Regional Anaesthesia for the Neonate

Numerous regional and local anaesthesia techniques are available for safe use in neonates and can be administered either in combination with general anesthesia or in the awake neonate. Regional anaesthesia provides effective analgesia with reduced drug requirement which is especially beneficial in view of the immature physiology and metabolism in the neonate. The reduced requirement of anaesthetic drugs facilitates stable hemodynamics, faster recovery and a decreased length of stay in the neonatal intensive care unit.


INTRUDUCTION
Over the last few decades, there has been a realization that neonates and infants also experience pain and demonstrate significant and vigorous pain behaviours [1].This has led to a paradigm shift in the peri-operative pain management strategies for the neonate.Regional anaesthesia is a technique that produces effective analgesia with minimal drug requirement and fewer side effects.In infants undergoing major abdominal surgery, administration of epidural analgesia was found to be associated with a significantly beneficial modification of the neuro-endocrine stress response when compared with postoperative morphine infusions alone [2].Further, a reduced need for postoperative mechanical ventilation has been observed in neonates who had received epidural analgesia for tracheo-oesophageal fistula repair [3].Neonates who did not receive a penile block or in cases where eutectic mixture of lidocaine and prilocaine (EMLA) was not applied for neonatal circumcision had an exaggerated pain response to later vaccinations as compared with neonates treated with a local anaesthetic technique [4].Finally, safety data generated from large, prospective studies and audits clearly show that the use of paediatric regional anaesthetic techniques is safe and of great benefit in the neonate [5].

IV analgesics alone: are they not sufficient?
The use of systemic opioids carries a significant risk of respiratory depression in the neonate who has an already depressed respiratory system.Their use is associated with considerable clinical side effects such as pruritus, nausea and vomiting which are difficult to assess in neonates but maybe expressed as being irritable, fussy and unsettled.Increased morbidity and mortality may be attributed to increased residual effects of anaesthesia along with excessive sedation.Co-administration of regional anaesthesia can prevent opioid induced hyperalgesia characterised by a paradoxical increase in pain in the post-operative period [7][8][9].Benefits of regional anaesthesia in the neonate

REVIEW ARTICLE
• Early return of gastrointestinal motility, improved splanchnic perfusion and early resumption of oral feeding which may be especially beneficial in necrotising enterocolitis as well as after gastroschisis repair [15].

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Local anaesthetics (LA) stimulate natural killer cells that play an important role in nonspecific cellular-mediated and antitumor immunity [17].
Regional block in the preterm neonate • Infants born prematurely are more prone to peri-operative respiratory complications including postoperative apnoea, hypoxia and bradycardia following general anaesthesia up to 60 weeks post conceptual age [20].

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The depressant effects halogenated agents on intercostal muscles, lung volumes, chemoreceptor, baroreceptor responses as well as associated conditions like bronchopulmonary dysplasia further add to the burden of post-anaesthetic complications.Difficult weaning from mechanical ventilation is a major concern in such patients.Parents and the neonatologist frequently desire to avoid the risks involved with general anaesthesia and re-intubation of the trachea [21][22][23].The awake regional technique is a useful alternative in such patients.
Technical and pharmacological differences in the neonate with regard to central neuraxial block Precision is required in neonates while establishing regional anaesthesia as absolute distances are very small and anatomical relationships with landmarks also differ (Table 1 & Figure 1).

Administering Regional Anaesthesia in the awake neonate
Surgeries such as circumcision and simple inguinal herniotomy can be safely performed under regional block in the awake neonate.Topical local anaesthetics at site of the block as well as IV cannula site, keeping the baby warm and a pacifier coated with 10% dextrose does the trick [24].
Standard monitoring devices (blood pressure cuff, pulse oximeter, electrocardiogram leads) should be applied prior to performing the block.During placement of the block use of nitrous oxide 50% and inhalational agent may help in the vigorous and active neonate.Sedation maybe used as appropriate, keeping in mind the baby`s general condition and the length of procedure.Since the duration of subarachnoid block is short (30-60 minutes), it necessitates an experienced surgeon and simple surgeries while avoiding it in complex or bilateral procedures.

