Editing OBGYN - Maternal-Fetal Physiology

=Maternal-Fetal Physiology=

==Objectives==
*List pertinent physiologic changes in various maternal systems
*Recognize that signs and symptoms in a pregnant patient are often more difficult to interpret
*Non-pregnant lab values and measurements are frequently abnormal in the pregnant state

==Case: First Trimester==
*21 y/o G1P0 at 8w0d by L=6 week US at the WVC (women's visit center at Wishard) presents for her OB registration appointment.
**She denies any LOF (leaking of fluid), VB (vaginal bleeding).
**Pt with C/C of cramping and dark “poop”, nausea and vomiting with heart burn.
*PMH: Denied
*PSocialH: Denied
*OB: G1
*Gyn: Denied
*Social Hx: Denied x 3
*Allergies: NKDA
*Medications: PNV (Prenatal Vitamin)
*VS: BP: 110/80 P: 80 T: 98.6 Weight: 65Kg Height: 5’1
*UA: WNL
*PE: WNL


==GI Issues in the First Trimester==
*Constipation:
**Iron (ferrous-sulfate) in the pre-natal vitamins slows GI motility and causes constipation.
**'''Progesterone: a smooth muscle relaxant; causes decreased bowel movement which can lead to increased time for water reabsorption and thus constipation'''
**Tx: give colace
**Could be as bad a month!
**There is fear of miscarriage throughout pregnancy so anything seeming abnormal (like not pooping) starts a fear of miscarriage.


*Nausea and Vomiting:
**beta-HCG causes n/v
***beta-HCG peaks at 10-12 weeks.
**{rogesterone: a smooth muscle relaxant; causes decreased bowel movement which can lead to n / v.


*Weight gain:
**can occur early or late, ideal is a progression.
**vomitting can lead to weight loss over the first weeks, but mom and baby will be ok
**Normal Weight for Height: about 20 lbs
**Underweight Women: about 30 lbs
**Overweight Women: about 16 lbs
**Only an addition 300 calories / day are necessary to feed a fetus.
***500 cal for twins

==Case: Second Trimester==
*21 y/o is now 20 weeks pregnant
*Presents to triage at Wishard with horrible heartburn after eating a deep fried twinkie at the state fair.  
*She threw-up so much in early pregnancy that she is making up for it now.
**She has gained 25 lbs (from 8 weeks to second trimester).
**That is a lot of weight gain.
*She denied any LOF (leaking of fluid), denied VB (vaginal bleeding) or cramping.
*She stated that she had some of the chalkie things and it didn’t make it better this time.
**Tums.
*She was given a GI cocktail in triage and she was still miserable.


*Differential Diagnosis:
**Constipation
***Small bowel obstruction
***Ask when they last deficated.
**Gallstones
***Increased estrogen and progesterone
***Slow emptying of the stomach
***Often already at high risk (four "F"s: fat, forty, fertile, female)
***Can look really, really, bad.
**Pancreatitis
**Appendicitis
***Appendix moves from right lower quadrant to midquadrant
***Can get tucked up behind the uterus

==First / Second Trimester GI Presentations==
*High levels of estrogen / progesterone in pregnancy lend themselves to gallstone formation
**Especially when woman gets pregnant a second time without having gallstones from a previous pregnancy removed.


*Recall that progesterone is a smooth muscle relaxant.
*Recall that progesterone is at high levels throughout pregnancy to maintain the uterine environment.
**Progesterone is really rampinig up during the first trimester.
*High circulating levels of progesterone can lead to:
**Increased GERD from relaxation of GE sphincter
**Constipation from delayed transit through large bowel 
**Increased N/V from delayed gastric emptying
**Stomach can still be full of content 8 hours later.
**“Full stomach” sensation


*Tx is often to keep pt from eating for 8 to 12 hours and then to switch to a little bit, throughout the day type consumption pattern.

==Case: Second / Third Trimester==
*21 y/o G1P0 at 28w0d
*Presents to triage at St. Francis Beech Grove.
*Patient has been brought in by her family “Doc I feel horrible.  I am dizzy.  I was sitting at the high-school football game, I stood up to cheer, my heart started racing and I felt like I was going to pass-out!  My ankles are swollen and I feel horrible."
*Denies LOF (leaking of fluid), VB (vaginal bleeding), CTXs (contractions).
*'''Endorses +FM (fetal movement).'''
*ED doctor noticed that she is '''breathing deeply.'''


