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Physiology Of Pregnancy Flashcards

1
Q

Effect of pregnancy on cardiac output
Effect during labour

Why?

A

Rises to 150% of normal by end of second trimester - increased HR, SV and reduced SVR
Transient rises in cardiac output of further 45-60% during contractions
Transient rise in cardiac output of further 80% immediate post delivery phase as a result of uteroplacenal transfusion of 300-500ml.

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2
Q

Effect of pregnancy on hr and sv

A

Hr increases 15% by end of first trimester and 25% by end of second
Sv increased 20% by end of first trimester and 30% by end of second
Both increase further in labour and on delivery.

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3
Q

How would the lithotomy position effect pregnant cardiac output vs supine?
What about left lateral

A

Lithotomy decreases by 17% vs supine
Left lateral increases by 13.5% vs supine
However note left lateral still causes some decrease overall vs non pregnant person

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4
Q

SVR in pregnancy and in non pregnancy

A

Pregnancy - 980 dyne.s.cm-5
Non pregnancy 1150 dyne.s.cm-5

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5
Q

Why does SVR decrease in pregnancy

A

Development of low resistance vascular bed and vasodilation from oestrogens, prostacyclin and progesterone

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6
Q

What is uterine blood flow at term

A

500-700ml/min

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7
Q

Pattern of systolic blood pressure during pregnancy
Effect of lying flat

A

Decreases during early / mid gestation retuning to non pregnant level at term
70% of mothers drop Bp by 10% lying flat
10% drop by 50%

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8
Q

What factors influence aortocaval compression in pregnancy

A

Position
Gestation
Systolic Bp
Presence of sympathetic block

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9
Q

How does blood bypass the aortocaval obstruction when lying supine

A

Vertebral venous plexuses emptying into azygos vein.

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10
Q

Why might aortocaval compression lead to fetal compromise

A

Vena cava compression reducing venous return lowering Bp and thus placenta perfusion
Aortic compression reducing aortic blood flow to placenta

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11
Q

ECG changes in pregnancy

A

Sinus tachycardia
Short pr and qt
Left axis deviation
St depression
T wave flattening

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12
Q

Echo changes in pregnancy

A

Left ventricular hypertrophy
50% increase lv mass at term
Increased tricuspid, pulmonary and mitral valve diameter
Tricuspid and pulmonary regurgitation
27% mitral regurgitation
Pericardial effusion

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13
Q

How do heart sounds change in pregnancy

A

Loud and sometimes spilt first heart sound
Third heart sound common
16% have fourth heart sound
Common mid systolic murmur

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14
Q

What factors can increase CVP in labour

A

Contractions - about 5cmH2O
Expulsion effort of the second stage - about 50cmH20
I’ve ergometrine - about 8cmH20

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15
Q

Change in plasma volume and cellular composition in pregnancy
Change in total blood volume over three trimesters

A

Plasma volume increases 50%
Red cell volume increases 18% following an initial dip
Results in 15% drop in Hb and HCT
Total blood volume increases 10-30-45% over each trimester

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16
Q

What happens to plasma volume post delivery
Implication

A

Sharp rise by 1 litre in 24hrs post delivery
Important in those with cardiac disease such as fixed cardiac output

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17
Q

Effect of pregnancy on immune system?

A

WBC rise (mainly neutrophils)
Overall however depressed immunity due to decreased reduced leukocyte function and increased adherence of neutrophils.

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18
Q

Effect of pregnancy on platelets

A

Enhanced platelet turnover
Thrombocytopenia in 1%
Platelet function normal

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19
Q

Effect of pregnancy on coagulation factors

A

All increase except XI and XIII which drop and II and V which stay the same
Especially high increase in I, VII, VIII, IX

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20
Q

What happens to plasma proteins during pregnancy
Consequences

A

Decrease in albumin concentration
Overall decrease in colloid osmotic pressure, increased ECF volume and oedema
Drug binding altered
Plasma cholinesterase concentration decrease 25%

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21
Q

Effect of pregnancy on bleeding pt and APTT

A

Decreases 20%

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22
Q

Anatomical changes to the respiratory system in pregnancy

A

Capillary engorgement of the mucosa in the nasal cavity, pharynx and larynx
Increased thoracic cage circumference due to flaring of ribs.
Upward displacement of diaphragm

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23
Q

Changes to lung mechanics during pregnancy

A

Decreased movement of chest wall, increased dependence on diaphragmatic movement
Bronchial smooth muscle relaxation reducing resistance

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24
Q

Changes to lung volumes during pregnancy

A

Tidal volume increases 45%
FRC decreases 20-30% due to decreased ERV and RV
Dead space increases
Closing capacity increases to near FRC increasing v/q mismatch
IRV increases

