Saphenous Nerve Block for Foot and Ankle Surgery

Purpose / Hypothesis This clinical study is a prospective, controlled, randomized, single-blinded trial designed to investigate the hypothesis that ultrasound-guided blockade of the saphenous nerve in conjunction with nerve stimulation has a higher success rate when compared to ultrasound alone. These research interventions represent what is considered to be an improvement on the standard practice at St. Paul's, which is to block the saphenous nerve with one of any number of saphenous nerve blocks, using a number of different techniques (i.e. ultrasound-guided, nerve stimulation, blind field block); the effectiveness of which has been inconsistent. The purpose of this study is to identify if one technique has a great success rate over another, which would ultimately result in increased success rates of saphenous nerve blocks and patient care.

Study Design The study will be a randomized, single-blinded trial of 80 subjects who are undergoing foot and ankle surgery. Informed consent will be obtained from all study subjects. Subjects will be randomized to one of two saphenous nerve block techniques to be administered by an experienced regional anesthesiologist at St. Paul's Hospital. Once the nerve block is completed the success will be evaluated by an investigator blinded to the procedure. Once the 30min evaluation is completed anesthetic care will be provided according to regular institutional practice and at the discretion of the attending anesthesiologist. The subject will then be contacted at 2 and 7 days after block administration to assess for delayed complications.

Intravenous access will be gained and non-invasive blood pressure measurements will be recorded every five minutes. Continuous electrocardiography and oxygen saturation monitoring will be maintained throughout the procedure and for at least 60 minutes afterwards. Light sedation will be provided, with the goal of maintaining verbal contact with the subject throughout the procedure. Where clinically appropriate, the study block may be preceded by an ultrasound-guided popliteal sciatic nerve block at the discretion of the attending anesthesiologist.

Saphenous nerve blockade will be preformed using a transsartorial approach. Subjects in both groups will be positioned prone. The ultrasound probe will be placed in the transverse plane on the medial aspect of the thigh 3-5cm cephalad to the superior border of the patella (area marked). An attempt will then be made to identify the saphenous nerve, which runs deep to the sartorius muscle within the subsartorial fascial plane. The nerve will appear hyperechoic, round or oval shaped. The anesthesiologist will have a maximum scan time of 3 minutes prior to needle entry. Up to 5 mL of 1% Lidocaine will be used for skin infiltration of the injection site. The block will then be preformed as to the protocols below depending on group allocation. A thirty minute evaluation of the saphenous nerve block will occur during the normal monitoring period after the placement of a block.

Following completion of the thirty-minute evaluation, anesthetic care will be provided according to regular institutional practice and at the discretion of the attending anesthesiologist. This may include spinal or general anesthesia.

All subjects will be contacted by telephone at two and seven days post procedure for a follow up interview to assess for delayed complications associated with the procedure.

The medications used for the nerve blocks in the study will include only ropivacaine 0.5% and lidocaine 1%. For subject sedation, midazolam and fentanyl will be used. None of these medications are considered study drugs; rather they are commonly used anesthetic medications. While used in the study, these drugs themselves are not being investigated. The same medications will be used on subjects not enrolled in the study.

Study Treatment Group 1 - Saphenous nerve block using ultrasound guidance The needle will be placed with the needle tip in close proximity (1-2 mm) of the target structures (the saphenous nerve if visible or in the subsartorial facial plane of the sartorius muscle if the nerve is not visible). A total of 10 mL of 0.5% ropivacaine will be used for the block. Before injection of any local anesthetic a gentle aspiration will be preformed, with a second aspiration after 5 mL of ropivacaine has been injected. Once injection of local anesthetic has commenced small needle adjustments are allowed to enhance spread. This will be done at the discretion of the regional anesthesiologist performing the block.

Study Treatment Group 2 - Saphenous nerve blockade using ultrasound guidance and nerve stimulation The needle will be place with the needle tip in close proximity (1-2 mm) of the target structure (the saphenous nerve if visible or in the subsartorial fascial plane if the nerve is not visible). The Pajunk MultiStim SENSOR nerve stimulator will then be turned on, starting at 1.0 milliamp (mA) until a tapping sensation is elicited in the medial or anterior aspect of the ankle. The amplitude of the nerve stimulator will then be gradually decreased with maintenance of the tapping sensation by making small adjustments in needle location. The end-point for nerve localization will be a tapping sensation in the area of the medial malleolus at ≤ 0.6 mA. The anesthesiologist will have a maximum search time of 5 minutes from needle entry to elicitation of the tapping sensation. Once a tapping sensation is elicited in the ≤ 0.6 mA range, 10 mL of 0.5% ropivacaine will be injected at the site. If a tapping sensation is elicited but not ≤ 0.6 mA within 5 minutes then 10 mL of 0.5% ropivacaine will be injected at the site where the lowest amplitude tapping sensation was elicited. If no tapping sensation is elicited from the subject after 5 minutes, an injection of 10 mL of ropivacaine will be made below the Sartorius muscle in the subsartorial fascial plane. Before injection of any local anesthetic a gentle aspiration will be preformed, with a second aspiration after 5 mL of ropivacaine has been injected. Once injection of local anesthetic has commenced small needle adjustments are allowed to enhance spread. This will be done at the discretion of the regional anesthesiologist performing the block.