Maternal & Fetal Physiology Mo PPT 1 Flashcards
How does MAC change during pregnancy?
A.MAC progressively decreases during pregnancy due to
- Hormonal (progesterone) changes
- INCREASED level of b-endorphin
MAC is DECREASED by 30-40%
How does sensitivty change in pregnancy to local anesthetics?
Increase sensitivity to LA, therefore reduce dose up to 30%
What will an obstruction of IVC by gravid uterus cause?
Obstruction of IVC by gravid uterus causes
- Distension of epidural venous plexus
- Increase epidural blood volume
a. DECREASE spinal CSF volume
b. DECREASE potential volume of epidural space
c. INCREASE epidural pressure - a and b will increase cephalad spread of LA during spinal and epidural anesthesia
- All the above factors increase during labor ???
- Risk of unintentional intra venous injection
What will increase cephalad spread of LA during spinal and epidural anesthesia?
Obstruction of IVC by gravid uterus causes
- Distension of epidural venous plexus
- Increase epidural blood volume
a.DECREASE spinal CSF volume
b.DECREASE potential volume of epidural space
c.INCREASE epidural pressure
a and b will increase cephalad spread of LA during spinal and epidural anesthesia
Maternal Cardiovascular Changes on
Blood Volume?
Blood volume
INCREASES
(25-40%)
Cardiovascular Changes to Plasma Volume?
Plasma volume
INCREASES
(55% –> Dilutional anemia)
Cardiovascular changes in pregancy on cardiac output?
Cardiac output
INCREASES (40%)
CV changes to stroke volume, EF in pregancy?
Stroke volume, EF –> INCREASES
CV changes on HR during pregnancy?
Heart Rate Increases
CV changes during pregnany when lying lateral and when lying supine?
Lateral BP DECREASES
SUPINE BP INCREASE
CV changes in your peripheral resistance (SVR) during pregancy?
DECREASES (-20%)
How does cardiac output change during pregnancy and delivery?

CO INCREASES 40%
HR INCREASE 15%
SV INCREASES 30%
Uterus receives 10% of CO
Uterine Contraction causes autotransfusion
COmpared to Pre-labor value; CO during labor:
- 1st stage CO INCREASES 20%
- 2nd stage CO INCREASES 50%
- 3rd STAGE CO INCREASES 80%
CO returns to prelabor values 24-48 hrs
CO returns to prepregancy values in 2 weeks
Twins cause CO to INCREASE 20% above a single fetus pregnancy.
Who is at risk for aortocaval compression and how do you treat it?
MO calls it supine hypotensive syndrome
A.Due to compression of aorta IVC by gravid uterus in supine position, at term
B.Pallor , sweating , N/V, dizziness, tachycardia, vertigo, apprehension and change in mental status
C.Avoid supine position
D.Turn the patient to one side (Right hip up 10-15 cm)
APEX –>
Mother’s right torso elevated 15 degrees
Should be used for anyone in second or third trimester
How does pregnancy effect maternal oxygen consumption?
Oxygen consumption (50%) INCREASES
How does pregancy effect materanal minute ventilation?
Minute ventilation (50%)
INCREASES
Vt –> INCREASES 40%
RR –> INCREASE 10%
How is maternal TV affected during pregnancy?
Tidal volume
INCREASED
How does pregnancy affect materan respiratory rate?
Respiratory rate
INCREASES
How does pregnancy affect maternal blood gas?
PO2 –> INCREASES
PCO2 –> DECREASE
(INCREASED production though)
HCO3 –> DECREASES
Per APEX:
Arterial pH = no change
PaO2 =Increased (104-108 mmHg)
PCO2 =Decreased (28-32 mmHg)
HCO3 =Decreased (20 mmol/L)
How does pregnancy affect the oxyhemoglobin disociation curve?
RIGHT Shift (INCREASED P50)
- Facilitates O2 unloading to the fetus
How does pregnancy affect lung volumes and capacities?
Functional residual capacity –> DECREASES
(INCREASED risk of hypoxemia )
as a result of:
DECREASED ERV (expiratory reserve volume) and RV (residual volume)
During pregnancy what of the respiratory system has NO change?
A.NO change in :
1.Dead space, lung compliance, pH, VC, FEV, FEV1 and diffusion capacity.
During pregnancy if mom is extremely hyperventilating causing fetal hypoxia and respiratory acidosis what happens?
A.Extreme hyperventilation by mom causes fetal hypoxia and respiratory acidosis by
1.Vasoconstriction of umbilical BF
2.Left shift of O2-Hb curve
During Pregnancy why is there a very high risk of hypoxia?
Very high risk of hypoxia in pregnancy due to
1.DECREASED FRC
2.INCREASED O2 consumption
3.INCREASED A-a gradient
Is pregancy a restrictive or obstructive lung condition?
Both restrictive and obstructive
Maternal hemotological changes:
Hgb –> INCREASED
Clotting factors –> INCREASED
GFR –> INCREASED
Estrogen INCREASES renin activity causing what?
