Anaesthetic Management of a Pregnant Patient for Emergency Appendicectomy

1. Key Physiological Changes in Pregnancy Relevant to Anaesthesia

Cardiovascular

• Cardiac output increases ~40% by end of first trimester (primarily via heart rate rise, later by stroke volume)
• Blood volume increases 50-55% above baseline by term; dilutional anaemia is expected
• After 18-20 weeks, the gravid uterus causes aortocaval compression in the supine position, reducing venous return and cardiac output - left uterine displacement is mandatory
• Vascular resistance falls; normal MAP is lower than non-pregnant values

Respiratory

• Diaphragm rises ~4 cm, reducing FRC by 20-30%
• Oxygen consumption increases ~20%; apnoeic desaturation occurs rapidly
• Progesterone-driven hyperventilation causes chronic respiratory alkalosis: normal PaCO2 ~30 mmHg, PaO2 ~103 mmHg, HCO3- ~20 mEq/L, pH ~7.44
• Airway oedema and friability from increased peripheral blood flow (starting 2nd trimester) makes intubation more difficult; video laryngoscopy should be available
• MAC for volatile agents is reduced ~25-40%

Gastrointestinal

• Progesterone and estrogen reduce lower oesophageal sphincter (LOS) tone
• Cephalad displacement of stomach by gravid uterus increases reflux risk
• Placental gastrin increases gastric acid secretion and lowers gastric pH
• All pregnant patients beyond the first trimester are considered full stomach regardless of fasting status
• Gastric emptying is further delayed by pain, anxiety, and opioids

Haematological / Pharmacological

• Plasma pseudocholinesterase activity reduced 25-30% from week 10 through 6 weeks postpartum (minimal clinical impact on succinylcholine duration)
• Reduced plasma albumin increases free fraction of protein-bound drugs
• Plasma volume expansion dilutes drug concentrations

2. Pre-operative Assessment and Preparation

• Sodium citrate 30 mL orally (non-particulate antacid) - immediately preoperative
• Ranitidine 150 mg IV / Omeprazole 40 mg IV
• Metoclopramide 10 mg IV (prokinetic; improves gastric emptying, raises LOS tone)

3. Choice of Anaesthetic Technique

Regional Anaesthesia (preferred when feasible)

• Favoured over GA to minimise fetal drug exposure and aspiration risk
• Spinal or combined spinal-epidural (CSE) is suitable for appendicectomy if the patient is cooperative and haemodynamically stable, and if the surgeon and anaesthetist are experienced
• However, in emergency appendicitis with peritonism, ileus, or when the patient is uncooperative or haemodynamically compromised, GA is usually required
• Regional techniques also allow titrated multimodal postoperative analgesia

General Anaesthesia (most common for emergency appendicectomy)

• Patient refusal of regional
• Peritonitis, haemodynamic instability
• Anticipated prolonged or converted laparoscopic procedure
• Gestational age making regional block level unreliable

4. General Anaesthesia - Step-by-Step Management

A. Operating Room Setup

• Left lateral tilt (15-30°) or manual left uterine displacement after 18-20 weeks
• Difficult airway trolley immediately available; video laryngoscope ready at the bedside
• Obstetric team and neonatal resuscitation equipment on standby if viable fetus

B. Preoxygenation

• Minimum 3-5 minutes of tidal volume breathing with 100% O2, or 8 deep breaths over 60 seconds
• Pregnant patients desaturate within 1-3 minutes of apnoea due to reduced FRC and increased oxygen consumption - adequate preoxygenation is non-negotiable
• Apply cricoid pressure (Sellick's manoeuvre) once preoxygenation complete; release if impeding intubation

C. Rapid Sequence Induction and Intubation (RSI)

• Use a 6.0-7.0 mm cuffed ETT (smaller size due to airway oedema)
• Confirm with capnography; do not ventilate mask before intubation during RSI (to avoid gastric insufflation)
• Failed intubation plan must be in place before induction

