Mod VII: Maternal –Placental – Fetal Unit Flashcards
Maternal –Placental – Fetal Unit
T/F: Fetal & Maternal circulations are 2 vastly different circulations
True
Maternal –Placental – Fetal Unit
The complex organ present only at birth joining the maternal and fetal circulations for physiologic exchange is also known as:
Placenta
Semipermeable membrane that provides an interface for maternal and fetal circulations
Composed of both maternal and fetal tissue and derives a blood supply from each
Maternal –Placental – Fetal Unit
The placenta is composed of both maternal and fetal tissue - How is the tissue on the maternal side called?
Basal plate
(tissue/spiral arteries)
Maternal –Placental – Fetal Unit
The placenta is composed of both maternal and fetal tissue - How is the tissue on the Fetal side called?
Chorionic villi
(3 tissue layers, interface for the fetus)
Maternal –Placental – Fetal Unit
What’s the name for the space separating the Basal plate and the chorionic villi? What happens in that space?
Intervillous space
Space separating the Basal plate and the chorionic villi
Chorionic villi/spiral arteries protrude
Maternal blood contacts fetal tissue
EXCHANGE of Respiratory gases, Nutrition, and Elimination of waste occurs
Fetal Component - Umbilical-Placental Circulation
What portion of fetal C.O. does the Umbilical-placental circulation receive?
50%
Fetal Component - Umbilical-Placental Circulation
What’s the rate of Fetal blood flow?
250 ml/min
Fetal Component - Umbilical-Placental Circulation
Describe blood flow from the fetus, through the placenta, and back to the fetus?
Blood enters placenta via 2 umbilical arteries → umbilical capillaries → traverse chorionic villi → cleansed/O2 → umbilical vein
Fetal Component - Umbilical-Placental Circulation
T/F: The Umbilical-Placental Circulation is a Low resistance system
True
Fetal Component - Umbilical-Placental Circulation
The Umbilical-Placental Circulation is a Low resistance system - What does it rely on to maintain umbilical-placental circulation?
Fetal CO
Fetal Component - Umbilical-Placental Circulation
Which one of these circulatory systems is autoregulated?
A. Umbilical-Placental Circulation
B. Uteroplacental circulation
A. Umbilical-Placental Circulation
B. Uteroplacental circulation (Not autoregulated)
Fetal Component - Umbilical-Placental Circulation
T/F: Umbilical-Placental Circulation is altered by pathophysiologic states
True
Fetal Component - Umbilical-Placental Circulation
Which factors affect umbilical-placental circulation?
Direct effects on umbilical vessels
Drug effects
Fetal Component - Umbilical-Placental Circulation
Direct effects on umbilical vessel that may affect umbilical-Placental Circulation include:
Cord compression/prolapse
Vasospasm from LA, vasopressors, maternal alkalosis
Increase in intervillous pressure (during uterine contraction)
Fetal Component - Umbilical-Placental Circulation
Drug that may affect Umbilical-Placental Circulation include
Benzodiazepines alter FHR variability
Tocolytics → fetal tachycardia
Fetal Component - Umbilical-Placental Circulation
Which drugs alter FHR variability?
Benzodiazepines
Fetal Component - Umbilical-Placental Circulation
Which drugs cause fetal tachycardia?
Tocolytics
(Tocolytics are medications used to suppress premature labor)
Maternal Component - Uteroplacental Circulation
T/F: Uteroplacental Circulation is autoregulated
False
Uteroplacental Circulation is not autoregulated
A drop in maternal BP will impair Uteroplacental blood flow
Increased uterine pressures during contractions will decrease Uteroplacental blood flow
Uterine vasculature remains sensitive to alpha-adrenergic agonists
Maternal Component - Uteroplacental Circulation
T/F: Uterine vasculature remains sensitive to alpha-adrenergic agonists
True
Maternal Component - Uteroplacental Circulation
Describe the change in uterine blood fow from nonpregnant state to term gestation:
UBF ↑ from 100mL/min (nonpregnant state) to
700 ml/min (term gestation; which is 20-40X’s pre pregnant)
[Uterine blood flow increases progressively during pregnancy from about 100 mL/minute in the nonpregnant state to 700 mL/minute (∼10% of cardiac output) at term gestation]
Maternal Component - Uteroplacental Circulation
UBF ↑ to 700 ml/min during pregnancy - How much more is that compared to pre-pregnant uterus blood flow?
