Brief Summary: The aim of this trial is to investigate if dexmedetomidine prolongs the duration of an adductor canal block. By using healthy volunteers the investigators can perform a bilateral adductor canal block 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 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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
QUADRUPLE
Enrollment
21
100 ug dexmedetomidine added to the ropivacaine nerveblock
20 ml Ropivacaine 5mg/ml
Placebo
Department of Anesthesiology Koege Hospital
Koege, Denmark
Difference in duration of sensory block between dexmedetomidine and placebo assessed as cold sensation with an alcohol swab
Duration is defined as time from block performance until recovery of cold sensation to an alcohol swab, assessed every hour post-block (and every half hour when pain scores during the tonic heat stimulation test is above 0) Time for sleep will be provided.
Time frame: 0-36 hours
Difference between dexmedetomidine and placebo in the duration of a sensory block assessed by pin-prick
Duration is defined as time from block performance until recovery of normal sensation, assessed on the hour post block Time for sleep will be provided.
Time frame: 0-36 hours
Difference between dexmedetomidine and placebo in the duration of a sensory block assessed as maximum pain during a tonic heat stimulation test
Duration is defined as time from block performance until recovery of normal sensation, assessed on the hour post block.Time for sleep will be provided. Recovery of normal sensation is defined as VAS pain scores ± 10 mm of the pre-block value. A Linear 100mm visual analogue scale (VAS) will be used.
Time frame: 0-36 hours
Difference between dexmedetomidine and placebo in the duration of a sensory block assessed as warmth detection threshold
Duration is defined as time from block performance until recovery of normal sensation, assessed on the hour post block Time for sleep will be provided. Recovery of normal sensation is defined as detection thresholds of ± 2 degrees C of the pre-block value. Time for sleep will be provided
Time frame: 0-36 hours
Difference between dexmedetomidine and placebo in the duration of a sensory block assessed as heat pain detection threshold
Duration is defined as time from block performance until recovery of normal sensation, assessed on the hour post block. Time for sleep will be provided. Recovery of normal sensation is defined as detection thresholds of ± 2 degrees C of the pre-block value.
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Time frame: 0-36 hours
Difference in maximum pain scores between dexmedetomidine and placebo during block and after recovery of normal sensation.
Pain scores during a tonic heat stimulation will be compared every hour post block and 1 h after pain scores have returned to the pre-block values. Time for sleep will be provided.
Time frame: 0-36 hours