[Diagnostic and therapeutic nerve blocks in pain therapy]

Diagnostic and therapeutic nerve blocks in pain therapy Abstract. Nerve blocks are not only performed in anaesthesiology to enable surgery, but also in pain therapy to diagnose and treat localised pain. For diagnostic purposes a minimal dose of local anaesthetic is applied directly to the nerve. Ultrasound has recently become the most precise and practicable tool to localise the nerve. When the effect of the block lasts as long as the predicted duration of the local anaesthetic, this confirms that the blocked nerve conducts the pain. In such cases, repetitive therapeutic blocks with local anaesthetics can be used to desensitise the nerve. A structural lesion of the nerve caused by heat (radiofrequency ablation), cold (cryoneurolysis) or even surgical nerve dissection can lead to long-term pain reduction. However, there is only weak evidence supporting these therapies and a relevant risk of pain due to deafferentation, and depending on the nerve, there could be persistent motor or sensitivity disturbances. Any intervention in humans includes placebo and nocebo effects. Those effects should be taken into consideration by asking the patient about previous experiences and their expectations for the intervention. The knowledge of placebo and nocebo effects can then be used to make the patient more comfortable during the procedure, to improve therapeutic effects and to reduce side effects. Problematic psychosocial factors and signs of centralised sensitivity should be evaluated in advance in order to consider withholding the use of interventional procedures in sensitised patients.