Neuromuscular monitoring in intensive care patients: milliamperage requirements for supramaximal stimulation

• Published in: British journal of anaesthesia : BJA Vol. 87; no. 4; pp. 625 - 627
• Main Authors: Harper, N.J.N., Greer, R., Conway, D.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.10.2001; Oxford University Press; Oxford Publishing Limited (England)
• Subjects: Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Biological and medical sciences; Critical Care - methods; Edema - physiopathology; Electric Stimulation - methods; Electromyography; Emergency and intensive care: techniques, logistics; equipment, neuromuscular monitor; Humans; intensive care; Intensive care medicine; Medical sciences; Monitoring; monitoring, neuromuscular function, supramaximal stimulus; Monitoring, Physiologic - methods; Neuromuscular Junction - physiopathology; Severity of Illness Index; Single-Blind Method; intensive care; equipment, neuromuscular monitor; monitoring, neuromuscular function, supramaximal stimulus; intensive care; monitoring, neuromuscular function, supramaximal stimulus; equipment, neuromuscular monitor; Human; Edema; Intensive care; Critically ill; Electrical stimulus; Amperage; Electromyography; Neuromuscular transmission; Monitoring
• ISSN: 0007-0912; 1471-6771
• DOI: 10.1093/bja/87.4.625

We investigated the effects of peripheral oedema on the supramaximal current required for neuromuscular monitoring of critically ill patients. We studied 32 sedated patients who had not needed a neuromuscular blocking drug. The presence of oedema over the volar aspect of both wrists was assessed by a blinded observer and graded (grade 0, no oedema; grade 1, mild oedema; grade 2, gross oedema). The supramaximal current was derived by applying an incrementally increasing current over the ulnar nerve and measuring the amplitude of the electromyographic (EMG) response of the first dorsal interosseous muscle. The supramaximal current was that current above which there was no significant increase in EMG amplitude. It was 40 mA in the absence of oedema. This current was significantly increased in the presence of grade 1 oedema (60 mA, Mann–Whitney test, P<0.01) and grade 2 oedema (82.5 mA, Mann–Whitney test, P<0.01). In the presence of oedema, the required supramaximal current decreased significantly after the application of pressure over the stimulating electrodes (Wilcoxon signed rank test, P<0.05). Supramaximal current in critically ill patients is increased in the presence of peripheral oedema. We recommend that nerve stimulators used for neuromuscular monitoring in the ICU are capable of delivering a stimulus current of at least 100 mA.