Background: Local anesthetic (LA) concentration and nerve block duration is sparsely described in a heterogenic study mass.

Aim: To investigate the effect of LA concentration on peripheral nerve block duration in healthy volunteers.

Methods: Randomization of 60 healthy volunteers who will receive 1 of 5 different volumes of LA (ropivacaine) using a constant dose.

Primary endpoint: Sensory nerve block defined by insensitivity towards cold.

Background:

Important factors for a safe and successful nerve block include volume, dose and concentration of local anesthetic (LA). Knowing the duration of peripheral nerve blocks is important to prevent pain breakthrough. With the advancements in ultrasound (US)-guided nerve block techniques it has been possible to substantially reduce the amount of LA required to perform a successful nerve block. This has reduced the risk of systemic toxicity. However, lowering LA volume may reduce nerve block duration, but the extent of this is sparsely described in a heterogenic study mass.

Diluted and large volumes of LA seem to correlate with nerve block duration. Furthermore, increasing LA concentration seems to increase the level of motor block, but not the block duration. A long-lasting nerve block without dense motor block is preferable for optimized pain control and better opportunities to rehabilitate/ambulate.

Aim:

To investigate the effect of LA concentration on common peroneal nerve block duration in healthy volunteers.

Methods:

Randomization of 60 healthy volunteers who will receive 1 of 5 different volumes of LA (ropivacaine) using a constant dose (10mg).

Primary outcome: Duration of sensory nerve block defined by insensitivity towards cold.

Secondary outcome: Duration of motor nerve block defined by either paresis or paralysis.

Explorative outcomes: Degrees of sensory and motor nerve block; Onset times of sensory and motor nerve block; Length of neural exposure to LA.

Inclusion criteria

1. Male or female from and above 18 years of age
2. ASA classification ≤ II

Exclusion criteria

1. BMI below 18 kg/m2
2. Former surgery to the lower extremity in which intervention is planned and surgery which may have caused neural damage to the common peroneal nerve/affected the sensory distribution area of the common peroneal nerve
3. Peripheral nerve disease
4. Allergy to LA
5. Pregnancy or breastfeeding
6. Enrolment in other investigational drug studies or recent clinical trials that may interfere with this study
7. Habitual use of any kind of analgesic treatment
8. Anatomic abnormalities preventing successful US-guided peripheral nerve catheter insertion