The Effect of Local Anaesthetic Volume on Nerve Block Duration and Nerve Block Duration Variability
Condition: Postoperative Pain
MeSH terms: Pain, Postoperative
Study type: Interventional
Phase: Phase 4

Summary: 
      The aim is to investigate the effect of perineural administration of a series of different
      volumes of local anaesthesia (ropivacaine 0.2%) on nerve block duration and the variability
      of the duration in the common peroneal nerve and the sciatic nerve in healthy volunteers.

      The hypothesis is that nerve block duration is correlated to local anaesthetic volume, but
      only to a certain degree. After a sufficient volume a 'saturation level' will be reached, and
      nerve block duration will not increase further.
    

Detailed description: 
      The trial is divided into two similar phases. Each phase will focus on a specific nerve.
      Phase 1 will focus on the common peroneal nerve and Phase 2 will focus on the sciatic nerve.

      After baseline measurements, the investigators will insert a peripheral intravenous catheter.
      Then, the investigators will insert a suture-method peripheral nerve catheter (Certa
      CatheterTM). Procedures will be done in a sterile manner as a standard of practice. The
      investigators will use an ultrasound (US)-guided short-axis, needle in-plane technique. For
      the US-scan, the investigators will use a linear or a curvilinear transducer.

      During interventions, volunteers will be monitored with continuous pulse oximetry. Placement
      of the peripheral nerve catheter will be facilitated by US using small injections of
      mepivacaine (carbocaine 2 %) in the skin and surrounding tissues and only isotonic saline (5
      mL) in the perineural space to prevent blocking of the nerve before ropivacaine injection.
      The catheter orifice will be placed by pulling either end of the catheter and guided by the
      built-in echogenic markings seen on US. Before injection of ropivacaine, the investigators
      will do careful aspirations through the catheter in order to prevent intravasal injection.

      Each ropivacaine injection will be administered via an infusion pump. This will ensure a
      constant infusion rate set to 10 mL per minute. During infusion, the volunteers will be
      monitored with continuous pulse oximetry.

      Before instigation of the ropivacaine infusion, the investigators will use US to verify full
      absorption of the isotonic saline in the perineural space.

      For each nerve, the subject will be randomly allocated to and receive one of five possible
      ropivacaine volumes. All volunteers and outcome assessors will be blinded to the ropivacaine
      administrations and infusion procedures. Outcome assessors will not be in the room, when the
      medication is prepared nor given. Preparation will take place behind a curtain and therefore
      also blinded to the volunteers.
    

Intervention name(s): Ropivacaine
Intervention type(s): Drug
Intervention description(s): Perineural injection.
Intervention MeSH terms: Ropivacaine
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Triple (Participant, Investigator, Outcomes Assessor)
Primary purpose: Treatment
Keywords: Regional anaesthesia