20-40X’s more than pre-pregnant uterus blood flow
Maternal Component - Uteroplacental Circulation
Uteroplacental Circulation Receives what portion of maternal C.O.?
Uteroplacental Circulation Receives 10% of maternal C.O
Maternal Component - Uteroplacental Circulation
Approximately what % of UBF perfuses the placenta?
80%
Maternal Component - Uteroplacental Circulation
Approximately what % of UBF perfuses the myometrium?
10%
Maternal Component - Uteroplacental Circulation
The smooth muscle tissue of the uterus is also known as:
Myometrium
Maternal Component - Uteroplacental Circulation
Why is perfusion to the uterus NOT AUTOREGULATED?
Uterine vascular bed maximally dilated
Maternal Component - Uteroplacental Circulation
What is uterine blood flow directly related to? What is UBF inversely related to?
UBF = PPP/UVR
UBF is directly r/t Placental Perfusion pressures (PPP)
UBF is inversely r/t Uterine Vascular Resistance (UVR)
Uterine and placental blood flow depend on maternal cardiac output and are directly related to uterine perfusion pressure and inversely related to uterine vascular resistance
Decreased perfusion pressure can result from maternal hypotension secondary to hypovolemia, aortocaval compression, or sympathetic blockade and decreased systemic resistance from either general or neuraxial anesthesia
Increased uterine venous pressure also can decrease uterine perfusion
This can occur from supine positioning with vena caval compression, frequent or prolonged uterine contractions, or significant prolonged abdominal musculature contraction (Valsalva) during pushing
Additionally, extreme hypocapnia (PaCO2 < 20 mm Hg) occasionally associated with hyperventilation secondary to labor pain can reduce uterine blood flow with resultant fetal hypoxemia and acidosis
Maternal Component - Uteroplacental Circulation
What are Fetal O2 transfer and CO2 elimination directly r/t?
Placental UBF
Maternal Component - Uteroplacental Circulation
What’s the Uterine Perfusion Equation aka UBF equation?
UBF = (MMAP – UVP)/ UVR = PPP/ UVR
UBF: Directly proportional to MAP/PPP
UBF: Indirectly proportional to UVR
MMAP: maternal mean arterial pressure
UVP: uterine venous pressure
UVR: uterine vascular resistance
PPP: placental perfusion pressure
Uteroplacental Circulation - Factors influencing UBF
Which factors affect UBF?
Maternal hypotension
Alterations in uterine tone
Maternal respiratory alterations
Catecholamines (endogenous/exogenous)
IV induction agents
Inhalation agents
N20
Uteroplacental Circulation - Factors influencing UBF
Which conditions may lead to Maternal hypotension and subsequent decrease in UBF?
Aortocaval compression
↓ MMAP → ↓ UPP/PPP → ↓UBF
↑ UVP → ↓ UBF
Hypovolemia
Regional & general anesthesia
(more to come)
Uteroplacental Circulation - Factors influencing UBF
Which conditions may cause Alterations in uterine tone and subsequent decrease in UBF?
Increased Uterine tone
↑ Uterine tone → ↑ UVP → ↓ UBF
Contractions
Contractions → ↑ UVP → ↓ UBF
Anesthetic drugs
(more to come)
Uteroplacental Circulation - Factors influencing UBF
Which maternal blood gas alterations may result in decreased UBF?
SEVERE hypoxia (low PaO2)
hypercarbia (high PaCO2)
hypocarbia (low PaCO2)
Uteroplacental Circulation - Factors influencing UBF
How do Catecholamines (endogenous/exogenous) cause a decrease in UBF?
