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Physiological Changes In Pregnancy

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Describes the various physicilogical changes in pregnancy

Describes the various physicilogical changes in pregnancy

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  • 1. Physiological changes in Pregnancy & its Anaesthetic implications
    • Dr. Shailendra.V.L. MBBS, DA, MD.
    • Specialist in Anaesthesia,
    • Bukariya General Hospital.
  • 2. Introduction
    • Rapidly growing fetus
    • Rising levels of progesterone, oestrogen, prostaglandin & HCG
    • Increasing size of uterus
    • All systems undergo changes
    • Placenta
  • 3. Changes in the pregnant patient
    • Changes due to uterine enlargement
    • Changes to support the foetus
  • 4. Changes in the systems
    • Cardiovascular System
    • Respiratory System
    • Haemopoietic System
    • Hepatic System
    • Renal System
    • Gastro-intestinal System
    • Metabolism & Nutrition
    • Central Nervous System
  • 5. Changes in uterus
    • Uterine blood flow increases from 50 ml/ min to 700 – 800 ml /min
    • Uterine weight increases from 30-60 g to 1000 g
  • 6. Uterine blood flow
    • Uterine Blood Flow - UBF:
      • Uteroplacental vascular bed is passive capacitance bed
      • Intervillous blood flow exhibits no auto regulation
      • UBF dependent on mean arterial pressure, aorto-caval compression & cardiac output
  • 7. Cardiovascular system
    • Changes in the cardiovascular system:
    • Intravascular fluid volume: + 35%
    • Plasma volume: + 45%
    • Erythrocyte volume: + 20%
    • Cardiac Output: + 40%
    • Stroke volume: + 30%
    • Heart rate: + 15%
    • Peripheral Circulation:
    • Systolic BP: no change
    • Diastolic BP: - 15%
    • Systemic Vascular Resistance: - 15%
    • Femoral venous pressure: + 15%
  • 8.  
  • 9. Cardiovascular system
    • Mean arterial pressure: MAP:
      • -Inspite of increase of cardiac output, MAP is maintained due to concomitant decrease in peripheral resistance
  • 10. Cardiovascular system
    • Compression of Inferior Venacava: IVC:
      • In supine position the gravid uterus compresses the IVC and decreases the CO without fall in the blood pressure called as Concealed caval compression.
      • Reasons for no fall in blood pressure are:
        • Reflex vaso constriction
        • Diversion of blood through paravertebral venous plexus
  • 11. Cardiovascular system
    • 8 to 15% of pregnant women have Overt Caval Compression (supine hypotensive syndrome)
      • Hypotension
      • Sweating
      • Bradycardia
      • Pallor
      • Nausea
      • Vomiting
    • Prevention of SHS: (aim is to displace the uterus)
      • Providing left lateral tilt 15 degrees
      • Placing wedge under the right buttock
  • 12. Cardiovascular system
    • Poseiro Effect:
    • Uterine artery is compressed during
    • uterine contractions & by the presenting
    • part of the fetus reducing the UBF
  • 13. Cardiovascular system
    • Physiological Anaemia in Pregnancy:
    • Total red cell mass increase by 30% (250-450ml)
    • Plasma volume increase by 50% (about 1250ml)
    • Overall increase of 40% blood volume with fall in haematocrit
  • 14. Cardiovascular system
    • Heart rate: increases by about 15 beats /min
    • Arterial pressure: minimal change noted
    • Heart Size: Gravid uterus pushes the diaphragm cepahalad & displaces the heart.
      • ECG shows false left axis deviation
      • Chest X ray shows (false) cardiac dilatation
  • 15. Respiratory system
    • Changes in the respiratory system:
    • Minute volume: + 50%
    • Tidal volume: + 40%
    • Breathing rate: + 10%
    • FRC: - 20%
    • Expiratory reserve volume: - 20%
    • Residual volume: - 20%
    • Oxygen consumption: + 20%
  • 16.  
  • 17. Respiratory system
    • Edematous mucosa of upper resp tract:
      • Smaller Et tubes
