Maternal Labor Analgesia

The National Institutes of Health State-of-the-Science statement on cesarean delivery on maternal request emphatically concluded that “maternal request for cesarean delivery should not be motivated by unavailability of effective [labor] pain management.” While most hospitals in the United States now offer labor analgesia, this is not necessarily the case in many parts of the world, and studies suggest that the introduction of epidural analgesia may be an effective approach to decrease the cesarean delivery rate in these settings.

Adequate maternal analgesia and perineal relaxation are also important for instrumental (forceps, vacuum) vaginal deliveries. Neuraxial techniques can optimize anesthetic conditions for these obstetric procedures (see Chapter 23 ).

External Cephalic Version

Singleton breech presentations occur in 3% to 4% of term pregnancies. The Royal College of Obstetricians and Gynaecologists and the American College of Obstetricians and Gynecologists (ACOG) caution against a vaginal breech delivery, given poorer neonatal outcomes compared with planned cesarean delivery. External cephalic version (ECV), a procedure by which manual external pressure is applied to the maternal abdomen to change the fetal presentation from breech to cephalic, remains a viable option. ECV is usually performed between 36 and 39 weeks’ gestation (see Chapter 34 ).

Meta-analyses of available trial data support the finding that neuraxial analgesia or anesthesia increases the success rate of attempted ECV. Moreover, these studies show that the use of neuraxial blockade does not appear to compromise maternal and fetal safety, and specifically it does not increase the risk for fetal bradycardia, placental abruption, or fetal death.

Intrauterine Resuscitation

Evidence of intrapartum fetal compromise (nonreassuring fetal status) should prompt the obstetric team (including obstetric, anesthesia, and nursing providers) to attempt intrauterine fetal resuscitation ( Box 26.4 ). These actions include changing maternal position to relieve aortocaval compression, administering vasopressors and intravenous fluid to treat maternal hypotension, discontinuing exogenous oxytocin administration, and, in cases of uterine tachysystole, administration of a tocolytic agent such as terbutaline or nitroglycerin (see Chapter 8 ).

Preanesthetic Evaluation

All women admitted for labor and delivery are potential candidates for the emergency administration of anesthesia, and an anesthesia provider ideally should evaluate every woman shortly after admission. Optimally, for high-risk patients, preanesthesia consultation should occur in the late second or early third trimester, even if a vaginal delivery is planned. This practice offers the opportunity to provide patients with information, solicit further consultations, optimize medical conditions, and discuss plans and preparations for the upcoming delivery. Early communication among the members of the multidisciplinary team is encouraged. In some cases, the urgent nature of the situation allows limited time for evaluation before induction of anesthesia and commencement of surgery; nonetheless, essential information must be obtained and risks and benefits of alternative anesthetic management decisions should be considered.

A focused preanesthetic history and physical examination includes (1) a review of maternal health and anesthetic history, relevant obstetric history, allergies, and baseline blood pressure and heart rate measurements; and (2) performance of an airway, heart, and lung examination consistent with the American Society of Anesthesiologists (ASA) guidelines (see Appendix B ).

Blood Products

Peripartum hemorrhage remains a leading cause of maternal mortality worldwide (see Chapters 37 and 39 ). There is little difference in blood loss between an uncomplicated elective cesarean delivery and an uncomplicated planned vaginal birth ; however, a cesarean delivery performed during labor or in the setting of abnormal placentation is associated with greater blood loss. Risk factors for peripartum hemorrhage are listed in Box 26.5 .

Preparation for obstetric hemorrhage includes (1) reviewing the patient’s history for anemia or risk factors for hemorrhage; (2) consulting with the obstetric team regarding the presence of risk factors; (3) reviewing reports of ultrasonographic or magnetic resonance images of placentation; (4) obtaining a blood sample for a type and screen or cross-match; (5) contacting the blood bank to ensure the availability of blood products; (6) obtaining and checking the necessary equipment (blood filters and warmers, infusion pumps and tubing, compatible fluids and medications, and standard clinical laboratory collection tubes; and (7) consulting with a blood bank pathologist, hematologist, and/or interventional radiologist in selected cases ( Box 26.6 ).

Currently, there is a lack of consensus as to which patients require a blood type and screen and which patients require a cross-match. The maternal history (previous transfusion, existence of known red blood cell antibodies) and anticipated hemorrhagic complications, as well as local institutional policies, should guide decision-making. In certain high-risk cases (e.g., suspected placenta accreta), blood products (e.g., 2 to 4 units of packed red blood cells) should be physically present near or in the operating room before making the surgical incision, if possible.

Monitoring

Attention should be given to the availability and proper functioning of equipment and monitors for the provision of anesthesia and the management of potential complications (e.g., failed tracheal intubation, cardiopulmonary arrest). Equipment should be checked on a daily basis and serviced at recommended intervals. The equipment and facilities available in the labor and delivery operating room suite should be comparable to those available in the main operating room.

