Exam 2 Fetal Stuff Flashcards
Blood supply to the placenta is mainly from
Uterine arteries
The uterine artery arises bilaterally from the
internal iliac arteries
In pregnancy, flow my differ between the R+L uterine arteries- explain
The vessel that supplies the placental side will have 18% increase in blood flow and 11% increase in diameter
How much is the uterine blood flow in the non-preg
50-100ml/min
How much is the uterine blood flow at term?
700-900ml/min
At term, how much uterine blood flow perfuses the placenta and how much perfuses the myometrium?
80% perfuses placenta
20% perfuses the myometrium
Maximal dilation of uterine vessels during pregnancy- So what is absent?
autoregulation is absent
Extreme hypocapnia does what to the uteroplacental blood flow?
Extreme hypocapnia (PaCo2<20mmHg) causes decreased UBF causing fetal hypoxemia and acidosis
UBF is directly proportional to
Uterine perfusion pressure (which is the difference between uterine arterial pressure and uterine venous pressure)
How do you calculate uterine perfusion pressure?
U arterial pressure - U venous pressure
Uterine perfusion pressure is directly proportional to
Uterine blood flow
UBF is inversely proportional to
Uterine Vascular resistance
Uterine Vascular resistance is inversely proportional to
UBF
How do you calculate UBF?
Uterine perfusion pressure/Uterine Vascular resistance
Or in other words UBF= UAP-UVP/UVR
What are the 3 major factors that decrease UBF?
Hypotension (decreases uterine perfusion pressure) Uterine vasoconstriction (Increases UVR) Uterine contraction (Dec UPP and Inc UVR)
What happens to uterine perfusion during contractions?
Decreases
What happens to uterine perfusion during uterine relaxation
Increases
What some things that can cause Decreased uterine arterial pressure?
Supine position (aortocaval compression)
Hemorrhage/hypovolemia
Drug-induced hypotension
Hypotension during sympathetic blockade
What are some things that can cause Increased uterine Venous pressure?
Vena caval compression
Uterine contractions
Drug induced uterine tachysystole (oxytocin, LA)
Skeletal muscle hypertonus (Scz, Valsalva)
What can cause Increased Uterine Vascular Resistance?
Endogenous vasoconstrictors - Catecholamines, Vasopressin
Exogenous Vasoconstrictors- Epi, Neo, ephedrine, LA
NA will cause (increased/decreased) uterine blood flow?
Both
How does NA increase UBF?
Increase by:
Pain relieve
Decreased sympathetic activity
Decreased maternal hyperventilation
How does NA decreased UBF?
Hypotension
Unintentional IV injection of LA or epi
Absorbed local anesthetic (little effect)
How do inhalational agents affect UBF?
0.5-1.5 MAC has little to no effect on UBF
How does ventilation effect UBF?
Moderate hypoxemia and hypercapnia have little effect
However Alkalosis will decrease UBF. So AVOID HYPERVENTILATION .
The maternal side of the placenta is called the
Basal plate or Dicidua Basilus
The fetal side of the placenta is called the
Chorion or Chorionic plate
What lies between the Basal plate and the Chorionic Plate?
Intervillous space
How much blood can be held in the intervillous space?
350ml
Where does O2/Nutrient Exchange occur in the placenta?
Terminal Arterioles/terminal villi
How much is UBF at term? Which is what % CO?
UBF at term
Max 700-900ml
Which is 10% of maternal CO
How much blood supplies the myometrium and Decidua?
Myometrium 150ml/min
Decidua 100ml/min
How much of the UBF supplies the intervillous space
80% of UBF supplies the intervillous space
Describe the maternal blood flow in regards to regulation of placental blood flow.
Spiral arteries can vasodilate as much as 10x normal diameter
Maternal blood flow enters at pressure of 70-80mmHg and rapidly decreases to 10mmHg
Describe the Fetal blood flow in regards to placental blood flow regulation
Fetal BF is controlled via effects of adrenomedullin (helps maintain placental vessel tone)
net efflux/influx of water is regulated by fetal blood pressure (fetal BP causes increase/decrease water across placenta)
Local autoregulator effects- Relaxin factors (prostacyclin and nitric acid) help control placental / Fetal circulation
Passive transport depends on
Concentration of electrochemical difference Molecular weight Lipid solubility Degree of ionization Membrane surface area and thickness
Facilitated transport depends on
Saturation kinetics
Competitive and noncompetitive inhibition
Sereospecificity
Temperature influences (inc temp=inc transfer)
With passive transport, the rate of diffusion is proportional to
the difference in the concentration gradient
Describe PO2 and PCO2 changes as blood moves from mother to placenta to fetus to placenta to mother
PO2/PCO2 Mother to placenta 98/28, Placenta to fetus (umbilical vein) 28/35, Fetus-to placenta (umbilical artery) 15/44, placenta to mother 33/37.
