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Physiological changes during pregnancy and uteroplacental circulation.

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Title: Physiological changes during pregnancy and uteroplacental circulation.


1
Physiological changes during pregnancy and
uteroplacental circulation.
www.anaesthesia.co.in
email anaesthesia.co.in_at_gmail.com
  • Presenter Dr. Anamika Sharma
  • Moderator Dr. Rachna Wadhwa

University College of Medical Sciences GTB
Hospital, Delhi
2
Contents
  1. Body weight and composition during pregnancy.
  2. Phases of pregnancy and labor.
  3. Anatomical changes in the pregnancy.
  4. System wise changes in the physiology during the
    pregnancy.
  5. Uteroplacental circulation and the factors
    affecting.

3
Anatomical changes in pregnancy
  • Uterus an intrapelvic organ till 12 weeks of
    gestation.
  • By 20 weeks- uterus reaches upto umbilicus.
  • By 34 weeks it reaches the costal margin.
  • Last 2 weeks fundal height decreases when fetal
    head descends in the pelvis.
  • Increased lumbar lordosis.

4
Pregnancy and labor
  • 1st TM 1st 12 weeks
  • 2nd TM 13-28 weeks
  • 3rd TM 29-40 weeks.
  • Stages of labor
  • Stage 1a) dilatation and the effacement of the
    cervix. b) formation of the lower uterine
    segment.
  • Stage 2 Complete dilatation of the cervix to
    the expulsion of the fetus.
  • Stage 3 Phase of placental separation.

5
BODY WEIGHT AND COMPOSITION
  • Maternal weight gain-12kgs.
  • Increased size of uterus(1kg)
  • Amniotic fluid(1kg)
  • Fetus and placenta(4kgs)
  • Blood volume and interstitial fluid(4kgs)
  • New fat and protein (2-4kgs)
  • First trimester - 1-2 kgs
  • Second trimester - 5-6 kgs
  • Third trimester - 5-6 kgs

6
Factors causing physiological changes in
pregnancy
  • Hormonal alterations
  • Mechanical effects of the gravid uterus.
  • Increased metabolic and oxygen requirements.
  • Metabolic demands of the fetoplacental unit.
  • Hemodynamic alterations a/w placental circulation.

7
Respiratory Changes during pregnancy
  • AIRWAY
  • Capillary engorgement of the mucosa - changes in
    the Mallampatti examination score.
  • Exaggerated by mild URI, fluid overload or the
    edema associated with PIH.
  • Intranasal manipulation can cause brisk
    epistaxis.
  • Breast engorgement can interfere with
    laryngoscopy.

8
Changes in the respiratory system at term
Variable Direction of change Magnitude
Minute ventilation(MV) ? 50
Alveolar ventilation ? 70
Tidal volume ? 40
Arterial PaO2 ? 10mm Hg(85-103mm)
Oxygen Consumption ? 20
Respiratory rate ? 15
Inspiratory lung capacity ? 5-15
Arterial pH ? 7.40-7.47
Vital capacity ?
Arterial PaCO2 ? 27-33.5 mm Hg
Serum bicarbonate ? 21-27 mEq/L
FRC ? -15-20
Expiratory reserve volume ? -20
Residual volume ? -20
9
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10
  • During labor ? MV - ?300 ?development of
    maternal hypocarbia( PaCO2 20mm Hg) and
    alkalemia(pHgt7.53) ?left shift of ODC ? loss of
    consciousness ?hypoventilation.
  • Obesity -?? vital capacity.
  • Supine position--susceptibility to atelectasis
    and ? A-a gradient.
  • Closing capacity may exceed FRC.
  • Oxygen consumption -- ? 63.

11
  • Anaesthetic implications respiratory function
    changes
  • rapidity of induction of inhaled anaesthetics-
    (?FRC and ?MV).
  • MAC of the potent anaesthetic agents ? by
    24-40(?sensitivity to inhalational anaesthetic
    agents).
  • Judicious dosing of the inhaled anaesthetics
    required ?loss of protective airway reflexes and
    cardiopulmonary depression at ? doses.
  • Susceptibility to hypoxia ?, use of ? FiO2.

