Physiology of Normal Pregnancy

Physiology of Normal Pregnancy

5/10/10

PY Mindmaps

OH

- fetus considered viable at 24-25 weeks with a weight of > 750g

Airway

- progesterone mediated hyperaemia and oedema of mucosal surfaces -> down size tubes

- difficult -> higher incidence of failure to intubate

Breathing

- higher O2 consumption

- desaturate quickly

- increased aspiration risk

- increased risk of pulmonary oedema (increased blood volume and lower oncotic pressure)

- mechanical ventilation can be problematic

- difficult to implement protective ventilation -> hypercapnia produces fetal acidosis

- cephalad movement of diaphragm @ 37 weeks -> place chest drain higher than normal

- spirometry, flow volume loops and peak flow rates -> unchanged

- TLC decreases 5% c/o cephalad movement of diaphragm

- FRC decreases by 20% -> decreased ERV and RV

- MV increases by 50% from increase in TV -> chronic respiratory alkalosis (pH 7.4 to 7.47, PaCO2 30-32mmHg, slightly elevated PaO2, kidneys excrete HCO3- to compensate to keep HCO3- 18-21mmol/L, BE 3-4)

- O2 consumption increased 20%

Circulation

- tachycardia, low BP, increased Q and warm peripheries -> normal in pregnancy

- aortocaval compression

- PAC’s can be helpful in severe PET, APO and cardiac disease (non-invasive Q monitors are useless)

- uterine bed is sensitive to vasoconstrictors

- phenylephrine better than ephedrine -> less fetal acidosis

- no evidence favouring any particular ionotrope

- diaphragm pushed upward and heart rotated to left -> changes Q waves inferiorly and gives TWI

- maternal blood volume increases 40%, red cell mass increases 25% -> relative anaemia of pregnancy

- normal ejection systolic murmur and third heart sound

- normal echo: increase in all cardiac chamber dimensions, increased LV thickness, small pericardial effusions, mild TR, mild MR

Coagulation

- x 5 increased in VTE -> prophylaxis is important

Gastrointestinal

- GORD -> aspiration

- hypoalbuminaemia from haemodilution

- increase in ALP

- appendicitis and cholecystitis happen

Genitourinary

- at 12/40 bladder becomes an abdominal structure -> susceptible to blunt trauma

- at 20/40 fundus at umbilicus -> susceptible to blunt or penetrating trauma

- GFR increases by 50% -> lower Cr, urea, uric acid

Placenta

- uterine blood flow @ term = 10% (600-700mL/min)

- under stress maternal blood flow will be maintained at the expense of the fetus

- oxygen consumption = 20mL/min -> can survive 10 min by shunting blood flow to vital organs and decreasing O2 consumption.

(TIME) -> its like the liver, kidney & the lungs all in one!

Transport

- gas exchange (O2 & CO2) – fetal Hb (higher concentration, greater affinity for O2)

- delivery of nutrients (glucose, aa, lipids)

- removal of wastes (urea, bilirubin)

- transport of other substances (drugs)

- heat transfer

Immunological

- protection of foetus from infection

- protection of foetus from rejection by mother (immunological barrier function) - trophoblast cells do display Class I or II MHC (major histocompatibility complex) proteins thus they cannot present antigen to lymphocytes and cannot be recognised by activated cytotoxic T lymphocytes.

Metabolic

- synthesis of glycogen, cholesterol, FFA's and enzymes

Endocrine

- synthesis of 4 main hormones: hCG, oestriol, progesterone, human placental lactogen

- synthesis of various other hormones & growth factors

Mother and Baby

- monitor for preterm labour

- think about placental transfer of drugs

- maintenance of placental perfusion and oxygenation

Jeremy Fernando (2011)