Techniques available
There are various techniques available to suit the surgical needs, caudal anaesthesia being the single most important technique (Figure 2).These can be used with sedation alone or in combination with general anaesthesia (Table 2).

Assessing the level of sensory block achieved:
Assessing the level of blockade may prove difficult in neonates, particularly if the neonates are sedated or concomitant general anaesthesia has been administered.Pin prick or response to cold stimuli (e.g., an alcohol swab) may be used as well as observation of vitals, rate and pattern of ventilation.Placing an electrocautery grounding pad on an infant's back by lifting the lower extremities will result in a trendelenburg position leading to an extremely high spinal level following the block.Therefore, while placing the cautery pad the baby should be lifted as a whole after spinal anaesthesia rather than lifting the lower extremities.
Special attention should be given while positioning the neonate for spinal anaesthesia as flexion of neck can lead to airway obstruction.
Central neuraxial block is not associated with clinically significant hypotension or bradycardia attributable to neonate's relative immaturity of sympathetic nervous system, lower vascular tone and relative smaller volume in lower extremities.
Routine fluid loading is unnecessary; however a working venous access must be obtained prior to performing spinal anaesthesia in neonates.

Ultrasound guided regional blocks in the neonate
The use of ultrasound (US) guidance when performing regional anaesthesia allows performance of regional block safely and effectively by allowing better recognition of the anatomy and localization of adjacent structures during needle placement.Another benefit is that lower volumes of local anaesthetic solutions are required which minimises the risk of local anaesthetic toxicity [25].
The use of US is of particular value in the neonate as the largely cartilaginous posterior vertebral column of neonates enables better penetration of the ultrasound radiation in order to visualize spinal structures [26].Furthermore, loss-of-resistance technique to identify the epidural space is difficult as the spinal ligaments are less fibrous.In a study on sixty neonates who received ultrasound guided block, good visibility of structures within the spinal canal, including the dura mater, ligamentum flavum and the termination of the spinal cord was reported [27].
Keeping in mind the advantages and with improvement in equipment, the use of ultrasound guided blocks in the neonate US guidance for peripheral and central neuro-axial blocks may become the norm rather than the exception.

COMPLICATIONS
There is a general apprehension amongst paediatric/ neonatal surgeons regarding regional anaesthesia in the neonate.Results from a prospective study performed by ADARPEF on more than 24,000 paediatric regional blocks demonstrated that the incidence of complications was approximately 1/1000 of which those attributed to epidural block was only 1/10,000, none of which resulted in any major or any long-term complication [5].The use of inappropriate adult-sized equipment in paediatric patients was found to be associated with 50% of complications [5,6].Presently, age-specific appropriate regional anaesthesia equipment is easily available.
The peri-operative complications of particular importance include:

Contraindications
Contraindications to regional anaesthesia include anatomic deformities, infection at the puncture site and presence of an underlying coagulopathy.Spinal and epidural anaesthesia should be avoided in hemodynamic instability, presence of a ventriculoperitoneal (or other ventricular) shunt, increased intracranial pressures and poorly controlled seizures.

CONCLUSIONS
Numerous regional and local anaesthesia techniques are available for safe use in neonates; the advancement in ultrasound technology has further supplemented the safety profile by minimising the injuries and decreasing the drug dosages.The key to success is adherence to dosage guidelines, sufficient knowledge and precision of technique as well as keeping anatomical differences in mind thereby minimising complications.Regional anaesthesia may offer immense benefits for our smallest and most susceptible patients.

Figure 1 :
Figure 1: Anatomical differences in neonatal and paediatric spinal cord

Figure 2 :
Figure 2: Caudal block-the most commonly used regional block in neonates

Table 1 :
Technical and pharmacological differences and anaesthetic implications

Table 2 :
Various techniques and the surgeries where they can be used.