The authors sought to determine whether a shallow needle approach to the axillary artery would improve complete sensory blocks of median, radial, and ulnar nerves as compared with a perpendicular approach when transarterial axillary block is performed using a scalp vein needle (23G, 3/4’).
Fifty-four patients were allocated equally to a perpendicular group (the PA group) or a shallow approach group (SA group). Sensory and motor scores were evaluated and compared in the two groups at 5-minute intervals for 20 minutes after block. The main outcome variables were rates of blockage of median, radial, and ulnar nerves.
Excellent block rates (defined as completion of surgery using brachial plexus block alone) were obtained in both groups (SA group 77.8% vs. PA group 70.3%, P = 0.755). However, the rate of blockage of all three nerves was significantly higher in the SA group (74% vs. 40.7%, P = 0.013). Furthermore, the rate of complete sensory block of the radial nerve at 20 minutes was significantly greater in the SA group (85.2% vs. 59.3%, P = 0.033).
A shallow needle approach to the axillary artery resulted in a significantly higher median, radial, and ulnar nerve block rate at 20 minutes after LA injection than a perpendicular approach.
Ultrasound is a popular method of guidance when performing axillary brachial plexus block, but ultrasound equipment is not always available [
Transarterial axillary brachial plexus block (TAAB) is well-established blind technique for achieving safe and reliable anesthesia of the upper extremities [
TAAB failure is usually attributed to malpositioning of local anesthetic (LA), and its subsequent diffusion away from the artery beyond the brachial plexus sheath into muscle [
We hypothesized when a scalp vein needle (23 G, 3/4’) is used for TAAB, that a shallow needle approach to the axillary artery would improve the accuracy of LA delivery within the brachial plexus sheath as compared with a perpendicular approach (Figs.
Perpendicular approach group (PA group) versus the shallow needle approach group (SA group). When the scalp vein needle (23 G, 3/4’) was advanced into the axillary artery, the needle was directed perpendicular to the axillary artery in the PA group (A), whereas in the SA group, a shallow needle approach to the axillary artery was used (B).
Fifty-four patients scheduled for surgery of the hand and wrist, were enrolled in the study, after obtaining ethical approval and receiving written informed consent from participants. Patients were aged from 18 to 80 years and were of American Society of Anesthesiologists (ASA) physical status I to III. The exclusion criteria applied were as follows; preexisting neuropathy in the operated limb, ASA > III, coagulation disorders, known allergy to local anesthetics, local infection at the puncture site, multiple injuries, chronic pain history, pregnancy, a body mass index ≥ 35 kg/m2, failure to cooperate, and refusal to participate. Data were collected from January 2015 to June 2015.
Patients were randomized to a perpendicular approach group (PA group, n = 27) or a shallow needle approach group (SA group, n = 27). Randomization was performed using a computer-generated random number table. Patients were not informed of group allocations. Supplemental oxygen (nasal cannulae at 4 L/min) and standard monitoring (noninvasive blood pressure, electrocardiogram, and pulse-oximetry) were applied throughout the procedure; anxiolysis was not established. All nerve blocks were performed by one of two second-grade anesthesiology residents (both had performed more than 20 transarterial axillary blocks, and were supervised by experienced regional anesthesia staff). If, after 10 minutes of attempting a nerve block, a resident could not identify arterial pulsation, more experienced staff took over, and the procedure was not included in this study. To check pulses, residents applied adequate pressure on the axillary artery. The primary end point of this study was the rate of complete sensory block of all three nerves (median, radial, and ulnar nerves) at 20 minutes after LA injection.
All blocks were performed using a blind, transarterial approach, and LA was achieved using 1.5% lidocaine and 1 : 200,000 epinephrine. The technique used was as follows [
Brachial plexus block was evaluated every 5 minutes for 20 minutes after LA injection by an independent observer unaware of group allocations. Sensory block was evaluated using an alcohol swab on dermatomes of the ulnar (fifth finger), median (palmar aspect of the second finger), radial (dorsum of the hand between the thumb and second finger), and MCN (lateral aspect of forearm) nerves. Patients quantified sensory block level using the following scale: 2 = normal sensation, 1 = blocked hand less cold than the unblocked hand, 0 = no sensation. Complete sensory block was defined as a score of 0 in ulnar, median, and radial dermatomes. Motor block was assessed by applying the following scale to whole arms: 2 = no paresis, 1 = partial paresis, and 0 = complete paresis. After completing the evaluation, patients were transported to the operating room for surgery.