The ASA standards for basic monitoring apply to the provision of anesthesia for all patients. Within obstetrics, basic monitoring consists of maternal pulse oximetry, electrocardiography (ECG), and noninvasive blood pressure monitoring, ^a

a Outside the operating room, and before the onset of labor, maternal blood pressure is ideally measured (using an appropriately sized cuff with a bladder length that is 80% and a width that is at least 46% of the arm circumference) after a rest period of 10 minutes or more, with the pregnant woman sitting or lying on her left side with her arm at the level of the right atrium. The onset (phase 1) and disappearance (phase 5) of Korotkoff sounds correspond to systolic and diastolic pressures, respectively

ECG abnormalities are often observed in late pregnancy and are believed to be caused by hyperdynamic circulation, circulating catecholamines, and/or altered estrogen and progesterone concentration ratios (see Chapter 2 ). During cesarean delivery with neuraxial anesthesia, ECG changes have a reported frequency of 25% to 60% ; in this setting, administration of droperidol, ondansetron, and oxytocin may be associated with prolongation of the QTc interval, and oxytocin administration may be associated with ST-segment depression. The significance of these ECG findings as an indicator of cardiac pathology remains unclear, because only a small minority of parturients experience myocardial ischemia as measured by elevated serum cardiac troponin levels or echocardiographic wall motion abnormalities. The placement of five ECG leads improves the sensitivity of detecting ischemic events; combining leads II, V ₄ , and V ₅ resulted in a sensitivity of 96% for detecting ST-segment changes in a nonobstetric population. In a prospective study of 254 healthy women undergoing cesarean delivery with spinal anesthesia, Shen et al. determined the incidence of first- and second-degree atrioventricular block (3.5% for each), severe bradycardia (< 50 bpm; 6.7%), and multiple premature ventricular contractions (1.2%). The investigators speculated that a relative increase in parasympathetic activity occurred as a result of spinal blockade of cardiac sympathetic activity. Most of the dysrhythmias were transient and resolved spontaneously.

Processed electroencephalogram monitors used to indicate the depth of anesthesia have received only limited evaluation in women undergoing cesarean delivery. Whether routine use of these monitors can reduce the incidence of intraoperative awareness during general anesthesia for cesarean delivery is unclear (see later discussion).

An indwelling urinary catheter is used in almost all women undergoing cesarean delivery. A urinary catheter helps avoid overdistention of the bladder during and after surgery. In cases associated with hypovolemia and/or oliguria, or anticipated significant blood loss, a collection system that allows precise measurement of urine volume is helpful.

The FHR is often assessed by a qualified individual before and after administration of anesthesia. However, data are insufficient to determine the value of FHR monitoring before elective cesarean delivery in patients without risk factors. Our practice is to monitor FHR until the abdominal skin preparation for cesarean delivery has begun.

In some cases of emergency cesarean delivery, a previously placed fetal scalp (or buttock) ECG electrode can be used to monitor the FHR before, during, and after the initiation of anesthesia. Typically, the fetal scalp electrode is removed when the surgical drapes are applied to the abdomen, but in some cases the scalp electrode may be left in place until just before delivery, when the circulating nurse reaches under the drapes to disconnect the electrode. Continuous FHR monitoring is useful in this setting for at least three reasons. First, the FHR abnormality often resolves; in some cases, the obstetrician will then elect to forgo the performance of a cesarean delivery. In other cases, the obstetrician may continue with plans to perform a cesarean delivery, but continuous FHR monitoring may facilitate the administration of neuraxial anesthesia. For example, an improved FHR tracing allows time for extension of epidural anesthesia or administration of spinal anesthesia. Second, continuous FHR monitoring may guide management in cases of failed tracheal intubation. If intubation fails and there is no evidence of fetal compromise, both the anesthesia provider and the obstetrician will have greater confidence in a decision to awaken the patient and proceed with an alternative anesthetic technique. By contrast, if there is evidence of ongoing fetal compromise, the anesthesia provider may decide to provide general anesthesia by means of a face mask or supraglottic airway, and the obstetrician may proceed with cesarean delivery (see Chapter 29 ). Third, intraoperative FHR monitoring allows the obstetrician to modify the surgical technique according to the urgency of delivery.

Invasive monitoring (e.g., arterial catheter), noninvasive cardiac output monitoring, or echocardiography may be indicated for individual patients at high risk for cardiopulmonary compromise.

Equipment

Labor and delivery units may be adjacent to or remote from the main operating rooms. In some facilities, the unit is located on a separate floor but shares a common operating room facility (used for other surgical procedures), whereas in others it is a geographically separate, self-contained unit with its own operating room facilities. Regardless of location, the equipment, facilities, and support personnel available in the labor and delivery operating room should be comparable to those available in the main operating room. In addition, personnel and equipment should be available to care for obstetric patients recovering from major neuraxial or general anesthesia.