*Pertinent Vitals:
**BP: 100/60
**P: 90
**T: 98.6
**RR: 16
**O2: 96% RA
**Weight: 80kgs 


*Labs ordered:
**CBC w/platelets
**CXR (chest xray)
**ABG (arterial blood gas)
**UA (urinary analytes)
**CMP (complete metabolic panel)
**Coags (coagulation studies)


*PE:
**Lungs: CTA B
**CV: Systolic murmur
**Abd: Gravid, NT
**Extrem: +1 pitting edema


*Lab results:
**WBC: 10,000 (slightly elevated) 
**Hgb / HCT: 10.5/31.7% (decrease)
**Platelets: 200,000 (slight decrease)
**Fibrinogen: 600 (increased)
**Bun / Cr: 3 / 0.6 (decreased)
**pH: 7.44
**pCO2: 30
**BiCarb: 21
**paO2: 103

==Physiological Changes in Pregnancy==

===Blood pressure in pregnancy===
*Pt blood pressure: 100/60
*Both systolic and diastolic BP decrease in 2nd trimester
*Systalic decreases 5-10 mmHg
*Diastolic decreases 10-15 mmHg
*We even take severe hypertensive pts off their meds.
*Normal


*Monitor from baseline!
**Athletes will have low baseline BP and therefore it will be a challenge to keep their BP up during pregnancy.

===Pulse in pregnancy===
*Pt's pulse: 90
*Increases 20 beats (peak at 32 weeks, middle of 3rd trimester)
*Normal

===Cardiac output in pregnanc===
*Recall that cardiac output (CO) is stroke volume (SV) multiplied by the heart rate (HR).
*CO increases at ''8 weeks'' and peaks at ''20 weeks''.
*CO increases by 30-50%
*CO rises to 4.5-6.0 L / min
 How do we know her stroke volume?
*Systolic ejection murmur is common (90% of women).
*S3 gallop is common (90% of women).
*'''Peripheral vascular resistance falls during pregnancy, too.'''
**Hence the swelling.
**Wear flipflops, wear compression socks
**Especially medical residents.

===Respiratory rate in pregnancy===
*Recall your standard respiratory volumes (see image below).
*'''Note that O2 demand (consumption) is increased by 15-20% in pregnancy.'''
*These volumes are affected by the displacement of the diaphragm rostrally.
*Note that '''respiratory rate should remain unchanged''' in normal pregnancy.
**This is possible because the tidal volume increases (because the minute ventilation increases).
*Functional residual capacity decreases by 20% because of displacement the uterus.


http://www.glowm.com/resources/glowm/graphics/figures/v3/0260/004f.gif
http://www.glowm.com/resources/glowm/graphics/figures/v3/0260/001f.gif


*So '''dyspnea ''is'' normal with pregnancy'''.

{|border=1
!Volume (mL)
!Definition
!Non-pregnant
!Pregnant
!Change
|-
!Total lung capacity
|Vital capacity + residual volume
|4200
|4000
| -4%
|-
!Vital Capacity
|Total lung capacity - residual volume
|3200
|3200
| 0%
|-
!Inspiratory Capacity
|Vital capacity - expiratory reserve volume
|2500
|2650
| +6%
|-
!Tidal volume
|Volume moved in and out with each normal breath
|450
|550
| +33%
|-
!Expiratory Reserve Volume
|Vital capacity - inspiratory capacity
|700
|550
| -20%
|-
!Inspiratory Reserve Volume
|Inspiratory capacity - total volume
|2050
|2050
| 0%
|-
!Residual volume
|Total volume - vital capacity
|1000
|800
| -20%
|-
!Functional Residual Capacity
|Residual volume + expiratory reserve volume
|1700
|1350
| -20%
|}

===Arterial blood gas (ABG) in pregnancy===
*NB: '''ABG should never be "normal" in pregnancy!'''
**Should have a respiratory alkalosis from blowing off their CO2 at higher rates.
**Should have a metabolic acidosis (compensatory).
*Many pregnant women will hyperventalate.
**Give them a bag in which to breath.
**Very hard to settle them down so important to give the bag quickly and pt will often become syncopous.


*Pt's ABG was:
**pH: 7.44 (
**pCO2: 30
**BiCarb: 21
**paO2: 103


*Recall that O2 consumption increases in pregnancy.
**15-20%
*Recall that minute ventilation (the amount of air breathed in over the course of one minute) is increased ''relatively more than the O2 consumption''.
**This means that '''more air is breathed in and out than is necessary for the rate of oxygen consumption.'''
**This is the '''definition of hyperventilation!'''
*Recall the chemical equation: CO2 + H20 <=> H2CO3 <=> HCO3 + H
*Recall that hyperventilation gives off CO2, dragging the equation to the left.
**That is, pCO2 will be decreased.
*Therefore pregnant, hyperventilating women become '''alkalotic''' (decreased H+).
**That is, pH will be high (less H+).
**This is a '''respiratory alkalosis'''.
*Recall that the kidneys can excrete HCO3 to compensate for loss of CO2 (because of hyperventilation) and thus draw the equation back to the right.
**Thus we expect the serum HCO3 to be low.
*Recall that in pregnancy there is an increased oxygen carrying capacity (facilitated by RBC volume increased by 50%).
**Thus we expect the pO2 to be high.


*Given this respiratory alkalosis and metabolic compensation, we expect:
**the pCO2 to be low: 26-32 mmHg (compared to non-pregnancy 38-45)
**the pH to be high (alkaline): 7.40-7.46 (compared to non-pregnancy 7.38-7.42)
**the HCO3 to be low: 18-21 mEq / L (compared to non-pregnancy 24-31)
**the pO2 to be high: 106-108 mmHg (compared to non-pregnancy 70-100)


*A high pCO2 is cause for alarm in the asthmatic pregnant woman.
*Also, pCO2 should be monitored carefully in the acutely infected pregnant woman because they are '''immune compromised''' and have '''very little respiratory reserve'''.

