OBGYN - Maternal-Fetal Physiology

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(OjTKwZ Very informative post.Really looking forward to read more.)
 
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=Maternal-Fetal Physiology=
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OjTKwZ Very informative post.Really looking forward to read more.
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==Objectives==
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*List pertinent physiologic changes in various maternal systems
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*Recognize that signs and symptoms in a pregnant patient are often more difficult to interpret
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*Non-pregnant lab values and measurements are frequently abnormal in the pregnant state
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==Case: First Trimester==
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*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.
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**She denies any LOF (leaking of fluid), VB (vaginal bleeding).
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**Pt with C/C of cramping and dark “poop”, nausea and vomiting with heart burn.
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*PMH: Denied
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*PSocialH: Denied
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*OB: G1
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*Gyn: Denied
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*Social Hx: Denied x 3
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*Allergies: NKDA
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*Medications: PNV (Prenatal Vitamin)
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*VS: BP: 110/80 P: 80 T: 98.6 Weight: 65Kg Height: 5’1
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*UA: WNL
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*PE: WNL
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==GI Issues in the First Trimester==
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*Constipation:
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**Iron (ferrous-sulfate) in the pre-natal vitamins slows GI motility and causes constipation.
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**'''Progesterone: a smooth muscle relaxant; causes decreased bowel movement which can lead to increased time for water reabsorption and thus constipation'''
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**Tx: give colace
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**Could be as bad a month!
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**There is fear of miscarriage throughout pregnancy so anything seeming abnormal (like not pooping) starts a fear of miscarriage.
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*Nausea and Vomiting:
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**beta-HCG causes n/v
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***beta-HCG peaks at 10-12 weeks.
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**{rogesterone: a smooth muscle relaxant; causes decreased bowel movement which can lead to n / v.
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*Weight gain:
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**can occur early or late, ideal is a progression.
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**vomitting can lead to weight loss over the first weeks, but mom and baby will be ok
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**Normal Weight for Height: about 20 lbs
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**Underweight Women: about 30 lbs
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**Overweight Women: about 16 lbs
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**Only an addition 300 calories / day are necessary to feed a fetus.
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***500 cal for twins
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==Case: Second Trimester==
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*21 y/o is now 20 weeks pregnant
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*Presents to triage at Wishard with horrible heartburn after eating a deep fried twinkie at the state fair. 
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*She threw-up so much in early pregnancy that she is making up for it now.
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**She has gained 25 lbs (from 8 weeks to second trimester).
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**That is a lot of weight gain.
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*She denied any LOF (leaking of fluid), denied VB (vaginal bleeding) or cramping.
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*She stated that she had some of the chalkie things and it didn’t make it better this time.
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**Tums.
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*She was given a GI cocktail in triage and she was still miserable.
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*Differential Diagnosis:
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**Constipation
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***Small bowel obstruction
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***Ask when they last deficated.
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**Gallstones
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***Increased estrogen and progesterone
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***Slow emptying of the stomach
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***Often already at high risk (four "F"s: fat, forty, fertile, female)
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***Can look really, really, bad.
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**Pancreatitis
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**Appendicitis
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***Appendix moves from right lower quadrant to midquadrant
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***Can get tucked up behind the uterus
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==First / Second Trimester GI Presentations==
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*High levels of estrogen / progesterone in pregnancy lend themselves to gallstone formation
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**Especially when woman gets pregnant a second time without having gallstones from a previous pregnancy removed.
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*Recall that progesterone is a smooth muscle relaxant.
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*Recall that progesterone is at high levels throughout pregnancy to maintain the uterine environment.
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**Progesterone is really rampinig up during the first trimester.
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*High circulating levels of progesterone can lead to:
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**Increased GERD from relaxation of GE sphincter
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**Constipation from delayed transit through large bowel
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**Increased N/V from delayed gastric emptying
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**Stomach can still be full of content 8 hours later.
