Recent advancements in regional anaesthesia

ABSTRACT

Patient safety, improved quality of care, and better patient satisfaction and functional outcomes are currently the topmost priorities in regional anaesthesia (RA) and all advancements in RA move in this direction. Ultrasonography-guided central neuraxial and peripheral nerve blocks, intracluster and intratruncal injections, fascial plane blocks, diaphragm-sparing blocks, use of continuous nerve block techniques, and continuous local anaesthetic wound infiltration catheters are now topics of popular clinical interest. The safety and efficacy of nerve blocks can be improved with the help of injection pressure monitoring and the incorporation of advanced technology in the ultrasound machine and needles. Novel procedure-specific and motor-sparing nerve blocks have come up. The anaesthesiologist of the current era, with a good understanding of the sonoanatomy of the target area and the microarchitecture of nerves, along with the backup of advanced technology, can be very successful in performing RA techniques. RA is rapidly evolving and revolutionising the practice of anaesthesia.

INTRODUCTION

The last few years have seen revolutionary changes in the field of regional anaesthesia (RA). As mentioned by some authors, RA is in the midst of a “renaissance”.[1] This is mainly due to better understanding of the relevant anatomy for the nerve blocks, microarchitecture of the nerves, the availability of newer equipment with the incorporation of advanced technology, and newer local anaesthetics (LAs) and adjuvants. The present era of multimodal analgesia, the coronavirus disease 2019 (COVID-19) pandemic, and the buzz over enhanced recovery after surgery (ERAS) have brought to the fore the clinical importance of RA. Patient safety and improved quality of care, including better patient satisfaction and outcomes, are currently the topmost priorities in RA, and all advancements in RA have moved in this direction. We reviewed the information available on the recent advancements in the practice of RA in databases such as PubMed and Google Scholar. The information thus compiled, which include newer techniques and technology that were developed to increase the success rate of the nerve blocks and to reduce patient harm and improve patient safety, are presented in this article.

ADVANCES IN REGIONAL ANAESTHESIA TECHNIQUES AND TECHNOLOGY

Ultrasound for central neuraxial block

Ultrasonographic scanning for central neuraxial block (CNB) is done using a low-frequency curvilinear probe in different planes by holding the probe in horizontal or vertical orientation with respect to the long axis of the body of the patient. The patient is either in the sitting or in the left lateral decubitus position, with maximum possible flexion at the lumbar level to allow further opening of the intervertebral spaces. There are five basic ultrasound (US) views of the spine: (1) transverse spinous process view [Figure 1a]; (2) transverse interlaminar/interspinous view [Figure 1b]; (3) parasagittal transverse process view [Figure 1c]; (4) parasagittal articular process view [Figure 1d]; (5) parasagittal oblique/interlaminar view [Figure 1e].

Figure 1.

(a) Transverse spinous process view. Placement of probe in horizontal orientation on the spinous process of the vertebra. Pointed, hyper-echoic shadow with dark anechoic shadow underneath. (b) Transverse interlaminar/interspinous view. Placement of probe in horizontal orientation in between two adjacent spinous processes. Hyperechoic posterior complex (PC) formed by posterior dura and ligamentum flavum with epidural space in between and anterior complex (AC) formed by vertebral body, posterior longitudinal ligament, and anterior dura seen. (c) Parasagittal transverse process view. Placement of probe in vertical orientation 3–4 cm lateral to midline. Finger-like long acoustic shadows (trident sign) seen. (d) Parasagittal articular process view. Probe at Figure 1c position moved medially. Shallower acoustic shadows formed by articular processes of adjacent vertebrae similar to continuous camel hump seen. (e) Parasagittal oblique/interlaminar view. Probe at Figure 1d position is tilted to look from lateral to medial direction into vertebral canal. Continuous hump-like shadows are replaced by intermittent saw tooth–like shadows of adjacent laminae. L: Lamina, ESM: Erector spinae muscle, TP: Transverse process, Pm: Psoas major muscle, TP: Transverse process, Pm: Psoas major muscle, AP: Articular process, AC: Anterior complex, PC: Posterior complex

