Obstetric Anesthesia Part I Flashcards
1
Q
The physiologic changes that occur during pregnancy are the result of:
A
- Increased metabolic demands
- Hormonal and anatomic changes
2
Q
How long do physiologic changes in pregnancy last?
A
- Begin early in pregnancy
- Last into the postpartum period
3
Q
When do cardiovascular changes begin during pregnancy?
A
- Early as the 4th week
- Continue to the postpartum period
4
Q
What happens to maternal heart rate (HR) at term?
A
Increases by 20% to 30% at term.
5
Q
How much does Cardiac Ouput increases during pregnancy?
A
- Increases ~ 40% over nonpregnant values.
- Starts in the fifth week of pregnancy.
6
Q
What factors contribute to the increase in cardiac output during pregnancy?
A
- Increase in stroke volume (SV) (20%–50%)
- To a lesser extent, heart rate (HR).
7
Q
What percentage of the cardiac output perfuses the gravid uterus at term?
A
- Approximately 10%
8
Q
Why does cardiac output increase immediately after delivery?
A
- Due to autotransfusion of blood from the contracting uterus.
- Increased venous return from aortocaval decompression.
- Increases 80% above pre-labor values
9
Q
How does the position of the heart change during pregnancy?
A
- During pregnancy, the diaphragm is displaced cephalad, shifting the heart up and to the left.
- Making the cardiac silhouette appear enlarged on x-ray examination.
10
Q
What is the percentage % increase of Blood volume during pregnancy?
A
- 25% to 40% throughout pregnancy.
- To prepare for normal blood loss associated with delivery.
11
Q
What are the changes of Plasma volume and RBC volume during pregnancy?
A
- Plasma volume increases by 40%-50%
- RBC volume increases by only 20%.
12
Q
What are the normal blood loss ranges for vaginal delivery and uncomplicated cesarean delivery?
A
- Normal blood loss for vaginal delivery is less than 500 mL.
- Uncomplicated cesarean delivery, it is 500 to 1000 mL.
13
Q
What compensatory mechanisms help tolerate blood losses at delivery?
A
- Increased total Blood volume.
- Increased Plasma volume.
These mechanism help tolerate blood loss.
14
Q
How is the Systemic vascular resistance (SVR) affected during pregnancy?
A
- Decreases by 21% by the end of a term pregnancy.
15
Q
SVR reduction during pregnancy is primarily due to reduced resistance in the following:
SVR= Systemic Vascular Resistant
A
- Uteroplacental vascular beds
- Pulmonary vascular beds
- Renal vascular beds
- Cutaneous vascular beds
16
Q
How much does Diastolic Blood Pressure (DBP) decreases during pregnancy?
A
Up to 15 mm Hg
Resulting in a decrease in MAP.
17
Q
Aortocaval compression, and what happens when it occurs?
A
- Decreases venous return to the heart and arterial flow to the uterus and lower extremities.
- Occurs when the gravid uterus compresses both the vena cava and the aorta.
- AKA: Aortocaval compression, or “syndrome of supine hypotension,”
18
Q
What are the consequences of aortocaval compression?
A
- Decreased cardiac output
- Compromise fetal perfusion
- Cause the mother to loose consciousness.
19
Q
How can the compressive effect of the uterus on the vena cava and aorta be reduced?
A
- By elevating the mother’s right torso by 15- 30 degrees.
- This maneuver is known as the left displacement of the uterus.
20
Q
When should left displacement of the uterus be used?
A
- For anyone in their second or third trimester of pregnancy.
- Alleviate aortocaval compression and its associated risks.
21
Q
Aortocaval Compression
A
22
Q
What factors in the coagulation cascade increase during pregnancy?
A
- Factors I (fibrinogen), VII, VIII, IX, X, & XII increase concentration.
- Through pregnancy and peak at term.
23
Q
How does von Willebrand factor (vWF) change during pregnancy?
A
- vWF increases up to 400% at term.
24
Q
What happens to factors XI and XIII during pregnancy?
A
Tend to decrease during pregnancy.
25
How do fibrinogen levels change during pregnancy?
* In the nonpregnant state average from 200 to 400 mg/dL.
* Late in pregnancy normally at least 400 mg/dL and may reach as high as 650 mg/dL.
26
What typically happens to the platelet count in the third trimester of pregnancy?
Remains stable or may be slightly decreased in the third trimester.
27
What is the overall trend in white blood cell count during pregnancy?
* WBC tends to rise during pregnancy.
28
What causes capillary engorgement in the upper airway during pregnancy?
Results in a **narrowed glottic opening and edema** in the:
* Nasal.
* Oral pharynx.
* Larynx.
* Trachea.
29
Why should nasal intubation be generally avoided in pregnant individuals?
