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Introduction
The rate of general anaesthesia (GA) for caesarean section (CS) has fallen from 55% (1989–1990) to 9.4% (2011–2012). Over the same time period there has been an increase in CS rates from 11.3% to 25%. Despite the rise in CS rate there are approximately 70% fewer obstetric GAs performed per year nationally.
The reasons for this include:
Increasing awareness of the risks of general anaesthesia in the parturient. The UKOSS study demonstrated a 1:224 risk of failed intubation
The introduction of pencil point spinal needles, which have reduced the risk of post dural-puncture headache to an acceptable level (0.25%)
Changes in maternal demographics: increasing numbers of women with morbid obesity and other co-morbidities
Alteration in maternal expectations. Better information antenatally regarding the risks and benefits of regional anaesthesia vs. general anaesthesia allows women to make informed choices.
Benefits of regional anaesthesia (RA) for the woman include:
The partner can be present throughout the delivery
Maternal/neonatal skin-to-skin contact at the time of delivery can facilitate bonding
The drugs used to provide RA do not affect uterine tone and there is minimal, if any, direct effect of these agents on fetal heart rate activity or fetal wellbeing
The addition of neuraxial opioids provides excellent postoperative analgesia
A reduction in the need for general anaesthesia reduces risks e.g. failed intubation.
Audit standards from the Association of Anaesthetists are that the proportion of CS under regional anaesthesia should be:
| • Category 1 CS | >50% |
| • Category 2–3 CS | >85% |
| • Category 4 CS | >95%. |
Types of central anaesthetic neuraxial blockade
The CNB technique for delivery is dictated by:
The experience of the anaesthetist
The urgency of the decision-to-delivery interval (DDI):
Category 1: immediate threat to the life of the mother or fetus (< 30 minutes)
Category 2: no immediate threat to the life of woman or fetus (< 75 minutes)
Category 3: requires early delivery (> 75 minutes)
Category 4: at a time to suit the woman and the maternity service
Co-morbidities, e.g.:
Obesity
Pre-eclampsia
Cardiac disease
Respiratory disease
Whether the in-situ epidural is satisfactory enough to top-up.
The contraindications to CNB are detailed in Chapter 10.
The absolute contraindications are:
Patient refusal
Sepsis – local to the insertion site and systemic
Pathological
Iatrogenic.
There are a number of situations where there is a judgement that the risks of CNB are less than the risks associated with GA, e.g. a woman that has a stable platelet count of 70 × 109/L, with a normal coagulation screen. She may be considered unsuitable for a labour epidural, but an acceptable risk for siting a spinal for operative delivery.
The multidisciplinary team should be made aware of any woman with morbidities that could complicate the performance of CNB as this may result in a delay in decision-to-delivery time. Complex cases should be supervised by a senior anaesthetist.
Preparation for central neuraxial blockade is as follows:
1. Patient:
a. A full medical history, to assess the woman’s suitability for CNB
b. Early identification of women who have an increased risk of operative delivery e.g. twin pregnancy, morbid obesity, medical co-morbidities, induction of labour
c. Appropriate examination and review of relevant investigations in light of the history
d. A full explanation of the procedure, including the benefits and risks of CNB (See Table 11.1)
e. Prompt access to translation services
f. Antacid prophylaxis
| Risks | Epidural | Spinal |
|---|---|---|
| Hypotension | 1:50 | 1:5 |
| Failure of CNB, resulting in GA conversion | 1:20 | 1:125 |
| Post dural puncture headache | 1:100 | 1:400 |
| Neurological damage | 1:1,000 (temporary) | |
| 1:13,000 (permanent) | ||
| Epidural abscess | 1:50,000 | |
| Meningitis | 1:100,000 | |
| Epidural haematoma | 1:170,000 | |
| Accidental unconsciousness | 1:5,000 | |
| Severe injury, including being paralyzed | 1:250,000 | |
Spinal anaesthesia
Operative delivery encompasses caesarean section, forceps and ventouse deliveries. Spinal anaesthesia is the commonest way of providing anaesthesia for operative delivery and is the most reliable of CNB techniques. The woman can be positioned in the sitting or lateral position, this may be dictated by the patient, fetal monitoring requirements or uncommon events such as cord prolapse.
Skin preparation
Controversy remains over the most appropriate antiseptic solution with which to clean the skin prior to insertion of CNB. The Royal College of Anaesthetists, The American Society of Anesthesiologists and The American Society of Regional Anesthesia all recommend the use of chlorhexidine in alcohol as the skin disinfectant of choice for CNB. A UK working party review in 2014 (see Further Reading) recommend the use of 0.5% chlorhexidine in alcohol for CNB, this being the agent that gives the best balance for risk of neurotoxicity vs. the risk of infection.
Chlorhexidine gluconate has the following characteristics:
Potent and broad spectrum
Effective against bacteria and yeast
Fast onset and long duration of action (when compared with povidone iodine)
Efficacious even in the presence of blood
Lower incidence of skin reactions (when compared with povidone iodine)
Chlorhexidine in alcoholic solution has improved bacteriostatic profile when compared with chlorhexidine in aqueous solution
There is an established risk of neurotoxicity in vitro and in animal studies; the risk of developing chronic adhesive arachnoiditis is extremely rare
There is limited in vivo evidence regarding the alterations in efficacy between 0.5% and 2% chlorhexidine
Meticulous attention should be given to reducing the risk of contamination of CNB equipment with chlorhexidine. Some advocate the use of pre-soaked sponge applicators or sprays; time must be allowed for the solution to dry
Hypersensitivity reactions have been described; most anaphylactic reactions have resulted from topical application to mucous membranes and the use of chlorhexidine-impregnated devices, although they can occur following contact with intact skin (see Chapter 23).