Visualisation of the sonoanatomy in the lumbar region is easier compared to the thoracic region, owing to the absence of many bony structures like ribs and the presence of the straight spine posteriorly in the midline which allows a window for ultrasonography (USG). US of the spine can be done before the procedure or real time.[2] Randomised controlled trials (RCTs) and case reports have shown that pre-procedural US of the spine in the subarachnoid block and in the epidural catheter placement is particularly useful in obese parturients, parturients in labour, parturients with preeclampsia, and those with morbid obesity, spine disease, kyphoscoliosis, and on anticoagulants.[3–6] Pre-procedural USG in these cases provides information related to identification of the intervertebral levels, determination of needle insertion point, angle of needle trajectory, and depth of needle insertion. Needle insertion point in the midline can be obtained from the transverse interlaminar view with or without parasagittal oblique view. For para-median needle insertion point, transverse spinous process views of two adjacent spines are used. Nevertheless, feasibility studies on real-time US-guided spinal anaesthesia (SA) using dynamic needle tip positioning are going on wherein the spinal needle is introduced after confirming the vertebral level with real-time US; the US probe continues to track the needle tip in real time by sliding/tilting with short-axis view. Real-time US-guided SA has been compared with pre-procedural US and has shown positive results.[7] A novel machine learning–based proprietary US software system called the spine level identification (SLIDE) system has been recently developed. The system automatically identifies the lumbar landmarks in real time as the operator slides the transducer over the lumbar spine.[8]

Intracluster and intertruncal injections

An intracluster injection is defined as the deposition of LA with the needle tip close to the main cluster and satellite clusters of neural elements that constitute the superior, middle, and inferior trunk at the level of the supraclavicular fossa. In the targeted intracluster technique for supraclavicular brachial plexus block (SCBPB), the neural elements are approached without actual identification of individual trunks because of poor resolution of US machines and poor understanding of connective sheaths around the brachial plexus. Intracluster injections are said to be advantageous in terms of quick onset of block when compared with eight corner pocket injections of LA for SCBPB.[9] However, intracluster injections can be intraneural, as shown in the cadaveric study by Retter et al.[10] where 24% of injections were sub-perineural.

Over the past two decades, with better availability of high-resolution US machines and a better understanding of sonoanatomy, it is possible to identify the paraneural sheath surrounding the brachial plexus at the supraclavicular[11] and the infraclavicular[12] fossa. Karmakar et al.[11] used a transverse oblique scan at the supraclavicular fossa to identify individual brachial plexus elements above the clavicle using sequential ultrasound imaging technique. Another approach which has been advocated is the intertruncal approach to SCBPB by Siddiqui et al.[13] This approach involves identification of individual trunks and two injections: first between the upper and middle trunk and the second between the middle and lower trunk. This is advantageous in comparison to intracluster injections as it avoids nerve injury. However, clinical studies are required before recommending intertruncal injections as the standard of care for SCBPBs.

Fascial plane block technique

In fascial plane blocks (FPBs), a large volume of dilute LA is deposited in the musculofascial plane without visualising the target nerves.[14] Some of the FPBs, like rectus sheath block (RSB) and pectoral nerves (PECS) block, do have a defined mechanism of action where the LA spreads to block the target nerves. However, some like the erector spinae plane (ESP) block act by proxy paravertebral mechanism. LA deposited in between the two fascial layers blocks the nociceptors situated in the plane and reaches the target nerves by bulk movement and diffusion across a concentration gradient and some degree of systemic absorption of LA.[15] Most of the FPBs provide isolated somatic analgesia. However, few FPBs like quadratus lumborum block (QLB) provide both somatic and visceral analgesia.

Numerous classifications have been used to categorise FPBs. A simple and easy classification is mentioned in this article [Table 1].[16,17]

Table 1.

