There has been a general trend away from general anaesthesia in many countries over the past few decades because of the associated potential morbidity and mortality, with about 90% of caesarean sections in the UK now performed under regional anaesthesia. General anaesthesia is usually reserved for those women who adamantly refuse a regional technique, for those in whom such a technique is contraindicated (e.g. by medical disease), or if there is lack of time. Conversion to general anaesthesia for inadequate regional anaesthesia may occur. In the UK, audit standards of up to 1% conversion rates have been recommended for elective sections and up to 2.5% for unplanned caesareans.
Problems and special considerations
The incidence of failure to intubate the trachea is approximately 1 in 300-500 in the obstetric population, compared with a 10-fold lower incidence in the general surgical population (see Chapter 38, Failed and difficult intubation).
For pulmonary aspiration of gastric contents, see Chapter 59, Aspiration of gastric contents, and Chapter 14, Gastric function and feeding in labour.
For hypovolaemia, see Chapter 78, Major obstetric haemorrhage. The extent of blood loss in fit young people is usually underestimated. Induction of general anaesthesia in an unresuscitated hypovolaemic mother may precipitate catastrophic cardiovascular collapse. Tachycardia should alert the anaesthetist to the possibility of hypovolaemia, although the significance of tachycardia may be difficult to assess in an extremely anxious mother who may also be in pain.
The risk of awareness during general anaesthesia for caesarean section is thought to be minimal if modern techniques are used (see Chapter 60, Awareness) but is considered higher than in the general population. Many cases of supposed intraoperative awareness are in fact episodes occurring during recovery from anaesthesia, but claims of intraoperative awareness are difficult to refute if the anaesthetic record is inadequate, and thus meticulous anaesthetic record keeping is vital. However, in the recent National Audit Project (NAP5) into awareness, the vast majority of reported cases of accidental awareness in obstetric patients were thought to be certain or probable cases of awareness, and occurred at induction. Some authorities recommend that all mothers are warned preoperatively of an extremely small risk of intraoperative awareness as part of the consent process, and that this warning is recorded in the preoperative assessment.
General anaesthesia is associated with a tendency towards longer immediate recovery, more pain (see Chapter 41, Postoperative analgesia), more postoperative nausea and vomiting, and more neonatal depression than regional anaesthesia. In addition, the parents do not experience the moment of birth as they do with spinal or epidural anaesthesia.
Management options
Preoperative assessment
The time available for preoperative anaesthetic assessment may be brief but vital aspects should not be omitted, especially any previous anaesthesia, drug allergy, recent oral intake, indication (and urgency) for caesarean section, and the mother’s airway.
Therapy to raise intragastric pH and minimise intragastric volume is given. It is usual to administer ranitidine (other drugs, e.g. omeprazole, may also be used) preoperatively, either orally or parenterally, depending on timing. This will be of benefit for extubation, another high-risk period associated with general anaesthesia. Metoclopramide is also given in many units. Some obstetric units advocate the administration of antacid prophylaxis routinely to every woman in labour, but this is controversial. 0.3 M sodium citrate (30 ml) is administered immediately before preoxygenation and induction of anaesthesia to neutralise any gastric contents.
Induction of anaesthesia
It is customary to induce anaesthesia for caesarean section in the operating theatre. The obstetric anaesthetist should check the anaesthetic machine in the obstetric theatre at least once a day. Most units will have a tray of emergency general anaesthetic drugs either prepared or ready to be drawn up quickly for emergency cases. A suitably trained anaesthetic assistant must be present before induction of general anaesthesia. There should be an airway trolley equipped with a range of differently sized tracheal tubes, intubation aids, laryngoscopes and equipment for dealing with failed intubation. The uterus must be displaced off the aorta and vena cava either manually (uncommon in the UK), by a wedge placed under the woman’s right hip, or by laterally tilting the operating table.
A large-bore intravenous cannula (14 G or 16 G) that is connected to a freely running infusion must be in place before induction of anaesthesia.
