Thirty Three Flashcards
(16 cards)
Describe the changes that occur in the mother’s CV system during pregnancy?
The most striking changes in maternal physiology occur in the cardiovascular system.
There is a tremendous increase in the total blood volume, up to a doubling of the usual
volume. This change begins early in the first trimester and continues throughout
gestation. There is a greater increase in the plasma volume compared to the red cell
volume resulting in the so-called “physiologic anemia of pregnancy”. The cardiac output
increases with contributions coming from both an increase in stroke volume as well as an
increase in resting heart rate.
Increased blood volume (.5-2X)
Increased cardiac output
o Increased heart rate
o Increased stroke volume
Increased heart size
Dextrorotation and flattening of the heart
The cardiac silhouette as seen on a chest radiograph will demonstrate an increase in size
and a rotation of the heart. This rotation is due to the elevation of the diaphragm as the
intra-abdominal contents are displaced upward by the enlarging uterus. Clinically one
will see a deviation of the point of maximal impulse of the heart to the left from its
normal position. One also hears a grade 2/6-holosystolic flow murmur along the sternal
border due to the increased blood flow through the heart. A diastolic murmur or a grade
three or greater systolic murmur during pregnancy are always abnormal and may indicate
underlying cardiac abnormalities.
What physical findings will be found during pregnancy that are related to the CV system? What causes them? What are the implications?
Physical Findings
Increased heart size
Deviation of PMI to left of midclavicular line
Grade 2/6 systolic murmur
In addition to these volume and anatomic changes there is also a decrease in plasma
onchotic pressure due to dilution of the plasma proteins. The capillaries are also more
permeable and both of these normal alterations explain the propensity for pregnant
women to develop dependent edema. Venous stasis occurs in the dependent extremities
due in part to the compression of the venous return by the gravid uterus. This stasis
predisposes the pregnant women to development of blood clots in the lower extremity.
The blood pressure should decrease in the mid-trimester and then rise toward but not
exceed the early pregnancy blood pressure near term. One of the more frequent and
serious complications of pregnancy is that of preeclampsia (hypertension & proteinuria)
which affects 6-8% of pregnant women. It is important to recognize that an elevation of
blood pressure is never a normal consequence of pregnancy.
What changes are seen in the respiratory system in pregnancy? What causes them? What is unchanged? What does this mean clinically?
The changes seen in the respiratory system show an increases respiratory rate at rest.
This amounts to 1-2 extra breaths per minute and is thought to be due to central
stimulatory effect of higher progesterone levels occurring in pregnancy. The tidal
volume increases, as does the oxygen consumption. The mother blows off the CO2
generated by the fetus and subsequently crosses the placenta. The additional oxygen
requirements of the developing fetus are met by the increase in oxygen consumption of
the mother. Of clinical importance is the fact that the maximal peak expiratory flow rate
is unchanged in pregnancy, thereby allowing the same monitoring for asthmatic patients.
Increased respiratory rate
Increased tidal volume
Increased O2 consumption
Maximal peak expiratory flow unchanged
What changes are seen during the renal system during pregnancy?
The functional changes in the renal system are largely explained by the increase in renal
blood flow. This leads to an increase in glomerular filtration rate and is demonstrated
clinically by an increased creatinine clearance. As expected you would also see a
decrease in the serum creatinine and BUN. The total urine output will increase as well.
Since the laboratories do not report out normal findings seen in pregnancy, one should
always be concerned if a pregnant woman has an upper limit of “normal” BUN or
creatinine. Since you expect them to decrease in pregnancy such values may herald a
significant compromise in renal function.
Anatomically the renal system shows hydroureters due to the compression of the ureters
as they cross the pelvic brim by the enlarging uterus. This change resolves by 6 weeks
post partum. The large uterus also compresses the bladder, reducing the bladder capacity
and leading to frequent urination. The relative stasis of urine in the upper collecting tree
makes the pregnant woman prone to pyelonephritis. Careful attention to monitoring for
bacteruria may prevent this complication during the prenatal course.
What changes occur in the GI system in pregnancy? Liver enzyme changes? Why?
The gastrointestinal tract also undergoes several changes as a consequence of pregnancy.
The bowel motility decreases due to the relaxation effect of progesterone on smooth
muscle. This contributes to the constipation that is common during pregnancy. There is
also a decrease in bile flow and this may contribute to the higher incidence of gallstones
seen in someone who has been pregnant. The interpretation of liver function studies is
more difficult during pregnancy. The alkaline phosphatase increases due to its
production by the placenta. Total bilirubin may be slightly increased. The serum
cholesterol is markedly increased in pregnancy and can be 2-4x normal. This is a normal
finding and therefore pregnancy is not the time to screen for problems with cholesterol.
