Physiological changes during pregnancy Flashcards
How much weight should women gain in pregnancy?
10-20 kg
Due to enlargement of:
- fetus
- placenta
- amniotic fluid
- enlargement of maternal organs and body compartments (uterus, breasts, fat, blood, extracellular fluid)
What happens if pregnant women lie supine?
Aortic and IVC compression
- maternal BP is normal or raised above the level of compression but dramatically reduced below that level
- blood supply to the uterus is below the level of aortic compression
- fetal compromised can occur without maternal hypotension
- the azygos venous sstem is dilated when the IVC is compressed - leads to engorgement of veins in spinal canal
What is uterine blood flow at term?
700 ml/min
Why is there a rise in cardiac output following felivery?
Due to autotransfusion of blood from the uterus
How does the spirometry trace differ in pregnant women compared to non-pregnant?
REDUCED
- FRC
- expiratory reserve volume
- residual volume
- total lung capacity
INCREASED
- tidal volume
- respiratory rate
- minute ventilation
Why is there a rapid decline in maternal PaO2 during apnoea?
- FRC is reduced
- O2 demand is increased
- therefore rapid fall in PaO2
What is the recommended pre-O2 strategy in pregnancy?
3 mins tidal breathing.
There is a faster rise in maternal end-tidal O2 concentration with pre-oxygenation due to the rise in minute ventilation and fall in FRC.
How does the maternal blood gas change in pregnancy?
PaCO2 falls early in pregnancy.
PaO2 is slightly raised.
pH becomes slightly more alkaline.
What ventilator settings should you use in a pregnant woman weighing 55kg?
RR - 15
Tidal volume - 480-460 mls
PaCO2 - 4.1 kPa
PaO2 - 14 kPa
What is the alveolar gas equation?
PAO2 = PIO2 - (PaCO2/R)
PAO2 - alveolar partial pressure of O2
PIO2 - inspired partial pressure of O2
PaCO2 - arterial partial pressure of CO2
R - respiratory quotient
Why is endobronchial intubation more likely in pregnant women?
The distance from teeth to carina is shortened because the diaphragm and chest contents are displaced cephalad as pregnancy advances.
How does the gastric pH and volume alter during pregnancy?
pH 2.4 (pregnant)
pH 3 (non-pregnant)
gastric volume 0.49 ml/kg (pregnant)
0.24 ml/kg (non-pregnant)
Is there any point in pregnancy that pregnant women don’t need an RSI?
Prior to 16-18 weeks gestation (if they have no other risk factors)
How long after delivery can you induce GA without an RSI in pregnancy?
48hrs after delivery
What are the blood changes in pregnancy?
40-50% increase in plasma volume
20-30% increase in red cell volume
Fall in Hb concentration
During labour WBC count increases
Why are pregnant women hypercoagulable?
Raised plasma levels of
- fibrinogen
- factors VII, X, XII
- decreased fibrinolysis
How does pregnancy affect the dose required of local anaesthetic?
Less local anaesthetic is needed for regional anaesthesia.
From late 1st trimester a dose reduction of 30% is required.
What are the renal changes in pregnancy?
- GFR increases 50-70%
- kidneys increase in size
- urinary collecting system dilates - leads to stasis of urine/acute pyelonephritis
- glycosuria is common (tubular reabsorption of glucose is overwhelmed)
- proteinuria is common
- plasma albumin falls
What are the normal values for urea and creatinine in pregnancy?
Urea 3.3 mmol/l
Creatinine 53 µmol/l
When does HCG peak during pregnancy?
At around 12 weeks (50 IU/ml)
When does progesterone peak in pregnancy?
Right before labour
What is hPL?
Human placental lagtogen (chorionic somatomammotrophin).
Peptide hormone with a structure and function similar to growth hormone. It causes impaired glucose tolerance due to insulin resistance.
What is hCG?
Peptide hormone produced by the embryo and later by the placenta.
It maintains the corpus luteum and hence maintains progesterone production.
When do heart rate and stroke volume peak in pregnancy?
HR peaks at 16 weeks
SV at 32 weeks
How much does cardiac output increase by in pregnancy?
40-50%
When is blood pressure the lowest in pregnancy?
20 weeks
