. Chisholm and Campbell (2001) described a case o superior sagittal sinus thrombosis that maniested as a postural headache. Chan and Paech (2004) reported persistent CSF leak in three women. Smarkusky and colleagues (2006) described pneumocephalus, which caused immediate cephalgia. Last, intracranial and intraspinal subarachnoid hematomas have developed ater spinal analgesia (Bi, 2021; Maronge, 2018; Moore, 2019).
Convulsions. Rarely, postdural puncture cephalgia is associated with temporary blindness and convulsions. Shearer and associates (1995) described eight such cases in 19,000 regional analgesia procedures done at Parkland Hospital. It is presumed that these also are caused by hypotension rom CSF leak. Immediate treatment o seizures and epidural blood patch were usually eective.
Bladder Dysfunction. With neuraxial analgesia, bladder sensation is likely to be obtunded and bladder emptying impaired or several hours ater delivery. As a consequence, bladder distention is a requent postpartum complication, especially i appreciable volumes o IV fuid are given. Millet (2012) randomized 146 women with neuraxial analgesia to either intermittent or continuous bladder catheterizations and ound that the intermittent method was associated with signicantly greater rates o bacteriuria.
Arachnoiditis and Meningitis. Local anesthetics used or neuraxial blocks are required to be ree o methylparaben or other preservatives. Tis practice, coupled with aseptic technique and disposable equipment, has made meningitis and arachnoiditis rare (Centers or Disease Control and Prevention, 2010; Maronge, 2018).
Contraindications to Spinal Analgesia Shown in Table 25-5 are absolute contraindications to spinal analgesia. Obstetrical complications that are associated with maternal hypovolemia and hypotension—or example, severe hemorrhage—are contraindications to spinal blockade. Te additive deleterious cardiovascular eects o spinal blockade plus acute blood loss in nonpregnant patients have been documented (Kennedy, 1968). Severe preeclampsia is another obstetrical complication in which decreased blood pressure can be encountered when neuraxial analgesia is used (Wallace, 1995). Tese eects are mitigated by judicial dosing o anesthetic solutions. Perhaps related, Ulubaşoğlu and colleagues (2018) reported that preeclamptic women undergoing general anesthesia required more antihypertensive medication than those with spinal analgesia.
Disorders o coagulation that result in poor hemostasis also preclude the use o neuraxial analgesia. Women with a bleeding diathesis such as von Willebrand disease or hemophilias carry an increased risk or subarachnoid hematoma ormation (Chap. 59, p. 1062). Rare subdural hematomas may mimic postdural puncture headaches (Lim, 2016). However, neuraxial analgesia can be saely perormed in these patients ollowing actor replacement and normalization o levels (Choi, 2009; Katz, 2015). As discussed earlier, these patients should receive consultation with an anesthesiologist prior to labor.
Te use o anticoagulation to prevent or treat venous thromboembolism is requently encountered during the peripartum period. No randomized studies guide the management o anticoagulation at the time o delivery, but consensus opinion is provided by the Society or Anesthesia and Perinatology (Leert, 2018). Briefy, women receiving >10,000 units/d o unractionated heparin are individually assessed regarding timing and dose o last injection. Tromboprophylaxis with lowmolecular-weight heparin (LMWH) should have a 12-hour delay. Terapeutic doses o LMWH merit a 24-hour delay.
Tis is discussed urther in Chapter 55 (p. 985). Spinal analgesia is also contraindicated i there is inection at the needle entry site. Other maternal conditions may pose relative contraindications to neuraxial analgesia. Many women with neurological disorders such as Chiari malormation or pseudotumor cerebri may be candidates or neuraxial analgesia ater consultation with an anesthesiologist and neurologist. Women with severe aortic stenosis or pulmonary hypertension also have a relative contraindication to spinal analgesia due to the deleterious eects o hypotension and diminished preload and aterload (Chap. 52, p. 926).
■ Epidural Analgesia
Relie o labor and childbirth pain, including cesarean delivery, can be accomplished by injection o a local anesthetic agent into the epidural space (see Fig. 25-3B). Tis potential space contains areolar tissue, at, lymphatics, and the internal vertebral venous plexus. Entry or obstetrical analgesia is usually through a lumbar intervertebral space. Although only one injection may be given, usually an indwelling catheter is placed or subsequent bolus administration or continuous inusion (Billingham, 2018). Inusions use a volumetric pump controlled either by the patient or by a caregiver. Under appropriate physician supervision, labor and delivery nursing personnel with specic training in the management o epidural inusions should be able to adjust dosage and also discontinue inusions.
