Decreased isometric skeletal muscle force in critically ill patients

Critically ill patients can develop muscle weakness that prolongs recovery. The aim of this study was to evaluate contractile parameters of the involuntary isometric skeletal muscle forces as measures of muscle weakness in critically ill patients.

Prospective, controlled trial performed in an intensive care unit (ICU) of a university hospital.

19 critically ill patients (diagnoses: intracranial bleeding n = 9; sepsis n = 6; others n = 4), who were ventilated and completely immobilised for one week. 20 healthy volunteers served as controls. We measured peak torques (PT), contraction times, half-relaxation times, peak rates of torque development and decay and torque latencies of the ankle dorsiflexors of the foot after peroneal nerve stimulation.

Patients (median Acute Physiology and Chronic Health Evaluation II score 21) had reduced PTs, medians 3.3 Nm (interquartile range 2.5 Nm) vs 4.1 Nm (2.0 Nm) in controls (P = 0.0003) for single pulse, 4.9 (4.7) vs 8.1 Nm (3.8) (P = 0.0001) for 2-pulse, 6.1 (6.3) vs 10.3 Nm (3.9) (P = 0.0009) for 3-pulse and 7.3 (6.4) vs 11.6 Nm (7.8), (P = 0.006) for 4-pulse stimulations, respectively. Contraction times were reduced and half-relaxation times increased compared with controls.

Assessment of involuntary isometric skeletal muscle forces can be readily measured in critically ill patients. After one week of critical illness, these patients have decreased force compared with healthy controls. This assessment approach will be further evaluated in a long-term study with a larger patient population.