Resources for the conduct and support of neuraxial anesthesia and general anesthesia should include those necessary for the basic delivery of anesthesia and airway management as well as those required to manage complications (e.g., failed tracheal intubation). The immediate availability of these resources is particularly important, given the frequency and urgency of anesthesia care. Consideration should be given to having some of the equipment and supplies immediately available in one location or in a cart (e.g., difficult airway cart, massive hemorrhage cart, malignant hyperthermia box) specifically located on the labor and delivery unit. Equipment and supplies should be checked on a frequent and regular basis. Securing special-situation equipment and supplies in a cart with a single-use breakthrough plastic tie helps ensure that the cart is kept in a fully stocked state.

Aspiration Prophylaxis

The patient should be asked about oral intake, although insufficient evidence exists regarding the relationship between recent ingestion and subsequent aspiration pneumonitis (see Chapter 28 ). Gastric emptying of clear liquids during pregnancy occurs relatively quickly; the residual content of the stomach (as measured by ultrasonographic assessment of the cross-sectional area of the gastric antrum 60 minutes after the ingestion of 300 mL of water) does not appear to be different from baseline fasting levels in either lean or obese nonlaboring pregnant women. Moreover, when measured by serial gastric ultrasonographic examinations and acetaminophen (paracetamol) absorption, the gastric emptying half-time of 300 mL of water is shorter than that of 50 mL of water in healthy, nonlaboring, nonobese pregnant women (24 ± 6 versus 33 ± 8 minutes, respectively).

The healthy patient undergoing elective cesarean delivery may drink modest amounts of clear liquids up to 2 hours before induction of anesthesia. Examples of clear liquids are water, fruit juices without pulp, carbonated beverages, clear tea, black coffee, and sport drinks. The volume of liquid ingested is less important than the absence of particulate matter. Patients with additional risk factors for aspiration (e.g., morbid obesity, diabetes, difficult airway) or laboring patients at increased risk for cesarean delivery (e.g., nonreassuring FHR pattern) may have further restrictions of oral intake, determined on a case-by-case basis.

Ingestion of solid foods should be avoided in laboring patients and patients undergoing elective surgery (e.g., scheduled cesarean delivery or postpartum tubal sterilization). A fasting period for solids of 6 to 8 hours, depending on the fat content of the food, has been recommended.

A reduction in gastric content acidity and volume is believed to decrease the risk for damage to the respiratory epithelium if aspiration should occur. Oral administration of a nonparticulate antacid (0.3 M sodium citrate , pH 8.4) causes the mean gastric pH to increase to greater than 6 for 1 hour; it does not affect gastric volume. Histamine-2 (H ₂ )-receptor antagonists (e.g., ranitidine, famotidine) , proton pump inhibitors (e.g., omeprazole), and metoclopramide reduce gastric acid secretion and volume but require at least 30 to 40 minutes to exert their effects. A systematic review of interventions used to reduce the risk for aspiration pneumonitis in women undergoing cesarean delivery found a significant reduction in the risk for gastric pH less than 2.5 with antacids (relative risk [RR], 0.17; 95% confidence interval [CI], 0.09 to 0.32), H ₂ -receptor antagonists (RR, 0.09; 95% CI, 0.05 to 0.18), and proton-pump inhibitors (RR, 0.26; 95% CI, 0.14 to 0.46), compared with no treatment or placebo. The combined use of an antacid and an H ₂ -receptor antagonist was found to be more effective in reducing pH less than 2.5 than administration of placebo or an antacid alone. However, in a randomized evaluation, sodium citrate was associated with a higher incidence and severity of nausea than an H ₂ -receptor antagonist (famotidine), suggesting that a H ₂ -receptor antagonist may be the preferred agent in selected patients. Metoclopramide is a promotility agent that hastens gastric emptying, increases lower esophageal sphincter tone, and decreases nausea and vomiting. Before surgical procedures, the timely administration of a nonparticulate antacid, an H ₂ -receptor antagonist, and metoclopramide should be considered, especially for nonelective procedures.

Prophylactic Antibiotics

Prophylactic antibiotic administration results in a 60% decrease in the incidence of endometritis, a 25% to 65% decrease in the incidence of wound infection, and fewer episodes of fever and urinary tract infections for both elective (nonlaboring) and nonelective (laboring) cesarean deliveries. The ACOG has recommended the prophylactic administration of a narrow-spectrum antibiotic, such as a first-generation cephalosporin, within 1 hour of the start of cesarean delivery.

