VALUE OF MUSCULAR RELAXATION MONITORING

Indication: Sensitivity to neuromuscular blocking agents differs betwe en individuals, and residual neuromuscular blockade is a common postop erative problem. Clinical signs such as head lift, hand grip, and insp iratory force are suitable means of showing residual blockade. However , an awake and cooperative patient is needed. Therefore, in clinical p ractice it is advantageous to use the responses evoked by a nerve stim ulator. Sites of nerve stimulation and differing muscle response: In c linical anesthesia, the ulnar nerve is the most popular site. The resp onse is evaluated by feeling the contractions of the adductor pollicis muscle. This muscle shows a slow onset of blockade and is highly sens itive to neuromuscular blocking agents. Therefore, the chance of overd osing the patient is decreased and during recovery additional safety i s gained, as it can be safely assumed that at the time of normalizatio n of the thumb twitches no residual blockade exists in the diaphragm o r larynx. On the other hand, absent twitches of the adductor pollicis using train-of-four stimulation do not preclude intraoperative activit y of more resistant muscles such as the diaphragm. Recording of evoked responses and patterns of nerve stimulation: In clinical anesthesia, tactile evaluation of the muscle response is the usual method. Mechano myography (Myograph(R)) with a force transducer is used as the referen ce standard. This method, as well as the measurement of acceleration ( Accelograph(R), TOF-Guard(R)) and electromyography (Relaxograph(R)) ar e mainly tools for teaching and research. Different patterns of nerve stimulation are used: during induction, single-twitch stimulation at 1 Hz; during profound blockade, posttetanic count stimulation (PTC); sur gical blockade is evaluated using train-of-four stimulation (TOF); and recovery is followed by double-burst stimulation (DBS). Using simple train-of-four stimulation during recovery, a device is needed with a r egistering capacity to accurately determine a TOF-ratio >0.7. Conclusi ons: Relaxometry allows monitoring of neuromuscular function independe ntly of the patient's cooperation, and should be standard. In the inte nsive care unit, relaxometry helps to minimize the risk of overdosing. However, muscular weakness can persist despite adequate drug dosage. Relaxometry is only part one of a concept. Intubating and operating co nditions are highly dependent on the depth of anesthesia, and the risk of postoperative residual blockade can be minimized by using short or medium action drugs.