202410192102

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Tags: Obstetrics, Neuraxial block

Neuraxial labour analgesia

Neuraxial techniques have consistently emerged as the gold standard in labour pain management, offering unparalleled efficacy compared to alternative modalities.

The choice of saline over air is often favoured due to its potential to mitigate adverse effects, such as a decreased incidence of postdural puncture headache (PDPH) and lower likelihood of uneven block distribution

EA vs CSE vs DPE

EA

Meta-analyses of trials comparing mixed parity parturients randomized to labor epidural analgesia, versus parenteral opioids, indicated a prolongation of the first and second stages of labor by 42 min and 14 min, respectively and no association with higher rates of cesarean delivery

CSE - Adv

CSE technique is increasingly favoured for its rapid onset of profound pain relief, particularly during advanced stages of labour. This method typically achieves analgesia within 2 to 10 minutes, compared to the 15 to 20 minutes required by traditional epidural analgesia

more uniform sensory blockade
enhanced coverage of the sacral dermatomes

Experts have raised concerns regarding the delayed confirmation of correct epidural catheter placement following CSE analgesia; however, evidence suggests that CSE technique is less prone to failure, potentially due to improved confirmation of midline needle placement in the epidural space through CSF visualisation

lower the incidence of unilateral anaesthesia cf EA

CSE - Disadv

maternal hypotension
opioid-induced pruritus

• ∴ lower opioid doses
• treat w/ nalbuphine
  • mixed agonist-antagonist at kappa & mu receptors

Fetal bradycardia ← uterine hypertonus

NNH 28 cf EA

underlying mechanism for fetal bradycardia following CSE initiation has not been fully elucidated, although a plausible theory is an abrupt reduction in catecholamines

A more rapid decline in epinephrine (i.e. a tocolytic) VS norepinephrine results in a sudden net loss of ß2 agonist activity, which can present as

• uterine irritability,
• tachysystole,
• tetanic contractions.
  If prolonged, uterine hypertonus → placental hypoperfusion → fetal bradycardia

Management involves

• basic measures for Intrauterine fetal resuscitation
  • call for assistance,
  • stopping oxytocin,
  • correcting maternal hypotension,
  • administering oxygen and bolus fluid,
  • instituting left uterine displacement
• administration of Tocolytics
  • (e.g., nitroglycerin or terbutaline)

no known effective preventive measures

prophylactic use of intravenous ephedrine 10 mg IV administration at the time of CSE placement has been ineffective in reducing the risk of fetal bradycardia

DPE

DPE analgesia offers a promising alternative. This technique facilitates quicker analgesic onset and better sacral spread than the epidural technique while potentially reducing side effects associated with CSE

DPE analgesia may be suitable for patients with suspected difficult airways or failed epidural labour analgesia, enabling confirmation of proximity to the dura with the dural puncture and spinal fluid return, but not eliciting adverse effects associated with CSE dosing

Concerns about postdural puncture headache (PDPH) associated with creating a hole in the dura have led to hesitancy in some to use either the CSE or DPE techniques. However, such concerns may not be well-founded, as evidenced by a study in nearly 20,000 women conducted in 2004 by Pan et al. They found that CSE or epidural technique had a similar need for an epidural blood patch

spinal needle shoulder be larger than 27G

Continuous spinal

The oldest catheter-based neuraxial technique is the continuous spinal technique, also called an intrathecal catheter (ITC)

In an attempt to reduce the incidence of PDPH, continuous spinal labor analgesia transitioned from the use of macro-(18G–20G) to micro- (28G–32G) catheters. While a reduction in PDPH was observed, an increase in the frequency of transient (0.4%) and permanent (0.1%, e.g., cauda equina syndrome) deficits was also reported

postulated causes of CES include

• caudal orientation of the catheter tip
• restricted flow rates,
• high local anesthetic concentrations → pooling by the nerves
  • (i.e., 5% lidocaine)

Postspinal pain syndrome (PSPS, also called transient radicular irritation) occurs more frequently in female, ambulatory patients who have been in the lithotomy position

potential advantages of using an ITC technique:

• analgesia onset rapid
  • w/ a dense and symmetric blockade
• minimal medication needed,
• conversion to surgical anesthesia is reliable

The incidence of PDPH is higher with macro-catheters, as a function of the larger 17G–18G epidural needle used to create a dural puncture; consequently, ITC as a de novo initiation technique is not routinely used

for Inadvertent dural puncture

ITC may be the most prudent alternative in some clinical situations, particularly when multiple prolonged attempts have been made, significant parturient distress is present, and delivery appears imminent

?keep ITC for 24h
extended time is purported to facilitate dural repair by fibrosis, as demonstrated in animal studies

a prospective study did not observe a significant difference in PDPH rates in which ITCs were left in situ for 24–36 h versus the epidural procedure being repeated at another interspace, the mode of delivery may have an impact; a lower incidence of PDPH was found in patients with an ITC who delivered via cesarean, versus vaginal delivery, perhaps due to CSF efflux that occurs with the strenuous Valsalva breathing patterns used for delivery

