Obstetric Anesthesia: A Case-Based and Visual Approach

With 32 engaging and dramatic cases and 174 colorful, insightful and innovative graphics, this book takes a fresh, creative and highly visual approach to the fundamentals of obstetric anesthesia as well as emerging knowledge and three emerging technologies: 1) pre-procedural ultrasound to facilitate neuraxial block placement, 2) point-of-care transthoracic echocardiography to guide maternal resuscitation, and 3) electrical cardiometry to trend maternal cardiac output and avoid fetal hypoxia.  Besides discussing the threats to fetal oxygenation presented by labor and the avoidance of maternal and fetal complications while providing excellent anesthesia, the book also explores the psychological and behavioral dimensions of obstetric anesthesia practice and promotes the obstetric anesthesiologist as a valued member of the obstetric care team who makes unique, insightful and empathic contributions to the overall excellent care of pregnant patients. Obstetric Anesthesia: A Case-Based and Visual Approach is an indispensable resource for medical students, residents, fellows, anesthesiologists, nurse anesthetists, nurse midwives, and obstetricians.

• Language: English
• Publisher: Springer
• Release date: Feb 20, 2020
• ISBN: 9783030264789

Book preview

Part IPregnancy, Anesthesia and Threats to Fetal Oxygenation

© Springer Nature Switzerland AG 2020

T. L. Archer (ed.)Obstetric Anesthesiahttps://doi.org/10.1007/978-3-030-26478-9_1

1. Normal Pregnancy, Labor, and Delivery––Without Epidural Analgesia

Thomas L. Archer¹  

(1)

Department of Anesthesiology 2008–2015, University of California San Diego School of Medicine, San Diego, CA, USA

Thomas L. Archer

Case Presentation

A 20-year-old woman, G1P0, presents to Labor & Delivery (L&D) in active labor at 40 weeks estimated gestational age (L-1). She has painful uterine contractions, and her cervix is 4 cm dilated on admission. The nurses easily start an IV in one of the prominent superficial veins of her forearm, and they position the patient in bed tilted toward her left side. The obstetric anesthesiologist visits the patient as a matter of routine—to introduce herself to the patient, to find out basic information about her medical history, and to answer any questions she may have about the options for pain relief during labor. The patient thanks the anesthesiologist for the visit, but says she is going to try to go natural (L-2). The first stage of labor is very painful, and the patient accepts a small dose of intravenous nalbuphine for analgesia, but continues to decline an epidural (L-3). Soon, her cervix becomes fully dilated, and she pushes or bears down with each contraction, performing a Valsalva maneuver to push the baby head first down the birth canal. After a painful and exhausting second stage of labor, she delivers a healthy baby girl and is joyful to be a new mother! The tired but happy mother receives her vigorous baby from the nurses and gets skin-to-skin contact with the baby immediately. The baby makes sucking movements with her mouth, and the mother puts the baby to her breast (L-4). The nurses check the uterine fundus and it is firm. Oxytocin is added to the mother’s intravenous fluid and infused at a low rate (L-5).

Lessons Learned

Lesson 1

Some of the physiological changes of normal pregnancy are shown in Boxes 1.1 and 1.2 [1] as well as Table 1.1 [2], while Fig. 1.1 graphically summarizes the hemodynamics of normal pregnancy before the onset of labor. The increased metabolic demands of pregnancy increase maternal oxygen consumption and cardiac output, and the growing uterus and placenta provide another path for blood flow, thereby lowering total systemic vascular resistance . The heart remodels while increasing 30% in weight and maternal blood volume increases by 40–50%. The high-resistance spiral arteries of the maternal endometrium also remodel and dilate to provide abundant perfusion of the intervillous spaces surrounding the chorionic villi. (A quick but important glance ahead to Chap. 13: fetal blood perfuses the chorionic villi and normally picks up oxygen from this abundant flow of maternal blood through the intervillous spaces. In preeclampsia, the remodeling and dilation of the maternal spiral arteries do not take place to an adequate degree and consequently the fetus sometimes does not get enough oxygen for normal growth.)

Table 1.1

Arterial blood gas (ABG) changes in normal pregnancy

At term, the mother has a respiratory alkalosis with metabolic compensation (less HCO3− buffer) [2]

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig1_HTML.png

Fig. 1.1

Hemodynamics of normal pregnancy. Abbreviations: BP blood pressure, CO cardiac output, IVC inferior vena cava, SVR systemic vascular resistance

Box 1.1. Hematologic, Cardiovascular, and Respiratory Changes of Pregnancy

Hematologic System

1.

