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CO is increased by ___% in the parturient.
How is the increased CO attained by the parturient?
Mostly due to increase in SV (30-35%) and also due to increase in HR (15-30%)
SVR is ____ in the parturient.
Decreased- contributes to hyperdynamic circulation.
Blood volume increases by ___% in the parturient.
With the increase in blood volume seen in the parturient, is there a greater increase in plasma volume or red cell mass?
Plasma volume, a hemodilution occurs; relative decrease in Hgb concentration.
What are the 2 purposes of the dilution anemia?
- Decreased viscosity to facilitate maternal / fetal exchange of nutrients / gases
- Reduces impact of maternal blood loss with delivery
Avg amount of blood loss with c-section?
With vaginal delivery
- C-section 1L
- Vaginal delivery 500 ml
Autotransfusion during delivery
During labor the contracting uterus auto transfuses 300-500 ml of blood compensating for the usual material blood losses at birth.
- AKA supine hypotension syndrome
- Uterus compresses the IVC and the lower aorta when the pt lies supine
- Reduction in venous return can cause as much as a 25% decrease in CO
S/sx of aortocaval compression
N/V, pallor, anxiety, sweating, lightheadedness
Treatment / prevention of aortocaval compression
- position change
- left tilt / right hip roll
- ephedrine / neo
Why was ephedrine once thought to be a better drug than neo for a parturient?
- B/c it has both alpha and beta effects that help to maintain CO and thus uterine blood flow
- It was thought that neo was a uterine VC (only in sheep)
When is the most critical time for the parturient?
- Immediate post partum period when CO is highest and thus places the greatest strain on the heart
- High circulating endogenous catecholamines
When does CO return to normal in the parturient?
2 weeks post partum
Hematologic effects of pregnancy
Hypercoagulable state (limit blood loss)
All coagulation factors except __ and ___ increase.
O2 consumption and MV throughout pregnancy and increase by ___%
MV increases mostly by an increase in ____
Anatomic dead space is _____, but physiological dead space is _____.
- decreased due to non functional alveoli improving 2/2 increased TV and MV
- PaCO2-decreases (more effective release of CO2 due to decreased physiological dead space)
- HCO3- decreases (compensatory response to prevent alkalosis)
T or F, PaO2 decreases by 10% during pregnancy
F, increased by 10%
What 2 factors help to prevent the oxyhemoglobin dissociation curve from shifting to the left?
- Low CO2 is countered by decreased bicarb which decreases pH to causes a right shift
- right shift = O2 given up more easily to the fetus
- Increase in 2,3 DPG
- PO2 for 50% saturation on the dissociation curve
- normally 27, increased to 30 with pregnancy
What factors cause a right shift on the oxyhemoglobin dissociation curve?
Increased temp, CO2, H (decreased pH- acidosis), increased 2,3-DPG
What happens with a right shift on the oxyhemoglobin dissociation curve?
O2 is given up more easily to the tissues / fetus
Effect of CO2 on the O2 dissociation curve
How does the Bohr effect effect the mom?
Blood CO2 decreases which causes a left shift which causes a stronger affinity btw Hgb and O2
How does the double Bohr effect effect the fetus?
- Enhances transport of O2 to the fetus
- CO2 from fetus enters blood, forms increased carbonic acid, increased H+ ions (decreased pH)
- Maternal blood picks up CO2 (from fetus) and gives up the O2
- Causes a RIGHT shift
Hgb can carry ____ O2 at a ___ PCO2
How is FRC changed?
Reduced by 20%
Important cause of M+M associated with anesthesia
- Pulmonary aspiration of stomach contents
- due to incompetence of LES
- Increased material gastric output
All parturients are considered full stomachs after ____ weeks gestation.
What is it?
- Gastric contents > 25 cc with a pH < 2.5
- Nonparticulant antacid (bicitra) just prior to induction
How are renal plasma flow and GFR affected by pregnancy?
An increase in what 2 substances contributes to swelling during pregnancy?
Renin and aldosterone
How are Bun and Cre changed during pregnancy?
decreased by 40%
How is serum albumin changed during pregnancy?
Mild decrease (dilutional 2/2 45% increase in plasma volume)
How are hepatic function and blood flow affected during pregnancy?
How is serum pseudocholinesterase affected by pregnancy?
- Lowest levels during 1st 7 post partum days
How is the succ dose adjusted for parturients?
Why is MAC reduced in parturients?
- Increased MV (more volatile delivered to alveoli per unit time)
- Reduced FRC favors rapid replacement of alveolar content with inspired agent
The epidural venous plexus is engorged during pregnancy- what effects does this have?
