Is accepted practice in regional anaesthesia really ‘best practice’?

As ultrasound-guided regional anaesthesia (UGRA) has developed, some techniques have become accepted as ‘best practice’, but based upon little or no evidence. Many of these may arguably make UGRA more complicated and perhaps even increase the risks. In this article we offer some tips based upon our experience, which we believe make nerve blocks easier. We also challenge some of the perceived non-evidence-based ‘gold standard’ practices.

In-plane or out-of-plane approach?

The perceived safety of in-plane (IP) compared with out-of-plane (OOP) blocks is not substantiated in the literature. Any needle approach may risk damage to small, poorly visualised nerves, but an IP approach may put relatively large nerves at risk, such as the dorsal scapular and long thoracic nerves, the nerve to vastus medialis and the common peroneal nerve during interscalene, subsartorial or adductor canal, and popliteal sciatic blocks, respectively (Fig. 1). Despite needle-tip visualisation being more challenging, many OOP techniques may therefore have a safer needle trajectory.¹ It can also be difficult to achieve a perfect IP view of both the needle tip and epineurium simultaneously, particularly when performing deeper blocks. Often the best image of the nerve may alter whilst obtaining the best image of the needle.

Fig 1.

Ultrasound image after a subsartorial block lateral to the femoral artery (FA) illustrating the OOP path taken and the potential IP path through the nerve to vastus medialis (NVM). IP, in-plane; OOP, out-of-plane.

Tip 1

In our experience all these blocks can be performed easily and safely using an OOP approach. The perpendicular OOP approach also adds the advantage of haptic feedback when the needle clicks through the fascia (cervical, subsartorial aponeurosis and sciatic paraneurium, respectively).

Circumferential local anaesthetic spread?

It is often recommended to create a ‘doughnut’ of local anaesthetic (LA) spread around individual nerves. Although satisfying on ultrasound (US), why might surrounding a nerve be better than not doing so? There is some evidence of quicker block onset, which may have value in patients undergoing surgery awake, but only one study showed improved efficacy.² The potential disadvantage of this technique is that multiple needle manipulations may be required in close proximity to the nerve, risking neural trauma; this may outweigh any potential advantages.³

For example, the femoral nerve block is often demonstrated with the needle passing under the nerve to inject below it and above it. Our experience is that solely injecting above and lateral to the femoral nerve is sufficient. Subsequently looking 1 cm distally, all the nerve branches are covered by LA despite the initial ‘unsatisfactory’ appearance at the site of injection.

Tip 2

Keep it simple. A single injection of LA is usually sufficient if it is in the correct place, particularly for analgesia. Scan a little proximal or distal to see the LA spread within the fascial plane and around the target nerve(s). Only then move your needle if the spread seems inadequate.

The nerve as primary target?

Many pictures of IP blocks depict the needle aiming directly at the nerve. Evidence shows however that in a significant number of cases the operator may still misinterpret the needle-tip position when using US.⁴ Best practice reviews have outlined multiple techniques for attempting to reduce nerve injury but fail to mention that not aiming to position the needle directly adjacent to the nerve may be the most successful mitigating factor.^5,6 Needle placement in close proximity to the nerve may risk subepineural placement and potential nerve damage.⁷ This may be one reason nerve damage has not decreased compared with when US was not widespread practice.⁸ Measuring opening pressure may help identify and reduce intrafascicular injections but our experience is that needle-to-nerve approximation is not usually necessary.

Hydrolocation helps to visualise the needle tip. The anechoic fluid acts as an acoustic window and also serves as a space into which the needle can be advanced. Until very high-resolution microultrasound becomes available, other techniques are being evaluated to determine the location of the needle tip. We therefore suggest that when possible the primary target should be the tissue space near the nerve but not the nerve itself. Indeed, perhaps we should be asking ourselves how far away from the nerve can we be and still achieve a good block rather than how close can we get?

Tip 3

If there is a space or potential space near the target nerve, aim the needle towards this space rather than directly at the nerve.

What volume or concentration of LA?

There is a balance between success and the incidence of adverse effects, whereas the duration depends on dose of LA. Studies of ED₉₅ may help but are specific to the block performed.

High concentrations of LA allow smaller volumes and result in quicker onset, longer duration and greater efficacy. However, this must be balanced against higher complications and an increased motor block. There is some evidence that intraneural LA may be toxic.⁹ It may be the LA concentration rather than volume or pressure that adversely affects outcome.^10,11

The volume of LA required is also a balance. Very low volumes, made possible by US, require closer proximity of the needle to the nerve, multiple needle manoeuvres and usually result in a shorter duration of block. Although using ultra-low volumes appears attractive, we do not recommend them. Even with the interscalene block, small volumes do not reliably prevent phrenic nerve paralysis but may result in a shorter block with the possible need for parenteral opioids.

High volumes are no longer required as the US image allows individual tailoring of drug volume per block. In general, once the area surrounding the nerve appears full, there is no advantage in using additional LA.

Tip 4

Do not use more than necessary for a single-shot nerve block. Remember that the interaction between volume and concentration used is a balance between block success and complications.

Conclusions

In our opinion, most of the perceived ‘best practices’ can be challenged. We encourage the reader to at least consider alternatives rather than to state that our methods are superior. Ultrasound is an important tool that has made regional anaesthesia easier and safer, but research may never answer all of the questions posed above. Ultimately, we should not allow our current practices to restrict the potential benefits.

Declaration of interests

The authors declare that they have no conflicts of interest.

Biographies

Tamer Abouzied FRCA MSc is a specialty trainee in anaesthesia in the West Yorkshire Deanery currently working at Leeds Teaching Hospitals NHS Trust. He is an honorary lecturer at Faculty of Medicine and health, University of Leeds. He was formerly an assistant lecturer in anaesthesia at Alexandria University Hospitals, Egypt. His main interests are regional anaesthesia and obstetric anaesthesia.

Andy Wilson FRCA FFICM is a consultant in anaesthesia at Leeds General Infirmary. He is the current president of the Yorkshire Society of Regional Anaesthesia and has been teaching regional anaesthesia for 30 years.

Matrix codes: 1A02, 2G01, 3A09