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**“Full stomach” sensation
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*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.
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==Case: Second / Third Trimester==
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*21 y/o G1P0 at 28w0d
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*Presents to triage at St. Francis Beech Grove.
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*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."
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*Denies LOF (leaking of fluid), VB (vaginal bleeding), CTXs (contractions).
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*'''Endorses +FM (fetal movement).'''
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*ED doctor noticed that she is '''breathing deeply.'''
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*Pertinent Vitals:
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**BP: 100/60
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**P: 90
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**T: 98.6
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**RR: 16
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**O2: 96% RA
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**Weight: 80kgs
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*Labs ordered:
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**CBC w/platelets
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**CXR (chest xray)
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**ABG (arterial blood gas)
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**UA (urinary analytes)
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**CMP (complete metabolic panel)
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**Coags (coagulation studies)
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*PE:
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**Lungs: CTA B
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**CV: Systolic murmur
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**Abd: Gravid, NT
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**Extrem: +1 pitting edema
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*Lab results:
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**WBC: 10,000 (slightly elevated)
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**Hgb / HCT: 10.5/31.7% (decrease)
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**Platelets: 200,000 (slight decrease)
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**Fibrinogen: 600 (increased)
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**Bun / Cr: 3 / 0.6 (decreased)
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**pH: 7.44
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**pCO2: 30
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**BiCarb: 21
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**paO2: 103
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==Physiological Changes in Pregnancy==
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===Blood pressure in pregnancy===
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*Pt blood pressure: 100/60
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*Both systolic and diastolic BP decrease in 2nd trimester
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*Systalic decreases 5-10 mmHg
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*Diastolic decreases 10-15 mmHg
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*We even take severe hypertensive pts off their meds.
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*Normal
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*Monitor from baseline!
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**Athletes will have low baseline BP and therefore it will be a challenge to keep their BP up during pregnancy.
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===Pulse in pregnancy===
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*Pt's pulse: 90
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*Increases 20 beats (peak at 32 weeks, middle of 3rd trimester)
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*Normal
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===Cardiac output in pregnanc===
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*Recall that cardiac output (CO) is stroke volume (SV) multiplied by the heart rate (HR).
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*CO increases at ''8 weeks'' and peaks at ''20 weeks''.
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*CO increases by 30-50%
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*CO rises to 4.5-6.0 L / min
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How do we know her stroke volume?
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*Systolic ejection murmur is common (90% of women).
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*S3 gallop is common (90% of women).
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*'''Peripheral vascular resistance falls during pregnancy, too.'''
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**Hence the swelling.
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**Wear flipflops, wear compression socks
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**Especially medical residents.
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===Respiratory rate in pregnancy===
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*Recall your standard respiratory volumes (see image below).
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*'''Note that O2 demand (consumption) is increased by 15-20% in pregnancy.'''
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*These volumes are affected by the displacement of the diaphragm rostrally.
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*Note that '''respiratory rate should remain unchanged''' in normal pregnancy.
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**This is possible because the tidal volume increases (because the minute ventilation increases).
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*Functional residual capacity decreases by 20% because of displacement the uterus.
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http://www.glowm.com/resources/glowm/graphics/figures/v3/0260/004f.gif
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http://www.glowm.com/resources/glowm/graphics/figures/v3/0260/001f.gif
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*So '''dyspnea ''is'' normal with pregnancy'''.
