1) Physiological changes in pregnancy include increased weight, blood volume, cardiac output and decreased FRC. 2) Respiratory changes include increased oxygen consumption and minute ventilation but decreased FRC leading to risk of atelectasis. 3) Renal changes involve increased GFR and decreased resorption causing mild glycosuria and proteinuria. 4) Hematological changes result in a hypercoagulable state with increased clotting factors and decreased platelets.

1. PHYSIOLOGICAL CHANGES IN
PREGNANCY
Presentor:Dr.FARHA FATIMA
Mentor: Dr.J.SRAVAN KUMAR
Chairperson: Dr.P.V.SHIVA (Professor of Anesthesiology, Niloufer Hospital)

2. BODY WEIGHT CHANGES:
• Mean maternal weight increases during pregnancy is 17% of pre-pregnancy
weight or 12 kgs (approx.)
• Due to –(i) Increase in size of breast tissue & uterus
(ii)Developmemt of the foetus and the placenta
(iii)Increase in blood volume and interstitial fluid
(iv)Deposition of new fat and proteins
• Expected weight gain in 1st trimester – 1 or 2 kgs
2nd trimester - 5 or 6 kgs
3rd trimester - 5 or 6 kgs

3. CNS:
 MAC decreases as much as by 40 % ----returns to normal on 3rd day post delivery.
 Progesterone(sedating) increases by 20 times at term
 Enhanced sensitivity to LA seen
 Dose of epidural is reduced by 30% - due to pressure exerted by enlarging uterus on
Inferior vena cava there is engorgement of epidural venous plexus which increases
epidural blood flow .
This causes (i) decrease in CSF volume
(ii)Decrease in potential volume of epidural space
(iii)increase in epidural space pressure [This may
complicate identification of the epidural space]
* Engorgement of epidural veins may result in placement of needle into a vein resulting
in intravascular injection of drug and bloody tap during the procedure.

4. CHANGES IN RESPIRATORY SYSTEM:
CHANGE IN
ANATOMICAL
CHANGES
UPPER
AIRWAYS
LUNG
VOLUMES
MINUTE
VENTILLATION
O2
CONSUMTION
METABOLIC
RATE

5. Anatomical changes:
1. Subcostal angle widens from 68.5 degree to 103.5 degree
2. The Antero posterior and Transverse diameter each increase by 2cm
Increase of 5-7cm in circumference of lower rib cage.
3. Position of diaphragm is elevated by 4cm
Vertical measurement of chest cavity decreases
4. Diaphragm excursion increases by 2cm

6. • Capillary engorgement of respiratory mucosa with friability and edema makes it
prone to trauma and bleeding Thus gentle laryngoscopy with
minimum attempts and smaller Endotracheal tubes are used (6-6.5mm)
1)UPPER AIRWAY CHANGES:
2)MINUTE VENTILLATION & OXYGENATION:
• MV(Minute Ventillation) increases 45-50% above non pregnant values .
(Increase is due to increase in T.V and not much change in the Respiratory rate.)
• P50 of Hb increases from 27 to 30 mm Hg. Higher P50 in mother and lower P50
in fetus favors off loading of O2 across placenta.

7. • O2 consumption at – Term increases by 20% of pre-labour values
-1st stage increases by 40% of pre-labour values
-2nd stage increases by 75% of pre-labour vaues
*In absence of analgesia , pain of labour can result in severe
hyperventilation causing PaCO2 to decrease below 20mm Hg.

8. :
Increase:
LUNG VOLUMES:
1. Inspiratory reserve volume (+5%)
2. Tidal volume (+45%)
LUNG CAPACITIES:
1. Inspiratory reserve capacity(+15%)
Dead space(+45%)
VENTILLATION:
1. Minute ventilation(+45%)
2. Alveolar ventilation(+45%)
Decrease:
LUNG VOLUMES:
1. Residual volume (-15%)
2. Expiratory reserve volume (-
25%)
LUNG CAPACITIES:
1. Total lung capacity(-5%)
2. Functional residual capacity-
FRC (by 20%) – returns to
normal after 48 hrs
LUNG VOLUMES & CAPACITIES:

