This is a clinical study to investigate and compare a new programmed intermittent bolus (PIB) delivery method for continuous popliteal sciatic nerve block for pain relief in patients undergoing major ankle surgery compared with the current practice of continuous local anesthetic infusion (CI).

Peripheral nerve blocks are commonly used for upper and lower limb surgery. Continuous popliteal sciatic nerve block achieved by delivery of local anesthetic through a perineural catheter plays an important role in post-operative pain control after major orthopedic surgeries of the ankle and foot. Factors affecting the success and clinical outcome of continuous sciatic nerve blocks include the accuracy of catheter placement, the local anesthetic dose (volume and concentration), and the infusion method.

Methods of local anesthetic infusion commonly used for peripheral nerve blockade include continuous infusion (CI) and CI combined with patient-controlled analgesic (PCA) boluses. A third option, regular intermittent boluses of local anesthetic, is not commonly used as it usually requires manual administration by a healthcare provider and is thus time and labor-intensive. Recently, however, infusion pumps capable of providing automated programmed intermittent bolus (PIB) dosing have become available.

The premise of PIB dosing is that it results in more extensive spread of local anesthetic around nerves, and thus more effective sensory block and analgesia. PIB dosing regimens have been extensively studied in labor epidural analgesia, where they have been shown to decrease local anesthetic consumption and improve maternal satisfaction when compared with continuous infusion regimens.

In contrast, there has been little investigation into PIB dosing regimens in the context of continuous peripheral nerve blockade. In 2005, Taboada et al 2 published a study that compared automated PIB dosing with CI dosing of local anesthetic for continuous popliteal sciatic nerve blockade. In both regimens, patients were also allowed to administer PCA boluses of local anesthetic as needed to improve the quality of the nerve block. The authors found that the automated PIB dosing regimen resulted in patients using less local anesthetic and fewer PCA boluses, while providing equivalent analgesia. There was a non-significant trend to lower pain scores in the PIB group of patients. These effects are attributed to better perineural spread of local anesthetic with the PIB regimen. No other studies have been conducted to confirm these benefits.

The reduced local anesthetic requirement is of particular advantage in patients who are discharged home with a nerve block catheter in situ as the supplied reservoir of local anesthetic will last longer. Ambulatory infusion pumps with both PIB and PCA features are now commercially available. The investigators hypothesize that a PIB+PCA dosing regimen using one of these new ambulatory infusion pumps will provide more effective postoperative analgesia with less local anesthetic consumption than the CI+PCA dosing regimen.

Inclusion Criteria:

• Inpatients having major foot and ankle surgery that will benefit from continuous popliteal sciatic nerve block with an indwelling catheter
• American Society Anesthesiologists (ASA) physical status I-III
• 18-85 years of age, inclusive
• 40-120 kg, inclusive
• 150 cm of height or greater

Exclusion Criteria:

• Patients who undergo iliac crest bone graft harvesting as part of their surgery
• Preexisting neurological deficits or peripheral neuropathy in the distribution of the sciatic nerve
• Local infection
• Contraindication to regional anesthesia e.g. bleeding diathesis, coagulopathy
• Chronic pain disorders
• History of use of over 30mg oxycodone or equivalent per day
• Allergy to local anesthetics
• History of significant psychiatric conditions that may affect patient assessment
• Pregnancy
• Inability to provide informed consent

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