■ Continuous Lumbar Epidural Analgesia
Complete analgesia or the pain o labor and vaginal delivery necessitates a block rom the 10 to the S4 dermatomes. For cesarean delivery, a block extending rom the 4 to the S1 dermatomes is desired. Te eective spread o anesthetic depends upon the catheter tip location and the dose, concentration, and volume o anesthetic agent used. Individual variations in anatomy or synechiae or septa in the epidural space may preclude a completely satisactory block. Last, the catheter tip may migrate rom its original location during labor.
Technique
One example o the sequential steps and techniques or perormance o epidural analgesia is detailed in Table 25-6. Beore injection o the local anesthetic therapeutic dose, a test dose is given containing small amounts o lidocaine and epinephrine. Te woman is observed or eatures o toxicity rom intravascular injection and or signs o either subarachnoid or subdural injection. I these are absent, analgesia is initiated with a ull dose o the anesthetic alone. Analgesia is maintained by a continuous inusion or by programmed intermittent boluses delivered by inusion pump (Billingham, 2018). Te addition o a short-acting, lipid-soluble narcotic—entanyl or suentanil— lowers the required amount o local anesthetic drug needed to achieve analgesia. Tis helps preserve motor unction (Lyons, 1997). One popular regimen is 0.0625- to 0.125-percent bupivacaine with 2-µg/mL entanyl. As with spinal blockade, close monitoring, including the level o analgesia, must be perormed by trained personnel. Appropriate resuscitation equipment, drugs, and personnel must be available during administration o epidural analgesia.
Complications
As shown in able 25-4, certain problems are inherent to epidural analgesia. High Spinal Blockade. Dural puncture with inadvertent and unrecognized either subarachnoid or subdural injection may cause total spinal blockade. In a study o more than 18,000 women, the incidence o recognized accidental dural puncture at the time o epidural analgesia was 0.91 percent (Sprigge, 2008). Management o this complication is described earlier (p. 474).
Ineffective Analgesia. Using currently popular continuous or intermittent epidural inusion regimens, 90 percent o women rate their pain relie as good to excellent (Sharma, 1997). In a study o almost 2000 parturients, Hess and associates (2001) ound that 12 percent complained o three or more episodes o pain or pressure. Its ecacy was more likely to decrease with rising body mass index (Dresner, 2006). Inadequate analgesia may result in patient dissatisaction. Catheter replacement should be considered.
Moreover, a poorly unctioning epidural catheter cannot be used or additional dosing o local anesthetic drugs or intrapartum cesarean delivery. Such conversion o labor epidural analgesia to cesarean delivery anesthesia has an approximately 20 percent ailure rate. Tis necessitates placement o a new regional block or general anesthesia (Mankowitz, 2016). In a Maternal Fetal Medicine Units (MFMU) Network study, 4 percent o women initially given epidural analgesia required a general anesthetic or cesarean delivery (Bloom, 2005). Also at times, perineal analgesia or vaginal delivery is di- cult to obtain, especially when lower volumes o epidural local anesthetic drugs are used. With this situation, additional doses can be given, or a pudendal block may be added.
Hypotension. Sympathetic blockade rom epidurally injected analgesic agents may cause peripheral vasodilation with resulting hypotension and diminished cardiac output. Hypotension is more common—20 percent—in women with an admission pulse pressure <45 mm Hg compared with 6 percent in those whose pulse pressure is >45 mm Hg (Miller, 2013). Pulse pressure is calculated by subtracting diastolic rom systolic blood pressure measurements. Obese women also have signi- cantly higher rates o hypotension (Vricella, 2011). In normal gravidas, hypotension induced by epidural analgesia usually can be prevented by rapid IV inusion o 500 to 1000 mL o crystalloid solution as described or spinal analgesia. Maintaining a lateral position also minimizes hypotension. Despite these precautions, hypotension is the most requent side eect and is severe enough to require treatment in a third o women (Sharma, 1997).
Central Nervous Stimulation. Convulsions are an uncommon but serious complication. Described earlier, the immediate management involves inusion o 20-percent intralipids and treatment with lorazepam or diazepam (p. 470).
Fever. Some women develop intrapartum ever ollowing epidural analgesia. Many studies are limited by the inability to control or other risk actors, such as labor length, duration o ruptured membranes, and number o vaginal examinations. With this in mind, the requency o intrapartum ever associated with epidural analgesia is 10 to 15 percent above the baseline rate (Lieberman, 2002). Te two general theories concerning the etiology o maternal hyperthermia are maternal-etal inection or dysregulation o body temperature (American College o Obstetricians and Gynecologists, 2019b). A study o placental histopathology in women given epidural analgesia identied intrapartum ever only when there was placental infammation (Dashe, 1999).
