Proposal for a Revised Classification of the Depth of Neuromuscular Block and Suggestions for Further Development in Neuromuscular Monitoring

摘要

See Editorial, p Anesthesiologists are experiencing new demands for the induction and maintenance of deep neuromuscular block for certain surgical interventions and simultaneously witnessing technical advances in neuromuscular monitoring equipment. The authors view this article as an educational proposal in a process that has gained new momentum and that addresses both clinicians and the manufacturers of medical devices. The discussion whether a deep or even total neuromuscular block might be justified for surgeries such as robot-assisted endoscopic, ophthalmological, or airway operations is still ongoing. Some authors state that maintaining a deep neuromuscular block between 1 and 3 post-tetanic counts during pneumoperitoneum or operations in the posterior chamber of the eye is mandatory.1,2 The authors support their claim with the well-accepted patient safety argument that inadvertent movements of insufficiently paralyzed patients can cause significant morbidity. It is self-explanatory that this cannot be proven in prospective, randomized studies. Fernando et al3 have demonstrated that even at the very low post-tetanic count value of 1, the diaphragm still can inadvertently contract. If this happens, endoscopic instruments can injure the intra-abdominal organs, large vessels, or other delicate structures. Another argument favoring deep block is the improved access to the operation field in the abdominal cavity by the surgeons, if the abdominal wall is completely relaxed.4,5 The application of lower insufflation pressures of carbon dioxide into the abdominal cavity during a very deep block may cause less postoperative pain associated with residual carbon dioxide below the diaphragm.6,7 Even if these findings remain controversial, we believe there is a need to redefine the nomenclature for the spectrum of neuromuscular block. With a clearer differentiation of deep block levels, we might facilitate future discussions. Naguib et al8 have proposed the following stratification of the neuromuscular block spectrum (Table 1), which is widely accepted. We consider the designated area for “deep block” in Naguib list, which ranges from a train-of-four count = 0 to a post-tetanic count ≥1 to be too broad. Although this classification may be sufficient for the majority of surgical purposes, for those who prefer to work with the very deep and narrow segment of post-tetanic counts values ranging from 1 to 3, this area should be specifically identified. For this particular range, we propose the term “profound block.” Thus, our slightly modified scale divides the original deep block as shown in Table 2.Table 1.: Original Neuromuscular Block Levels by Naguib et al8Table 2.: Modified Neuromuscular Block LevelsWhen extubating a patient’s trachea, the difference between “minimal” and “shallow” block is important. We believe that a distinction between a deep and profound block is also justified, considering their significance for specific surgeries. We must emphasize that the proposal for introducing the profound block level into this list of definitions is not meant to encourage clinicians to achieve deeper block levels than they otherwise would. However, for some surgical procedures, such as intraocular, where even minor patient movements may be disastrous, and when diaphragmatic contractions must be prevented to avoid increases in intracranial pressure associated with tracheal suctioning, profound levels of block are recommended.3,9 Ultimately, these are decisions that each clinician must make based on individual clinical need. Our proposal merely fine-tunes the set of definitions of the various depths of neuromuscular block in an attempt to standardize the terminology. In addition, although profound block may be necessary in certain settings to prevent injury, the clinician cannot and must not assume that this technique is devoid of significant side effects. First, many clinicians do not have unrestricted access to sugammadex, while neuromuscu