Classification of fascial plane blocks

Body region	Part of region	Fascial plane block
EXTREMITY	UPPER	Pericapsular nerve group (PENG) block (Shoulder) Clavipectoral fascial plane block
	LOWER	Adductor canal block PENG block Fascia Iliaca Compartment Block: Suprainguinal/Infrainguina Infiltration between popliteal artery and capsule of knee joint (I-PACK)
TRUNK	THORAX	Erector spinae plane block Pectoral nerve (PECS) type 1 and type II blocks Parasternal blocks Serratus anterior plane block Retrolaminar block Midpoint transverse process-to-plane block External oblique intercostal block Paraspinal-intercostal plane block
	ABDOMEN	Quadratus lumborum block Rectus sheath block Transversus abdominis plane (TAP) block

FPBs have modest analgesic efficacy and can be a part of a multimodal analgesia regime. The quality of the block achieved is not as dense as in a peripheral nerve block (PNB) because the LA is injected into a plane that has nerves or because it migrates towards the target structures. Local anaesthetic systemic toxicity is a potential complication secondary to the systemic absorption of LA from interfascial planes.[14,15] FPBs such as the rhomboid intercostal block have been used for pain management following thoracic and breast surgeries.[18]

Combined FPBs along with mild sedation through propofol infusion are now being administered as the sole anaesthetic technique in high-risk patients with comorbidities: for example, ESP, PECS1, and serratus anterior plane (SAP) for breast cancer surgery.[19] Posterior transversus abdominis plane (TAP) block and lateral QLB combination can be used for lower abdominal surgery.[20]

The learning curve for FPBs is relatively low, which makes them simple to learn and perform. Although USG remains the standard of care for performing FPBs, a few of them can be done using the loss of resistance technique (e.g., TAP block) or landmark-guided techniques (e.g., deep SAP block).

Diaphragm-sparing blocks

Any brachial plexus block above the clavicle—namely interscalene block (ISB) and its variants like supraclavicular block or cervical plexus block—have the potential of phrenic nerve paralysis, resulting in hemidiaphragmatic paresis (HDP); this incidence is high following ISB. This is worrisome in a patient having underlying respiratory disease as it can cause decompensation[21] due to reduction of respiratory function by almost 20%.

Several techniques have been devised to reduce the incidence of phrenic nerve paralysis.[22] These include USG-guided ISB, low-volume blocks,[5] use of dilute LA solution, and the injection of LA 4 mm lateral to the brachial plexus in the supraclavicular approach.

Alternative diaphragm-sparing blocks have been proposed. These include the US guided C7 root blocks,[22] superior trunk block,[21] suprascapular and axillary nerve block combination, infraclavicular anterior suprascapular nerve block (<10% incidence of HDP), USG-guided ESP block at T2-3 level,[23] and the costoclavicular block (0% incidence of phrenic nerve paralysis).[24,25] The costoclavicular block is a promising block and provides anaesthesia and analgesia equivalent to ISB.[25] Further trials are needed to study the efficacy of these blocks as a sole anaesthetic and for postoperative pain management.[21]

Segmental spinal anaesthesia

Severe hypotension, apnoea, neurological complications, and high or total SA are some of the undesirable effects of SA techniques. These can be avoided by giving a spinal segmental block that includes the deposition of a low dose of LA in the subarachnoid region near the nerves supplying the operative field to enable and limit anaesthesia only in that field. The blood pressure, heart rate, oxygen saturation, and end-tidal carbon dioxide always remain within normal limits throughout the surgical procedure because the sympathetic block produced by the segmental SA is rarely complete and some preservation of the sympathetic reflex for challenging situations typically occurs.[26]