A.Physiological anemia of pregnancy
1.Estrogen INCREASES renin activity –>75% increase in blood volume (dilutional effect)
2.Low crit is good for placental blood flow
−Give iron or folic acid
What clotting factors are increased during pregnancy?
INCREASED clotting factors (VII, fibrinogen)
1.Hypercoagulable state helps to prevent blood loss during labor
APEX says: I, VII, VIII, IX, X, XII are INCREASED
What happens to maternal platelet count, folate level, and plasma ACh esterase activity during pregnancy?
A.DECREASED platelet count (10%)
B.DECREASED Folate level
C.DECREASED plasma acetylcholine esterase activity
1.Return to normal in 2-4 weeks postpartum
Maternal renal changes during pregnancy?
A.INCREASE GFR and renal plasma flow
B.DECREASE BUN and creatinine
C.DECREASE renal threshold for glucose and amino acids –> glycosuria and proteinuria
Maternal GI changes in pregnancy?
A.DECREASE LES pressure, INCREASED acid and INCREASED intragastric pressure –> reflux (heart burns)
B.INCREASED gastrin secretion
APEX says:
INCREASED gastric volume, DECREASES pH due to an increase in gastrin
How does pregnancy affect gastric emptying?
Before Onset of Labor: no change
After onset of labor: slow
What do you do for slow gastric emptying during pregnancy (after onset of labor)?
A.Slow gastric emptying
1.Give metochlorpromide (Reglan) to
−INCREASE gastric emptying (move forward)
−Tighten up LES
Due to slow gastric emptying after onset of labor, what is a pregnant women as risk for?
Increase risk of aspiration
Maternal Endocrine Changes?
A.INCREASE TBG, INCREASE total T3 and T4
B.No change in free T3 and T4
C.Insulin resistance due to placental lactogen
D.INCREASE cortisole
E.INCREASE endorphins at term
What is the first site of nutrient and gas exchange between mother and fetus?
Placenta
What separate maternal blood from fetal blood?
Placental Membrane
What are the 2 fetal components of the placenta?
A.Fetal component
- Cytotrophoblast − inner layer of chorionic villi. Cyto makes cells
- Syncytiotrophoblast − outer layer of chorionic villi; secretes HCG (Human Chorionic Gonadotropin)
What is the function of Cytotrophoblast?
A.Fetal component
1.Cytotrophoblast − inner layer of chorionic villi. Cyto makes cells
What is the function of Syncytiotrophoblast?
2.Syncytiotrophoblast − outer layer of chorionic villi; secretes HCG (Human Chorionic Gonadotropin)
What is the materanl component of the placenta?
B.Maternal component
1.Decidua basalis − derived from the endometrium. Maternal blood in lacunae
How does pregnancy affect uterine blood flow?
At term uterine blood flow increases 500-700 ml/min 10% of CO
Pressure Dependent
What conditions can reduce uterine blood flow?
1.Supine position: aortocaval compression
2.Maternal hypotension
- Uterine contractions
- Oxytocin
- Catecholamines (stress)
- Vasopressors
- LA in high doses
What kind of drugs can pass across placental barrier?
A.Drugs passage across placental barrier
1.Smaller molecular weight, lipid soluble and non-ionized can pass
Is uterine blood flow autoregulated?

E.Not autoregulated
- DECREASE BP –> DECREASE BF
- INCREASE SVR –> DECREASE BF
F.Uterine contraction –>Decreases BF
G. a-stimulant –> DECREASE BF
*Uterine BF is dependent on MAP, CO, uterine vascular resistance*
Normal Fetal HR?
120-160 bpm
Fetal Bradycardia HR
< 120 bpm
What is the only factor that influences blood flow through the placenta?
Maternal BP
What 3 part does the placental membrane have?
- Fetal trophoblast
a. Cytotrophoblast (inner layer); make cells
b. Syncytiotrophoblast (outer invading layer; secrete HCG) - Fetal connective tissue
- Endothelium of the fetal capillaries
Fetal Circulation
1.Oxygenated blood from placenta enters through _________.
Fetal Circulation
- Oxygenated blood from placenta enters through umbilical veins
- Most of the blood bypass fetal liver via the ductus venosus and mix with deoxygenated blood in inferior vena cava
- Foramen ovale shunts blood from right atrium (á pressure) directly into left atrium (â pressure)
- Blood is shunted away from fetal lungs (áá resistance)
- Ductus arteriosus connects pulmonary artery directly to aorta
- Deoxygenated blood returns to placenta via the umbilical arteries
Fetal circulation
Most of the blood bypass fetal liver via the _____ _____ and mix with deoxygenated blood in inferior vena cava
2.Most of the blood bypass fetal liver via the ductus venosus and mix with deoxygenated blood in inferior vena cava
Fetal circulation
_____ _____ shunts blood from right atrium (INCREASES pressure) directly into left atrium (DECREASES pressure)
1.Foramen ovale shunts blood from right atrium (INCREASES pressure) directly into left atrium (DECREASES pressure)
Fetal Circulation
1.Blood is shunted away from fetal lungs (_______resistance)
Blood is shunted away from fetal lungs (INCREASES resistance)
Fetal Circulation
______ _____ connects pulmonary artery directly to aorta
1.Ductus arteriosus connects pulmonary artery directly to aorta
Fetal Circulation
1.Deoxygenated blood returns to placenta via the _____ ______
1.Deoxygenated blood returns to placenta via the umbilical arteries
Pathway of Blood through fetal circulation:
Umbilical vein –> ductus venosus –> inferior vena cava –> right atrium –> left atrium (through foramen ovale) –> left ventricle –> aorta –>body
What do the umbilical arteries do?