Tis suggests that ever is due to inection. Sharma (2014) randomized 400 nulliparas with labor epidural analgesia to receive 2 g ceoxitin prophylactically versus placebo. It was hypoth esized that epidural-related ever was due to inection and that prophylactic antimicrobials should signicantly reduce the rate o ever. Approximately equal proportions—40 percent—o women developed ever ≥38°C during labor. Tis result suggests that inection is unlikely to cause the ever associated with epidural analgesia during labor. Whatever the mechanism, women with persistent ever are usually treated with antimicrobials or presumed chorioamnionitis.
Te other proposed mechanisms include alteration o the hypothalamic thermoregulatory set point, impaired peripheral thermoreceptor input to the central nervous system with selective blockade o warm stimuli, or imbalance between heat production and heat loss. Del Arroyo and colleagues (2019) suggested that bupivacaine blocks release o antipyretic interleukins.
Back Pain. An association between epidural analgesia and back pain has been reported by some. In a prospective cohort study, Butler and Fuller (1998) reported that back pain ater delivery was common with epidural analgesia, however, persistent pain was inrequent. Based on their systematic review, Lieberman and O’Donoghue (2002) concluded that available data do not support an association between epidural analgesia and development o de novo, long-term backache. Miscellaneous Complications. A spinal or epidural hematoma is a rare complication o an epidural catheter (Grant, 2007). Tese are considered neurological emergencies, and treatment is usually surgical. Epidural abscesses are rare, and the most common pathogen is Staphylococcus aureus (McQuaid, 2018). Tese may be managed conservatively with IV antibiotics, but surgical intervention may be necessary. For both conditions, timely neurosurgical consultation is important. Uncommonly, the plastic epidural catheter is sheared o (Noblett, 2007). Computed tomography can localize the retained ragment. For a tip let in the epidural space, surveillance is reasonable in the absence o symptoms. With neurological changes or with ragments in the subarachnoid space, neurosurgical consultation is recommended (Mitra, 2007). Last, an association o epidural analgesia and autism spectrum disorder seems unlikely (Mikkelsen, 2021).
Effect on Labor
Most studies, including ve combined randomized trials rom Parkland Hospital shown in Table 25-7, report that epidural analgesia prolongs labor and increases the use o oxytocin stimulation (Sharma, 2004). Alexander and associates (2002) examined the eects o epidural analgesia on the Friedman (1955) labor curve (Chap. 22, p. 424). Tere were 459 nulliparas randomly assigned to receive patient-controlled epidural analgesia or patient-controlled IV meperidine. Compared with original Friedman criteria, epidural analgesia prolonged the active phaseo labor by 1 hour. In a cohort study, similar labor durations were observed or both spinal-epidural and epidural analgesia (Poma, 2019).
Te eect o labor epidural on the second stage is unclear. Prolongation o the second stage was particularly true in earlier studies, at a time when higher concentrations o local anesthetic drugs were used. Tis association has been attributed to local-anesthetic-induced motor blockade and resultant impaired maternal expulsive eorts. Chestnut and associates (1999) reported that, with epidural analgesia, operative vaginal delivery occurred more requently because o prolonged second-stage labor. In a systematic review, Anim-Somuah and colleagues (2018) reported that epidural analgesia prolongs the rst stage by 32 minutes and the second stage by 15 minutes. Craig and coworkers (2015) randomly assigned 310 nulliparous women with labor epidural analgesia to receive 0.125-percent bupivacaine plus entanyl or epidural entanyl alone during second-stage labor. Epidural bupivacaine analgesia did cause motor blockade during the second stage, however, the duration o the second stage was not longer. Neither obstetrical nor neonatal outcomes were dierent between the two groups. Patient satisaction was high with both methods.
Fetal Heart Rate. Hill and associates (2003) examined the eects o epidural analgesia with 0.25-percent bupivacaine on etal heart rate patterns. Compared with IV meperidine, no worrisome eects were identied. Reduced beat-to-beat variability and ewer accelerations were more common in etuses whose mothers received meperidine (Chap. 24, p. 450). Based on their systematic review, Reynolds and coworkers (2002) reported that epidural analgesia was associated with improved neonatal acid-base status compared with meperidine.
Cesarean Delivery Rates. A contentious issue in the past was whether epidural analgesia increased the risk or cesarean delivery. Early evidence that it did was rom an era when dense motor blockade resulted rom high concentrations o local anesthetic agents. Now however, with the administration o dilute anesthetic solutions, the risk or cesarean delivery is not increased.
Several studies conducted at Parkland Hospital were designed to answer this and related questions. From 1995 to 2002, a total o 2703 nulliparas at term and in spontaneous labor were enrolled in ve trials to evaluate epidural analgesia techniques compared with IV meperidine. Te results rom these are summarized in Table 25-8 and show that epidural analgesia does not signicantly raise cesarean delivery rates (Sharma, 2004). Te American College o Obstetricians and Gynecologists (2019b) and the American Society o Anesthesiologists (2016) also conclude that epidural analgesia is not associated with a greater cesarean delivery rate.
