Abstract ID: A33
Abstract Title: Ultrasound assessment of paresthesia and electrical stimulation for nerve localization: A sensitivity study
Poster Type: Either
ABSTRACT BODY
Introduction:Recent reports of incosistency in eliciting a motor response after paresthesia suggest that current nerve localization techniques may be unreliable (1,2).With the aid of ultrasound imaging, this study evaluates the sensitivity of paresthesia and electrical stimulation for nerve localization during axillary block.
Materials and Methods: After IRB approval and informed consent, 17 patients (9 male and 8 female, 20-79 y.o., 64-86 kg, 152-186 cm, ASA physical status I-II) undergoing elective hand or wrist surgery were recruited. The brachial plexus at the axilla was examined using a linear L12-5 MHz probe and a PHilips-ATL HDI 5000 ultrasound unit. After identification of the axillary artery and the ulnar, median, and radial nerves, a 2", 22G insulated needle (Stimuplex, Braun Medical, Bethlehem,PA) was inserted under sterile conditions and advanced to contact each of the three nerves individually under ultrasound guidance. Once the needle tip was judged in contact with the target nerve (indicated by nerve movement), the patient was asked to report feeling of paresthesia defined as "pins and needles", tingling or electric-like sensation anywhere in the upper extremity. Thereafter, a nerve stimulator (Stimuplex, Braun Medical) set at 2Hz and 100 microseconds duration was turned on and the current amplitude increased gradually until a motor rsponse was observed or 5.0 mA was reached. The location of the motor response and the minimal stimulating current were recorded. After paresthesia and nerve stimulation testing, 14 ml of a mixture containing equal parts of 2% lidocaine and 0.5% bupivacaine with 1:200,000 epinephrine was injected at each of the three nerves (total 42 ml). Block success was defined as complete motor and sensory anesthesia in the regions inervated by the three target nerves within 30 minutes.
Results:16 patients completed the study and 1 patient was withdrawn due to protocol violation. Of the 48 documented instances of needle-nerve contact, paresthesia was found in 15% (7/48) and positive nerve stimulation up to 5 mA in 79% (38/48) of cases. Only 54% of the cases had a motor response at ≤ 0.5 mA. Block success within 30 min was 94% (15/16).
Discussion:Our preliminary data suggest that paresthesia and nerve stimulation with an insulated needle both have low sensitivities for nerve localization during axillary block.
References:
1) Choyce A, Chan V, Middleton W, et al. What is the relationship between paresthesia and nerve stimulation for axillary brachial plexus block? Reg Anesth Pain Med 2001; 26:100-104
2) Urmey W, Stanton J. Inability to consistently elicit a motor response following sensory paresthesia during interscalene block administration. Anesthesiology 2002; 96: 552-554
ATTACHED FILES
Reg Anesth Pain Med 2004; 29(2):A33