Physiology of pregnancy (parts 1-3)
When is acceleration considered a change in baseline?
if acceleration last longer than 10 minutes
What is the increase in minute ventilation at term?
increases 30-50% (primarily due to increase in TV)
What is variability?
indicates balance between sympathetic and parasympathetic ANS activity and appropriate cardiac activity
What does capillary engorgement result in?
narrowing of glottic opening and friable airway exacerbated by preeclampsia and pushing
Mild proteinuria is normal. What does significant proteinuria suggest?
preeclampsia
What causes variable decelerations?
umbilical cord compression and acute intermittent decreases in umbilical cord blood flow
In the presence of normally functioning uteroplacental unit, fetal oxygenation is determined primarily by ________
uterine blood flow
What causes late decerlatations?
-decreased uterine blood flow and placental dysfunction (insufficiency) -Maternal hypotension or hypovolemia -Placental dysfunction: preeclampsia, chronic hypertension, diabetes
What does IVC compression result in? What about Aortal compression?
IVC = decrease venous return to the heart Aortal = compromised blood flow distal to L3-L4 (uterine blood flow/fetal oxygen)
During which period is the pregnant woman with cardiac disease most at risk for cardiac decompensation?
Immediately after delivery
Identify factors that can decrease FHR variability: (8)
-fetal sleep -asphyxia -acidosis (scalp pH <7.2) -premature fetus -hypoxia -CNS depressants administered to mother (opioids, barbiturates, inhalational anesthetics, MgSO4) -cardiac conduction disturbances -encephalopathy
How does neuraxial anesthesia decrease uterine blood flow?
-hypotension (more with SAB) -unintentional IV injection of LA and/or epi -Absorbed LA
What causes variability to increase?
-increases with fetal gestational age -fetal movement
Why is Glycosuria is more common during pregnancy?
-lowered renal threshold for glucose excretion -the ↑ GFR delivers an overwhelming glucose load to the renal tubules
What are the hematologic changes?
-most coagulation factors increase -Protein C and S (anticoagulants) decrease *hypercoagulable
Why does uterine vasoconstriction decrease uterine blood flow?
-pain or stress releases catecholamines (NE) -extreme hypocapnia (pCO2 <20) can reduce uterine blood flow -exogenous vasoconstrictors: vasopressors
How does neuraxial anesthesia increase uterine blood flow?
-pain relief = decreased circulating catecholamines -Decreased SNS activity -Decreased maternal hyperventilation
What are the three layers of the uterus?
-perimetrium (outside) -myometrium (middle) -Endometrium (inside)
What kind of drugs have increased placental transfer?
-small size/molecular weight -lipid soluble -uncharged -lower albumin binding affinity
Why is the pregnant woman with cardiac disease most at risk for cardiac decompensation after delivery?
-Uterine contraction during labor displaces 300-500 mL of blood from uterus to maternal central circulation -Gravid uterus obstruction of inferior vena cava is released and increases venous return to the heart -There is the greatest increase in CO at this time
Identify anesthetic drugs that do not transfer readily across the placental membrane:
"He Is Going Nowhere Soon" -Heparin -Insulin -Glycopyrrolate -Non-depolarizing muscle relaxants -Succinylcholine (depolarizing muscle relaxant), -Sugammadex
What are the classifications of fetal heart rate variability?
-absent -minimal = less than 5 bpm -moderate = 6-25 bpm -marked = >25 bpm
What are anesthesia implications for OB airways?
-avoid nasal instrumentation -Use 6.5 or 7.0 tube -Prophylactic placement of epidural in patients with assessed difficult airway
What are late decelerations?
-begins 10-30 seconds AFTER onset of uterine contraction -descent and return to baseline gradual and smooth -occurs with each contracton
Describe the benefits/risks of neuraxial analgesia
-better pain relief and reduced risk of fetal acidosis -longer second stage labor and increased incidence of assisted vaginal delivery
How much should we reduce LA dosage for a SAB? why?
-by 25% -Decreased CSF volume -more rostral (cephalad) spread of LA -Pregnancy-induced enhanced nerve tissue sensitivity to LA
The pregnant woman tolerates the blood loss associated with birth because her total blood volume expands by _______ during pregnancy.
-90-100 mL/kg -1000-1500 mL of extra blood in circulation
What variable decelerations indicates fetal asphyxia?
-<60 bpm -prolonged (>60s) -recurrent
How do the oxygen requirements change?
-At term, O2 demand increases by 20-50% -During stage two labor, O2 demand increases by 100-300%
After 20 weeks gestation, what are interventions that can help relieve aorto-caval compression in the pregnant mother?
