Perineural Dexmedetomidine for Ulnar Nerve Block.

The aim of this trial is to investigate if dexmedetomidine prolongs the duration of an ulnar nerve block. By using healthy volunteers the investigators can perform bilateral ulnar nerve blocks and thereby control for a systemic effect to clarify if the effect is actually peripheral or systemic. The investigators hypothesis is that dexmedetomidine as an adjunct to a local anaesthetic prolongs the duration of a peripheral nerve block by a peripheral mechanism.

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 an ulnar nerve block.

Method:

The participants will attend two trial days.

On one trial day the volunteers will receive bilateral ulnar nerve blocks. In one arm they will receive the local anaesthetic ropivacaine 4ml 5mg/ml and placebo (saline) and in the other arm ropivacaine 4ml 5mg/ml and dexmedetomidine 100μg. The dexmedetomidine administered perineurally is absorbed and redistributed and will influence the two nerve blocks equally systemically. On the other trial day the participants will receive ropivacaine 4ml 5mg/ml and placebo (saline) and in the other arm ropivacaine 4ml 7.5mg/ml and placebo (saline). The allocation is blinded to volunteer and investigator.

In this setup we therefore have a perineural- and a systemic dexmedetomidine group and also a placebo group , and a group testing if higher doses of local anesthetics will prolong the duration of a nerve block.

The duration of the nerve block will be measured by 3 different tests: pinprick, temperature test (alcohol) and Pain during tonic heat stimulation. All tests are validated within pain research.

Eligibility Criteria:
Inclusion Criteria:

* Participants must understand the protocol fully and sign the written in-formed consent.
* ASA 1-2
* BMI \> 18 to \< 30
* For fertile women: safe contraceptives for the last month and a nega-tive urin HCG.

Exclusion Criteria:

* Participants unable to cooperate in the trial.
* Participants unable to speak or read Danish
* Allergy to study medication.
* Alcohol consumption \>21 units for men and \>14 for women per week
* Daily intake of prescription painkillers within the last 4 weeks.
* Over the counter painkillers during the last 48 hours.
* Neuromuscular defects or wounds on the arms or hands preventing test performance.
* Diabetes Mellitus
* 2. degree heart block
* Sick sinus node.
* For fertile women a positive urine HCG