Physiological changes-in-pregnancy 1

Physiological changes in pregnancy

Dr Megha AggarwalUniversity College of Medical Sciences & GTB

Hospital, Delhi

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Today’s seminar

1. Introduction

2. Why to know the changes during pegnancy

3. Systems affected

4. Anaesthetic implications

5. Changes during labour

6. Changes during puerperium

Introduction

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 affectedBody wt & metabolism

Respiratory

Cardiovascular

Hematopoietic

Gastrointestinal

CNS

Hepatobiliary

Renal

Endocrine

Pharmacological

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

Respiratory1. 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) Se) Subglottic airway dilatation (progesterone, cortisone,

relaxin) →↓pulmonary resistance (-50%)

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

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 diaphragmaticdiaphragmatic > thoracic - advantage during high regional blockade

Continued…

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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 > ↑O2 consumption → ↑ ∆ AV O2

late gestation: ↑CO < ↑O2 consumption → ↓ ∆ AV O2

e) FRC < closing capacity → small airways close

during normal tidal ventilation → predisposes to hypoxia

Anaesthetic implications

PARAMETER CONSEQUENCE

1. MV ↑ Faster denitrogenation

2. ↓FRC + ↑O2 consumption Rapid hypoxia during apnoea

3. ↑MV + ↓FRC Faster inhalational inductionFaster emergenceFaster changes in depth

4. Mucosal engorgement Difficult airway

5. Predominant diaphragmatic breathing

High spinal does not affect MV & PaCO2 much

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)

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

Continued…

PARAMETER CHANGE

1.CO +40%

2. SV +30%

3. HR +15%

4. SBP No changeNo change

5. DBP -15%-15%

6. SVR -15%

7. Femoral venous P +15%

Note: fall in DBP while SBP is unaffected

Continued…

Continued…

Blood pressure

Position Age Parity max. in supine ↑with age nullipara> multipara min. in lateral

SV(↑) SBP SBP unaffected vsl distensibility(↑compliance)BP

DBP SVR(↓) DBP ↓

↓PP

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.

WhyWhy no fall inno fall in bloodblood pressurepressure ??1.Reflex vasoconstriction

2.Diversion of blood through paravertebral & epidural venous plexus, ovarian veins – maintains VR

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. OxfordOxford positionposition

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.

Hematology & Coagulation

PARAMETER CHANGE

1. BV +45%

2. Plasma volume + 55%

3. RBC volume +33%

4. Hemoglobin -17%

5. Hematocrit 35.5%

Table showing % change in RBC and plasma volume

T1 T2 T3 1hr 1wk 6wk

BV

(%

∆ fr

om p

rep

reg

nan

cy)

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

Plasma

RBC

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

Continued…

Coagulation

Hypercoagulable, ↑ fibrinolysis, ↑platelet turnover

↑FDP↑Plasminogen

↓AT III↑coagulation factors↑fibrinopeptide A

TEG↓PT/PTTK

BT unaltered

Gastrointestinal system

Anatomical

1. ↑Angle of GE junction2. Cephalad displacement of stomach & intestine3. Vertical rather than horizontal stomach

Physiological

1. Relaxed LES (progesterone) ↓barrier P.2. Delayed gastric emptying (narcotics, anticholinergics, pain of labour)

Anaesthetic implications

1. Consider gravida as FULL STOMACH beyond 1st trimester

2. Give aspiration prophylaxis

3. Regional anaesthesia / inhalational analgesia preferred

4. Plan RSI

Risk of aspiration pneumonitis

1. Ph < 2.5 (nearly all)

2. Gastric vol > 25 ml ( 60%)

3. ↓ LES tone + ↑ intragastric P + ↓ gastric emptying

4. Recent food intake prior to labour/ surgery

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)

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

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

Pelvic widening & resultant head down tilt

SPINAL EPIDURAL

1. 1. ↓ S↓ Segmental dose 1. 1. ↑ Dural puncture

2.2. Rapid onset & longer duration

2.2.↓↓SSensitivity of hanging drop technique (+epidural P)

3. 3. Requirement normalise at

24-48 hr PP

3.3.Unintentional i.v. injection

4. 4. ↑ Rostral spread (esp. during uterine contraction)

4. 4. ↓↓Segmental dose (small doses) (↑neural sensitivity)

5. 5. Same spread with large doses (unaltered extravascular epidural vol)

Anaesthetic implications

Hepatobiliary system

Progesterone →↓ cholecystokinin→↓GB emptyingProgesterone →↓ cholecystokinin→↓GB emptying

Altered bile compositionAltered bile composition

Serum bilirubin & liver enzymes

↑upto upper limit of normal range

Gallstones

Renal

CHANGE CONSEQUENCE

1. Renal plasma flow↑(70%)

GFR ↑ +

Plasma expansion

Renal indices < normal

(creatinine ↓0.5-0.6)

BUN ↓ 8-9)

2. ↑GFR + ↓absorption threshold

Mild glycosuria(1-10g/dl)

Proteinuria(<300mg/d)

3. Ureter & renal pelvis dilate Pyelonephritis

Progesterone + estrogen → +RAAS → Na & H2O retention

↑ 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

Continued…

Estrogen, progesteroneHpl, prolactin, contrainsulin factors cortisol, FFA

hyperinsulinemia (resistance) lipogenesis, hyperlipidemia, hyperketonemia

Fasting hypoglycemia (foetal consumption)PP hyperglycemia& hyperinsulinemia

Endocrine

GLUCOSE METABOLISM

ensure continuous glucose supply

to foetus

4

Continued…

LIPID METABOLISM ↑HDL, LDL, TG Hyperlipidemia of pregnancy is not atherogenic

PROTEIN METABOLISM + nitrogen balance

Continued…

THYROID

Thyromegaly due to ↑ placental HCG (↓TSH )

↑ T3 + T4

↑TBG (estrogen)

Free T3/T4

unchangedEuthyroid

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 β rec. )

4. Pressor response – inconsistent refractory5. LA toxicity – unaffected

Changes during labour

RESPIRATORY SYSTEM

O2 requirement > consumption → Anaerobic metabolism

Stage I Stage II

MV +75-150% +150-300%

O2 need +40% +75%

Continued… CARDIOVASCULAR SYSTEM ↑sympathetic activity

↑cardiac contractility, SVR, VR(↑CVP)

↑CO (+10,+25,+40 in stage I,II,III) (+15-25% during each contraction)

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

Continued…

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…

Hematological

Blood loss

600 ml –vaginal

delivery

1L – caesarean

section

Same for RA/GA

PARAMETER PREPREGNANT AT

BV 1st wk = 25%

6-9 wk = +10%

Hb 6 wk

Protein 6 wk

TLC D-1 = 15000

6 wk >prepreg.

Fibrinolysis Immediate postpartum

Clotting + at placental separation

Fibrinogen & platelet count

↑ D3 – D5

Thrombosis

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References

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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