Peripheral Nerve Block

A nerve block is a form of regional anaesthesia in which a local anaesthetic is injected near a specific nerve or group of nerves. This interrupts transmission of pain signals and provides targeted anaesthesia to a defined area of the body.

The fundamental principle behind peripheral nerve blocks is simple:

Block impulse transmission in peripheral nerves → prevent pain perception in the cortex.

In the emergency department, nerve blocks are highly effective. They provide rapid, site-specific analgesia and can significantly improve patient comfort during procedures such as fracture reduction, dislocation management, and laceration repair.

Classifying Nerve Blocks

The question I was attempting to answer when I started writing this page was “Types of local nerve blocks used in ED?” (April 2023 - Paper 1). But very soon I realised there is no simple, universal classification system. I feel that the most practical and clinically relevant way to approach this is by anatomy.

Upper Extremity Blocks
These target the brachial plexus or its branches.

Eg: Axillary nerve block, Supraclavicular brachial plexus block

Lower Extremity Blocks
Commonly used for hip, femur, and below-knee injuries.

Eg: PENG (Pericapsular Nerve Group) block, Fascia iliaca block, Popliteal sciatic nerve block

Truncal Blocks
Useful for thoracic and abdominal wall analgesia.

Eg: Serratus anterior plane block, Transversus abdominis plane (TAP) block

Steps Before Performing a Nerve Block (CIMPLE-D)

CIMPLE-D is a mnemonic to maintain a systematic approach to nerve block

Consent

IV access

Monitoring
Continue for at least 30 minutes post-block

Positioning and preparation

Local anaesthetic selection

Equipment and endpoint

Documentation

“Block on arrival” protocol

“On Arrival Block,” wherein a brachial block is given to a severely injured upper extremity as the first step of the management protocol in the main operating room, bypassing the emergency department. The idea behind it is that the patient is only resuscitated once, instead of twice.

This is primarily practised in specialised trauma centres and is not routine ED practice.

Advantage

Immediate pain relief

Allows pain-free initial examination

Avoids the administration of major opioids

Facilitates the use of a tourniquet if there are major bleeding wounds

Allows us to obtain good radiographs without an overlap of bones, which usually happens when the radiographs are taken within a bandage.

An important contraindication is the suspicion of a brachial plexus injury, which can cause the local anaesthetic to seep in through the open dural sleeve and cause total spinal anaesthesia.

“On Arrival Block” was set up at Ganga Hospital, Coimbatore, India, during the early 90s by the anesthesiologist Ravindra Bhat and the plastic surgeon Raja Sabapathy.

Local Anaesthetics

Local anaesthetics are generally classified according to their biochemistry into two groups, the esters and the amides.

Ester local anaesthetics	Amide local anaesthetics
Cocaine	Lignocaine
Procaine	Prilocaine
Tetracaine	Mepivacaine
Chloroprocaine	Ropivacaine
ㅤ	Bupivacaine

Mechanism

Local anaesthetics bind to voltage-gated sodium channels when they are in their open state.

(One needs to know that these drugs block other ion channels as well (potassium, calcium, etc), and the exact relevance of this remains the subject of debate. For the purpose of this question, the mechanism of action is via blockade of voltage-gated sodium channels.)

Once the local anaesthetic blocks the channel by stabilising its inactivated state, it has several concentration-dependent effects:

There is a decrease in the amplitude of the action potential

The refractory period is lengthened

Action potential conduction can cease

Local anaesthetics selectively produce insensitivity to pain and temperature, block autonomic neurotransmission at normal doses, and only produce a motor block with very high concentrations (differential block)

Bupivacaine is said to be the agent with the greatest specificity for sensory fibres.

The magnitude of the local anaesthetic effect depends on the frequency with which the nerve fibre is stimulated. This suggested that the drug required an open sodium channel to function. The more the channels open, the more they get blocked. This use-dependent phenomenon is also occasionally referred to as phasic block.

Commonly Used Local Anaesthetics

Understanding dosing and duration is critical.

Drug	Dose	Notes
Lignocaine 2% (without adrenaline)	4.5 mg/kg	ㅤ
Lignocaine 2% (with adrenaline)	7 mg/kg	ㅤ
Ropivacaine 1%	3 mg/kg	Duration: 4–24 hours
Bupivacaine 0.5%	2 mg/kg	Avoid in pregnancy
Mepivacaine	4 mg/kg	Avoid in pregnancy

Needles Used for Nerve Blocks

Blunt-tip 22G block needle

Quincke spinal needle (20–22G)

Tuohy epidural needle (for deeper blocks)

Why Prefer Blunt Needles?

