Does Perineural Dexmedetomidine Prolong Duration of a Nerve Block?

Background:

Efficient pain management promoting mobilization and convalescence is essential in an ideal perioperative course. Regional nerve blocks are a central element in postoperative regimes for many patients and it is therefore important that these nerve blocks are both long lasting and efficient. This trial will investigate whether it is possible to optimize the postoperative pain management when adding dexmedetomidine to the local anaesthetic ropivacaine in peripheral nerve blocks.

The prolonging effect of using dexmedetomidine as adjunct in peripheral nerve blocks have been investigated in several studies. However, it remains uncertain whether the effect is mediated by a systemic-, a peripheral- or a combined systemic/peripheral mechanism. In this trial the adjuvating effect of dexmedetomidine will be investigated using the adductor canal block. This is a nerve block that besides being efficient as pain treatment after knee surgery, is primarily sensory, and therefore augments mobilization after total knee arthroplasty.

Method:

On the trial day the volunteers will receive bilateral adductor canal blocks. In one thigh they will receive the local anaesthetic ropivacaine 20ml 5mg/ml and placebo (saline) and in the other thigh ropivacaine 20ml 5mg/ml and dexmedetomidine 100μg. The allocation is blinded to volunteer and investigator.

The duration of the nerve block will be measured by five different tests: Temperature test, Pinprick, Pain during tonic heat stimulation, Warmth detection threshold and pain detection threshold. All tests are validated within pain research.

Inclusion criteria

• American Society of Anesthesiologists class 1
• Body Mass Index 18-30

Exclusion criteria

• Allergy to study medication
• Earlier trauma or surgery to lower limb
• Diabetes Mellitus
• Alcohol or drug abuse
• Daily intake of opioids or steroids last 4 weeks
• Daily intake of any analgesics last 48 hours Heart block Sick sinus node.