A.Umbilical arteries (2)− return deoxygenated blood from fetal internal iliac arteries to placenta
What do umbilical veins do?
B.Umbilical vein (1) − supplies oxygenated blood from placenta to fetus, drain into IVC via ductus venosus or liver
Give the name and function of 3 important shunts
A.Three important shunts
- Ductus Venosus –>Allows blood to bypass liver
Location: Umbilical Vein –> Superior Vena Cava
2.Foramen Ovale –>Shunts blood from right atrium to left atrium to bypass lungs to perfuse upper body (heart and brain)
Location: Right atrium –> Left atrium
- Ductus Arteriosus –> shunts blood from pulmonary trunk to aorta to perfuse lower body
Location: pulmonary artery –> proximal descending aorta
What is the most serious risk factor associated with surgery during pregnancy?
1.Uterine asphyxia is the most serious risk factor associated with surgery during pregnancy
Delayed gastric emptying time is treated how?
prophylactic antacids
What preventive measure do you put in place to prevent DVT in mother during a c-section?
1.Thromboembolism- prevent DVT with pneumatic compression stockings during C/S
What is the most frequent complication of a spinal and epidural? How is it treated?
1.Hypotension is the most frequent complication of spinal and epidural; treated by
−Left uterine displacement, IV hydration and ephedrine
What is given to stop a premature contraction?
b 2 agonist e.g. ritodrine is given to stop premature contraction
What are maternal and fetus s/e of ritodrine?
8.Side effect of ritodrine
−Mom: hypokalemia, hyperglycemia, tachycardia
−Fetus: : hypokalemia, hyperglycemia, tachycardia (+/-)
What do you not want to give with ritodrine?
10.Avoid atropine with ritodrine ( can cause tachy –> pulmonary edema)
What does magnesium sulfate do to your volatile anesthetic?
10.Mag sulf INCREASES sensitivity to both depolarizing and non-depolarizing muscle relaxant , therefore, DECREASE the dose
Lidocaine causes _____ ______ and INCREASE tone
10.Lidocaine (in high dose) causes uterine vasoconstriction and INCREASE tone
- More ion trapping of LA (low fetal blood pH)
- ______ + ______ = ionized (cannot cross; trapped in fetus)
−______ + _____ = un-ionized (cross)
10.More ion trapping of LA (low fetal blood pH)
−Base + acid = ionized (cannot cross; trapped in fetus)
−Base + base = un-ionized (cross)
1.Always consider patient (mom) “stomach full” INCREASED high risk of aspiration
What fo you want to give?
- Always consider patient (mom) “stomach full” INCREASE high risk of aspiration
- H2 blockers and metoclopramide
1.Lumbar epidural –MC
−S/E hypotension. Give what?
1.Lumbar epidural –MC
−S/E hypotension. Give ephedrine and IV fluid
What are problems with GA?
1.Problems with GA
−Rapid desaturation, laryngeal spasm/edema, aspiration
What is the level of block for csection?
1.Level of block for C/S is T4
- MC adverse effect of regional is hypotension
- Give what?
- MC adverse effect of regional is hypotension
- Give phenylephrine with fluid
9.Most common cause of polyhydramnios is ____ _____.
9.Most common cause of polyhydramnios is esophageal atresia
What is most commonly injured during abdominal hysterectomy
9.Femoral nerve is most commonly injured during abdominal hysterectomy
9.Common peroneal nerve may injure during vaginal hysterectomy —> ______ ______
9.Common peroneal nerve may injure during vaginal hysterectomy –> foot drop
9.Lumbosacral nerve is most commonly injured during _______
9.Lumbosacral nerve is most commonly injured during vaginal delivery
What are most common cause of anesthesia-related maternal mortality
9.Airways complications are most common cause of anesthesia-related maternal mortality
Adult Spinal Cord Ends At?
L1 or L2
Adult Dural Sac ends at?
S1 or S2 ???
Infant Spinal Cord ends at
L3
Infant Dural Sac ends at ?
S3
When does the fetal heart start beating?
4 weeks gestation
When is surfactant production?
23/24 weeks
How much pressure is needed to open airways?
25- 40 mmHg