Block performance time was defined as time from completing the sterile preparation to final withdrawal of the scalp vein needle. Onset time was defined as time required to obtaining complete sensory block of all three nerves. Anesthesia grade was assessed after surgery using a 4-point scale, where: excellent = completion of surgery with only brachial plexus block; good = when intravenous (IV) ≤ 100 μg fentanyl was needed, insufficient = when additional ulnar nerve block was performed at the elbow level, but surgery was completed successfully; and failure = when general anesthesia was required to complete surgery. When a patient requested sedation during surgery, midazolam 2–5 mg was administered after confirming no pain at the incisional site based on anesthesiologist’s decision (anesthesiologists were also unaware of group allocations).
In a preliminary study, complete sensory block of all three nerves was achieved in 4 of 7 in a control group (perpendicular approach), but in 6 of 7 in an experimental group (shallow needle approach) at 20 minutes after LA injection. Power analysis showed 24 patients were required per group for an α value of 0.05 and a power of 90%, and thus, 27 patients were recruited per group to cope with a possible dropout rate of 10%. Results are presented as mean ± standard deviations, medians [interquartile ranges], or as numbers (%). The statistical analysis was conducted using SPSS ver. 12.0 for Windows (SPSS Inc., USA). The Chi-squared test was used to analyze categorical data, and the student’s unpaired
Patient demographic data are provided in
Patient Characteristics in the Two Study Groups
PA group (n = 27) | SA group (n = 27) | P value | |
---|---|---|---|
Age (yr) | 46 ± 15 | 49 ± 15 | 0.531 |
Sex (M/F) | 19/8 | 12/15 | 0.054 |
Height (cm) | 168 ± 8.6 | 165 ± 8.4 | 0.201 |
Weight (kg) | 68 ± 11.7 | 66 ± 9.0 | 0.467 |
ASA PS class (I/II/III) | 13/12/2 | 17/10/0 | 0.257 |
Values are mean ± SD, or number of patients. PA group: perpendicular approach to the axillary artery, SA group: shallow needle approach to the axillary artery. ASA PS: American Society of Anesthesiologists physical status.
Experimental data are presented in
Intra-operative Group Comparisons
PA group (n = 27) | SA group (n = 27) | P value | |
---|---|---|---|
Type of surgery | |||
Hand/wrist | 23/4 | 17/10 | 0.062 |
Fracture/non-fracture | 6/21 | 8/19 | 0.535 |
Block performer (A/B) | 13/14 | 12/15 | 0.785 |
Surgery time (min) | 40 [20–62] | 40 [32–55] | 0.449 |
Tourniquet time (min) | 41 [23–60] | 40 [30–50] | 0.381 |
Block performance time (min) | 5 [4–6] | 5 [4–6] | 0.477 |
Onset time (min) | 15 [15–20] | 10 [6.25–20] | 0.134 |
Rate of all 3 nerves blocked (n) | 11/27 (40.7%) | 20/27 (74%) | 0.013 |
Anesthesia grade | |||
Excellent/good/ insufficient/fail | 19/6/1/1 | 21/5/0/1 | 0.755 |
Sedative/analgesic drugs (total dosage) | |||
Midazolam (mg) | 46 | 29 | 0.597 |
Fentanyl (μg) | 550 | 500 | 0.860 |
Values are medians [interquartile ranges] or numbers of patients. PA group: perpendicular approach to the axillary artery, SA group: shallow needle approach to the axillary artery. Procedural time was defined as time from sterile preparation completion to the last needle withdrawal. Onset time was defined as time required to obtaining full sensory blocks of median, ulnar, and radial nerves.
