Association of Expectations and Pain Relief After Diagnostic Nerve Blocks

Expectations are a major driver of change in health-related outcomes and are related to reduced pain after medical treatment. However, studies on expectations and their relation to pain relief after nerve blocks are largely lacking and there is a paucity of high-quality research in this area. These blocks are frequently used in interventional pain therapy to confirm a particular diagnosis (diagnostic blocks), and to predict if a patient could profit from a particular therapy (prognostic blocks). To current knowledge, there are no studies that specifically assess the association of expectation and response to pain relief after nerve blocks. A further aspect is longer lasting pain relief (i.e. sometimes for days or even weeks) that is sometimes observed in clinical practice after diagnostic nerve blocks and often attributed to a placebo effect. This may lead clinicians to perform block "series" in a therapeutic attempt. Such efforts can be controversial, since the duration of action of local anesthetics is limited to a few hours only - e.g. typically to 2-4 hours in the case of lidocaine, a short acting amino amide and one of the most widely used substances.

There are no investigations on prolonged pain relief after nerve blocks and despite decades of their use in clinical practice, there is hardly any research available.

Hypothesis and primary objective The investigators' goal is to evaluate the association of patients' outcome-related expectations with the short-term success of diagnostic blocks and to assess whether expectations contribute to longer-lasting therapeutic effects. Therefore, they will conduct a prospective cohort study of patients receiving diagnostic nerve blocks in our tertiary pain clinic. According to current recommendations on clinical outcome assessment, pain intensity, physical functioning, emotional functioning and ratings of improvements are all collected. We hypothesize that expectations play a major role in the extent of pain relief in % as well as its duration after the application of local anesthetics, i.e. in this case longer than 2-4 hours for lidocaine.

They will also analyze other potentially influential factors such as depressive symptoms, anxiety and catastrophizing - these are secondary objectives. Thus, they aim to quantify the effect of expectations, assess the therapeutic potential of nerve blocks, improve the accuracy of pretests and exclude patients from clinical pathways who are unlikely to profit from them.