Maternal physiology Flashcards
1
Q
Hormonal changes?
A
- Progesterone - Smooth muscle relaxation, vasodilation, bronchodilation, dilation of renal tract and decreased GI motility . Thermogenic, N/V.
- Reversal occurs 3-4 weeks after delivery
2
Q
Aorto-caval compression?
A
- Compression of the IVC and aorta by uterus
- Starts at 13wks/ Relevant at 20wks/ Maximal at 36-38wks
- About 70% experience hypotension and 5-8% shock (supine hypotension syndrome)
3
Q
CVS changes ? See picture
A
- Increased CO 50%
- Increase HR 25%
- Increased SV 25%
- Decreased SVR 20%
- Increased EF%
- Decreased SBP <10% and DBP < 20%
- Uteroplacental transfusion of 500mls
- Increased SNS activity - Attenuated by epidural analgesia
4
Q
Respiratory changes ?
A
- Reduced chest wall compliance - Increased breast size, upward displacement of diaphragm & increased thoracic cage circumference 5-7cm
- Airway mucosal oedema.
- Increased TV - 45%
- Increased mV - 45%
- Decreased FRC - 20%
- Decreased RV - 15%
- RR - No changes
- Increase in oxygen consumption by 30-60%
5
Q
Normal ABG in pregnancy ?
A
- PO2 = 13kPa or 100mmHg
- Low PCo2 - 28-33mmHg
- Low bicarbonate 18-22
- Respiratory alkalosis
- Increase in 2,3-DPG production 30% . Favours right shift of ODC
- Increase P50 from 26.7 to 30.4mmHg
- Right shift of ODC to favour oxygen delivery to foetus
6
Q
Haematological changes?
A
- Plasma volume increased 50% by 32 weeks
- RBC volume increased by 20-30%
- Decrease in Hb and haematocrite 15%
- Increased in white cell count
- Increase fibrinogen (decreased fibrinolysis) and clotting factors except XI and XIII
- Decreased platelets
7
Q
Plasma changes?
A
- Total plasma protein concentration falls - Low albumin and globulin/fibrinogen increases
- Reduced plasma protein causes - Reduction in colloid osomotic pressure 5mmHg, durg-binding capacity of plasma changes and plasma conc. pseudocholinesterase decreases by 20-25%
8
Q
Renal function changes?
A
- Progesterone causes dilation and atony
- Increased urinary tract infection
- RBF increases 30-50% at 30 weeks
- eGFR increases by 40% and then falls towards term
- Decreased plasma conc. of urea and creatinin
- Decreased plasma osmolality
- Protenuria and glycosuria 300mg & 10g respectively
- Upregulation of the RAAS (increased angiotensin II)
9
Q
GIT changes ?
A
- Upward displacement of the stomach and intestine
- Intragastric pressures increase from 7-8 to 13-17cmH2O
- Barrier pressure reduced - LOS pressure - Gastric pressure
- GORD due to decreased barrier pressure.
- Increased gastrin production and pH < 2.5
- Gastric emptying not delayed during pregnancy but only during labour - In the presence of opioids.
10
Q
CNS changes ?
A
- Epidural veins are engorged with increase epidural pressures - Increased abdo pressure, increase 4-10cmH2O in labout and 60cmH20 during pushing.
- Increased sympathetic tone
11
Q
MKS changes?
A
- Increased mobility of the sacroilliac joint, sacrococcygeal and pubic joint
- Lumbar lordosis
12
Q
Utero-placental flow?
A
- There are two arteries from the foetus
- There is one vein to the foetus
- Blood flow increases from 50-700ml (3-12%) of CO at term.
- Limited autoregulation - Decreased vascular resistance and response to vasoconstrictor.
13
Q
Factors decreasing uterine blood flow during pregnancy ?
A
- Systemic hypotension
- Uterine vasoconstriction - Pre-eclampsia.
- Uterine contractions
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
15
Q
Placental exchange ?
A
- Fick’s law of diffusion
- Osmotic and hydrostatic pressures - water
- Facilitated diffusion - glucose
- Active transport - Amino acid, vit B12, fatty acids and ions
- Vascular transport - Immunoglobulins, iron facilitated by ferritin / transferrin
16
Q
Maternal drug concentration?
A
- Route - Highest after IV, epidural and IM similar + systemic absorption will be greater in vascularised tissues
- Total maternal dose
- Volume of distribution and drug metabolism
17
Q
Foetal drug concentration?
A
- Elimination is less effective
- Less plasma protein binding capacity
- Less mature enzyme systems compared to mother
- Some drugs might go back to the mother
18
Q
Drugs transfer?
A
- Foeto-maternal pH - Dependent on pKa of the drug & only unionised fraction of the drug crosses
- ion trapping of basic drugs occur - LA close to blood pH will be unionised, hence diffuse readily
- Acidotic foetus increase ionizaton of drug thus unable to cross membrane back across placenta - Hence toxicity.
- 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
- This is the effect of the pH on the affinity of Hb for O2
- A decrease in pH (high CO2) causes right shift of the ODC - Allows the offloading of O2 to tissue
- If pH increases (Low CO2) O2 affinity increases to encourage uptake
21
Q
Placenta-Oxygen transport?
A
- HbF in foetal blood - 75% to 84%
- HbF is on the left side of the ODC - P50 foetal (21mmHg) or 2.8kpa and adult (27mmHg) or 3.6kpa
- High concentration of Hb takes up more O2
22
Q
Double Bohr’s effect ?
A
- Maternal uptake of CO2 from foetus - Shifts curve to the right
- Favours transfer of O2 to the foetus
- Foetal side - CO2 is given up - ODC shifts to left, favouring O2 uptake.
23
Q
CO2 transport?
A
- Placental membrane is highly permeable to CO2 which is 20 times more diffusible than O2
- Dissolved CO2 is 8% in blood
- Crosses the placenta by simple diffusion
- Bicarbonate (62%)
- Carbamino haemoglobin (30%)
24
Q
CO2 & Haldane effect ?
A
- An increase or decrease in O2 leads to a decrease in CO2 affinity or increase in CO2 affinity
- The feto-maternal transfer of O2 produced de-oxyHb in the maternal blood that has greater affinity for CO2 than OxyHb
- As foetal blood takes up O2 it enhances CO2 release. This is the double Haldane effect accounting for 46% of transplacental transfer of CO2