Around 45% increase in blood volume and 15% increase in red cell mass.

2.

Decreased hematocrit and blood viscosity.

3.

Enhanced blood coagulation: Increased fibrinogen and 20% shortened PT and PTT.

4.

Decreased platelet count and increased platelet turnover.

5.

Increased blood stasis in the legs due to compression of the inferior vena cava by the gravid uterus, associated with an increased risk of deep vein thrombosis and pulmonary embolus.

Cardiovascular System

1.

Reversible 30% increase in heart mass (reverses after delivery).

2.

Cardiac output increases 35% by 12 weeks, 50% for the rest of pregnancy, and 60–100% during labor.

3.

Increased cardiac output leads to increased symptoms from stenotic heart lesions or pulmonary hypertension, and these symptoms may require palliative interventional procedures such as termination of pregnancy, balloon mitral valvuloplasty, or aortic valve replacement. Pulmonary hypertension is particularly dangerous in pregnancy.

4.

New valvular incompetency or electrical conduction changes. All murmurs are not flow murmurs, but most murmurs are innocent.

Respiratory System

1.

Combined maternal and fetal oxygen consumption and carbon dioxide production increase 40–50% over the nonpregnant state.

2.

Functional residual capacity (FRC) of lung decreases by 20%—and even more with obesity, supine position, or anesthesia. Since oxygen demand is increased in pregnancy and since the oxygen reserve in the FRC is decreased, the pregnant patient has a significantly diminished capacity to tolerate apnea!

3.

Increased work of breathing: 33% increase in tidal volume and a 30–50% increase in minute volume. Respiratory rate probably does not increase in pregnancy, but respiratory rate is the first vital sign to change as a result of blood loss. So an increased respiratory rate should not be attributed to pregnancy!

4.

Normal arterial blood gases (ABGs) in pregnancy are shown in Table 1.1, in comparison to the nonpregnant state.

Airway hypervascularity and swelling are common in pregnancy—especially with pushing and in preeclampsia when capillaries are leaky—and one should try not to instrument the nose for airway management in a pregnant patient.

Box 1.2. Endocrine, Renal, and Gastrointestinal Changes of Pregnancy

Endocrine System

1.

Patient’s obesity combined with placental hormones (human placental lactogen, placental growth hormone, cortisol, and progesterone) may cause gestational diabetes or exacerbate existing diabetes.

2.

Gestational diabetes occurs in 4% of pregnancies and tends to recur in subsequent pregnancies. Gestational diabetes also increases the risk of type 2 diabetes later in life.

Insulin requirement increases during pregnancy and falls rapidly after delivery of the placenta; hence, the patient’s insulin dose must be decreased immediately after delivery!

Musculoskeletal System

1.

Increased lumbar lordosis—which tends to close down the interlaminar spaces.

2.

Backache is common in pregnancy.

3.

Increased body weight increases stress on joints.

Renal System

1.

An increased glomerular filtration rate is accompanied by a normal decrease in blood urea nitrogen (BUN) and creatinine.

2.

Ureteral obstruction with hydronephrosis and pyelonephritis are common in pregnancy.

3.

One out of every 200 pregnant women will have urolithiasis.

Gastrointestinal System

1.

Gastroesophageal reflux disease (GERD) is common due to increased intra-abdominal pressure and progesterone-induced relaxation of the lower esophageal sphincter.

2.

Gastric emptying may be normal in pregnancy, but is probably impaired during labor. Despite this, light meals are sometimes provided to women in early labor to provide energy.

Non-particulate sodium citrate (Bicitra) is usually given orally to patients prior to cesarean delivery. IV metoclopramide and famotidine are sometimes used to promote gastric emptying and stop production of stomach acid, respectively.

It is important for the OB anesthesiologist to realize that the cardiovascular and respiratory systems of pregnant patients are working hard even before the onset of painful labor, and that the parturient’s other organ systems have changed substantially due to the pregnancy, as shown in Boxes 1.1 and 1.2 and Table 1.1.

Lesson 2

The atmosphere of a Labor & Delivery (L&D) unit is very different from that of the operating room (OR). Box 1.3 presents commonalities and differences between the OB and OR environments. For example, non-MDs—nurses, midwives, husbands or partners, doulas, parents, and friends—all play a much greater role in patient care in L&D than in the OR. Also, autonomy and control are very important issues for most mothers in labor, and success in OB anesthesia depends in part on respecting this psychological reality . Care is usually a negotiated process, and whenever it is medically, logistically, and ethically permitted, the OB anesthesiologist should try to tailor the anesthesia experience to the patient’s wishes. Box 1.4 presents specific body language and nonverbal communication suggestions for interviewing the OB patient. The OB anesthesiologist in modern practice has the opportunity to function as an integral and continuously available member of the L&D team. In this role, the anesthesiologist can perform some or all of the following functions:

1.

