The caesarean section (CS) rate in much of the developed world has increased markedly in recent decades. In England the rate has stabilised since about 2007 (Figure 33.1). The rates are similar in the devolved countries; in Wales and Scotland the CS rate is currently about 1-2% higher, and in Northern Ireland about 5% higher, than in England. There is wide variation between units. There has been general concern over increasing CS rates and the associated complications, notwithstanding the benefits that CS might have in individual cases. Since CS is such an important procedure in obstetrics, and anaesthetic-related maternal deaths commonly involve emergency CS, it is important that obstetric anaesthetists have an understanding of the practical aspects relating to obstetric indications and techniques.
Classification and delivery time
Traditionally, CS was classified as elective (i.e. a date is given beforehand) or emergency (the rest). The latter group is thought by many obstetricians and obstetric anaesthetists to be too broad, since it includes cases in which immediate delivery is required (e.g. severe fetal compromise or cord prolapse) as well as cases in which there is little urgency (e.g. early spontaneous labour in a mother with a breech scheduled for elective CS the next day). This led to the reclassification of CS into four categories (Table 33.1), and this classification has been adopted by all the major UK bodies involved in this field.
Although intended as an audit tool (e.g. to monitor outcomes and allocation of staff), the classification has been used to guide management (e.g. second operating theatre opened for category-1 cases). However, attempts to link the categories to acceptable maximum times to delivery (e.g. 30 minutes for category 1) are hampered by the unwillingness of obstetricians to commit themselves to ‘acceptable’ delays for categories 2 and 3 in case of a bad outcome. In addition, maximum times to delivery are controversial and not based on good science: the often-quoted maximum of 15-30 minutes for fetal compromise is derived largely from work in the 1960s in which animal fetuses were exposed to varying durations of intrauterine hypoxia and the degree of subsequent fetal damage assessed. Most cases of cerebral palsy are now known to be related to factors arising before labour.
Figure 33.1 Caesarean section rates in England, 1980-2016 (from NHS HospitalEpisodes Statistics).
Table 33.1 Classification of caesarean section
1 Immediate threat to life of woman or fetus
2 Maternal or fetal compromise which is not immediately life-threatening
3 Needing early delivery but no maternal or fetal compromise
4 At a time to suit the woman and maternity team
The category is assigned at the time of decision to operate; e.g. an episode of fetalcompromise caused by aortocavalcompression responding to therapy, followed some hours later by caesarean section for failure to progress, would be graded as category 3, not 2. Similarly, a case booked as an elective procedure for (representation could eventually be classified as category 3 if the mother goes into labour before the chosen date of surgery. Also applies whether or not the woman is in labour.
A number of audits within maternity units have found that meeting the particular standard set is extremely difficult to achieve in practice because of delays at each stage of the process (e.g. calling the anaesthetist/anaesthetic assistant, moving the mother to the operating theatre, preparing the surgical equipment, etc.). Finally, the defined time period itself varies: the time from decision to skin incision, from decision to delivery, and from informing the anaesthetist to skin incision or delivery have all been quoted in various recommendations or guidelines.
Analysis of data from the Royal College of Obstetricians and Gynaecologists (RCOG) Sentinel audit of CS in the UK in 2000 suggests that poorer maternal and neonatal outcomes were associated with decision-to-delivery intervals exceeding 75 minutes, but not intervals of 31-75 minutes. Recent guidance from the Joint Standing Committee of the RCOG and the Royal College of Anaesthetists (RCoA) reiterated that all maternity units in the UK should be using the same classification for CS, that every individual woman in labour should be considered to have a continuum of risk, and that the 30-minute interval should be considered as an ‘audit standard’ and not the ‘gold standard’ in which to deliver a baby in an emergency. Updated guidance from the National Institute for Health and Care Excellence (NICE) states that category 1 and 2 CS should be performed ‘as quickly as possible’ and that for category 2, within 75 minutes ‘in most situations’. Further, delivery times of 30 minutes for category 1, and both 30 and 75 minutes for category 2 CS, should be used as audit standards for the unit and not to judge performance for any individual CS.
