starting with basics

1. PHYSIOLOGICAL CHANGES IN
PREGNANCY AND
UTEROPLACENTAL BLOOD FLOW
SPEAKER : Dr OMAR KAMAL

2. MATERNAL PHYSIOLOGICAL CHANGES…
 result of hormonal alterations,
 mechanical effects of the gravid uterus,
 increased metabolic and oxygen
requirements,
 metabolic demands of the fetoplacental unit,
 hemodynamic alterations associated with
the placental circulation

3. CARDIO VASCULAR
 increase in plasma volume as well as in
red cell and white cell volumes The
plasma volume increases by 40% to
50%, whereas the red cell volume goes
up by only 15% to 20%.. Physiological
pregnancy of anaemia..
 mother's body compensates for it by
increased cardiac output, increased
PaO2, and a rightward shift in the
oxyhemoglobin dissociation curve.

4.  Two current hypothesis
 (1) caused by initial vasodilation, which
stimulates hormones such as renin,
angiotensin, and aldosterone or
 (2) characterized by an early increase in
sodium retention (due to an increase in
mineralcorticoids) that retains fluid, causing
an increase in blood volume

5. Clinical implications :
 enlarging uterus ,needs of the fetoplacental
unit,
 they become hypercoaguable as the
gestation progresses.( 1,7,8 9,10,12 and
fibrinogen)
 it protects the parturient from the bleeding at
the time of delivery
 8 weeks post delivery for blood volume to
return normal

6. CARDIO VASCULAR
 Cardiac output starts increasing from 5th week,
increases by 30% to 40% , and the max increase
is attained around 24 weeks’ gestation.
 Heart rate increases by 20 to 30 %
 CO increases further during labor and may show
values 50% higher than prelabor values.
 In the immediate postpartum period, CO
increases maximally and can rise 80% above
prelabor values
 The increase in stroke volume as well as in heart

7.  Heart rate
 Stroke volume
 Cariac output
 Cvp
 Pcwp
 Svr
 Pvr
 Sys blood pressure
 Pulmonary art
pressure
20-30 % increase
20-50 increase
30-50 increase
Unchanged
Unchanged
20% decrease
30% decrease
Slight decrease
Slight decrease

8.  CO, HR, and stroke volume decrease to pre-
labor values 24 to 72 hours postpartum and
return to nonpregnant levels within 6 to 8
weeks after delivery
 DBP drops by 15 mm Hg, decrease because
of an associated decrease in SVR..
 estradiol-17b and progesterone hormones
resonsible , Prostacyclin, nitric oxide for
vascular changes..

9. ANESTHETIC IMPLICATIONS…
 when the parturient lies supine, chance of
aorto caval compression..
 Symp : maternal tachycardia, arterial
hypotension, faintness, and pallor
 Left uterine displacement maintained

10.  Hyperdynamic state of pregnancy in patients
with heart disease and low myocardial reserve,
there is increase in myocardial work which may
precipitate pulmonary congestion…
 adequate pain relief must be given by
continuous epidural analgesia…
 Healthy gravida wil tolerate upto 1500 ml blood
loss as ther is hemodilution and increased
volume..
 Because of engorgement of epidural veins,
accidental intra vascular injection is common..

11.  Cephalad spread of LA drug during regional
anesthesia is more in pregnant patients due to
1) Decreased volume of csf
2) Decreased protein concn reduces protein binding
3) Increased neuro sensitivity to LA..
Hence dose requirement reduces upto 25 to 40 %..
 Maternal BP should be maintained and should not
go less than 20 % of the preoperative values
during regional block..
 Ephedrine is the preferred drug over peripheral
vaso constricors in spinal hypotension

12. Effect of Pregnancy on Cardiovascular
Investigations
Investigation Findings
Chest radiography
Apparent cardiomegaly
Enlarged left atrium (lateral views)
Increased vascular markings
Straightening of left-sided heart border
Postpartum pleural effusion
Electrocardiography
Right-axis deviation
Right bundle branch block
ST-segment depression of 1 mm on left
precordial leads
Q waves in lead III
T-wave inversion in leads III, V2, and V3
Echocardiography
Trivial tricuspid regurgitation (up to 43%-93% at
term)
Pulmonary regurgitation (up to 94% at term)
Increased left atrial size by 12%-14%
Increased left ventricle end-diastolic
dimensions by 6%-10%
Inconsistent increase in left ventricle thickness
Mitral regurgitation (28% at term)
Pericardial effusion (40% postpartum

