Since Harold Randall Griffith pioneered by the use of curare during anaesthesia by administering it to a young man during an appendectomy in Montreal, the practice of anaesthesiology has completely changed and the world of Neuromuscular Blocking has been thoroughly fine-tuned: increased knowledge and clinical experience, development of new Neuromuscular Blocking Agents (NMBA) with fewer side-effects and well-studied pharmacokinetic profiles, introduction of new antagonizing drugs such as Sugammadex, as well as refinement of neuromuscular block measuring instruments. NMBAs are routinely administered to patients in a multiplicity of anaesthetic settings, and the possibility and availability of instruments allowing the accurate measurement of the degree of neuromuscular block has raised the standards of their use and reversal. The absence of a residual neuromuscular blockade is now widely considered an anesthetic must, as incomplete recovery has been long-established as a strong contributor to post-anesthesia morbidity and mortality. Considering the proven inconsistent, inter/intra-variable and inaccurate character of the human senses to estimate adequate neuromuscular recovery after NMBA use, the proper assessment of neuromuscular recovery can only be done by means of objective methods.3 For this purpose, one of the most widely used methods is the Train of Four (TOF): transcutaneous application of a series of 4 square-wave supra-maximal electrical stimuli over the course of a nerve of choice (most commonly the ulnar nerve). These are applied at a frequency of 2Hz, and each with a duration of 0,2ms. These stimuli elicit a motor response on the adductor pollicis muscle, which on its turn dictates the abduction of the thumb. The acceleration of this movement can be followed by means of an uni/multi-directional accelerometer attached to the thumb. The ratio of the acceleration of the 4th and 1st elicited contractions is called the TOF-Ratio, and this TOF-ratio is a clinically and scientifically established method of assessing neuromuscular block recovery. A value of 1 translates a full recovery of the muscular function of a patient. In modern Anesthesia, the bar for deeming a recovery as adequate has been set at a minimum of a TOF-Ratio of \>0.9, with some authors advocating a ratio of 1 as the only acceptable and complications-avoiding result.

Although an effective measurement of muscular recovery parameters is necessary, daily clinical limitations dictate other practices. Medical devices are expensive and not always available for immediate use. Some devices are also only able to deliver the electrical impulses, but not to measure acceleromyographic parameters. These limitations often force anaesthesiologists to undertake on-the-spot guess-practices (assuming recovery based on a particular NMBA's half-life and its last administered dose), or "d'office" actions (standard NMBA reversal) to determine if a patient has adequately recovered. These methods are inherently associated with major pitfalls/iatrogenic side-effects and are major determinants of a high post-operative morbidity and mortality.

In this study the investigators aim to assess the capability of a dedicated smartphone application to transform and incorporate a Smartphone's accelerometric data to accurately measure the TOF-Ratio in an anaesthesia setting and to compare it to commercially used and established neuromuscular block measuring devices.