- Cephalad spread of LA (decreased CSF volume and epidural space)
- Epidural catheter placement is more difficult
How is Vd affected in the parturient?
Increased 2/2 45% increase in plasma volume
MAC is reduced by ____ and LA requirements are reduced by ____ during pregnancy.
Uterine blood flow percent of CO
What factors decrease uterine blood flow?
- Maternal hypotension
- Uterine VC
- Uterine contractions
How is material hypotension treated?
- Fluids 500 -1000 ml
- Ephedrine pre-treat 25 mg IM
- Epidural with minimal LA concentration / volume
- Right uterine displacement
Causes of maternal hypotension
- Sympathetic blockade after RA
- Aortocaval compression
Blood flow equals…
arterial pressure - venous pressure / vascular resistance
- union of maternal and fetal tissue
- exchange of physiological nutrients and respiratory gases
- waste elimination by fetus
How many umbilical arteries?
Umbilical arteries flow to?
Umbilical vein flows to?
What is umbilical blood flow?
at term 120 ml / kg / min or about 360 ml / min
How are substances exchanged across the placental membrane (5 ways)?
diffusion, bulk flow, active transport, pinocytosis, breaks
What major substance(s) travels via diffusion?
- Respiratory gases (CO2)
- Fatty acids
- Small ions
What major substance travels via bulk flow?
- via hydrostatic or osmotic gradient
What major substance travels via breaks?
Fetal Rh+ red cells can be exuded into the material circulation
What are the villi in the placenta?
- Projections of fetal tissue
- It is here that exchange takes place btw fetus and mom
What percent of uterine blood flow supplies the intervillous space and what percent supplies the myometrium?
- 80% intervillious space
- 20% myometrium
What compensatory mechanisms allow the fetus to survive for up to 10 minutes in the setting of O2 deprivation?
- redistribution of fetal blood flow to brain, heart, and placenta
- decreased O2 consumption
- anaerobic metabolism
The fetal Hgb-O2 dissociation curve is shifted to the ____, meaning _____.
The maternal Hgb-O2 dissociation curve is shifted to the ____ right, meaning ______.
- Left, fetal Hgb has a greater affinity for O2
- Right, maternal Hgb has less of an affinity for O2
Fetal blood is (acidotic or alkalotic), while maternal blood is (acidotic or alkalotic).
- Fetal blood= alkalotic (carries a lot of CO2 into the placenta which diffuse out and into the maternal blood)= left shifted
- Maternal blood= acidotic (accepts CO2 from fetus)= right shifted
In simplest terms, the double Bohr effect:
encourages maternal blood to give up more O2 than is typical and more the fetus to take up for O2 than usual
Fetal hgb can carry as much as ___ to ___% more O2 can maternal Hgb. Is this a L or R shift?
T or F, Hgb can carry more O2 at a high PCO2?
F, Hgb can carry more O2 at a LOW PCO2
Maternal 2,3 DPG levels are (increased or decreased) to offset the effect of maternal hyperventilation.
increased, mom is RIGHT shifted
What type of Hgb makes up the majority of Hgb in the fetus?
While interuterine, the _____ are non-functional and the liver is _____.
How much of the fetal CO does the placenta receive?
What is the goal of fetal circulation? How is this achieved?
- Maximally perfuse the placenta and bypass nearly all of the nonfunctional lung and liver
- Via anatomical shunts
Describe the path of fetal blood flow
- Well oxygenated blood from the placenta, thru umbilical vein, ductus venosus (bypass liver), IVC, RA, thru FO, to LA, LV to brain and upper limbs
- Deoxygenated blood from the SVC, to RA, RV, PA, DA (bypass lungs), descending aorta, to 2 umbilical arteries, to placenta for oxygenation
Why is the blood entering the RA from the SVC deoxygenated?
This blood has been used to perfuse the brain and upper body
Avg O2 sat of blood entering the RA from the IVC?
- Located on left side of the atrial septum that overlies the FO
- Prevents blood from moving from LA to RA
At birth, fetal circulation shifts to adult circulation, the amount of SVR and PVR change to allow this. How do SVR and PVR change?
- SVR INCREASES- due to loss of blood flow thru low rx placenta, increases pressures in LA and LV
- PVR DECREASES- due to expansion of lungs with 1st breath, VD occurs, this reduces PA, RA, and RV pressures
Negative intrathoracic pressures in the newborn's 1st breath equal
40-60 cm H20
How does the FO close?
- Due to the pressure changes in the heart
- Low right sided pressures and high left sided pressures
T or F, even if permanent anatomic closure does not occur the higher left vs. right sided pressures keep the FO closed?
