Continuous audit by the Obstetric Anaesthetists’ Association (OAA) suggests that half to two-thirds of caesarean sections (CS) in the UK are currently done under single-shot spinal anaesthesia.
Problems and special considerations
Rapid onset of widespread vasodilatation coupled with the effect of aortocaval compression means that hypotension is an almost inevitable accompaniment to spinal anaesthesia unless specific precautions are taken. Left uterine displacement, frequent blood pressure measurement and instant availability of intravenous fluid and vasopressors are prerequisites for the safe use of this technique.
Careful assessment of the level of block is essential before starting the operation. Despite an apparently adequate block, pain may still occur, although this is less likely than if an epidural anaesthetic has been used. Mothers should be warned of this possibility in advance, and adequate treatment, even to the extent of inducing general anaesthesia, must be offered.
The incidence of postdural puncture headache (PDPH) is related to the size and type of needle used. Pencil-point and conical-tip needles, such as the Sprotte and Whitacre, are associated with a much lower rate of headache than Quincke needles with a cutting tip, so much so that a 24 G pencil-point needle is probably better than a 27 G Quincke needle.
Meningitis and encephalitis are extremely rare. However, once the dura mater has been penetrated, the cerebrospinal fluid (CSF) is particularly susceptible to contamination, and it is considered mandatory to use a completely aseptic technique, including the wearing of mask, gown and gloves.
Management options
Suitability of the technique
In experienced hands, spinal anaesthesia can be almost as fast as general anaesthesia, and there are few occasions when the urgency of the situation means that there is no time for this technique. If the mother already has an effective epidural in situ then, time permitting, this should be topped up in preference to establishing a new block. If time is short, a single-shot spinal has been suggested as an alternative to general anaesthesia in a mother with an epidural in situ. If spinal supplementation of an existing epidural block is thought appropriate, it may be necessary to use a reduced dose if an epidural top-up has recently been given, as there have been case reports of very high blocks in these circumstances.
Spinal anaesthesia is contraindicated in patients with hypovolaemia, coagulation disorders (whether iatrogenic or pathological) and systemic sepsis. Although regional anaesthesia was traditionally avoided previously if massive blood loss was expected, such as in placenta praevia, many anaesthetists would now use a spinal block in this situation. There is some evidence to suggest that blood loss and the need for blood transfusion is reduced if regional anaesthesia is used in these circumstances.
Although traditionally favoured as being better for the baby than general anaesthesia, there is evidence that spinal anaesthesia may be associated with greater neonatal acidosis than after epidural or general anaesthesia, possibly related to the rapidity of onset and cardiovascular changes. However, the rapid onset and more profound block compared with epidural anaesthesia, and the greater maternal safety profile compared with general anaesthesia, make spinal anaesthesia the technique preferred by most obstetric anaesthetists for CS.
Preoperative preparation
Preoperative assessment may be compromised by the urgency of the case, but should include assessment for difficult intubation, since general anaesthesia may be needed if the block is unsatisfactory. An explanation of the technique should be given, and the mother should be warned about the risks of hypotension with associated nausea and vomiting, and intraoperative sensations of tugging or stretching. The possibility of pain during the operation must be mentioned, although she should be reassured that this is unusual and will be treated if necessary with intravenous opioids, inhaled nitrous oxide or even general anaesthesia. Most mothers prefer their partners to be present for the delivery, and it is good practice to involve them in these discussions so that they are aware of what may happen.
Preparation
Standard monitoring is mandatory, and good intravenous access is essential. Most anaesthetists prefer to perform spinal anaesthesia with the patient on the operating table, since this minimises the need for movement after the local anaesthetic has been administered. Sitting and lateral positions are both acceptable, although there is evidence that the former may be easier if the bony landmarks are difficult to palpate. The block tends to develop more rapidly in the lateral position, probably owing to the slope of the vertebral canal in this position in women (the hips are wider than the shoulders, causing a downward slope towards the head, unlike in men, in which the opposite tends to occur).
Administration of the spinal anaesthetic
Full asepsis should be used, and an interspace below L3 should be chosen to ensure that the needle tip is well below the termination of the cord. A pencil-point or conical-tip needle is standard practice in obstetrics nowadays. Once free-flowing CSF has been identified, the chosen dose of local anaesthetic should be administered over 10-20 seconds. ‘Dry tap’ or pain during insertion or injection should be a signal to withdraw the needle and try again.
Drugs
Hyperbaric bupivacaine 0.5% is the most commonly used local anaesthetic for spinal anaesthesia in the UK. A dose of 10-15 mg (2-3 ml) is typically used for de novo spinal anaesthesia, although low-dose techniques (< 10 mg) have been used in an attempt to reduce hypotension and nausea/vomiting - though at the expense of less reliable anaesthesia. Fentanyl 15-20 µg, preservative-free morphine 75-100 µg, or diamorphine 0.3-0.4 mg is usually added for postoperative analgesia. However, caution must be observed when using intrathecal morphine, as there have been case reports associated with delayed respiratory depression. This is thought to be less likely with intrathecal diamorphine, and there have been no case reports to date of delayed respiratory depression in the obstetric population with diamorphine.
