FRCA Notes

Anaesthesia and non-obstetric surgery in pregnancy

Neither the core nor intermediate curriculum explicitly mention knowledge of this topic, choosing to dance euphemistically around it with items such as: "explains why anaesthetic techniques must be modified in the pregnant patient" and "explains the potential impact of anaesthetic technique on patient outcome".

Nevertheless, this topic has appeared as either SAQ or CRQ on four occasions in the past ten years; 2014 (33% pass rate), 2016 (58%), 2019 (32%) and most recently in 2022 (50%).

The examiners reports, aside from lamenting generally poor answers, consistently make reference to a lack of knowledge on risks to the foetus and steps in reducing these.

A recent BJA Education article on the topic raises suspicion of the question reappearing in a CRQ soon...

Resources

  • Approximately 1 - 2% of pregnant women require non-obstetric surgery during their pregnancy
  • Challenges arise from a need to simultaneously:
    • Ensure the safety of the parturient
    • Consider foetal wellbeing and minimise foetal risk
    • Account for the physiological, anatomical and pharmacological changes associated with pregnancy

Common indications for non-obstetric surgery in pregnancy
Appendicitis
Cholecystitis
Trauma
Malignancy
For other gynaecological disease

Timing of non-obstetric surgery in pregnancy

  • First trimester - 45%
  • Second trimester - 35%
  • Third trimester - 20%

Maternal

  • Peri-operative maternal outcomes for general abdominal, pelvic and trauma surgery are similar to those of non-pregnant women
  • The rate of 30-day mortality and overall morbidity is not different between pregnant and non-pregnant women undergoing the same surgery
  • Studies support use of a laparoscopic approach with inflation pressure <15mmHg as it is associated with fewer materno-foetal complications

  • Common maternal complications include:
    • Reoperation (3.6%)
    • Infection (2%) or other wound-associated morbidity (1.4%)
    • Prolonged mechanical ventilation or need for re-intubation (2.0%)
    • VTE (0.5%)
    • Death (0.25%)

Foetal

  • Foetal risks arise from:
    • The disease process itself
    • Intra-operative disturbances to uteroplacental blood flow i.e. maternal hypoxia/hypotension
    • Anaesthetic drugs
      • All modern anaesthetic agents at clinical doses are not reported to be teratogenic
      • Inadequate evidence base to establish effects of anaesthesia on neurodevelopment, but using regional techniques and reducing duration of GA is advised
    • Surgery

  • Said risks include:

Foetal Risk Notes
Foetal loss Risk of spontaneous miscarriage during the 1st trimester (10.5%) or overall (5.8%) is 3x higher than parturients not undergoing surgery
Pre-term labour 50% higher than patients who aren't undergoing surgery in pregnancy
Risk increases as the pregnancy progresses
Need for LSCS Higher
Low birth weight Higher incidence


  • Exposure to anaesthesia may adversely affect neurodevelopment in the foetus, therefore:
    • Elective surgery is contraindicated in pregnancy
    • Elective surgery should be delayed until at least 6 weeks post-partum
    • If surgery cannot be delayed until after delivery, the 2nd trimester (13 - 28 weeks) may be the optimal timing

Effects by gestational age


Gestation Effect
<2 weeks 'All or nothing' i.e. no effect or pregnancy will be lost
3 - 8 weeks Anaesthesia is best avoided as organogenesis is taking place
>8 weeks Risk of growth retardation, premature delivery/labour and foetal loss
>28 weeks (3rd trimester) Risk of precipitating premature labour

Factors to consider

  • The disease process
    • Acute infectious or inflammatory illnesses requiring surgery can induce pre-term labour due to increased uterine irritability via:
      • The disease process itself
      • Maternal pyrexia
      • Surgical handling of uterus intra-operatively, intentional or not
  • The proposed surgery and whether regional techniques might be suitable
  • The seniority of the team; ideally senior surgeon and senior anaesthetist
  • Stage of pregnancy and its physiological effects
  • Choice of anaesthetic drugs and foetal impact (see below)

Induction agents

  • Propofol
    • Does not alter uterine blood flow but decreases perinatal survival, so manufacturer advises against use in pregnancy
    • Often used as first line induction agent for pregnant patients due to familiarity amongst anaesthetists

  • Thiopentone
    • In animal studies is teratogenic in high doses
    • Causes reduced uteroplacental blood flow (up to 35%) due to cardio-depressant effect and reduced SVR
    • Increased risk of AAGA in pregnant patients undergoing GA LSCS using thiopentone

  • Ketamine
    • Can increase uterine tone and therefore reduce uteroplacental blood flow, so should be avoided

NMBA

  • Are non-teratogenic
  • The drugs do not (readily) cross the placenta due to being bulky, water-soluble, charged molecules
  • There may be prolonged duration of action (except atracurium) due to:
    • Alterations in hepatic metabolism of aminosteroid agents
    • Acquired pseudocholinesterase deficiency affecting suxamethonium

  • Of note, sugammadex is not recommended for routine reversal of neuromuscular block in pregnancy
  • It can encapsulate progesterone and potentially disrupt the integrity of the pregnancy

Volatile agents

  • Nitrous oxide
    • Teratogenic in rats if used at high concentration for prolonged periods
    • As such is felt to be safe for use in humans due to short time periods and as Entonox

  • Volatile agents
    • Potential teratogenicity in animals
    • Effects in pregnant humans unclear; sevoflurane or isoflurane recommended if use is required
    • Cause relaxation of the gravid uterus and are therefore not likely to cause pre-term labour
    • NB MAC is reduced by the effect of progesterone

Analgesics

  • Paracetamol is not known to be harmful in pregnancy
  • Opioids are considered safe in pregnancy at appropriate doses
  • NSAIDs are contraindicated
    • May cause closure of the ductus arteriosus in utero and persistent pulmonary HTN of the new-born
  • Amide local anaesthetics are not teratogenic but can increase uterine tone so should be avoided

Perioperative management of the parturient undergoing non-obstetric surgery during pregnancy


  • Standard anaesthetic pre-assessment, though naturally comes with an obstetric twist
  • Perform essential investigations only
  • Ensure adequate VTE prophylaxis
  • Standard fasting rules apply
    • Routine antacid/prokinetic prophylaxis from 12 - 14 weeks gestation due to delayed gastric emptying, relaxed LOS and reflux risk
    • Some suggestion this is overkill and an individualised approach may be preferable

  • Assess foetal wellbeing with ultrasound and CTG; document foetal heart rate

Monitoring

  • AAGBI as standard
  • Arterial line may facilitate better steadying of the haemodynamic ship
  • Foetal monitoring if practicable, although CTG may look abnormal under GA and requires specialist interpretation

Choice of technique

  • Use regional technique wherever possible
  • Moderate and deep sedation have both been used safely in pregnancy
  • LMA relatively contraindicated from 12 weeks onwards due to delayed gastric emptying
  • RSI technique relatively indicated due to higher aspiration risk (although evidence base would suggest this may not be as great as is described)
  • Be mindful of higher incidence of difficult airway and hypoxaemia from reduced FRC

Positioning

  • Left lateral tilt from 18 - 20 weeks to mitigate effects of aortocaval compression

Other goals

  • Maintain normal physiology as much as possible (obviousy)
  • Maintain uteroplacental blood flow by avoiding hypoxia or deranged CO2
  • Minimise uterine handling
  • Ensure adequate intra-operative VTE prophylaxis

  • Foetal heart rate monitoring
  • Ongoing lateral tilt
  • Analgesia: paracetamol + opioids + regional technique ± local anaesthetic wound infiltration
  • VTE prophylaxis