Nerve blocks

Nerve blocks are a common treatment for pain relief. They can be used for diagnostic, prognostic or therapeutic purposes. Nerve block techniques include local infiltration of painful areas, peripheral nerve blocks, and central blocks (spinal, epidural and caudal blocks).

Nerve blocks can be used for diagnostic, prognostic or therapeutic purposes in the management of pain. Nerve blocks can be administered using various techniques, the different methods of using nerve blocks depend on their location, the reason for the nerve block, as well as the medical guidelines for their use.

Indications for diagnostic nerve blocks

  • To define the precise source of pain.
  • To distinguish local from referred pain (pain that originates in an area away from the site of the pain), visceral (pain from the internal organs) from somatic pain (pain originating from the walls of the body), and peripheral (pain originating from the nerves that extend from the spinal cord) from central pain (pain the originates from the brain or spinal cord).
  • To determine if pain is maintained by the sympathetic nervous system (a division of the part of the nervous system where we have no voluntary control, responsible for out "fight" or "flight" response)
  • To allow assessment of the contribution of pain to immobility or muscle spasm.

Indications for prognostic blocks

  • To allow assessment of the benefits and risks of neurolytic and neurodestructive blocks. A prognostic local anaesthetic block can be a guide as to whether pharmacological treatment, definitive neurolytic blocks or surgical management should be considered.

Indications for therapeutic blocks

  • To provide prompt and effective analgesia, either prophylactically (eg local anaesthetic prior to suturing) or following injury (eg femoral nerve block for a broken leg).
  • To allow adequate examination, intervention or mobilisation of an injured area without the requirement for sedation or general analgesia.

Contraindications

Contraindications to local anaesthetic nerve blocks include (when nerve blocks should not be used):

  • Patient refusal
  • Drug allergy
  • Coagulopathy
  • Infection at the injection site

Complications

Complications of nerve blocks include:

  • Systemic toxicity of the local anaesthetic, including dizziness, tinnitus, blurred vision, perioral or tongue numbness, tremors, sedation, seizures, arrhythmias and low blood pressure.
  • Nerve injury.
  • Damage to other structures around the site of the injection.
  • Pain at the injection site.
  • Local haematoma.

How to prepare for a nerve block

  • It is important to have a comprehensive discussion about the nerve block procedure with the doctor prior to it being performed. Once your doctor has discussed all the pros and cons of the procedure and has given you all the required information, he will ask for your consent.
  • The doctor performing the procedure may need to perform some simple tests before deciding whether or not to go ahead, these may include a blood test and some scans.
  • Before the procedure the doctor may or may not request that you take some sedating medication, it is not always needed, and heavy sedation is generally avoided.
  • A patient who is about to receive regional anaesthesia needs to have their intake of fluids and food restricted. This is because there is always the risk of vomiting and regurgitation of food, as well as the possibility of the doctor needing to revert to using a general anaesthetic, in which case all patients need to be starved beforehand.
  • Nerve blocks can be performed as a short day surgery procedure or an inpatient procedure, this depends on the type of block used and patient factors.

What to expect during and after a nerve block

  • Initially there is a stinging sensation with the injection of the blocking substance.
  • There may also be a change in sensation (paraesthesia) in the area of the nerve block, and sensations such as pressure, tissue tension and altered temperature sensation may be experienced. These feelings are normal, and are not due to incorrect technique.
  • The doctor will test the effect of the nerve block by performing an examination of the nervous system in the affected area.
  • After the procedure there is a period of time where there will be altered sensation in the area where the block was administered, this feeling will persist until the block completely regresses.

