A19. Methods of local anesthesia (conduction anesthesia, regional anesthesia)

Page created on October 21, 2021. Last updated on December 18, 2024 at 16:58

Introduction

Regional anaesthesia refers to using local anaesthetics to render a specific area of the body anesthetised. It is used for operative anaesthesia but also for post-operative analgesia. They don’t cause loss of consciousness, but they may be combined with anaesthetics to achieve this.

Many adult surgeries can be performed with regional anaesthesia alone, without general anaesthesia. Regional anaesthesia is becoming more and more popular, as they have various advantages compared to general anaesthesia:

• It’s better for elderly
• Cheaper
• There’s no need for airway management, avoiding potential complications
• Less opioids are needed
• Less post-operative nausea and vomiting (PONV)
• Reduced postoperative pain
• Few cardiovascular and pulmonary side effects

Types

There are various types:

• Central regional anaesthesia (neuraxial block) – anaesthesia of the spinal cord
  • Epidural anaesthesia
  • Subarachnoid (spinal) anaesthesia
  • Combined spinal-epidural anaesthesia
• Peripheral regional anaesthesia (nerve block) – anaesthesia of peripheral nerves
  • Major (multiple nerves or a plexus)
    • Cervical plexus block
    • Brachial plexus block
    • Interscalene block
    • Supraclavicular block
    • Infraclavicular block
    • Axillary block
  • Minor (single nerve)
    • Sciatic nerve block
    • Femoral nerve block
    • Digital nerve block
  • Intravenous regional anaesthesia
  • Intraarticular anaesthesia
• Local anaesthesia
  • Infiltration anaesthesia
  • Topical anaesthesia

Indications

Regional anaesthesia is preferable in:

• Oncological surgery
• Orthopaedic/traumatological surgery
• C-section
• Lower limb revascularisation
• Obese patients
• Elderly patients (prevents post-operative cognitive dysfunction (POCD)
• Paediatric surgery (in addition to GA)

Central regional anaesthesia

Central regional anaesthesia, also called neuraxial block, refers to either epidural or subarachnoid anaesthesia. Both types may cause haemodynamic changes, especially hypotension, due to blockade of the sympathetic fibres.

Epidural anaesthesia involves injection of local anaesthetic with or without opioids into the epidural space to act on spinal nerve roots. Nerve roots around the site of injection are affected, while leaving the nerve roots above and below mostly unaffected. Epidural anaesthesia may be administered at any vertebral level. The drugs are administered via a catheter for continuous infusion.

Epidural anaesthesia is often used for surgeries in the lower body, like C-section, hernia repair, knee surgery, or during labour. It may also be used for postoperative or chronic pain management with an epidural catheter.

Subarachnoid anaesthesia, also called spinal anaesthesia, involves injection of local anaesthetic with or without opioid into the subarachnoid space to act on the spinal cord. Unlike epidural anaesthesia, all motor and sensory function below the level of injection is blocked. Spinal anaesthesia is usually administered as a single injection.

Spinal anaesthesia may only be placed in the lumbar region. It has more rapid onset than epidural, but also causes more rapid haemodynamic changes than epidural. Like epidural anaesthesia, it is often used for surgeries of the lower body, below the level of the umbilicus.

Epidural and spinal anaesthesia may be combined, called combined spinal-epidural anaesthesia (CSE).

Peripheral regional anaesthesia

Peripheral regional anaesthesia is also known as a nerve block or conduction anaesthesia. With this modality local anaesthetic is administered around the nerve supplying the area to be anaesthetised. This may take place some distance from the surgical site, like for example a brachial plexus block for hand surgery. The result is anaesthesia of the area supplied by the nerve distal to the area of injection.

Nerve blocks are often used for anaesthesia of fingers and toes as well (digital nerve block), in which case local anaesthetic is injected to each side of the digit, as close to the nerves passing there as possible. There is one dorsal and one palmar/plantar digital nerve on each side of the digit, and so local anaesthetic should be deposited at four sites across two injections.

Local anaesthesia

Local anaesthesia involves either infiltration anaesthesia or topical anaesthesia.

Infiltration anaesthesia is similar to nerve blocks but differ in that the aim of infiltration anaesthesia is not to anaesthetise the nerve itself, but the nerve endings in a certain area of tissue. Local anaesthetic is injected directly into and around the area to be anaesthetised, from which it will disperse in the tissue. This is simpler than nerve blocks and preferred for most cases, except for toes and fingers. Infiltration anaesthesia is often used for wounds which are to be examined or sutured, or for skin biopsy.

Topical anaesthesia refers to applying local anaesthetic topically to the area to be anesthetised, often as a spray or gel. This is useful for the upper airway before laryngoscopy, endoscopy, or intubation, and before bladder catheterisation. Topical anaesthesia is especially useful in children.

Intravenous regional anaesthesia

Intravenous regional anaesthesia (IVRA) or Bier block involves isolating an exsanguinated limb from the circulation with a tourniquet and injecting the local anaesthetic intravenously. It’s simple, safe, and effective, and especially suitable for short procedures and outpatient surgery. Prilocaine and lidocaine are typically used.