Timing of Epidural Placement. Earlier studies indicated that epidural placement in early labor was linked to a higher risk o cesarean delivery (Lieberman, 1996; Rogers, 1999; Seyb, 1999). Tese observations prompted at least ve randomized trials, which showed that the timing o epidural placement has no eect on the risk o cesarean birth, orceps delivery, or etal malposition (Chestnut, 1994a,b; Luxman, 1998; Ohel, 2006; Wong, 2005, 2009). Tus, withholding epidural placement until some arbitrary cervical dilation has been attained serves only to deny women maximal labor pain relie.
Safety
Among nearly 20,000 women who received epidural analgesia in the MFMU Network study cited earlier, no anesthesiarelated maternal deaths were reported (Bloom, 2005). Ruppen and colleagues (2006) reviewed data rom 27 studies involving 1.4 million pregnant women who received epidural analgesia. Teir calculated adverse-event rates were 1:145,000 or deep epidural inection, 1:168,000 or epidural hematoma, and 1:240,000 or persistent neurological injury. More recently, the Society or Obstetric Anesthesia and Perinatology established the Serious Complication Repository Project (D’Angelo, 2014). During a 5-year period, more than 228,000 women had neuraxial analgesia. Tere were no maternal deaths related to anesthesia, but two each were attributed to cardiac arrest and myocardial inarction. Tere were our cases o epidural abscess or meningitis, 58 high-spinal-level neuraxial blocks (1 in 4000), 27 neurological injuries, and 16 respiratory arrests (1 in 10,000).
Contraindications
As with spinal analgesia, contraindications are listed in
able 25-5.
Thrombocytopenia. Although low platelet counts are intuitively worrisome, the level at which epidural bleeding might develop is unknown. Epidural hematomas are rare, and their incidence was estimated to be 0 to 0.6 percent in women whose platelet count is <70,000/µL (Goodier, 2015; Lee, 2017). Te American College o Obstetricians and Gynecologists (2019b) and Society or Obstetric Anesthesia and Perinatalogy (Bauer, 2021) have concluded that women with a platelet count o ≥70,000/µL may be candidates or neuraxial analgesia.
Anticoagulation. Women receiving anticoagulation therapy who are given regional analgesia are at increased risk or spinal cord hematoma and compression (Chap. 55, p. 985). Te American College o Obstetricians and Gynecologists (2019b) has concluded the ollowing:
1. With prophylactic unractionated heparin (UFH) in a dose o 5000 units twice daily, regional analgesia is not contraindicated.
2. With an intermediate dose o UFH (7500 to 10,000 units), it is likely low risk to proceed with neuraxial analgesia at a point more than 12 hours ater the last dose.
3. With a high dose o UFH (>20,000 units), it is likely low risk to use regional analgesia at a point more than 24 hours ater the last dose i the activate partial thromboplastin time (aP) is within normal range or the anti-Xa level is undetectable.
4. With thromboprophylaxis with LMWH, needle or catheter placement or removal should be delayed 12 hours or more.
5. With treatment doses o LMWH, placement or removal o a neuraxial catheter should be delayed or 24 hours. Severe Preeclampsia-Eclampsia. Concerns with neuraxial analgesia in women with severe preeclampsia include hypotension as well as hypertension rom pressor agents given to correct hypotension. Additionally, pulmonary edema may ollow inusion o large volumes o crystalloid. Tese risks are outweighed by the disadvantages o general anesthesia (American College o Obstetricians and Gynecologist, 2020). O these, tracheal intubation may be dicult because o upper airway edema. Also, general anesthesia can lead to severe, sudden hypertension that can cause pulmonary or cerebral edema or intracranial hemorrhage.
With improved techniques or inusion o dilute local anesthetics into the epidural space, most have come to avor epidural blockade or labor and delivery in women with severe preeclampsia. In a study rom Parkland Hospital, Lucas and associates (2001) randomly assigned 738 women with hypertension to epidural analgesia or patient-controlled IV analgesia during labor. A standardized protocol or prehydration, incremental epidural administration, and ephedrine use was employed. Tey concluded that labor epidural analgesia was sae in women with hypertensive disorders.
Trombocytopenia is seen with severe preeclampsia complicated by hemolysis, elevated liver enzyme levels, low platelet count—HELLP syndrome (Chap. 40, p. 689). Discussed earlier and in general, it seems sae to use neuraxial techniques i the platelet count is ≥70,000/µL (American College o Obstetricians and Gynecologists, 2019b, 2020). Women with severe preeclampsia can have remarkably diminished intravascular volume compared with normal pregnancy (Zeeman, 2009). Conversely, total body water volume is increased because o the capillary leak caused by endothelial cell activation (Chap. 40, p. 693). Tis imbalance is maniested as pathological peripheral edema, proteinuria, ascites, and total lung water. For all o these reasons, aggressive volume replacement raises the risk or pulmonary edema, especially in the rst 72 hours postpartum (American College o Obstetricians and Gynecologists, 2019b). In one study, 3.5 percent o women with severe preeclampsia developed pulmonary edema when preloaded without a protocol limit to the volume inused (Hogg, 1999).