13. RESPIRATORY CHANGES…
 Starts at 4th week of gestation
Clinical implications :
1. A decreased FRC as well as increased oxygen
consumption can cause a rapid development of
maternal hypoxemia.
2. Decreased FRC, increased MV, as well as a
decreased minimal alveolar concentration (MAC) will
make parturients more susceptible to inhalational
anesthetics
3. Avoid nasal intubation, and smaller ETT should be
used for oral intubation Because of the increased
edema, vascularity, and friability of the mucous
membrane

14.  TV : + 40 %
 RR : + 15 %
 MV : + 50 %
 Alveolar ventilation : +70 %
 Airway resistance : - 36 %
 Total pulmonary resistance : - 50 %
 Total compliance : - 30 %
 Dead space }
 Fev1 } no change
all parameters return to normal levels within 6 to
12 weeks post partum

15. VOLUMES AND CAPACITIES… BLOOD GASES
 FRC : - 20 %
 RV : - 20 %
 ERV : - 20 %
 ILC : + 5 %
 Diffusing capacity : - 5 %
 Vital capacity : no change
 Closing volume : no change
 Paco2 : -10 to – 20 mmhg
 Pao2 : + 10 mmhg
 Arterial PH : no change
 S. bicarb : - 4 meq/l
 O2 consumption : + 20 %

17. ANESTHETIC IMPLICATIONS
AIRWAY MANAGEMENT :
 Laryngoscopy becomes difficult due to breast
engorgement and weight gain.. Short handle
laryngoscope can be used..
 Small et should be used and avoid nasal intubation
RESPONSE TO ANAESTHETICS :
 MAC of potent inhalational drugs found to be
decreased in pregnancy
 Decrease in FRC with increase in MV increases the
rapidity of induction with inhalational drugs, hence
induction n recovery is rapid
 Rapid induction with inhalational agents due to
increased MV with decreased FRC.

18.  a decreased FRC , with preexisting alterations in
closing volume as a result of smoking, obesity, or
scoliosis have early airway closure with advancing
pregnancy, leading to hypoxemia and impaired organ
perfusion.
 The resulting decrease in the FRC/CC ratio causes
faster small-airway closure when lung volume is
reduced;
 thus, parturients can desaturate at a much faster rate
as compared with nonpregnant women.
 The rapid development of hypoxia as a result of
decreased FRC, increased oxygen consumption, and
airway closure may be minimized by administration of

19.  1ST stage of labour : due to pain, paients
hyperventilate leading to maternal alkalosis(
pco2 18 mmhg), consequentlly causing fetal
acidosis due to :
1. decreased uteroplacental perfusion (
hypocarbia causes vasoconstriction)
2. shifting of the maternal oxygen dissociation
curve to the left
Effective epidural analgesia alone can diminish
maternal hyperventilation markedly

20. RENAL SYSTEM
 GFR and RPF is increased by 50 % during
pregnancy by 4th month of gestation
 A rise in the filtration rate decreases plasma
blood urea nitrogen (BUN) and creatinine
concentrations by about 40% to 50% ..
 Tubular reabsorption of sodium is increased.
glucose and amino acids not absorbed
efficiently; hence glycosuria and aminoaciduria
develop in normal gestation
 The renal pelvis and ureters are dilated, and
peristalsis is decreased.

21. ANAESTHETIC IMPLICATIONS
 Increase in volume of distribution for drugs
 Drugs which are renall excreted have to be
given in higher than normal dosages.

