Joshua Hamsher, MS4
Article: Sohoni et al. “Forearm ultrasound-guided nerve blocks vs landmark-based wrist blocks for hand anesthesia in healthy volunteers.” American Journal of Emergency Medicine 2016; 34: 730-734.
Idea: Injuries to the hand account for a significant percentage of presenting complaints in emergency departments throughout the world. Of these injuries, it is often necessary to provide some form of analgesia in order to adequately explore, manipulate, and repair the wound. In recent years, with the increase usage of ultrasounds in emergency departments, it has become common clinical practice to utilize ultrasound-guided blocks for the forearm as oppose to the more conventional method of landmark-based blocks. However, the overall effectiveness of the ultrasound-guided vs landmark-based has never been adequately evaluated. Therefore, this study compares the analgesic efficacy of the two methods and compares the clinical outcomes.
Study: This study was a prospective, randomized, double-blinded controlled trial that was completed in two days of February 2011.
Inclusion Criteria: Healthy volunteers from a single urban emergency medicine residency program that were over the age of 18 years, and able to provide informed consent.
Exclusion Criteria: Anyone with a history of upper extremity nerve injury, history of smoking, bleeding diathesis or taking any medications that could increase bleeding tendency, or a known allergy to lidocaine.
Twelve subjects were recruited to undergo a total of 18 pairs of nerve blocks. Study participants could elect for the specific nerve block they would like (for a total of 3 median, 7 ulnar, and 8 radial nerves. The same ultrasound trained emergency room physician completed all of the nerve blocks. After randomization, the physician would inject a landmark-based block on the right and an ultrasound guided block on the right, with one of the injections being 3 mL of lidocaine without epinephrine with bicarb, and one being a placebo of 3mL normal saline. On the left arm, the study participant would receive the same injections with the placebo and lidocaine injections switched. Both the physician and study participant were unaware of which injection was which. The nerve distributions for the blocked nerve were then assessed at 15, 30, 45, and 60 minutes to assess for analgesia.
Primary Endpoints
Performance of the block at 15 minutes.
Secondary Endpoint
Performance of the block at 30, 45, 60 minutes.
Subjective pain experienced by the study participant.
Time to perform each block from when needle entered skin to when needle was removed for landmark-based, or until physician deemed completion of block on ultrasound guided method.
Results: Following the 15-minute post injection checks, 14 out of 18 (78%) nerves blocked with the ultrasound-guided block were considered successful blocks. For the landmark-based blocks, only 10 of the 18 (56%) of the nerves blocked were considered successful. In general, the effectiveness of all blocks decreased over each 15-minute interval. Using a random intercept hierarchical model, the ultrasound-guided forearm block was found to have a 22% (p=0.032) higher rate of success than the landmark-based block.
The average ultrasound-guided block took 66.8 seconds, while the average landmark-based block took an average of 32.0 seconds. Additionally, the mean pain score measured on a Likert Scale for ultrasound block was 1.4, while it was 1.6 for the landmark-based approach. Subjects felt that the pain was greater in 5 of 18 (28%) of the ultrasound injections, and 10 of 18 (56%) landmark-based injections. Additionally, no immediate or delayed post-block complications were observed.
Takeaway: In a relatively small study of healthy volunteers, ultrasound-guided forearm nerve blocks result in better block success rates than the traditional landmark based approach. Interestingly, the amount of lidocaine (3 mL) used in this study was less than the amount traditionally used on patients with lacerations (typically about 5mL). This lack of sufficient analgesic may have influenced the effectiveness of each of the nerve blocks. Additionally, the study population used (healthy residents with an average BMI of 23.7) does not accurately represent patient populations with higher rates of obesity and increased body habitus. Therefore, it would be prudent to consider additional studies that incorporated these higher BMI individuals. Until then, this study does demonstrate that ultrasound-guided forearm nerve blocks are associated with decreased subjective pain, as well as increased efficacy. Thus, using an ultrasound to place a forearm nerve block is reasonable decision when encountering such patients in the emergency department.