Pregnancy Flashcards
How much does CO increase by in pregnancy?
CO increases by 50% by 2nd trimester up till birth
SV increases by 30%, HR by 25% at term
How much does CO increase by during 3rd stage of labour and why?
3rd stage of labour is following birth, prior to delivery of placenta
During 3rd stage, CO reaches up to 80% above 3rd trimester levels, partly due to uteroplacental transfusion
increase in CO is more due to increased SV.
There is a decrease in bp despite raised CO due to vasodilatation leading to drop in SVR and bp
what happens to SVR during pregnancy and why?
SVR decreases during pregnancy due to low resistance vascular bed and vasodilatory effect of progesterone, oestrogen and prostacyclin
normal SVR
versus pregnant SVR
Normal SVR 1700 dyn.s/cm5
Pregnancy SVR 979 dyn.s/cm5
What happens to BP in pregnancy?
BP falls in normal pregnancy (diastolic BP to a greater extent). 8% of mothers can have a fall of 30-50%
Blood flow distribution changes with:
12% perfusing placenta
kidneys and skin inceased
liver and brain unchanged
From how many weeks can the gravid uterus cause IVC and aortic compression?
13/40. particularly at 20/40 onwards
lie patient in left lateral to ease this
What happens to venous pressure in pregnancy
unchanged, unless marked IVC compression
CVP during contractions: 5 cmH20
CVP during delivery 50 cmH20
CVP during IV ergometrine 8
What happens to plasma volume in pregnancy
-plasma volume rises by upto 50%
by term, and further 1L 24hr post-partum. Returns to normal 6 days post partum. Mediated via oestrogen & progesterone on the renin-angiotensin-aldosterone system.
What happens to RBC & haematocrit in pregnancy
RBC vol initially decreases until 8/40, normalises by 16/40, then increases by 30% by term. Mediated via EPO.
As 30% increase in RBC at term is less than 50% increase in plasma volume at term, the haematocrit and Hb levels decrease.
What happens to WCC during labour
WCC increase up to 15 x10^9 during labour due to polymorphonuclear cells
What are the airway changes during pregnancy?
As early as 1st trimester:
-tissue oedema
-upper airway capillary engorgement
These can lead to epistaxis, vocal changes and nasal obstruction, plus potential for difficult airway
-rib flaring leading to increased thoracic cage circumference by 5-7cm.
-diaphragm pushed higher by gravid uterus later in pregnancy
-bronchial smooth muscles relaxes reducing airway resistance
What changes in lung mechanics and lung volumes occur during pregnancy?
During pregnancy there is an INCREASE: in:
-alveolar ventilation by 70%
-VT by 45%
-RR by 10%
-Minute ventilation by 50% due to increased VT
Progesterone and oestrogen both act as respiratory stimulants
O2 consumption increases to 35% above pre-pregnancy levels
DECREASES:
-FRC reduces by 20-30% at term due to reduced RV
-CC encroached on FRC leading to V/Q mismatch (+/- hypoxia)
-PaCO2 is decreased to 4kPa during the first trimester
Changes to blood gas during pregnancy:
-Fall in PaCO2 to 3.7-4.2 (norm is 4.7-6.0)
-Fall in HCO3 to 18-21 to compensate (norm 22-26)
-Compensation is not complete so pH increases by 0.04
-PaO2 slightly higher due to lower PaCO2 levels
-Towards term, O2 consumption & CO2 production increase by 60%. O2 delivery and PO2 slowly decline, enhanced by supine position due to aortocaval compression & dependent airway closure.
which direction does Oxyhaemoglobin dissociation curve shift?
Although decreased PaCO2 tends to shift left, there is an overall right shift due to 30% increase in 2,3 DPG. Raised 2,3DPG reduces Hb affinity for O2 & thus helps facilitate O2 shift across placenta
Pulmonary vascular resistance at term?
PVR at term reduces from 778 to 119 dyn.s/cm5. Pulmonary BF therefore increases. This will not lead to an increase in pressure in pulm artery, capillaries or right ventricle in healthy parturient
What happens to the GI barrier pressure in pregnancy
barrier pressure is significantly reduced in pregnancy
barrier pressure = LOS pressure- intragastric pressure
LOS returns to normal 48hr post-partum
What % of pregnant women have heartburn? How many weeks can this start from?