Catecholamines cause increased UVR
UBF = PPP/UVR
Increased UVR → ↓ UBF
Uteroplacental Circulation - Factors influencing UBF
How does Ephedrine affect UBF?
Alpha and beta-adrenerguc receptor stimulant
Stimulates both alpha and beta-adrenerguc receptors thus provides cardiac stimulation, w/ subsequent increase in peripheral and UBF
Traditionally drug of choice in treatment of maternal hypotension
Has no effect on actual uterine contraction
Ephedrine, which has considerable β-adrenergic activity, has traditionally been considered the vasopressor of choice for hypotension during pregnancy
However, clinical studies suggest that the α-adrenergic agonist phenylephrine is more effective in treating hypotension in pregnant patients and is associated with less fetal acidosis than ephedrine
Uteroplacental Circulation - Factors influencing UBF
How does Phenylephrine affect UBF?
Pure alpha-adrenergic stimulant
Pure alpha-adrenergic agents have thought to increase maternal BP at the expense of utero-placental flow
Pure alpha → uterine artery vasoconstriction →↓ UBF at high doses
Recent studies suggest there is no difference btw the use of Ephedrine or Neo
Recent studies: small doses of Phenylephrine (50ug) improve maternal hemodynamics w/ adverse effects of fetus
Phenylephrine may be safely used to treat maternal hypotension
Ephedrine or Neo have no effect on actual uterine contraction
Uteroplacental Circulation - Factors influencing UBF
What’s a potentially negative effect of giving high dose Phenylephrine?
Pure alpha → U_terine artery_ vasoconstriction →↓ UBF
Uteroplacental Circulation - Factors influencing UBF
T/F: Recent studies suggest there is no difference btw the use of Ephedrine or Neo
True
Uteroplacental Circulation - Factors influencing UBF
T/F: Recent studies: small doses of Phenylephrine (50ug) improve maternal hemodynamics w/ adverse effects of fetus
True
Uteroplacental Circulation - Factors influencing UBF
T/F: Phenylephrine may be safely used to treat maternal hypotension
True
Uteroplacental Circulation - Factors influencing UBF
T/F: Ephedrine or Neo have no effect on actual uterine contraction
True
Uteroplacental Circulation - Factors influencing UBF
When is the use of more potent vasoconstrictors such as Epi or NorEpi indicated?
Severe cases of hypotension
(where volume resuscitation and Ephedrine and Phenylephrine are innefective)
Uteroplacental Circulation - Factors influencing UBF
What’s an indirect effect of IV induction agents on UBF?
Hypotension, which… Decreases UBF
This is an Indirect effect = Not direct effect
Uteroplacental Circulation - Factors influencing UBF
T/F: IV induction agents directly decrease UBF
False
IV induction agents indirectely decrease UBF
Uteroplacental Circulation - Factors influencing UBF
Eventhough there is concern for decreased UBF with administration of IV induction agents, why is it not recommended to administerd smaller doses of these agents?
Smaller dosing may result in light anesthesia & activation of SN
Which could cause even Greater reduction in UBF!!!
Uteroplacental Circulation - Factors influencing UBF
Smaller dosing of IV induction agents may result in light anesthesia & activation of SNS → Greater reduction in UBF. Which two induction agents are exceptions to this?
Ketamine
Etomidate
Uteroplacental Circulation - Factors influencing UBF
Which dose of Ketamine ↑ UBF? via which mechanism?
Ketamine
1.5 mg/kg → ↑MAP → ↑ UBF
<strong>[</strong>Ketamine in doses of less than 1.5 mg/kg does not appreciably alter uteroplacental blood flow; its hypertensive effect typically counteracts any vasoconstriction]
Uteroplacental Circulation - Factors influencing UBF
Which dose of Ketamine ↓ UBF? via which mechanism?
Ketamine
> 2mg/kg → uterine hypertonicity → ↓ UBF
<strong>[</strong>Uterine hypertonus may occur with ketamine at doses of more than 2 mg/kg]
Uteroplacental Circulation - Factors influencing UBF
Which IV induction agent is recommended in the presence of hypovolemia? - Why?
