Catheter Over Needle vs Catheter Through Needle

Background: Total Knee Replacement Surgery is a commonly performed procedure that causes significant post-operative pain. Continuous femoral nerve blocks are widely used for analgesia as part of a multimodal analgesic regimen for this surgery. They provide sustained analgesia which allows early physiotherapy for rehabilitation. Currently the most common technique for inserting catheters for continuous femoral nerve blocks is to feed a catheter though a needle (CTN) which has been placed close by the nerve. There is a significant rate of leak and dislodgement of these catheters which can lead secondary failure where the catheter is no longer providing analgesia by blocking the nerve (primary failure occurs when the nerve block catheter fails to provide any analgesia from the start). The system to be investigated has a catheter over the needle (CON) which is left in place after the needle is withdrawn. The proposed benefit of this is that there will be a reduction in leak rates and dislodgement. This is because using a CON technique means that the biggest hole will be the diameter of the catheter, rather than CTN where the biggest hole will be the diameter of the needle therefore allowing leak around the outside of the catheter.

Objectives: To ascertain whether or not the catheter over needle technique is superior to catheter through needle technique in terms of a leak rate.

Trial plan: To recruit 108 patients who are having total knee replacement surgery into the study and randomise them into having either CON or CTN continuous femoral nerve blocks.

Inclusion criteria

• Patients presenting to Sir Charles Gairdner Hospital for elective, unilateral, primary total knee replacement.
• Body mass index 18-40 kg/m2
• American Society of Anaesthetists (ASA) grade I-III

Exclusion criteria

• Allergy to local anaesthetic
• Inability to cooperate
• Inability to read, speak and understand English
• Less than 18 years old