Assessment of involuntary muscle function in patients after critical injury or severe sepsis

Study of involuntary skeletal muscle function (MFA) has been well accepted in the area of nutrition assessment and potentially offers a means for following progress of the critically ill patient. We report on the application of this technique to intensive care patients.

MFA was performed by study of the contraction/relaxation characteristics of the adductor pollicis muscle of the thumb after ulnar nerve stimulation. Serial measurements were made in 16 critically injured patients and 28 patients with severe sepsis and were compared with those obtained from 26 control subjects. Extent of loss of total body protein (TBP) was quantified with in vivo neutron activation.

Significant difficulties exist in applying this technique to intensive care patients. In the critically injured, only five acceptable traces could be obtained from a possible 58 measurements. For patients with severe sepsis it was possible to obtain an acceptable trace on 12 of 56 occasions. Neuromuscular blockade and lack of patient cooperation were significant impediments to MFA study. Although frequently perceived as unpleasant by these patients, there was no long-term morbidity associated with MFA. No significant differences were seen in maximal relaxation rate at 30 Hz (MMR30) or force frequency ratios (F10/50 and F30/ 50) between trauma patients and controls. In the sepsis patient group, a significantly higher F10/50 was measured (52% +/- 3% severe sepsis vs 40% +/- 1% control subjects, p < .01). Six patients had MFA measured approximately 21 days after the illness, by which stage they had lost 11% of their initial TBP. Compared with control subjects, no significant differences were observed in MRR30 or F30/50, whereas a higher value for F10/50 was measured (48% +/- 1% critical illness vs 40% +/- 1% control subjects, p < .01).

The MFA technique is difficult to apply to intensive care patients. No significant disturbance to MFA is seen after critical injury. Severe sepsis results in an elevation of F10/ 50 only. When able to be obtained, MFA results do not reflect the extent of proteolysis but are indicative of the state of cellular energetics.