Flashcards in Exam 2 Fetal Stuff Deck (107)
Blood supply to the placenta is mainly from
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
How much is the uterine blood flow at term?
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
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?
What happens to uterine perfusion during uterine relaxation
What some things that can cause Decreased uterine arterial pressure?
Supine position (aortocaval compression)
Hypotension during sympathetic blockade
What are some things that can cause Increased uterine Venous pressure?
Vena caval compression
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?
How does NA increase UBF?
Decreased sympathetic activity
Decreased maternal hyperventilation
How does NA decreased UBF?
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?
How much blood can be held in the intervillous space?