Thoracic spinal anaesthesia (TSA) is the performance of SA at the thoracic vertebral level. Cord trauma with high thoracic puncture is the major concern. However, it has been found that there is a greater depth of the posterior subarachnoid space at midthoracic levels than at lumbar and upper thoracic levels.[27] Forty-five to 60 degrees of angulation of the needle is required for puncturing at the thoracic level. This position increases the distance to a point that allows needle advancement without touching the cord. Nevertheless, the incidence of paraesthesia has been reported to be less (6.1%) during thoracic spinal puncture with cut-point needle and pencil point needle compared to the lumbar approach (20%).[28]

High segmental SA can be performed safely with proper precautions with low dose of LA. Hypobaric, hyperbaric, and isobaric LA solutions have been used for segmental SA. In thoracic puncture, isobaric or hyperbaric anaesthetics can be used, with or without opioids. Isobaric solutions injected at the level of the fifth thoracic space can simultaneously block sensitive and motor roots, thereby providing safe anaesthesia. Hyperbaric solution can provide a longer-lasting sensory block than a motor block.[29] In the thoracic region, the latency of thoracic spinal anaesthesia is practically immediate and does not differ between hyperbaric and isobaric solutions.[30]

The best patient position for administering TSA is the sitting position with shoulders relaxed and the head and back flexed. Evidence shows that there is not much difference between the use of cutting needle or pencil point needle; however, the cutting needle may be safer. Both the median and the paramedian approach can be used, and the median approach may be technically more challenging. The spinal needle insertion point for TSA and LA volume can be selected anywhere between T4 and T12 depending on the type of surgery performed (Breast surgery T5-T6, LA volume 1.1–1.4 ml; Colon resection T4-T5, LA volume 1.7 ml; Gastrostomy T8-T9, LA volume 1 ml; Gastrectomy T6-T8, LA volume 0.9–1.2 ml; Laparoscopic cholecystectomy T8-T11, LA volume 1.5–2.5 ml; Laparotomy for abdominal malignancies T9-T10, LA volume 2 ml). Bupivacaine/levobupivacaine/ropivacaine with adjuvants such as opioids, dexamethasone, clonidine, and midazolam can be used.[31]

Mastering the technique of segmental SA can help in the anaesthesia management of critically ill patients with comorbidities, considering the risk-benefit ratio over general anaesthesia. Few studies including RCTs on segmental TSA have shown that it provides better patient satisfaction with superior postoperative analgesia and fewer complications in breast cancer surgery compared to GA.[32] Nonetheless, evidence on the technique including case reports is steadily building up and it shows that TSA may be used in patients where other anaesthetic techniques pose a higher risk of mortality.[33] Well-designed RCTs on TSA in different population groups need to be conducted in the future.

NEWER TECHNIQUES FOR PROLONGATION OF DURATION OF REGIONAL ANALGESIA

Continuous PNBs through catheters provide prolonged analgesia, reduce opioid consumption, and enhance patient satisfaction after painful surgeries including outpatient orthopaedic procedures.[34] The techniques for delivering LAs through peripheral nerve catheters include continuous infusions, patient-controlled boluses, and programmed intermittent boluses. Although their clinical benefits have been firmly established, systematic reviews and meta-analyses have found limited supportive data to endorse any one technique over the others.[35]

Continuous wound infiltration with LA wound infusion catheters is also used to control acute postoperative pain. Fenestrated catheters (number depending on the wound size) are directly implanted into the wound subcutaneously at the end of surgery and are connected aseptically to a portable elastomeric infusion system. Studies have shown that this technique is fast, less invasive, safe, easy to perform, and provides good postoperative control of up to 48 hours.[36] The technique is more effective in areas with dense subcutaneous tissue. However, it is associated with the risk of infection and catheter dislodgement.

Liposomal bupivacaine is approved for use in nerve blocks and local wound infiltration and is designed to provide longer pain control.[37] It is an extended-release formulation of bupivacaine that utilises technology that employs multi-vesicular liposomes containing bupivacaine, resulting in sustained release of bupivacaine into the tissue for 72 to 96 hours.

