Assessment of adductor pollicis muscle function in critically ill patients

Skeletal muscle wasting is a recognised finding in the critically ill, but few data exist concerning the strength of peripheral skeletal muscles in patients on the Intensive Care Unit (ICU). This may be because previously available techniques involved measurement of force during a maximal voluntary contraction (MVC) and on ICU this type of test may be unreliable since it is effort dependent. We therefore used a novel, non-volitional technique, supramaximal magnetic stimulation of the ulnar nerve (Harris et al.: AJRCCM 1998, 157:A359), to measure adductor pollicis twitch tension (Tw AP) in 14 patients (10M 4F), mean age 44 (range 24–73) years, with a range of diagnoses. Severity of illness was scored within 24 h of admission to ICU and median (95% CI) Apache II score was 19.5 (14–28). Median length of stay (95% CI) (at the time of testing) was 11 (5–17) days. Fourteen healthy volunteers (10M 4F) mean age 44 (21–78) years, served as controls. Median (95% CI) Tw AP in the patients was 3.6 (23–5.9) N and in the controls 7.9 (5.3–9.9) N (P < 0.01, Mann Whitney U Test). Our data show that patients with critical illness are weaker than ambulant controls. The reasons for the observed differences in strength are likely to be multifactorial; further studies are therefore warranted to elucidate the specific causes of this weakness and the relationship between skeletal muscle weakness and failure to wean from mechanical ventilation.