Acceleromyographic Assessment of Neuromuscular Blockade: TOF-Watch-SX Versus TOFscan

30 patients presenting for elective surgical procedures with an expected duration greater than 60 minutes will be enrolled in this study. ASA I to III patients requiring neuromuscular blockade in the operating room will be eligible for enrollment. All neuromuscular management will be conducted as recommended by the Good Clinical Research Practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents guidelines

Monitoring will consist of standard ASA monitors, which include manual blood pressure measurements, continuous EKG monitoring, pulse oximetry, capnography, and infrared gas analysis. The placement of the TOFscan to the dominant or non-dominant hand will be determined using a computer-generated randomization table. The TOF-Watch-SX will be placed on the other hand.

Anesthetic induction will be as per usual routine clinical care, consisting of propofol 2.0-2.5 mg/kg and fentanyl 100 μg; rocuronium 0.6 mg/kg will be given over 5 seconds through a fast-running IV after baseline neuromuscular data are collected. General anesthesia will be maintained with sevoflurane 1.0-3.0%, with the concentration of inhalational agent adjusted to maintain blood pressure within 20% of baseline values. The depth of anesthesia will also be adjusted to maintain Bispectral Index (BIS monitor) values between 40-60, as per usual clinical practice. Core temperature will be maintained > 35°C and hand temperature > 32°C using an upper extremity warming blanket. Additional doses of rocuronium can be administered (5-10 mg) if required for surgical relaxation (a TOF count of 2-3 during TOF stimulation). No NMBAs will be administered during the last 20 minutes of the procedure. At the completion of surgery, neuromuscular blockade will be reversed with neostigmine 50 µg/kg plus glycopyrrolate, per usual standard of care.

Upon arrival to the operating room, neuromuscular monitoring surface electrodes will be applied. All monitoring will be conducted while the patient is under general anesthesia for the surgical procedure. Surface electrodes (non-invasive EKG electrodes) will be placed on the cleansed skin over the ulnar nerve of both arms near the wrist. The electrodes will be connected by leads to the nerve stimulator component of the TOF-Watch-SX on one arm and the TOFscan on the other arm. The transducer (AMG sensor which measures acceleration) of the TOF-Watch-SX will be placed on the thumb of the corresponding hand. A 75-150g preload (via the Hand adapter) will be applied as per standard recommendations. On the other hand, the transducer (three-dimensional AMG sensor) of the TOFscan will be placed on the thumb using the integrated hand adapter. During the surgical procedure, both devices will be activated simultaneously, and the responses to nerve stimulation recorded.

After induction of anesthesia, but before administration of rocuronium, calibration and stable baseline signals will be achieved for the TOF-Watch-SX and the TOFscan as suggested by the Good Clinical Research Guidelines. After the baseline data are collected, the neuromuscular blocking agent (rocuronium) will be administered. Data relating to onset (a TOF ratio decreases from 1.0 to 0.3 or less on the TOF-Watch-SX display), maintenance (the TOF ratio is less than 0.3 and constant on the TOF-Watch-SX display), and reversal (an increase in the TOF ratio from 0.2 to 0.9 or above) will be recorded. At these same times, data from the TOFscan will be recorded. Monitoring will continue until full recovery of neuromuscular function is noted (a TOF ratio of at least 0.9 or greater on the TOF-Watch-SX device display). At this time, the anesthesia agents will be turned off and the patient awakened and extubated. After surgery, data recorded simultaneously from the TOF-Watch-SX and the TOFscan will be compared.