FRCA Notes

General Anaesthesia for LSCS

LSCS under GA was the subject of a CRQ in March 2020 (60% pass rate); the examiner feedback mostly chastised candidates for a lack of knowledge of NAP5.

Resources

  • The use of GA in the obstetric setting is decreasing, accounting for <25% of LSCS (2011)
  • Indeed it is estimated that only 6% of LSCS require GA and tracheal intubation

  • GA benefits from rapidity, with a median time of onset quicker than that of other modalities
    • In a retrospective cohort study the median time from entering theatre to knife-to-skin was 6mins, nearly half that of spinal or top-up and a quarter that of CSE
  • However it carries a number of risks which should be accounted for
  • Aspiration and pneumonitis, either at induction or emergence from anaesthesia (overall incidence rare; 2 in 10,000 GAs)
  • Difficult airway, failed intubation and higher risk of airway-related mortality and FONA
  • Higher rate of AAGA
  • Mortality, which is significantly lower than it has been historically but is still reported
  • Higher incidence of low neonatal 5min Apgar scores

Respiratory

  • Airway engorgement and potential for difficult airway → prepare for difficult airway and use smaller ETT size
  • Increase (A)MV → pre-oxygenation is quicker
  • Reduced FRC → faster desaturation during apnoeic period; 17% will experience SpO2 <90%

Cardiovascular

  • Aortocaval compression → requires left tilt lest there be reduced preload
  • Increased cardiac output → onset of action of drugs is faster, but so is their re-distribution and there is a lower peak concentration
  • Presence of hypertensive disorders of pregnancy can lead to exaggerated pressor response to laryngoscopy

Neurological

  • Reduced MAC, but higher rate of AAGA
  • Increased sensitivity to opioids

Gastrointestinal

  • The barrier pressure is reduced in pregnancy → higher risk of aspiration under GA & RSI is required from the start of the 2nd trimester onwards

  • None of the commonly used anaesthetic agents have been proven to be teratogenic, including induction agents, NMBA, opioids or local anaesthetics
  • It is critical to avoid maternal hypotension and hypoxia during GA
    • Maternal arterial pressure is the prime determinant of foetal perfusion
    • Inadequate maternal oxygenation will lead to foetal hypoxaemia

  • GA is historically linked with lower base deficit and higher umbilical artery pH than neuraxial anaesthesia
  • The effect is partly explained by the effects of aortocaval compression, maternal haemodynamics and choice of vasopressor rather than the technique itself

  • Appropriate planning and preparation:
    • Airway & anaestehtic assessment
    • Acid prophylaxis
    • Intra-uterine foetal resuscitation ongoing whilst preparing
    • Use of WHO surgical checklist and specific obstetric GA checklist

Oxygenation

  • Routine use of the head-up position to improve FRC and airway manipulation/laryngoscopy
  • Pre-oxygenation until EtO2 >90%
  • Can use tight-fitting face mask, supplemented with either HFNO or low-flow (10-15L/min) nasal oxygen (both nasal oxygenation techniques appear to be equally effective)
  • Gentle mask ventilation before intubation with pressure <20cmH2O

Drug choice

  • Propofol benefits over thiopentone from:
    • Availability
    • Familiarity
    • Reduced incidence of drug errors
    • Reduced incidence of AAGA
    • Better suppression of airway reflexes
  • Further doses of induction agent should be available and given if difficult intubation is encountered

  • Rocuronium and suxamethonium remain viable NMBA

  • Short-acting opioids may play a part in obstetric RSI, to attenuate cardiovascular responses to laryngoscopy
  • This is particularly pertinent in the pre-eclamptic parturient or those with cardiovascular disease
  • No evidence of worse neonatal outcomes or reduced Apgar scores with short-acting opioid use

Laryngoscopy

  • Routine use of a laryngoscope familiar to the anaesthetist, be it VL or DL
  • Cricoid pressure should be reduced/removed early in the event of poor view
  • Max 2+1 attempts, before following the OAA/DAS algorithm for failed intubation in Obstetrics

Analgesia


  • Awareness under GA is more common in those undergoing LSCS (1 in 670) compared to the baseline rate (1 in 19,000 overall)
  • Obstetrics accounted for 0.8% of surgeries during NAP5 but 10% of the reports of AAGA
  • Awareness is most common either at, or shortly after, induction owing to potential gap between IV drug administration and inhalational anaesthetic commencing
  • There are multiple factors associated with GA in obstetrics that make AAGA more likely:
Anaesthetic factors Patient factors Organisational factors
RSI Female gender Emergency surgery
Use of NMBA Obesity OOH surgery
Use of thiopentone Higher incidence of difficult airway Junior anaesthetist
Inadequate MAC at KTS
Drug error
(e.g. cefuroxime in place of thio.)