Paediatric Regional Anaesthesia: Differences in Performance Compared with Adults

Overview and Rationale for Paediatric Regional Anaesthesia

• Paediatric regional anaesthesia (PRA) encompasses peripheral nerve blocks, neuraxial techniques (spinal, epidural, caudal), and catheter-based continuous infusion techniques.
• The fundamental goals, surgical anaesthesia, postoperative analgesia, and opioid-sparing, are shared with adult practice, but the anatomical, physiological, and pharmacological differences between children (particularly neonates and infants) and adults profoundly affect how these techniques are performed, dosed, and monitored.
• A critical operational difference is that PRA is almost universally performed under general anaesthesia or deep sedation in children, rather than in the awake patient as is conventional in adults.
• This is supported by large-scale safety data from the Paediatric Regional Anaesthesia Network (PRAN) and multiple international audits covering over 100,000 blocks.

Anatomical Differences and Their Technical Implications

Neuraxial Anatomy

• The more caudal conus position in neonates means lumbar spinal techniques carry a higher risk of direct cord injury if the correct interspace is not identified; the L4-L5 interspace is the recommended level for neonatal spinal puncture.
• The loose epidural fat in infants facilitates longitudinal spread of local anaesthetic from caudal injections, allowing catheters threaded from the sacral hiatus to reach thoracic levels, a unique paediatric technique.

Peripheral Nerve Anatomy

Peripheral nerves in neonates and small infants are less myelinated and have less surrounding connective tissue. This means:

• Onset of block is faster
• Spread of local anaesthetic around nerve fascicles is more extensive
• Volume requirements per unit weight are generally lower, though weight-based dosing is still used
• Ultrasound guidance has become the standard of care for peripheral nerve block placement in children; structures are superficial and highly echogenic, making real-time visualisation straightforward.
• Continuous ultrasound-guided caudal injection increases first-puncture success and lowers the risk of vascular puncture and inadvertent subcutaneous injection compared to landmark technique.

Physiological Differences Affecting Block Performance

Cardiovascular Response to Neuraxial Block

• Unlike adults, neonates and young children (under approximately 8 years) demonstrate a markedly attenuated haemodynamic response to neuraxial sympathectomy.
• This is attributed to the relatively underdeveloped sympathetic nervous system and lower resting sympathetic tone.

In practice:

• Significant hypotension following spinal or epidural block is uncommon in infants and young children
• Fluid preloading prior to neuraxial block is generally not required (unlike adults)
• This physiological difference is clinically advantageous, particularly for the awake spinal technique in high-risk ex-premature infants undergoing inguinal hernia repair

Respiratory Effects and Apnoea Risk

• Spinal and regional anaesthesia offers a specific advantage in the ex-premature infant population.
• Prematurity is the strongest predictor of postoperative apnoea (OR 22; 95% CI 4-109).
• Primary regional anaesthesia (spinal, caudal, or combined) reduces the incidence of early apnoea (0-0.5 h) compared to general anaesthesia, though late apnoea rates (0.5-12 h) are not significantly different.
• This underpins the role of awake spinal anaesthesia in ex-premature infants (post-menstrual age ≤ 60 weeks) having inguinal hernia repair, where avoiding volatile agents reduces but does not eliminate apnoea risk.
• Neurodevelopmental outcomes at 2 and 5 years do not differ between regional and general anaesthesia groups.

Pharmacokinetic Differences

Key differences affecting local anaesthetic dosing in neonates and infants:

• The reduced plasma protein binding increases the free fraction of amide local anaesthetics, increasing LAST risk.
• Neonatal hepatic immaturity slows metabolism of amide agents (lidocaine, bupivacaine, ropivacaine).
• For continuous infusions in neonates and young infants, maximum infusion rates must be reduced relative to older children and adults.

Dosing practices for peripheral nerve blocks in children are noted to sometimes approach or exceed safe dose limits, and this occurs more commonly in younger children, a key safety concern.

Specific Techniques: Performance Differences

Spinal Anaesthesia

• The shorter duration of spinal block in neonates is clinically important, the surgery must be completed within the block window.
• The higher cerebrospinal fluid volume per kilogram in infants ($\sim$ 4 mL/kg vs $\sim$ 2 mL/kg in adults) contributes to greater dilution of intrathecal local anaesthetic and shorter block duration.

Intrathecal opioids provide prolonged analgesia after surgery in children and reduce blood loss during paediatric spinal fusion; however, high doses of intrathecal morphine have been associated with respiratory failure and ICU admission.

Epidural and Caudal Anaesthesia

• The caudal approach to the epidural space is the most commonly performed neuraxial technique in children and is largely unique to paediatric practice.
• It exploits the easily identifiable sacral hiatus, the loose epidural fat, and the predictable spread of local anaesthetic to provide analgesia for lower abdominal, perineal, and lower limb surgery.