Etomidate
(cardiovascular stability)
[Etomidate likely has minimal effects, but its actions on uteroplacental circulation have not been well described]
Uteroplacental Circulation - Factors influencing UBF
What’s the direct effect of inhalation agents on UBF?
Direct decrease uterine smooth muscle contractility
(Dose dependent)
Uteroplacental Circulation - Factors influencing UBF
What’s the indirect effect of inhalation agents on UBF?
Indirectly decrease UBF
(Dose dependent)
(Done via ↓ <strong>C.O./SVR</strong>→ ↓ MMAP; recall that UBF=MMAP/UVR)
Uteroplacental Circulation - Factors influencing UBF
In general, which dose of inhalation agents has minimal effect on UBF?
<1 MAC
<strong>[</strong>Volatile inhalational anesthetics decrease blood pressure and, potentially, uteroplacental blood flow. In concentrations of less than 1 MAC, however, their effects are generally minor, consisting of dose-dependent uterine relaxation and minor reductions in uterine blood flow]
Uteroplacental Circulation - Factors influencing UBF
How does N20 affect UBF when used alone?
Nitrous oxide alone can vasoconstrict the uterine arteries
↑ SNS activity/constant uterine contraction → ↓ UBF (theory)
Minimal effects when combined with volatile agents
<strong>[</strong>Nitrous oxide has minimal effects on uterine blood flow when administered with a volatile agent. In animal studies, nitrous oxide alone can vasoconstrict the uterine arteries]
Uteroplacental Circulation - Factors influencing UBF
Which Technique of using N2O decreases uterine atony and blood loss?
0.5 MAC volatile agent + N2O
Leads to decreased uterine atony and blood loss
Uteroplacental Circulation - Factors influencing UBF
What’s the direct effect of Regional anesthesia on UBF?
No direct effect UBF
Studies proven it to be beneficial (esp. pre-eclamptic pt)
Uteroplacental Circulation - Factors influencing UBF
Studies have proven Regional anesthesia to be beneficial (esp. pre-eclamptic pt) in increasing UBF. How is this achieved?
Via ↑ intervillous blood flow
Uteroplacental Circulation - Factors influencing UBF
What’s the indirect effect of Regional anesthesia on UBF?
Decrease UBF
[via sympathectomy (↓BP)]
Uteroplacental Circulation - Factors influencing UBF
How do blood levels of Local anesthetics affect UBF?
↑↑↑ concentrations => uterine arterial vasoconstriction
=> ↑uterine tone => ↓ UBF
<strong>[</strong>High blood levels of local anesthetics—particularly lidocaine—cause uterine arterial vasoconstriction. Such levels are seen only with unintentional intravascular injections and occasionally following paracervical blocks (in which the injection site is in close proximity to the uterine arteries), and local absorption or injection into these vessels cannot be ruled out)]
Normal serum concentration => Clinically insignificant effect
Uteroplacental Circulation - Factors influencing UBF
There is ↓ UBF & ↑uterine tone at ↑↑↑ concentrations of local anesthetics - When is this notable?
Direct myometrial injection
PARACERVICAL block
Uteroplacental Circulation - Factors influencing UBF
What are some deleterious clinical effects of PARACERVICAL block?
Increased LA concentration (esp. bupivacaine)
→ vasoconstriction uterine artery + ↑ uterine tone
→ ↓ UBF => FETAL BRADYCARDIA due to asphyxia
Uteroplacental Circulation - Factors influencing UBF
Why must adverse changes in uterine perfusion pressures be addressed RAPIDLY?
To avoid fetal compromise!!
Uteroplacental Circulation - Factors influencing UBF
Adverse changes in uterine perfusion pressures must be addressed RAPIDLY to avoid fetal compromise!! - How is this acheived?
IV fluids
LUD
Vasopressors
Avoid maternal hyperventilation