Antibiotics with efficacy against gram-positive, gram-negative, and some anaerobic bacteria are commonly used for prophylaxis for cesarean delivery. Appropriate coverage includes intravenous ampicillin 2 g, cefazolin 1 g, or ceftriaxone 1 g. Appropriate antibiotic coverage should last for 3 to 4 hours; therefore, ampicillin may be less appropriate owing to a shorter half-life than the cephalosporins. In parturients with a significant allergy to beta-lactam antibiotics (e.g., history of anaphylaxis, angioedema, respiratory distress, or urticaria), intravenous clindamycin with gentamicin is a reasonable alternative.

Because of the greater volume of distribution, higher doses of antibiotics may be considered in women with a body mass index (BMI) greater than 30 kg/m ² or an absolute weight greater than 120 kg. After administration of cephazolin 2 g, Pevzner et al. observed that the minimum inhibitory tissue concentration for gram-negative rods was not achieved at the time of skin incision or closure in 20% of obese women and 33% of morbidly obese women.

A 2016 randomized controlled trial addressed whether surgical site infection prophylaxis should be broadened to cover species commonly associated with postcesarean infection (e.g., ureaplasma). Women undergoing cesarean delivery after labor or rupture of membranes were randomized to receive standard antibiotics with or without the addition of azithromycin (500 mg). Although the addition of azithromycin decreased the prevalence of the composite infection endpoint by one-half (6.1% versus 12.0%), almost three-fourths of the trial participants were obese, raising concern that the standard antibiotics may have been underdosed. The 2018 ACOG guidelines suggest that prophylactic azithromycin administration may be considered for nonelective cesarean delivery.

In the past, prophylactic antibiotics were typically administered after umbilical cord clamping because of concern that fetal antibiotic exposure might mask a nascent infection and/or increase the likelihood of a neonatal sepsis evaluation. However, a meta-analysis demonstrated that preincision antibiotic prophylaxis reduces the incidence of postcesarean endometritis and total maternal infectious morbidity, without evidence of adverse neonatal effects. Thus, current guidelines recommend administration of prophylactic antibiotics within 60 minutes before the start of the cesarean delivery.

Aseptic Technique

In the early 19th century, Ignác Semmelweis observed that puerperal fever, known as “childbed fever,” was most likely transmitted when the first stage of labor was prolonged and multiple individuals performed vaginal examinations with contaminated hands. Since that time, the practice of hand hygiene has caused a significant reduction in maternal and neonatal infectious morbidity.

The immunologic changes of pregnancy may impair clearance of infections. Epidural abscess and meningitis have been reported as complications of neuraxial procedures in obstetric patients (see Chapter 31 ). As a consequence, obstetric anesthesia providers should always give careful attention to aseptic technique, especially during performance of a neuraxial procedure. Proper sterile technique for neuraxial procedures includes wearing a face mask, performing hand hygiene, and donning sterile gloves (see Chapter 12 ). Attention should also be given to the careful preparation of anesthetic drugs during administration of either general or neuraxial anesthesia. An increasing number of institutions are using premixed solutions of local anesthetic and opioid (prepared under aseptic conditions in a hospital or compounding pharmacy) to limit breaches in aseptic technique during the administration of neuraxial anesthesia.

Intravenous Access and Fluid Management

The establishment of functional intravenous access is of critical importance to the successful outcome of many clinical situations in obstetric anesthesia practice. According to the Hagen-Poiseuille equation, the infusion rate of fluid through a catheter is directly related to the pressure gradient of the fluid and the fourth power of the catheter’s radius, and inversely related to the viscosity of the fluid and the catheter’s length. Because the size of the catheter, more than the size of the vein, dictates the flow rate, the use of a short, large-diameter catheter (e.g., 16- or 18-gauge) is associated with the best flow.

In general, a smaller but functional catheter is more important than a larger catheter that is unreliable or requires frequent manipulation. Smaller catheters may be acceptable in an emergency; volume and blood resuscitation can be satisfactorily achieved using 20- and 22-gauge catheters (without evidence of greater red blood cell destruction) with the use of dilution, pressurization, or both. However, in situations when more rapid resuscitation is needed, especially when large blood loss is anticipated, or administration of multiple blood products is required, the anesthesia provider may choose to insert a central venous catheter.

Although the administration of intravenous fluids may decrease the incidence of neuraxial anesthesia-associated hypotension, initiation of anesthesia should not be delayed to administer a fixed volume of fluid, particularly in the case of an emergency cesarean delivery, in which the life and health of the mother and the infant are best preserved with timely delivery. Vasopressors can be used for both prophylaxis and treatment of hypotension. The type of fluid (crystalloid, colloid) and the volume, rate, and timing of administration are relevant factors in the prevention and treatment of hypotension. In most situations, a balanced salt solution such as lactated Ringer’s solution is acceptable. Blood products are most often administered with normal saline. Crystalloid or colloid solutions that contain calcium or glucose should not be administered with blood products, owing to the risks for clotting (caused by reversal of the citrate anticoagulant) and clumping of red blood cells, respectively.