Lower risk of intraneural injection

Lower risk of intravascular injection

Reduced the chance of unintended subarachnoid placement

Relevant Nerve Anatomy

A basic understanding of nerve structure helps explain both block success and complications.

A peripheral nerve consists of:

Axons (afferent and efferent)

Endoneurium – surrounds individual axons

Perineurium – encloses fascicles

Epineurium – outer connective tissue layer

Nerves typically lie within a fascial plane or sheath, allowing movement while protecting them from mechanical stress.

Mechanism of Block
Local anaesthetic is injected perineurally (around the nerve sheath), and it diffuses inward toward axonal membranes
Outer (mantle) fibres are blocked first (i.e. proximal areas affected first) while recovery occurs in reverse (i.e. distal function returns first)

Complications of Nerve Blocks

Block failure

Bleeding

Infection

Injury to surrounding structures

Permanent nerve injury (rare but serious)

Local anaesthetic systemic toxicity (LAST)

Rare: inadvertent subarachnoid injection → total spinal anaesthesia
Contraindications

Contraindications

Inability to cooperate

Local infection at the injection site

Neurovascular compromise

Suspected compartment syndrome

Relative contraindication

Coagulopathy

Poor ultrasound visualisation

Pre-existing neurological deficit

Local Anasthetic Toxicity (LAST)

LAST is an iatrogenic life-threatening acute neurologic/cardiac adverse reaction resulting from infiltration of local anaesthetic that enters the systemic circulation.

Signs and Symptoms

Neurologic Symptoms	Cardiovascular Symptoms
Auditory changes, tinnitus.	Tachycardia.
Metallic taste.	Hypertension.
Circumoral numbness or paresthesias.	Diaphoresis.
Visual disturbance (e.g., blurred vision).	Late Symptoms
Dizziness.	Respiratory Depression
Dysarthria.	Bradycardia and AV block
Tremor or muscular twitching.	Widened QRS complexes.
Anxiety.	ㅤ
Delirium.	ㅤ
Late Symptoms	ㅤ
Seizure	ㅤ
Somnolence	ㅤ
Coma	ㅤ

Treatment

Stop further administration

Stabilise ABCs

Lipid Emulsion therapy

Loading: 1.5 ml/kg (over 2-3 minutes).
This dose can be repeated after 5 minutes for 2 or more times for persistent hemodynamic instability.
The bolus(es) should immediately be followed by a continuous infusion at 0.25-0.5 ml/kg/min.

Arrythmia

Amiodarone is the front-line antiarrhythmic for ventricular arrhythmias.
If epinephrine is required, it should be dose-reduced.

Seizures

First-line therapy is with benzodiazepines
Use propofol cautiously, as this may promote cardiac collapse.
Avoid phenytoin, because phenytoin exerts anti-sodium channel activity.
Ketamine and/or levetiracetam could be reasonable antiepileptic agents in this context

Cardiopulmonary bypass or ECMO - For refractory LAST

Hematoma Bock

Method of providing local anaesthesia around the site of a fracture when reduction or manipulation is required by injecting an anaesthetic into the hematoma that forms around the fracture site.

Advantage

It provides excellent pain control. Multiple trials and reviews confirm similar or superior pain control compared to sedation.

Avoids the resource demands of procedural sedation

Allows earlier discharge due to shorter procedure time.

Does not require Ultrasound guidance

Lower frequency of complications when compared to procedural sedation

It cannot be used in open fractures.

Adverse events

are rare.

Infection

local anaesthetic toxicity

compartment syndrome

Fascia Illiaca Block

The fascia iliaca block is a commonly used regional anaesthesia technique and serves as an effective alternative to a femoral nerve or lumbar plexus block. It is particularly useful in patients with neck of femur fractures, where rapid and effective analgesia is essential.

The principle behind this block is simple: a large volume of local anaesthetic deposited beneath the fascia iliaca spreads medially and laterally, reaching the femoral nerve and often the lateral femoral cutaneous nerve.

Anatomy

Three major nerves contribute to hip innervation:

Femoral nerve

Obturator nerve

Lateral femoral cutaneous nerve

The fascia iliaca lies anterior to the iliacus muscle and forms a compartment between the fascia iliaca and the iliopsoas muscle. It runs from the iliac crest medially, where it merges with the fascia of the psoas muscle. Both the femoral nerve and lateral femoral cutaneous nerve ( and sometimes the obturator nerve) lie within this compartment, allowing anaesthetic spread along this plane.

