Validation of the TOF Cuff Monitor® Which Measures Neuromuscular Block on the Upper Arm

Neuromuscular blocking agents (NMBAs) are frequently used in anesthesia for tracheal intubation, artificial ventilation, and continued muscle relaxation during surgical interventions. It is of particular importance to measure the neuromuscular block for several reasons:

• To monitor the onset of neuromuscular block and to intubate when deep muscular relaxation is attained.
• To choose the best antagonist and its dosage dependent of the degree of neuromuscular block (for instance sugammadex for deep neuromuscular block or neostigmine for superficial block).
• To avoid antagonization of neuromuscular block in the case of complete recovery of neuromuscular function.

It is proven that monitoring of neuromuscular block reduces patient mortality. It avoids postoperative residual curarization, which is associated with complications such as hypoxemia, bronchoaspiration and pneumonia. Therefore the development and validation of new and efficacious neuromuscular monitoring devices is of great importance.

Neuromuscular monitoring is done by stimulating with an electric current a nerve and to measure the response of the corresponding muscle. In clinical practice acceleromyography is the most often used quantitative measurement method, because it is much easier to apply than other established quantitative neuromuscular monitoring methods such as mechanomyograpy and electromyography. Acceleromyography is based on the piezoelectric effect where mechanical forces at play on the surfaces of certain materials, such as crystals or ceramics, induce an electrical current. According to Newton's second law of motion, force equals mass times acceleration (F=m x a). At constant mass, the acceleration measured and the voltage thereby generated can be used to derive the force of the stimulated muscle. It is standard practice to stimulate the ulnar nerve at the wrist and to measure the movement of the adductor pollicis. In the research setting acceleromyography (TOF Watch SX® monitor) is an established and widely used method. This method requires freedom of movement of the patient's thumb. Unfortunately this is not always possible due to the constraints of patient positioning during the operation. The TOF Cuff® monitor is a modified non-invasive blood pressure cuff that incorporates stimulating electrodes in its inner surface and is based on the stimulation of the peripheral nerve in the arm (brachial plexus, ulnar and median nerves principally). The evoked neuromuscular activity is recorded through the changes in pressure generated in the inner part of the cuff by the muscular activity after the stimulus. Moreover, this device can be used for non-invasive reading of the blood pressure. This device has been validated with mechanomyography, but was never been compared with acceleromyography, which is the most common used neuromuscular monitoring method.

Inclusion criteria

• Patients, age ≥18 to 65 years
• Patient with American Society of Anesthesiology [ASA] status I or II
• Patient able to read and understand the information sheet and to sign and date the consent form
• Patient scheduled for elective surgery lasting at least 60 minutes

Exclusion criteria

• Patient with a history of allergy or hypersensitivity to rocuronium
• Patient with pacemaker
• Patients with neuromuscular disease
• Patients with preoperative medications known to influence neuromuscular function (for instance aminoglycosides, phenytoin, lidocaine)
• Patients with electrolyte abnormalities (for instance, hypermagnesemia)
• Patients with a body mass index <19 or >30 kg m2
• Patient having participated in any clinical trial within 30 days, inclusive, of signing the informed consent form of the current trial
• Patients undergoing interventions that need a continuous deep NMB (for surgical reasons).