Anaesthetic Considerations & Management of Non-Obstetric Surgery in Pregnant Patients

1. Physiological Changes Relevant to Anaesthesia

Airway

• Oedema of upper airway mucosa (especially after 20 weeks) → increased risk of difficult/failed intubation (8× more common than non-pregnant)
• Capillary engorgement → friable mucosa, easy bleeding with airway instrumentation
• Use smaller ETT (6.5–7.0 mm); have video laryngoscopy available

Respiratory

• FRC reduced by 20–30% (diaphragm elevation)
• O₂ consumption increased ~20% → rapid desaturation on apnoea
• Hyperventilation of pregnancy: PaCO₂ ~32 mmHg (normal); avoid hypocapnia (uteroplacental vasoconstriction) and hypercapnia (fetal acidosis)
• Pre-oxygenate for ≥3 minutes before induction

Cardiovascular

• Cardiac output ↑ 40–50%, blood volume ↑ 40–50%
• Systemic vascular resistance ↓
• Aortocaval compression (after 18–20 weeks): patient must be in left lateral tilt ≥15°; supine hypotension syndrome can reduce uteroplacental flow by 30–40%
• Maintain MAP ≥ baseline (vasopressors: phenylephrine preferred in non-labouring; ephedrine acceptable but may cause fetal acidosis)

Gastrointestinal

• Progesterone → lower oesophageal sphincter tone
• Delayed gastric emptying, raised intragastric pressure from gravid uterus
• Aspiration risk from ~18–20 weeks (some advocate from the onset of progesterone effects in 1st trimester)
• Aspiration prophylaxis: sodium citrate 30 mL + ranitidine/omeprazole + metoclopramide preoperatively
• RSI with cricoid pressure is standard

Renal & Metabolic

• GFR ↑ 50%; normal creatinine ~0.5–0.6 mg/dL
• Protein binding altered; volume of distribution increased → drug doses may need adjustment
• Plasma cholinesterase activity ↓ ~25–30% → prolonged succinylcholine effect

Haematological

• Dilutional anaemia (Hb ~10.5–11 g/dL acceptable)
• Hypercoagulable state → VTE prophylaxis essential perioperatively

2. Timing and Urgency

3. Trimester-Specific Considerations

First Trimester (0–12 weeks)

• Organogenesis is occurring → theoretical teratogenic risk from anaesthetic agents
• In practice, no anaesthetic agent at clinical doses has been proven teratogenic in humans
• Greatest risk: spontaneous abortion (occurs in up to 15% regardless of surgery)
• Avoid N₂O in first trimester if feasible (inhibits methionine synthase; animal studies)

Second Trimester (13–28 weeks) — Preferred window for elective/semi-elective surgery

• Organogenesis complete
• Uterus not yet maximally large
• Lowest preterm labour risk

Third Trimester (>28 weeks)

• Maximum physiological burden on the mother
• Greatest risk of preterm labour
• Uterus very large → severe aortocaval compression, reduced FRC
• Near term: consider combined surgery + caesarean delivery

4. Preoperative Assessment

• Obstetric review before surgery
• Document gestational age, fetal position, placental location
• Fetal heart rate (FHR) documentation pre- and postoperatively
• Assess for preterm labour risk
• Investigations: CBC, clotting, crossmatch; consider USS
• Inform consent: risk of spontaneous abortion, preterm labour, fetal loss (unrelated to teratogenicity)

5. Choice of Anaesthetic Technique

Regional Anaesthesia — Preferred when feasible

• Avoids fetal drug exposure
• Avoids airway manipulation
• Reduces aspiration risk
• Epidural or spinal for lower abdominal/pelvic/limb surgery
• Limitation: unable for upper abdominal or thoracic surgery; anxiety, positioning may be problematic

General Anaesthesia — When necessary

• RSI is standard from ~18–20 weeks (or earlier if symptomatic reflux)
• Propofol (safe; crosses placenta but rapidly redistributed) — preferred induction agent
• Succinylcholine 1.5 mg/kg (increased dose due to increased volume of distribution; prolonged effect due to reduced pseudocholinesterase — clinically minimal)
• Rocuronium 1.2 mg/kg + sugammadex as alternative to succinylcholine

