physiological changes-in-pregnancy 1
TRANSCRIPT
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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