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