A common approach is to use adjuvants with LAs in single-injection PNBs, CNBs, intravenous regional anaesthesia, and wound infiltration to speed the onset of analgesic action, prolong the analgesic effect, and reduce the dose of LA. The adjuvants should not prolong the adverse effects of the LA and should produce minimal central nervous system–related side effects. The search for such an adjuvant continues and newer adjuvants have been added to the existing armamentarium. Dexamethasone 4–10 mg, buprenorphine 0.3 mg, clonidine 1–2 μg/kg, and tramadol 200 mg are currently the best perineural/perineuronal adjuvants. Dexmedetomidine 0.5–1 μg/kg has also been found to produce good clinical results as a perineural adjuvant.[38,39] Clonidine 150 μg/kg and morphine 5 mg are good intraarticular LA adjuvants.[38]

There is ample evidence to support the use of alpha-2 agonists (clonidine 3 μg/kg and dexmedetomidine 1 μg/kg) as adjuncts to LA wound infiltration. Fentanyl, ketorolac, dexamethasone, magnesium, ketamine, non-steroidal anti-inflammatory drugs (NSAIDs), steroids, neosaxitoxin, methylene blue, and several other agents are other adjuncts to LAs for wound infiltration; however, more well-designed studies need to be conducted on them.[40]

ADVANCEMENTS IN THE PROMOTION OF THE SAFETY OF REGIONAL ANAESTHESIA

Safety in RA can be achieved by avoiding paraesthesia-based nerve block technique, use of USG, reducing the number of needle passes, reducing the LA dose, and avoiding vascular puncture and neural damage (e.g., by using dual modality such as USG and neurostimulation).[41]

USG-guided blocks are associated with limitations such as vision within the narrow beam, inability to see through bone, air, and increasing depths of tissue.[41,42] The needle visibility decreases as the depth and angle of the needle increases. The incidence of nerve damage remains at 0.05% for a persistent neuropathy to 1.9% for a transient neurologic adverse event. The demarcation between the paraneurium, epineurium, and perineurium, or between nerve bundles and individual fascicles is not visible in USG.[43] Hence, to overcome these limitations, novel approaches to nerve block needle tracking and visualisation have been devised. These include micro-ultrasound at the tip of the needles and tip-tracker needles with a piezo element embedded at its distal end that can track the needle tip in-plane and out-of-plane.[44] There are other aids to improve the view of the needle tip such as needle guides, alterations in needle or needle tip design such as vibrating needle tip, needle tips with photoacoustic effect, needle tip with sensor technology to allow needle detection at greater depth and steeper angles, electromagnetic or global positioning system, three-and four-dimensional US to monitor the spread of LA, optical tracking, augmented (virtual) reality, robotic assistance, and computerised needle detection.[45] However, the evidence for these solutions is currently weak. Echogenic needles, beam steering, and compound imaging can improve needle visibility.[46]

High needle diameter, intraneural needle tip location, non-echogenicity of the needle, and high injection rates (>15 ml/min) can increase injection pressure.[47] Injection pressure monitoring helps in getting an alert on intraneural needle tip placement while monitoring the pressure generated during injection. There are many manometers and syringe pumps with a fixed pressure injector that have been validated in animals, cadavers, and in case series. These include control disc stimulation device, BSmart (B. Braun, Melsungen, Germany), improvised pressure gauge, compressed air injection technique, and an optical fibre pressor sensor embedded within the shaft of the needle developed by Saporito et al.[48] The SAFIRA system is a recently launched system for injection pressure monitoring.[49] Exploratory studies have been published recently on the use of a combination of real-time injection pressure sensing and minimal intensity stimulation (with an impedance analyser coupled with a nerve stimulator) during PNB.[50]

Deliberate intraneural injections have been used in volumes of 0.5 ml in isolated peripheral nerves such as the sciatic nerve or the medial nerve.[43] These carry the risk of intra-fascicular disruption which is riskier in the brachial plexus, which in turn has lower connective tissue–to–neural tissue ratio.[41,42] Needle trajectory tangential to nerve circumference makes it more likely that the needle will touch and move away rather than penetrate the epineurium.[43]

