202407061852

Status:

Tags: Obstetrics, Neuraxial block

EA

epidural technique takes approximately 50 attempts to achieve a consistent and confident success

Sitting vs lateral

Benefits of lateral position

identify the space

↑ accuracy w/ USG

Nocebo-induced hyperalgesia during LA injection

→ use kind words

Paramedian vs midline

Bevel direction

Bevel facing cephalad

Bevel facing to one side may ↑ unilateral block → useful in e.g. orthopaedics

LOR

LOR first described 1921 (Sicard & Forestier)

air vs NS: no difference in

avoid LOR to air if

Air Cx

CSF saline
warm cold
pH > 8 pH < 7
glucose -
protein -
→ Need all 4 to differentiate
(add a drop of thiopentone → CSF turn turbid)

Test dose

problems w/ adrenaline

Saline prior to catheter

= epidural saline pre-distention
↓ blood in catheter (evidence w/ older nylon catheter)
? ↓benefit w/ new (= softer) catheters

Securing the catheter

catheter naturally moves w/ soft tissue (up to 4cm movement in BMI >30)
→ allow to change posture before taping

but 7cm inside ↑ unilateral block

Initial dosing

↓ conc of LA w/ ↑ volume

Epidural opioid

↓ LA dose
↓ motor block → ↓ instrumental delivery
↑ maternal satisfaction

epidural fentanyl

Patchy / unilateral block

Reasons for failed block

?top up before shift out

Failure of EA / labour neuraxial analgesia

definition varies & unclear e.g.

Risk factors

Patient factor

Sacral block sparing

sacral nerve fibers, compared to lumbar nerve fibers, are more difficult to block ∵ larger diameter and thicker myelin sheaths

analgesic solutions administered in the lumbar epidural space have a greater propensity for cephalad, rather than caudal, spread

Using a lower lumbar insertion point diminishes the distance to the sacral elements but does not appear to fully mitigate sacral sparing

lignocaine

Inadvertent dural puncture

Epidural hyperthermia

Conversion to anaesthesia for CS

History

Between 1970 and 1998 in the USA, almost one-fifth of maternal deaths associated with obstetric anaesthesia were related to the administration of epidural anaesthesia, many following the administration of bupivacaine 0.75% and the result of inadvertent high or total spinal blockade or LA systemic toxicity (LAST)

Drug used

The fastest onset of sensory blockade when converting the epidural is achieved using lidocaine 2% and adrenaline (epinephrine)

Fentanyl further ↓ onset time

The addition of ropivacaine 0.75% to the epidural top-up solution reduces the need for supplementation during surgery.

It is possible that the fentanyl contained in the epidural solution administered for labour could have already produced a near-maximal effect, explaining the observed difference in the emergency compared with elective Caesarean section.

Bicarbonate can facilitate the alkalinisation of the epidural top-up solution, increasing the unionised fraction of lidocaine available to cross the neuronal membrane and possibly increasing the lipid solubility of fentanyl and its penetration into both the spinal cord and systemic circulation

Evaluation of block

Loss of sensation to touch up to and including the T5 dermatome is required to prevent pain reliably during Caesarean section.

Given that the afferent nerves carrying sensation of pain from the pelvic organs are thought to accompany the sympathetic nerves and enter the spinal cord around T10 to L1 and that the neuraxial blockade is required to be much higher than T10, other non-conventional nerve pathways must be involved in the transmission of pain in Caesarean section

It could be that some of the pelvic afferent nerves follow the sympathetic nerves through the intra-abdominal plexuses and the greater splanchnic nerve to reach the spinal cord as high as T5. It may be that the visceral pain is not of pelvic origin but originates from other intra-abdominal structures innervated by the afferent nerves which enter the spinal cord at T5

In neuraxial blockade, loss of sensation to cold is found to be many dermatomes higher than the level at which sensation to sharp pinprick is lost and this, in turn, is observed to be several dermatomes higher than loss of sensation to touch. Nevertheless, there is not a constant relationship between the dermatomal levels assessed by these three sensory modalities with significant variation within and between individuals

Test dose: controversial
"every top-up dose is a test dose"

The decision of where to best initiate the labour epidural conversion continues to be debated and is influenced by many factors including the local logistics and urgency of Caesarean section

Conversion failure (of EA for C section)

defined as

major factors:

Conversion failure implies other risks:

guidelines from the RCoA state that the rate of conversion from neuraxial to GA for Category 1 and Categories 1–3 Caesarean section overall should be <15% and 5%, respectively

Breakthrough pain in labour could be a marker of a poorly functioning epidural or may signify dysfunctional labour

Management Drawbacks and risks
CSE Longer time to perform
Difficult to choose the optimal intrathecal dose of LA
Untested epidural catheter if subsequent epidural dosing needed
Potential of LAST with epidural administration of additional LA
General anaesthesia Accidental awareness
Complications associated with aspiration and failed intubation
Greater maternal and neonatal sedation
Increased risk of poor uterine tone and blood loss
Related to depressed Apgar scores at 5 min, the need for bag mask ventilation and admission to neonatal intensive care
Increased postoperative pain and PONV
Impairment of early breast feeding and maternal–neonatal bonding
Manipulation or replacement of epidural Longer time to perform
Potential of LAST with epidural administration of additional LA
Spinal Difficulty in obtaining cerebrospinal fluid and increased risk of block failure
Difficult to select the optimal intrathecal dose of LA
Decreases in the intrathecal dose of LA further increase the risk of block failure
Potential of high or total spinal with standard or modestly reduced intrathecal dose of LA

It can be challenging to perform a spinal in the context of a failed labour epidural conversion because of the associated difficulty in obtaining CSF. This could be attributable to the collapse of the subarachnoid space below the termination of the spinal cord secondary to the volume effect of the epidural bolus. Spinal anaesthesia performed within 30 min of a failed labour epidural top-up has been associated with an increased risk of failure and may reflect the erroneous assumption that the free flow of clear fluid must be CSF rather than previously injected LA within the epidural space

References

Ten Tips to Optimize Your Epidural Technique

Conversion of Labour Epidural Analgesia to Surgical Anaesthesia for Emergency Intrapartum Caesarean Section

Episode 50 — CSE vs Epidural Debate With Mike Hofkamp and Jacqueline Galvan

Episode 229 — Keywords Part 19 — Epidurals

Boon, J.M., Abrahams, P.H., Meiring, J.H. and Welch, T. (2004), Lumbar puncture: Anatomical review of a clinical skill. Clin. Anat., 17: 544-553. https://doi.org/10.1002/ca.10250

Paramedian Lumbar Epidural Technique Why You Should Adopt It - Jeremy Collins, MD

Failed epidural for labor: what now? - Minerva Anestesiologica 2017 November;83(11):1207-13 - Minerva Medica - Journals

Conversion of Labour Epidural Analgesia to Surgical Anaesthesia for Emergency Intrapartum Caesarean Section - BJA Ed

Neuraxial Labor Analgesia Initiation Techniques - BPRCA