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{|border=1
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!Volume (mL)
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!Definition
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!Non-pregnant
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!Pregnant
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!Change
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|-
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!Total lung capacity
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|Vital capacity + residual volume
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|4200
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|4000
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| -4%
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|-
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!Vital Capacity
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|Total lung capacity - residual volume
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|3200
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|3200
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| 0%
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|-
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!Inspiratory Capacity
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|Vital capacity - expiratory reserve volume
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|2500
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|2650
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| +6%
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|-
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!Tidal volume
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|Volume moved in and out with each normal breath
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|450
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|550
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| +33%
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!Expiratory Reserve Volume
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|Vital capacity - inspiratory capacity
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|700
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|550
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| -20%
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|-
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!Inspiratory Reserve Volume
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|Inspiratory capacity - total volume
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|2050
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|2050
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| 0%
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!Residual volume
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|Total volume - vital capacity
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|1000
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|800
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| -20%
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!Functional Residual Capacity
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|Residual volume + expiratory reserve volume
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|1700
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|1350
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| -20%
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|}
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===Arterial blood gas (ABG) in pregnancy===
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*NB: '''ABG should never be "normal" in pregnancy!'''
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**Should have a respiratory alkalosis from blowing off their CO2 at higher rates.
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**Should have a metabolic acidosis (compensatory).
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*Many pregnant women will hyperventalate.
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**Give them a bag in which to breath.
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**Very hard to settle them down so important to give the bag quickly and pt will often become syncopous.
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*Pt's ABG was:
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**pH: 7.44 (
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**pCO2: 30
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**BiCarb: 21
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**paO2: 103
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*Recall that O2 consumption increases in pregnancy.
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**15-20%
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*Recall that minute ventilation (the amount of air breathed in over the course of one minute) is increased ''relatively more than the O2 consumption''.
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**This means that '''more air is breathed in and out than is necessary for the rate of oxygen consumption.'''
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**This is the '''definition of hyperventilation!'''
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*Recall the chemical equation: CO2 + H20 <=> H2CO3 <=> HCO3 + H
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*Recall that hyperventilation gives off CO2, dragging the equation to the left.
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**That is, pCO2 will be decreased.
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*Therefore pregnant, hyperventilating women become '''alkalotic''' (decreased H+).
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**That is, pH will be high (less H+).
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**This is a '''respiratory alkalosis'''.
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*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.
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**Thus we expect the serum HCO3 to be low.
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*Recall that in pregnancy there is an increased oxygen carrying capacity (facilitated by RBC volume increased by 50%).
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**Thus we expect the pO2 to be high.
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*Given this respiratory alkalosis and metabolic compensation, we expect:
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**the pCO2 to be low: 26-32 mmHg (compared to non-pregnancy 38-45)
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**the pH to be high (alkaline): 7.40-7.46 (compared to non-pregnancy 7.38-7.42)
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**the HCO3 to be low: 18-21 mEq / L (compared to non-pregnancy 24-31)
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**the pO2 to be high: 106-108 mmHg (compared to non-pregnancy 70-100)
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*A high pCO2 is cause for alarm in the asthmatic pregnant woman.
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*Also, pCO2 should be monitored carefully in the acutely infected pregnant woman because they are '''immune compromised''' and have '''very little respiratory reserve'''.
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{|border=1
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!Measure
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!Non-pregnant
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!Pregnant
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!Change
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!Reason
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!pH
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|7.38 - 7.42
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|7.4 - 7.46
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|Higher
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|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+).
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!pCO2 (mmHg)
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|38 - 45
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|26 - 32
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|Lower
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|Because minute ventilation increases more than oxygen consumption (CO2 breathed off faster than oxygen consumed).
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!pO2 (mmHg)
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|70 - 100
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|101 - 106
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|Lower
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|Because RBC volume is increased.
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!HCO3- (mEq / L)
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|24 - 31
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|18 - 21
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|Lower
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|Because the kidneys are excreting HCO3- in an attempt to compensate for respiratory alkalosis.
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!O2 saturation (%)
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|95 - 100
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|95 - 100
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|None
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|}
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*Importance:
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**'''A normal pregnant woman has a compensated respiratory alkalosis (with a compensatory metabloic acidosis) and a diminished pulmonary reserve.'''
