[Ultrasound in local anaesthesia. Part I: technical developments and background]

[Hygiene aspects in ultrasound-guided regional anesthesia]

BACKGROUND

Sterile and clean working conditions are one of the keystones of medical practice and this is also true for ultrasound-guided regional anesthesia. The routine clinical practice in ultrasound-guided regional anesthesia does not always comply with the principles of sterile and clean working conditions in medicine: therefore, patients are exposed to potential hazards regarding the transmission of pathogens via the ultrasound equipment.

OBJECTIVE

This article deals with the question of whether sterile working conditions in ultrasound-guided regional anesthesia are a relevant topic with medical and economic implications. Is it possible to implement the general recommendations for sterile working conditions in ultrasonography for the specific application of ultrasound-guided regional anesthesia?

MATERIAL AND METHODS

A search of the available literature and published guidelines in the field of sterile working conditions with ultrasound was carried out.

RESULTS

The association between cross-infections and ultrasound equipment is undeniable. Many methods for cleansing and disinfection of ultrasound equipment have been published. All these methods are associated with advantages and disadvantages. The direct sterilization of ultrasound probes with high-percentage alcohol can damage ultrasound probes (especially linear). The use of self-adhesive sterile ultrasound probe covers is a practical method to achieve sterile working conditions in ultrasound-guided regional anesthesia.

CONCLUSION

The use of sterile ultrasound probe covers and sterile ultrasound contact media is an important prerequisite to avoid cross-infection between patients. An appropriate scientific evaluation should serve as evidence in this field.

Nerve localization techniques for peripheral nerve block and possible future directions

BACKGROUND

Ultrasound guidance is now a standard nerve localization technique for peripheral nerve block (PNB). Ultrasonography allows simultaneous visualization of the target nerve, needle, local anesthetic injectate, and surrounding anatomical structures. Accurate deposition of local anesthetic next to the nerve is essential to the success of the nerve block procedure. Due to limitations in the visibility of both needle tip and nerve surface, the precise relationship between needle tip and target nerve is unknown at the moment of injection. Importantly, nerve injury may result both from an inappropriately placed needle tip and inappropriately placed local anesthetic. The relationship between the block needle tip and target nerve is of paramount importance to the safe conduct of peripheral nerve block.

METHODS

This review summarizes the evolution of nerve localization in regional anesthesia, characterizes a problem faced by clinicians in performing ultrasound-guided nerve block, and explores the potential technological solutions to this problem.

RESULTS

To date, technology newly applied to PNB includes real-time 3D imaging, multi-planar magnetic needle guidance, and in-line injection pressure monitoring. This review postulates that optical reflectance spectroscopy and bioimpedance may allow for accurate identification of the relationship between needle tip and target nerve, currently a high priority deficit in PNB techniques.

CONCLUSIONS

Until it is known how best to define the relationship between needle and nerve at the moment of injection, some common sense principles are suggested.

Pilot study of neuraxial imaging by ultrasound in infants and children

BACKGROUND

Ultrasonography is becoming an important adjunct in regional anesthesia. Epidural anesthesia may pose significant challenges in infants and children because of difficulties in identifying the epidural space. In addition, epidural catheters are sometimes difficult to advance. The present study was performed to evaluate an optimal ultrasound technique for direct visualization of neuraxial structures in children.

METHODS

A total of 32 infants and children scheduled for minor surgery were prospectively included in a high-resolution ultrasound study. Scans were performed using either a sector or linear probe and views from a longitudinal paramedian, median and transversal angle at lumbar and thoracic levels of the spinal cord were analyzed.

RESULTS

In all children investigated, the linear probe generated better images than the sector probe. Of the various scanning perspectives, the paramedian longitudinal approach offered the best views at both cord levels. Broken down by age groups, the best visibility was clearly obtained in neonates up to 3 months of age (P < 0.0001 Vs all other age groups). In older children, the quality of ultrasound decreased in an age-dependent manner.

CONCLUSIONS

Paramedian longitudinal scans with linear probes are the most favorable method of imaging neuraxial anatomy at lumbar and thoracic cord levels in infants and children, with the best results in neonates up to 3 months of age. Based on these results, and using real time imaging, a practical technique for ultrasound-guided epidural anesthesia for neonates and infants at lumbar and thoracic levels of the spinal cord is planned.