Spinal anaesthesia-induced hypotension may be seen in almost three-quarters of women undergoing CS in the absence of preventive measures, and carries the risk of undesirable maternal and fetal effects, especially if it is prolonged. A preload of 1000-2000 ml was traditionally used before the spinal dose was given. However, ‘co-loading’ (giving 400-800 ml fluid together with a prophylactic vasopressor) is now widely used, and this avoids excessive fluid administration. Colloid solutions have been shown to be more efficacious than crystalloids at preventing hypotension, but they are more expensive and there is a small risk of allergy. A vasopressor must be to hand, and phenylephrine is now the vasopressor of choice as it has been shown to cause less fetal acid-base disturbance than ephedrine, although the latter may be administered in the presence of bradycardia or in women with certain cardiac conditions in whom its ^-agonistic effects may be beneficial. Recent consensus guidelines recommend that phenylephrine is given as a prophylactic infusion, with an aim to preserve maternal systolic blood pressure at or above 90% of the baseline reading. Infusions may be associated with more cardiovascular stability, but the doses given greatly exceed those when bolus injections are used.
After the injection, the mother should be moved quickly but carefully into a left-wedged supine position, ensuring that there is no head-down tilt, and the blood pressure checked at 1-2-minute intervals. Some practitioners prefer to turn the mother into a full lateral posture, avoiding the wedged supine position until just before draping and incision. Some prefer to tip or turn the woman to the right side for a few minutes, before turning her to the left-tilted position, in order to obtain a more symmetrical block.
Testing the block
To minimise the risk of pain, the block should extend up to T5 on both sides when testing to touch, and this is now considered the gold standard. A block to light touch extending to T5 has been shown to be associated with a low incidence of intraoperative pain and a reduced need for intraoperative supplementation, compared with the same extent of block to pinprick or cold sensation. Although a complete block below the upper level is fairly certain when spinal anaesthesia is used, it is good practice to check that the sacral segments are covered and that the mother cannot straight leg raise against gravity. A recalcitrant block can be extended by using a variety of techniques such as turning from side to side, coughing, a Valsalva manoeuvre or judicious head-down tilt. The extent of the block and the modality used for testing must always be recorded.
Failed or inadequate spinal anaesthesia after an apparently uncomplicated injection is usually caused by technical errors such as displacement of the spinal needle (leading to partial or total loss of the intrathecal drug) or under-dosage, or occasionally by the presence of anatomical abnormalities in the subarachnoid space. Subsequent management and the decision to re-attempt neuraxial blockade or to administer general anaesthesia would largely be determined by maternal and fetal risk factors and the urgency of the clinical situation. In patients with partially effective spinal anaesthesia and an existing level of neuraxial block, a combined spinal-epidural might enable titration of the dose and reduction of the risk of a high block with repeat intrathecal injection.
During the operation
The patient should be watched for premonitory signs of hypotension, such as pallor, yawning or nausea. Bradycardia may indicate a high block affecting the sympathetic cardiac accelerator fibres, or be related to the use of phenylephrine. The mother may complain that her chest ‘feels heavy’; this sensation is common when the intercostal muscles are affected, and reassurance should be offered. Complaints of discomfort or pain may occur despite an initial satisfactory block and must be managed promptly and effectively (see Chapter 49, Breakthrough pain during caesarean section).
After the operation
Positional changes may cause sudden cranial spread of the block even at this late stage. Standard postoperative monitoring and observations must be ensured (see Chapter 33, Caesarean section). The sitting position may be carefully adopted if the blood pressure is stable. The mother should not be moved to the ward until there is cardiovascular stability and the block is receding. Anaesthetic follow-up for symptoms of PDPH or persistent block should continue for 48 hours.
Key points
• Pencil-point or conical-tip needles should be used to minimise the risk of postdural puncture headache.
• Hypotension is almost invariable and may be actively prevented by the prophylactic use of vasopressors.
• The extent of the block must be tested and recorded, and the patient should be warned of the risk of pain.
Further reading
Arzola C, Wieczorek PM. Efficacy of low-dose bupivacaine in spinal anaesthesia for Caesarean delivery: systematic review and meta-analysis. Br J Anaesth 2011; 107: 308-18.
Butwick AJ, Columb MO, Carvalho B. Preventing spinal hypotension during Caesarean delivery: what is the latest? Br J Anaesth 2015; 114: 183-6.
Heesen M, Klohr S, Rossaint R, Straube S. Prophylactic phenylephrine for caesarean section under spinal anaesthesia: systematic review and meta-analysis. Anaesthesia 2014; 69: 143-65.
Kinsella SM, Carvalho B, Dyer RA, et al. International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia. Anaesthesia 2018; 73: 71-92.
Langester E, Dyer RA. Maternal haemodynamic changes during spinal anaesthesia for caesarean section. Curr Opin Anaesthesiol 2011; 24: 242-8.