-Avoid supine position if possible -If supine, shift uterus to the left greater than 15 degrees (table tilt or wedge under right hip/back) -Have mother lay on her side
Why do pregnant women have "difficult airways" (i.e. difficult to ventilate and difficult to intubate)
-Capillary engorgement of larynx, naso and oropharynx -Generalized edema -cephalad displacement of thorax -breast enlargement -Narrow glottis
Describe early decelerations
-Decrease in FHR (usually 10-40 bpm) that starts and ends with uterine contraction -gradual decrease in rate -loss of variability with contraction -NOT associated with fetal distress
What are variable decelerations?
-FHR decelerations that occur before, during, or after uterine contraction, but not every contraction -vary in appearance, depth, duration, and shape
How does pregnancy impact the FRC and RV?
-FRC decreases by 20% (further decrease with supine, GA, neuraxial anesthesia) -RV decreases by 15%
How can fetal metabolism be sustained by such a low PO2?
-Fetal HGB 15-17 g/dL -bohr effect - CO2 released from fetal blood into maternal circulation - facilitates Hgb uptake of O2 -Hemoglobin F carries more O2
What is the explanation for "physiologic anemia of pregnancy"?
-Plasma volume increases by 55%; RBC increase by 30% -Dilutional effects -HGB typically remains >11 g/dL
Why is a laboring pregnant woman considered to have a "full stomach", regardless of the time of last oral intake?
-The stomach is displaced upward -Progesterone reduces LES tone -Gastric emptying is slowed/gastric volume increases during labor
Why does the cardiac output increase?
-There is an increase in blood volume by 90-100 mL/kg -Increase in SV by 25% -Increase in HR by 20%
Interpret normal American College of Obstetricians and Gynecologists category 1 based on patient history and FHR assessment:
-Tracings are normal, strongly predictive of normal fetal acid-base status. The fetus can be followed in a standard manner -Baseline rate = 110-160 bpm -Moderate variability, no late or variable decelerations -Early decelerations and accelerations may not be present
What is deceleration?
-decrease in FHR -classified as early, variable, or late
What is a normal fetal HR in term fetus?
110-160 bpm; higher FHR in immature fetus
At term, how much does the CO increase?
30-50%
Delivery should be considered if the scalp pH is _________
<7.2
The pregnant woman can become hypoxic twice as quickly as the nonpregnant woman, especially during periods of apnea (e.g. intubation). What causes this?
Decreased FRC (gravid uterus pushing up on lungs) + increased oxygen consumption = hypoxemia 2X quicker!
What auscultated heart sound is not considered normal during pregnancy?
Diastolic murmurs
FHR variability detection is most accurate with ______
Direct fetal scalp electrode
The placenta normally implants into what layer of the uterine wall?
Endometrium (inside layer)
What is the single best indication of fetal well-being?
Fetal Heart rate variability
What is fetal tachycardia at term? What causes this?
Greater than 160 bpm -Fetal asphyxia -maternal fever -prematurity -maternally administered drugs such as atropine, terbutaline, ephedrine
What causes early decelerations?
Head compression - vagally-mediated
What factors can potentially decrease uterine blood flow during pregnancy?
Hypotension, uterine vasoconstriction, uterine contrctons
Does pregnancy impact the FEV1, FEV1/FVC, flow-volume loop?
No, no change
What are the symptoms of supine hypotension syndrome?
Pallor, tachycardia (sometimes bradycardia), sweating, nausea, hypotension, and dizziness
Is uterine myometrium skeletal muscle or smooth muscle?
Smooth muscle
Following the 20th week of gestation, what induction technique must we use?
Rapid sequence ETT induction
1In the pregnant uterus, what blood vessel(s) deliver waste products, CO2, and deoxygenated blood from the fetus to capillaries of the placental villi for delivery to and elimination from the mother's circulation?
Two umbilical arteries -from fetus to mother
What do variable decelerations normal decline to?
Usually declines to <100 bpm
What is the average maternal blood loss with vaginal delivery? With C-section?
Vaginal = 600 mL C-section = 1,000 mL
What does VEAL CHOP stand for?
Variable --> cord compression Early --> Head compression Acceleration --> Okay Late --> Placental insufficiency
Are late decorations concerning?
YES - may be associated with fetal distress -evaluate fetal scalp pH -improve fetal oxygenation, address maternal hypotension
What is acceleration?
an abrupt increase in FHR >15 bpm above baseline -generally indicates adequate oxygenation
What cause cause hypotension?
aortal-caval compression, hemorrhage, sympathetic blockade, drug induced
when does the greatest increase in CO occur?
during labor and immediately after deliver
Why do uterine contractions decrease uterine blood flow?
elevate uterine venous pressure and compress arterial vessels
What is fetal bradycardia? Causes?
less than 110 bpm -Fetal or maternal hypoxia -decreased uterine blood flow -Fetal head or cord compression -Maternally administered drugs