Dural sac cross-sectional area (DSCA), which is the sagittal anteroposterior diameter of the dural sac, is another highly effective parameter to determine the minimum effective anaesthetic volume (MEAV) of LA for SA. The dose of SA can be modified and optimised to control the sensory level according to the ratio of the DSCSA. This is useful especially in geriatric patients with spinal canal stenosis.[51]

Neuraxial and regional block Fit (NRFit) connectors dedicated toward injections into the neuraxial space and in PNBs have been assigned by the International Organization for Standardization (ISO). Some authors recommend the use of these connectors in the practice of RA to prevent the inadvertent neuraxial injection of medications intended for systemic use and thus improve patient safety.[52]

Novel nerve blocks, especially motor-sparing and procedure-specific blocks, keep getting added to the existing armamentarium of nerve blocks to improve the efficacy of analgesia, provide early ambulation, and improve patient satisfaction and safety. The high-volume proximal adductor canal (Hi-PAC) block is one such promising motor-sparing, dual target, single-injection technique for below-knee surgeries that can avoid the delay in diagnosis and treatment of acute compartment syndrome.[53] The dual sub-sartorial block is another novel motor-sparing technique for total knee arthroplasty.[54] The search for the optimum approach to the target nerve, MEAV, type, and concentration of LA is unending. USG reduces the MEAV for nerve blocks.

ONGOING CHALLENGES IN THE FIELD OF REGIONAL ANAESTHESIA

US-guided blocks definitely score over the conventional techniques owing to their several advantages. However, the cost and the availability of US machines are the major limiting factors for their routine use. Also, lack of proper training of anaesthesiologists in their correct application often leads to failure and complications. This and the lack of definitive evidence of the superiority of some novel RA techniques lead to underutilisation of the upcoming techniques.[1] All this means that there is an urgent need to educate and improve the technical proficiency of anaesthesiologists in our country in ultrasound-guided regional anaesthesia (USGRA). This can be done through departmental heads encouraging the use of RA and setting up of more USGRA regional training centres in all parts of our country, especially in medical colleges and civil hospitals. Nevertheless, the use of augmented reality and artificial intelligence (AI) in the enhancement of RA training and performance is being currently contemplated.

SCOPE FOR FURTHER RESEARCH AND ADVANCEMENTS IN REGIONAL ANAESTHESIA

Computer-aided detection[55] is one of the applications of AI, which may become routine in the future for nerve localisation and needle tracking in USGRA. This technique uses de-speckling filters, thereby increasing the contrast of the region of interest and reducing background speckle. This is again based on the image recognition principle. Nerveblox, which was developed as a trademark (SmartAlpha Inc, 2019, Ankara, Turkey), is an AI-based image interpretation guidance software for US-guided and select peripheral nerve and interfascial plane blocks. Nerveblox, when connected to the video output of any existing US device, autodetects key anatomical landmarks on the US image for a specific nerve block type.[56] Such devices need to be further researched. The day may not be far when all USG machines will have AI incorporated into them and robots will be in action performing RA blocks with 100% success and no complications. RA research networks need to be established in all countries. Nonetheless, research grants and funding of studies on RA need to be encouraged. High-quality studies including well-powered RCTs are needed to compare and study novel RA approaches. More research studies on the effects of the nerve blocks on long-term functional and patient-centred outcomes need to be conducted. Cadaveric dye studies and AI-based studies on the drug distribution path can help define the exact volume of LA required for the selective targeting of sensory, motor, and sympathetic nerve fibres.

SUMMARY

RA interventions that are safe, effective, fast-acting, and that are accompanied by patient comfort and satisfaction, early recovery, and good functional outcomes are steadily developing. We are living in an era wherein the clinical applications of RA are fast growing and so are the paradigms of research on RA.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.