The Impact of Local Anesthetic Dilution on Possible Blinding for Nerve Blocks

This study aims to determine the appropriate dosage of a placebo anesthetic to enable future placebo-controlled studies that can more accurately examine the effects of nerve blocks. The main challenge in conducting such studies is the difficulty in blinding participants and researchers due to the noticeable effects of nerve blocks, such as numbness and motor impairments.

The goal is to find a placebo solution that can:

* Mimic the sensations of a real nerve block
* Not provide actual pain relief
* Allow for effective blinding in future studies

By developing an appropriate placebo, researchers hope to:

* Enable more rigorous investigations into the efficacy of nerve blocks for pain management
* Conduct comprehensive placebo-controlled studies, which are currently lacking in the field
* Overcome the obstacle of ensuring successful blinding in nerve block research This study is focused to establish a methodology for creating a convincing placebo that can be used in future research to more accurately assess the true effects of nerve blocks in pain medicine.

Nerve blocks are medical procedures commonly used in pain management for three main purposes: diagnosis, prognosis, and treatment. For diagnostic nerve blocks, the goal is to identify the source of pain. The underlying idea is straightforward: if numbing a specific nerve stops the pain, that nerve is likely the source of the problem. Conversely, if the pain persists after the nerve is numbed, it suggests that the issue lies elsewhere.

Prognostic nerve blocks serve a different function; they are used to test whether a future treatment might be successful. If a temporary nerve block alleviates pain, it indicates that a more permanent treatment targeting that nerve could be effective. Therapeutic nerve blocks aim to provide long-lasting pain relief, helping patients engage in physical therapy or acting as a treatment on their own.

Despite their widespread use, there is insufficient solid scientific evidence to fully support the effectiveness of nerve blocks. Most studies conducted so far rely on observational data rather than controlled experiments. This lack of robust evidence raises concerns because diagnostic and prognostic blocks may lead to incorrect diagnoses or ineffective treatments. Additionally, therapeutic blocks can be invasive and costly, yet their effectiveness is not always guaranteed.

One significant challenge in researching nerve blocks is the difficulty of conducting placebo-controlled studies. For these studies to be valid, researchers need to ensure that neither the patients nor the assessors know who received the actual treatment and who received a placebo. However, this is complicated by the fact that nerve blocks often cause noticeable numbness or weakness, making it easy to identify who received the real treatment.

Researchers are exploring the possibility of using very low doses of anesthetic that might provide pain relief without causing noticeable numbness or weakness. If successful, this approach could allow for proper "blinded" studies where neither patients nor researchers can tell who received the actual treatment.

In summary, while nerve blocks play an important role in pain medicine, more research is needed to confirm their effectiveness. Finding ways to conduct proper placebo-controlled studies is crucial for ensuring that these treatments truly benefit patients.

Eligibility Criteria:
Inclusion Criteria:

* ASA I - II, both sexes
* ≥ 18 years old
* \< 65 years old
* Written informed consent as documented by signature

Exclusion Criteria:

* Known allergy or hypersensitivity to a ropivacaine, amide local anesthetics or ultrasound gel
* Any history of chronic or acute pain at the moment of enrollment into the study
* Treatment with any substance having a relation to pain or pain modulation (antidepressants, opioids, benzodiazepines, anticonvulsants)
* Intake of any analgesic 48 hours prior to the conduction of any of the study stages
* Severe coagulopathy
* History of cardiovascular disease
* History of alcohol abuse or the intake of psychotropic drugs
* Pregnancy, ruled out by history
* Infection at the injection site or a systemic infection
* Fever of unknown origin
* Motor or sensory abnormalities in the arm
* Previous enrollment into the current study