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25
Change in minute ventilation in pregnancy What drives this
Increases by 50% due to tidal volumes, rr remains same Increased progesterone and co2 production
26
Effect of pregnancy on DLCO (diffusing capacity of lungs for carbon monoxide)
Increases first trimester then decreases then normal
27
Effect of pregnancy on blood gases
Co2 decreases Bicarb excretion increases to maintain pH dropping BE Slight elevation of pH as compensation not complete Slight increase in PaO2
28
What causes dysponea in pregnancy? Prevelance
Likely due to low co2 60%
29
What is the change in oxygen consumption during pregnancy
Increase 30-60%
30
Why do pregnant women become hypoxic on induction
Reduced FRC Increased metabolic demand
31
Why are pregnant women more at risk of aspiration
Decreased barrier pressure at LOS due to increased intragastric pressure and lower LOS pressure, displaced intraabdominal oesophagus, relaxation from progesterone Lower ph in stomach Increased gastric volume Decreased gastric emptying during labour (due to analgesia!)
32
Changes to the CNS during pregnancy
Increased venous pressure below gravid uterus diverted through vertebral plexus in epidural space - epidural volume reduced Epidural pressure slightly positive, during contraction rises to 2-8cmH2O, and during expulsion between 20-60 cmH2O CSF pressure increases due to aortocaval compression and with contractions/expulsion Increased SNS tone MAC is reduced by around 40%
33
Clinical considerations for anaesthesia during pregnancy due to neurological changes of pregnancy
Epidural and spinal anaesthetics will spread further thus less needed for same level of block Sympathetic block will have greater relative effect thus sudden drop in BP due to increased baseline tone Less inhalational agent needed.
34
Endocrine changes during pregnancy
Increased melanocyte stimulating hormone causing pigmentation Increased thyroid gland size and production but also increased thyroid binding globulin so thyroid levels actually remain the same Increased corticosteroid production and prolonged cortisol half life Increased size of adrenal cortex zona fasciculata Increased size and weight of pituitary Increased pancreatic beta islets and increased number of receptor sites for insulin however resistance to insulin due to lactogen, prolactin etc and raised BM due to cortisol etc.
35
Why are pregnant women more at risk of sheehans syndrome
Increased size and weight of pituitary makes it more at risk of ischaemia and necrosis on haemorrhage - the portal circulation means it operates at a lower pressure than systemic so generally vulnerable.
36
Renal changes in pregnancy
Increase GFR Decreased reabsorbative capacity due to increased volume of urine RAAS increases leading to na and water retention Progesterone triggers smooth muscle relaxation leading to urinary stasis and dilated collecting system Increased renal bicarb excretion to counter resp alkalosis
37
Liver and biliary system changes in pregnancy
Minor changes to liver enzymes ( increase in alp) Progesterone decreases Ckk release so less gall bladder contraction and more gallstones Decreased plasma cholinesterases
38
Msk changes in pregnancy
Relaxin simulates ligamental relaxation Widens pubis symphysis and increases sacroiliac and sacrococcygeal joints mobility Enhanced lumbar lordosis to maintain centre of gravity with gravid uterus Half of pregnant women experience lower back pain as a result of above
39
Rough weight gain in pregnancy What proportion is due to fetus, amniotic fluid placenta and uterus?
10kg 40%
40
Formation of the placenta
Trophoblast of blastocyst infiltrates into endometrium Differentiates into syncytiotrophoblast and cytotrophoblast The cytotrophoblast cells covered in syncytiotrophoblast extend out into lacunae of maternal blood in the endometrial decidua Cytotrophoblastic cells grow into maternal spiral vessels destroying surrounding smooth muscle tissue reducing their ability to vasoconstrict and decreases distance between maternal and fetal blood.
41
What causes pre eclampsia
Failure of cytotrophoblast cells to destroy spiral artery smooth muscle so they still respond to vasoconstriction
42
How does maternal blood flow through the placenta?
Uterine blood vessels Spiral arteries (open ended) Intravillous space (past the villous trees of fetal circulation) Collecting veins Uterine blood vessels
43
Flow of fetal circulation through the placenta
Internal iliac arteries Umbilical arteries x2 (deoxygenated blood) Chorionic arteries Villous tree Chorionic vein Umbilical vein (oxygenated)
44
Formula for uterine blood flow
UBF = (uterine artery pressure - uterine venous pressure)/uterine vascular resistance
45
Factors that decrease uterine artery pressure