Te risk o pulmonary edema can be reduced or obviated with judicious prehydration—usually with 500 to 1000 mL o crystalloid solution. Specically, in the study by Lucas and colleagues (2001) cited earlier, no instances o pulmonary edema developed among the women in whom the inused crystalloid preload volume was limited to 500 mL. Moreover, vasodilation produced by epidural blockade is less abrupt i the analgesia level is achieved slowly with dilute solutions o local anesthetic agents. With vigorous IV crystalloid therapy, cerebral edema also may develop (Chap. 40, p. 701. Last, most cases o pharyngolaryngeal edema are related to aggressive volume therapy (Heller, 1983).
■ Epidural Opioid Analgesia
Opioids alone usually will not provide adequate analgesia, and they are oten used as an adjunct to a local anesthetic agent such as bupivacaine (Wang, 2020). Tis combination lowers the local anesthetic drug concentration needed to achieve analgesia, which in turn creates a less dense motor blockade. Other benets are rapid onset o pain relie and a decrease in shivering. Common side eects include pruritus and urinary retention. Nalbuphine, a mixed opioid agonist/antagonist, will abolish these symptoms without aecting the analgesic action. When neuraxial morphine is given or postoperative pain, monitoring or respiratory depression is necessary as discussed earlier (p. 472) (Bauchat, 2019).
■ Combined Spinal–Epidural Techniques
Te combination o spinal and epidural techniques (CSE) has risen in popularity and may provide rapid and eective analgesia or labor and then or cesarean delivery. An epidural needle is rst placed in the epidural space. A small-gauge spinal needle is then introduced through the epidural needle into the subarachnoid space—this is called the needle-through-needle technique (see Fig. 25-3A). A single bolus o an opioid, a local anesthetic, or sometimes a combination is injected into the subarachnoid space. A subarachnoid opioid bolus results in the rapid onset o proound pain relie with virtually no motor blockade (Poma, 2019). Te spinal needle is withdrawn, and an epidural catheter is then placed into the epidural space. Te epidural catheter remains and permits repeated analgesia dosing. Miro and associates (2008) compared epidural analgesia with CSE analgesia or labor in 6497 women and ound the overall outcomes and complications to be similar. Poma and coworkers (2019) also ound comparable analgesia results with epidural or CSE techniques. Tey noted that subarachnoid suentanil was associated with lower uterine contractility, but labor duration was not aected. A greater incidence o etal heart rate abnormalities related to uterine hypertonus has been reported with CSE analgesia (Abrão, 2009; Beamon, 2014). Te analgesia ailure rate is 11.6 percent or traditional labor epidural and 6.6 percent or CSE (Booth, 2016). Although CSE provides a aster onset o labor analgesia, the intrathecal injection o local anesthetic drugs and/or narcotic may cause hypotension and pruritus.
■ Continuous Spinal Analgesia During Labor
Te technique o continuous spinal analgesia or relie o labor pain is seldom used because o postdural puncture headaches (American College o Obstetricians and Gynecologists, 2019b). With redesigned needles and catheters, Arkoosh (2008) randomized 429 women to either continuous spinal or conventional epidural analgesia during labor. Complication rates between these two neuraxial techniques did not dier.
■ DuralPuncture Epidural Analgesia
Gaining popularity, this technique is similar to CSE, but initial steps dier. First, a single dural puncture is made using a 25-gauge spinal needle placed through the epidural needle shat (see Fig. 25-3A). No anesthetic is injected, but the needle can help conrm correct subarachnoid space placement by the drip o CSF rom its distal hub. Ater removal o the spinal needle, the epidural catheter is threaded into the epidural space (see Fig. 25-3B). Te dural puncture allows or a small amount o local anesthetic drugs to be translocated rom the epidural space to the subarachnoid space.
Tis aids a aster onset o pain relie than traditional epidural analgesia. Without the intrathecal injection, dural-puncture epidural analgesia is associated with ewer side eects than CSE analgesia and provides better block quality than an epidural (Chau, 2017).
A review o ve studies with 581 patients showed dural puncture epidural technique was associated with a aster onset o analgesic eects, a reduction in provider-initiated boluses “top-ups,” and better sacral coverage. Te incidence o post-dural puncture headache was not signicantly increased (Heesen, 2019). A study conrmed ewer top-ups and a greater local anesthetic drug sparing eect evaluating the combined use o this technique and the intermittent bolus drug delivery mode (Song, 2021).
