Continuous sciatic nerve block with a new catheter

Background and Goal of study
A new catheter for continuous peripheral nerve block has been developed and preliminary cadaver studies suggest high success rates for initial placement with possible repositioning in case of displacement 1, 2. 
The needle is curved and connected to a 19-G nylon catheter with a detachable hub. The Hub covers the connection. and allows injection during needle insertion. The part of the catheter closest to the needle is filled by alternating regions of glue and air.. The distal part of the catheter is patent and extends to a Luer-lock injection port. Two exit holes are placed at the transition between the interrupted part and the patent part of the catheter (fig.1-3)
The aim was to investigate if the catheter could be accurately placed for  sciatic nerve blocks
 
Material and Methods
We conducted a single center, double blinded, placebo-controlled, randomized trial in 16 healthy volunteers following ethical approval (H-15000927). A catheter was inserted in each leg in the popliteal region with ultrasound (US) using the short axis approach. The volunteers were randomized to receive 15ml lidocaine (20mg/ml) in one side and 15ml 0,9% saline in the contralateral side.  We assessed cold sensation on the lateral part of the lower leg and measured voluntary muscle force for dorsi- and plantarflexion and surface EMG (sEMG).
Successful placement of the catheter was defined as a 20% decrease in gross isometric dorsiflexion and loss of cold sensation on the lateral part of the lower leg. 
After return of normal sensory and motor function the volunteers performed a series of physical exercises simulating mobilization and physiotherapy including walking up and down 2 flights of stairs. 
We performed a second injection of local anaesthetic (LA) and placebo in the catheters. Catheter position was assessed with US. A second investigator blinded to earlier assessments tested cold sensation and muscle force.
Results and Discussion
94% (95% CI [72-99%]) of primary placements were successful although all patients had loss of cold sensation
The peroneal nerve was more often affected than the tibial nerve with regard to motor force and sEMG.
 
After physical exercise, all catheters were assessed by US with repeated injection of LA and assessment of motor and sensory function. 11 of 15 catheters with initial successful placement had both sensory and motor block and were never displaced more than 0.5 cm. 
Conclusion 
This new catheter can be placed with high success rates for initial placement. Physical exercise may cause displacement in some cases but will need to be tested in a clinical setting. Unlike common catheter designs the new catheter resembles a suture. This feature enables repositioning in case of displacement.

Continuous sciatic nerve block with a new catheter - primary placement and secondary displacement