Indications
CS may be performed for the benefit of the mother, the fetus or both (Table 33.2), although in practice maternal indications will ultimately affect the fetus adversely if not relieved, and vice versa. For elective CS, 39 weeks is commonly chosen as the optimum gestation, reflecting a balance between the benefit to the neonate of a longer gestation and the greater risk of spontaneous labour and emergency surgery. An elective CS may also be the chosen mode of delivery by the mother, once she has been informed of the risks and benefits, and offered counselling if appropriate.
Table 33.2 Indications for caesarean section
Previous caesarean section
Elective
Following trial of labour
Other
Maternal disease
Worsening pre-existing disease, e.g. cardiac
Associated with pregnancy, e.g. pre-eclampsia
Placenta praevia or abruption
Maternal exhaustion/choice
Obstructed labour/failure to progress
Malpositions
Multiple pregnancy
Fetal compromise
Cord prolapse
Procedure
For lower-segment CS, skin incision is usually low transverse (i.e. in the L1 dermatome) but may be midline. Once exposed, the rectus sheath is split longitudinally and stretched laterally and the peritoneum incised. The uterus is incised transversely in its thin lower segment. A ‘classical’ CS involves a midline incision, and the uterus is incised longitudinally in its upper segment. Classical CS is associated with a greater risk of haemorrhage, infection and ileus but is quicker to perform and easier than lower-segment CS. It may be indicated if the lower segment is poorly formed, e.g. in premature delivery, and in placenta praevia, transverse or unstable lie or uterine fibroids.
Uterine incision is accompanied by removal by suction of amniotic fluid if the membranes have not ruptured (mothers and partners may find the noise alarming if unexpected). Delivery of the baby may be difficult if the head has descended well into the pelvis, and may require forceps. If the placenta has already started to separate, the uterus may contract around the baby’s head, especially if CS is in the second stage of labour. Increased inspired concentration of volatile agent has been used to relax the uterus during general anaesthesia. Glyceryl trinitrate 50-100 µg intravenously or sublingually, repeated as necessary, has also been used to good effect and is suitable during regional anaesthesia.
The time between induction of general anaesthesia and delivery (the I-D interval) may affect fetal wellbeing, since if it is very short, the induction agent may be present in the fetus at high levels; and if it is very long, fetal accumulation of inhalational agents may occur.
The time from uterine incision to delivery (the U-D interval) is thought to be more important, since placental disruption may occur once the uterus is incised; fetal acidosis is unlikely if the U-D interval is less than 3 minutes.
Following delivery of the baby, oxytocin (Syntocinon) is given (typically 5 U slowly intravenously, though there is evidence that smaller doses, between 0.5 U and 3 U, may be effective). Rapid injection of larger doses may cause severe tachycardia, hypotension and electrocardiogram changes suggestive of myocardial ischaemia and may be no more effective than smaller doses. Uterine contraction may be aided by vigorous rubbing of the uterus; an oxytocin infusion may be required (e.g. 40 U in 500 ml saline at ~125 ml/h), especially after prolonged augmented labour, multiple delivery, in the presence of polyhydramnios and with a previous history of postpartum haemorrhage or multiple deliveries. Increasingly, this infusion is requested as routine prophylaxis rather than treatment of uterine atony for all cases by the obstetricians. An analogue of oxytocin, carbetocin (typically 100 µg intravenously), is longer-acting and may be a suitable alternative; evidence to date suggests a reduced incidence of postpartum haemorrhage and need for postoperative infusion or further oxytocics.
Once the baby and placenta have been delivered, the uterus is checked for tears and then sutured. Many obstetricians prefer the ease of access conferred by exteriorising the uterus, although this may be accompanied by discomfort and nausea/vomiting during regional anaesthesia, bradycardia and an increased incidence of air embolism. The obstetrician should always check with the anaesthetists before performing this manoeuvre.
