Preoperative Investigations

For a healthy parturient undergoing a routine cesarean delivery with an otherwise uncomplicated pregnancy, there is currently no evidence for any specific laboratory tests. Although it has been commonplace for a full blood count including platelet count, group and save, and clotting screen to be performed, the evidence suggests that this is not justified. The National Institute for Health and Care Excellence (NICE) guidance for cesarean delivery recommends that pregnant women should be offered a hemoglobin assessment to identify anemia. Blood loss of more than 1,000 ml is infrequent in cesarean delivery (it occurs in 4–8 percent), but it is a potentially serious complication.² The guidance also recommends that healthy women with uncomplicated pregnancies should not be routinely offered group and save or clotting screen prior to cesarean delivery.

If the patient’s history warrants a platelet count in order to perform neuraxial blockade, then there must be consensus on the lower level of platelet count that is acceptable. The British Committee for Standards in Haematology has published guidance suggesting platelet counts that are safe for delivery: 50 × 10⁹/Liter for vaginal delivery and 80 × 10⁹/Liter for cesarean delivery and neuraxial anesthesia.³ This is discordant with the recommendations from the American College for Hematology, which suggests any level above 50 × 10⁹/Liter, regardless of mode of delivery.⁴ There is a single report in the literature of an epidural hematoma occurring in a pregnant woman in the presence of thrombocytopenia (71 × 10⁹/Liter).⁵ The debate surrounding the “safe” level of thrombocytopenia for neuraxial blockade is unlikely to be investigated by a clinical trial and therefore for the foreseeable future will be guided by expert consensus opinion.

Aspiration Prophylaxis

Parturients are at increased risk of aspiration of gastric contents for several reasons when compared with the nonpregnant population. First, progesterone causes relaxation of the musculature at the gastroesophageal junction and delayed gastric emptying. Second, the gravid uterus causes increased intra-abdominal pressure, tending to force the stomach contents upward. In addition, a paper by Mendelson described respiratory failure secondary to aspiration pneumonitis in pregnant women. It has been a cornerstone of anesthetic practice to prevent this.⁶

Prior to elective cesarean delivery, standard adult fasting guidelines should be adhered to.⁷ Women waiting for planned surgery should not be subjected to long periods of starvation and/or fluid deprivation and should be encouraged to drink clear fluids up until 2 hours preoperatively. Women presenting for elective cesarean delivery will usually be assessed preoperatively in clinic, at which time antacid prophylaxis will be prescribed for both the evening before and the morning of surgery. A recent Cochrane review looked at interventions to reduce the risk of aspiration pneumonitis at cesarean delivery.⁸ The report suggested that although the available studies were of poor quality, current evidence supported the combination of H₂-receptor antagonists and antacids as being more effective than either one alone or no prophylaxis. They concluded that neither proton pump inhibitors nor the prokinetic metoclopramide were effective. Despite this evidence, metoclopramide is currently routinely prescribed preoperatively for cesarean delivery in many units.

Neuraxial Techniques for Cesarean Delivery

The incidence of general anesthesia for cesarean delivery has dropped dramatically over the past few decades. The safety benefits of regional anesthesia over general anesthesia in pregnant patients are well documented and are summarized in Table 23.2.¹⁰ In the United Kingdom, regional anesthesia is used for 94.9 percent of elective and 86.7 percent of emergency cesarean deliveries.¹¹ The choice of anesthesia ultimately rests with the competent mother. Information for mothers is available in a variety of formats, especially via the Obstetric Anaesthetist’s Association website, which should help them make an informed choice in conjunction with discussion with the anesthetic team.

Spinal Anesthesia

Single-shot spinal anesthesia is probably still the most common neuraxial technique used for elective cesarean delivery. This may well be the result of the more widespread use of pencil-point spinal needles, which have lead to a reduction in post–dural puncture headache to less than 1 percent. Spinal anesthesia has become preferred in most situations over epidural anesthesia due to the shorter onset time, improved patient comfort, superior quality of surgical anesthesia, and fewer complications.¹² It is associated with less fetal exposure due to the least amount of absorption of local anesthetic into the maternal circulation. The technique is usually performed at the level of L3 or below because in 20 percent of patients the conus medullaris has been shown to extend below the level of the body of L1, in addition to the finding that anesthetists more commonly underestimate the level of insertion.¹³

In the United Kingdom, the most commonly used intrathecal local anesthetic is bupivacaine 0.5% in dextrose 80 mg/ml (“heavy” or hyperbaric bupivacaine). The dose chosen to produce a reliable block may depend on patient height, but evidence for this is lacking. Patient positioning and the size of the gravid uterus may have more influence. A recent Cochrane review compared the use of isobaric and hyperbaric bupivacaine in cesarean delivery and concluded that the use of hyperbaric bupivacaine appeared to be associated with less likelihood of conversion to general anesthesia and that the time to reach sensory block to T4 was shorter. There was no difference in the need for supplemental analgesics and no other significant differences between the two local anesthetics.¹⁴