* Due to the risk of a narrowed glottic opening and upper airway edema.
* A 6.5-to-7-mm cuffed oral endotracheal tube is recommended when intubation is necessary.
30
What might be beneficial for obese pregnant patients with enlarged breasts during intubation?
* May benefit from the use of a short-handled laryngoscope during intubation.
* Data handle laryngoscope
31
How does oxygen (O2) consumption change during term pregnancy?
* Increases by up to 33% at rest.
* 100% or more during the second stage of labor in term pregnancy.
32
What causes the increase in minute ventilation during term pregnancy?
* Primarily due **to a 40% increase in tidal volume.**
* At term is increased by 50%,
* The respiratory rate remains unchanged or increases by only 10%.
33
What happens to the normal arterial partial pressure of carbon dioxide (Paco2) during pregnancy?
* By 12 weeks of gestation, the normal Paco2 decreases to approximately 30 to 32 mm Hg.
* Remains in this range throughout pregnancy.
34
How are functional residual capacity (FRC), expiratory reserve volume, and residual volume affected during pregnancy?
* FRC, expiratory reserve volume, and residual volume decrease.
* Primarily due to upward pressure on the diaphragm, resembling restrictive lung disease.
35
Factors contributing to rapid **arterial desaturation** in the apneic pregnant patient:
* The combination of decreased FRC (20%)
* Increased oxygen (O2) consumption in pregnancy
36
Do vital capacity and closing capacity (CC) change during pregnancy?
No, vital and closing capacities (CC) do not change during pregnancy.
37
How do increased cardiac output and the shift in the oxyhemoglobin dissociation curve contribute to oxygen delivery during pregnancy?
* Rightward shift help maximize oxygen delivery to both the mother and fetus.
38
What can cause maternal Paco2 to drop below 15 mm Hg during pregnancy?
* Increase in Minute ventilation
| Up to 300% during contractions
39
Know this APEX Table
40
Know this APEX table.
41
Summary of Physiologic changes
42
How much does uterine blood flow increase to at term?
Up to 700-900 mL/min at term.
43
Does uterine blood flow autoregulate?
* No, uterine blood flow does not autoregulate.
44
What primary factors affect uterine blood flow in a low-resistance system?
* Depends on mean arterial pressure (MAP).
* Cardiac output.
44
What factors affect/depend on Uterine Blood Flow?
* MAP.
* CO.
* Uterine vascular resistance.
45
What does recent evidence suggest about using phenylephrine and ephedrine in maintaining placental perfusion and fetal pH in healthy mothers?
* They are efficacious as ephedrine in maintaining placental perfusion and fetal pH in healthy mothers.
46
What physiochemical drug characteristics favor placental transfer?
- Low molecular weight (< 500 Daltons)
- High lipid solubility
- Non-ionized
- Non-polar
47
Where does pain begin in the first stage of labor, and which nerve roots are involved?
- Pain begins in the lower uterine segment and cervix.
- Pain signals travel to the T10 - L1 posterior nerve roots.
48
What additional areas contribute to pain in the second stage of labor, and which nerve roots are involved?
- In the second stage of labor, pain impulses also come from the vagina, perineum, and pelvic floor.
- Pain impulses travel from the perineum to the S2 - S4 posterior nerve roots.
49
How should neuraxial techniques be extended to manage labor pain effectively during both stages?
* Neuraxial techniques providing analgesia to T10-L1 during the first stage must be extended to cover S2 - S4.
* During the second stage of labor for total coverage from T10 - S4.
50
Pain in Labor and Delivery Chart
51
What are the three stages of labor?
- Stage 1: Beginning of regular contractions to full cervical dilation (10 cm)
- Stage 2: Full cervical dilation to delivery of the fetus (Pain in the perineum begins during stage two)
- Stage 3: Delivery of the placenta
52
What does the Friedman curve illustrate?
Illustrates the normal progress of labor.
53
What is dysfunctional labor, and how can it be managed?
* Dysfunctional labor occurs when labor does not follow the expected pattern.
* Oxytocin may be required to help the labor progress in such cases.
54
How can understanding the Friedman curve be helpful in anesthesia practice during labor?
* It can help make informed decisions about anesthetic techniques used during labor's progression.
55
APEX Stages of Labor Table
56
Intrapartum Fetal Evaluation
57
Why is the fetal heart rate important in intrapartum fetal evaluation, and what does it indicate?
* The fetal heart rate is a surrogate measure of overall fetal well-being.
* Provides an indirect method to assess fetal hypoxia and acidosis.
58
What factors affect fetal oxygenation, and how does the fetus respond to stress?
* Is influenced by uterine and placental blood flow.
* The fetus responds to stress with peripheral vasoconstriction, hypertension, and a baroreceptor-mediated reduction in heart rate.
