Neuraxial Anaesthesia in Obstetrics
Last updated 22nd Jan 2018 - Tom Heaton
As noted in the discussion on C-section, neuraxial anaesthesia is the preferred technique for c-section due to its better risk/benefit profile.
This profile will similarly apply to many other obstetric surgical interventions.
The anaesthetic approach will vary slightly amongst the 3 different from (spinal, epidural, combined) but there are some common features in the approach.
This profile will similarly apply to many other obstetric surgical interventions.
The anaesthetic approach will vary slightly amongst the 3 different from (spinal, epidural, combined) but there are some common features in the approach.
Preoperative
A full history from the patient and medical notes is an essential starting point.
This will vary depending on the clinical scenario, and is similar in many ways to a general anaesthetic assessment, but some common important features include:
Examination will be guided by the history.
An examination of the lumbar surface anatomy may provide insight into whether regional anaesthesia may be difficult.
Investigations will be guided by any comorbidity.
Common essential investigations include:
Crossmatched blood may be requested in some clinical scenarios:
Consent is a very important part of the preoperative assessment.
This should be used to explain the nature of the anaesthetic plan, the reasoning and the risks and adverse effects.
Useful information is available from the Obsteric Anaesthetists’ Association, who have patient advice leaflets. http://www.oaa-anaes.ac.uk/home
There will be some variability in the incidence of adverse effects and risk depending on the technique ( the values below are for spinal anaesthesia), but common risks to discuss include:
This will vary depending on the clinical scenario, and is similar in many ways to a general anaesthetic assessment, but some common important features include:
- Obstetric history
- Nature of C-section? Indication?
- Parity of mother
- Problems in previous pregnancies/deliveries?
- Problems in this pregnancy?
- Nature of C-section? Indication?
- Anaesthetic history
- Previous obstetric anaesthesia?
- Previous obstetric anaesthesia?
- Past medical history
- Drug history
- Anticoagulants? E.g. LMWH
- Anticoagulants? E.g. LMWH
- Allergies
- Airway assessment
- Fasting status
- Elective antacid medication is appropriate in fasted patients (150mg oral ranitidine +/- oral sodium citrate)
- Elective antacid medication is appropriate in fasted patients (150mg oral ranitidine +/- oral sodium citrate)
Examination will be guided by the history.
An examination of the lumbar surface anatomy may provide insight into whether regional anaesthesia may be difficult.
Investigations will be guided by any comorbidity.
Common essential investigations include:
- Bloods
- Hb
- Group and screen - cross-match not routinely indicated (see below for indications)
- Hb
- Ultrasound - placental position
Crossmatched blood may be requested in some clinical scenarios:
- Anticipated haemorrhage
- Placenta praevia
- Coagulopathy
- Multiple pregnancy
- Placenta praevia
- Antibodies/concerns over difficulty obtaining crossmatched blood quickly
- Preop Hb below 10 g/dl
Consent is a very important part of the preoperative assessment.
This should be used to explain the nature of the anaesthetic plan, the reasoning and the risks and adverse effects.
Useful information is available from the Obsteric Anaesthetists’ Association, who have patient advice leaflets. http://www.oaa-anaes.ac.uk/home
There will be some variability in the incidence of adverse effects and risk depending on the technique ( the values below are for spinal anaesthesia), but common risks to discuss include:
- Sensation - it is nearly universal to feel sensations even under spinal anaesthesia, and the patient should have this well explained. Additional pain relief is needed in about 1 in 20
- Failure - conversion to GA may be necessary in some cases - 1 in 50 with spinal
- Hypotension - also very common, especially with spinal anaesthesia. Can present with nausea or lightheadedness - 1 in 5
- Itchiness - a frequent side effect of the neuraxial opioids - 1 in 3 patients
- Shivering - a frequent side effect with spinal anaesthesia
- Postoperative pain
- Postdural puncture headache - 1in in 500
- Nerve injury
- Transient nerve sensation common (on performance of technique)
- Temporary - 1 in 2000
- Permanent - 1 in 24,000
- Transient nerve sensation common (on performance of technique)
- Infection - epidural abscess 1 in 50,000, meningitis 1 in 100,000
- High spinal - 1 in 2000
Intraoperative
Full AAGBI monitoring is an essential requirement.
Large bore IV access is also essential (usually one 16g cannula is sufficient - local anaesthetic for insertion is advisable).
Fluids should be running freely prior to commencement of neuraxial blockade.