■ Local Infiltration Analgesia
A local block is occasionally useul to augment an inadequate or “patchy” regional block that was given emergently. Rarely, local inltration may be needed to perorm an emergency cesarean delivery to save the lie o a etus in the absence o anesthesia support. wo methods are described here.
In one technique, the skin is inltrated along the proposed incision, and the subcutaneous, muscle, and rectus sheath layers are injected as the abdomen is opened. Injection o large volumes into the atty layers, which are relatively devoid o nerve supply, is avoided to limit the total dose o local anesthetic needed. Cooper and coworkers described using 52 mL o 0.5- percent lidocaine with 1:200,000 epinephrine. Tis delivered 260 mg o lidocaine. Related to lidocaine toxicity, higher lidocaine volumes can be used when paired with epinephrine, because vasoconstriction lowers the intravascular transer o anesthetic. Te maximum dose is 7 mg/kg. Others have used 1-percent procaine with or without epinephrine (Larsen, 1971; Ranney, 1975).
A second technique involves a eld block o the major branches supplying the abdominal wall, to include the 10th, 11th, and 12th intercostal nerves and the ilioinguinal and genitoemoral nerves (Nandagopal, 2001). As shown in Figure 25-4, the ormer group o nerves is located at a point midway between the costal margin and iliac crest in the midaxillary line. Te latter group is ound at the level o the external inguinal ring. A total o our skin punctures, two on each side, are made. First, at the intercostal block site, the needle is directed medially, and injection is carried down to the transversalis ascia, avoiding injection o the subcutaneous at. Five mL o 0.5-percent lidocaine with epinephrine are injected. Te needle is redirected but not removed, and similar dosing is delivered to sites located at a 45-degree angle cephalad and caudad. Te other side is then injected. Second, at the ilioinguinal and genitoemoral sites, the injection is started at a spot 2 to 3 cm lateral rom the pubic tubercle at a 45-degree angle. Last, the skin overlying the planned incision is injected.
■ Transversus Abdominis Plane Block
Tis block may be used or those with suitable training (Young, 2012). It is usually perormed under ultrasound guidance and involves injection o a local anesthetic into the transversus abdominis plane (AP) between the internal oblique and transversus abdominis muscles (Fig. 2-2, p. 14). Te nerves lying in this plane supply the anterior abdominal wall at the 6 to L1 dermatomes. Ng and colleagues (2018) concluded that high- versus low-dose local anesthetics perormed comparably.
Local inltration or AP blocks can be used also or postoperative pain control. Te AP block in one trial was not superior to local wound inltration (awk, 2017). Gao and associates (2019) demonstrated that pain relie with the AP block was comparable with that rom patient-controlled IV analgesia. Another study ound that the AP block was equivalent to intrathecal morphine or postoperative pain (Kwikiriza, 2019). Last, Prabhu and coworkers (2018) reported that a liposomal bupivacaine incisional block was not superior to placebo.
TABLE 25-6. Technique for Labor Epidural Analgesia
Obtain informed consent and consult the obstetrician
Monitoring includes the following:
Blood pressure every 1–2 minutes for 15 minutes after giving a bolus of local anesthetic
Continuous maternal heart rate monitoring during analgesia induction
Continuous fetal heart rate monitoring
Continual verbal communication
Hydration with 500–1000 mL of Ringer lactate solution
The woman assumes a lateral decubitus or sitting position
The epidural space is identified by the needle’s loss of resistance during insertion
The epidural catheter is threaded 3–5 cm into the epidural space
After a negative aspiration, a test dose of 3 mL of 1.5% lidocaine with 1:200,000 epinephrine is injected between contractions. Epinephrine is injected after careful aspiration to avert intravascular injection and after a uterine contraction. This minimizes the chance of confusing tachycardia that results from labor pain with that of tachycardia from intravenous injection of the test dose. A positive test dose manifests as symptoms of an intravascular injection of lidocaine and epinephrine, which are tinnitus, circumoral numbness, dizziness, heart rate increase >20 bpm in 1 minute. Another potential symptom is
an inability to raise the lower extremities against gravity in 4 min, which reflects the effects of a subarachnoid space injection.
