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Primary Physiology > Physiology Of Pregnancy > Flashcards

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
Q

Change in minute ventilation in pregnancy
What drives this

A

Increases by 50% due to tidal volumes, rr remains same
Increased progesterone and co2 production

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26
Q

Effect of pregnancy on DLCO (diffusing capacity of lungs for carbon monoxide)

A

Increases first trimester then decreases then normal

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27
Q

Effect of pregnancy on blood gases

A

Co2 decreases
Bicarb excretion increases to maintain pH dropping BE
Slight elevation of pH as compensation not complete
Slight increase in PaO2

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28
Q

What causes dysponea in pregnancy?
Prevelance

A

Likely due to low co2
60%

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29
Q

What is the change in oxygen consumption during pregnancy

A

Increase 30-60%

30
Q

Why do pregnant women become hypoxic on induction

A

Reduced FRC
Increased metabolic demand

31
Q

Why are pregnant women more at risk of aspiration

A

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
Q

Changes to the CNS during pregnancy

A

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
Q

Clinical considerations for anaesthesia during pregnancy due to neurological changes of pregnancy

A

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
Q

Endocrine changes during pregnancy

A

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
Q

Why are pregnant women more at risk of sheehans syndrome

A

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
Q

Renal changes in pregnancy

A

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
Q

Liver and biliary system changes in pregnancy

A

Minor changes to liver enzymes ( increase in alp)
Progesterone decreases Ckk release so less gall bladder contraction and more gallstones
Decreased plasma cholinesterases

38
Q

Msk changes in pregnancy

A

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
Q

Rough weight gain in pregnancy
What proportion is due to fetus, amniotic fluid placenta and uterus?

A

10kg
40%

40
Q

Formation of the placenta

A

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
Q

What causes pre eclampsia

A

Failure of cytotrophoblast cells to destroy spiral artery smooth muscle so they still respond to vasoconstriction

42
Q

How does maternal blood flow through the placenta?

A

Uterine blood vessels
Spiral arteries (open ended)
Intravillous space (past the villous trees of fetal circulation)
Collecting veins
Uterine blood vessels

43
Q

Flow of fetal circulation through the placenta

A

Internal iliac arteries
Umbilical arteries x2 (deoxygenated blood)
Chorionic arteries
Villous tree
Chorionic vein
Umbilical vein (oxygenated)

44
Q

Formula for uterine blood flow

A

UBF = (uterine artery pressure - uterine venous pressure)/uterine vascular resistance

45
Q

Factors that decrease uterine artery pressure

A

Hypovolaemia
Aortocaval compression
Sympathetic block

46
Q

Factors that increase uterine venous pressure

A

Contractions
Aortocaval compresssion
Valsalva maneuver

47
Q

Factors that increase uterine vascular resistance

A

Maternal htn
Preeclampsia
Vasoconstrictors

48
Q

PO2 in fetal artery and vein

A

Fetal artery 2.0
Fetal vein 3.9

49
Q

PCO2 in fetal artery and vein

A

Artery 5.9
Vein 4.7

50
Q

What drives transfer of O2 from mother to fetus across the placenta?

A

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
Q

How is co2 carried in fetal blood with percentages? Which state crosses the placenta readily

A

Dissolved 8% -crosses readily
Bicarbonate 62%
Carbamino haemoglobin 30%
Fractions of carbonic acid and carbonate

52
Q

How does oxygen transfer effect co2 diffusion across the placenta?

A

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
Q

How do nutrients cross the placenta

A

Glucose - facilitated transport - steriospecific for d isomer
Amino acids - secondary active transport usually with na
Fatty acids - diffuse across

54
Q

Which Ig crosses the placenta? How?

A

IgG by Pinocytosis

55
Q

Hormones released by the placenta

A

Human chorionic gonadotropin
Human placental lactogen
Hypothalamic releasing factor
Hypothalamic inhibitory factor
Oestrogen
Progesterone
Thyroid stimulating hormone
Prostaglandins

56
Q

What are the main hormonal changes in pregnancy

A

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
Q

Factors which could effect fetal maternal drug concentration ratios

A

Site of fetal sampling
Time between administration and sampling
Bolus or infusion of drug

58
Q

Factors effecting placental drug transfer

A

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
Q

Do muscle relaxants cross the placenta? Why

A

No, highly ionised

60
Q

Which drugs will placental blood flow have a larger impact on for transfer to fetus

A

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
Q

What law determines diffusion of drug across placenta by concentration gradient

A

Ficks law

Q = kA.([m]-[f])/D
Rate = constant.area.(maternal conc - fetal conc)/diffusion difference

62
Q

How readily do opioids cross the placenta?
F/M ratios for pethadine, morphine, fentanyl, alfentanyl

A

In significant amounts
Pethadine 1
Morphine 0.61
Fentanyl 0.37-0.57
Alfentanyl 0.3

63
Q

Why is alfentanyls F/M ratio so low

A

Highly protein bound

64
Q

How does pethadine behave across the placenta when administered in labour

A

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
Q

Why do local anaesthetics readily cross the placenta
What is the issue when in the fetus

A

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
Q

Which local anaesthetics diffuse across the placenta more than others? Why?

A

Lidocaine, mepivicaine more so than bupivicaine due to less protein binding.

67
Q

How easily do inhalational anaesthetics travel across the placenta
What can this cause

A

Rapidly as highly lipid soluble.
Diffusion hypoxia before delivery

68
Q

F/M ratios of induction agents

A

Thiopental - 0.4 - 1.1
Ketamine 1.3
Propofol 0.65-1.15

69
Q

What effects propofols F/M ratio specifically

A

Maternal protein concentration as it is highly protein bound.

70
Q

How readily do atropine and glycopyrronium travel across the placenta

A

Atropine - readily
Glycopyrronium - poorly

71
Q

F/M ratio of ephedrine

A

0.7

72
Q

How readily do benzodiazepines cross the placenta

A

Diazepam readily (fm ratio of 2 within 2hrs!)
Midazolam less so fm ratio of 0.76

Primary Physiology (15 decks)

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