Obstetric Anatomy, Physiology, and Pathophysiology

Question 1

How does blood volume change during pregnancy?

How does this affect the hematocrit?

Answer 1

The blood volume increases as pregnancy progresses. The
total increase is about 25-40% over normal values at term.
Because the red blood cell mass only increases by about 20%,
there is a relative anemia present.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1127.

Question 2

How does the change in blood volume alter blood

viscosity in the pregnant patient?

Answer 2

Because the increased blood volume has fewer red blood cells,
it is less viscous. It is believed that this may be a key factor in
maintaining patency of the uteroplacental blood supply.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
21.

Question 3

How does blood pressure change with pregnancy?

Answer 3

The change in blood pressure roughly follows the changes in
the systemic vascular resistance which decreases slightly in
early pregnancy and as much as a 20% decrease by term. In
contrast to the SVR, however, the blood pressure usually
returns to baseline at term.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
19.

Question 4

How does systemic vascular resistance change
during pregnancy? What is responsible for this
change?

Answer 4

SVR decreases by as much as 21% by term. Much of this
change is due to the decreased resistance in the vasculature of
the uterus, placenta, kidneys, and lungs.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1127

Question 5

How is myocardial contractility affected by

pregnancy?

Answer 5

Myocardial contractility is increased.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
17.

Question 6

How does left ventricular end-diastolic and endsystolic
volume change during pregnancy? How
does this affect ejection fraction?

Answer 6

The left ventricular end-diastolic volume increases during
pregnancy, but there is no change in the end-systolic volume.
As a result, the ejection fraction during pregnancy is increased.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
17.

Question 7

How does cardiac output in the pregnant patient

compare to that of the nonpregnant patient?

Answer 7

By the end of the first trimester, the cardiac output is 15-25%
higher than nonpregnant values.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
17.

Question 8

How long after delivery does cardiac output remain

elevated?

Answer 8

Cardiac output reaches as high as 80% above normal
immediately after delivery and returns to normal slowly over a
period of about 14 days.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1127.

Question 9

How does pregnancy affect coagulation? What is

gestational thrombocytopenia?

Answer 9

Pregnant patients exhibit an escalation in their ability to form
and dissolve clots. About 7.6% of pregnant women exhibit a
platelet count less than 150,000/microliter which is referred to
as gestational thrombocytopenia.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
23.

Question 10

What is the most common cardiac valvular defect

seen in parturients?

Answer 10

Mitral stenosis is the most common cardiac valvular defect seen
in pregnant patients. It typically presents symptoms such as an
increased incidence of pulmonary edema, atrial fibrillation, and
atrial tachycardia. Although general or regional anesthesia is
used for cesarean sections in these patients, most practitioners
utilize epidural segmental anesthesia during vaginal delivery to
minimize the incidence of symptoms due to the disorder.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
892.

Question 11

What clotting factors are decreased in pregnancy?
What factors are unchanged? What factors are
increased?

Answer 11

Factors XI and XIII are decreased in pregnancy. Factors II and
V are unchanged. Virtually everything else is increased (factors
I, VII, VIII, IX, X, and XII).
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
22.

Question 12

How is the blood leukocyte count affected by

pregnancy?

Answer 12

The white blood cell count increases from around 6,000/mm3 to
about 11,000/mm3 predominantly due to an increase in
polymorphonuclear cells. The white blood cell count increases
to 13,000/mm3 during labor and as high as 15,000/mm3 on the
first postpartum day. Within a week postpartum, WBC levels fall
to around 9,000/mm3.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
23.

Question 13

How are albumin levels affected by pregnancy?

How does this affect the colloid osmotic pressure?

Answer 13

Plasma albumin levels fall from 4.5 g/dL to 3.3 g/dL by term,
which results in a decrease in the colloid osmotic pressure by
about 5 mmHg.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
22.

Question 14

How would you expect the arterial blood gas of a

parturient at term to appear and why?

Answer 14

Oxygen consumption increases by about 33%, but minute
ventilation increases by 50% at term. The increased alveolar
ventilation results in an increase in the PaO2 to about 106
mmHg and a decrease in the PaCO2 to about 30-32 mmHg.
The plasma base (HCO3-) decreases from about 26 to 22
mEq/L, thus, the pH is essentially unchanged.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1129.

Question 15

How does inspiration change in the parturient at term

and why?

Answer 15

Inspiration is due almonst entirely to diaphragmatic excursion.
Because the thoracic cage is already expanded at rest, further
expansion is very limited.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
19.

Question 16

How would you expect lung volumes to change

during pregnancy?

Answer 16

The inspiratory capacity increases slightly due to increases in
the tidal volume and inspiratory reserve volume. This is offset
by an equivalent decrease in expiratory reserve volume. The
functional residual capacity decreases by about 20% by term
and is primarily due to the elevation of the diaphragm as the
uterus enlarges. Total lung capacity is only slightly reduced.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
20.