• Volatile agents (sevoflurane, desflurane, isoflurane): safe; provide uterine relaxation (may increase intraoperative bleeding for uterine surgery)
• N₂O: generally avoided in 1st trimester; acceptable in 2nd/3rd if needed; avoid in bowel obstruction
• Opioids: safe perioperatively; neonatal respiratory depression only if delivery occurs within 4 hours of large doses
• Benzodiazepines: avoid in 1st trimester (disputed teratogenicity); if needed in 3rd trimester, monitor for neonatal withdrawal

• All NMBDs cross placenta minimally; generally safe
• Sugammadex: appears safe; limited data in pregnancy

• Neostigmine + glycopyrrolate (glycopyrrolate preferred over atropine as it crosses placenta less)

6. Intraoperative Fetal Monitoring

• FHR monitoring with Doppler/CTG is recommended for viable gestations (>24 weeks) during procedures
• Below 18 weeks: FHR monitoring by Doppler pre- and postoperatively is acceptable
• A qualified obstetric team should be available when monitoring viable fetus intraoperatively
• Interpret FHR in context of maternal haemodynamics; maternal hypotension is the most common cause of fetal bradycardia

7. Key Intraoperative Goals ("MATECC" mnemonic)

8. Specific Surgical Scenarios

Laparoscopic Surgery (e.g., appendicectomy, cholecystectomy)

• Safe in all trimesters — preferred over open in most cases (less postoperative pain, earlier mobilisation, lower VTE risk)
• Use open/Hasson technique for trocar insertion (avoid injury to gravid uterus)
• Limit intra-abdominal pressure to ≤12–15 mmHg
• Trendelenburg may be poorly tolerated
• CO₂ pneumoperitoneum → hypercarbia → fetal acidosis: monitor ETCO₂ carefully; may need to increase minute ventilation

Trauma/Orthopaedic Surgery

• Prioritise maternal resuscitation
• Fetal hypoxia follows maternal haemodynamic compromise
• Blood products early; permissive hypotension is NOT appropriate in pregnancy
• MRI preferred for imaging (no ionising radiation)

Cardiac Surgery (Cardiopulmonary Bypass)

• High-risk: fetal mortality 10–30% on CPB
• Maintain high flow rates (>2.5 L/min/m²), MAP >70 mmHg on bypass
• Normothermic or mild hypothermia preferred
• Pulsatile flow preferred
• Continuous FHR monitoring essential

Neurosurgery

• Head-elevated position can exacerbate aortocaval compression — optimise positioning
• Mannitol: crosses placenta but generally acceptable short-term; may cause fetal dehydration
• Avoid hyperventilation (PaCO₂ <30 mmHg) → uteroplacental vasoconstriction

9. Postoperative Management

• Continue FHR monitoring for ≥24 hours post-surgery in viable gestations
• Adequate analgesia (undertreated pain → catecholamine release → uteroplacental vasoconstriction)
  • Paracetamol: first-line; safe
  • NSAIDs: avoid after 28 weeks (premature closure of ductus arteriosus); limit to <48h before 28 weeks
  • Opioids: safe short-term; monitor neonate if near-term
  • Neuraxial analgesia: excellent option
• VTE prophylaxis: LMWH + compression stockings; early mobilisation
• Tocolysis: routine prophylactic tocolytics not recommended; treat preterm contractions if they occur (indomethacin <32 weeks, nifedipine, atosiban)
• Obstetric review postoperatively

10. Drugs to Avoid / Use Cautiously

11. Communication and Documentation

• Multidisciplinary team: anaesthetist + obstetrician + surgeon + neonatologist (if near term)
• Neonatologist on standby if gestation ≥28 weeks
• Document all decisions, FHR records, drug doses, and fetal outcome
• Counsel patient thoroughly regarding risks to both mother and fetus

Summary