Other precautions (as per National Audit Project 3 recommendations) that should be employed at the time of CNB include:
Thorough hand washing with appropriate preparation
Hat, mask, sterile gown, gloves and drape
The recommended level for siting a spinal needle (25–27 gauge) is L3/4. Use of higher intervertebral spaces may result in damage to the cauda equina, particularly in view of the lack of reliability in confirming lumbar levels when using bony landmarks. See Chapter 18 for ultrasound of spine.
Spinal anaesthesia relies on distribution of local anaesthetic and/or opioids in the cerebrospinal fluid (CSF). Glucose levels in CSF are approximately two-thirds of that in venous blood. Use of a glucometer can help to confirm CSF if there is doubt. Whilst performing CNB, good communication with the woman is essential; it is important for the woman to report any issues with pain or paraesthesia on injection. If this occurs, then changing the direction of the needle can remedy the situation, if not then resiting the block is the safest option.
A reduced spinal dose of local anaesthetic (2.2–3.0 mL of 0.5% heavy bupivacaine) is required in the parturient as there is a smaller CSF volume in the lumbar region and greater sensitivity of nerve fibres to local anaesthetic. The cephalad displacement of CSF from the lumbar region is a result of caval compression and increased fat in the epidural space. Opioid analgesics are generally added to the local anaesthetic mixture to enhance the efficacy of the spinal block. The main contraindications to spinal opioid analgesia are opioid allergy and an active herpetic eruption.
Assessment of the block
The sensory block height should be assessed and documented prior to skin incision. Sensory examination should move caudad to cephalad bilaterally in the midaxillary or midclavicular lines.
The adequacy of regional anaesthesia for caesarean section has been assessed using a range of sensory modalities, including light touch, pinprick and cold. Absence of light touch sensation up to T5 dermatome is widely accepted to indicate an adequate level of block for caesarean section. Sacral anaesthesia is also essential as the S2–S4 dermatomes innervate the peritoneum overlying the lower uterine segment. Instrumental deliveries do not require the same height of block and can be commenced when certain of sacral anaesthesia and a block to T8. However, should the instrumental delivery be unsuccessful, the anaesthetist must assess the block height to ensure that it has reached an appropriate level to proceed to caesarean section under regional anaesthesia.
A survey of UK obstetric anaesthetists in 2010 showed that 74% still checked the block height with cold sensation to ethyl chloride alone. Concerns regarding the reliability of use of cold sensation to evaluate block height relate to the multimodal transmission of sensation. Cold, transmitted by Aδ fibres, may not be distinguished from cold discomfort, transmitted by C fibres. Aβ fibres may also be activated, transmitting light touch and possibly pressure sensation.
When sharp pinprick is used to assess block height, it is important to document the exact end point:
Total loss of all sensation to the pinprick
The pinprick is recognized as a touch
The pinprick is recognized as being sharp, but is less sharp than normal
The pinprick feels normal.
If the block is inadequate prior to skin incision then there are three options, which need to be discussed with the obstetricians:
Repeat the spinal anaesthetic, the second dose is dependent on the block height from the previous spinal (1.0–2.2 mL 0.5% heavy bupivacaine)
Postponement of the case in the elective setting
Conversion to GA.
Pain during CS under regional anaesthesia is one of the most common causes of obstetric anaesthetic litigation. It is essential to document thoroughly the woman’s concerns and offer alternative solutions, e.g. low-dose intravenous opioid analgesia, local anaesthetic infiltration by the surgeon or conversion to GA. Each step must be acted on promptly and the outcome of the intervention recorded.
Combined spinal epidural (CSE)
Indications for a combined spinal epidural approach for operative delivery include:
Anticipated prolonged surgery with the potential to exceed the anaesthetic duration of a single shot spinal (e.g. multiple previous CS, obesity, combined CS and tubal ligation):
a standard intrathecal dose is administered; the epidural catheter is in place for intraoperative supplementation if the spinal block regresses over time
Parturients with cardiac co-morbidities where sudden cardiovascular changes are undesirable:
a reduced intrathecal volume (1.0–2.0 mL) is injected to lessen the hypotension from sympathetic blockade; the block height can then be extended using the epidural catheter, thus minimizing cardiovascular instability.
There are two recognized techniques for CSE insertion:
1. Needle-through-needle technique: This is the commonest approach. The epidural space is located with a Tuohy needle, a spinal needle is passed through the Tuohy needle to puncture the dura and deposit medication in the CSF. The spinal needle is withdrawn and a catheter is then threaded into the epidural space. The risks of this technique include:
a. Threading the epidural catheter through the dural puncture created by the spinal needle
Related posts:
Non-regional analgesia techniques for labour
Anaesthesia for other obstetric indications: cervical suture, external cephalic version, controlled ARM, manual removal of placenta and perineal repair
Endocrine disease in pregnancy, including diabetes mellitus, thyroid and adrenal disease
HIV and infectious disease in pregnancy, including herpes, syphilis and hepatitis
Haematologic disease in pregnancy
Clinical governance and patient safety
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