Ultrasound-Guided Epidural Catheter Insertion in Children

Epidural catheters (EC) are often used in pediatric patients for intraoperative and postoperative pain relief. The small anatomical structures and catheter insertion under general anesthesia make it more difficult to perform EC and to prevent damage. In this study we investigated the use of ultrasound (US) in detecting neuraxial structures during insertion and placement of EC in children. ASA I-II children scheduled for elective surgery under combined general and epidural anesthesia were studied. Patients received balanced anesthesia using sevoflurane, opioids and rocuronium. Before EC insertion US examination in a lateral position was done to visualize and identify neuraxial structures. Quality of visualization and site and depth of structures were recorded. Using a sterile kit to hold the US probe in position and enable the visualization of the neuraxial structures, an epidural cannula was inserted, using the loss of resistance technique, as the EC passed under US control to the desired level. Of 25 children, 23 were evaluated. Epidural space, ligamentum flavum, and dural structures were clearly identified and the depth to skin level estimated in all patients. Loss of resistance was visualized in all patients with a lumbar epidural approach. Correlation of US measured depth and depth of loss of resistance was 0.88. In eight of 23 patients EC could be visualized during insertion and in 11 others it could be visualized with additional US planes. US is an excellent tool to identify neuraxial structures in both infants and children. The size and the incomplete ossification of the vertebra allow exact visualization and localization of the depth of the epidural space, the loss of resistance, and all relevant neuraxial structures.

IMPLICATIONS

Epidural catheters in children are mostly inserted under sedation or general anesthesia. This study showed that the use of ultrasound could help visualize all relevant neuraxial structures and their site and depth from the skin.

Ultrasonography in the current practice of regional anaesthesia

Ultrasound imaging techniques in regional anaesthesia are becoming a subject of major interest. The quality of blocks and analgesia is relevant to the perioperative outcome of patients and the development of perfect blocks has always been a focus in regional anaesthesia research. Several studies in neuroaxial anaesthesia and peripheral blocks have found that puncture processing performed under ultrasound guidance is easier and more effective than that performed without such guidance, thus ultrasound imaging techniques are being developed for clinical practice. One of the major advantages of these techniques is that they provide the opportunity to show the patient the anatomical situation before the puncture--using a near harmless and effective technique. A second advantage is that the puncture process and the application of medication can be demonstrated and clearly observed during the performance. If there is a problem with the spread or the application, the processing of the block can be immediately modified to improve the quality of the technique.

Ultrasound guidance for infraclavicular brachial plexus anaesthesia in children

Ultrasonography may offer significant advantages in regional anaesthesia of the upper and lower limbs. It is not known if the same advantages demonstrated in adults also apply to children. We therefore performed a prospective, randomised study comparing ultrasound visualisation to conventional nerve stimulation for infraclavicular brachial plexus anasesthesia in children. Forty children scheduled for arm and forearm surgery underwent infraclavicular brachial plexus blocks with ropivacaine 0.5 ml.kg(-1) guided by either nerve stimulation or ultrasound visualisation. Evaluated parameters included sensory block quality, sensory block distribution and motor block. All surgical procedures were performed under brachial plexus anaesthesia alone. Direct ultrasound visualisation was successful in all cases and was associated with significant improvements when compared with the use of nerve stimulation: lower visual analogue scores during puncture (p = 0.03), shorter mean (median) sensory onset times (9 (5-15) min vs. 15 (5-25) min, p < 0.001), longer sensory block durations (384 (280-480) min vs. 310 (210-420) min, p < 0.001), and better sensory and motor block scores 10 min after block insertion. Ultrasound visualisation offers faster sensory and motor responses and a longer duration of sensory blockade than nerve stimulation in children undergoing infraclavicular brachial plexus blocks. In addition, the pain associated with nerve stimulation due to muscle contractions at the time of insertion is eliminated.

Neuraxial blocks for anaesthesia and analgesia in children

PURPOSE OF REVIEW

The use of regional techniques in paediatric anaesthesia has increased dramatically. Our aim is to produce a comprehensive review of the recent literature on neuraxial blockade in infants and children, focusing on three topics: choice of local anaesthetic and adjunct drugs, technical aspects and complications.

RECENT FINDINGS

The current literature shows a trend towards using the single isomers (levobupivacaine or ropivacaine) rather than racemic bupivacaine. In addition, opioids as adjuncts are being challenged by clonidine and ketamine, which have more benign side effects. The spread of radiopaque dye within the epidural space (which may mimic that of local anaesthetic solutions) appears to be highly variable, although distribution is related to the volume injected. Recent techniques (e.g. ultrasound or stimulating catheters) have been developed to accurately identify the position of epidural catheters. In contrast to adults, neuraxial blockade using local anaesthetic solutions is associated with stable cardiovascular variables, even in children with congenital heart disease. Although the incidence of complications associated with paediatric neuraxial blockade is low, the potential risks must always be considered.

SUMMARY

It is likely that the use of epidural ketamine or clonidine as adjuncts to local anaesthetics will grow. Alternatives, such as midazolam, may offer advantages in particular circumstances, although rigorous evaluation of the safety of these solutions when injected along the neuraxis and the development of formulations without preservatives are needed. The use of stimulating caudal catheters or ultrasound-guided techniques appears to offer promising options for the future to more accurately position catheters.