Traditionally, approximately 1 L of crystalloid solution has been administered intravenously (as “prehydration” or “preload”) to prevent or reduce the incidence and severity of hypotension during neuraxial anesthesia for cesarean delivery. However, prehydration, even with large volumes (30 mL/kg), is minimally effective in preventing neuraxial anesthesia-induced hypotension. Although an initial study found that administering crystalloid solution at the time of the intrathecal injection (“co-load”) was more efficacious than prehydration in preventing hypotension, later studies did not support this finding, likely because the infusion rate was too slow. Colloid, administered before or at the time of the intrathecal injection, is more effective than crystalloid for preventing hypotension. Colloid administered before the intrathecal injection (preload) is equally efficacious as commencing administration at the time of injection (co-load). In healthy patients, we rapidly administer approximately 1 L of crystalloid starting at the time of initiation of neuraxial anesthesia. For patients at high risk for hypotension or the consequences of hypotension, colloid may be administered before or at the time of initiation of neuraxial blockade. Hypotension despite fluid administration is treated with vasopressors (see later discussion).

Supplemental Medications for Anxiety

The administration of benzodiazepines, even low doses (e.g., midazolam 0.02 mg/kg), may result in amnesia ; as a consequence, benzodiazepines are typically avoided during awake cesarean delivery. However, on occasion, particularly in women with severe anxiety or undergoing an emergency cesarean delivery, the use of low doses of intravenous midazolam or an opioid may facilitate performance of a neuraxial technique, awake tracheal intubation, or the induction of general anesthesia. Anxiolytics may also assist in mitigating the feelings of distress during the birthing experience, which may lessen the risk for developing posttraumatic stress disorder. The use of low doses of sedative or anxiolytic agents has minimal to no neonatal effects. In a trial of healthy women randomized to receive intravenous midazolam (0.02 mg/kg) and fentanyl (1 µg/kg ^b

b The Institute for Safe Medicine Practices (ISMP) has recommended that health care providers never use µg as an abbreviation for micrograms, but rather they should use mcg ( http://www.ismp.org/tools/errorproneabbreviations.pdf , accessed April 6, 2018). The use of the symbol µg is frequently misinterpreted and involved in harmful medication errors. The abbreviation may be mistaken for mg (milligrams), which would result in a 1000-fold overdose. The symbol µg should never be used when communicating medical information, including pharmacy and prescriber computer order entry screens, computer-generated labels, labels for drug storage bins, and medication administration records. However, most scholarly publications have continued to use the abbreviation µg. The editors have chosen to retain the use of the abbreviation µg throughout this text. However, the editors recommend the use of the abbreviation mcg in clinical practice.

Positioning

After 20 weeks’ gestation, most practitioners position patients with left uterine displacement to minimize aortocaval compression. The supine hypotension syndrome, which is caused by compression of the aorta and inferior vena cava by the gravid uterus, can manifest as pallor, tachycardia, sweating, nausea, hypotension, and dizziness. Uteroplacental blood flow is compromised by decreased venous return and cardiac output, increased uterine venous pressure, and compression of the aorta or common iliac arteries.

The full lateral position minimizes aortocaval compression but does not allow performance of cesarean delivery. Fifteen degrees of left lateral tilt (left uterine displacement) has been proposed to significantly reduce the adverse hemodynamic consequences of the supine position, although both the aorta and inferior vena cava may remain partially compressed. However, most anesthesia providers overestimate the degree of lateral tilt. These elements may explain the results of a 2013 systematic review that concluded that left compared with right lateral tilt was associated with some maternal and fetal benefit, but outcomes were not dramatically different among different positions. Overall, data were insufficient to prove or disprove the benefits of tilting or flexing the operating room table or using wedges or mechanical displacers during positioning for cesarean delivery.

Whether left uterine displacement is necessary in the context of patients receiving a co-load of fluid and a prophylactic phenylephrine infusion at the time of induction of spinal anesthesia has been questioned. In healthy, term women undergoing elective cesarean delivery, there was no difference in neonatal acid-base status in women randomized to the supine position versus left uterine displacement, despite mean maternal cardiac output being lower in the supine group. The trial excluded women at increased risk for aortocaval compression (e.g., polyhydramnios, multiple gestation, obesity) or women with impaired placental perfusion (e.g., fetal growth restriction, preeclampsia). Given these limitations, and the apparent absence of adverse maternal or fetal effects with lateral uterine displacement, the routine use of this technique should not be abandoned. Anesthesia providers should recognize that (1) susceptibility to aortocaval compression varies among individuals, (2) visual estimates of lateral tilt may be in error, and (3) in symptomatic women, increasing the extent of left uterine displacement may be beneficial. Lateral tilt should be used in all women in mid- to late pregnancy after the administration of neuraxial or general anesthesia, with greater tilt used when feasible if aortocaval compression is suspected as the cause for maternal or fetal compromise.

