Pregnancy physiology and anesthetia for anesthetia

1. Physiological Changes in Pregnancy
and Anaesthetic Implications
Understanding Maternal Adaptations and Their Impact
on Anaesthetic Management
DR SAMADHAN B.PAGARE
JUNIOR RESIDENT
MD ANAESTHESIA
LTMMC SION MUMBAI

2. Introduction
• - A series of physiological and anatomical
adaptations occur in pregnancy
• - These changes affect all organ systems to meet the
needs of the mother and the fetus
• Largely due to oestrogen and progesterone.
• - Important for safe anaesthetic planning and
management because it’s a unique challenge to
anaesthetist to take care of two patients
simultaneously.

3. .
• This changes can be due to
• HORMONAL ALTERATION
• MECHANICAL EFFECT OF GRAVID UTERUS
• INCREASED OXYGEN AND METABOLIC
REQUIREMENT
• HAEMODYNAMICAL ALTERATION

4. CARDIOVASCULAR SYSTYM
- ↑ Blood volume (up to 40–50%)
- volume 45%
- Heart Rate , stroke Volume (20-50%)
• - ↑ Cardiac output (30–50%)
• - ↓ Systemic vascular resistance
• - Supine hypotension syndrome (aortocaval compression)
• CVP / PAWP( pulm.artery wedge pressure) UNCHANGED

5. ……
• Fluid retention is most fundamental systemic
change during normal pregnancy
• Total plasma volume is increased 45% with marked
expansion occur in ECF with some increased in
intracellular water
• Factors contributing..
• Increased sodium retention
• Decreased in thirst threshold
• Decreased in plasma oncotic pressure

6. …….
• At term maternal blood volume has increased by
1000-1500 ml ,allowing to tolerate the blood loss
associate with delivery
• Normal delivery = 400-500 ml
• C section =800-1000 ml blood loss
• Blood volume wll return to normal after 1-2 weeks
after delivery

7. ………
• Cardiac output (40%) increased to meet accelerates maternal
and fetal metabolic demand
• This is due to increased in stroke volume (30%) as heart rate
increased only slightly
• Heart rate elevation occurs in response to increased o2
demand
• Co – 40% at 12 weeks
• _50% for rest of pregnancy
• 60- 100 % during labour and after delivery
• CO highest right after delivery( release of aorto-caval
compression ) due to uterine contraction

8. …….
• Peripheral vascular resistance decreases due to
vaso-dilatory effect of progesterone and the
proliferation of low resistance vascular bed in the
inter-villous spaces of the placenta
• Despite the increase in blood volume there is no
changes in central venous pressure (CVP) during
pregnancy ,this is likely due to dilated systemic and
pulmonary circulations.
• Cardiac chambars enlarge and myocardial
hypertrophy is noted on ECG

9. Anaesthetic Implications – CVS
• - Hypotension risk with regional anaesthesia
• -- Fluid preloading before neuro-axial ax
• It preserve utero placental blood flow
• - Avoid supine position (left lateral tilt) – Aorto-
caval compression -- blood flow to kidneys ,utero-
placental circulation and LL -- Fetal hypoxia
• - Increased risk of pulmonary oedema
• - Careful fluid and vasopressor use

10. Respiratory Changes
• Changes in the RS during pregnancy involves the upper
airways, minute ventilation ,lung volumes and oxygen
consumptions
• - ↑ Tidal volume -40% to eliminates co2
• minute ventilation – 50%
• - ↓ Functional residual capacity (FRC) - 20%
• - ↑ Oxygen consumption – 20-50 %
• - RR – unchanged or slightly increased
• - Airway mucosal oedema

11. ……
• Major physiological changes in RS are due to a
combination of both hormonal and mechanical factors.
• Dyspnea is common complaints in pregnancy
• Due to increased metabolic demand o2 consumption
and MV increased, increased progesterone – sensitized
respiratory centers to carborn dioxide – directly
stimulating ventilation
• Paco2 decreased to (28-32) ; significant respiratory
alkalosis is prevented by a compensatory decreased in
hco3 concentration

12. Anaesthetic Implications –
Respiratory
• - Rapid desaturation during apnoea -
preoxygenation prior to induction to avoid hypoxia
• - Difficult airway (edema, weight gain)– smaller
endotracheal tubes if needed
• Adjust ventilator settings for increased minute
ventilation
• Risk of aspiration due to decreased lower
esophageal sphincter tone

13. Gastrointestinal Changes
Upward and ant.displacement of the stomach by
gravid uterus – incompetence of gastro-esophageal
sphincter -↓ Lower oesophageal sphincter
tone( increased progesterone) – risk of aspiration
• - ↑ Intragastric pressure
• Hyper –secretion of gastric acid due to increased
placental Gastin
• - Delayed gastric emptying

14. Anaesthetic Implications – GI
• Narcotics and anti cholinergic reduce lower
esophageal sphincter pressure used with
precaution
• Pharmacological prophylaxis against aspiration
• - Use of antacids, H₂ blockers, prokinetics
• Supine position with lateral tilt
• No positive pressure ventilation before intubation
• - Rapid sequence induction (RSI) for GA

15. Haematological Changes
• - ↑ Plasma volume > ↑ RBC mass → physiological
anaemia
• - ↑ Clotting factors → hypercoagulable state
• - ↓ Platelets (mild thrombocytopenia)

16. Anaesthetic Implications –
Haematology
• - Assess coagulation before neuraxial block
• - Risk of thromboembolism
• - DVT prophylaxis may be needed

17. Central Nervous System Changes
• - ↑ Sensitivity to anaesthetic agents due to high
progesterone
• - ↓ MAC (minimum alveolar concentration) (30%) –
for volatile anesthetics
• - Engorgement of epidural veins increased risk of
epidural hematoma

18. Anaesthetic Implications – CNS
• - Reduced dose of local anaesthetics –
increased diffusion of LA to the receptor site
- increased sensitivity of nerve fibers to LA
( LOWER CONC NEEDED)
-
• - Increased risk of high spinal block
• - Caution with epidural placement

19. RENAL CHANGES
• Renal vasodilatation increased renal blood flow
early during pregnancy
• Increased cardiac output – increased GFR and RPF
(renal plasma flow ) by 50%
• Increased RENIN AND Aldosterone level promote
Na + retention leading to volume overload
• Decreased renal tubular threshold for glucose and
amino acid – mild glycosuria and proteinuria

20. Anaesthetic importance
• = clearance of urea ,uric acid and creatinine
•
• plasma concentration of sr,creatinine and
BUN
• BUN and creatinine levels that would be considered
marginally elevated in pre-pregnant patients are usually
indicative of severe renal imparement in pregnancy

21. Hepatic effect
• Hepatic function and blood flow are unchanged
• A mild decreased in sr albumin is due to an
expanded plasma volume .Thus the free fraction of
albumin-bound medication is increased
• A 25-30% decreased in sr psuedocholinesterase
activity is also present at term ,but it rarely
produces prolongation of succinylcholine action
• Increased cholesterol gall stone formation
(progesterone)

22. Conclusion
• - Pregnancy alters physiology significantly
• - Anaesthetic techniques must be adapted –careful attention
to assessment of the airway ,preoxygenation is essential and
should be with tight face mask for at least 3 mint
• Rapid sequence induction with cricoid pressure is mandatory
• Intubation may be difficult be ready for difficult intubation
preparation
• The MAC is slightly reduced
• - Understanding changes improves maternal and fetal
outcomes

23. Do good to others ,it will come in unexpected ways……. Buddha