Introduction Residual neuromuscular blockade is a common occurrence in the post-anesthesia care unit (PACU) when neuromuscular blocking agents (NMBAs) have been used in the operating room. The only method of reliably detecting residual neuromuscular blockade is through the use of quantitative neuromuscular monitors. Unfortunately, several barriers exist that have prevented the widespread use of these devices. For instance, there is a paucity of quantitative neuromuscular monitors commercially available. Also, two modalities of quantitative monitoring, kinemyography and acceleromyography, rely on movement of the muscles of interest, a characteristic frequently compromised during patient positioning for surgical procedures in which the patient's arms are secured under surgical drapes (laparoscopic, bariatric, robotic, spine, and neurosurgical procedures) or in uncooperative awake patients in the PACU or intensive care unit (ICU). The aim of this investigation is to determine the different muscle sensitivities to NMBA and reversal agents by comparing responses at two different monitoring sites as measured with a new quantitative monitor. EMG measures electrical activity within the muscle following peripheral nerve stimulation and is unaffected by involuntary patient motion or by restricted muscle movements from surgical positioning. We plan to compare measurements obtained with two TetraGraph devices, one monitoring the adductor pollicis (thumb) muscle and the other monitoring adductor digiti minimi (5th digit) muscle, during onset, maintenance, and recovery of neuromuscular blockade. This will include monitoring every 20 sec for onset of blockade (defined as time from Train-of-Four ratio, TOFR=1.0 until Train-of-four count, TOFC=0) following rocuronium administration, during maintenance of neuromuscular block as required by surgical conditions, and following reversal administration until adequate recovery is documented (train-of-four ratio, TOFR ≥0.9).

Medication of the patient, surgical procedure

Upon entering the operating room, all patients underwent monitoring using electrocardiograms, noninvasive blood pressure measurements, and pulse oximetry. An intravenous catheter was inserted into either the forearm or the dorsal vein. Anesthesia was initiated with intravenous fentanyl (2.0 mg/kg) and propofol (1.5 to 2.5 mg/kg) and was maintained using sevoflurane (end-tidal concentration of 1.0 to 1.3%) in an air-oxygen mixture, with additional fentanyl given as needed. Before tracheal intubation, the patients were manually ventilated with 100% oxygen via facemask. Oxygen saturation was kept above 96%, and normocapnia was maintained. A forced air warming system (Bair Hugger, Arizant Healthcare Inc., Eden Prairie, Minnesota, USA) was used to keep the body temperature at or above 36°C. Intraoperative hypotension was treated with ephedrine, norepinephrine, or a fluid bolus, according to clinical indications. Ondansetron 4mg IV was routinely administered to prevent postoperative nausea and vomiting.

Neuromuscular Management Before the induction of anesthesia, after appropriate skin cleaning, single-use surface TetraGraph electrodes were placed over the ulnar nerve and thumb to assess the adductor pollicis response on one hand, and over the ulnar nerve and fifth digit to assess the abductor digiti minimi response on the other hand. Following the induction of anesthesia, train-of-four (TOF) stimulation was applied to both muscle groups at a frequency of 2 Hz for 1.5 seconds every 15 seconds, after the automated calibration of supramaximal current and responses. Once stable baseline TOF responses were established, all patients received 0.6 mg/kg of rocuronium intravenously. Measurements were taken every five minutes during the intraoperative period until the administration of sugammadex. After that, we monitored the spontaneous recovery of the rocuronium-induced neuromuscular block until three consecutive TOF counts of 2 (TOFC2) were observed at both monitoring sites. Additional doses of rocuronium (0.1-0.2 mg/kg) were administered as necessary to maintain a Train of Four (TOF) count of ≤2. At the end of the surgery, sugammadex was given at a dose of 2 mg/kg. After administering sugammadex, measurements were taken every 20 seconds until the patient was extubated. Following the measurements obtained with both devices at the specified intervals, and once the TOF ratio exceeded 0.9, the devices were disconnected, and the patients continued along the standard recovery pathway.

Rescue medication After pharyngoscopy, rescue medication is given if necessary, i.e. below 90% TOF, depending on the type of muscle relaxant used. If an aminosteroid muscle relaxant is used, the patient is given 2 mg/kg sugammadex, while if a benzylisoquinoline muscle relaxant is used, 0.05 mg/kg neostigmine and 0.015 mg/kg atropine are administrated to antagonise the drug effect.