D. Maintenance

• Volatile agent (sevoflurane or desflurane) or TIVA with propofol infusion
• FiO2 0.5 (50% oxygen) is standard; avoid hypoxia; excessive O2 is not harmful in this setting
• Target EtCO2 28-34 mmHg - this reflects the physiologically normal PaCO2 of pregnancy. Avoid maternal hypocarbia (EtCO2 <28 mmHg) as this causes uterine artery vasoconstriction and left-shifted oxyhemoglobin dissociation curve, reducing O2 delivery to fetus. Equally avoid hypercarbia
• Maintain normothermia (warming blanket)
• Keep mean arterial pressure within 20% of baseline to preserve uteroplacental perfusion; use vasopressors (ephedrine or phenylephrine) if needed
• Maintain left uterine displacement throughout
• N2O: acceptable short-term but avoid in first trimester (theoretical concern - inhibits methionine synthase); can be used in 2nd/3rd trimester if needed

E. Laparoscopic Technique Considerations

• Pneumoperitoneum pressure ≤15 mmHg to minimise reduction in cardiac output and uteroplacental perfusion
• Head-up positioning may worsen venous return; minimise steep positioning
• CO2 absorbed from pneumoperitoneum - adjust ventilation to maintain EtCO2 28-34 mmHg
• SAGES guidelines: indications for laparoscopy same as non-pregnant; normocapnia should be maintained

F. Intraoperative Fetal Monitoring

• Previable fetus (<24 weeks): Doppler FHR before and after procedure
• Viable fetus (≥24 weeks): Continuous electronic FHR monitoring is recommended if feasible; requires obstetrician availability to perform emergency delivery if indicated
• Loss of FHR variability under GA is expected; fetal bradycardia is more concerning and may indicate maternal hypoxia, hypotension, acidosis, or excessive hyperventilation

G. Emergence and Extubation

• Extubate fully awake, on her side if possible, with intact protective airway reflexes
• Aspiration risk is highest at induction and emergence
• Ensure complete reversal of neuromuscular blockade (train-of-four >0.9) before extubation

5. Postoperative Management

Analgesia (Multimodal)

Monitoring

• Continuous CTG monitoring for at least 24 hours postoperatively
• Watch for signs of preterm labour (uterine contractions, cervical changes)
• Obstetric review prior to discharge

Tocolysis

• Routine prophylactic tocolysis is not recommended
• May be considered in consultation with obstetrics if preterm contractions develop, but evidence is limited
• Treat the underlying cause (pain, infection) first

6. Trimester-Specific Considerations

7. Drug Safety Summary

• Safe in pregnancy: Propofol, thiopentone, succinylcholine, rocuronium (+ sugammadex), volatile agents (standard doses), paracetamol, fentanyl, morphine (short-term), local anaesthetics (bupivacaine, ropivacaine, lidocaine)
• Use with caution: Ketamine (may increase uterine tone at high doses), benzodiazepines (generally safe short-term), N2O (avoid 1st trimester), NSAIDs (trimester-dependent)
• Avoid if possible: Methotrexate, aminoglycosides in high doses, high-dose opioids near delivery without neonatal team ready
• All general anaesthetic drugs cross the placenta; at standard doses, no currently used anaesthetic drug is proven teratogenic in humans

8. Team Communication

• Pre-briefing: Anaesthesiologist, surgeon, scrub nurse, obstetrician, neonatologist (if viable fetus) should all be present or contactable
• Plan for emergency Caesarean section must be discussed and documented before induction
• Failed intubation drill to be rehearsed (CICO plan - cannot intubate, cannot oxygenate)

• Miller's Anesthesia, 10e (Ch. 58: Obstetric Anesthesia - Physiologic Changes During Pregnancy, Nonobstetric Surgery During Pregnancy, Anesthetic Management, Laparoscopy, Postoperative Analgesia)
• Haataja et al., Scand J Surg 2023 (PMID 37329286) - Systematic Review: Non-obstetric surgery during pregnancy and effects on maternal/fetal outcomes