Adequate preoxygenation must always precede induction of anaesthesia, regardless of the urgency. It is crucial to ensure a tight fit of the facepiece and, if a circle system is being used, at least 12 l/min of oxygen. The standard recommendation is preoxygenation for 3 minutes or 4-5 vital capacity breaths, although a better guide is the difference between the inspired and expired oxygen content, indicated on the gas monitor (in ideal conditions, with no leak, both should exceed 90% when de-nitrogenation is complete). Some units now routinely employ transnasal high-flow humidified oxygen for preoxygenation and apnoeic oxygenation during intubation of obstetric patients.
Monitoring of the mother should include blood pressure, capnography, electrocardiography, pulse oximetry and end-tidal volatile concentration.
The patient should be draped and catheterised while preoxygenation is happening, to minimise duration of fetal exposure to anaesthetic agents. Traditionally, rapid-sequence induction of anaesthesia with thiopental and suxamethonium would be standard practice in the UK, but this is now the subject of debate. Although use of all induction agents has been described in the literature, the use of propofol has been particularly discussed since recent NAP5 and Confidential Enquiries into Maternal Deaths (CEMD) reports. The NAP5 report suggested that awareness might be associated with the use of thiopental (especially if relatively small doses are given to obese women), whereas the CEMD report commented on thiopental overdosing in unwell parturients. This has led to calls to replace thiopental with propofol for caesarean section, advocates of propofol citing familiarity with dosing, less potential for drug errors and reduced time for preparation for its use. On the other hand, advocates of thiopental cite familiarity in the obstetric setting, understanding of fetal effects, and haemodynamic stability associated with its use. Propofol has been associated with a slightly less favourable neonatal acid-base profile, though the clinical significance of this is disputed. Whichever drug is chosen, anaesthetists must be confident in its use and dosing in the variety of clinical situations seen with the obstetric population. A normal induction dose for the healthy parturient would be 5 mg/kg thiopental or 2.5 mg/kg propofol; these doses may need to be reduced for the mother who is unwell or has hypovolaemia or a fixed cardiac output, while they might need increasing in obesity. More than just an induction dose of hypnotic agent may need to be given, especially if intubation is difficult and the time to achieve adequate brain levels of volatile agent is prolonged.
Suxamethonium 1-1.5 mg/kg is the most commonly used neuromuscular blocking agent in the obstetric population. Use of rocuronium has been advocated instead of suxamethonium, on the basis that intubation conditions will be maintained for long enough to achieve intubation if the latter is unsuccessful on the first attempt. The traditional counter-argument has always been that the intubation conditions produced by suxamethonium are the best, within the shortest time, and if intubation fails, the return of muscle power favours earlier self-ventilation. However, with the introduction of sugammadex, rocuronium (1 mg/kg) may become the drug of choice, since sugammadex (16 mg/kg) has been shown to reverse the effects of rocuronium within 2-3 minutes (compared with the offset of suxamethonium of up to 10 minutes in late pregnancy). As sugammadex is a relatively new drug, familiarity with its use is still limited, especially in obstetrics; furthermore its cost is high and the incidence of anaphylaxis associated with its use is still not known.
Opioids are traditionally withheld until after delivery of the baby, to avoid neonatal effects. However, the NAP5 report suggested that ‘appropriate use of opioids’ should be employed to avoid accidental awareness, and administration of opioids such as fentanyl as part of the induction of anaesthesia, even in rapid-sequence induction, has also been advocated in guidelines for difficult intubation in obstetrics.
The induction agent may be supplemented with hypotensive agents and/or opioid analgesics in mothers with pre-eclampsia or cardiac disease, in order to reduce the sympathetic response to intubation (see Chapter 86, Hypertension, pre-eclampsia and eclampsia).
Cricoid pressure is applied before consciousness is lost and maintained until the airway is secured and tracheal intubation confirmed (see Chapter 37, Cricoid pressure).
Every obstetric anaesthetist should be familiar with both failed intubation and failed ventilation drills, and should mentally rehearse these before every induction of general anaesthesia in the obstetric patient. Every obstetric theatre should have monitoring equipment that includes measurement of end-tidal carbon dioxide, and there should be access to specialised airway equipment, e.g. for cricothyroid access and a fibreoptic endoscope.