She visits each patient admitted to L&D as early as possible after admission—unless the patient expresses a desire not to see the anesthesiologist.

2.

During the visit, the anesthesiologist introduces herself and explains that she is there just to get to know the patient a little—in the interest of optimizing care and being available in case of an emergency. She might even make a joke to the effect that she is not there to sell an epidural but rather that she just wants to briefly get to know the patient and answer any questions she may have.

3.

The anesthesiologist performs a 2-minute history and physical designed to pick up any red flags related to the pregnancy and the possible need for anesthesia—such as diabetes, obesity, a history of abnormal bleeding, or airway or back problems.

4.

The visit also provides an opportunity to make face-to-face contact with the nurses taking care of the patient and to see with one’s own eyes exactly what is going on in that specific labor room.

A common objection to these routine OB anesthesia consultations after a patient is admitted is that they take time, but they can usually be completed in 5 minutes or less. Furthermore, these visits can give both the patient and the anesthesiologist a sense of relief by allowing them to meet one another at a relatively stress-free point in the patient’s labor course. An early visit can be seen as an insurance policy—if there is an emergency, you already know about the patient’s airway, basic medical history, and personality, and some level of trust and mutual knowledge has been established between the patient and the anesthesiologist.

In recent years, the team approach to medical care on L&D has drawn much more attention than in the past, and companies have appeared that help train medical teams to work together more effectively and with less stress.

Box 1.3. Commonalities and Differences Between the Obstetric (OB) and Operating Room (OR) Environments

In Both OB and the OR

We are working in a highly sensitive and emotional environment.

The patient is wide awake (at least initially).

Family may be present.

Emotions run high—both for good and for ill.

We are on stage—anything we say or do may be held against us.

Hence, our behavior and demeanor (bedside manner) matter a great deal in both environments!

Only in OB

We have two patients—and both may be completely healthy!

The patient wants to be wide awake for a normal, happy event.

The patient usually wants to remember everything.

Anesthesia for vaginal delivery is usually not obligatory. Only cesarean delivery requires anesthesia.

The need for anesthesia is unpredictable (except for scheduled cases).

Family members may stay with patient during the procedure (birth).

Family dynamics may enter into the process of care.

Patients are often in pain when we meet them for the first time.

Box 1.4. Specific Body Language and Nonverbal Communication

Suggestions

Visibly sanitize your hands before and after the visit.

Introduce yourself and your team by name.

Explain why you are there.

Shake hands with everyone in the room.

Sit down for the interview.

Sit or stand facing everyone (don’t turn your back on anyone).

Make eye contact.

Use open-ended questions and learn what’s on the patient’s mind.

Give your undivided attention to the patient and listen well.

Lesson 3

Unmedicated labor involves painful uterine contractions, and both pain in itself and uterine contractions (whether they are painful or not) have hemodynamic consequences. When the uterus contracts, it squeezes blood out of itself and into the veins which drain the uterus, as shown in Fig. 1.2. If the inferior vena cava is unobstructed, this extra volume of blood (termed autotransfusion) quickly returns to the heart and causes a temporary increase in cardiac output, as is also shown in Fig. 1.2. The peak of painful uterine contractions as measured by external tocography is followed in approximately 20–40 seconds by a peak in maternal cardiac output [3–6]. This phenomenon is seen most clearly when the mother is not pushing, since the Valsalva maneuver has variable effects on venous return and cardiac output. The hemodynamic simulation shown in Fig. 1.3 is similar to those obtained in patients in the first stage of labor without epidural analgesia [5, 6].

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig2_HTML.jpg

Fig. 1.2

Hemodynamics of normal uterine contractions . The contracting uterus squeezes a bolus of autotransfused blood into the inferior vena cava, which then promptly appears as an increase in cardiac output if the inferior vena cava is unobstructed. Abbreviations: CO cardiac output, IVC inferior vena cava

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig3_HTML.png

Fig. 1.3

When the inferior vena cava is not obstructed, increases in maternal cardiac output follow the peak of uterine contraction by about 20–40 seconds, as at Point A. Note: The peaks of uterine contractions are derived from external monitor recordings. Abbreviation: IUP intrauterine pressure

Figure 1.4 shows the same simulated patient episode as shown in Fig. 1.3 but with the cardiac output broken down into heart rate and stroke volume . Figure 1.4 shows that the increases in cardiac output due to painful uterine contractions are largely due to increases in heart rate and that the effects of autotransfusion on stroke volume during painful labor are variable.

