Physiological changes in pregnancy

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Physiological changes in pregnancy

• Dr Megha Aggarwal

University College of Medical Sciences GTB
Hospital, Delhi
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Todays seminar

• Introduction
• Why to know the changes during pegnancy
• Systems affected
• Anaesthetic implications
• Changes during labour
• Changes during puerperium

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Introduction
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• Changes occur in pregnancy to
• 1. Support the foetus
• 2. Prepare mother for delivery
• Changes are due to
• 1. Hormonal changes
• 2. Increasing size of uterus
  and foetus
• 3. Anatomical changes

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Why study these changes?

1. To differentiate normal from abnormal
2. To understand its anaesthetic implications
3. To make the process of delivery smooth
4. To anticipate and manage complications

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Systems affected
Body wt metabolism
Respiratory
Cardiovascular
Hematopoietic
Gastrointestinal
CNS
Hepatobiliary
Renal
Endocrine
Pharmacological
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Body wt. metabolism

• Wt GAIN 17
• 12 kg T1 1-2 kg
• T2 5-6 kg
• T3 5-6 kg
• BMR 15 at term
• O2 consumption 35 (?needs of fetus, uterus,
  placenta)
• 40 in stage I of
  labour
• 75 in stage II of
  labour

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Respiratory

• Anatomical
• a) Rib cage and breast enlargement-
  laryngoscopy difficult
• b) Diaphragm pushed cranially- changes in
  lung vol
• c) ? mucosal engorgement
• nasal epistaxis
• nasal
  intubation difficult
• oropharyngeal smaller ETT
• ?mallampatti score
• d) ?Chest wall compliance (lung compliance
  unaffected)
• e) Subglottic airway dilatation (progesterone,
  cortisone, relaxin) ??pulmonary resistance (-50)

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Changes in lung vol and capacities
PARAMETER CHANGE
1. TV 45
2. FRC -20
3. ERV -25
4. Dead space 45
5. RR No change/
6. MV 45
7. Alveolar ventilation 45
Note change in MV is solely due to ?in TV and
not RR
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Continued
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Continued

• 2. Physiological changes
• 1. ?MV ? ? TV (RR unchanged)
• 1. Progesterone (?CNS
  sensitivity to CO2)
• 2.?CO2 production
• alkalosis (compensatory but
  incomplete?HCO3- ??pH
  . by 0.02-0.06)
• 2. Breathing diaphragmatic gt thoracic -
  advantage during high regional blockade

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Continued

• 3. Blood gases
• a) Paco2_- ?to 30 mm Hg by 30 wk, no
  further change
• b) ? Paco2_- ETco2 0 (because no. of
  unperfused
• 
  alveoli i.e. DS ? due to ?CO)
• c) ? PaO2 to 107 mmHg but ?when supine
• d) ? AV O2
• early gestation ?CO gt ?O2
  consumption ? ? ? AV O2
• late gestation ?CO lt ?O2
  consumption ? ? ? AV O2
• e) FRC lt closing capacity ? small
  airways close during normal tidal
  ventilation ? predisposes to hypoxia

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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
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Circulatory changes

• Examination- 1.Apical impulse in 4th ICS
  laterally
• 2.Loud S1
• 3.A2P2 changes less with
  respiration
• 4.S3 in 16 cases
• 5.Grade I - II early
  mid-diastolic murmur at
• left sternal border.
• 6. Asymptomatic
  pericardial effusion
• ECG 1.Sinus tachycardia ( ?PR QT interval)
• 2.ST depression T inversion in left
  precordial
• leads
• 3.Left axis deviation (false)

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Continued

• ECHO 1. Enlargement of chambers
• 2. LVH
• 3. Annular dilatation of all
  valves except Aortic
• (regurgitation)
• 4. ? LVEDV but no change in
  filling P(PCWP/CVP)
• (because of cardiac
  dilatation hypertrophy)
• 5. LVESV-unchanged
• Chest X Ray 1. Apparent cardiomegaly
• 2. ? LA (lateral view)
• 3. ? vascular markings
• 4. Straightening of left
  heart border
• 5. Pleural effusion
  

?EF
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Continued
PARAMETER CHANGE
1.CO 40
2. SV 30
3. HR 15
4. SBP No change
5. DBP -15
6. SVR -15
7. Femoral venous P 15
Note fall in DBP while SBP is unaffected
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Continued
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Continued

• Blood pressure
• Position Age
  Parity
• max. in supine ?with age
  nulliparagt multipara
• min. in lateral
• SV(?)
• SBP
  SBP unaffected
• vsl distensibility(?complianc
  e)
• BP
• DBP SVR(?)
  DBP ?