Problems and special considerations
Surgical problems relating to the procedure itself include difficulty caused by adhesions (especially following previous CS or other abdominal surgery), haemorrhage, surgical trauma to the baby, difficulty delivering the baby with the risk of fetal hypoxia or physical trauma, difficulty delivering the placenta and damage to neighbouring structures. There may be large veins on the anterior wall of the uterus, and wide transverse incisions may extend to the uterine angles when the baby is delivered, leading to severe bleeding. Usual blood loss is ~400-700 ml (increased with general anaesthesia) but is notoriously difficult to estimate accurately. There is an increased risk of placenta accreta in women who have had previous CS, especially if the placenta overlies the previous scar.
Anaesthetic problems include those of general or regional anaesthesia generally. Pain during CS under regional anaesthesia has replaced awareness under general anaesthesia as the main reason for litigation associated with CS. Chest pain and/or electrocardiographic changes may occur; their cause is unknown (although small air emboli or coronary artery/ oesophageal spasm have been suggested) and they may occur independently of each other. Elevations of maternal troponin I levels have also been reported. Shoulder-tip pain may occasionally occur, probably related to blood irritating the diaphragm. Other possible problems related to the procedure include air or amniotic fluid embolism and allergic phenomena.
Postoperative problems are as for any surgery and include infection and thromboembolism. Prophylactic antibiotics have been shown to reduce infection; although they are traditionally given after delivery to avoid exposing the fetus to the drug, and in case a severe maternal allergic reaction should occur, NICE guidelines suggest administration before skin incision. Heparin is given prophylactically to women at high risk of thromboembolism in some units and to all women in others. If the former, the RCOG guidelines should be followed. NICE guidelines suggest that observations (including assessment of pain and sedation) should be half-hourly for 2 hours after CS, then hourly, up to 12 hours after intrathecal diamorphine. Postoperative analgesia is discussed in Chapter 41.
Management options
The choice of anaesthetic technique depends on the degree of urgency, whether an epidural catheter is already in place, specific obstetric factors (e.g. complicated surgery anticipated) or anaesthetic issues (e.g. known difficult intubation, previous back surgery), the personal preference of the anaesthetist and the wishes of the mother (see Chapters 34-36).
Absolute figures are unavailable, but recent surveys have shown that over 90% of CS are performed under regional anaesthesia in the UK, reflecting the above preferences and the widely perceived greater safety of regional over general anaesthesia for CS. Particular concerns are the possibly inadequate exposure of anaesthetic trainees to general anaesthesia for CS, the greater tendency of trainees to use general anaesthesia (especially for emergency CS) than more experienced consultants, and the anxiety caused when this occurs. There is also concern that the incidence of failed intubation in obstetrics is increasing, and that this may be related to the above factors.
Key points
• The caesarean section rate in the UK is ~25-30%.
• Indications may be maternal, fetal or both.
• Complications include shoulder-tip, abdominal or chest pain, air or amniotic fluid embolism, haemorrhage, surgical trauma and awareness.
Further reading
Lucas DN, Yentis SM, Kinsella SM, et al. Urgency of caesarean section: a new classification. J R Soc Med 2000; 93: 346-50.
National Institute for Health and Care Excellence. Caesarean Section. Clinical Guideline 132. London: NICE, 2004. https://www.nice.org.uk/guidance/cg132 (accessed December 2018).
Royal College of Obstetricians and Gynaecologists, Royal College of Anaesthetists. Classification of urgency of caesarean section: a continuum of risk. Good Practice 11. London: RCOG, 2010. www .rcog.org.uk/classification-of-urgency-of-caesarean-section-good-practice-11 (accessed December 2018).
Yentis SM. Whose distress is it anyway? ‘Fetal distress’ and the 30-minute rule. Anaesthesia 2003; 58: 732-3.