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Anaesthesia in Pregnancy

for Non-obstetric surgery

  • Occurs in 2 % of women
  • Incidence of conditions similar to the non pregnant population.
  • Balances the needs of two patients.

Foetal Safety

Airway

Intrauterine asphyxia is the greatest risk of surgery.

  • Extreme care to maintain maternal oxygenation and haemodynamic stability

  • Maternal hypoxaemia = uteroplacental vasoconstriction

  • Uteroplacental circulation NOT autoregulated therefore entirely dependent on adequate maternal BP & CO

Issues:

  • Bag mask ventilation more challenging due to increased soft tissues in the neck
  • Laryngoscopy more difficult
  • Increased vocal cord oedema and vascularity.
  • Rapid desaturation

Technique:

  • Careful 02 Pre-ox. ET02 > 0.9
  • Head up pre-ox
  • Consider polio or short handle

Breathing

oEsophageal (LOS Tone)

Issues:

  • 02 demand increased up to 60% at term
  • Met by increased CO and MV
  • MV - secondary to increased respiratory rate (progesterone = respiratory stimulant.
  • Mild alkalosis with renal compensation
  • Decreased FRC. Exacerbated by supine position.

Technique:

  • Maintain relative hypocarbia to preserve faeto-maternal C02 diffusion gradient.

Gastro-intestinal Changes:

  • Reduced LOS tone secondary to progesterone
  • Increased risk of aspiration exacerbated by anatomical changes

Technique:

  • >16 wks gestation consider aspiration prophylaxis.
  • RSI with cricoid pressure
  • Extubate fully awake in LL position.

Circulation:

Drugs:

Issues:

  • CO increased by 50%. Peaks end of 2nd Trimester.
  • Mediated by SV 30% and HR by 25%
  • Contractility unchanged
  • ECG - LAD, mild ST changes, flow murmurs.
  • Aorto-veno compression - affects CO by 20%!
  • 35% increase in circulating volume (mainly plasma.
  • Pro-thrombotic state.

Technique:

  • 15 deg left lateral tilt
  • Thromboprophylaxis as appropriate.

Pharmacokinetics:

  • MAC reduced by 30% (circulating endorphins, progesterone & oestrogen).
  • Decreased in plasma cholinesterase levels
  • Decreased plasma protein binding secondary to physiological hypoalbinaemia

Teratogenicity:

  • 1st 2 weeks = all or nothing phenomenon
  • 3 - 8 weeks most important time for organogenesis
  • Generally foetus is at greater risk of asphyxia than teratogenic effect of anaesthetic drugs.
  • Drugs to avoid

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