Full WHO safety checks are also essential.
Mechanical VTE prophylaxis should be in place.
Once the team is ready, neuraxial anaesthesia can be commenced.
Once performed, the patient will lie supine, with left tilt to ease aortocaval compression.
As noted below, with spinal anaesthesia, prophylactic vasopressor infusion is usually commenced to offset the sympathetic blockade and resulting hypotension.
The adequacy of the block should now be checked. It is common to use ethyl chloride spray to test for loss of cold sensation.
After this is confirmed, a catheter is inserted (essential to reduce the risk of bladder injury) and the patient can be prepped and draped.
Other key points in the anaesthetic management:
Large bore IV access is also essential (usually one 16g cannula is sufficient - local anaesthetic for insertion is advisable).
Fluids should be running freely prior to commencement of neuraxial blockade.
Full WHO safety checks are also essential.
Mechanical VTE prophylaxis should be in place.
Once the team is ready, neuraxial anaesthesia can be commenced.
Once performed, the patient will lie supine, with left tilt to ease aortocaval compression.
As noted below, with spinal anaesthesia, prophylactic vasopressor infusion is usually commenced to offset the sympathetic blockade and resulting hypotension.
The adequacy of the block should now be checked. It is common to use ethyl chloride spray to test for loss of cold sensation.
After this is confirmed, a catheter is inserted (essential to reduce the risk of bladder injury) and the patient can be prepped and draped.
Other key points in the anaesthetic management:
- Prophylactic antibiotics are usually administered prior to skin incision
- Oxytocin (5 units) is routinely given immediately after delivery to stimulate uterine contraction.
- Further uterotonics may be requested by the obstetrician.
- Once surgery is complete, administration of a NSAID is common (unless contraindicated) to optimise postoperative analgesia e.g. 100mg diclofenac PR.
Postoperative
Patients will be recovered as per after other surgery.
An appropriate postoperative analgesia regime should be prescribed and explained to the patient.
This will often require a multimodal approach, and take into account breastfeeding and transmission of medications.
Patients who have received neuraxial opioids should have this documented and appropriate observations instigated.
PRN antiemetics should also be provided.
Appropriate VTE risk assessment is essential given the increased risk associated with surgery.
An appropriate postoperative analgesia regime should be prescribed and explained to the patient.
This will often require a multimodal approach, and take into account breastfeeding and transmission of medications.
Patients who have received neuraxial opioids should have this documented and appropriate observations instigated.
PRN antiemetics should also be provided.
Appropriate VTE risk assessment is essential given the increased risk associated with surgery.
Spinal Anaesthesia
This is the most common method of anaesthesia for patients undergoing c-section in both the elective and urgent setting.
Advantages:
Disadvantages
Continuous spinal anaesthesia via an intrathecal catheter has been used historically but is now uncommon due to the high incidence of dural puncture headache.
It may still be found in the case of inadvertent dural puncture during an epidural insertion, when insertion of the catheter intrathecally is a well recognised approach.
However, the routine approach is via a single-shot spinal.
Advantages:
- Dense anaesthetic block
- Fast onset
- Minimal drug transfer to foetus
Disadvantages
- Most notable impact on CVS stability
- Single shot
- Finite duration
- Difficult to adjust if inadequate
- Finite duration
Continuous spinal anaesthesia via an intrathecal catheter has been used historically but is now uncommon due to the high incidence of dural puncture headache.
It may still be found in the case of inadvertent dural puncture during an epidural insertion, when insertion of the catheter intrathecally is a well recognised approach.
However, the routine approach is via a single-shot spinal.
Technique
The same pre-, intra- and post anaesthesia factors apply as for the other regional techniques.
The provision itself:
Anaesthetic agent
As with other spinal techniques, 0.5% heavy bupivacaine is the most common agent.
A dose of 2.5ml is commonly employed (with opioid).
300 micrograms diamorphine is the most common opioid added, as it provides good postoperative analgesia with a better side effect profile.
Other options include:
In the event of block failure (usually inadequate height) then a management option is to insert an epidural catheter and provide a top up via this to achieve the desired anaesthesia.
If no block at all has occurred then the injection was not intrathecal and a repeat attempt at spinal can be tried.
General anaesthesia will be the default option in the event of ongoing difficult and clinical urgency.
The same pre-, intra- and post anaesthesia factors apply as for the other regional techniques.