12
Role of maternal preoxygenation
  • Hypoxemia develops rapidly
  • d/t ?FRC
  • ? O2 consumption.
  • FRC lt Closing capacity in supine position.
  • During apneic periods rate of PaO2 fall, more
    than twice in parturient.
  • After complete denitrogenation
  • apneic period is 6-8 min. in non pregnant
  • 2-3 min. in pregnancy.

13
Anaesthetic implications
PARAMETER CONSEQUENCE
1. MV ? Faster denitrogenation
2. ?FRC ?O2 consumption Rapid hypoxia during apnoea
3. ?MV ?FRC Faster inhalational induction Faster emergence Faster changes in depth
4. Mucosal engorgement Difficult airway
5. Predominant diaphragmatic breathing High spinal does not affect MV PaCO2 much
14
Hematological changes
  • Plasma volume -? 40mL/kg - 70mL/kg(45)
  • RBC volume -? 25ml/kg - 30ml/kg(30)?
    Physiological anemia of pregnancy.
  • Leukocyte levels- ?12000-21000/mL.
  • Platelet count- ?/?20 but no alteration in BT.
  • Clotting factors hypercoagulable state, general
    ? in all the clotting factors.

15
  • Fibrinogen ?? to 400-650mg/dL(normal-200-450mg/dL)
    ? ?ESR value
  • Factors VII, VIII and X ?? after the 3rd month of
    pregnancy.
  • Factors II, V and XII ?
  • Factors XI and XIII- slightly ?.
  • Clotting factors return to normal within 2 weeks.
  • .

16
CVSHemodyanamics in pregnancy.

CO Starts to increase by 5 wks.
CO End of the 1st TM 30-40
CO end of the 2nd TM 50
2ND Stage of labor 40
With each uterine contraction 15-20
Immediately post partum 75-80 above prelabor values.
Returns to pre pregnant levels by 2 weeks post partum.
17
CVS Hemodynamicscont.
SV 20-50
Contractility 10
Systemic vascular resistance -20
Pulmonary vascular resistance -30
18
CVS-Examination
  • Innocent grade I/II systolic heart murmur.
  • Doppler and echo studies- ?end diastolic chamber
    size ? in total LV wall thickness, asymptomatic
    pericardial effusion, trivial MR and TR.
  • Diaphragmatic rise shifts the position of the
    heart leftwards, enlarged appearance on CXR.
  • ECG shows increase in benign dysrhythmias,
    reversible ST, T and Q wave changes and some LAD.

19
  • The findings indicating heart disease
  • overtly symptomatic patient
  • systolic murmurgtgrade III
  • any diastolic murmur
  • severe arrythmias
  • unequivocal cardiac enlargement on chest X
    ray.

20
  • Maternal BV markedly ?during pregnancy.
  • Immediate post-partum-- 35-40 ?in BV, due to
    auto transfusion of 300-500 ml blood.
  • Healthy parturient - tolerate up to 1500 mL of
    blood loss.
  • Women with cardiac and pulmonary disease remain
    at risk after the delivery due to ?CO.
  • Epidural block beneficial -cardiac diseases.
  • Normal nonpregnant blood volume is reached by
    7-14 days post partum.

21
CVSMeasurement of BP.
  • Auscultatory better than oscillometric.
  • Diastolic BP represents Phase V(disappearance)
    Korotkoffs not Phase IV(muffling).
  • Position Dependent left arm in the left
    decubitus .
  • SV(?)
  • SBP
    ?SBP unaffected
  • vsl distensibility(?complianc
    e)
  • BP
  • DBP SVR(?)
    DBP ?

22
  • Despite ?CO, BP remains static during pregnancy
    because of 21 and 34 ? in systemic and
    pulmonary vascular resistance and an ? aortic
    compliance.
  • Oxytocin with a free water infusion can cause
    volume overload.
  • High Hb. level(gt14gm) indicates a low volume
    state caused by preeclampsia, HT or inappropriate
    diuretics

23
  • AORTOCAVAL COMPRESSION
  • 15 pregnant patients near term develop signs of
    shock, hypotension, pallor, sweating, nausea,
    vomiting when they assume supine position.
  • This syndrome was described by Howard et al as
    supine hypotension syndrome now known as
    aortocaval compression syndrome.
  • Symptoms are because of the lack of the venous
    return to the heart.
  • Compression of the IVC is most common in the late
    pregnancy.