      • Gentle suctioning & larngoscopy
    • Decreased FRC, ERV,RV:
    • Increased O2 consumption:
      • Pre-oxygenation prior to induced apnea
    • Rate of fall in PaO2 per minute of apnea is 159mm hg in pregnant and 59 mm hg in non-pregnant state
  • 18.  
  • 19. Haemopoietic system
    • Physiological anemia of pregnancy
    • Fibrinogen, factors VII, VIII and X increased
    • Makes the blood hypercoaguable & increases the risk of thromboembolism
    • This hypercoaguability along with uterine inversion helps in reducing blood loss after delivery
  • 20.  
  • 21. Gastro-intestinal system
    • Decrease in lower oesophageal tone
    • Delay in gastric emptying:
      • Pylorus is pushed upwards & forwards making it non-dependent
      • Relaxant effect on gastric smooth muscle
    • Increased intragastric pressure
  • 22. Hepatic system
    • No alterations in the liver function
    • Serum cholinesterase activity 
    • Does not interfere with the suxamethonium (Scoline) R metabolism
  • 23. Renal system
    • Renal plasma flow ↑
    • Glowmerular filtration rate ↑
    • Tubular reabsorbtion rate ↑
    • Blood Urea Nitrogen 40% 
  • 24.  
  • 25. Metabolism & Nutrition
    • Basal metabolic rate: ↑ by 15 to 20%
    • Weight gain upto 11 kgs
    • Serum protein concentration ↓
    • Albumin concentration ↓
    • Drugs are less bound to serum proteins thereby increasing the free drug availability
  • 26. Nervous system
    • ↓ in minimum alveolar concentrations
    • exaggerated lumbar lardosis contribute to cephalad spread of the local anaesthetic
    • engorged epidural plexus of veins will decrease the amount of the local anaesthetic in epidural blocks
    • engorged epidural veins will block the inter-vertebral foramina and prevent the escape of the local anaesthetic
  • 27. Placental functions
    • Metabolism
    • Endocrine secretion
      • Human chorionic gonadotrophin
      • Human chorionic somatotrophin
      • Progesterone
      • Estrogen
    • Molecular transfer
  • 28. Placental blood flow
    • Placental Blood Flow = 500-700ml/min
    • ( approximately 10% of the Cardiac output)
    • Maternal blood pressure
    • Maternal cardiac output
    • Vasomotor tone of the uterine vessels
    • Pathological changes of the placenta
    • State of uterine contraction
  • 29. Placental drug transfer
    • Passive-diffusion is the mechanism
    • Q/t = {k x A x (Cm-Cf)} / D
    • Q: quantity of free drug (non ionized & non protein bound) crossing to placenta
    • t : per unit of time
    • k: diffusional coefficient of the drug
    • A: total area available for transfer
    • Cm-Cf: difference between maternal & fetal drug concentrations
    • D: distance across the membrane
  • 30. Placental transfer of drugs
    • Diffusion Coefficient depends on:
      • molecular weight
      • spatial configuration
      • degree of ionization
      • lipid solubility
    • Most anaesthesia drugs cross the placental barrier except the muscle relaxants because of their large size molecule (quaternary ammonia compounds)
  • 31. Anaesthetic implications
    • Pre-anaesthetic considerations:
      • Starvation
      • Respiratory infection
      • Prophylaxis against pulmonary aspiration
  • 32. Anaesthetic implications
    • General Anaesthesia:
      • Posture
      • Tracheal Intubation
      • Placental transfer of drugs
      • Pre oxygenation
  • 33. Anaesthetic implications
    • Regional Anaesthesia:
      • Posture
      • Technique
      • Vasopressors
      • Oxygen supplementation
  • 34. Summary
    • Cardiovascular changes
    • Respiratory changes
    • Gastro-intestinal changes
    • Haemopoietic changes
    • Placental transfer of drugs
  • 35. Bibliography
    • Anaesthesia & Co-existing diseases-Stoelting
    • Short Practice of Anaesthesia – Churchill Davidson
    • Refresher Course Lectures, Manipal, ISA 1989
  • 36.
    • Thank you

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