{|border=1
!Measure
!Non-pregnant
!Pregnant
!Change
!Reason
|-
!pH
|7.38 - 7.42
|7.4 - 7.46
|Higher
|Because CO2 is being breathed off at a higher rate than the kidneys are excreting HCO3- so the equation is pulled to the left (away from H+).
|-
!pCO2 (mmHg)
|38 - 45
|26 - 32
|Lower
|Because minute ventilation increases more than oxygen consumption (CO2 breathed off faster than oxygen consumed).
|-
!pO2 (mmHg)
|70 - 100
|101 - 106
|Lower
|Because RBC volume is increased.
|-
!HCO3- (mEq / L)
|24 - 31
|18 - 21
|Lower
|Because the kidneys are excreting HCO3- in an attempt to compensate for respiratory alkalosis.
|-
!O2 saturation (%)
|95 - 100
|95 - 100
|None
|
|}


*Importance:
**'''A normal pregnant woman has a compensated respiratory alkalosis (with a compensatory metabloic acidosis) and a diminished pulmonary reserve.'''
*Cause:
**Progesterone: relaxes the smooth muscle
**Diaphragm raised 4cm

===CBC in pregnancy===
*Plasma Volume and RBC Mass
**Plasma volume increases by about 50%
**RBC volume increases by about 30%
*Result:
**“Physiologic anemia of pregnancy”
**The mean Hgb is about 11.5 g/dl
*At 28 weeks, get new labs.
*'''Will likely need to start iron.'''
**Start at or below 10.
**Yucky tasting, makes woman feel horrible.
**''Necessary for proper oxygenation.''

===Coagulation in pregnancy===
*'''In pregnancy the pt is hypercoaguable'''
**This is the body's way to not die from bleeding when the parasite is ejected / ripped from the internal surface of the uterus.
*DIC is the number 1 cause of death in laboring women around the world.
**Not so much here in the US.
*Procoagulant’s are increased: I, VII, VIII, IX, X and Fibrinogen.
*Prevents Peripartum Hemorrhage
*Can lose 1500mL without blinking.
*Over 2000 mL lost, start worrying b/c coag factors are becoming deficient.

===Renal System in pregnancy===
*Bun & Serum Creatinine decreases by about 25%
**Low because of increased blood volume, increased GFR, increased blood flow to the kidneys
*Plasma osmolarity decreases by about 10 mOsm / kg H20
*Increase in tubal reabsorption of sodium
*Marked increase in renin and angiotensin levels
**But '''markedly reduced vascular sensitivity to their hypertensive effects'''
*Increased glucose excretion
**Fine during labor, a coping mechanism.
**Labs at 28 weeks detect gestational diabetes.


*Anatomic:
**Kidney size increases
**Kidney weight increases
**Ureteral dilation (right side greater than left side)
***Because of the angle of the uterus
**Bladder becomes an intra-abdominal organ


*Hemodynamic:
**GFR increase by 50%
**Renal plasma increased by flow by 75%
**'''Creatinine Clearance increases to 150-200 cc / min'''
***Most important kidney function test in pregnancy


*Swollen Ankles:
**Recall that the Plasma Volume Increases 50% in pregnancy.
**Recall that there is decreased Systemic Vascular resistance in pregnancy.
**Recall that there is renal retention of Na and H20 in pregnancy.
***Leads to a total increase of 6 – 8 L in total body H20!
***2 / 3rd extracellular
***1 / 3rd intravascular
***Intravascular increase is put in the "dependent" (affected by gravity) areas like the lower venous system.
**Hard to move fluids through the venous system.

==Case: Caring Family==
*The patient’s husband lies her flat in an effort to keep her comfortable.
*The fetus’s FHTs (fetus heart tones) drop to 80.
*But, the ROCK STAR medical student wedges the patient quickly on her left side and the FHT’s recover quickly!
**Turns her off the vena cava.
**Aids in venous return to the heart and therefore to oxygenation of blood for mom and baby.


*What happened to the cared-for mother?
*Gravid Uterus placed pressure on the IVC which resulted in decreased “utero-placental blood flow.”
**Cardiac output falls
**Blood is shunted '''to the brain''' and
**Blood is shunted '''away from the uterus and placenta'''
**This causes a ''reflex fetal bradycardia''

==Importance of Physiology==
*All can be abnormal in the Non-Pregnant state:
**Decreased BP
**Swollen ankles
**CXR: cardiomegaly, leftward deviation
**Systolic Ejection murmur
**Dyspnea
**Anemia
**Hypercoaguable
**NORMAL for Pregnancy

==Maternal Physiology Review==
http://mypage.iu.edu/~pbaenzig/medschoolfiles/icm/obgyn/Pages_from_111202_OBGYN_4_Maternal_Fetal_Physiology_Slides.png