Numbers of patients that achieved a sensory or motor score of 0 at 20 minutes after LA injection are presented in
Numbers of Patients that Developed a Sensory or Motor Score of 0 at Different Times after Local Anesthetic Injection
PA group | SA group | P value | |
---|---|---|---|
M 5 min | 5 (18.5%) | 9 (33.3%) | 0.214 |
M 10 min | 8 (29.6%) | 15 (55.6%) | 0.054 |
M 15 min | 16 (59.3%) | 16 (59.3%) | 1.000 |
M 20 min | 22 (81.5%) | 23 (85.2%) | 0.715 |
U 5 min | 10 (37%) | 8 (29.6%) | 0.564 |
U 10 min | 14 (51.9%) | 15 (55.6%) | 0.785 |
U 15 min | 18 (66.7%) | 17 (63%) | 0.776 |
U 20 min | 21 (77.8%) | 22 (81.5%) | 0.735 |
R 5 min | 2 (7.4%) | 7 (26%) | 0.068 |
R 10 min | 3 (11.1%) | 14 (51.9%) | 0.001 |
R 15 min | 11 (40.7%) | 14 (51.9%) | 0.413 |
R 20 min | 16 (59.3%) | 23 (85.2%) | 0.033 |
All three 5 min | 0 (0%) | 5 (18.5%) | 0.019 |
All three 10 min | 1 (3.7%) | 12 (44.4%) | < 0.001 |
All three 15 min | 8 (29.6%) | 12 (44.4%) | 0.260 |
All three 20 min | 11 (40.7%) | 20 (74.1%) | 0.013 |
MC 5 min | 3 (11.1%) | 2 (7.4%) | 0.639 |
MC 10 min | 6 (22.2%) | 10 (37%) | 0.233 |
MC 15 min | 13 (48.1%) | 14 (51.9%) | 0.785 |
MC 20 min | 18 (66.7%) | 19 (70.4%) | 0.770 |
Motor 5 min | 5 (1.8%) | 8 (29.6%) | 0.340 |
Motor 10 min | 10 (37%) | 12 (44.4%) | 0.580 |
Motor 15 min | 14 (51.9%) | 16 (59.3%) | 0.584 |
Motor 20 min | 15 (55.6%) | 17 (63%) | 0.580 |
Values are number of patient (%). PA group: perpendicular approach to the axillary artery, SA group: shallow needle approach to the axillary artery. M: median nerve, U: ulnar nerve, R: radial nerve, All three: median, ulnar, and radial nerves, MC: musculocutaneous nerve.
Paresthesia during TAAB occurred in one patient in the PA group, and in two patients in the SA group. No case of hematoma formation was observed at any injection site. At one-week follow-up visits, no patient complained of persistent paresthesia, no neurologic sequelae were detected, and no patient complained of tourniquet-related pain or any other complication.
The major finding of this randomized, controlled study was that the block rates of median, radial, and ulnar nerves around the axillary artery at 20 minutes after LA injection were significantly greater when a shallow needle approach was used during TAAB.
The rates of ‘excellent’ anesthetic grade (when surgery was finished with only brachial plexus block) were similar in the two groups (SA group 77.8% vs. PA group 70.3%, P = 0.755). However, we considered the rate of blockage of all three nerves more meaningful because failure to block one nerve territory can result in failed anesthesia if surgery is conducted in an area innervated by an unblocked nerve [
To ensure LA spread within the brachial plexus sheath, we performed TAAB as high in the axilla as possible because terminal nerves tend to spread far away from the artery even inside the sheath in the distal upper arm [
Scalp vein needles are widely used for nerve blocks or irrigation [
TAAB is based on the known anatomical proximities of all three nerves to the axillary artery within the brachial plexus sheath [
Most cases of incomplete anesthesia after TAAB are caused by unreliable blockade of the MCN and radial nerves [
The present study has a number of limitations that require consideration. First, the direction of needle tip was determined by arm extension and not by axillary artery location, and thus, we were not able to measure angles of needle approach to the axillary artery. We believe that the angle between needle tip and axillary artery in the SA group was around 45 to 60 degrees as shown in
Second, we blocked the MCN outside the sheath separately [
Third, two anesthesiologists performed all blocks in the present study, and they were not blinded to group allocations. However, the sensory and motor test evaluations were performed by an independent blinded observer. Therefore, we believe unintentional bias had little impact on overall results [
Fourth, we used complete sensory block instead of surgical block, because we evaluated block scores for 20 minutes, which was compatible with ranges of onset times in the two groups [
Fifth, the total volume injected to block all three nerves was 30 ml. TAAB is a volumetric technique, and thus, an increase in volume can enhance block quality, although considerations of LA toxicity restrict injection volume [
Sixth, we believed LA would be better distributed in the SA group within the sheath of axillary brachial plexus, but we did not confirm intra-sheath placement of the needle tip or LA distribution by ultrasound or contrast radiography [
In conclusion, LA injection using a shallow needle approach to the axillary artery during TAAB was found to have a significantly higher rate of blocking median, radial, and ulnar nerves at 20 minutes post-injection than a perpendicular needle approach. In addition, the shallow needle approach also resulted in a significantly higher rate of complete sensory block of the radial nerve than the perpendicular approach.