Maintenance

flowchart LR
      A("Before 1980s
      manual bolus") --> B["From 1980s
      CEI"]
      B --> B1("Early 1990s
      PCEA")
      B1 --> B2("After 2000
      PIEB")

This phenomenon can be explained by the pharmacodynamics of nerve blocks, where continuous infusion in the extraneural space establishes a diffusion gradient, leading to an equilibrium between intraneural and extraneural concentrations and subsequent blockade of both sensory and motor nerve fibers

The combination of PCEA with CEI as a background infusion improved analgesia consistency, but increased the risk of anaesthetic consumption and the risk of instrumental vaginal delivery

Since the early 2000s, programmed intermittent epidural bolus (PIEB) has been utilised to achieve a wider sensory block and better homogeneous distribution, often in conjunction with CEI or PCEA

PCEA + CEI vs CEI alone

• ↓ total local anaesthetic doses,
• ↓ motor block,
• ↓ need for intervention,
• ↑ pain relief
• ↑ patient satisfaction

PIEB vs CEI

• ↓ total LA consumption
• ↑ maternal satisfaction
• ↓ need for intervention w/ top-ups
• ↓ motor block
• ↓ instrumental vaginal deliveries

Emerging techniques such as computer-integrated PCEA (CIPCEA) allow for adaptive maintenance based on usage patterns, providing flexible analgesia adjustments over time

Bolus rate

The rate of bolus delivery seems to impact effectiveness, with high velocity injections favourable, although this may increase the risk of hypotension and motor block

LA choice

Traditionally, epidural solutions for labour analgesia employed highly concentrated local anaesthetic solutions, which often resulted in increased motor blockade and reduced maternal satisfaction

the shift towards more dilute local solutions has yielded promising outcomes. Studies have consistently shown that using lower concentrations of local anaesthetics is associated with a lower incidence of assisted vaginal deliveries, less motor block, greater ambulation, and a shorter second stage of labour compared to high concentration solutions

↓ motor block while maintaining effective analgesic levels → facilitate more effective pushing and patient engagement in the second stage of labour

low conc. = <0.125%

Adjuvants

Opioids

Neuraxial opioids play a crucial role in labour analgesia, exhibiting a synergistic effect when combined with local anaesthetic. This combination enhances analgesic effects, allowing a reduction in local anaesthetic dosing and consequently lowering the risk of systemic toxicity

The addition of a lipophilic opioid such as fentanyl or sufentanil has shown promise, potentially reducing the local anaesthetic requirements by up to four-fold

This combined approach not only minimises the required dose for each agent, thus limiting toxicity, but also extends the duration of analgesic effects, diminishes motor block, and enhances patient satisfaction when compared to the use of local anaesthetic alone

Extensive evidence supports the use of high-volume, low-concentration dosing of local anaesthetic in combination with a lipophilic opioid for epidural labour analgesia. This approach ensures comprehensive coverage from T10 to S3 with less motor block and better labour outcomes

= "Low dose EA"

Meta-analyses endorse the use of low-concentration local anaesthetic solutions, such as ≤0.1-0.15% bupivacaine, which pose no increased risk of assisted vaginal delivery compared to non-epidural analgesia

non-opioids

Clonidine & dexmedetomidine

Both α2-receptors agonists exert their analgesic effects through the α2-receptors located in the spinal cord

Intrathecal clonidine dosing ranges from 15-45 μg, with a study from Missant et al. demonstrating the potential for stronger and prolonged analgesia, although with a trade-off of significant refractory hypotension.

both oral and intravenous administration of clonidine and dexmedetomidine have been found to prolong the anaesthetic effect of intrathecal local anaesthetics.

For epidural administration doses of 30-150 μg have shown a good analgesic effect. However, doses of 75 μg and higher may lead to sedation, hypotension, and bradycardia, and alterations in foetal heart rhythm

Adrenaline

Epinephrine also acts through α2-receptors, although vasoconstrictive effects might be involved as well

It can contribute to epidural administration by significantly reducing the minimum local analgesic concentration (MLAC) of bupivacaine, thereby improving quality of analgesia

Disadv

• ↑ incidence maternal motor deficit
• possible prolongation of labour duration
• the need for pre-prepared solutions
  • → complicating storage and raising drug prices

beneficial effect in the context of labour epidural analgesia remains uncertain

Neostigmine

Neostigmine exhibits its effect as an indirect parasympathomimetic by inhibiting cholinesterase, thereby prolonging and enhancing the effect of acetylcholine on muscarinic and nicotinic receptors.

While it can be administered intrathecally or epidurally with good analgesic effect, it is associated with severe nausea and vomiting which precludes recommendation for its routine use

References

Neuraxial Analgesia for Labour - BJA Ed

Initiation and Maintenance of Neuraxial Labour AnalgesiaA Narrative Review - BPRCA

Neuraxial Labor Analgesia Initiation Techniques - BPRCA