Following ethics approval, eligible patients meeting the inclusion/exclusion criteria will be consented in pre-assessment unit or day surgery at least 2 hours prior to surgery. Patients will then be randomized into two groups:
1. Popliteal and saphenous nerve block catheter insertion with 10 mL 1% ropivacaine injection into each (Treatment group)
2. Popliteal and saphenous nerve block catheter insertion with 10 mL 5% dextrose injection into each (Sham)
All syringes will be blinded to the anesthesiologist in the case. Each patient will have two syringes for before and for after surgery - one set for treatment and one sham. Depending on the randomization they will get first one before surgery and then the other after surgery. Popliteal and saphenous nerve block catheters will be inserted under ultrasound guidance using the catheter-over-needle technique whereby the location of the tip of the catheter can be easily determined. All nerve block catheters will be performed by experienced acute pain physicians who have been performing interscalene blocks under ultrasound guidance for at least 5 years. Successful catheter placement will be verified by following the spread of the injectate, which will occur just before induction of general anesthesia in the operating room. Induction of general anesthesia will follow a standardized protocol with the intravenous administration of sufentanil 0.2 mcg/kg, propofol 2 mg/kg, and rocuronium 0.5 mg/kg. General anesthesia will be maintained with sevoflurane, which will be age-adjusted to 1.0 minimum alveolar concentration (MAC) to begin the case and then adjusted from there as per protocol. Sedline, Masimo® will be used to monitor the depth of anesthesia. The intraoperative patient state index (PSI) target will be 25 - 50. As per protocol, adjustments of the age-adjusted MAC will be performed as follows at every measuring point:
A PSI of either below 25 or of over 50 will always be treated with an adjustment of the age-adjusted MAC value. The same is done if the heart rate and/or the blood pressure is outside of +/- 20% of baseline. The primary goal is to treat any of the above changes with an adjustment to the age-adjusted MAC value. The anesthesiologist will always be able to administer an analgesic, should this be clinically necessary. The patient will be given a bolus of 1 mcg/kg of remifentanil and this will be recorded. The age-adjusted MAC value will be recorded every 5 minutes until the anesthesiologist reduces the anesthetic in preparation for extubation. At the conclusion of surgery and before general anesthesia is ended, the patients will receive the second set of solutions injected into their catheters.
Postoperatively, patients will go to post-anesthesia care unit (PACU). The distribution of the sensory or motor block will then be checked and recorded 30 minutes after arriving in PACU in both groups. The numerical rating scale (NRS) for pain will also be recorded in PACU at 0, 15, 30 and 45 minutes. The patients will there be assessed by members of the acute pain service team and treated as necessary before being transferred to the ward.
The patient, operating room anesthesiologist and the data collection personnel will be blinded.