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*Cause:
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**Progesterone: relaxes the smooth muscle
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**Diaphragm raised 4cm
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===CBC in pregnancy===
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*Plasma Volume and RBC Mass
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**Plasma volume increases by about 50%
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**RBC volume increases by about 30%
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*Result:
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**“Physiologic anemia of pregnancy”
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**The mean Hgb is about 11.5 g/dl
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*At 28 weeks, get new labs.
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*'''Will likely need to start iron.'''
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**Start at or below 10.
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**Yucky tasting, makes woman feel horrible.
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**''Necessary for proper oxygenation.''
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===Coagulation in pregnancy===
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*'''In pregnancy the pt is hypercoaguable'''
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**This is the body's way to not die from bleeding when the parasite is ejected / ripped from the internal surface of the uterus.
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*DIC is the number 1 cause of death in laboring women around the world.
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**Not so much here in the US.
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*Procoagulant’s are increased: I, VII, VIII, IX, X and Fibrinogen.
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*Prevents Peripartum Hemorrhage
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*Can lose 1500mL without blinking.
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*Over 2000 mL lost, start worrying b/c coag factors are becoming deficient.
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===Renal System in pregnancy===
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*Bun & Serum Creatinine decreases by about 25%
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**Low because of increased blood volume, increased GFR, increased blood flow to the kidneys
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*Plasma osmolarity decreases by about 10 mOsm / kg H20
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*Increase in tubal reabsorption of sodium
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*Marked increase in renin and angiotensin levels
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**But '''markedly reduced vascular sensitivity to their hypertensive effects'''
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*Increased glucose excretion
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**Fine during labor, a coping mechanism.
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**Labs at 28 weeks detect gestational diabetes.
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*Anatomic:
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**Kidney size increases
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**Kidney weight increases
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**Ureteral dilation (right side greater than left side)
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***Because of the angle of the uterus
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**Bladder becomes an intra-abdominal organ
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*Hemodynamic:
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**GFR increase by 50%
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**Renal plasma increased by flow by 75%
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**'''Creatinine Clearance increases to 150-200 cc / min'''
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***Most important kidney function test in pregnancy
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*Swollen Ankles:
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**Recall that the Plasma Volume Increases 50% in pregnancy.
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**Recall that there is decreased Systemic Vascular resistance in pregnancy.
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**Recall that there is renal retention of Na and H20 in pregnancy.
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***Leads to a total increase of 6 – 8 L in total body H20!
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***2 / 3rd extracellular
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***1 / 3rd intravascular
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***Intravascular increase is put in the "dependent" (affected by gravity) areas like the lower venous system.
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**Hard to move fluids through the venous system.
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==Case: Caring Family==
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*The patient’s husband lies her flat in an effort to keep her comfortable.
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*The fetus’s FHTs (fetus heart tones) drop to 80.
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*But, the ROCK STAR medical student wedges the patient quickly on her left side and the FHT’s recover quickly!
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**Turns her off the vena cava.
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**Aids in venous return to the heart and therefore to oxygenation of blood for mom and baby.
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*What happened to the cared-for mother?
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*Gravid Uterus placed pressure on the IVC which resulted in decreased “utero-placental blood flow.”
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**Cardiac output falls
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**Blood is shunted '''to the brain''' and
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**Blood is shunted '''away from the uterus and placenta'''
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**This causes a ''reflex fetal bradycardia''
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==Importance of Physiology==
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*All can be abnormal in the Non-Pregnant state:
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**Decreased BP
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**Swollen ankles
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**CXR: cardiomegaly, leftward deviation
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**Systolic Ejection murmur
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**Dyspnea
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**Anemia
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**Hypercoaguable
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**NORMAL for Pregnancy
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==Maternal Physiology Review==
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http://mypage.iu.edu/~pbaenzig/medschoolfiles/icm/obgyn/Pages_from_111202_OBGYN_4_Maternal_Fetal_Physiology_Slides.png
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Current revision as of 18:11, 15 December 2013

OjTKwZ Very informative post.Really looking forward to read more.

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