80% pregnancies
Can commence at <20/40
RSI is required from the start of 2nd trimester as that is when LOS tone decreases.
What happens to gastric emptying during pregnancy and labour?
slows only during labour (& worsened by opiates). Therefore higher risk of aspiration with GA
epidural space changes in pregnancy:
aortocaval compression results in engorgement of epidural veins, reducing the volume of epidural space, therefore, solutions will spread more rapidly if injected into it.
Pressure in epidural space is positive (Compared to negative in non-pregnant patient) with pressure rising to 8 cmH2O during contractions, or 60cmH20 during expulsion.
Subarachnoid space changes in pregnancy
CSF pressure is increased due to aortocaval compression. Baseline between contractions of 28 cmH2O, 2nd stage of labour rises to 70 cmH20. Norm=2.5-20 cmH2O
Sympathetic nervous system changes
increases during pregnancy
max at term
effect is largely on venous capacitance of lower limbs to help counteract IVC compression, therefore sympathetic block may result in a much larger drop in BP than in non-pregnant patients
Why is LA doses for spinal/epidural reduced in pregnancy?
reduced epidrual & CF volumes
increased nerve fibre sensitivty to LA
reduced PaCO2 leads to reduced buffering capacity & LA remain free bases for longer
Effect of pregnancy on MAC
MAC is reduced by 40% ?likely due to increased progesterone levels
Thyroid gland changes
increased size and vascularity to develop a goitre with increased iodine uptake. Thyroid binding globulin doubles therefore T3/T4 remain constant so the mother remains euthyroid
Adrenal gland
size remains constant
corticosteroids increase by upto x5 by term
T1/2 of cortisol is increased due to reduced clearance.
anterior pituitary gland blood supply and importance in pregnancy/delivery
increases in weight
anterior pituitary blood supply is via a low-pressure hypothalamo-hypophyseal portal system which is sensitive to changes in BP.
Sheehans syndrome may develop with peripartum hypovolaemia (ischaemic pit)
(in contrast, posterior pituitary has rich blood supply from various arteries so is not susceptible to ischaemia during drops in BP.
What is Sheehans syndrome
rare condition caused by severe postpartum haemorrhage leading to anterior pituitary gland damage
What hormones are released by posterior pituitary
oxytocin and ADH
What hormones are released by anterior pituitary
FSH
LH
TSH
GH
ACTH
Prolactin
Pancreas
-islets of langerhans and B cell number increase
-increased insulin production & receptor sites
-increased insulin resistance from pregnancy hormones, causing larger conc of glucose following a meal, allowing better placental transfer
renal changes
-renal plasma flow increase by 50%
-GFR increase to 150ml/min (norm 90-120)
-reduced tubular reabsorption so glycosuria & proteinuria occur
-drugs that are renally excreted may need to be given in higher dose than normal#
-RAS & progesterone lead to Na+ & water retention -> K+ conservation & reduced plasma osmolality. Progesterone causes smooth muscle relaxation-> increased UTI risk.
liver changes
-ALP increases x 3 (produced by placenta)
-reduced protein synthesis->reduced plasma cholinesterase-> increased duration of NMB (rarely clinically sig)
-Gall stone risk increases due to progesterone mediated reduction in cholecystokinin -> reduced contractile response
MSK changes
-ligamentous relaxation due to placental production of relaxin-> widened pubic symphysis, increased joint mobility
- lumbar lordosis results from gravid uterus-> lower back pain
-Melanocyte stimulating hormone causes hyperpigmentation of face, neck, abdo (linea nigra)
weight gain
10-12kg due to increased body waater, fat, foetus, placenta, amniotic fluid and uterine & breast enlargement
placenta blood supply
-blood supplied from maternal spiral arteries
-venous drainage from intervillous spaces to uterine veins.
-two umbilical arteries carry deoxygenated blood away from foetus
-oxygenated blood travels to the foetus by 1 umbilical vein
Chorion & Decidua
-Chorion- foetal part made from trophoblast & mesoderm (part of developing ovum ‘blastocyst’
-Decidua- part of endometrium.