Types of Nerve Blocks

Peripheral Nerve Blocks Lower extremity Nerve Blocks Indications

  • Hip joint surgery
  • Knee joint surgery
  • Long bone surgery
  • Trauma
  • Skin grafts
  • Sympathetic blockade

Nerve Blocks of the Abdomen and Thorax Two different pain pathways control pain in the abdomen and thorax, one for the organs (visceral) and another for the walls and other components (somatic) of those regions. The visceral components of the pain can be controlled by a central neuraxial nerve block with peripheral nerve blocks being used to reduce the somatic components of pain. Peripheral nerve blocks are therefore quite useful in the settings of operations involving the walls of the abdomen or the thorax. Indications

  • Abdominal surgery
  • Inguinal hernias
  • Chest wall trauma
  • Chest wall surgery
  • Bilateral or midline surgery or trauma
  • Chronic pain conditions

Upper extremity Nerve Blocks The upper limb is almost entirely innervated by a group of nerves called the brachial plexus apart from a few areas. It is for this reason that peripheral nerve blocks have great use in this region. It is possible to successfully anaesthetise the limb both operatively and post operatively with a single injection in the area of the brachial plexus. Indications

  • Shoulder surgery
  • Surgery of the upper arm and elbow
  • Forearm surgery
  • Wrist and hand surgery
  • Trauma
  • Chronic pain
  • Post-operative analgesia

Central Neuraxial Nerve Blocks There are three main forms of central neuraxial nerve blocks:

  • Spinal (aka intrathecal or subarachnoid)
  • Epidural (aka extradural or peridural)
  • Caudal (sacral epidural)

Spinal anaesthesia In this technique spinal anaesthesia is achieved by the injection of a small amount of a local anaesthetic agent into the fluid surrounding the spinal cord. It is generally injected below the level L1/2, since this is where the spinal cord ends. Two factors that determine the efficacy of spinal anaesthesia are the posture of the patient during and after the procedure as well as the quality and spread of the block itself. The effect of posture on the degree of blockade depends on the type of solution used. The effects of spinal nerve blocks on the nervous system are the greatest in the region where the anaesthetic agent is injected. They can have various effects on the respiratory cardiac and gastrointestinal systems and because of this they should be used with caution. Spinal anaesthesia takes 2 to 5 mins to take effect and lasts for 2 to 3 hours. The amount of drug needed per shot is approxim
ately 2.5 to 4mL. There is equal impairment of both motor and sensory function. Indications Elective and emergency surgical procedures below the level of the belly button. Epidural anaesthesia Epidural anaesthesia is delivered by the administration of a local anaesthetic solution into the epidural space (a space that surrounds the spinal cord). The height of the block is determined by a variety of different factors, these include:

  • The weight of the drug
  • The volume of the drug
  • Where the injection is administered
  • The age of the patient
  • Increased pressure in the abdomen
  • Position of the patient
  • The technique used to perform the procedure

The effects of epidural anaesthesia on other organs are similar to those seen with spinal anaesthesia. Epidural anaesthesia takes 20 to 30mins to take effect and lasts for 3-5 hours. The amount of drug needed is approximately ten times more than that needed in spinal anaesthesia. The impairment of sensory function is generally greater than the impairment in motor function. Indications

  • Surgery e.g. chest, abdominal and lower extremity
  • Acute pain relief e.g. post operative, trauma
  • Chronic pain e.g. cancer

Caudal anaesthesia The effect of this sort of anaesthesia is limited to the nerves in the lower part of the body, more specifically the lumbar and sacral nerves. This form of anaesthesia therefore has the added benefit of not having systemic effects on other organ systems. However this sort of anaesthesia can cause problems with peoples bowel and bladder function. Indications

  • Adult
    • Surgery e.g. anorectal, gynaecological and orthopaedic
    • Obstetric
    • Chronic pain
  • Paediatric
    • Major abdominal and orthopaedic surgery
    • Inguinal hernia repair
    • Genital surgery

References

  1. Analgesic. 2002. eTG complete [Internet]. Melbourne: Therapeutic Guidelines Ltd; 2006 Jan. Accessed 2006 April 9.
  2. Fischer HBJ & Pinnock CA, 2004, ‘Fundamentals of Regional Anaesthesia’, Cambridge University Press, Worcestershire
  3. Rice S. A. et.al. 2003, ‘Clinical Pain Management: Practical Applications and Procedures’, Oxford University Press, London.