The provision itself:
- Spinal anaesthetic at target of L3/4 space
- Lie supine fairly promptly with left tilt
- Commence prophylactic vasopressors infusion
- For example, 30ml/hr of 100mcg/ml phenylephrine
- Closely assess for CVS changes with the onset of sympathetic blockade
- Assess for level of block
- Loss of motor power in legs usually signifies suitability for catheter insertion
- A target level of T4 is required (caudal block is usually complete unlike in epidural anaesthesia).
- Commencement of surgery
Anaesthetic agent
As with other spinal techniques, 0.5% heavy bupivacaine is the most common agent.
A dose of 2.5ml is commonly employed (with opioid).
300 micrograms diamorphine is the most common opioid added, as it provides good postoperative analgesia with a better side effect profile.
Other options include:
- Fentanyl (15 mcg) - minimal postoperative analgesia
- Morphine (100 mcg) - long postoperative analgesia but higher incidence of nausea and respiratory depression
In the event of block failure (usually inadequate height) then a management option is to insert an epidural catheter and provide a top up via this to achieve the desired anaesthesia.
If no block at all has occurred then the injection was not intrathecal and a repeat attempt at spinal can be tried.
General anaesthesia will be the default option in the event of ongoing difficult and clinical urgency.
Epidural Anaesthesia
This involves provision of anaesthesia via an epidural catheter (different from epidural analgesia used in labour).
Indications for this regional approach include:
Advantages:
Disadvantages:
Indications for this regional approach include:
- Epidural catheter already in situ (from labour analgesia)
- Maternal pathology which makes rapid CVS changes undesirable
- Potential need for prolonged surgical time (which would make single shot spinal anaesthesia of insufficient duration)
Advantages:
- More CVS stability
- ‘Top ups’ possible,
- allowing a more prolonged regional anaesthesia
- Titration of effect
- allowing a more prolonged regional anaesthesia
- Can provide postoperative analgesia
Disadvantages:
- Poorer block quality than spinal anaesthesia
- Slow onset
- High doses of local anaesthetic
Technique
The same pre-, intra- and post anaesthesia factors apply as for the other regional techniques.
A modification to the consent may involve a discussion around the different block density that can be expected.
The procedure involves:
Local anaesthetic options for top up include:
Fentanyl 100mcg can be given to improve the quality of the block.
Diamorphine 2.5mg may be given at the end for a more prolonged analgesia post operatively
The same pre-, intra- and post anaesthesia factors apply as for the other regional techniques.
A modification to the consent may involve a discussion around the different block density that can be expected.
The procedure involves:
- Insertion of an epidural catheter (as per for labour analgesia which is discussed elsewhere) or use of an in-situ catheter
- Test dose of anaesthetic agent e.g. 3ml 0.5% bupivacaine
- Administer epidural top up (see below)
- Ensure adequate block level (T4 to S4)
- Position supine with left lateral tilt
- Administer fluid +/- vasopressors to offset hypotension (likely to be less than with spinal anaesthesia)
Local anaesthetic options for top up include:
- 0.5% bupivacaine - 5ml every 4-5min (max 2mg/kg per 4 hours)
- 0.5% levobupivacaine - 5ml every 4-5min (max 2mg/kg per 4 hours)
- 0.5% ropivacaine - 5ml every 4-5min (max 2mg/kg per 4 hours)
- 2% lidocaine - 5ml every 2-3 mins (max 20ml)
Fentanyl 100mcg can be given to improve the quality of the block.
Diamorphine 2.5mg may be given at the end for a more prolonged analgesia post operatively
Conversion of a Labour Epidural
Patients with an epidural catheter in situ for labour analgesia may require urgent obstetric surgery.
This can be a challenging decision process.
This arises because in the event that an epidural top-up provides inadequate regional anaesthesia, the only option is to proceed to general anaesthesia.
This is because the administered volume in the epidural space compresses the volume of the CSF, making any attempt at spinal anaesthesia risk for a high block.
Two questions are relevant when faced with such a situation:
What is the time pressure?
In a true category 1 caesarean section, the time delay in establishing epidural anaesthesia is often too long to make it a safe approach.
In these cases general anaesthesia is often provided anyway.
This would seem to not be absolute, and more down to the ability of the anaesthetist and system they are working in to provide appropriate anaesthesia quickly (which may be very possible via an epidural route if appropriately streamlined).
How trustworthy is the epidural?
The epidural catheter needs to be adequately positioned, and have adequate epidural spread of anaesthetic agent to establish a bilateral, multilevel and continuous block.
