Spinal anaesthesia is the most popular mode of neuraxial anaesthesia used for caesarean section [8, 10]. The incidence of post-dural puncture headache, which for many years made the technique unacceptable, has been dramatically reduced with the evolution in small gauge spinal needles with pencil point tips. Spinal anaesthesia is fast and effective and there is an extremely low risk of systemic toxicity as the doses of drugs used are minimal. The addition of intrathecal opioids (fentanyl, morphine and diamorphine) has been demonstrated to improve the quality of block and reduce intraoperative pain and is recommended [11, 12]. Morphine and diamorphine (though not fentanyl) can contribute to post-operative analgesia between 12 and 24 h.

The most significant acute complication of spinal anaesthesia is maternal hypotension, which occurs in up to three quarters of women without prophylactic measures [13]. This can be associated with maternal nausea and vomiting and impaired uteroplacental perfusion that can lead to foetal acidaemia. Prophylactic measures to avoid/minimize hypotension are mandatory and include the use of an intravenous fluid bolus, given as a pre-load or co-load and the use of vasopressor drugs. For many years ephedrine was the main vasopressor used for the treatment of spinal hypotension. This was based on studies in pregnant ewes that demonstrated it was associated with less reduction in uterine blood flow and thus recommended it over metaraminol and other α-adrenoreceptor agonists [14]. However, subsequent work demonstrated that although blood pressure control was better with ephedrine than without, there was no improvement in neonatal outcome; indeed, the use of ephedrine was associated with a higher incidence of umbilical arterial pH < 7.2 compared to controls [15]. This renewed interest in vasopressors with more α-agonist activity (phenylephrine and metaraminol) and studies with these agents showed there was improved foetal acid-base status compared with ephedrine [16]. Subsequently, phenylephrine has emerged as the vasopressor of choice to minimize hypotension associated with spinal anaesthesia [17]. There has been some debate about whether phenylephrine should be given as an infusion started immediately after initiation of spinal anaesthesia or as a bolus dose (either given only in response to a fall in blood pressure or prophylactically). Prophylactic administration of phenylephrine could potentially cause reactive hypertension and associated bradycardia. A meta-analysis looking at the use of prophylactic phenylephrine for caesarean section under spinal anaesthesia concluded that a continuous infusion started immediately after initiation of spinal anaesthesia significantly reduced the incidence of spinal hypotension compared with bolus doses given only in response to a fall in blood pressure [17]. In addition, a more recent study demonstrated a reduction in anaesthetists’ workload by the use of an algorithm adjusting the infusion rate of a prophylactic phenylephrine infusion according to changes in blood pressure and heart rate [18]. The ideal infusion regimen that will control the maternal blood pressure, with minimal maternal side effects, while avoiding maternal hypertension has not yet been identified.

A major reason cited as to why general anaesthesia continues to be used over spinal anaesthesia in cases of extreme urgency is speed, general anaesthesia being perceived as faster and consistently reliable. Although spinal anaesthesia can be almost as fast as general anaesthesia in skilled anaesthetists there are inherent aspects, such as the time required for an adequate surgical block to develop, that will in general make it slower than general anaesthesia [19]. The ‘rapid sequence spinal’ has been described as an approach for spinal anaesthesia for Category 1 caesarean section [20]. Principles of this approach include using a ‘no-touch’ technique and using sterile gloves only, utilizing other staff members to perform i.v. cannulation, limiting the number of attempts to one and preparing the patient for general anaesthesia during attempted spinal insertion. The authors of this study reported successful reduction in the decision to delivery interval with this approach; however, concerns exist around minimizing the aseptic technique.

The role of epidural anaesthesia in emergency caesarean section is largely confined to when an existing labour epidural is extended to provide surgical anaesthesia. Epidural anaesthesia alone is generally not preferred for elective caesarean section as the quality of anaesthesia is less than that achieved by spinal anaesthesia. The ability to site an epidural when the woman is in labour and then utilize that epidural should caesarean section be required can avoid the need for general anaesthesia. The use of epidural analgesia in this context can be particularly useful in ‘high-risk’ women who may require intrapartum delivery.

Before extending a labour epidural block for caesarean section, it is vital to ensure that the epidural has been working well during labour. Other considerations when extending a labour epidural block for caesarean section include the choice of drug and where the top-up drug should be administered.

The choice of local anaesthetic agent to use in this situation has been widely but not extensively studied. Comparison of these studies is limited by a number of factors including differing end points and the use of different labour analgesia regimens. The ideal agent should have a fast onset but be associated with minimal side effects as a large bolus of local anaesthetic is being administered over a short time period. A meta-analysis on the subject looked at 11 randomized controlled trials, involving 779 parturients [21]. The local anaesthetic agents used in the various studies were classified into three groups: 0.5% bupivacaine or levobupivacaine; 2% lidocaine and 1: 200 000 epinephrine, with or without fentanyl; and 0.75% ropivacaine. The authors found that lidocaine and epinephrine, with or without fentanyl, resulted in a significantly faster onset of sensory. The bupivacaine or levobupivacaine group was associated with a significantly increased risk of intraoperative supplementation compared with the other groups. The addition of fentanyl to a local anaesthetic resulted in a significantly faster onset but did not affect the need for intraoperative supplementation. The authors concluded that if the speed of onset is important, then a lidocaine and epinephrine solution, with or without fentanyl, was preferable, but for quality of epidural block then 0.75% ropivacaine preferable. There were insufficient trials to assess the effect of adding sodium bicarbonate in this meta-analysis, although it was noted that the reduction in onset time appeared more pronounced when bicarbonate was added in two studies. However, the time required to prepare solutions of drugs could outweigh any reduction in onset times, and there are safety implications when mixing drugs in emergency situations [22].

The location where the epidural ‘top-up’ should be given is controversial and can be affected by a variety of factors including the urgency of delivery, local practice factors and the layout of an individual unit [23]. Initiating the ‘top-up’ in the labour ward can help to expedite the establishment of an adequate block height and minimize the decision to delivery interval. However, any large epidural top-up is associated with the risks of significant hypotension, high blockade and local anaesthetic toxicity. The anaesthetist’s ability to effectively monitor for the development of these complications and manage them may be compromised by being in the delivery room. If the top-up is given only after the patient has arrived in the operating room there may not be sufficient time to allow an adequate block height to develop and general anaesthesia may be required [24]. A compromise would be to administer a small dose of local anaesthetic in the delivery room and then giving the rest of the top-up once the patient has arrived in theatre.

The use of general anaesthesia for caesarean section has fallen dramatically in the past two decades particularly in the resourced world. It has been estimated that less than 5% of all elective caesarean deliveries in the United States and United Kingdom are performed under general anaesthesia. Recommendations from the United Kingdom are that less than 15% of emergency (Category 1, 2 and 3 caesarean sections) and 5% of elective (Category 4 CS) be performed with general anaesthesia [9].