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig4_HTML.png

Fig. 1.4

Same simulated patient recording as in Fig. 1.3, with cardiac output broken down into stroke volume and heart rate. When uterine contractions are painful, the increase in cardiac output following the contraction is produced largely by an increase in heart rate, as at Point A. The relationship of the contraction to stroke volume is less clear. When contractions are painless under epidural analgesia (Figs. 1.5 and 1.6), the increase in cardiac output after each contraction is produced primarily by an increase in stroke volume, rather than heart rate. Abbreviation: IUP intrauterine pressure

In contrast to the situation seen in Figs. 1.3 and 1.4 for patients with painful contractions, when uterine contractions are not painful, the increases in cardiac output caused by autotransfusion are mediated largely by increases in stroke volume, while the heart rate changes relatively little, as shown in Figs. 1.5 and 1.6.

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig5_HTML.png

Fig. 1.5

Hemodynamics of pain-free labor . Cardiac index and intrauterine pressure in a laboring patient who is pain-free due to epidural analgesia. Peaks of cardiac index follow peaks of intrauterine pressure by an average of 40 seconds. Fifty minutes of simulated data for same patient episode as in Fig. 1.6. Abbreviations: CI cardiac index, arbitrary units; IUPC intrauterine pressure measured by catheter, arbitrary units

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig6_HTML.png

Fig. 1.6

Hemodynamics of pain-free labor . Stroke index (SI, left axis, arbitrary units), heart rate (HR, left axis, arbitrary units) and intrauterine pressure (IUPC, right axis, arbitrary units) in a laboring patient who is pain-free due to epidural analgesia. When uterine contractions are pain-free and the inferior vena cava is open, the increases in cardiac output following uterine contractions are largely produced by an increase in stroke volume, rather than heart rate. Fifty minutes of simulated data for same patient episode as in Fig. 1.5. Abbreviations: HR heart rate, IUPC intrauterine pressure measured by catheter, SI stroke index

A glance ahead: If the vena cava is obstructed (most commonly by the gravid uterus itself), the autotransfused blood returns to the heart more slowly, via the collateral lumbar, epidural, and azygos veins. A rapid increase in cardiac output immediately following uterine contractions may be an indication that the inferior vena cava is unobstructed [4], and it has been proposed that cardiac output in the pregnant patient can be used as a marker for the patency of the inferior vena cava and the adequacy of venous return in various patient positions [4].

Figure 1.7 shows the heart rate and stroke volume of a simulated patient during her final 9 hours of painful labor (averaged over 5-minute time intervals).

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig7_HTML.png

Fig. 1.7

Simulated hemodynamics of an entire labor without epidural analgesia . In this figure, heart rate and cardiac output are averaged approximately every 5 minutes from admission until after delivery. Of note are the large increases in heart rate and cardiac output during the second stage of labor and the rapid decrease of both of those parameters after delivery. This simulated patient’s heart rate reaches 180 beats/min right before delivery, which would be a threat to a patient with cardiac disease. Note: Times along x-axis are arbitrary time markers in the format: hours:minutes:seconds

Figure 1.8 focuses on the second stage of labor, delivery, and the immediate postpartum period of the same simulated patient episode as shown in Fig. 1.7, with measurements taken every 10 seconds. One can easily see from both figures that the second stage of labor, culminating in the actual delivery, involves dramatic increases in both heart rate and cardiac output.

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig8_HTML.png

Fig. 1.8

Simulated hemodynamics of the final 2 hours of the same labor as is shown in Fig. 1.7. These are simulated measurements taken every 10 seconds, and they therefore show short-term fluctuations in heart rate and cardiac output. In this simulation, cardiac output is maximal during the second stage of labor, and heart rate is maximal right at delivery. The traditional teaching is that cardiac output in labor is maximal right after delivery due to the relief of aortocaval compression and the autotransfusion of blood into the central circulation from the involuting uterus, but recent authors are questioning that teaching [7]. Note: Times along the x-axis are arbitrary time markers in the format: hours:minutes:seconds

Tachycardia by itself—even in the absence of an increase in cardiac output— presents a severe challenge to pregnant women with ischemic heart disease or hypertrophic cardiomyopathy, and epidural analgesia for labor can greatly decrease the stress on the maternal cardiovascular system presented by the increased heart rate and cardiac output associated with painful labor.

