Avoiding neurological complications

Avoiding block related neurological complications involves:

1. Avoiding nerve trauma secondary to repeated needle-nerve contact.

2. Avoiding intraneural needle placement and/or injection.

3. Avoiding central neuraxial needle placement/injection.

4. Avoiding drug errors.

Avoiding nerve trauma secondary to repeated needle-nerve contact

Recent animal studies have shown that repeated needle-nerve contact results in histological nerve changes consistent with nerve trauma. 1 The clinical significance of these histological changes are unclear, but they would probably manifest as short lived minor neurological symptoms e.g. numbness +/- tingling.

Implication: Use ultrasound needle guidance to minimise needling and repeated needle-nerve contact.

Avoiding intraneural injection

Despite recent evidence showing that intraneural injection of small LA volumes does not invariably result in prolonged neurological deficit, 2 the most widely held view is that intraneural injection should be avoided. This is because regardless of needle tip configuration or needle trajectory, intraneural needle placement causes disruption to a nerve’s structural integrity. 3 Furthermore, intrafascicular LA injection strongly correlates with prolonged neurological deficit. 4 Fine bore needles can certainly be placed within nerve fascicles.

The problem with peripheral nerve block injection monitoring is that no one monitor can reliably rule out intrafascular needle placement/injection. For example, modern ultrasound machines can easily detect intraneural injection, but they do not have the resolution to identify intrafasicular vs. extrafascicular needle placement. Current nerve stimulator technology has a very high positive predictive value. That is, if a motor response is present at stimulation thresholds of < 0.2 mA (without any dextrose injected prior to stimulation), intraneural needle placement is almost certain. 5 However, the absence of a motor response at high stimulation thresholds (upwards of 1.0 mA), does not rule out an intraneural needle location. 5 One explanation is that the needle may be adjacent sensory neurons but distant to motor neurons. Recently, injection pressure monitoring has been suggested as protecting against LA injection related nerve injury: low injection pressures ruling out harmful intrafascicular injection. However, this technology also has its limitations as other factors unrelated to intrafascicular injection may result in high injection resistance e.g needle/catheter orifice obstruction by fascia. Furthermore, recent evidence suggests that intrafascicular injection may not invariably be associated with high injection pressures. 6

Implication: So what can the operator do to guard against intraneural and more importantly, intrafascicular LA injection? The only intervention that can eliminate intrafascicular (and probably also intraneural) injection is to use an 18G (or larger) Tuohy needle. The needle’s calibre is such that it is simply not possible to place inside a nerve fascicle, and with the exception of the sciatic nerve, its diameter and tip configuration virtually precludes it from being placed inside a nerve. Where possible, the needle should be inserted so it approaches the nerve along its long axis (rather than perpendicular), which will further protect against nerve impalement.

Ultrasound, nerve stimulation and injection pressure monitoring are all useful in providing additional operator reassurance regarding appropriate extraneural injection.

Avoiding central neuraxial needle placement

Complications related to central neuraxial needle placement have been some of the most devastating and include not only epidural, subdural and total spinal block, but also permanent neurological deficit, hemiplegia (secondary to injection related syrinx formation) and death. Blocks associated with these complications include paravertebral block (including lumbar plexus) and interscalene block. Interscalene block is frequently implicated for one unique reason: interscalene block is the only peripheral nerve block where it has been common practice to angle the needle directly towards the neuraxis. It has been suggested that an intracordal syrinx can form secondary to intraneural nerve root injection with subsequent proximal tracking of the LA into the spinal cord. To avoid these complications:

For interscalene block:

1. Preferably use an anterolateral needle approach which makes intervertebral foramen penetration virtually impossible.

2. Limit needle tip depth to one half the distance from the skin to the vertebral column (< 1.25 cm in most but certainly < 2.5 cm).


For both interscalene and paravertebral blocks:

3. Use a blunt large calibre needle (e.g. an 18 G Tuohy) which will make nerve root implalement impossible and dural puncture unlikely.

4. If a catheter is placed, use an anterolateral needle approach for interscalene, and leave no further that 3-4 cm beyond the needle tip.


Avoiding drug errors

This subject is clearly beyond the scope of this page. Of particular relevance to regional anesthesia is the recent practice of emptying a drug ampoule into a pot on the regional block tray for the anesthesiologist to aspirate into a syringe. We strongly discourage this practice as it increases the risk of inadvertently injecting alcoholic chlorhexidine around nerves or into the epidural space.



1.         Steinfeldt T, Poeschl S, Nimphius W, et al. Forced needle advancement during needle-nerve contact in a porcine model: histological outcome. Anesth Analg 2011;113:417-20.

2.         Bigeleisen PE. Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury. Anesthesiology 2006;105:779-83.

3.         Rice AS, McMahon SB. Peripheral nerve injury caused by injection needles used in regional anaesthesia: influence of bevel configuration, studied in a rat model. Br J Anaesth 1992;69:433-8.

4.         Hadzic A, Dilberovic F, Shah S, et al. Combination of intraneural injection and high injection pressure leads to fascicular injury and neurologic deficits in dogs. Reg Anesth Pain Med 2004;29:417-23.

5.         Bigeleisen PE, Moayeri N, Groen GJ. Extraneural versus intraneural stimulation thresholds during ultrasound-guided supraclavicular block. Anesthesiology 2009;110:1235-43.

6.         Lupu CM, Kiehl TR, Chan VW, et al. Nerve expansion seen on ultrasound predicts histologic but not functional nerve injury after intraneural injection in pigs. Reg Anesth Pain Med 2010;35:132-9.