How does the DA close?
- DA constricts due to increased O2 in the area (blood backflows from aorta into the DA)
- Flow stops within 1-8 days
What happens if the DA does not close?
Elevated PA pressures (due to backflow from LV to aorta thru DA to pulmonary arteries)
How does the DV close?
- Blood flow from the umbilical vein ceases and the muscular walls of the DV contract
- Not really sure exactly why it closes
Persistent pulmonary hypertension
- persistent fetal circulation
- occurs due to acidosis or hypoxia in the 1st days of life
- R to L shunt occurs across the FO or the DA which causes hypoxia and acidosis, which then causes more shunting
- a vicious cycle is created
What pressure change will cause a R to L shunt in the newborn?
Anything that causes PVR to exceed SVR
What 3 diseases are included in PIH?
- HELLP syndrome
In what pts is PIH most commonly seen in?
Primigravidas, < 20 yo
What BP is considered PIH?
SBP > 140 and SBP >90
Potential complications of PIH?
ARF, cerebral hemorrhage, and pulmonary edema
- Hemolytic Elevated Liver enzymes
- Low Platelets
When does pre-eclampsia typically occur?
After the 20th week of gestation
Describe the patho of pre-eclampsia
- Hyperdynamic CV state
- Increased CO
- Generalized VC
- Overall decreased plasma volume (compared to normal parturient)= hypovolemia
- SQ tissue edema is common
How can PIH lead to HELLP
- Get tissue hypoxia due to VC
- Renal and hepatic dysfunction can result
How is uterine activity affected in pre-eclampsia?
Increased, uterus can become hyperactive and markedly sensitive to oxytocin
Why is proteinuria seen in pre-eclampsia?
Due to decreased GFR
Severe pre-eclampsia marked by seizures / CNS involvement
Priority in the PIH pt
Control symptoms associated with end organ involvement
Priority in the eclamptic pt
Control convulsions (increased O2 consumption)
T or F, maternal mortality is unaffected by the number of convulsions?
F, mortality increases with the number of convulsions
How are convulsions controlled?
- Mg 2-4 g
- Benzos- valium 2-5 mg, versed 1-4 mg
- Barbs- thiopental 50-100 mg
- GA if unable to control seizures to protect airway and deliver the fetus
Issues associated with HELLP
- Activation of the coagulation cascade
- Hemolytic anemia
- Destruction of Plts
- Liver suffers portal necrosis / ischemia resulting in elevated LFTs
S/sx of HELLP
- H/A, blurred vision, N/V, "band pain" around upper abdomen, tingling in extremities, HTN
T or F, HELLP can also present after delivery?
Definitive tx for PIH
- delivery of fetus and placenta
- control of disease process if fetus is too immature to be delivered
What does tocolytic mean?
Stops uterine contractions
- anti-sz agent, tocolytic, mild general VD
- Lowers maternal BP and improves uterine blood flow
abn neuromuscular transmission (can result in maternal weakness- including respiratory insufficiency)
T or F, hydralazine, BB, and CCB benefit mom and fetus in the tx of PIH?
F, benefit mom, but do not appear to improve fetal outcome
Lumbar epidural analgesia
- Superb analgesia during L+D
- Decreased maternal endogenous catecholamines lowers materal O2 requirements
- Improves uterine blood flow
Proper technique for LEA
- Manage HTN
- Ensure absence of severe coagulopathy
- Supplemental O2
- Adequate but cautious pre-hydration (500 ml)
- Pulse ox and FHR monitor
Can LEA be converted to provide analgesia for C-section?
Yes, give 1-2 L prior for expected T4 level
Why might a parturient with PIH have a difficult airway?
Airway edema is exacerbated
Can ketamine be used for induction for an emergency C-section for a pt with PIH?
NO, will further increase BP
Considerations regarding propofol, NDMR, succ for emergency section in PIH pt
- Reduced doses of propofol
- Defasciculating doses of NDMR are unnecessary (previous Mg use)
- Succ 1.5 mg / kg
Volatile agent dosing for emergency section for PIH pt
1.5 MAC for 1st minute then 2/3 to 1/2 MAC
T or F, the use of ST low concentrations of inhalational agents are not associated with decreased uterine activity, increased uterine bleeding, or neonatal depression
Risks associated with neonate born to PIH mom
- Higher risk for prematurity
- Usually SGA
- Higher risk asphyxiation, drug depression, and meconium aspiration
Why is close monitoring of the postpartum PIH mom needed for 24-48 hours?
Prone to convulse or develop pulm edema with 24 hours of delivery
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