• For thoracic and major abdominal surgery in children, epidural catheters may be placed via the lumbar or thoracic interspace or threaded cephalad from the caudal approach.
• Epidural ropivacaine/sufentanil combinations are used; however, catheter-related complications in neonates with neuraxial catheters are notable, a US multicentre safety analysis reported a 13.3% complication rate (catheter malfunction, contamination, vascular puncture) in neonates with neuraxial catheters, though no complications resulted in long-term sequelae and serious complication risk was 0.3/10,000.

In young children having laparotomy, early epidural catheter removal occurred in 35% of cases, most commonly due to inadequate analgesia and technical failure, reflecting the challenges of catheter management in this population.

• Continuous epidural infusions provide effective postoperative analgesia in children of all ages.
• Epidural infusions of local anaesthetic provide similar analgesia to systemic opioid infusion.
• Epidural opioids alone are less effective than epidural local anaesthetic or combinations of local anaesthetic and opioid.

Major Plexus Blocks

The same plexus blocks used in adults (brachial plexus, femoral nerve, sciatic nerve, fascia iliaca) are applicable in children, with modifications:

• Ultrasound guidance is standard and facilitates accurate needle placement in small anatomical spaces
• Weight-based volume dosing (ml/kg) replaces fixed-volume dosing
• Continuous catheter techniques are used in hospital and post-discharge with low secondary failure rates
• Peripheral nerve blocks, wound infiltration, and caudal local anaesthetic all provide effective analgesia for day-stay paediatric inguinal surgery

Safety Profile: Age-Related Differences

Overall Complication Rates

Large-scale paediatric audits demonstrate that PRA has a low overall complication rate, comparable to adult practice, when performed under general anaesthesia by experienced practitioners.

Age-Specific Risk

Younger age is consistently associated with higher complication rates:

• Neonates vs older children: OR 2.9 (95% CI 1.2-7.0) for complications
• Neonates: 1.13% complication rate vs 0.3-0.8% in older children
• Dosing errors: 0.3% in children < 12 months vs 0.07% in children > 12 months
• Infants < 6 months: 0.4% vs 0.1% in children > 6 months

Blocks Under General Anaesthesia vs Awake

• A critical safety finding specific to paediatric practice is that blocks placed under general anaesthesia have a lower combined incidence of major adverse events (LAST and neurological deficit together: 2.2/10,000) compared to blocks placed awake or with sedation (15.2/10,000).
• This is the inverse of the adult paradigm, where awake techniques are preferred to allow neurological feedback during needle placement.

This paradox is explained by the inherent difficulty of obtaining reliable neurological feedback from a distressed, moving child, the risk of sudden movement during needle placement, and the ability to use real-time ultrasound under controlled conditions when the child is anaesthetised.

LAST in Children

• LAST risk is higher in neonates and infants due to pharmacokinetic factors above.
• Lipid emulsion 20% is used for resuscitation in paediatric LAST (neonates to 18 years) with the same dosing recommendations as adults; higher doses have led to adverse effects in children.

Adjuvant Medications

Several adjuvants extend block duration and quality in children:

Adjuvants should demonstrate a viable local mechanism of action beyond systemic administration and must be safe and non-toxic in the paediatric context.

Perioperative Management

Pre-procedure Assessment and Consent

• Risk stratification must account for age (neonates and infants at higher risk of complications, dosing errors, and LAST)
• Parental consent includes specific discussion of age-related risk data from PRAN audits
• Consider GA vs sedation vs awake technique based on age and clinical context

Technique Selection Principles

• PRA under GA is standard and safe; this should be clearly communicated to families and non-paediatric colleagues who may question this practice
• Ultrasound guidance is strongly recommended for all peripheral blocks and epidural catheter insertion
• For ex-premature infants (≤ 60 weeks PMA) having inguinal hernia repair: consider awake spinal to reduce early apnoea risk
• Caudal block is the first-line neuraxial technique for lower abdominal/perineal/lower limb surgery in infants and young children

Dosing Safety

• Use weight-based dosing with strict maximum dose limits, particularly in infants < 12 months
• Reduce epidural infusion rates in neonates (relative to older children) due to immature hepatic metabolism
• Have lipid emulsion 20% immediately available for all paediatric regional procedures
• Dosing errors are more common in younger children, independent double-check of calculated doses is essential

Monitoring

• Enhanced postoperative monitoring for apnoea in ex-premature infants following any anaesthetic, including regional
• Neuraxial catheter sites in neonates require vigilant monitoring for catheter malfunction, contamination, and vascular puncture (13.3% complication rate)
• Inadequate epidural analgesia and technical catheter failure are common (35% early removal in one series), have a clear rescue analgesia plan

Specific Block Applications