?PP
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Continued

• Aortocaval compression starts at 13-16 wk
• 1.Concealed caval compression.
• In supine position gravid uterus compresses IVC
  ?CO without fall in the blood pressure.
• Why no fall in blood pressure ?
• 1.Reflex vasoconstriction
• 2.Diversion of blood through paravertebral
  epidural venous plexus, ovarian veins maintains
  VR

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Continued

• 2.Overt caval compression (supine hypotensive
  syndrome)
• Hypotension, sweating, bradycardia, pallor,
  nausea, vomiting.
• Due to uncompensated ?VR
• Prevention of SHS (aim is to displace the
  uterus)
• 1.Providing left lateral tilt 15 degrees
  beyond 28wk
• 2.Placing wedge under the right buttock
• 3. Oxford position

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Compression of aorta IVC in supine lateral
tilt position
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Anaesthetic implications
PARAMETER CONSEQUENCE
1. ?RA filling ?SV CO (25)
2. Chronic partial IVC obstruction Venous stasis, phlebitis, edema in lower limbs
3. Epidural plexus engorged ?ed spinal LA requirement
4. Systemic hypotension ? Uterine venous P Compromised uteroplacental blood flow
Note Adverse hemodynamic effects ?ed after
engagement of fetal head.
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Hematology Coagulation
PARAMETER CHANGE
1. BV 45
2. Plasma volume 55
3. RBC volume 33
4. Hemoglobin -17
5. Hematocrit 35.5
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Table showing change in RBC and plasma volume
Plasma
RBC
BV (? from prepregnancy)
T1
T2
T3
1hr
1wk
6wk
Note 1. Hemodilution - patency of uteroplacental
vascular bed 2. Facilitates exchange of
resp. gases, nutrients metabolites 3.
Reduces impact of maternal blood loss at delivery
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Continued

• Plasma proteins
• 1. ?Total proteins - ?unbound ( active) drug
• 2. ?cholinesterase conc. (25) but no change
  in duration of action of Sch.
• Immunity
• 1. Leukocytosis mainly PMN but function is
  impaired (?chemotaxis adherence)
• a) ? Infection
• b) diagnosis difficult
• c) ? s/s of autoimmune disorders
• 2. ?Antibody titers to HSV, Measles, Influenza
  A

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Continued

• Coagulation
• Hypercoagulable, ? fibrinolysis,
  ?platelet turnover

?FDP ?Plasminogen
?AT III ?coagulation factors ?fibrinopeptide A
BT unaltered
TEG ?PT/PTTK
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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)
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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
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Nervous system

• Vertebral column
• 1. ? Lumbar lordosis - ?vertebral interspinous
  distance
• 2. Distended epidural veins ? CSF volume
• 3. Positive Lumbar epidural P (difficult
  identification)
• 4. CSF P unaffected (? during uterine
  contraction)

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Continued
1. ? pain threshold at term labour ? endogenous neuropeptides
2. ? MAC / ED95 1.Sedative effect of progesterone 2. ? CNS serotonergic activity 3. of endorphin system
Dependence on sympathetic nervous system ?
progressively a) counteracts adverse
effects of aortocaval compresion b)
greater preloading during neuraxial blockade
c) pharmacological sympathectomy can cause
marked ? in BP
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Continued

• ?Spinal anaesthetic dose requirement (25)
• 1.? Neural suseptibility to LA
• 2. Epidural plexus engorgement
• 3. CSF changes a)?CSF protein (?unbound drug)
• b)? CSF pH (?
  unionised drug)
• 4. Pelvic widening resultant head down tilt in
  lateral position
• 5. Apex of thoracic kyphosis higher