59
What does fetal heart rate variability indicate, and what is the normal range?
* Suggests an intact central nervous system and the healthy functioning of the sympathetic (SNS) and parasympathetic (PNS) nervous systems.
* The normal range of fetal heart rate variability is 6 - 25 bpm.
60
How is variability categorized, and what do different categories indicate?
Variability can be categorized as:
* Minimal (< 5 bpm)
* Moderate (6 - 25 bpm)
* Marked (> 25 bpm)
* Absent (a worrisome finding)
61
What are some factors that can reduce fetal heart rate variability?
- CNS depressant drugs (opioids, sedatives, anesthetic agents, barbiturates, MgSO4),
- Hypoxemia
- Fetal sleep
- Acidosis
- Certain congenital conditions like anencephaly and cardiac anomalies.
62
What is an acceleration in fetal heart rate (FHR), and what does it indicate?
- An acceleration is an abrupt increase in the FHR above baseline.
- Accelerations occur in response to fetal movement and indicate adequate oxygenation.
63
When is the FHR pattern considered reactive, and what does it mean?
* Is considered reactive when two or more accelerations occur in a 20-minute period.
* It suggests that the fetus responds well to stimuli and is likely healthy.
64
What are the three types of decelerations in FHR, and how are they classified?
* Early
* variable
* late
* Based on their timing concerning the contractions during labor.
65
What causes early decelerations in FHR?
Fetal head compression during uterine contractions.
66
How do early decelerations affect the fetal heart rate?
* Heart rate decrease of <20 bpm from baseline.
* Mirroring uterine contractions.
67
Do early decelerations pose a risk of fetal hypoxemia?
No, early decelerations do not pose a significant risk of fetal hypoxemia.
68
Early decelerations have an onset and offset that:
- Parallel uterine contraction
- They typically lose variability with each deceleration.
69
Late decelerations occur due to:
* Uteroplacental insufficiency
* Leads to decreased uteroplacental perfusion and fetal compromise.
70
When does FHR fall during Late Deceleration?
* After the peak of contraction.
* It returns to baseline after the contraction.
71
Late decelerations are associated with:
* Contraction and characterized by a gradual reduction in FHR.
72
Late decelerations are caused by conditions like:
- Maternal hypotension
- Hypovolemia
- Acidosis
- Preeclampsia causes late decelerations.
73
Late Deceleration poses a risk for:
- Fetal hypoxemia
- Requires urgent assessment of fetal status.
74
Variable decelerations occur due to:
Umbilical cord compression.
75
Variable decelerations show:
There is no consistent pattern concerning uterine contractions.
76
During Variable decelerations, Umbilical compression leads to:
Baroreceptor-mediated reduction in FHR.
77
Variable decelerations are usually:
Self-limiting and maintaining variability during deceleration.
78
Variable Decelerations
- Prolonged fetal compromise may extend FHR recovery time.
- They pose a risk for fetal hypoxemia and require urgent assessment of fetal status.
79
How does ACOG categorize fetal heart rate (FHR) tracings?
ACOG categorizes FHR tracings into a three-tiered system.
80
What defines Category I FHR tracings, and what do they predict?
- Category I FHR tracings are normal with a normal baseline HR, moderate variability, absent variable, and late decelerations.
- They predict normal acid-base balance.
81
What do Category II FHR tracings include, and what do they indicate?
- Category II FHR tracings include those not classified as Category I or III.
- They do not predict abnormal acid-base status and require continued observation.
82
Describe Category III FHR tracings and what they predict.
- Category III FHR tracings have fetal bradycardia or absent variability with recurrent late or variable decelerations.
- They predict abnormal acid-base status and necessitate prompt intervention.
83
What caution should be exercised when considering neuraxial analgesia in the presence of nonreassuring FHR tracing?
If the FHR tracing suggests hypoxia, caution should be used when deciding to proceed with neuraxial analgesia.
84
What factors should be carefully considered regarding fetal compromise and anesthetic intervention?
Consider the severity of fetal compromise and the possibility of worsening it with anesthetic intervention.
85
Under what circumstances might the obstetric team request a neuraxial anesthetic for a patient with nonreassuring FHR tracing?
The obstetric team may request a neuraxial anesthetic in anticipation of a possible urgent and unplanned operative vaginal delivery or cesarean delivery.
86
What is intrauterine resuscitation, and what are some interventions involved in it?
- Intrauterine resuscitation includes interventions to improve the condition of a compromised fetus in utero.
87
What are some examples of Intrauterine Interventions?
* Changing maternal position
* Rapid IV fluid infusion
* Discontinuing oxytocin
* IV pressor support for maternal Hypotension
* Rocolytic agents
* Maternal oxygen administration to correct maternal hypoxia.
