Intraoperative Monitoring of Neuromuscular Blockade

There is a global trend of new guidelines highly recommending quantitative neuromuscular monitoring in the operating room. In fact, it is almost certain that quantitatively monitoring the depth of intraoperative muscle paralysis may permit the rational use of muscle relaxants and avoid some of the major related complications, namely postoperative pulmonary complications. A specific culture related to this issue is necessary to integrate quantitative monitoring of muscle relaxants as part of a major monitoring entity in anesthetized patients. For this purpose, it is necessary to fully understand the physiology, pharmacology and concept of monitoring as well as the choice of pharmacological reversal, including the introduction of sugammadex a decade ago.

Quantitative Neuromuscular Monitoring and Postoperative Outcomes: A Narrative Review

Over the past five decades, quantitative neuromuscular monitoring devices have been used to examine the incidence of postoperative residual neuromuscular block in international clinical practices, and to determine their role in reducing the risk of residual neuromuscular block and associated adverse clinical outcomes. Several clinical trials and a recent meta-analysis have documented that the intraoperative application of quantitative monitoring significantly reduces the risk of residual neuromuscular blockade in the operating room and postanesthesia care unit. In addition, emerging data show that quantitative monitoring minimizes the risk of adverse clinical events, such as unplanned postoperative reintubations, hypoxemia, and postoperative episodes of airway obstruction associated with incomplete neuromuscular recovery, and may improve postoperative respiratory outcomes. Several international anesthesia societies have recommended that quantitative monitoring be performed whenever a neuromuscular blocking agent is administered. Therefore, a comprehensive review of the literature was performed to determine the potential benefits of quantitative monitoring in the perioperative setting.

Neuromuscular Blockade Monitoring

Neuromuscular monitoring is essential for optimal management of neuromuscular blocking drugs. Postoperative residual neuromuscular blockade continues to occur with an unacceptably high incidence and is associated with adverse patient outcomes. Use of a peripheral nerve stimulator and subjective tactile or visual assessment is useful for intraoperative management of neuromuscular blockade, especially when the patient's hand is accessible. Quantitative monitoring is necessary for confirmation of adequate reversal and for identification of patients who have recovered spontaneously and therefore should not receive pharmacologic reversal agents. Guidelines, as well as more user-friendly monitoring equipment, have created momentum toward improving routine perioperative neuromuscular monitoring.

Neuromuscular Monitoring in the Perioperative Period

Neuromuscular monitoring devices were introduced into clinical practice in the 1970s. Qualitative neuromuscular monitors, or peripheral nerve stimulators, provide an electrical stimulus to a motor nerve and the response of corresponding muscle subjectively evaluated. A standard peripheral nerve stimulator provides several patterns of nerve stimulation, including train-of-four (TOF), double-burst, tetanic, and post-tetanic count. Qualitative (and quantitative) monitors are needed to determine onset of neuromuscular blockade, maintain the required depth of muscle relaxation during the surgical procedure, and assess an appropriate dose of reversal agent. However, absence of fade measured with a peripheral nerve stimulator does not exclude residual neuromuscular block; TOF ratios as low as 0.4-0.6 may be present when fade is no longer observed. In addition, the risk of incomplete neuromuscular recovery may be influenced by monitoring site. The adductor pollicis is more sensitive to the effects of neuromuscular blocking agents (compared to the muscles surrounding the eye), and monitoring at this site may more accurately reflect recovery of pharyngeal muscles (the last muscles to recover from the effects of neuromuscular blocking agents, in which dysfunction may persist even at a TOF ratio of 1.0). Quantitative monitors are devices that measure and quantify the degree of muscle weakness and display the results numerically. Several different technologies have been developed, including mechanomyography, electromyography, acceleromyography, kineograph, and phonomyography. Lower doses of anticholinesterases may be used to effectively reverse neuromuscular blockade at TOF ratios of 0.4-0.6; quantitative monitoring is required to determine that this level of neuromuscular recovery has occurred. As clinical tests of muscle strength, peripheral nerve stimulators are unable to determine whether full recovery of neuromuscular function is present at the end of the surgical procedure. The use of quantitative monitors is essential in excluding clinically important muscle weakness (TOF ratios <0.9 to 1.0) at the time of tracheal extubation.