24
Compression of aorta IVC in supine lateral
tilt position
25
  • Pooling of the venous blood and ?venous pressure
    in the lower torso and lower extremities cause ?
  • tendency towards phlebitis and venous
    varicosities.
  • Blood from the obstructed IVC ?
    paravertebral(epidural) veins ? azygos system.
    Venodilatation ? accidental epidural vein
    puncture.
  • Prevention Left uterine displacement(LUD).
  • Left tilt of the table by 15 degrees or wedge or
    bag to elevate the right buttock and back by
    10-15 cms.
  • Avoid trendlenburg position without LUD.

26
NERVOUS SYSTEM CHANGES
  • ?MAC near term.
  • MAC returns to normal values within 3-5 days
    after delivery.
  • ?maternal beta- endorphins.
  • Increased intra abdominal pressure ? Engorgement
    of epidural veins? ? spinal CSF volume
    accidental intravascular injection in epidural or
    caudal block.
  • ? lumbar lordosis.
  • Apex of thoracic kyphosis at a higher level.

27
  • 30 reduction in the LA requirements for SAB.
  • Swelling of the epidural veins ??CSF
    volume.
  • Labor? ?CSF pressure.
  • ?neurosensitivity to LA.
  • ? cephalad spread caused by widening of the
    pelvis when the injections are made in the
    patients in the lateral position.

28
Pelvic widening resultant head down tilt
29
GIT Changes
  • LES tone? d/t upward gastric displacement by the
    gravid uterus, muscle relaxation by the
    progestins.
  • Gastric emptying may be prolonged during
    pregnancy but certainly during labor(? by opiates
    and anticholinergics).
  • Gastrin secreted from placenta??acid, chloride
    content, volume and enzyme levels of the stomach.
  • Increased chances of aspiration d/t ? LES tone,
    nausea, obesity, drugs, ketosis, recent food
    ingestion.

30
Gastrointestinal system
Anatomical 1. ?Angle of GE junction 2. Cephalad
displacement of stomach intestine 3.
Vertical rather than horizontal stomach



Physiological 1. Relaxed LES (progesterone)
?barrier P. 2. Delayed gastric emptying
(narcotics, anticholinergics, pain of
labour)
31
  • At risk for Mendelsons syndrome due to acid
    material.
  • Solid material a/w atelectasis, lung abscess and
    mechanical obstruction.

32
Anaesthetic implications
  • Risk of aspiration pneumonitis
  • Ph lt 2.5 (nearly all)
  • Gastric vol gt 25 ml ( 60)
  • ? LES tone ? intragastric P ? gastric
    emptying
  • Recent food intake prior to labour/ surgery

1. Consider gravida as FULL STOMACH beyond 1st trimester
2. Give aspiration prophylaxis
3. Regional anaesthesia / inhalational analgesia preferred
4. Plan RSI
33
RENAL CHANGES
  • ?RPF- 40-90
  • ?GFR- 50-60 by 4th month of gestation and
    return to normal by 3rd TM.
  • ?RPF and GFR ??creatinine clearance, ?upper limit
    of normal BUN and creatinine by 40.
  • Normal pregnancy- BUN- 6-9mg/dl and
    creatinine-0.4-0.6 mg/dl.
  • ? RAAS activity??total body sodium and water.
  • Threshold for ADH secretion reset??plasma
    osmolality

34
  • ?angiotensin but ?sensitivity
  • Glucosuria of 1-10 gms and proteinuria of 300
    mg/day common.
  • Renal calyces, pelvis and ureters dilate after
    3rd month of gestation progesterone and
    compression of ureters at the pelvic brim.
  • Urinary stasis?frequent UTIs

35
Hepatic and Endocrine
  • ?SGOT, LDH, ALP, GGT and cholesterol levels.
  • Abnormal bromsulphthalein excretion test.
  • Serum bil.- unaltered.
  • Total protein and AG ratio-?, ?ser. albumin.
  • Unbound plasma cortisol-2.5X
  • Serum cholinesterase activity-?24 before
    delivery and by 33 at 3 days post partum, normal
    by 2-6 weeks post partum.

