OBGYN - Maternal-Fetal Physiology
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Revision as of 21:56, 2 December 2011
Contents |
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
First Trimester
- 21 y/o G1P0 at 8w0d by L=6 week US at the (WVC) 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
- PSxH: 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:
- Constipation:
- Mechanism: ferrous-sulfate in the pre-natal vitamins slows GI motility
- Tx: give colace
- Nausea and Vomiting:
- Constipation:
***beta-HCG (peaks 10-12 weeks) ***progesterone: a smooth muscle relaxant; causes decreased bowel movement which can lead to increased time for water reabsorption and thus constipation ***decreased GI motility
- weight gain:
- average Weight Gain
- Normal Weight for Height: about 20 lbs
- Underweight Women: about 30 lbs
- Overweight Women: about 16 lbs
- average Weight Gain
- weight gain:
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.
- 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.
- She was given a GI cocktail in triage and she was still miserable.
- Differential Diagnosis:
- Constipation
- Small bowel obstruction
- Gallstones
- Pancreatitis
- Appendicitis
- Constipation
First / Second Trimester GI Issues
*Estrogen / Progesterone Gallstones
- Recall that progesterone is a smooth muscle relaxant.
- Recall that progesterone is at high levels throughout pregnancy to maintain the uterine environment.
- 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
- “Full stomach” sensation
- During pregnancy, the appendix is moved medially such that appendicitis pain will present mid-quadrant.
Second / Third Trimester GI Issues
- 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.
- 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, UA (urinary analysis), CMP (complete metabolic panel), Coags (coagulation studies) What is ABG?
- 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
- Are all these values normal or abnormal?
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
- Normal
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 (compared to a normal of...) 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.
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).
- So dyspnea is normal with pregnancy.
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% |
ABG in pregnanc
- Pt's ABG was ?
- PH: 7.44
- pCO2: 30
- BiCarb: 21
- paO2: 103
- Acidic?
- Basic
- Hyperventilate?
- Hypoventilate?
Respiratory System in pregnancy
- ABGs: PH= 7.40, PCO2=26-32, BiCarb= 18-21, PO2= 101-106
*Pertinence: Relative Hyperventilation:
- O2 consumption increases by 15-20%, minute ventilation increases to a greater degree
*Pertinence: Relative Hyperventilation
- Leading to decreased pCO2
*Relative Respiratory Alkalosis (26-32)
- PH is usually slightly alkaline (7.40-7.46) due to renal excretion of HCO3 (serum 18-21 (+/-) 1.6 lowers the serum bicarb)
- Hyperventilation and increased O2 carrying capacity, pO2 is slightly elevated (106-108)
- Pertinence: A normal pO2 in a pregnant patient is frequently abnormal
- Changes in ABG
Measure | Non-pregnant | Pregnant | Change |
---|---|---|---|
pH | 7.38 - 7.42 | 7.4 - 7.46 | Looser |
pCO2 (mmHg) | 38 - 45 | 26 - 32 | Lower |
pO2 (mmHg) | 70 - 100 | 101 - 106 | Lower |
HCO3- (mEq / L) | 24 - 31 | 18 - 21 | Higher |
O2 saturation (%) | 95 - 100 | 95 - 100 | None |
- Importance:
- A normal pregnant woman has a compensated respiratory alkalosis and a diminished pulmonary reserve.
- Respiratory Alkalosis with a compensatory metabloic acidosis.
- Cause:
- Progesterone
- 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
Coagulation in pregnancy
- In pregnancy the pt is hypercoaguable
- Procoagulant’s are increased: I, VII, VIII, IX, X and Fibrinogen.
- Prevents Peripartum Hemorrhage
Renal System in pregnancy
- Bun & Serum Creatinine decreases by about 25%
- 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
- Anatomic:
- Kidney size increases
- Kidney weight increases
- Ureteral dilation (right side greater than left side)
- 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
- 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.
Caring Family
- The patient’s husband lies her flat in an effort to keep her comfortable.
*The fetus’s FHT’s drop to 80.
- But, the ROCK STAR medical student wedges the patient quickly on her left side and the FHT’s recover quickly!
- What happened?
- Gravid Uterus placed pressure on the IVC that in turn decreased “utero-placental blood flow.”
- Regional Blood Flow Redistribution:
- 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 with a leftward deviation
- Systolic Ejection murmur
- Dyspnea
- Anemia
- Hypercoaguable
- NORMAL for Pregnancy
Maternal Physiology Review