Equipment in Regional Anesthesia
1. Peripheral Nerve Stimulators
Basic design
Dedicated vs. non dedicated stimulators
Safety issues
2. Needles
Insulated vs. noninsulated
Short bevel vs. long bevel
Needle gauge
Needle length
3. Continuous Catheters
Peripheral Nerve Stimulators
Desirable Characteristics:
Constant current output
Clear Digital Reading
Variable Output Control
Linear Output
Clearly Marked Polarity
Short pulse width
Pulse of 1 or 2 Hz
Battery Indicator
Low maximum output of 5mA
Low resistance Connectors
Non dedicated stimulators - used also for NMJ monitoring
 Only use as a last resort
 Make sure electrodes are on low current setting
Dedicated stimulators - used solely for peripheral nerve blockade
 Compensate for differences in tissue resistance
 Always low current setting, maximum usually 5 mA
 No extra buttons (e.g. TOF/tetanus)
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Ideal Stimulator:
4. Safety Tips
a. Electrode connections:
Negative to Nerve / Needle (Black to block)
Positive to Patient / EKG Pad (red)
If the positive electrode is connected to the needle, the nerve is slightly
hyperpolarized. At any given current the twitch response will be less. This will
predispose the patient towards nerve injury as the needle will be too close to the
nerve in order to achieve an acceptable twitch endpoint. Most dedicated nerve
stimulators are designed to avoid this by using an alligator clip on the positive
electrode and a male connector on the negative electrode.
b.
Check that circuit is complete prior to needle insertion and just after skin
penetration.
c.
Ideal = 0.3-0.5 mA
Acceptable twitch: 0.5 mA – 1.0 mA
? Too close 0.1mA – 0.2 mA
d.
What if a paresthesia occurs before an optimal twitch?
Accept it if: reliable patient
reliable distribution
you didn’t move!!!
the patient didn’t move!!!
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e.
If your assistant is unfamiliar explain the stimulator PRIOR to needle insertion.
Start at 1.5 mA. Advance needle -- stop --- nerve stim adjusted -- stop --- advance
needle---see what happens to the twitch ---stop --- nerve stim adjusted …..
Bottom line: Do NOT move needle while stimulator is being adjusted and vice
versa.
f.
Do not inject if burning pain/constant paresthesias/or resistance to I
injection. STOP, withdraw the needle 1-2 mm and try again. If symptoms
persist remove needle!!
g.
Aspirate and inject every 3-5 mL
Needles
1. Insulated vs non-insulated:
 Non-insulated less reliable as
shaft can also stimulate
 Can be used if employ 2 Hz,
lower current, and move needle
slowly
2. Short bevel (30-45 degrees) vs long bevel (12-15 degrees):
 Inconclusive. Nerve penetration less likely with short bevel, damage may be more
severe and delayed with short bevel if nerve is penetrated?
 Will feel fascial "pops" better with blunt/short bevel
3. Needle gauge:
 Usually 24-21 gauge
 Smaller gauge - the increased resistance to injection may make it difficult to tell if
the injection is intraneural.
 Larger gauge (18/20) will require a local skin wheal. Used mainly for catheter
techniques.
4. Needle length:
 1 inch for interscalene/supraclavicular/axillary
 Generally need longer needles for the lower extremity.
 Exception - Infraclavicular approach -- need 2-4 inch needle
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
Femoral/popliteal should be OK with 2 inch needle unless the patient is obese.

Sciatic - generally need 4 inch needle
Continuous Catheters
1. Approaches:
 Upper Extremity: Interscalene, Infraclavicular, Axillary
 Lower Extremity: Femoral, Sciatic, Popliteal Fossa
 Trunk: Paravertebral, intercostals
2. Catheter Needle sets:
 18-21G, Insulated Short beveled, Touhy, Sprotte
 Catheter through needle sets usually 18G
 Cannula over needle sets usually 20G – 21G
 More recently – stimulating catheter sets
 40% secondary block failure rate with catheters
 Catheter stimulated prior to initiation of block
 Stimulating catheters ideal for ambulatory patients
3. Technique
 Peripheral Nerve Stimulation
 Paresthesia techniques not used due to larger sizes of needles
4. Helpful Hints
 Pay strict attention to sterile technique (prep/drapes) i.e. similar to epidurals
 Orient the needle bevel along the axis of the nerve sheath
 If the cannula/catheter won’t thread make sure that the neural sheath has been
distended with 3-5mL of local or saline before threading. If the catheter/cannula
still won’t thread try rotating the bevel/lowering the angle
 Secure the catheter with mastisol/steri strips/ tegaderm (similar to epidurals).
Catheters can also be tunneled to increase longevity.
 Make sure the catheter connector is easily accessible
 Ensure the efficacy of the nerve block by appropriate bolus of local anesthetic
before starting the infusion
 Common infusion 0.2% ropivacaine , or bupivacaine 0.125% , 4-10 ml/h
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References:
1. Pither, C. Review Article: The Use of Peripheral Nerve Stimulators for Regional
Anesthesia in Reg. Anesth pp 49-58, Apr 1985
2. Hadzic A and Volka J. Peripheral Nerve Stimulators for Nerve Blocks from
www.nysora.com
3. Selander, D. Peripheral Nerve Injury after Regional Anesthesia in Complications of
Regional Anesthesia Ed Finucane B. pp110-111, 1999
4. Enneking F. Catheter Placement for Continuous Regional Anesthesia in Peripheral
Nerve Blocks: A Color Atlas Ed Chelly J. p140, 1999
5. Pham-Dang, C. Continuous Peripheral Nerve Blocks with Stimulating Catheters. Reg.
Anesth pp. 83-88, Apr 2003
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