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A6024 - Limb Muscle Weakness in ICU Patients Is More Severe than Previously Reported
Author Block: G. S. Supinski1, P. F. Netzel2, L. P. Callahan2; 1Pulmonary, Critical Care and Sleep Medicince, University of Kentucky, Lexington, KY, United States, 2Pulmonary, Critical Care and Sleep Medicine, University of Kentucky, Lexington, KY, United States.
Rationale: ICU acquired weakness (ICUAW) is a serious consequence of critical illness, contributing to respiratory failure and reductions in ambulation. Importantly, a recent study suggested that diaphragm dysfunction in ICU patients is far more severe than limb muscle weakness, but this previous study only employed manual muscle testing to assess limb weakness. No previous study has employed purely objective techniques to assess and compare diaphragm and limb muscle strength in ICU patients. Objective: The purpose of the present study was to compare diaphragm strength to quadriceps strength in mechanically ventilated ICU patients using magnetic stimulation techniques. Methods: Studies were performed on 47 mechanically ventilated patients in the University of Kentucky ICU. Diaphragm strength was assessed as the transdiaphragmatic twitch pressure generated in response to supramaximal bilateral magnetic stimulation of the phrenic nerves (PdiTw). Quadriceps strength was assessed as the force generated at the ankle with the leg supported by a rigid frame, with stimulation of the femoral nerve using supramaximal magnetic impulses (QuadTw). Force-magnetic field strength curves were determined by assessing responses to magnetic field strengths from 60-100% (Magstim 200 Stimulator) and the average of the three best twitches at 100% strength was taken as twitch force. Results: Diaphragm strength, as judged from the PdiTw, averaged 5.3 ± 0.4 cm H2O in our patient population. This value is comparable to that obtained in previous assessments of diaphragm strength for ICU patients and is approximately 20% of the PdiTw reported for normal, healthy adults. Quadriceps strength, assessed by the QuadTw, averaged 5.0 ± 0.7 N, a value approximately 9% of the QuadTw found in healthy adults. There was a poor correlation between PdiTw and QuadTw, r=0.025, p=0.869, suggesting that limb and diaphragm weakness are not modulated by the same pathophysiological pathways. Quadriceps strength was inversely related to the duration of ICU care prior to measurement (r=0.29, p=0.04) but diaphragm strength did not correlate with ICU duration (r=0.10, p=0.52). Conclusions: These data indicate that limb muscle weakness in ICU patients is far more severe than previously reported using less objective, volitional techniques. Our data also indicate that the severity of quadriceps weakness is a function of the duration of ICU care, while diaphragm weakness is not. Additional studies are needed to determine the time course of changes in limb muscle strength in ICU patients and to test the effects of anabolic agents on this parameter.