The placenta provides ___ ml O2/min/kg fetal body weight.
The placenta provides 8ml of o2/min/kg of fetal body weight
The placenta has ____ the O2 transfer efficiency of the adult lung
1/5
Factors that effect the transfer of respiratory gasses and nutrients from placenta to fetus
Ratio of maternal to fetal placental blood flow
O2 partial pressure gradient between the 2 circulations
Diffusion capacity of the placenta
Maternal and fetal Hgb capacities
O2 affinities
Acid/Base balance of fetal/maternal blod
How does glucose cross the placenta
simple diffusion and stereospecific-facilitated diffusion
How does insulin cross the placenta
It doesn’t
List the factors affecting drug transfer across the placenta
Lipid solubility Protein binding Tissue binding pKa pH Blood flow
How does molecular weight affect placental transfer
<1000 will cross (ex morphine) >1000 will not transer
How does charge of molecule affect placental transfer
Uncharged will cross, Charged will not transfer
How does lipid solubility affect placental transfer
Lipophilic agents cross, hydrophilic agents will not transfer
How to pH versus drug pKa affect placental transfer
Higher proportion of UNionized drug in maternal plasma will transfer, higher proportion of Ionized drug in maternal plasma will not cross
3 factors minimizing drug effects on the fetus
Dilution (drug diluted before reaching fetal circulation)
Fetal CO (shunted blood does not circulate)
Acid / Base status of fetus (“ion trapping”)
What drug do NOT cross the placenta
Glycopyrollate
Heparin
NMB-both types
Neo (Phenylephrine)
What drugs Do cross the placenta
Pretty much everything other than Glyco, Heparin, NMBs, and Neo.
How many mls of amniotic fluid at term?
400ml Between 10-20 weeks, vol increases from 25ml-400ml
Amniotic fluid consists of
Fetal urine and respiratory secretions
In fetal tissues, hypoxia occurs at O2 tension of
<17mmHg
What is the normal O2 tension of the fetus
20-25mmHg. SO if hypoxia occurs at 17mmHg, there is a very small margin of safety.
*Remember PO2/PaCo2 from the flow diagram was 28/35 (Placenta to Fetus)
In fetal tissues, hypoxia can occur at what O2 tension?
17mmHg or less…small margin of safety
Does the fetus have a good oxygen reserve?
Nope
What % of O2 from blood flow to the uterus is used for placental processes?
40% The Placenta is a “conduit and consumer” of O2
What is the normal range for glucose in the fetal circulation? How does obtain this?
54-90mg/dl The only glucose available for the fetus is what transfers across the placenta
The fetus produces ____x as much heat and maintains a temp of _____ greater than the mother
2x, 0.5 degrees Cel, > the mother
Due to high fetal metabolic rate, net flow of heat is from _____ to ______.
Fetus to mother
Fetus generates heat via (Metabolic activity or thermogenic mechanisms)?
Metabolic activity. (nonshivering thermogenesis occurs due to mitochondria, fat vacuoles, sympathetic innervation and blood vessels).
The ability to generate heat via thermogenic mechanisms isn’t developed until the end of gestation.
What is the normal length of the fetus as 12wks, 20wks, 40wks?
12w=10cm, 20w=25cm, 40wk=53cm
Wt at 23wks, 7mos, 8mos, and birth
23weeks=1lb
7mos=3lb
8mos=4lb
birth=7lb
How long after fertilization do gross characteristics of all organs begin to develop?
1 month
How long until details are developed in the organs?
2-3months
When are the organs grossly the same as the neonate?
4 months
The fetal circulation receives the CO from the (R or L ventricle)
BOTH- “Ventricles work in parallel”
What connects the umbilical vein to the IVC
Ductus Venosus
What connects the RA to LA?
Foramen Ovale
What connects the PA to the Descending Aorta?
Ductus Arteriosus
What structures does blood flow through as it leaves the placenta headed to the fetus…in order starting with Umbilical Vein
Umbilical Vein Ductus Venosus IVC RA LA LV Brain SVC RV PA Ductus Arteriosus Descending Aorta Lower extremities Hypogastric arteries Umbilical Artery Placenta
What is the normal Fetal Intravascular Volume?
110ml/kg
What % of the fetal blood volume is in the placenta?
25% (80ml/kg is in the fetus, 110ml/kg total)
The Blood volume in the FETAL BODY is about____ ml/kg
80ml/kg Remember 110ml/kg total (fetus and placenta) 25% is in the placenta, 80ml/kg is in the actual fetus. She is gonna F this right up on the exam.