-trophoblast part of chorion then invades decidua allowing close contact of foetal tissue to maternal blood (decidua basalis has maternal spiral arteries)
Placenta abnormalities:
1. placenta accreta
2. placenta increta
3. placenta percreta,
- placenta accreta: (A -at)chorionic tissue reaches uterine muscles, no plane of cleavage between placenta & its attachment to uterus
- Placenta increta (in)- chorionic tissue penetrates uterine muscle
- Placenta percreta (passes through)- chronionic tissues incades through whole muscles and reaches serosa or invades surrounding organs.
Placenta vascular system
trophoblastic invasion around spiral arteries allows reduced vasoconstriction starts 10/40, complete by 16/40.
-failure of trophoblastic invasion ->increased VR in placental bed-> IUGR. Finding in pre-eclampsia.
Foetal arteries (x2) arise from foetal internal iliac arteries.
uterine blood flow
-maternal placental vascular system is low pressure (10mmHg)
-upto 200 spiral arteries
-total uteroplacental BF 500-800ml/min at term.
-placenta 500g, 20cm diameter, 3cm thick
UBF= uterine art pressure- uterine venous pressure/ uterine VR
UBF is reduced by increased uterine venous pressure (contractions), maternal hypotension, increased vascular reistance
uterine blood flow equation
UBF= uterine art pressure- uterine venous pressure/ uterine VR
what can reduce uterine blood floww
UBF is reduced by increased uterine venous pressure (contractions), maternal hypotension, increased vascular reistance
define tocolysis
give examples
Tocolysis refers to the use of medications to suppress premature uterine contractions and delay preterm labor. The goal is to prolong pregnancy, typically for 48 hours to 7 days, allowing time for interventions such as corticosteroids (to enhance fetal lung maturity) or maternal transfer to a specialized unit.
e.g salbutamol
Sevo
Iso
Magnesium,
N2O has no effect on uterine tone making it useful during GA for section
effects of progesterone during pregnancy
-increased basal temp
-bronchodilation
-smooth muscle relaxation
-decreased GI motility & constipation
-renal tract dilatation
tell me about oxytocics e.g syntocinon)
used to cause uterine contraction e.g to induce labour, in those making slow progress, and after delivery at c section to ensure uterine contraction and reduce intrauterine bleeding
Ergometrine (given along to produce contraction, or with syntocinon to form snytometrine) causes vomiting
-can be given in pre-eclampsia but typically should avoid ergometrine as it causes a risk in BP
-most (excluding ergometrine) cause hypotension and tachcardia thus should be given slowly
examples of drugs able to cross placenta
warfarin
morphine
lignocaine.
glyco cannot as it a quarternary amine therefore charged.
lignocaine has less protein binding thatn bupivicaine therefore more crosses the placenta
ND NMBs are large polar molecules therefore not lipid soluble and unable to cross placenta
tell me about ergometrine
ergometrine is an agonist at alpha 1 adrenoreceptor, 5HT and dopaminergic receptors.
-casies uterine contraction, therefore can be used to aid delivwry of placenta or help gain control of PPH in atonic uterus.
-SE: HTN, thus avoid in pre-eclampsia.
what do Prostaglandin F2alpha drugs do?
give examples
what are SE
prostaglandin F2alpha drugs cause uterine contraction
e.g carbaprost, haemabate.
SE: bronchoconstriction (avoid in asthma), tachycardia, hypotension
Tell me about pre-eclampsia
-pre-eclampsia is characterised by HTN and proteinuria after 20/400.
-occurs in 5-6 pregnancies
-eclamptic seizures should be terminated by magnesium, which should then be continued and fetus delivered asap
–eclamptic fits can occur uto a week after delivery
-pre-eclampsia commonly causes thrombocytopenia thus platelets must be checked regularly during labour.
-can progress to eclampsia (fitting) or HELLP syndrome (haemolysis, elevated liver enzymes, low platelets) or both
1.absolute CI to epidural:
- relative CI to epidural
- Absolute contraindications to epidural are: Patient refusal, allergy to local anaesthetic, infection (cellulitis) over the site of placement, coagulopathy, raised intracranial pressure, profound hypovolaemia.
- Relative contraindications include: bacteramia, nerological disorders (eg MS, syringomyelia), fixed cardiac output state (eg aortic stenosis, HOCM), previous spinal surgery, anatomical abnormalities (eg spina bifida)
