Adductor pollicis twitch tension assessed by magnetic stimulation of the ulnar nerve

Many critically ill patients develop significant skeletal muscle weakness i n the Intensive Care Unit (ICU), which ultimately may cause difficulties in weaning from mechanical ventilation and a protracted, expensive ICU stay. Reliable monitoring of muscle strength in this environment is difficult. Th e purpose of this study was to develop a reproducible, nonvolitional method of measuring adductor pollicis (AP) muscle function by magnetic stimulatio n of the ulnar nerve (MSUN) that could be applied to patients in the ICU an d operating theater (OT). Fifty subjects (32 healthy control subjects [12 o f whom were elderly], 12 ICU patients with critical illness [mean APACHE II score 20], and six otherwise healthy patients requiring minor surgery in t he OT) received MSUN. In 12 of the normal subjects electrical stimulation o f the ulnar nerve (ESUN) and MSUN were compared and AP twitch tension (Tw A P) and surface electromyogram (EMC) were measured. Close agreement was foun d between supramaximal Tw AP (median [95% CI] for MSUN 6.3 N [5-7.2 N] and ESUN 6.9 N [5.2-7.8 N] [p = NS]). Median (95% CI) values with MSUN for the 20 young and 12 elderly control subjects were 6.9 N (5.3-7.4 N) and 7.1 N ( 4.4-9.8 N). Median (95% CI) Tw AP for the ICU group was 4.2 (2.2-6.7 N) and for the OT group was 5.8 (4-9.1 N). Tw AP was significantly reduced in ICU patients compared with age-matched controls (p = 0.01). MSUN can be used t o measure neuromuscular function in both the laboratory and clinical settin gs including the ICU.