Combined Spinal-Epidural Anesthesia

Many units have adopted combined spinal-epidural (CSE) anesthesia as their primary approach for elective cesarean delivery. The technique may be performed at either two separate interspaces (usually the more cranial for the spinal component and the space below for the epidural component) or may be performed at a single interspace, often using a needle-through-needle approach using commercially available locking kits. This technique has the advantage of rapid onset of the spinal portion combined with the ability to maintain anesthesia via the epidural component and is a useful technique if the duration of surgery is longer than anticipated. Several studies have demonstrated the superiority of CSE anesthesia over conventional epidurals for cesarean delivery in terms of reliability of analgesia and muscle relaxation. Another advantage of CSE anesthesia is the ability to use a lower initial dose in the spinal, which can be increased via the epidural component. This may be advantageous in some cardiac conditions, in preeclampsia, and where a labor epidural has failed and there is concern that a normal-dose spinal may lead to an unacceptably high block. CSE techniques, of course, mean a risk of complications relating to both epidural and spinal anesthesia, including accidental dural puncture and possible increased risk of neural damage. Interestingly, CSE has been compared to spinals in terms of sensory block height. Although some preliminary work suggested the sensory block height may differ between CSE and spinals (using equivalent intrathecal doses) for elective cesarean delivery¹⁵, this has not been confirmed in subsequent studies.^{16, 17}

General Anesthesia

Possible indications for general anesthesia for an elective cesarean delivery include contraindications to regional anesthesia or maternal request. General anesthesia for cesarean delivery is associated with higher mortality than neuraxial blockade, as demonstrated by complications arising from general anesthesia documented in the Confidential Enquiries into Maternal Deaths.¹⁸ Airway difficulties are encountered more commonly than in the nonobstetric population. This is due to a combination of anatomical and physiological changes that occur during pregnancy, including upper airway edema (which may be exacerbated by preeclampsia), breast enlargement, and excessive weight gain.¹⁹ The presence of the gravid uterus reduces functional residual capacity, which, combined with increased overall oxygen requirements, may accelerate the onset of desaturation during apnea.²⁰ Pulmonary aspiration is one of the main concerns of general anesthesia in obstetric patients, and guidelines should be strictly adhered to for the administration of antacid prophylaxis, particularly if a general anesthetic is planned. The use of a rapid-sequence induction to reduce the incidence of pulmonary aspiration has remained largely unchanged for the past six decades, traditionally with thiopentone and suxamethonium (1.5 mg/kg) but more recently using propofol and rocuronium (up to 1.2 mg/kg of body weight) with the availability of sugammadex to specifically reverse rocuronium-induced neuromuscular blockade. There has been increased interest in the use of videolaryngoscopes and second-generation supraglottic airway devices (such as the LMA Proseal™), which have been used successfully in obstetric patients undergoing general anesthesia.²¹ Indeed, these devices were recommended for use in the 2015 joint Obstetric Anaesthetists’ Association/Difficult Airway Society guidelines for the management of difficult and failed intubation in obstetrics.²⁰

Accidental awareness under general anesthesia (AAGA) in obstetrics is another concern. It has long since been believed that the incidence of AAGA is higher in obstetrics than in nonpregnant patients, and this has been shown in several epidemiological studies.^{22, 23} It is thought that concerns about the deleterious effects of anesthetic drugs on the fetus (both directly and via the impact of maternal hemodynamics), the potential to increase maternal blood loss through decreased uterine tone, and the decreasing use nationally (in the United Kingdom) of thiopentone and of general anesthesia globally in obstetrics may have lead to an increase in cases of awareness. In the Fifth National Audit Project of the Royal College of Anaesthetists and Association of Anaesthetists of Great Britain and Ireland (AAGBI), obstetric general anesthesia was associated with a 10-fold overrepresentation of awareness cases when compared with other surgical specialities.²⁴ Monitoring of pregnant patients should be carried out according to standard AAGBI guidelines. Anesthesia is generally maintained with inhalational agents using end-tidal agent monitoring to titrate the anesthetic depth. The NAP5 study showed that the use of specific depth of anesthesia monitors (e.g., bispectral index [BIS] monitoring) during obstetric anesthesia was sparse (particularly in the United Kingdom), and it was suggested that this might reflect either the lack of confidence that these monitors provide clinically useful information or the perceived impracticality (because of slow response time) of using such monitors in obstetrics.^{23, 24}