9. *Minimally affected : Vital capacity , Closing capacity

10. • Decrease in FRC + Increase O2 consumption
cause rapid O2 desaturation during periods of apnoea
[Pre-oxygenation is important to prevent hypoxemia]
• FRC reduces due to the growing uterus that elevates the diaphragm up and decreases
the Residual volume and Expiratory reserve volume.
• The ratio of FRC/Closing capacity reduces which favors small airway closure with
reduced lung volumes in supine position leading to Atelectasis.
• CXR: shows prominent vascular markings due to increased pulmonary blood volume
and elevated diaphragm.
• Increase in MV + Decrease in FRC Accelerate uptake of inhalational
anaesthetics

11. Cardiovascular system:
• Cardiac output increases (by 40%) due to increase in Heart Rate (20%)
+ Stroke volume (30%)
• Blood volume increases:
 Plasma volume increases by 55%
 Red cell mass increases by 45%
Results in dilutional anaemia and
decrease in blood viscosity.
• Right shift of Hb-dissociation curve
• Systemic vascular resistance decreases Decrease in Diastolic BP
Decrease in Systolic BP(lesser
degree)
• Myocardial hypertrophy
• Central venous pressure, Pulmonary capillary wedge pressure --- are
unchanged despite of increase in plasma volume due to concurrent increase
in venous capacitance

12. • In 1st trimester, the maternal intravascular fluid volume begins to increase as a
result of –Renin , angiotensin , Aldosterone – which promote sodium and water
retention. These changes are likely induced by progesterone.
• The physiological anemia in pregnancy does not reduce the O2 delivery due to
coincident increase in Cardiac output
• This increase in Intravascular fluid volume compensates for the average blood loss
of 300-500ml in vaginal delivery
800-1000ml in Caeserean-section
• Ejection fraction increases
Reason: Left ventricular end diastolic volume increases but end systolic volume
remains same

13. • Uterine blood flow increases from baseline of 50ml/min to 700-
900ml/min at term .
-90% of this flow perfuses intervillous space
-10% of this flow perfuses myometrium

14. Cardiac Output:
• Highest seen immediately after delivery (80-100% above prelabour values)
Seen due to auto transfusion from—1)final uterine contraction
2)reduced vascular capacitance from loss
of placenta
3)decreased lower extremity venous
presssure from release of aortocaval
compression.
• This massive increase in C.O is a moment of unique risk for patients with
cardiopulmonary disease (particularly valvular stenosis & pulmonary HTN)

17. • Apex beat shifted to 4th Intercostal space
• Accentuated S1
• Grade 1 or 2 systolic ejection murmur at Left sternal border (due to mild
regurgitation at tricuspid valve from increased cardiac volume.
• S3 may be heard
• Sometimes S4 heard (due to increase in blood volume and turbulent
flow)
• Diaphragm shifts the position of heart upwards and anteriorly so on CXR:
it appears as cardiomegaly
• ECG: Left axis deviation, T-wave changes can be seen.
Clinical findings:

18. Supine Hypotension syndrome:
• Aortocaval compression in supine position
• So, the return of blood from lower extremities is from
1)Epidural veins
2)Azygous veins
3)Vertebral veins
• Presents as – Pallor , sweating, nausea and vomiting.
• Compensated by reflexive increase in sympathetic activity
Increases systemic vascular resistance
Thus maintains SBP (despite low C.O)
• In such cases when Neuraxial or General anesthetic is given there is
reduced sympathetic tone and impairs the compensatory response.
• Can be prevented by placing a wedge of >15degree under Right thigh.
• Chronic partial caval compression in 3rd trimester causes pedal edema,
varices, venous stasis, venous thromboembolism.

19. RENAL CHANGES:
• Renal plasma flow increases Decrease in Sr.Creatinine (0.5-0.6mg/dl)
Decrease in BUN (8-9mg/dl)
Glomerular filtration rate increases
• Mild glycosuria(1-10g/d)
• Proteinuria <300mg/d
• Decrease in plasma osmolality by 8-10 mosm/kg
• Serum globulins increase
• Total protein concentration decreases—causes reduction in colloid oncotic
pressure
Due to decreased renal tubular
resorption capacity

21. Renal changes contd.
• Enlargement of uterus
Dilatation of ureter , calyces with reduced bladder capacity

22. GIT CHANGES:
• Intragastric pressure increases(due to gravid uterus)
• Gastric motility is reduced
• Stomach is displaced upward &anteriorly by uterus
Promotes incompetence of gastroesophageal sphincter
Gastroesophageal reflux
Esophagitis
Regurgitation &
Aspiration