As noted in the ‘labour analgesia’ epidural notes, there is unlikely to be epidural anatomy that results in entirely missed dermatomes, and inadequate blocks is often due to a unilateral problem.
This may be due to catheter position.
The features which may guide this decision process will vary on the clinical situation (e.g. the overall risk of having a GA) and the clinicians and patients approach to risk.
Factors that may help with the decision include:
This can be a challenging decision process.
This arises because in the event that an epidural top-up provides inadequate regional anaesthesia, the only option is to proceed to general anaesthesia.
This is because the administered volume in the epidural space compresses the volume of the CSF, making any attempt at spinal anaesthesia risk for a high block.
Two questions are relevant when faced with such a situation:
- What is the time pressure for surgery?
- How trustworthy is the epidural?
What is the time pressure?
In a true category 1 caesarean section, the time delay in establishing epidural anaesthesia is often too long to make it a safe approach.
In these cases general anaesthesia is often provided anyway.
This would seem to not be absolute, and more down to the ability of the anaesthetist and system they are working in to provide appropriate anaesthesia quickly (which may be very possible via an epidural route if appropriately streamlined).
How trustworthy is the epidural?
The epidural catheter needs to be adequately positioned, and have adequate epidural spread of anaesthetic agent to establish a bilateral, multilevel and continuous block.
As noted in the ‘labour analgesia’ epidural notes, there is unlikely to be epidural anatomy that results in entirely missed dermatomes, and inadequate blocks is often due to a unilateral problem.
This may be due to catheter position.
The features which may guide this decision process will vary on the clinical situation (e.g. the overall risk of having a GA) and the clinicians and patients approach to risk.
Factors that may help with the decision include:
- Satisfaction of insertion - if inserted by the clinician, was inserted easy and uncomplicated
- Satisfaction of analgesia - has pain relief been good since insertion. Persisting unilateral symptoms are an adverse feature for an epidural top-up.
Combined Spinal Epidural (CSE)
his technique aims to combine the advantages of spinal and epidural anaesthesia.
Indications:
Advantages
Disadvantages
Indications:
- Anticipated prolonged surgery
- Maternal pathology that makes rapid CVS changes undesirable.
Advantages
- More CVS stability (if low spinal dose used)
- ‘Top ups’ possible,
- allowing a more prolonged regional anaesthesia
- Titration of effect
- allowing a more prolonged regional anaesthesia
- Fast onset
Disadvantages
- Technically more difficult
- Higher failure rate
- Still potentially CVS disturbance
Technique
The main parts of the technique are as per the other neuraxial approaches.
The technique involves the combination of a single shot spinal anaesthetic, and the insertion of an epidural catheter.
There are two main approaches to this:
Needle through needle
A single needle is used.
This may be a specially designed CSE needle, or simply a Tuohy needle, with the passing of the 25g spinal needle through it.
Two needle
Two injections at separate levels are performed
The main parts of the technique are as per the other neuraxial approaches.
The technique involves the combination of a single shot spinal anaesthetic, and the insertion of an epidural catheter.
There are two main approaches to this:
- Needle through needle
- Two needle
Needle through needle
A single needle is used.
This may be a specially designed CSE needle, or simply a Tuohy needle, with the passing of the 25g spinal needle through it.
- The epidural space is located by the usual technique
- The spinal needle is passed through the needle, and further into the deeper CSF
- After CSF aspiration, the spinal anaesthetic is injected
- The epidural catheter is then passed down the Tuohy needle, and positioned as normal
- The Tuohy needle is withdrawn
- The catheter is tested by careful aspiration and assessment of falling meniscus (test dosing is unreliable because of the spinal anaesthetic)
Two needle
Two injections at separate levels are performed
- An epidural is inserted first, as per normal technique
- The catheter is left in situ and the Tuohy needle removed
- The spinal anaesthetic is then performed at a separate intervertebral space
Complications
There are several well recognised adverse effects from neuraxial anaesthesia where appropriate management is needed.
Hypotension
Very common with spinal anaesthesia.
Regional blockade of the sympathetic ANS fibres resulting in vasodilation.
Aortocaval compression can also contribute.
Management involves managing the appropriate cardiovascular components.
Preload:
More problematic if patients are hypovolaemic, which will usually be in the context of haemorrhage (hence the relative contraindication of spinal anaesthesia).
In these case, adequate volume replacement is required (which will usually be with blood)
Electively, crystalloid loading is commonly performed, although the benefits are not clear.
