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EDAIC Online course (BCSAC 2021) > Maternal physiology > Flashcards

Maternal physiology Flashcards

1
Q

Hormonal changes?

A
  1. Progesterone - Smooth muscle relaxation, vasodilation, bronchodilation, dilation of renal tract and decreased GI motility . Thermogenic, N/V.
  2. Reversal occurs 3-4 weeks after delivery
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2
Q

Aorto-caval compression?

A
  1. Compression of the IVC and aorta by uterus
  2. Starts at 13wks/ Relevant at 20wks/ Maximal at 36-38wks
  3. About 70% experience hypotension and 5-8% shock (supine hypotension syndrome)
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3
Q

CVS changes ? See picture

A
  1. Increased CO 50%
  2. Increase HR 25%
  3. Increased SV 25%
  4. Decreased SVR 20%
  5. Increased EF%
  6. Decreased SBP <10% and DBP < 20%
  7. Uteroplacental transfusion of 500mls
  8. Increased SNS activity - Attenuated by epidural analgesia
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4
Q

Respiratory changes ?

A
  1. Reduced chest wall compliance - Increased breast size, upward displacement of diaphragm & increased thoracic cage circumference 5-7cm
  2. Airway mucosal oedema.
  3. Increased TV - 45%
  4. Increased mV - 45%
  5. Decreased FRC - 20%
  6. Decreased RV - 15%
  7. RR - No changes
  8. Increase in oxygen consumption by 30-60%
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5
Q

Normal ABG in pregnancy ?

A
  1. PO2 = 13kPa or 100mmHg
  2. Low PCo2 - 28-33mmHg
  3. Low bicarbonate 18-22
  4. Respiratory alkalosis
  5. Increase in 2,3-DPG production 30% . Favours right shift of ODC
  6. Increase P50 from 26.7 to 30.4mmHg
  7. Right shift of ODC to favour oxygen delivery to foetus
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6
Q

Haematological changes?

A
  1. Plasma volume increased 50% by 32 weeks
  2. RBC volume increased by 20-30%
  3. Decrease in Hb and haematocrite 15%
  4. Increased in white cell count
  5. Increase fibrinogen (decreased fibrinolysis) and clotting factors except XI and XIII
  6. Decreased platelets
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7
Q

Plasma changes?

A
  1. Total plasma protein concentration falls - Low albumin and globulin/fibrinogen increases
  2. Reduced plasma protein causes - Reduction in colloid osomotic pressure 5mmHg, durg-binding capacity of plasma changes and plasma conc. pseudocholinesterase decreases by 20-25%
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8
Q

Renal function changes?

A
  1. Progesterone causes dilation and atony
  2. Increased urinary tract infection
  3. RBF increases 30-50% at 30 weeks
  4. eGFR increases by 40% and then falls towards term
  5. Decreased plasma conc. of urea and creatinin
  6. Decreased plasma osmolality
  7. Protenuria and glycosuria 300mg & 10g respectively
  8. Upregulation of the RAAS (increased angiotensin II)
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9
Q

GIT changes ?

A
  1. Upward displacement of the stomach and intestine
  2. Intragastric pressures increase from 7-8 to 13-17cmH2O
  3. Barrier pressure reduced - LOS pressure - Gastric pressure
  4. GORD due to decreased barrier pressure.
  5. Increased gastrin production and pH < 2.5
  6. Gastric emptying not delayed during pregnancy but only during labour - In the presence of opioids.
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10
Q

CNS changes ?

A
  1. Epidural veins are engorged with increase epidural pressures - Increased abdo pressure, increase 4-10cmH2O in labout and 60cmH20 during pushing.
  2. Increased sympathetic tone
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11
Q

MKS changes?

A
  1. Increased mobility of the sacroilliac joint, sacrococcygeal and pubic joint
  2. Lumbar lordosis
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12
Q

Utero-placental flow?

A
  1. There are two arteries from the foetus
  2. There is one vein to the foetus
  3. Blood flow increases from 50-700ml (3-12%) of CO at term.
  4. Limited autoregulation - Decreased vascular resistance and response to vasoconstrictor.
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13
Q

Factors decreasing uterine blood flow during pregnancy ?

A
  1. Systemic hypotension
  2. Uterine vasoconstriction - Pre-eclampsia.
  3. Uterine contractions
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14
Q

Fick’s rate of diffusion, formular?

A

Rate of diffusion = k x A x (P2-P1)/ D

k = Diffusion constant depndent on solubility and temperature of gas

A = Area for gas exchnage

P = Difference in partial pressure of gas on either side of the membrane

D = Thickness of the membrane

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15
Q

Placental exchange ?

A
  1. Fick’s law of diffusion
  2. Osmotic and hydrostatic pressures - water
  3. Facilitated diffusion - glucose
  4. Active transport - Amino acid, vit B12, fatty acids and ions
  5. Vascular transport - Immunoglobulins, iron facilitated by ferritin / transferrin
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16
Q

Maternal drug concentration?

A
  1. Route - Highest after IV, epidural and IM similar + systemic absorption will be greater in vascularised tissues
  2. Total maternal dose
  3. Volume of distribution and drug metabolism
17
Q

Foetal drug concentration?

A
  1. Elimination is less effective
  2. Less plasma protein binding capacity
  3. Less mature enzyme systems compared to mother
  4. Some drugs might go back to the mother
18
Q

Drugs transfer?

A
  1. Foeto-maternal pH - Dependent on pKa of the drug & only unionised fraction of the drug crosses
  2. ion trapping of basic drugs occur - LA close to blood pH will be unionised, hence diffuse readily
  3. Acidotic foetus increase ionizaton of drug thus unable to cross membrane back across placenta - Hence toxicity.
  4. Highly pritein bounds drugs (Bupivacaine) will have reduced placental transfer and lower F/M ratio compared to those with lower plasma binding (Lidocaine & Mepivacaine)
19
Q

Oxygen transport?

A

See picture

20
Q

Bohr’s effect ?

A
  1. This is the effect of the pH on the affinity of Hb for O2
  2. A decrease in pH (high CO2) causes right shift of the ODC - Allows the offloading of O2 to tissue
  3. If pH increases (Low CO2) O2 affinity increases to encourage uptake
21
Q

Placenta-Oxygen transport?

A
  1. HbF in foetal blood - 75% to 84%
  2. HbF is on the left side of the ODC - P50 foetal (21mmHg) or 2.8kpa and adult (27mmHg) or 3.6kpa
  3. High concentration of Hb takes up more O2
22
Q

Double Bohr’s effect ?

A
  1. Maternal uptake of CO2 from foetus - Shifts curve to the right
  2. Favours transfer of O2 to the foetus
  3. Foetal side - CO2 is given up - ODC shifts to left, favouring O2 uptake.
23
Q

CO2 transport?

A
  1. Placental membrane is highly permeable to CO2 which is 20 times more diffusible than O2
  2. Dissolved CO2 is 8% in blood
  3. Crosses the placenta by simple diffusion
  4. Bicarbonate (62%)
  5. Carbamino haemoglobin (30%)
24
Q

CO2 & Haldane effect ?

A
  1. An increase or decrease in O2 leads to a decrease in CO2 affinity or increase in CO2 affinity
  2. The feto-maternal transfer of O2 produced de-oxyHb in the maternal blood that has greater affinity for CO2 than OxyHb
  3. As foetal blood takes up O2 it enhances CO2 release. This is the double Haldane effect accounting for 46% of transplacental transfer of CO2

EDAIC Online course (BCSAC 2021) (35 decks)

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