The Combined Ventricular Output (CVO) is what at mid gestation and what at term?
210ml at mid gestation. Increases to 1900ml at 38weeks (500ml/kg)
Fetal hearts begins beating at _____ weeks at ___bpm
4th week, 65bpm
HR steadily _____ until reaches around ____bmp
HR increases up to around 140bpm
True alveoli develop at ____weeks
36weeks
When does the majority of alveoli develop?
6-18 months of life
What causes the Reduction in PVR at birth–Pick 4!
Expulsion of lung liquid
Abrupt surge in pulmonary blood flow
Creation of alveolar surface tension
Predominance of vasodilators vs vasoconstrictors
Surfactant is composed of mostly-
Lipids (90%) with the remainder being proteins
Where is surfactant produced?
Surfactant is formed in the Endoplasmic Reticulum and Golgi Apparatus in Type 2 alveolar cells
At 20 weeks, 90% of the amniotic fluid is provided by what organ?
Fetal Kidneys
Has 2 alpha chains and 2 gamma chains
Hgb F
What is the Tetramer for Hbg A?
2 alpha chains and 2 beta chains
Hbg F has a greater affinity for ____ and a lower affinity for _____
greater affinity for oxygen,
lower affinity for 2-3 DPG
The p50 in the adult is____, while the p50 in the fetus is _____.
Adult p50=27
Fetal p50=19
The fetal oxyhgb saturation curve is shifted to the _____ compared to the mother.
Left
Meconium stained amniotic fluid means either
decreased clearance or increased passage (stress or infection)
What are the 3 potential detrimental effects of meconium stained amniotic fluid?
- Umbilical cord vessel constriction, vessel necrosis, and production of thrombi.
- Decreased antibacterial properties of amniotic fluid by altering zinc levels
- Fetal aspiration-neutralizes action of surfactant, promotes lung tissue inflammation through activation of neutrophils, possibly result in meconium aspiration syndrome
What are the 4 compensatory responses of the healthy fetus to uterine contractions?
- Decreased O2 consumption
- Vasoconstriction of nonessential vascular beds
- Redistribution of blood flow to vital organs
- Humoral responses to enhance fetal cardiac function during hypoxia (release of epi, vasopressin, endogenous opioids).
What are abrupt changes in FHR above baseline?
Accelerations (Past 35wks, peak of at least 15bmp above baseline, lasting >15 sec).
- Prolonged lasts for at least 2 min
- > 10 min = new baseline
Which deceleration occurs with each uterine contraction with <20bpm below baseline?
Early- thought to be result of vagal reflex to mild hypoxia, not ominous.
Late Decelerations -
Begin 10-30 seconds AFTER beginning of uterine contraction and end 10-30 sec after end of uterine contraction
Define FHR variability
Fluctuation in FHR of 2 cycles or greater per min
*normal- reflects presence of normal intact pathways
Diff Dx with decreased FHR variability:
hypoxia, sleep state, neurologic abnormalities, decreased CNS from drug exposure (opioids)
What is Ominous with FHR variabilities
Late decelerations and decreased or absent variability is ominous.
What is the normal FHR?
Normal is 110-160bpm- determined by assessing mean HR over 10 min.
What type of deceleration varies in depth, shape and duration and is usually d/t umbilical cord compression?
Variable- she also says during 2nd stage of labor, can be d/t compression on fetal head.
What type of pattern appears regular, smooth, wavelike and may signal fetal anemia; effect of maternal opioid
Sinusoidal (looks like v tach)
What type of pattern is excessive alteration in variability (>25bpm) and may signal acute fetal hypoxia
Saltatory (looks like v fib)
ACOG recommendations for FHR monitoring how often
HIGH RISK Q 15 min during 1st stage of labor Q5 min during 2nd stage LOW RISK Q 30m 1st stage Q 15m 2nd stage
Discuss the ACOG 3 tier system to categorize FHR patterns
CAT 1 (normal) strongly predictive of normal fetal acid/base status at the time of observation CAT 2 (indeterminate) not predictive of abnormal fetal acid/base status, but without adequate evidence to classify as normal or abnormal CAT 3 (abnormal) predictive of abnormal fetal acid/base status at the time of observation and requires prompt evaluation.
CAT 3 tracings include:
Absent baseline FHR variability and any of the following: Recurrent late decelerations Recurrent variable decelerations Bradycardia Sinusoidal pattern
CAT 1 tracings include
Baseline HR 110-160bpm Baseline FHR variability: moderate Accelerations: present of absent Late or variable decelerations: ABSENT Early Decelerations: present of absent
