What is a field block in regional anesthesia?

What is a Field Block in Regional Anesthesia?

A field block is a regional anesthesia technique where local anesthetic is infiltrated around the border of the surgical field, leaving the operative area itself undisturbed, allowing the anesthetic to diffuse into the surgical site from the surrounding tissues. 1, 2

Technical Definition and Mechanism

• Field blocks involve injecting local anesthetic into adjoining tissues surrounding the surgical area, with subsequent diffusion into the operative field rather than targeting specific nerves. 1
• This technique differs fundamentally from nerve blocks (which target specific nerves or plexuses) and neuraxial blocks (which target the epidural or intrathecal space). 1, 3
• The anesthetic creates a "wall" of anesthesia around the surgical site by infiltrating the tissue planes circumferentially. 2

Clinical Applications in Orthopedics

• In orthopedic practice, field blocks are typically employed for minor procedures of the hand or foot. 1
• Field blocks are particularly useful in ambulatory and emergency room settings where they offer advantages over general anesthesia by reducing systemic side effects and providing more cost-effective resource utilization. 1
• This technique is also commonly used for procedures on the ear and lips in head and neck surgery. 2

Technical Considerations

• Epinephrine may be added to the local anesthetic in field blocks to enhance vasoconstriction and prolong the duration of anesthesia. 2
• The smallest effective dose should be used, and aspiration before injection is essential to prevent systemic toxicity. 2
• Lidocaine 1% is the preferred agent for many field block procedures due to its rapid onset and moderate duration of action. 4
• The maximum safe dose of lidocaine is 7 mg/kg with epinephrine and 4.5 mg/kg without epinephrine. 4

Advantages Over Other Techniques

• Field blocks leave the operative area undisturbed, which can be advantageous when direct infiltration into the surgical site might distort anatomy or interfere with the procedure. 2
• They are less technically demanding than peripheral nerve blocks, which require precise anatomical knowledge and nerve localization. 1, 2
• Field blocks avoid the time-consuming application required for more complex regional techniques, making them practical in emergency situations. 5

Pain Reduction Strategies During Administration

• Using a small gauge needle (27-30G) minimizes injection pain. 4
• Warming the anesthetic solution to approximately 40°C significantly reduces patient discomfort during infiltration. 4
• Slow infiltration rate and vibration of the skin during injection can decrease administration pain. 4
• Buffering the anesthetic with sodium bicarbonate reduces injection pain, particularly for larger areas. 4

Safety Considerations

• Systemic toxicity is rare with field blocks and can be prevented by using the smallest effective dose and aspirating before injection. 2
• Calculate maximum allowable dose before administration to prevent local anesthetic systemic toxicity (LAST). 6
• Treatment guidelines for LAST and rescue medications (intralipid) should be readily available during administration. 3