Terminology

Preprocedure

Procedure

Post Procedure

Abbreviations

• Peripheral nerve block (PNB)
• Local anesthetic (LA)
• Local anesthetic systemic toxicity (LAST)

Synonyms

• Nerve blocks
• Regional nerve block
• Regional block
• Regional anesthesia

Definitions

• PNB: Temporary blockade of peripheral neural conduction to achieve analgesia &/or anesthesia
• LA: Class of medications that temporarily abolish neural conduction, and, when used peripherally, they block sensory (nociception) and motor function
  • Due to different physical properties of peripheral sensory (nociceptors) and motor neurons, with sensory nerves that transduce pain being primarily unmyelinated vs. motor neurons that are myelinated, onset and duration of blockade differs depending on volume and concentration of LA, with former being blocked 1st and recovering 1st, whereas latter is blocked later and blockade resolves later
  • Duration of LA also depends on site of injection
    • Highly vascular regions will tend to "wash out" LA when compared to avascular regions
• LA adjuncts: Medications whose primary indication is not for nerve block but utilized to synergize duration of LA
• Peripheral nerve catheter: Catheter that is placed near nerves or intrafascial planes to provide more prolonged analgesia than that of single-shot nerve block
• Procedural nerve block anesthesia: Dense nerve block that results in loss of motor and sensory function such that there is no sensation to procedural stimulus
  • Achieved with concentrated LA and high LA volume
• Procedural nerve block analgesia: Blockade of sensory nociceptors that only spares motor function; its primary use is for nociceptive pain blockade only
  • Achieved with less concentrated LA
• LAST: When blood levels of LA become supratherapeutic, there is adverse effect of CNS, initially characterized by tinnitus, metallic taste in mouth, escalating to seizures, and eventually to cardiovascular collapse; it is treated with lipid emulsion
• Lipid emulsion (Intralipid) 20%: Lipid-based medication that binds to LA in bloodstream and renders drug inactive; it acts as vacuum and is utilized as rescue medication for LAST; it is administered initially as bolus and then as infusion

Clinical Implications

• Regional nerve blocks
  • Medications
    • LA
    • Neurolytic agents
    • Contrast
    • Adjuvants, such as steroids and epinephrine
• Targets
  • Discrete nerves
  • Nerve plexuses (branching network of intersecting nerves)
  • Discrete interfascial planes
  • Potential spaces
• 2 techniques can be used to perform PNB
  • Nonimage guided
    • Paraesthesia technique
      • Nerves are identified by guiding needle "blindly" toward typical anatomical location of nerves until eliciting paresthesias and injection of LA
    • Nerve stimulation
      • Specialized needle that conducts small electrical current is guided toward nerves until motor or sensory response is elicited
  • Image guidance
    • Ultrasound: Enables relatively rapid identification of neurovascular structures with subsequent real-time in-plane guidance of needle toward these structures
      • Needle can be precisely guided, and LA spread can be seen
      • Requires thorough knowledge of sonoanatomy of neurovascular regions
      • Visualization can be challenging, as image quality is dependent on ultrasound capabilities, transducer placement, and patient factors, such as body habitus
      • Excellent hand-eye coordination is essential for in-plane guidance of needle
    • Fluoroscopy: Can precisely guide block needle within bony structures and regions of body
      • Needle is guided blindly toward anatomical landmarks
      • Requires contrast and radiation to confirm placement
      • Imaging quality is independent of patient body habitus
      • In some instances, it can be faster than ultrasound, especially with patient with challenging body habitus (morbidly obese)
    • CT: Can precisely guide block needle toward location of neural structure(s) in stepwise fashion, navigating through and around body structures
      • Excellent for deep nerve blocks at discrete anatomical locations (obturator nerve within obturator groove in pelvis) and fascial plane blocks
      • Excellent imaging of body structures independent of patient body habitus
      • Difficult to identify discrete nerves and assess LA spread
      • Requires contrast and radiation to confirm placement
      • Relatively time consuming
    • Magnetic resonance (MR) imaging: Can precisely guide needle toward neural structure(s) with subsequent visualization of LA spread within or adjacent to nerve(s)
      • High-fidelity visualization of deep nerves and anatomy irrespective of patient body habitus
      • No contrast or radiation utilized
      • Expensive and relatively time consuming

Indications

Contraindications

Preprocedure Imaging

Getting Started

General Safety Guidelines for Regional Nerve Blocks

Anticoagulant/Antiplatelet

Patient Position/Location

Equipment Preparation

Procedure Steps

Findings and Reporting

Alternative Procedures/Therapies

Expected Outcome

Things To Do

Things To Avoid

Problems

Complications