23. Administration of non particulate antacid ( increases
the gastric pH)
Rapid sequence induction with cricoid pressure
Placement of cuffed endotracheal tube
Aspiration can be prevented by:

24. HEPATIC CHANGES: (overall unchanged)
1. Sr.Transaminases
2. Sr.LDH
3. Sr.ALP
4. Sr.Albumin – mild decrease due to increase in plasma volume
5. Increased progesterone Decreases Cholecystokinin
Incomplete emptying of gallbladder
Gall stones in pregnancy
Slight increase
6. Lower plasma protein concentration due to hemodilution results in
elevated free blood levels of highly protein bound drugs.

25. HEMATOLOGICAL CHANGES:
• Pregnancy is a Hypercoagulable state
• Fibrinogen ,Factor VII, VIII, IX, X, XII Increase
• Factor XI , XIII , antithrombin III – decreases
• Factor II remains unchanged.
• Leucocytosis (up to 21,000/micro lt)
• Platelet count decreases by 10% in 3rd trimester.
• Folate and iron deficiency anaemia (Increased iron requirement in
pregnancy)

26. Gestational thrombocytopenia:
• Seen in 8% of healthy women
• Platelet count is below 1,50,000/cumm
• Doesn’t usually drop below 70,000/cumm & is not associated with any
abnormal bleeding.
• Is a diagnosis of exclusion
• It results due to a combination of hemodilution and accelerated platelet
turn over.
These changes result in 20% decrease in PT and aPTT during normal
pregnancy.

27. ENDOCRINE/METABOLIC CHANGES:
• In first trimester there is insulin sensitivity.
• Insulin resistance is seen due to human placental lactogen produced
by placenta
This causes hyperplasia of pancreatic beta cells
*Diabetogenic state
• Free fatty acids
• Ketones
• Triglyceride
Increase
• Glucose
• Amino acids
Decrease

28. • Secretion of HCG + Increase in Estrogen
Promote thyroid hypertrophy and increase Thyroid binding
globulin
T3 & T4 increase Free T3 & T4 are normal
TSH is normal
• Basal metabolic rate increases by 15%

29. Adrenocortical function:
• CBG(corticosteroid binding globulin ) doubles due to estrogen induced
enhancement of hepatic synthesis .
Increases plasma concentration of Cortisol
• Free cortisol increases due to greater production and reduced clearance .
• Clearance of betamethasone is increased ( as it is metabolised by
placental enzymes)

30. MUSCULOSKELETAL EFFECTS:
• Relaxin increases
Ligamentous laxity of spine Increased risk of back injury
(back pain)
Care must be taken while
positioning the patient
and pelvic ligaments
• Back pain can also be due to enlarging uterus that exaggerates the
lumbar lordosis causing more mechanical stress on lower back.

31. • Exaggerated lumbar lordosis stretches
lateral femoral cutaneous nerve of thigh
Meralgia paresthetica
• Increase in breast tissue
can cause difficult intubation

32. Technical difficulty in administering
neuraxial anesthesia

33. Increase in rostral spread of
hyperbaric drugs

34. Intravenous anesthetics:
1.PROPOFOL:
• Propofol requirement decreases by 10% during 1st trimester
• Elimination half life is unaffected
2.THIOPENTONE:
• Induction dose is -18% lower in 1st trimester
- 35% lower at term
• Half life is 26.1 hrs (11.5 hrs in non-pregnant women)
Reason: Due to increased volume of distribution more than the
increase in clearance .
• Circulating endogenous analgesic peptide increases which
increases the threshold to pain during delivery
Thus the Intravenous anesthetic dose required is less

35. CHRONOTROPIC AGENTS & VASOPRESSORS:
• Pregnancy reduces chronotropic response of Isoproterenol &
epinephrine due to down regulation of beta-adrenergic receptors.
Treatment of hypotension requires higher dose of vasopressors.

36. REFERENCES:
1)Chestnuts’s obstetric anesthesia (5th edition)
2)Stoeltings’s pharmacology & physiology in anesthetic
practice (5th edition)
3)Morgan & Mikhail’s clinical anesthesiology (5th edition)

37. THANK YOU!