At the level of the inguinal crease, structures are arranged (medial → lateral) as:

Femoral vein

Femoral artery

Femoral nerve

Structures pierced during the procedure:

Skin

Subcutaneous tissue

Fascia lata (first “pop”)

Fascia iliaca (second “pop”)

Contraindications

Beyond the contraindications mentioned above.

Significant swelling around the fracture site

Previous femoral bypass surgery due to adhesions.

Peripheral neuropathy in the affected limb

Recent failed block

Landmark technique

Palpate the anterior superior iliac spine (ASIS) and the pubic tubercle, which together define the inguinal ligament. This ligament is mentally divided into thirds, and the injection site is identified 1–2 cm below the junction of the lateral and middle third.

Care should be taken to palpate and avoid the femoral artery, which lies more medially.

The needle is inserted perpendicular to the skin and advanced slowly. As it passes through the tissues, two distinct losses of resistance may be appreciated: Fascia lata and Fascia iliaca. Hence, the term two-pop technique.

After confirming negative aspiration, the local anesthetic is injected. A properly placed injection should encounter minimal resistance, indicating that the compartment is being expanded.

A blunt needle is preferred for this technique, as it enhances the ability to feel these “pop” sensations and reduces the risk of inadvertent injury.

Usg Guided Technique

There are 2 approaches

Infrainguinal Approach

In the infrainguinal approach, the patient is positioned supine, and a high-frequency linear probe is placed over the inguinal crease. The femoral artery is first identified, followed by the iliopsoas muscle, which appears hypoechoic, and the femoral nerve, which appears hyperechoic. Move your probe laterally until you visualise the sartorius muscle at the edge of the screen. You can see the bright hyperechoic fascia running under this and over the iliopsoas muscle. This is the area you are aiming for.

The needle is advanced in-plane toward the space beneath the fascia iliaca. A small test injection helps confirm correct placement. When positioned appropriately, the local anaesthetic spreads by separating the fascia from the underlying muscle (“unzipping” appearance).

The key endpoint is the medial and lateral spread of anaesthetic beneath the fascia iliaca, ensuring adequate nerve coverage.

Suprainguinal Approach

The suprainguinal approach allows for more proximal spread and potentially improved analgesic coverage.

The probe is placed in a sagittal orientation over the ASIS and moved slightly medially to identify key structures: Iliopsoas muscle, Internal oblique muscle and Sartorius muscle.

The fascial layers form a characteristic “bowtie sign”, which serves as an important visual landmark. Depositing anaesthetic beneath this fascia facilitates wider and more cranial spread within the compartment.

Key aspects

A relatively large volume of local anesthetic (20–40 mL) is required for effective spread

It provides excellent analgesia for hip and femoral shaft fractures

The obturator nerve is not reliably blocked, which may explain incomplete pain relief in some patients

PENG Block (PEricapsular Nerve Group)

A powerful motor-sparing single-injection block for pelvis and hip fractures

Indications

Acetabulum and pubic rami fractures

Intertrochanteric hip and femoral neck fractures

Anatomy

The hip capsule is divided into 2 sections—anterior and posterior parts.

The anterior portion has nociceptive fibres, whereas the posterior part contains mechanoreceptors. This suggests the deposition of local anaesthetics in the fascial plane between the psoas muscle and the upper pubic branch contributes to anaesthesia of these nerves, thereby enhancing analgesic coverage.

USG Guided Technique

The PENG block is performed only under ultrasound guidance using a low-frequency probe.

The patient is positioned in a supine position, and the hip is extended. A low-frequency curvilinear probe is initially placed over the anterior superior iliac spine (ASIS) and then moved medially while being slightly rotated (about 45°) to align with the pubic ramus.

The key landmarks to identify are the anterior inferior iliac spine (AIIS), the iliopubic eminence (pubic ramus), and the psoas tendon. The target space for injection lies between the psoas tendon anteriorly and the pubic ramus posteriorly.

Two main techniques are:

In-Plane Technique

The in-plane technique is preferred as it allows continuous visualization of the needle.

A needle is inserted from lateral to medial at an angle of approximately 30–45°, advancing in the plane between the psoas tendon and the pubic ramus. Once the tip is correctly positioned, 15–20 mL of a long-acting local anaesthetic such as 0.5% ropivacaine is injected. Proper placement is confirmed by the spread of local anaesthetic lifting the psoas tendon.

Out-of-Plane Technique

The out-of-plane technique uses a similar probe position, but the needle is inserted perpendicular to the probe, making visualisation more difficult. It is therefore less commonly used.

Koh et al., 2025. compares the analgesic effect of PENG block and fascia iliaca block in an RCT and concluded that there is no significant difference between the two techniques in any outcome.