Figure 1.8 is at odds with the traditional teaching that the maternal cardiac output is maximal right after delivery, since cardiac output falls immediately after delivery in this simulation, when the patient would no longer be working hard and would no longer be in pain. Some authors [7] suggest that the increase in cardiac output after delivery is usually due to exogenous oxytocin administration, not relief of aortocaval compression, and this is probably true.

As can be seen from Figs. 1.7 and 1.8, painful labor and delivery are a challenge to the maternal cardiorespiratory system, and the increased cardiac output during the second stage of labor would be particularly dangerous in patients with stenotic lesions such as mitral or aortic stenosis or pulmonary hypertension, since the increased flow would require an increased pressure gradient across a fixed stenosis. Hence, epidural analgesia for labor can greatly decrease the stress on the maternal cardiovascular system represented by the increased cardiac output demands of painful labor.

In summary, the hemodynamic and metabolic stress of painful labor could be life-threatening in patients with heart or lung disease, and it is for this reason that epidural analgesia is not only a source of pain relief but can also be a protection to the mother with a compromised cardiorespiratory system.

Lastly, the obstetric anesthesiologist should be aware that pregnancy constitutes a stress test for life [8] which can reveal latent organ system vulnerabilities that may cause problems many years after the patient’s childbearing years are over. Examples of a positive stress test for life would be (1) the appearance in later life of cardiovascular or cerebrovascular disease in women who have had preeclampsia or (2) the development of type 2 diabetes in women who have experienced gestational diabetes .

Lesson 4

Immediate skin-to-skin contact between mother and baby, if possible, is now the standard of care, in order to promote bonding between mother and child. Nipple stimulation through breastfeeding leads to the release of endogenous oxytocin from the posterior pituitary which helps promote uterine contractions and hemostasis, as well as bonding between mother and infant through oxytocin’s behavioral effects.

Lesson 5

Figure 1.9 shows the normal situation of the placental circulation during gestation (fetus not shown): the myometrium is relaxed, and the remodeled spiral arteries which pass through it provide abundant perfusion of the placenta.

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig9_HTML.png

Fig. 1.9

Before delivery (fetus not shown), the placenta is perfused by spiral arteries fed from the uterine arteries. In this schematic diagram, the myometrium is relaxed—before the onset of labor or between contractions during labor—and the fetus is receiving adequate oxygen

Normally, after delivery, uterine contractions completely shear the placenta off the uterine wall and then expel it through the birth canal. In the absence of any impediment to its contracting further, the uterus then normally contracts completely and becomes firm. It is this contraction of uterine smooth muscle (termed living ligatures) which stops the bleeding from the spiral arteries in the placental bed and thereby prevents postpartum hemorrhage, as shown in Fig. 1.10.

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig10_HTML.png

Fig. 1.10

Hemostasis in the uterus after delivery is provided by contraction of the myometrium (uterine smooth muscle) and resultant compression of the spiral arteries in the placental bed. Hemostasis immediately after birth is not primarily the result of the functioning of the coagulation system, although the endometrium is abundantly supplied with tissue factor to promote coagulation

This is a key concept for understanding postpartum hemorrhage : if the uterus cannot completely contract due to retained products of conception (placenta or membranes), or if the uterus is tired and unable to contract for metabolic reasons (overdistention, infection, or prolonged and augmented labor), then postpartum hemorrhage will occur. Figure 1.11 shows how failure of the uterine myometrium to contract (uterine atony) leads to postpartum hemorrhage from uncompressed spiral arteries.

../images/331586_1_En_1_Chapter/331586_1_En_1_Fig11_HTML.png

Fig. 1.11

If the myometrium does not contract after placental separation and expulsion , the spiral arteries continue to bleed, constituting a postpartum hemorrhage due to uterine atony

References

1.

Resnik R, Lockwood C, Moore T, Greene M, Copel J, Silver R. Creasy & Resnik’s maternal- fetal medicine. 8th ed. Philadelphia: Elsevier, Inc.; 2019. p. 141–7.

2.

Chestnut D, Wong C, Tsen L, Ngan Kee W, Beilin Y, Mhyre J. Chestnut’s obstetric anesthesia: principles and practice. 5th ed. Philadelphia: Elsevier Saunders; 2014. p. 21.

3.

Archer T. Transthoracic echocardiography and electrical cardiometry elucidate the hemodynamics of autotransfusion during labour under epidural analgesia. Int J Obstet Anesth. 2017;31:113–5. Epub 2017 Mar 24Crossref

4.

Archer T, Shapiro A, Suresh P. Cardiac output measurement, by means of electrical