Question 17

How does oxygen demand and minute ventilation
change during pregnancy? How do PaO2 and
PaCO2 levels change?

Answer 17

By term, oxygen demand increases by about 33% and minute
ventilation increases by about 50%, mostly due to an increase
in tidal volume. The PaCO2 is usually between 30 and 32
mmHg and the PaO2 is higher than 100 mmHg at term.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1129

Question 18

How do airway resistance and lung compliance

change with pregnancy?

Answer 18

Lung compliance and airway resistance don’t change. Airway
resistance stays roughly the same because of the competing
effects between the relaxation of bronchiolar smooth muscle by
progesterone versus increased airway resistance caused by
factors such as upper airway edema.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 1146.

Question 19

When do cardiovascular changes begin to occur in
pregnancy? What are the changes that occur early
in pregnancy?

Answer 19

Cardiovascular changes begin to occur as early as 4 weeks.
The heart rate increases by 20-30% by term. Starting in the
5th week, the cardiac output begins to increase, primarily by an
increase in stroke volume, but also by the increase in heart
rate. By term, it has increased by about 40%.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1127

Question 20

Why are pregnant patients at higher risk for

aspiration?

Answer 20

Pregnancy results in more acidic gastric secretions and a
decreased lower esophageal sphincter tone.
Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC,
Ortega R. Clinical Anesthesia. 7th ed. Philadelphia, PA:
Lippincott Williams and Wilkins; 2013: 1146.

Question 21

How does thyroid function change with pregnancy

and why?

Answer 21

Follicular hyperplasia and increased vascularity result in a 50-
70% increase in the size of the thyroid gland in pregnant
patients. Estrogen induces an increase in total T3 and T4
levels by the end of the first trimester.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
26.

Question 22

At what point during pregnancy should rapidsequence

induction be considered mandatory?

Answer 22

The general recommendation is to utilize a rapid sequence
induction of general anesthesia for patients at or past the 12th
week of gestation due to the increased risk of aspiration.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 1129

Question 23

Does pregnancy result in an increased or decreased

sensitivity to insulin?

Answer 23

The release of the hormone lactogen by the placenta causes an
increase in insulin resistance during pregnancy.
Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut’s
Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009:
26.

Question 24

What is meant by arrest of descent?

Answer 24

Arrest of descent is failure of the head to descend 1 cm in
station after adquate pushing. It may require c-section, but a
crash induction is unlikely as the situation is not necessarily
emergent.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 861.

Question 25

You are preparing to induce general anesthesia for a post-partum patient undergoing tubal ligation. Should you utilize a rapid sequence induction for this patient?

Answer 25

Yes. The recommendations for rapid sequence induction also apply in this situation because it is not known when the gastric volume and acidity and lower esophageal sphinter tone return to normal. Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis, MO: Elsevier Saunders Company; 2014: 1129.

Question 26

What is the minimum fasting period for an elective | cesarean section?

Answer 26

Because parturients have decreased gastric emptying times and an increased risk for gastric reflux, the minimum fasting period for an elective cesarean section is 6 hours for light meals and 8 hours for heavy meals. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill; 2013: 845.

Question 27

What is the incidence of hydronephrosis in pregnant | patients and what explains this?

Answer 27

The incidence of hydronephrosis is 80% in pregnant patients. The increased blood and interstitial volume produce a compensatory increase in renal volume. The urinary collecting system (collecting ducts, calcyes, renal pelvis, and ureters) dilate substantially, producing hydronephrosis in 80% of pregnant women by mid-term. Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut's Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009: 25

Question 28

How do plasma levels of renin and angiotensin II | change during pregnancy?

Answer 28

Despite the increased blood volume levels, plasma renin and angiotensin II levels are increased. In fact, by the third trimester, plasma renin activity is 12 times greater in parturients. The sensitivity of the vasculature to angiotensin II is decreased but sensitivity to norepinephrine is not changed. Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut's Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009: 17-23

Question 29

Pain during the first stage of labor is usually confined | to what dermatomes? The active stage of labor?

Answer 29

During the first stage of labor, the pain is due primarily to uterine contractions and cervical dilation and thus is confined to the T10-T11 dermatomes. As it progresses to the active phase of labor, however, it will involve the T10-L1 dermatomes. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill; 2013: 846.

Question 30

How much blood is typically lost during an | uncomplicated vaginal delivery?

Answer 30

About 600 mL. Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut's Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009: 23

Question 31

What polypeptide is associated with the | development of back pain in pregnant patients?

