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