36
  • ?bound T3 and T4 by 50, free hormones are normal
  • ? Calcium dependent nitric oxide synthase
    activity.
  • ?ANP
  • ?insulin sensitivity in the last half of
    pregnancy d/t placental insulinase production.
  • ?resting blood glucose levels and ?post prandial
    blood glucose levels.

37
Endocrine
ensure continuous
glucose supply to foetus
GLUCOSE METABOLISM
4
Estrogen, progesterone Hpl, prolactin,
contrainsulin factors cortisol,
FFA
hyperinsulinemia (resistance)


lipogenesis, hyperlipidemia, hyperketonemia

Fasting hypoglycemia (foetal consumption) PP
hyperglycemia hyperinsulinemia
38
Uteroplacental circulationPlacental anatomy.
  • Placenta - villous haemochorial type.
  • At term wt- 500 gm, diameter 20cms, 3 cm thick.
    Normal fetal to placental weight ratio 61
  • Fetal maternal blood is separated by 3
    structures
  • cytotrophoblast.
  • syncytiotrophoblast(metabolically active), has
    got endocrine function.
  • connective tissue.

39
  • The placenta - consist of a basal and a chorionic
    plate.
  • a semipermeable membrane -interface for the
    maternal and fetal circulation.
  • The intervillous space separates the plates and
    is subdivided by decidual tissue.
  • Chorionic villi and spiral arteries protrude into
    this intervillous space.
  • Maternal blood flows into the intervillous
    space(80) from the spiral artery.

40
Placental Anatomy cont.
41
Mechanisms of exchange.
  • Substances are exchanged across the placenta by 5
    mechanism
  • Diffusion ( FA.CO2.respiratory gases,Na)
  • Active transport.(AA.Ca,Fe,water sol vitamin) a.
    Primary active transport. b. Secondary active
    transport.
  • Bulk flow.
  • Pinocytosis ( Fe).
  • Breaks

42
Uterine Blood Flow
  • ? throughout the pregnancy, at term700ml/min10
    of the CO
  • Blood flow? and resistance ?
  • Maximally dilated under normal conditions, no
    autoregulation, capable of VC by alpha adrenergic
    action, unresponsive to ? gas tensions.
  • Flow proportional to mean perfusion pressure.

43
Factors causing decreased uterine blood flow
  • Uterine contractions
  • Hypertonus abruptio placentae, tetanic
    contractions, overstimulation with oxytocin.
  • Hypotension sympathectomy, hypovolemic shock,
    aortocaval compression.
  • Hypertension essential, pre-eclamptic.
  • Vasoconstriction endogenous sympathetic
    discharge, adrenal medullary activity.
  • Vasoconstrictors exogenous most
    sympathomimetics, exception is ephedrine(B
    adrenergic)

44
Summary
  • CO increases during pregnancy as a result of ?SV
    and HR.
  • Pregnant women should not lie supine after 20
    weeks of gestation to prevent aortocaval
    compression.
  • Increased blood volume of pregnancy allows the
    parturient to tolerate blood loss of delivery
    with minimal hemodynamic perturbation.
  • Oxygen demand and delivery both are increased.

45
  • Higher sympathetic tone in pregnancy.
  • Pre-oxygenation mandatory.
  • Increased risk of failed intubation.
  • Sensitivity to inhaled anesthetics and local
    anesthetics-?.
  • Analgesia for labor requires epidural block-
  • T10-L1- 1st stage of labor.
  • T12-S4- 2nd stage of labor.

46
References
  • Obstetric anaesthesia principles and practice-
    David H Chestnut
  • Obstetric anaesthesia- Schneider, 2nd edition.
  • Anaesthesia Co-existing diseases-Stoelting
  • Millers anaesthesia- 7th edition.
  • Clinical anesthesiology by Morgan et al - 4th
    edition
  • Textbook of obstetrics- DC Dutta

47
Thank You
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email anaesthesia.co.in_at_gmail.com
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