The intracellular enzymes, the transaminases, should be unchanged in pregnancy. The
only time transaminases are seen in the circulation is in the presence of hepatic cell death.
Therefore, an elevation of transaminase in pregnancy heralds potentially serious
conditions, such as the sever vasoconstriction seen in preeclampsia, viral infection and
drug toxicity, to name a few. The liver dependent clotting factors are usually increased in
pregnancy contributing to the so-called hypercoaguable state of pregnancy.
Liver Function Studies in Pregnancy
Alkaline phosphatase increased
Bilirubin: normal or slight increase
Transaminase no change
Cholesterol increased
Liver dependent clotting factors increased
Describe the changes in thyroid hormone during pregnancy.
During pregnancy there is an increase in total thyroid hormone but this is due to an
increase in the amount of protein-bound hormone. The free T3 and T4 are essentially
unchanged in pregnancy. The thyroid-stimulating hormone (TSH) can be used to screen
for thyroid dysfunction during pregnancy and should not change just due to the pregnant
state. It is very difficult on clinical grounds to make diagnosis of thyroid disease during
pregnancy due to the normal symptoms associated with pregnancy: fatigue, weight gain,
hair and skin changes and changes in bowel function.
Describe how pregnancy affects the pancreas and glucose homeostasis.
The demands on the pancreas to maintain glucose homeostasis increase during
pregnancy. The fetus serves as a drain on the maternal glucose level leading to a
tendency of some patients to exhibit symptoms of hypoglycemia if they go without a
meal for a long time. The fasting glucose level is usually decreased. There is an
accelerated breakdown of maternal insulin by enzymes of placental origin and a relative
insulin resistance. If a mother has normal insulin reserves, the blood sugar will be
maintained in the normal range. However, if these reserves are depleted, gestational
diabetes will ensue. The postprandial blood sugars tend to be slightly increased in
pregnancy. Since insulin does not cross the placenta, the fetal blood sugar is maintained
by its own inherent insulin production.
Blood Sugar Controls in Pregnancy
Insulin resistance
Lower fasting blood sugar
Elevated postprandial sugar
Increased insulin production
Describe uterine changes during pregnancy.
Uterine changes in pregnancy include a tremendous hypertrophy of myometrial cells to
accommodate the growing fetus. The uterine vasculature dilates and a large low
resistance shunt develops in the maternal circulation as a result of this low resistance flow
through the uterus. As pregnancy progresses, there is a gradual increase in contraction
activity that ultimately results in the onset of labor and delivery of the fetus. The control
of labor and its onset is still poorly understood and a number of factors play a role in this
process.
What are some miscellaneous changes that occur during pregnancy?
Other pregnancy related changes are an increase in basal body temperature by about 0.5
degrees. The average weight gain is between 18-32 pounds distributed 2-3 pounds the
first trimester and an average of 3 pounds per month each month thereafter. This weight
gain is explained by an increase in fat deposition, an increase in total body water, uterine
weight, breast size and the of course the weight of the baby and placenta.
What are fetal nutritional needs dependent on for the first five weeks? After that?
Prior to 5 weeks gestation, the embryo relies on internal cellular stores and passive
diffusion for its nutritional needs. After that time the placenta begins to function and the
supply of nutrients and oxygen is dependent on the maternal and fetal cardiac systems as
well as how well the placenta allows passage of these substances. The placental
development requires an orderly implantation and differentiation of trophoblasts to
provide a normal communication with the uterine vasculature.
Describe the timing, mechanism, and problems involved with the transport of nutrients from mother to fetus.
The placenta is primarily a respiratory organ that allows the passive diffusion of oxygen
to the fetus and the exchange of carbon dioxide down a concentration gradient from fetus
to mother. Fatty acids cross slowly to the fetus whereas glucose passes freely. A
problem arises when the mother is diabetic and she has elevated levels of blood glucose.
This high maternal blood sugar will be reflected in the fetal circulation. At the time of
delivery the glucose supply is suddenly terminated yet the fetal insulin level remains
elevated for several hours. This will drive the newborns blood sugar to extremely low
levels with consequent harm to the baby. This emphasizes the importance of maternal
glucose control during pregnancy and at the time of labor.
Amino acids are actively transported in an energy dependent fashion against a
concentration gradient. Protein hormones such as insulin and thyrotropin hormone do not
cross the placenta to any appreciable extent.
