Increase metabolic demands of both the mother and the fetus are met by an increase in cardiac output. How much is this increased?
CO increases 40%, mostly d/t increased SV (30-35%) and slightly because of increased HR (15-30%)
In pregnancy does SVR increase or decrease?
Blood volume increases how much during pregnancy?
Blood volume increases progressively after 7weeks gestation and peaks at approximately 33weeks
Why don't we see circulatory overload during pregnancy with the increase in CO?
It's more of a shift of volume (1000-15000ml) to the uterus, kidneys, breasts, and striated muscle
What causes dilutional anemia in the pregnant patient?
Although both increase, Plasma volume increases more (45%) than red cell mass (25%)
Why is dilutional anemia good in pregnancy?
Facilitates maternal and fetal exchange of nutrients, gases, and metabolites (decreased viscocity)
Reduces the impact of maternal blood loss at delivery (500ml vag; 1000ml Csec)
What is autotransfusion mean during labor?
The contracting uterus auto transfuses 300-500ml of blood which helps compensate for the maternal blood loss during labor
This causes a further increase in CO up to 50% (SV increases so HR decreases to compensate)
What is aortocaval compression (supine hypotension syndrome)?
Uterus compresses on IVC and lower aorta when the mom lies supine
Reduces venous return and can decreases CO by 25%
How does the mom compensate for supine hypotension syndrome?
Unanesthetised state-mom compensates with increase SVR and HR
Also, blood begins to flow through collateral veins at the paravertebral venous plexous (including epidural veins)
Mom can change position d/t symptoms she feels
What happens under anesthesia during supine hypotension syndrome?
compensatory mechanisms aren't there so resultant hypotensioinReduced blood flow to kidneys, lower extremities, and to the uteroplacental unit, compromising the fetus
What are the s/s of supine hypotension syndrome?
N/V, pallor, anxiety, & sweating
How do we treat supine hypotension syndrome?
Left tilt, RIGHT HIP ROLL
When is the MOST CRITICAL TIME for the paturient?
immediate post partum period when CO is highest and greatest strain on heart
Why is immediately after birth the most critical time?
The auto transfusion from the uterus, complete sudden relief of IVC obstruction, and high circulating endogenous catecholamines
Hematologic effects of pregnancy create a hypercoagulable state which helps limit blood loss during delivery. What two coagulation factors DON'T increase?
11 & 13 (board question)
What happens to oxygen consumption and minute ventilation during pregnancy?
Increases throughout and peaks at 50% above normal at end of 2nd trimester
How do we get the increase in minute ventilation in pregnancy?
TV increases 40% & RR increases 15%
Anatomic dead space is unchanged by physiologic dead space decreases during pregnancy, why?
some non-functional alveoli improve because of the increased TV/MV
This decrease narrows the arterial EtCO2 graident (more effective release of CO2)
Overall, alveolar ventilation is about ___% higher at the end of gestation
The arterial and alveolar CO2 tensions are decreased by this increased ventilation during pregnancy so what happens to the PaCO2?
Since PaCO2 decreases, the mom develops alkalosis, what happens to compensate for that?
Serum bicarbonate decreases 15% as well
Increase in maternal levels of 23DPG (because alkalosis causes left shift and we don't want the mom holding on to O2)
What is the Bohr effect
At the lung, CO2 goes from blood to alveoli, so less pCO2 and less H+ in the blood because a decrease in blood carbonic acid
Shifts the curve to the left which helps uptake of oxygen from the alveolus
Opposite occurs at fetus, CO2 from fetus goes to mom's blood, increases carbonic acid in mom so increase H+ and right shift so it releases oxygen to the fetus
What is the Double Bohr Effect? (enhances the transport of Oxygen to the fetus)
HgB carry more oxygen at a low PCO2 than at a high PCO2
Fetal blood entering placenta has high PCO2 but it goes to mom's blood
Transfer of CO2 makes fetal blood alkalotic and mom's blood acidic so mom's blood gets a right shift and releases oxygen easier to the fetal blood (which is relatively alkaline and has affinity for the oxygen)
How much does FRC decrease in pregnancy and what does that mean to us?
Reduction in oxygen storage capacity, combined with increased oxygen consumption, leads to a rapid desaturation in apnic parturient
Why is the pregnant patient difficult to intubate?
Engorgement of resp mucosa predisposes the upper airway to trauma & obstruction during DL
Gentle technique & small ETT is prudent
Why is the pregnant patient an RSI?
Uterus causes gradual cephalad displacement of abdominal contents
Incompetent gastoesophageal sphincter (d/t displacement and elevated progesterone levels)
Epidural w/minimal LA concentration/vol + narcotic for pain control
Right uterine dysplacement
We should do frequent monitoring after epidural placement, especially for the first __min post-block
What causes uterine vascular vasoconstriction?
Caused by stress release of endogenous catecholamines (sympathetic discharge) or exogenous sympathomimetics
Why do uterine contractions cause decreased uterine blood flow?
decreased blood flow by elevating uterine venous pressure brought on by the increased intramural pressure of the uterus, this action even compresses the arterial vesssels in the myometrium (so transfers to the baby and cord as well)
How many arteries and veins are in the cord?
2 umbilical arteries
1 umbilical vein (vein visits the fetus)
What % of the fetus CO goes to the placenta (via the two umbi arteries)?
What are the villi in the placenta? (what is it's purpose)
The villi are projections of fetal tissue
The placenta blood goes to the capillaries in the villi where exchange occurs
This is where the fetal blood is cleaned and oxygenated before returning to the fetus via the umbi vein
Maternal blood goes through the uterine arteries into the large maternal sinuses surrounding and bathing the villus again where exchange occurs and then flows back into the uterine veins into the maternal systemic circulation
Umbilical blood flow is what?