22. GIT..
 Gastrointestinal motility, food absorption, and
lower esophageal sphincter pressure are
decreased due to an increased level of plasma
progesterone
 Shift in the position of stomach changes the angle
of GE junction
 Gastric emptying time is significantly prolonged
during labor and hence gastric volume is
increased
 risk of regurgitation on induction of general
anesthesia depends on the gradient between the

23. HEPATIC CHANGES
 Hepatic blood flow is unchanged
 Abnormal LFT s do not indicate hepatic disease
 Total proteins and albumin level decreased.
 The albumin–globulin ratio decreases because of
the relatively greater reduction in albumin
concentration
 Significance : the free fractions of protein-bound
drugs can be expected to increase
 Serum cholinesterase activity is reduced by 25 t0
30 % , but not associated with prolonged
neuromuscular blockade as volume of distribution
for s . Cholinesterase is high at term

24. ANESTHETIC IMPLICATIONS
 Antacid prophylaxis should be given before
induction
 No solid food should be given during labour
 Narcotics delay gastric emptying time and
decreases LES tone..

25. CHANGES IN THE CENTRAL AND PERIPHERAL
NERVOUS SYSTEMS
 The MAC is decreased by 25% to 40% with different
inhalational anesthetics due to increased
progesterone…
 A wider dermatomal spread of sensory anesthesia
was observed in parturients following the use of
epidural anesthesia
 Reduced epidural space volume caused by an
engorged epidural venous plexus because of
aortocaval compression ..
 Maternal b- endorphin blood level increase during
gestation proportional to frequency & duration of
uterine contraction. Lumbal epidural analgesia blocks
it

26. OTHER SYSTEMS..
 MUSCULO : Hormone relaxin is responsible for
both the generalized ligamentous relaxation and
softening of collagenous tissues.
 Hyperpigmentation of certain parts of the body
such as the face, neck, and midline of the
abdomen due to MSH
 Enlargement of breasts
 IOP decrease during pregnancy;
(1) increased progesterone levels,
(2) presence of relaxin,
(3) decreased production of aqueous humor due to
increased secretion of HCG

27. CLINICAL IMPLICATIONS
 Relaxation of ligaments and collagen tissue
of the vertebral column leads to lordosis..
 Enlarged breasts with short necks make
intubation extremely difficult
 Changes in IOP in parturients produce visual
disturbances..

28. FETAL CIRCULATION

31. FETAL CIRCULATION..
 Fetal circulation is characterized by the presence
of 3 main shunts placenta, foramen ovale, and
ductus arteriosus
 The placenta oxygenates the blood, which
courses up through umblical vein(portal sinus and
ductus venosus) to IVC then into the right atrium.
IVC also receives less oxygenated blood returning
from the lower body
 The right atrium is divided by a structure called
the crista dividends ,so this relatively well-
oxygenated blood is shunted from the right atrium
through the foramen ovale into the left atrium,
thereby bypassing the right ventricle and
pulmonary vasculature…

32.  The two separate circulations, well oxygenated
and de oxygenated are maintained by the
structure of the right atrium,
 It effectively directs entering blood to either the
left atrium or the right ventricle, depending on
its oxygen content, which is facilitated by the
pattern of blood flow in the IVC..
 The well-oxygenated blood tends to course
along the medial aspect of the IVC and the
less oxygenated blood stays along the lateral
vessel wall

33.  From LA to LV then ascending aorta
supplying brain and upper extremeties..
 Blood returns from the upper body to the right
heart by SVC, where it is directed by the crista
dividends into the right ventricle, from which it
is then pumped out through pulmonary artery.
 The pulmonary vascular bed has a high
vascular resistance because the alveoli are
relatively closed and filled with fluid, and the
blood vessels are compressed

34.  Blood that leaves the right ventricle by the
pulmonary artery is shunted (90%) through the
ductus arteriosus and down the descending
aorta and
 10 % to the pulmonry vasculature only enough
blood flow to ensure growth and development of
the lungs, including surfactant production
 Clamping of the umbilical cord and initiation of
ventilation produce enormous circulatory
changes in the newborn

35.  The transition of the alveoli from a fluid-filled
to an airfilled state results in a reduced
compression of the pulmonary alveolar
capillaries with a reduction in PVR
 It is accompanied by constriction of the
ductus arteriosus secondary to oxygenation.
 This results in an increase in pulmonary
blood flow and an increase in left atrial
pressure so the foramen ovale functionally
closes

36. UTEROPLACENTAL BLOOD FLOW
 Maintenance of uteroplacental blood flow is
the hallmark for fetal well-being..
 UBF= UAP-UVP/ UVR(uterine vascular
resist)
 At term, 10% of the cardiac output (700
mL/min) supplies the uterus
 The placental vasculature remains maximally
dilated, thus placental blood flow will mainly
depend upon perfusion pressure