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Pelvic widening resultant head down tilt
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Anaesthetic implications
SPINAL EPIDURAL
1. ? Segmental dose 1. ? Dural puncture
2. Rapid onset longer duration 2.?Sensitivity of hanging drop technique (epidural P)
3. Requirement normalise at 24-48 hr PP 3.Unintentional i.v. injection
4. ? Rostral spread (esp. during uterine contraction) 4. ?Segmental dose (small doses) (?neural sensitivity)
5. Same spread with large doses (unaltered extravascular epidural vol)
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Hepatobiliary system

• Progesterone ?? cholecystokinin??GB emptying
• Altered bile
  composition
• Serum bilirubin liver enzymes
• ?upto upper limit of normal range

Gall stones
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Renal
Progesterone estrogen ? RAAS ? Na H2O
retention
CHANGE CONSEQUENCE
1. Renal plasma flow?(70) GFR ? Plasma expansion Renal indices lt normal (creatinine ?0.5-0.6) BUN ? 8-9)
2. ?GFR ?absorption threshold Mild glycosuria(1-10g/dl) Proteinuria(lt300mg/d)
3. Ureter renal pelvis dilate Pyelonephritis
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Continued

• ? Kidney size ? normal at 6 wk postpartum
• ? creatinine clearance ?normal at 8-12 wk
  postpartum
• ? frequency of micturition-
• 6-8wk ? resetting of osmoregulation (polyuria
  polydipsia)
• late pregnancy ? P on bladder by presenting part

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


lipogenesis, hyperlipidemia, hyperketonemia

Fasting hypoglycemia (foetal consumption) PP
hyperglycemia hyperinsulinemia
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Continued

• LIPID METABOLISM
• ?HDL, LDL, TG
• Hyperlipidemia of pregnancy is not atherogenic
• PROTEIN METABOLISM
• nitrogen balance

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Continued

• THYROIDThyromegaly due to ? placental HCG
  (?TSH )

? T3 T4
Free T3/T4 unchanged
Euthyroid
?TBG (estrogen)
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Pharmacological

• 1. Sch. - ?pseudocholinesterase (-25) but no
  effect on
• duration of action
• 2. NDMR - Rapid prolonged effect
• 3. ?Chronotropic response to isoproterenol
  epinephrine
• (downregulation of ß rec. )
• 4. Pressor response inconsistent
• refractory
• 5. LA toxicity unaffected

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Changes during labour

• RESPIRATORY SYSTEM
• O2 requirement gt consumption ? Anaerobic
  metabolism

Stage I Stage II
MV 75-150 150-300
O2 need 40 75
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Continued

• CARDIOVASCULAR SYSTEM
• ?sympathetic
  activity
• ?cardiac contractility, SVR,
  VR(?CVP)
• ?CO (10,25,40 in stage
  I,II,III)
• (15-25 during each
  contraction)

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Changes in puerperium

• Cardiovascular
• Relative hypervolemia
  ?VR (?CVP)
• (autotransfusion)
• Nervous system
• Spinal LA dose requirement reaches
  prepregnant level at 24-48 hr

TIME CO
Immediate PP 75
D-2 Just below predelivery
2 wk 10
12-24 wk Prepregnant
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Continued
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• Respiratory

PARAMETER PREPREGNANT LEVEL AT
FRC 1-2 wk
O2 consumption 6-8 wk
TV 6-8 wk
MV 6-8 wk
Alveolar PCO2 6-8 wk
Mixed venous PCO2 6-8 wk
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Continued
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PARAMETER PREPREGNANT AT
BV 1st wk 25 6-9 wk 10
Hb 6 wk
Protein 6 wk
TLC D-1 15000 6 wk gtprepreg.
Fibrinolysis Immediate postpartum
Clotting at placental separation
Fibrinogen platelet count ? D3 D5 Thrombosis

• Hematological
• Blood loss
• 600 ml vaginal
• delivery
• 1L caesarean
• section
• Same for RA/GA

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References
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• 1. Obstetric anaesthesia principles and
  practice- David H Chestnut
• 2. Anaesthesia Co-existing diseases-Stoelting
• 3. Millers anaesthesia
• 4. Short Practice of Anaesthesia Churchill
  Davidson
• 5. Textbook of obstetrics- DC Dutta

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