An agent to counteract hypotension, such as phenylephrine or metaraminol, must be to hand (although hypotension is usually less marked than with neuraxial anaesthesia).
Perioperative and postoperative management
Traditional practice is to use 50% nitrous oxide in oxygen plus a volatile anaesthetic agent (e.g. isoflurane) to ventilate the lungs, reverting to conventional mixtures of 70% nitrous oxide in 30% oxygen after delivery of the baby, aiming for a total MAC of about 1.0 depending on the situation (though the use of nitrous oxide in general is becoming less frequent, and general anaesthesia using an air/oxygen mixture is increasingly used). The volatile agent should be continued throughout anaesthesia. In severe fetal compromise, 100% oxygen with a corresponding increase in the inspired concentration of volatile agent may be chosen. Some authorities advocate a higher MAC of up to 1.3 until opioids have been given; this can be rapidly reduced if uterine contractility is affected.
A short-acting non-depolarising neuromuscular blocking drug should be used when the suxamethonium has worn off, and if the surgeon is fast it may not be necessary to use further neuromuscular blockers after the initial dose of suxamethonium. Deaths have occurred from inadequate reversal of neuromuscular blockade following the use of long-acting drugs; this and the risk of awareness during emergence from anaesthesia make the use of neuromuscular blockade monitoring mandatory.
Oxytocin (Syntocinon) is usually given as a slow intravenous bolus of 5 U at delivery of the baby (although lower doses of 0.5-3 U may be adequate), often followed by an intravenous infusion of 40 U in 500 ml saline at ~125 ml/hour. Antibiotics were traditionally administered after delivery of the baby, but current National Institute for Health and Care Excellence (NICE) recommendations are for administration before skin incision.
Adequate analgesia should be given following delivery of the baby. A combination of a long-acting opioid such as morphine (7.5-15 mg) and a non-steroidal anti-inflammatory drug (NSAID) such as diclofenac is used in many units. It is important to obtain preoperative consent to rectal administration of drugs. Intravenous paracetamol is also routinely given intraoperatively.
At the end of surgery, residual neuromuscular blockade is reversed and the mother is usually turned into the left lateral position before the trachea is extubated. It is important to remember that the risk of aspiration is also present at extubation and possibly during the initial phase of recovery from anaesthesia. Extubation of the trachea should not be performed until there is evidence of return of protective reflexes.
The mother must be nursed in a properly equipped recovery room by trained staff before returning to the postnatal ward. Deaths have occurred because of inadequately staffed and equipped recovery facilities.
Patient-controlled opioids are popular for postoperative analgesia, and NSAIDs appear to be particularly effective in combating ‘afterpains’ of uterine involution. NSAIDs should not be used in women with severe pre-eclampsia or severe asthma. Bilateral ilioinguinal block, transversus abdominis plane blocks and rectus sheath blocks have also been used. Further aspects are discussed in Chapter 41, Postoperative analgesia.
Heparin should be given according to local protocol.
Current evidence suggests that a woman may breastfeed her baby as soon as she has adequately recovered from the general anaesthetic.
Key points
• All obstetric patients requiring general anaesthesia should be considered high-risk.
• Emergency general anaesthesia is associated with increased morbidity and mortality.
• Failure to intubate the trachea is ~10 times more common in the obstetric population than in the general surgical population.
Further reading
Dahl V, Spreng UJ. Anaesthesia for urgent (grade 1) caesarean section. Curr Opin Anaesthesiol 2009; 22: 352-6.
Lucas DN, Yentis SM. Unsettled weather and the end for thiopental? Obstetric general anaesthesia after the NAP5 and MBRRACE-UK reports. Anaesthesia 2015; 70: 375-9.
Sia AT, Fun WL, Tan TU. The ongoing challenges of regional and general anaesthesia in obstetrics. Best Pract Res Clin Obstet Gynaecol 2010; 24: 303-12.