Ensure preload reduction from
Afterload
Reduced systemic vascular resistance from the sympathetic ANS blockade is often a significant contributing factor to hypotension.
Whilst bolus doses of vasopressor agents have commonly been used in the past, it is more common to use vasopressor infusions e.g. phenylephrine 100 mcg/ml.
This will commonly be commenced prophylactically at the time of spinal injection (e.g. 30m/hr) and titrated to effect.
Rate
Excessive tachycardia is unlikely to be a contributing factor to hypotension.
Bradycardia may result as a reflex from vasopressor use, from vasovagal responses, or in some cases from an excessively high spinal (with blockade of the sympathetic ANS cardioaccelerator fibres).
An anticholinergic can be used e.g. atropine.
Inadequate Anaesthesia/Analgesia
This is a recognised adverse feature of a neuraxial approach, occurring in about 5% of cases.
Careful testing before surgical preparation should ensure that this is detected prior to surgery commencing.
However, in some cases an apparently adequate block can still leave patients experiencing excess discomfort intraoperatively.
Discussion with the patient and surgeons is essential to gather information on the location of the pain, likely causes and stage of surgery.
Some steps are commonly associated with notable discomfort e.g. externalisation of the uterus, and can be managed with reassurance about the nature and temporary timeframe.
If this unlikely to be a temporary situation, then management options include:
Hypotension
Very common with spinal anaesthesia.
Regional blockade of the sympathetic ANS fibres resulting in vasodilation.
Aortocaval compression can also contribute.
Management involves managing the appropriate cardiovascular components.
Preload:
More problematic if patients are hypovolaemic, which will usually be in the context of haemorrhage (hence the relative contraindication of spinal anaesthesia).
In these case, adequate volume replacement is required (which will usually be with blood)
Electively, crystalloid loading is commonly performed, although the benefits are not clear.
Ensure preload reduction from
Afterload
Reduced systemic vascular resistance from the sympathetic ANS blockade is often a significant contributing factor to hypotension.
Whilst bolus doses of vasopressor agents have commonly been used in the past, it is more common to use vasopressor infusions e.g. phenylephrine 100 mcg/ml.
This will commonly be commenced prophylactically at the time of spinal injection (e.g. 30m/hr) and titrated to effect.
Rate
Excessive tachycardia is unlikely to be a contributing factor to hypotension.
Bradycardia may result as a reflex from vasopressor use, from vasovagal responses, or in some cases from an excessively high spinal (with blockade of the sympathetic ANS cardioaccelerator fibres).
An anticholinergic can be used e.g. atropine.
Inadequate Anaesthesia/Analgesia
This is a recognised adverse feature of a neuraxial approach, occurring in about 5% of cases.
Careful testing before surgical preparation should ensure that this is detected prior to surgery commencing.
However, in some cases an apparently adequate block can still leave patients experiencing excess discomfort intraoperatively.
Discussion with the patient and surgeons is essential to gather information on the location of the pain, likely causes and stage of surgery.
Some steps are commonly associated with notable discomfort e.g. externalisation of the uterus, and can be managed with reassurance about the nature and temporary timeframe.
If this unlikely to be a temporary situation, then management options include:
- Nitrous oxide - administered via the anaesthetic machine with O2
- IV opioids e.g. alfentanil 250 mcg to effect
- Wound infiltration with local anaesthetic (if cutaneous in nature)
- Conversion to general anaesthesia
Links & References
- Birnbach, D. Browne, I. Anaesthesia for obstetric, in: Miller’s Anaesthesia (7th ed).
- Allman, K. Wilson, I (eds). Oxford handbook of anaesthesia (3rd ed). 2012. Oxford University Press
- Heazell, A. Clift, J (eds). Obstetrics for anaesthetists. 2008. Cambridge University Press.
- Levy, D. Anaesthesia for caesarean section. BJA CEPD reviews. 2001. 1(6):171-176
- McGlennan, A. Mustafa, A. General anaesthesia for caesarean section. CEACCP. 2009. 9(5): 148-151.
- Obstetric Anaesthetists’ Association. Information for mothers. Available at: http://www.oaa-anaes.ac.uk/home
- Difficult Airway Society. Guidelines for the management of difficult and failed intubation in obstetrics. 2015. Available at: https://www.das.uk.com/guidelines/obstetric_airway_guidelines_2015
- Rucklidge, M. Hinton, C. Difficult and failed intubation in obstetrics. 2012. CEACCP. 12(2): 86-91
