Maternal and Fetal Physiology Flashcards
What are 4 neurological changes the mother experiences?
- MAC is decreased
- Epidural space becomes smaller
- CSF volumes are decreased and epidural veins are engorged
- Increased sensitivity to LAs
What 5 things happen to mother’s ventilation?
- TV increased 40% at term
- RR increased by 15%
- MV increased nearly 50%
- PaCO2 decreased to 28-32
- FRC decreased by 20%
Does the mother have an overall respiratory/metabolic acidosis/alkalosis?
With increased MV, resp alkalosis occurs but compensatory metabolic acidosis occurs via excretion of HCO3 to maintain normal pH.
Why is it important to preoxygenate a mother prior to induction?
FRC is decreased coupled with increased maternal oxygen consumption can rapidly lead to maternal hypoxia during induction of GA.
What two things should be kept in mind with ETT selection for mother?
- Use smaller ETT tube
2. Avoid nasal intubation or instrumentation (due to mucosal venous engorgement).
Does the mother exhibit a left or right shift on oxyhemoglobin curve?
Right shift (P50=30).
What 6 cardiovascular changes can be seen in the mother?
- Increased plasma volume (45%)
- PVR drops 15%
- CO increases
- Response to adrenergic drugs is blunted
- Cardiac hypertrophy on CXR
- Heart murmurs often present
What happens to mother’s RBC and plasma?
Increase in plasma volume (45%) and increase in RBC (20) creates hypervolemia; however, there is a relative anemia (due to plasma dilution).
Is there an increase or decrease in Renin production/secretion in the mother?
Increase in renin which increases aldosterone which increases sodium/H2O retention.
T/F: Active phase of labor has the highest cardiac output?
False; Postpartum CO can be increased by 80% because the placenta is removed and there is less vascular bed to perfuse/restrict flow
List the phases of labor and their relative increase in cardiac outputs:
Latent Phase=15%
Active phase=30%
Second Stage=45%
Postpartum=80%
What is aortocaval compression?
Also called supine hypotension syndrome; Both great vessels get compressed while mother is supine.
What are symtomes of Aortocaval Compression?
Hypotension Pallor Nausea Vomitting Diaphoresis
What is the treatment for aortocaval compression?
Left lateral uterine tilt position (can also try right lateral if no change in symptoms).
Why are mothers at higher risk of pulmonary embolism?
Hypercoagulable state = increased Factors I, VII, VIII, IX, X, XII
What are the 5 hematological changes we see in mothers?
- Increased Factors I, VII, VIII, IX, X, XII
- Decreased factors XI, XIII
- Unchanged II, V
- PT dec 20%, PTT dec 20%
- Cell mediated immunity depressed.
What 3 renal changes can be seen in the mother?
- RBF and GFR increase by 50% by 16th week
- Serum BUN and Crt reduced
- Mild glycosuria and proteinuria are common.
Overall, what are the 3 net effects of the GI changes we will see in the mother?
- Reduced gastroesophageal sphincter tone (LES).
- Increased acid production
- Slowed gastric emptying
What anesthetic consideration are there due to the GI changes in the mother?
- Increased risk of symptomatic aspiration
2. Treat like full stomach RSI/cricoid/etc
T/F: most patients will have less than 25cc w/ a pH of greater than 2.5 in their stomach?
False; Most will have greater than 25cc and a pH less than 2.5 in their stomach.
What hepatic change can occur with mothers?
20% decrease in pseudocholinesterase levels (but there is an increase in Vd which cancels out the problems with DNMBDA).
What is the most common elective surgery performed during pregnancy? WHY?
Gallbladder removal
Decreased CCK release and contractile response creates sluggish GB and gallstones.
What causes mothers plasma glucose levels to be higher and why?
Relative insulin resistance allows for more fetal glucose transfer (facilitates offloading ofm\ glucose to fetus)
Aside from compensatory mechanisms, how long can a fetus survive once there is no oxygen supply and why?
2 minutes because fetal stores are approx 42ml O2 and consumption (without compensatory mechanisms) is 21ml/min.
Which direction is the oxyhemoglobin curve shifted in the fetus?
Left shift (and also higher amount of hemoglobin).
Does maternal or fetal Hgb have a high affinity for CO2?
Maternal Hgb
In the mother, how much blood flow does the uterus receive?
10% of CO (600-700ml/min).
What three factors influence uterine blood flow (UBF)?
- Systemic blood pressure
- Uterine vasoconstriction
- Uterine contractions.
What happens to UBF with neuraxial analgesia?
Can increase due to reduction in maternal catecholamines which would reduce vasoconstriction.
What affects does N2O and opioids have on UBF?
None or very little
What effect does propofol have on UBF?
Mild decrease in UBF via maternal hypotension.
What effect does ketamine have on UBF?
No net effect at does less than 1.5mg/kg
What effect do volatile anesthetics have on UBF?
Decrease UBF secondary to hypotension, but minor effect under 1 MAC.
What anesthetic drug can cause uterine vasoconstriction?
High serum levels of LAs
T/F: Hypoxia and alkalosis can increase L to R shunting
False; Hypoxia and acidosis can increase R to L shunting via the PDA
Describe the first Stage of Labor?
Onset of true labor until complete cervical dilation.
Has a Latent phase and an Active Phase
Describe the Latent phase of the 1st stage of labor?
Minor dilation 2-4cm, infrequent contractions.
Describe the active phase of the 1st stage of labor?
Progressive dilation to 10cm and regular contractions (3-5min)
Describe the 2nd stage of labor?
Time from complete dilation until infant delivered.
Describe the 3rd stage of labor?
Time from delivery of infant until placenta is delivered.
Which type of HR decelerations are most concerning?
Late decelerations
What is the most common cause of early decels?
Head compression= basically a vagal response.
What is the main cause of late decels?
Compression of vessels/uteroplacental insufficiency
What is the main cause of variable decels?
Less ominous.
Typically from umbilical cord compression.
