Monitoring neuromuscular blockade in the ICU

Whenever a muscle relaxant is used, its effect should be monitored. The infusion rate ( Table,!,) can then be adjusted in order to optimize the level of block, thereby avoiding inadequate or excessive block. The optimum technique is yet to be determined. A train of four supramaximal stimuli, delivered from a handheld nerve stimulator attached over the ulnar nerve at the wrist with self-adhesive surface electrodes, is used in the author's ICU. The movements of the thumb are observed by either visual or tactile means. A useful general rule is to maintain the level of block where the first twitch of the train of four is present. If there is no response, the infusion rate of relaxant is decreased, and if there are two or more twitches, the infusion rate is increased. The use of complex equipment designed either to quantify the movements of the thumb using a force or acceleration transducer or to measure the electromyogram of the adductor pollucis muscle are unnecessary for routine clinical purposes.

The use of surface (ECG type) electrodes is convenient, but the response may vary from day to day. It is important to change electrodes at least daily, clean the skin carefully, and maintain a constant position if possible. Accumulation of tissue edema is common in ICU patients, and this may reduce the intensity of what was a supramaximal stimulus. It is usually possible to reduce this problem by exerting firm pressure over the electrodes for 1 to 2 min before stimulating.

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