Answer 31

In addition to the lordotic strain the gravid uterus places on the lumbar spine, the corpus luteum and placenta release a polypeptide called relaxin that promotes remodelling of collagen fibers and connective tissue. The serum levels of relaxin is positively correlated with the incidence of back pain in pregnant patients. Chestnut DH, Polley LS, Tsen LC, Wong CA. Chestnut's Obstetric Anesthesia. Philadelphia, PA: Mosby Elsevier; 2009: 26.

Question 32

What are the five mechanisms by which molecules | cross the placental barrier?

Answer 32

There are five mechanisms of placental exchange: 1) Diffusion, by which small ions, respiratory gases, and most anesthesia drugs under 1000 daltons cross, 2) Bulk flow, which is how water crosses the membrane, 3) Active transport, which is responsible for the transfer of amino acids, vitamins, calcium, and iron, 4) Pinocytosis, which is how larger molecules such as immunoglobulins cross the placental barrier, and 5) Breaks in the placental membrane which allow the mixing of maternal and fetal blood. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill; 2013: 830-831.

Question 33

What is the difference between gestational | hypertension, pre-eclampsia, and eclampsia?

Answer 33

Gestational hypertension is the appearance of hypertension without proteinuria or edema during pregnancy. Preeclampsia is hypertension with proteinuria and edema during pregnancy. If a preeclamptic patient develops seizures, the condition is referred to as eclampsia. HELLP syndrome is a form of preeclampsia characterized by hemolysis, elevated liver enzymes, and a low platelet count. Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases. 6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 563-567.

Question 34

What are the manifestations of preeclampsia?

Answer 34

Manifestations of preeclampsia include: hypertension, hypovolemia, oliguria, decreased colloid oncotic pressure, pulmonary edema, arterial hypoxemia, grand mal seizures, decreased uterine blood flow, disseminated intravascular coagulation, cerebral edema, cerebral hemorrhage, acute tubular necrosis, and HELLP syndrome (hemolysis, elevated liver enzymes, low platelets). Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases. 6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 567.

Question 35

How does pre-eclampsia affect airway management | in parturients and postpartum patients?

Answer 35

Patients with pre-eclampsia may exhibit laryngeal edema following protracted forceful expulsion of the fetus and may require a smaller endotracheal tube. Jaffe RA, Samuels SI. Anesthesiologist's Manual of Surgical Procedures. 4th ed. Philadelphia, PA: Lippincott Williams and Wilkins, 2009: 829.

Question 36

What is HELLP syndrome?

Answer 36

HELLP syndrome is an abnormal condition associated with pregnancy in which the patient exhibits hemolysis, elevated liver enzymes, and a low platelet count. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill; 2013: 864-865.

Question 37

What is placental abruption?

Answer 37

Abruption of the placenta can result in massive blood loss and is one of the most common causes of fetal demise. If the abruption is mild, a vaginal delivery may be attempted, but at any sign of fetal distress an emergency cesarean section must be carried out. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill; 2013: 862.

Question 38

What is the difference between placental abruption, | placenta accreta, and placenta previa?

Answer 38

Placenta accreta is the abnormal adherence of the placenta to the myometrium. Massive hemorrhage may occur when the attempt to remove the placenta after delivery is made. Abruptio placentae is the premature separation of a normally implanted placenta after 20 weeks gestation. Abdominal pain is always present, but the amount of bleeding and the corresponding treatment depends upon the degree of separation of the placenta. Placenta previa is the partial or total covering of the cervical os by the placenta. It is associated with painless vaginal bleeding and typically develops at about 32 weeks gestation when the lower uterine segment forms. Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases. 6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 566-570.

Question 39

What is persistent occiput posterior?

Answer 39

Persistent occiput posterior is an abnormal fetal presentation that results in prolonged and painful delivery. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill; 2013: 861.

Question 40

What is the difference between placenta accreta, | placenta increta, and placenta percreta?

Answer 40

Placenta accreta is a condition where the placenta adheres to the surface of the myometrium, placenta increta refers to placental implantation within the myometrium, and placenta percreta refers to the condition where the placenta completely penetrates the myometrium. Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis, MO: Elsevier Saunders Company; 2014: 1153.

Question 41

What factors increase the risk for placenta accreta?

Answer 41

Patients with placenta previa who have had one previous csection are 20-25% more likely to have placenta accreta, (penetration of the myometrium by placental villi). After four or more c-sections, the incidence of placenta accreta increases by more than 67%. Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis, MO: Elsevier Saunders Company; 2014: 1153.

Question 42

What is the most common cause of painless vaginal | bleeding during pregnancy?

Answer 42

Placenta previa is the most common cause of painless vaginal bleeding during pregnancy and may be treated with bedrest and scheduled c-section or even vaginal delivery if the bleeding is mild. Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail's Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill; 2013: 862.