Hypovolaemia Aortocaval compression Sympathetic block
46
Factors that increase uterine venous pressure
Contractions Aortocaval compresssion Valsalva maneuver
47
Factors that increase uterine vascular resistance
Maternal htn Preeclampsia Vasoconstrictors
48
PO2 in fetal artery and vein
Fetal artery 2.0 Fetal vein 3.9
49
PCO2 in fetal artery and vein
Artery 5.9 Vein 4.7
50
What drives transfer of O2 from mother to fetus across the placenta?
High maternofetal oxygen concentration gradient Left shift of fetal ODC Bohr effect causing further left shift of ODC in fetal blood and right shift in maternal High fetal hb concentration
51
How is co2 carried in fetal blood with percentages? Which state crosses the placenta readily
Dissolved 8% -crosses readily Bicarbonate 62% Carbamino haemoglobin 30% Fractions of carbonic acid and carbonate
52
How does oxygen transfer effect co2 diffusion across the placenta?
Haldane effect Fetal o2 rises reducing fetal hb affinity for co2 releasing it Maternal o2 falls increasing maternal hb affinity for co2 absorbing it
53
How do nutrients cross the placenta
Glucose - facilitated transport - steriospecific for d isomer Amino acids - secondary active transport usually with na Fatty acids - diffuse across
54
Which Ig crosses the placenta? How?
IgG by Pinocytosis
55
Hormones released by the placenta
Human chorionic gonadotropin Human placental lactogen Hypothalamic releasing factor Hypothalamic inhibitory factor Oestrogen Progesterone Thyroid stimulating hormone Prostaglandins
56
What are the main hormonal changes in pregnancy
Rapid rise in HCG stimulating corpus luteum to secrete progesterone maintaining viability of pregnancy. This role is taken over by the placenta by week 8. Human placental lactogen is released by the plea beta causing lipolysis, gluconeogenesis and anti insulin effects Oestrogen is secreted by the placenta stimulating uterine expansion
57
Factors which could effect fetal maternal drug concentration ratios
Site of fetal sampling Time between administration and sampling Bolus or infusion of drug
58
Factors effecting placental drug transfer
Lipid solubility - more lipid soluble more easily transferred Degree of ionisation - non-ionised fraction can cross, ionised not pH of maternal blood - effects degree of ionisation and protein binding Protein binding - diffusion of protein bound drugs negligible Molecular weight of drug - <600daltons readily diffuse Maternal fetal concentration gradient Placental blood flow
59
Do muscle relaxants cross the placenta? Why
No, highly ionised
60
Which drugs will placental blood flow have a larger impact on for transfer to fetus
Highly diffusible ones - less diffusible ones there is very little change on placental transit so flow doesn’t matter, but Highly diffusible drugs drop in concentration on transit so faster flow has bigger effect
61
What law determines diffusion of drug across placenta by concentration gradient
Ficks law Q = kA.([m]-[f])/D Rate = constant.area.(maternal conc - fetal conc)/diffusion difference
62
How readily do opioids cross the placenta? F/M ratios for pethadine, morphine, fentanyl, alfentanyl
In significant amounts Pethadine 1 Morphine 0.61 Fentanyl 0.37-0.57 Alfentanyl 0.3
63
Why is alfentanyls F/M ratio so low
Highly protein bound
64
How does pethadine behave across the placenta when administered in labour
Rapidly metabolised in mother (t1/2 4hrs) but readily crosses placenta with F/M ratio of 1 and due to decreased metabolism in fetus has t1/2 of 19 hrs and it’s active metabolite norpethidine 62hrs!
65
Why do local anaesthetics readily cross the placenta What is the issue when in the fetus
Low molecular weight (around 240-280 daltons), highly lipophilic and low degree of ionisation in maternal circulation. When in fetal circulation more acidic conditions so more ionisation of the local anaesthetic so doesn’t diffuse back thus accumulates
66
Which local anaesthetics diffuse across the placenta more than others? Why?
Lidocaine, mepivicaine more so than bupivicaine due to less protein binding.
67
How easily do inhalational anaesthetics travel across the placenta What can this cause
Rapidly as highly lipid soluble. Diffusion hypoxia before delivery
68
F/M ratios of induction agents
Thiopental - 0.4 - 1.1 Ketamine 1.3 Propofol 0.65-1.15
69
What effects propofols F/M ratio specifically
Maternal protein concentration as it is highly protein bound.
70
How readily do atropine and glycopyrronium travel across the placenta
Atropine - readily Glycopyrronium - poorly
71
F/M ratio of ephedrine
0.7
72
How readily do benzodiazepines cross the placenta
Diazepam readily (fm ratio of 2 within 2hrs!) Midazolam less so fm ratio of 0.76

Primary Physiology (15 decks)

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