1 & 2. Physiology changes in pregnancy Flashcards
If asked to describe the physiological changes in pregnancy what categories do we go through?
CVS
Haem
Resp
GI
CNS
ECR
Renal
Hepatic
MSK
Weight
What are the CVS changes in pregnancy?
Heart axis changes: TWI in V2 and left axis deviation
CO: 40% by end of first, 50% 2nd, extra 45% during labour (pain) and 80% during third stage (uteroplacental transfusion). SV 25% and HR 25% (rise to 30w then plateau)
SVR: decreases. Vasodilation from progesterone. 1700 to 979.
Venous pressure: normal unless ACC. CVP up 5 cmH2O in contractions, 50 during delivery and up 8 with ergometrine for around 60 mins.
BP: falls to nadir at 20w, then normal by term. Sys -8 and diastolic - 25. 12% goes to placenta (20 x normal - 700 ml/min at term). More to kidneys and skin.
ACC: starts around 13w, peaks 36-38w. 15deg tilt from 20w.
70% drop by 10% and 8% drop by 30-50%. Lower limb and foetus hypoperfusion.
What is supine hypotension syndrome?
ACC effects stay after tilting (shock)
What are the haematological changes in pregnancy?
TBV: 10, 30 and 45%, by end of 1st, 2nd and 3rd trimester.
Plasma: up 50% by term and 1L in 24h post. Returns to normal by day 6 post. Due to oestrogen, progesterone and RAAS.
RBC: reduces until 8w, normal by 16 and up by 30% by term. EPO. Dilutional anaemia. Aim Hb over 11.
WBC: up to 15 in labour. Polymorphonuclear cells.
Coag: XI, XIII and antithrombin 3 up.
2, 5 and platelets the same.
Increased platelet turnover, increased clotting and decreased fibrinolysis.
Increased FDP, decreased bleeding time PT and APTT.
Proteins: decreased albumin and plasma pseudocholinesterase by 25% (hydrolysis of choline esters (sux and mivacurium)
Gives decreased colloid pressure, altered drug binding, increased ESR and viscosity.
What are the respiratory changes in pregnancy?
Anatomical;
1st trimester = upper airway oedema and capillary engorgement (difficult nasal and epistaxis)
Rib flare, thoracic circumference up by 5-7cm (diaphragm)
Diaphragm rises
Carina more cephalad
Bronchial smooth muscle relaxation
Volumes:
Lung compliance same, but chest wall down to diaphragmatic breathing
Up = MV (50%), Vt (45%), RR (10%) and alveolar ventilation (70%)
Down = FRC (20-30%), ERV, TLC. Closing capacity encroaches, causing VQ mismatch.
PVR decreases (119 - 78). No increase in PAP etc.
ABG: increased ventilation = reduced CO2 (3.7-4.2) and bicarb (18-21) so pH down by 0.04.
Initial PaO2 rise (more room in alveoli), but then O2 demand up by 60% so falls slightly.
O2 curve: rightward shift due to 30% more 2-3 DPG (increased offloading)
What are the GI changes in pregnancy?
Barrier pressure reduced (LOS - intragastric pressure)
Progesterone causes smooth muscle relaxation and gravid uterus increases pressure and causes sliding hiatus.
Emptying only decreased in labour (opiates). Increased secretions and decreased pH.
Needs RSI from 16w - 48h post.
What are the CNS changes in pregnancy?
What does this mean for LA’s and MACs?
Epidural space: venous engorgement (azygous) = less space = more spread. Positive pressure during contractions and expulsion (+++)
CSF: increased due to ACC. Baseline up 28cm H2O between contractions and up 70 in second stage. Contents the same.
SNS: increased action. Mainly in lower leg veins to counteract ACC
LA’s: decreased central space and increased nerve sensitivity. Decreased CO2 = less buffering and increased time that LAs are free bases.
MAC: reduced by 30-40% (? Progesterone). Increased beta-endorphins
What are the endocrine changes in pregnancy?
Pituitary: becomes bigger, more vascular so sensitive to BP change (Sheehans - ischaemia)
Thyroid: bigger with higher iodine uptake. 2x TBG so free T3 and 4 the same.
Pancreas: increased islets and beta cells = increased insulin and receptors. Insulin resistance = higher post prandial sugars (higher placental gradient).
Adrenals: CS x 5. Cortisol increased due to decreased clearance.
What happens to the kidneys in pregnancy?
Flow: egfr increased by 50% (150ml/min) = reduced CR and Ur
Decreased tubular reabsorption so glycosuria and proteinuria
RAAS and progesterone: Na and water retention = increased K and decreased plasma osmolality
Progesterone: smooth muscle dilatation = stasis and increased UTI
What are the hepatic changes in pregnancy?
ALP produced by placenta so triples
Reduced CCK (cholecystokinin): reduced contractile response to stones.
What happens to the MSK system and weight during pregnancy?
Placental relaxin causes ligaments to relax.
Increased lumbar lordosis from gravid uterus
Increased melanocyte stimulating hormone = increased pigment (linea nigra)
Normal weight gain is 11-16kg