If the test dose is negative, 10–15 mL of 0.0625–0.125% bupivacaine are injected to achieve a sensory T10 level After 15–20 minutes, the block is assessed using loss of sensation to cold or pinprick. If no block is evident, the catheter is replaced. If the block is asymmetrical, the epidural catheter is withdrawn 0.5–1.0 cm and an additional 3–5 mL of 0.25% bupivacaine is injected. If the block remains inadequate, the catheter is replaced. The woman is positioned in the lateral or semilateral position to avoid aortocaval compression Subsequently, maternal blood pressure is recorded every 5–15 minutes. The fetal heart rate is monitored continuously The level of analgesia and intensity of motor blockade are assessed at least hourly
GENERAL ANESTHESIA
rained personnel and specialized equipment—including beroptic intubation—are mandatory or the sae use o general anesthesia. A common cause o death cited is ailed intubation. Te latter occurs in approximately 1 o every 390 general anesthetics administered to pregnant women (Kinsella, 2015). Tis relatively higher mortality rate suggests that neuraxial analgesia is the preerred method o pain control and should be used unless contraindicated (American College o Obstetricians and Gynecologists, 2019b; American Society o Anesthesiologists, 2016). In two reports rom the MFMU Network, 93 percent o more than 54,000 cesarean deliveries were perormed using neuraxial analgesia (Bloom, 2005; Brookeld, 2013).
Racial and ethnic disparities exist, and a higher incidence o general anesthesia use is seen among non-white women (Butwick, 2014; Lange, 2017). It is oten used or emergent cesarean delivery or acute etal distress (Metogo, 2021). In contrast, with obstetrical anesthesiologist subspecialists, the overall likelihood that neuraxial analgesia will be used is higher (Cobb, 2019).
■ Patient Preparation
Beore anesthesia induction, several steps should be taken to help minimize complication risks. First, antacid administration shortly beore anesthesia induction has probably decreased mortality rates rom general anesthesia more than any other single practice. Te American Society o Anesthesiologists ask Force on Obstetrical Anesthesia (2016) recommends timely administration o a nonparticulate antacid, an H2-receptor antagonist, or metoclopramide. For many years, we have recommended administration o 30 mL o Bicitra—sodium citrate with citric acid—a ew minutes beore anesthesia induction by either general or major neuraxial block. I more than 1 hour has passed ater the rst dose was given and anesthesia has not yet been induced, a second dose is given.
Lateral uterine displacement also is provided as the uterus may compress the inerior vena cava and aorta when the mother is supine. With uterine displacement, the duration o general anesthesia has less eect on neonatal condition than i the woman remains supine (Craword, 1972).
Last, because unctional reserve lung capacity is diminished, and oxygen consumption is increased, the pregnant woman becomes hypoxemic more rapidly during periods o apnea than do nonpregnant patients. Obesity exacerbates this tendency. o minimize hypoxia between the time o muscle relaxant injection and intubation, nitrogen is replaced by oxygen in the lungs. Tis preoxygenation is accomplished by administering 100-percent oxygen via ace mask or 2 to 3 minutes beore anesthesia induction. In an emergency, our vital capacity breaths o 100-percent oxygen via a tight breathing circuit will provide similar benet (Norris, 1985). High-fow nasal oxygen was ound to be inerior to administration by ace mask (Shippam, 2019; an, 2019).
■ Induction of Anesthesia
Drugs used to induce general anesthesia include propool, etomidate, and ketamine. Propool has the undesirable side eect o hypotension. Etomidate is associated with ewer hemodynamic changes. Ketamine also may be used or induction o general anesthesia in hemodynamically unstable women.
■ Intubation
Immediately ater a patient is rendered unconscious, a muscle relaxant is given to aid intubation. Succinylcholine, a rapidonset and short-acting agent, is used. Cricoid pressure—the Sellick maneuver—is applied by a trained assistant to occlude the esophagus rom the onset o induction until intubation is completed. Beore the operation begins, proper placement o the endotracheal tube must be conrmed.
As discussed, and although uncommon, ailed intubation is a major cause o anesthesia-related maternal mortality. A history o prior dicult intubation and a careul anatomical assessment o the neck and the maxilloacial, pharyngeal, and laryngeal structures may help predict intubation complications. Even in cases in which the initial airway assessment was unremarkable, edema may develop intrapartum and present considerable challenges.
Morbid obesity is a major risk actor or ailed or dicult intubation.
Te American Society o Anesthesiologists ask Force on Obstetric Anesthesia (2016) stresses the importance o appropriate preoperative preparation. Tis includes the immediate availability o specialized equipment such as dierent-shaped laryngoscopes, laryngeal mask airways, and video laryngoscopes, as well as equipment or transtracheal ventilation and awake oral intubation with a beroptic bronchoscope.
Following ailed intubation, the woman is ventilated by mask and cricoid pressure is applied to reduce the aspiration risk. Surgery may proceed with mask ventilation, or the woman may be allowed to awaken. In those cases in which the woman has been paralyzed and in which ventilation cannot be reestablished by insertion o an oral airway, by laryngeal mask airway, or by use o a beroptic laryngoscope, then a lie-threatening emergency exists (Eskander, 2019). o restore ventilation, percutaneous or even open cricothyrotomy is perormed, and jet ventilation begun. Failed intubation drills have been recommended to optimize response to such an emergency.
