Mod VII: Maternal –Placental – Fetal Unit Flashcards

Question

_{Maternal Component - Uteroplacental Circulation} The smooth muscle tissue of the uterus is also known as:

Answer 1

**Myometrium**

Answer 2

Uterine vascular bed **maximally dilated**

Answer 3

**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}

Answer 4

Placental UBF

Answer 5

**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}

Answer 6

Maternal hypotension Alterations in uterine tone Maternal respiratory alterations Catecholamines (endogenous/exogenous) IV induction agents Inhalation agents N20

Answer 7

**Aortocaval compression** ^{↓ MMAP → ↓ UPP/PPP → ↓UBF} ^{↑ UVP → ↓ UBF} **Hypovolemia** **Regional & general anesthesia** ^{(more to come)}

Answer 8

**Increased Uterine tone** ^{↑ Uterine tone → ↑ UVP → ↓ UBF} **Contractions** ^{Contractions → ↑ UVP → ↓ UBF} **Anesthetic drugs** ^{(more to come)}

Answer 9

SEVERE **hypoxia** (low PaO2) **hypercarbia** (high PaCO2) **hypocarbia** (low PaCO2)

Answer 10

Catecholamines cause **increased UVR** UBF = PPP/UVR Increased UVR → ↓ UBF

Answer 11

**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

Answer 12

**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**

Answer 13

Pure alpha → U_terine artery_ **vasoconstriction** →↓ UBF

Answer 14

Severe cases of hypotension ^{(where volume resuscitation and Ephedrine and Phenylephrine are innefective)}

Answer 15

**_Hypotension_**, which... Decreases UBF This is an **Indirect effect** = Not direct effect

Answer 16

**False** IV induction agents indirectely decrease UBF

Answer 17

Smaller dosing may result in **light anesthesia** & _activation of SN_ Which could cause even **Greater reduction in UBF!!!**

Answer 18

**Ketamine** **Etomidate**

Answer 19

_Ketamine_ **1.5 mg**/kg → ↑MAP → **↑ UBF** _{[Ketamine in doses of less than 1.5 mg/kg does not appreciably alter uteroplacental blood flow; its hypertensive effect typically counteracts any vasoconstriction]}

Answer 20

_Ketamine_ **\> 2mg/kg** → **_uterine hypertonicity_** → **↓ UBF** _{[Uterine hypertonus may occur with ketamine at doses of more than 2 mg/kg]}

Answer 21

**Etomidate** (cardiovascular stability) _{[Etomidate likely has minimal effects, but its actions on uteroplacental circulation have not been well described]}

Answer 22

Direct _decrease **uterine smooth muscle contractility**_ (Dose dependent)

Answer 23

**Indirectly decrease UBF** ^{(Dose dependent)} _{(Done via ↓ C.O./SVR→ ↓ MMAP; recall that UBF=MMAP/UVR)}

Answer 24

**\<1 MAC** _{[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]}

Answer 25

Nitrous oxide alone can _vasoconstrict the uterine arteries_ ↑ SNS activity/constant uterine contraction → **↓ UBF** (theory) _Minimal effects_ when **combined with volatile agents** _{[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]}

Answer 26

**0.5 MAC** volatile agent **+ N2O** Leads to decreased uterine atony and blood loss

Answer 27

**No direct effect UBF** ^{Studies proven it to be beneficial (esp. pre-eclamptic pt)}

Answer 28

Via **↑ intervillous blood flow**

Answer 29

**Decrease UBF** **[via** sympathectomy (↓BP)]

Answer 30

↑↑↑ _concentrations_ =\> uterine arterial vasoconstriction =\>**↑uterine tone =\>** **↓ UBF** ^{[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

Answer 31

Direct myometrial injection PARACERVICAL block

Answer 32

**Increased LA concentration** (esp. bupivacaine) → vasoconstriction uterine artery + ↑ uterine tone → ↓ UBF =\> **FETAL BRADYCARDIA** due to asphyxia

Answer 33

To avoid **fetal compromise**!!

Answer 34

IV fluids LUD Vasopressors Avoid maternal hyperventilation

Mod VII: Maternal –Placental – Fetal Unit Flashcards

(62 cards)