An interventional randomized controlled crossover trial, to illuminate if durations in nerve block durations are predictable within the same subject.

An interventional randomized controlled crossover trial, with the purpose to elucidate the reproducibility in nerve block duration on 20 healthy volunteers in Denmark.

There will be two trial arms:

1: Day one; Right side low dose nerve block and left side high dose nerve block. Repeated after 24 hours. Day three; Left side low dose nerve block and right side high dose nerve block. Repeated after 24 hours

2: Day one; Left side low dose nerve block and right side high dose nerve block Repeated after 24 hours Day three; Right side low dose nerve block and left side high dose nerve block Repeated after 24 hours

All volunteers will receive two peripheral nerve blocking catheters adjacent to the common peroneal nerve and will be treated two times on each side with Lidocaine 0.5% 5 mL and 10 mL.

Inclusion Criteria:

1. Age 18 years
2. ASA classification ≤ II

Exclusion Criteria:

1. Allergy to local anaesthetics
2. Body weight 40 kg
3. Possible peripheral nerve injury or disease, including polyneuropathy and diabetes
4. Enrolment or recent participation in studies that may interfere with this study
5. Habitual use of any kind of analgesic medications
6. Anatomic abnormalities preventing successful US-guided Certa Catheter™ insertion.
7. Pregnancy or breastfeeding

The process of intervention-implementation and intervention will not be in the participant's line of sight.

Investigators will not be in the room during the intervention. Outcome assessors will not be in the room during the intervention.