■ Inhalational Anesthetics
Once the endotracheal tube is secured, a volatile halogenated agent is given to provide amnesia and analgesia. Te most commonly used volatile anesthetics in the United States include desfurane and sevofurane. Tese gases can also produce uterine relaxation when given in high concentrations. Tese are used when relaxation is a requisite, such as or internal podalic version o the second twin, breech decomposition, ex utero intrapartum treatment (EXI) procedures, and replacement o the acutely inverted uterus.
■ Extubation
Te endotracheal tube may be saely removed only i the woman is conscious to a degree that enables her to ollow commands and is capable o maintaining oxygen saturation with spontaneous respiration. Consideration should be given to emptying the stomach via a nasogastric tube beore extubation. As induction has now become saer, extubation may be relatively more perilous. O 15 anesthesia-related deaths o pregnant women rom 1985 to 2003 in Michigan, none occurred during induction, whereas ve resulted rom hypoventilation or airway obstruction during emergence, extubation, or recovery (Mhyre, 2007).
■ Fasting
Data are insucient regarding asting times or clear liquids and the risk o pulmonary aspiration during labor. Te American Society o Anesthesiologists ask Force on Obstetrical Anesthesia (2016) and the American College o Obstetricians and Gynecologists (2017) recommend that modest amounts o clear liquids such as water, clear tea, black coee, carbonated beverages, and pulp-ree ruit juices be allowed in uncomplicated laboring women. As discussed in Chapter 30 (p. 550), enhanced recovery ater surgery (ERAS) protocols provide consumption o these same liquids up to 2 hours beore scheduled surgery (Wilson, 2018b). Obvious solid oods should be avoided. A asting period o 6 to 8 hours, depending on the type o ood ingested, is recommended or uncomplicated parturients undergoing elective cesarean delivery or puerperal tubal ligation. Te amount o gastric fuid—2 mL/kg—in nonlaboring women is almost the same as that in nonpregnant women (Van de Putte, 2019). However, pregnancy is associated with horizontal shit o the stomach and a reduced esophageal sphincter tone. Our policy at Parkland Hospital is to allow clear liquids in low-risk uncomplicated laboring women in whom vaginal delivery is anticipated.
■ Aspiration
Massive gastric acidic inhalation may cause pulmonary insu- ciency rom aspiration pneumonitis (Mandell, 2019). Such pneumonitis has in the past been the most common cause o anesthetic deaths in obstetrics and thereore deserves special attention. o minimize this risk, antacids should be given routinely, intubation should be accompanied by cricoid pressure, and regional analgesia should be employed when possible.
Pathophysiology
In 1952, eabeaut demonstrated experimentally that i the pH o aspirated fuid was below 2.5, severe chemical pneumonitis developed. It was later demonstrated that the gastric fuid pH o nearly hal o women tested intrapartum was <2.5 (aylor, 1966). Te right mainstem bronchus usually oers the simplest pathway or aspirated material to reach the lung parenchyma, and thereore, the right lower lobe is most oten involved. In severe cases, involvement is bilateral and widespread.
Te woman who aspirates may develop evidence o respiratory distress immediately or several hours ater aspiration, depending in part on the material aspirated and the severity o the response. Aspiration o a large amount o solid material causes obvious signs o airway obstruction. Smaller particles without acidic liquid may lead to patchy atelectasis and later to bronchopneumonia.
When highly acidic liquid is inspired, decreased oxygen saturation along with tachypnea, bronchospasm, rhonchi, rales, atelectasis, cyanosis, tachycardia, and hypotension are likely to develop. At the injury sites, there is pulmonary capillary leakage and exudation o protein-rich fuid containing numerous erythrocytes into the lung interstitium and alveoli. Tis causes decreased pulmonary compliance, shunting o blood, and severe hypoxemia.
Suspicion o aspiration demands close monitoring or evidence o pulmonary damage. Respiratory rate and oxygen saturation as measured by pulse oximetry are the most sensitive and earliest indicators o injury. Radiographic changes may not appear immediately and may be variable. Tereore, chest radiographs alone should not be used to exclude aspiration.
Treatment
Inhaled fuid should be immediately and thoroughly wiped rom the mouth and removed rom the pharynx and trachea by suction. Saline lavage may urther disseminate the acid throughout the lung and is not recommended. I large particulate matter is inspired, bronchoscopy may be indicated to relieve airway obstruction. Use o corticosteroid therapy or prophylactic antimicrobial administration are not supported by clinical or experimental evidence (Mandell, 2019). I inection develops, however, vigorous treatment is given. Etiological agents have shited rom anaerobic or mixed inections to bacteria causing community- or hospital-acquired pneumonitis (Metlay, 2019). Tese inections are discussed in Chapter 54 (p. 962). I acute respiratory distress syndrome develops, mechanical ventilation with positive end-expiratory pressure may prove liesaving (Chap. 50, p. 885).
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