Continuous Versus Automated Bolus Infusion in Sciatic Nerve Catheters

This study is developed to determine if the local anaesthetic dose can be reduced by the use of intermittent bolus technique compared to continuous infusion when the nerve catheter is placed underneath the paraneurium by ultrasound guidance in the popliteal fossa. Our primary outcome is local anesthetic use the first 48 hours after connecting the peripheral nerve catheter. Our hypothesis is that with an intermittent bolus less local anaesthetic is necessary the first postoperative 48 hours after surgery for adequate postoperative analgesia. As secondary outcomes the investigators study pain scores, motor block, sensory block, feeling of numbness, patient satisfaction, sleep quality and rescue analgesia during the nerve block and afterwards.

Patients scheduled for foot surgery under general anaesthesia and a popliteal nerve catheter will be asked to take part and give informed consent. The anaesthesiologist performing the block, the patient and the independent observer will be blinded to the study group and the settings of the pump (CADD®-Solis) will be regulated and the data collected after 48 hours by an independent pain nurse or anaesthetist who is aware of the study group but does not register any other parameters.

Patients will be randomised by a computer-generated sequence, concealed by sealed envelopes. The envelope will be opened and the pump prepared by an independent pain nurse or anaesthesiologist who will not participate in registration of the parameters except extracting information out of the pump when the catheter is removed.

We expect to detect a 20 % increase in local anaesthetic dose for the continuous administration group (230 mg/48 hour). We used a standard deviation of 25%(58 mg) from a previous study. The minimum sample size required is 20 patients per group for a power of 80% with a 2-tailed significance level of 5%. We decided to include 25 patients in each group.

Before surgery

An IV access and standard monitoring is used throughout the procedure. A pre puncture scan will be performed and an experienced anaesthesiologist will perform all blocks. The block is performed in the lateral decubitus with a 12-18 MHz (megahertz) linear probe (BK medical®) and a solo long needle-catheter set (Pajunk®,18 gauge needle, 20 gauge catheter). The nerve will be visualised in a short axis image and the puncture will be done out of plane. Confirmation of accurate needle tip position will be confirmed by injection of nacl 0,9% (sodium chloride) and the appearance of a "twin- or triple halo sign". After confirmation of correct needle tip position 15 ml levobupivacaine 0,25% (chirocaine® Abbot)will be injected in between de peroneal and tibial nerve as an initial bolus. After injection a will be advanced 4 cm beyond the needle tip.

Correct catheter placement will be confirmed by ultrasound. A detailed description of block performance will be registered according to our standard hospital policy. The sensory block of the peroneal and tibial nerve will be separately tested by loss of cold sensation before transfer to the operating room, at least 20 minutes after the initial injection of lidocaine. When no block is detected it is considered as a block failure and the patient will be excluded from the study.

After performing the popliteal block the patients will be transferred to the operating room and receive general anaesthesia by an independent anaesthesiologist. Surgery will be performed with a tourniquet at 300 mm Hg. Standard monitoring is used during surgery (ecg, pulse oximetry and non invasive blood pressure measurement). Duration of surgery will be registered.

After the operation the patient will be transferred to the recovery room. Here the popliteal catheter will be connected pain pump (which will be defined as t=0) with an infusion protocol according to the study group:

C group: continuous infusion of levobupivacaine 0,125% (chirocaine ®, Abbot) B group: Intermittent bolus of levobupivacaine 0,125 ( chirocaine®Abbot) Both groups will have the possibility of administering a pca (patient controlled analgesia) bolus of 6 ml.

The Pump (CADD®-Solis Smiths medical) which will be started in the recovery room by an independent pain nurse or anaesthetist who is aware of the appointed study group (C group or B group). Pain scores ,motor block,sensory block and presence of numbness will be registered when the patient is awake enough to evaluate these parameters.

The patient will then be transferred to the ward after clear instructions of how to use the pain pump.The study will continue until 48 hours after starting the pump. Pain scores will be registered every four hours at the ward as well as feeling of numbness and sleep quality at regular intervals. During night hours (00-06)when the patient is sleeping pain scores will be registered as "S".When pain control is insufficient at the PACU or on the ward patients will receive paracetamol 1gr IV(Paracetamol® )and ketorolac (taradyal®) 30 mg IV. Tramadol ( contramal ®) 2 mg/kg will be given as rescue analgesia. On day one rescue analgesia will be provided orally .

All rescue analgesia or other medication will be registered.

48 hours after starting the pain pump the pump will be removed and all data will be collected and filed by an independent pain nurse or anaesthetist. This file will consist of a detailed description of the history of local anaesthetic administered, including total anaesthetic dose at 6,12,24 and 48 hours , frequency of extra boluses required and time intervals.

Before removing the nerve catheter the depth of the catheter is checked and bolus of nacl will be infused under ultrasound guidance and if possible correct placement can be confirmed after two days. Then the catheter will be removed.

After stopping the pump the patient will be asked if he or she was satisfied by the postoperative analgesic technique:

1. Satisfied
2. Sufficient
3. Not satisfied

The patient is discharged but is asked to register the exact time point when sensation and motor function (when a motor block was present) after catheter removal appeared. The patient will be called two days after discharge to register these parameters.

Eligibility Criteria:
Inclusion Criteria:

* scheduled for for surgery for hallux valgus pathology with general anesthesia and a popliteal nerve catheter (=sciatic nerve block)

Exclusion Criteria:

* neuromuscular disease,
* chronic pain,
* peripheral neuropathy in lower limb,
* contraindication for popliteal nerve block,
* unable to use pca (patient controlled analgesia),
* patient refusal