The use of a slight (10 degrees) head-up position may help reduce the incidence of hypotension after initiation of hyperbaric spinal anesthesia. A 30-degree head-up position significantly increases functional residual capacity compared with the supine position in term parturients, although this effect diminishes with increasing BMI. In morbidly obese patients receiving general anesthesia, a 25-degree head-up position may be particularly useful to improve denitrogenation and glottic view during direct laryngoscopy ; this position can be accomplished with blankets or commercially available devices (see Chapters 29 and 49 ). If blankets are used to create the ramp position, they should be stacked rather than interlaced, to allow for rapid removal and readjustment of the head and neck position if necessary. The ideal position aligns the external auditory meatus and the sternal notch in a horizontal plane; this position (1) aligns the oral, pharyngeal, and tracheal axes (“sniffing position”) and (2) facilitates insertion of the laryngoscope blade (see Fig. 29.7 ).

Theoretically, the Trendelenburg (head-down) position may augment venous return and increase cardiac output. The value of this approach in preventing hypotension during neuraxial anesthesia has been questioned. After the initiation of hyperbaric spinal anesthesia, the Trendelenburg position has been reported to result in more cephalad spread of anesthesia in one study but not in others. However, this position had no effect on the incidence of hypotension after administration of hyperbaric spinal anesthesia.

The optimal patient position for initiation of neuraxial anesthesia may depend on clinical circumstances and the preferences and skills of the anesthesia provider (see Chapter 12 ). Whether the use of the lateral or the sitting position is best for routine initiation of neuraxial anesthesia is controversial. Advocates of the lateral position cite a reduction of vagal reflexes, which can result in dizziness, diaphoresis, pallor, bradycardia, and hypotension. Moreover, the lateral position may allow better uteroplacental blood flow than the sitting position, but this is controversial. The lateral position may also be associated with a small increase in maternal cardiac index, stroke volume index, heart rate, and systolic blood pressure compared with the sitting or supine positions. Further, in a randomized controlled trial, the severity and duration of hypotension were greater in women randomly assigned to receive CSE anesthesia (hyperbaric spinal bupivacaine with fentanyl) in the sitting position than the lateral position, despite no differences in the level of sensory blockade.

Some parturients find the lateral position more comfortable during administration of neuraxial anesthesia, whereas others find the sitting position more comfortable. Moreover, because uterine compression of the vena cava diverts blood into the epidural venous plexus, the use of the lateral position can reduce hydrostatic pressure and engorgement of the epidural venous plexus. Studies suggest that epidural catheter placement in the lateral recumbent head-down position results in lower risk for lumbar epidural venous plexus cannulation than the sitting or the lateral recumbent horizontal position in both obese and nonobese parturients.

Magnetic resonance imaging and computed tomography studies show that the cross-sectional area and the anteroposterior diameter of the dural sac at the level of the L3–L4, L4–L5, and L5–S1 interspaces are significantly influenced by posture. Lumbar cerebrospinal fluid (CSF) pressure is lower and dural sac cross-sectional area smaller in the recumbent compared with the upright position. Theoretically, the lateral position may be of value during advancement of an epidural needle because it minimizes the prominence of the dural sac. By contrast, a bulging dural sac might be preferable during administration of spinal or CSE anesthesia. Bulging of the lumbar dural sac—particularly in the sitting position—may decrease the force required to create a dural puncture with a Tuohy epidural needle, but this possibility is unproven.

The sitting position also has some advantages, including easier landmark recognition in obese parturients and ease of positioning patients in a symmetrical position (the spine is often rotated in the lateral position because the bottom shoulder is fixed). Given that there is no evidence that one position is universally better than the other, patient position for initiating neuraxial anesthesia is largely a matter of practitioner preference. However, anesthesia providers should be facile with the placement of needles for neuraxial techniques in both the sitting and lateral positions, because the sitting position should not be used in some situations (e.g., umbilical cord prolapse, footling breech presentation).

Supplemental Oxygen

The routine administration of supplemental oxygen during elective cesarean delivery with neuraxial anesthesia is controversial. It became a common practice following the seminal report by Fox and Houle that demonstrated improved oxygenation, better umbilical cord blood acid-base measurements, and less time to sustained respiration in the neonate, when mothers undergoing cesarean delivery with neuraxial anesthesia breathed 100% oxygen instead of air for at least 10 minutes. However, later evidence suggested that routine oxygen administration may be unnecessary, ineffective and possibly detrimental. A 2016 meta-analysis of randomized trials performed in low-risk women undergoing elective cesarean delivery found that the administration of supplemental oxygen compared with room air was associated with higher maternal oxygen saturation, maternal Pa o ₂ , umbilical vein P o ₂ , and umbilical artery P o ₂ , but no differences in 1- and 5-minute Apgar scores.