At term is 120ml/kg/min or about 360ml/min
What are the 5 mechanisms by which substances are exhcanged across the placenta?
Diffusion (Resp gases, fatty acids, small ions)
Bulk flow (d/t hydrostatic or osmotic gradient-water)
Active Transport (AA, water soluble vitamins, some ions)
Pinocytosis (lg molecules, pinched off enclosed vesicles)
When might we see breaks in the plasma (which is when thin filmy villi may break off within the intervillous space and the contents may be extruded into the maternal circulation)??
When fetal Rh+ red cells are deposited in the vascular system of the Rh- mom
___% of uterine blood flow passes in to the intervillous space of the placenta while ___% supplies the actual myometrium of the uterus
Oxygen has the lowest storage to utilization ratio to the fetus but the fetus can survive up to 10min of oxygen deprivation, why???
Redistribution of fetal blood flow to the brain, heart, & placenta
Decreased oxygen consumption
Transfer of oxygen across the placenta is dependent on...........
the ratio of maternal blood flow to fetal umbilical blood flow.
Well oxygenated blood from the placenta has a PaO2 of 40torr (maternal is 95-104torr)
What 3 things aid in the oxygen transfer from mother to fetus?
Fetal HgB is left shifted and Maternal is Right shifted (with increased 23DPG)
HgB concentration in the fetus is about 50% more than the mother
Double Bohr Effect
The HgB of the fetus is mainly fetal hemoglobin and is synthesized by the fetus prior to birth. Fetal HgB can carry as much as __-___ more oxygen than maternal HgB (left shift)
20-30%, this means that at at given PO2, the fetal HgB can carry as much as 20-30% more oxygen than the maternal HgB
What is the main goal of the fetal shunts?
to maximally perfuse the placenta and to bypass nearly all of the nonfunctional lung and liver
What are the three fetal shunts?
What is the average oxygen saturation of the blood in the umbi vein; what about after it mixes with the ductus venosus?
80%; sats drop to 67% after mixing
What is the septum primum?
A small valve located on the left side of the atrial septum that overlies the foramen ovale
Helps to prevent blood from moving in reverse direction
The first breath of the newborn generates initial negative intrathoracic pressures in the range of __-___cmH2O
How much does the pulmonary blood flow increase from fetal to newborn?
5fold; because of vasodilation of the pulmonary blood vessels
Which shunt closes d/t pressure and which d/t O2 level?
Foramen ovale closes d/t LA > RA pressure and so septum primum has blood forcing it to close the PFO
Ductus arteriosus is closed when the muscular walls of the ductus arteriosus constrict because of increased oxygen in the area (fetal PaO2 20torr & newborn PaO2 100torr)
How does the ductus venosus close?
Not sure why but when blood flow through the umbi vein stops, the muscular walls of the ductus venosus contract strongly within 1-3 hrs and consequently the portal venous pressure rises from 0 to 10 torr, which forces blood through the liver sinuses
What is persistent fetal circulation (aka persistent pulmonary HTN)
if the neonate experiences hypoxia or acidosis during first few days of life
R->L shut across PFO or PDA causes more hypoxia and acidosis which causes more shunting, etc.
***Avoid acidosis and hypoxia!**
Who is more at risk for pregnancy induced HTN?
primigravidas uner 20yrs of age (under 20 have 5fold increased risk)
What is pregnancy induced HTN?
Multi-organ disease process primarily marked by an increase in BP (SBP>140/DBP>90)
What does HELLP stand for?
What are the potential maternal complications with pregnancy induced hTN?
acute renal failure
When does preeclampsia usually occur?
After the 20th week gestation
What end organ involvement is there in pre-eclampsia?
hyperdynamic CV state: generalized vasoconstriction and increase in CO
Plasma volume is decreased (hypovolemia)
SubQ tissue edema (also CNS and larynx)
Tissue hypoxia causes renal and hepatic dysfunction
Decreased GFR and CC, lg amt of serum proteins are lost in urine
Mild hepatic involvement (unless HELLP)
Uterine activity is increased and the uterus can become hyperactive and markedly sensitive to oxytocin
When does severe preeclampsia progess to ecclampsia?
When seizures /convulsions occur
What might the initial stages of ecclampsia be? What happens next?
mom may roll her eyes while facial and hand muscles twitch slightly
Tonic stage occurs soon after the initial stage and includes twitching and teeth clenching, arms and legs go rigid, lasts for up to 30sec
Clonic stage the spasm stops but the muscles jerk violently, these seizures can last up to 2min after which the patient may lose consciousness
What is the first priority in the eclamptic patient?
to control convulsions
Benzodiazepines (Valium 2-5mg or Versed 1-4mg)
Barbiturates (Thiopental 50-100mg)
If not able to control seizures, GA is initiated to protect the airway and deliver the fetus
What is the main problem in HELLP?
Activation of the coagulation cascade
Cross linking of fibrin in the liver's sm. vessels leads to hemolytic anemia as the RBC pass through-plts are also destroyed this way
Liver portal necrosis->elevated liver enzymes
What are the symptoms of HELLP?
Gradual w/onset of HA, Blurred vision, N/V, "band pain" around upper abdomen and tingling in the extremities
HTN may be seen but can be mild
DIC is 20% of HELLP patients
What is the definitive therapy for pregnancy induced HTN?
delivery of the fetus and placenta
Maturation of the fetus is rate limiting factor so control of the disease is the 2nd best choice