37. MEASUREMENT OF UBF
 The ratio of the peak systolic waveform and diastolic
trough of blood flow velocity (S/D) ,
 a high S/D ratio is associated with reduced placental
perfusion
 Fetal oxygen transfer depends on oxygen affinity and
the oxygen-carrying capacity of maternal and fetal
blood.
 The oxygen carrying capacity will ultimately depend
on hemoglobin concentration and the oxyhemoglobin
dissociation curve shifted to the left in the fetus as
compared with the mother
 Hb conc mother 12gm/100ml and fetal 15gm
 This benefits the fetus by increasing oxygen uptake
across the placenta.

38. CLINICAL IMPLICATIONS
 Fetal oxygenation will depend on the uterine
vein oxygen content and umbilical vessel
blood flow..
 fetal oxygen delivery averages 24mL
O2/min/kg and that oxygen consumption is
3mL O2/min/kg.
 Compensation takes place either by
increased oxygen extraction or by
redistribution of the fetal circulation

39.  Carbon dioxide (CO2) exchange will depend
upon umbilical as well as uterine blood flow
 Acute respiratory acidosis can be caused by
an accumulation of CO2 because of a
decrease in either uterine or umbilical blood
flow
 Fetal acidosis during maternal
hyperventilation due to :
(1) maternal hypocapnia (<25mmHg) will
cause uterine and umbilical vessel
vasoconstriction..

40. 2) Mechanical hyperventilation will increase
intrathoracic pressure and reduce venous
return as well as cardiac output and thus
reduce uteroplacental blood flow..
3) maternal alkalosis will shift the oxygen-
hemoglobin dissociation curve to the left, and
thus the fetus will have difficulty extracting
oxygen

41. FACTORS ALTERING UBF
1) Uterine contraction reduces UBF..Contractions
measured by observing intrauterin pressure
 20 mmhg- no effect
 30 mmhg- decrease UBF by 50 %
 40 mmhg- completely stop intervillous
perfusion..
2) Decreased UBF due to
a) Aortocaval compression by the large gravid
uterus in supine position
b) sympathectomy from regional anesthesia and
c) hypovolemia from severe hemorrhage.

42. 3) Pathological conditions :
a)PIH (pre-eclampsia),
b) diabetes, and
c) overdue dates or postmature pregnancy.
4) Pharmacological agents :
Iv induction agents :
 thiopental : reduction in placental blood flow of 35%
and no drop in mean maternal artery blood pressure
 Diazepam,midaz : higher doses reduces UBF by
reducing MAP

43.  Etomidate, propofol : Propofol was associated
with the greatest drop in MAP, whereas
etomidate was seen to be the most cardiostable
agent
 Halothane, isoflurane : deep level of anaesthesia
wil reduce UBF by decreasing maternal arterial
pressure
 sevoflurane : Sevoflurane and isoflurane at
equianesthetic concentrations (0.46 MAC hr)
were observed to produce similar drops in blood
pressure and heart rate changes during the
operation.

44.  When less lidocaine (blood level, 2 to 4mg/mL)
is used, during epidural anesthesia, no
significant decrease in uterine blood flow was
observed even after prolonged infusion ..
 Ropivacaine and bupivacaine do not cause
vasoconstriction or reduce uteroplacental blood
flow in therapeutic doses.
 cocaine is associated with a significantly higher
degree of uterine vasoconstriction and reduced
uteroplacental blood flow

45. PLACENTAL TRANSFER OF ANAESTHETIC DRUGS
 Drugs cross the placenta by three main processes:
simple diffusion, active transport, or pinocytosis.
 factors : molecular weight, protein binding, degree of lipid
solubility, maternal drug concentration maternal and fetal
pH.
 The Fick principle governs the rate of transfer of a drug
across a membrane:
 Q/t = K * A (Cm-CF) / D
 Q/t is the rate of diffusion,
 K is the diffusion coefficient,
 A is the surface area of membrane available for exchange,
 Cm - Cf is the concentration gradient between the
maternal and fetal circulations, and
 D is the thickness of the membrane

46. Thank you