The use of a fractional inspired concentration of oxygen (F io ₂ ) of 0.35 to 0.4 (which cannot be obtained by using a nasal cannula or a simple face mask with a flow rate less than 6 L/min ) does not improve fetal oxygenation during labor or elective cesarean delivery. Although respiratory function can deteriorate in parturients receiving neuraxial anesthesia, maternal or fetal hypoxemia does not normally occur when parturients breathe room air. An F io ₂ of 0.6 in nonlaboring women undergoing elective cesarean delivery with spinal anesthesia increases the umbilical venous oxygen content by only 12%; an increase in oxygen content is not observed when the uterine incision-to-delivery (U-D) interval exceeds 180 seconds.

Supplemental oxygen may have detrimental effects. High levels of maternal F io _2, are necessary for significant maternal-fetal oxygen transfer, but also result in the formation of reactive oxygen species and subsequent peroxidation of lipids, alteration of cellular enzymatic functions, and destruction of genetic material. Known to extend ischemia-reperfusion injury, deplete antioxidants, and suppress immune function, free radicals have also been implicated in the pathogenesis of disorders related to prematurity, including neonatal retinopathy, bronchopulmonary dysplasia, necrotizing enterocolitis, and intraventricular hemorrhage.

Nonetheless, the emergency cesarean delivery of the compromised fetus should include maternal oxygen administration of high F io ₂ , particularly in the setting of uterine contractions, which can exacerbate fetal compromise; in these situations, supplemental oxygen may reduce the severity of fetal hypoxia with limited oxygen free-radical effects. Term (but not preterm) fetuses may be able to withstand the adverse effects of these reactive oxygen species through a compensatory increase in antioxidants during labor. Antioxidants, the defense against reactive oxygen species, consist of enzymatic inactivators (superoxide dismutase, catalase, peroxidase) and scavengers (ascorbate, glutathione, transferrin, lactoferrin, ceruloplasmin). The activity of these compensatory mechanisms and their relationship to gestational age and labor suggest that the highest risk for ischemia-reperfusion injury occurs in preterm fetuses before the onset of labor.

The a use of high F io ₂ (greater than 0.6) improves oxygen transfer to hypoxic fetuses for a limited period (approximately 10 minutes); beyond this time, continued hyperoxia, especially in the setting of restored perfusion, increases reactive oxygen species, placental vasoconstriction, and fetal acidosis. A lower F io ₂ may be of benefit in some situations. Of interest, when asphyxiated infants are immediately resuscitated at birth with air instead of 100% oxygen, better short-term outcomes have been observed ; this finding may be a result of the shift in the balance between beneficial oxygenation and detrimental free radicals.

All women who are at risk for requiring general anesthesia for emergency cesarean delivery should receive an F io ₂ of 1.0 after transfer to the operating table to simultaneously promote maternal oxygenation and denitrogenation; denitrogenation significantly reduces the risk for maternal hypoxemia during apnea before tracheal intubation.

Although the value of supplemental oxygen use during elective cesarean delivery with neuraxial anesthesia of a noncompromised fetus is questionable, some obstetric anesthesia providers place nasal cannulae or a mask to monitor ventilation using expired carbon dioxide analysis.

Neuraxial versus General Anesthesia

Overall, neuraxial (epidural, spinal, CSE) techniques are the preferred method of providing anesthesia for cesarean delivery; specific benefits and risks of each technique dictate the eventual choice. In contemporary practice, neuraxial anesthesia is administered to some patients who would have received general anesthesia in the past. Umbilical cord prolapse, placenta previa, and preeclampsia with severe features are no longer considered absolute indications for general anesthesia. For example, in some cases a prolapsed umbilical cord can be decompressed, and if fetal status is reassuring, a neuraxial technique can be used. In an analysis of obstetric anesthesia trends in the United States between 1981 and 2012, a progressive increase was noted in the use of neuraxial anesthesia, especially spinal anesthesia, for both elective and emergency cesarean deliveries. Neuraxial anesthesia is now used for more than 95% of elective cesarean deliveries and 80% of emergent cesarean deliveries in the United States. Similar increases have occurred in other developed as well as developing countries.

The greater use of neuraxial anesthesia for cesarean delivery has been attributed to several factors, including (1) the growing use of epidural techniques for labor analgesia, (2) an awareness of the possibility that an in situ epidural catheter may decrease the necessity for general anesthesia in an urgent situation, (3) improvement in the quality of neuraxial anesthesia with the addition of an opioid to the local anesthetic, (4) appreciation of the risks of airway complications during general anesthesia in parturients, (5) the desire for limited neonatal drug transfer, and (6) the ability of the mother to remain awake to experience childbirth and to have a support person present in the operating room. Spinal anesthesia is considered an appropriate technique even in the most urgent settings; in a tertiary care institution with an average of 9500 cesarean deliveries annually, neuraxial anesthesia was used in more than 99% of cesarean deliveries over a 6-year period. In the setting of a category 1 (immediate threat to life of woman or fetus) cesarean delivery, Kinsella et al. described a “rapid-sequence spinal” technique, by which skin preparation, spinal drug combinations, and the spinal technique were simplified; the median time from positioning until satisfactory neuroblockade was 8 minutes (interquartile range [IQR] 7 to 8, range 6 to 8).