Describe fetal blood flow (order of arteries/veins). What can effect the perfusion of the placenta? What are some possible results? What is the fetal PO2 like? Why? What is a normal fetal heart rate? How is it controlled?
Fetal blood flow varies significantly from a child or adults. Blood comes from the
placenta to the baby through the umbilical vein and then travels through the ductus
venosus to the inferior vena cava and then the right atrium. Within the heart the blood is
shunted across the foramen ovale to the left side and then out the aorta. Blood from the
right heart crosses through the patent ductus arteriosus to the aorta and then through the
umbilical arteries back to the placenta.
Areas of admixture of
oxygenated and unoxygenated
blood are shown in the shaded
boxes. Perfusion of the
placenta form both sides has
profound consequences for
fetal well-being. Impaired
perfusion can cause growth
abnormalities and fetal death.
This shunting allows an admixture of oxygenated and unoxygenated blood.
Approximately 40% of the fetal cardiac output goes to the placenta. The fetal pO2 will
be lower than an adult due to this mixing of blood. The normal fetal heart rate is between
120 and 160 bpm. There is a trend to see a gradual slowing of the heart rate as the baby
matures. There is also a variability of the heart rate moment to moment that is controlled
by the CNS mechanisms, primarily the vagal nerve output.
What are some ways in which the fetus adapts to stress? What happens to maternal CO2? Why?
The fetal adaptation to stress is critical to its survival. The baby can decrease its activity
to conserve oxygen and can shunt its blood preferentially to the brain. When these
compensation mechanisms are exceeded poor outcomes can result. The maternal CO2
decreases from 40 mm Hg to 34 mm Hg to provide a concentration gradient to allow
removal of fetal CO2
What is fetal growth like initially? Later on? What clinical implications does this have?
Fetal growth in early gestation is primarily through hyperplasia and an increase in cell
number whereas at the end of pregnancy growth is due to cell hypertrophy. Insults to
growth early gestation are therefore more likely to result in a symmetrically small infant.
Later in pregnancy the bay may be able to conserve blood flow and growth of the brain
and an asymmetry in growth with a larger head in comparison to the body may be seen.
What are some indicators of fetal health? Explain them.
Since it is difficult and risky to sample the fetal circulation to measure such things as pH
and oxygen concentration, the obstetrician is left with other end points to assess fetal
status. The amniotic fluid volume reflects fetal renal perfusion since the majority of
amniotic fluid comes from fetal urination. If the volume is low it may mean that the fetus
is shunting blood away from the kidneys to conserve flow to the brain. The fetal heart
rate may change with bradycardia, a distinctly ominous sign, or a loss of variability
reflecting a lack of control by higher centers or an intrinsic depression myocardial
activity due to acidosis. Using ultrasound one can assess how well blood is flowing from
the fetus to the placenta through the umbilical vein or from the mother to the placenta
through the uterine arteries by utilizing Doppler studies. Elevated Doppler values or no
diastolic blood flow indicates a high resistance to flow through the placenta and poor
placental function. In addition, Doppler study of the fetal cerebral blood flow may show
maximal dilation suggestion the fetal compensation to stress.
Indicators of Fetal Health
Baseline heart rate and variability Amniotic fluid volume Fetal activity Fetal muscle tone Fetal breathing activity Fetal growth Doppler flow through the umbilical arteries, uterine arteries and fetal cerebral arteries
What is ARDS? What happens? How can it be prevented?
The most common serious neonatal complication seen is that of respiratory distress
syndrome. There is a direct correlation between gestational age and the risk of
developing this problem. The type II pneumocystis are responsible for the production of
the surfactants that provide for the maintenance of the surface tension that keeps the
alveoli from collapsing at end expiration. The phospholipids that make up the surfactants
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are at very low levels until 32-33 weeks gestation. At 34 weeks roughly one-half of
infants will have a mature lung profile as determined by an amniocentesis. Exceptions to
this rule exist primarily for diabetic patients where the baby’s lungs generally mature at a
later date. The original test for pulmonary maturity was the lecitin/sphingomyelin ration.
Lecitin is the major component of surfactant and sphingomyelin is present in a constant
amount in amniotic fluid. An L/S ration above 2.0 generally indicates mature lungs.
Phosphatidylglycerol is a phospholipid that appears later in gestation but when present is
an even more reliable indicator of maturity. Other assays provide similar information and
taken together provide a way for the physician to determine if the baby is likely to have
mature lungs and aid in a decision on whether or not to deliver the infant.
