18. Shear stress
high velocity to support
the sustained increases in cardiac out put
High-velocity flow increases shear stress on
the vascular lining, where it could become
damaging
20. Reynolds equation
Haematocrit is the primary determinant of
blood viscosity
Anaemia reduces stress levels and lessens the
risk of vascular endothelial damage
21. Reynolds equation
The likelihood of turbulence can be predicted
NR is Reynolds number,
v is mean blood velocity,
d is vessel diameter,
ρ (rho) is blood density,
η is blood viscosity.
30. Increase in blood flow to the skin, resulting in
warm, clammy hands and feet
Dissipate heat from the metabolically active
feto-placental unit
31. Edema
Fetus, placenta, and amniotic fluid = ~8–10 kg
at term compresses inferior vena cava and other
smaller veins
32. Compression causes venous pressures in the
lower extremities to rise
Increases mean capillary pressure and
Increases net fluid filtration from blood to the
interstitium
Edema
33. Fall in colloid osmotic pressure
by 30%– 40% during pregnancy
(from ~25 mm Hg prior to pregnancy to ~15 mm Hg postpartum)
Edema
36. Progressive increase in minute ventilation
to ~50% over non-pregnant values during the
second trimester
Respiratory system
37. Minute ventilation increase is effected largely by
An increase in tidal volume and
Small rise in respiratory rate (2–3 breaths/min)
Respiratory system
38. Net effect is that
PaO2 rises by ~10 mm Hg,
and PaCO2 falls by ~8 mm Hg,
causing a slight respiratory alkalosis (<0.1 pH )
Respiratory system
39. 20% decrease in
Functional reserve capacity,
Expiratory reserve capacity,
Residual volume
caused by a rise in the diaphragm
Respiratory system
40. Changes in Respiratory Function in Pregnancy
Variable Non-Pregnant
Term
Pregnancy
Tidal volume ↑ 450 mL 650 mL
Respiratory rate 16 min–1 16 min–1
Vital capacity 3200 mL 3200 mL
Inspiratory reserve volume 2050 mL 2050 mL
Expiratory reserve volume ↓ 700 mL 500 mL
Functional residual capacity ↓ 1600 mL 1300 mL
Residual volume ↓ 1000 mL 800 mL
PaO2 slight ↑ 11.3 kPa 12.3 kPa
PaCO2 ↓ 4.7–5.3 kPa 4 kPa
pH slightly ↑ 7.40 7.44
42. Physiological Changes of Pregnancy Which Increase the
Risk of Hypoxaemia
Interstitial oedema of the upper airway,
especially in pre-eclampsia
Enlarged tongue and epiglottis
Enlarged, heavy breasts which may impede
laryngoscope introduction
Increased oxygen consumption
Restricted diaphragmatic movement, reducing FRC
46. Gastrointestinal Changes
Reduction in lower oesophageal sphincter
pressure
Increase in intragastric pressure and a decrease
in the gastro-oesophageal angle
47. Placental gastrinincreases gastric acidity
Gastrointestinal motility decreases but gastric
emptying is not delayed during pregnancy
However, it is delayed during labour but returns
to normal by 18 h after delivery
Gastrointestinal Changes
48. Liver Function Changes in Pregnancy
Parameter
Change in
Pregnancy
Albumin Decreased
Alkaline phosphatase Increased (from placenta)
ALT/AST No change
Plasma cholinesterase Decreased
49. Pregnancy induces a hypercoagulable state
Coagulation Changes in Late Pregnancy
51. Haematological changes
Plasminogen unchanged
Plasminogen activator reduced
Plasminogen inhibitor increased
Fibrinogen-stabilizing factor falls
gradually to 50% of non-pregnant
value
Fibrinogen increased from 2.5 (non-pregnant
value) to 4.6–6.0 g L–1
Factor II slightly increased
Factor V slightly increased
Factor VII increased 10-fold
Factor VIII increased – twice non-pregnant
state
Factor IX increased
Factor X increased
Factor XII increased 30–40%
Factor XI decreased 60–70%
Factor XIII decreased 40–50%
Antithrombin IIIa decreased slightly