Maternal mortality following general anesthesia has been a primary motivator for the transition toward greater use of neuraxial anesthesia for cesarean delivery. A study compared the anesthesia-related maternal mortality rate from 1979 to 1984 with that for the period from 1985 to 1990 in the United States. The estimated case-fatality risk ratio for general versus neuraxial anesthesia was as high as 16.7 in the years 1985 to 1990; however, a similar analysis by the same group of investigators found a nonsignificant risk ratio of 1.7 in the years 1991 to 2002. This shift may reflect technological advances in the devices available for airway management and their widespread dissemination (e.g., supraglottic airways, fiberoptic bronchoscopes). Of interest, these data may overstate the relative risk associated with general anesthesia, because this method of anesthesia is used principally when neuraxial anesthetic techniques are contraindicated for medical reasons or time constraints.

The type of maternal morbidity differs with the use of neuraxial anesthetic techniques and general anesthesia. A systematic review of randomized and quasi-randomized controlled trials comparing major maternal and neonatal outcomes with the use of neuraxial anesthesia and general anesthesia for cesarean delivery found less maternal blood loss and shivering but more nausea in the neuraxial anesthesia group. The intraoperative “perception” of pain was greater in the neuraxial group, but the time elapsed before the first postoperative request for analgesia was longer. Prospective audits of post-cesarean delivery outcomes have indicated that in the first postoperative week, patients who received neuraxial anesthesia had less pain, gastrointestinal stasis, coughing, fever, and depression and were able to breast-feed and ambulate more quickly than patients who received general anesthesia.

Neonatal outcomes associated with maternal anesthetic selection require further study. Apgar and neonatal neurobehavioral scores are relatively insensitive measures of neonatal well-being, and umbilical cord blood gas and pH measurements may reflect the reason for the cesarean delivery rather than differences in the effect of the anesthetic technique on fetal/neonatal well-being. In a meta-analysis, lower umbilical cord blood pH measurements were associated with spinal, but not epidural, anesthesia compared with general anesthesia. However, the study included both randomized and nonrandomized trials and both elective and nonelective procedures, and most trials were conducted in an era when ephedrine was used to support maternal blood pressure (see later discussion). In a systematic review of randomized trials in which the indication for cesarean delivery was not urgent, no differences in umbilical cord arterial blood pH measurements were found among general and neuraxial anesthetic techniques.

Overview of Neuraxial Anesthetic Techniques

Table 26.5 outlines the advantages and disadvantages of the various neuraxial anesthetic techniques for cesarean delivery. With all neuraxial techniques, an adequate sensory level of anesthesia is necessary to minimize maternal pain and avoid the urgent need for administration of general anesthesia. Because motor nerve fibers are typically larger and more difficult to block, the complete absence of hip flexion and ankle dorsiflexion most likely indicates that a functional sensory and sympathetic block is also present in a similar (primarily lumbosacral) distribution. However, because afferent nerves innervating abdominal and pelvic organs accompany sympathetic fibers that ascend and descend in the sympathetic trunk (T5 to L1), a sensory block that extends rostrally from the sacral dermatomes to T4 should be the goal for cesarean delivery anesthesia.

TABLE 26.5

Advantages and Disadvantages of Neuraxial Anesthetic Techniques for Cesarean Delivery

Neuraxial Technique	Advantages	Disadvantages
Epidural	No dural puncture required Can use in situ catheter placed for earlier administration of labor analgesia Ability to titrate extent of sensory blockade Continuous intraoperative anesthesia Continuous postoperative analgesia	Slow onset of anesthesia Larger drug doses required than for spinal techniques: • Greater risk for maternal local anesthetic systemic toxicity • Greater fetal drug exposure
Combined spinal-epidural	May be technically easier than spinal anesthesia in obese patients Low doses of local anesthetic and opioid Rapid onset of dense lumbosacral and thoracic anesthesia Ability to titrate extent of sensory blockade Continuous intraoperative anesthesia Continuous postoperative analgesia	Delayed verification of functioning epidural catheter
Continuous spinal	Low doses of local anesthetic and opioid Rapid onset of dense anesthesia Ability to titrate extent of sensory blockade Continuous intraoperative anesthesia	Large dural puncture increases risk for post–dural puncture headache Possibility of overdose and total spinal anesthesia if the spinal catheter is mistaken for an epidural catheter
Single-shot spinal	Technically simple Low doses of local anesthetic and opioid Rapid onset of dense lumbosacral and thoracic anesthesia	Limited duration of anesthesia Limited ability to titrate extent of sensory blockade

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