%0 Thesis %9 Doctoral %A Puthucheary, ZA %B Medicine (Division of) %D 2014 %E Montgomery, HE %F discovery:1425686 %I UCL (University College London) %K Muscle, Intensive care, protein synthesis, protein homeostasis %P 197 %T Acute skeletal muscle wasting in the critically ill %U https://discovery.ucl.ac.uk/id/eprint/1425686/ %X Introduction: Critical illness survivors demonstrate skeletal muscle wasting with associated functional impairment. I prospectively characterised this process, and defined the pathogenic roles of altered protein synthesis and degradation. Methods: Critically ill patients (n=63, 59% male, age 54.7±18.0 years, APACHE II score 23.5±6.5) were recruited <24 hours following intensive care admission. Muscle loss trajectory was determined through serial ultrasound measurement of rectus femoris cross-sectional area (RFCSA) and, in a subset, quantification of myofibre area (FibreCSA) and protein/DNA ratio. Histopathological analysis was performed. Muscle protein synthesis and breakdown rates were determined and respective signalling pathways examined. Results: RFCSA decreased significantly, (-17.7±12.1%, [p<0.001]), underestimating muscle loss determined by FibreCSA (-10.3±10.9% vs.-17.5±30.2%, p=0.31), or protein/DNA ratio (-10.3±10.9% vs. -29.5±41.5%, p=0.03). Fall in RFCSA was greater in multi- than single-organ failure (-21.5±10.5% vs. - 7.2± 9.7%, p <0.0001), even by day 3 (-8.7±16.3% vs. -1.8± 9.6%, p<0.01). Myofibre necrosis occurred in >50% (20/37) of subjects. Protein synthesis was depressed to levels observed in fasted controls (0.035±0.018%/hr vs. 0.039±0.011%/hr, p=0.57), and increased by day 7 (0.076±0.066%/hr, p=0.03) to levels associated with fed controls (0.065+0.018%/hr, p=0.30,) independent of nutritional load. Protein breakdown remained elevated throughout (8.5±5.7 to 10.6±5.7mmol phe/min/IBW, p=0.4).Principal component analysis of intracellular signalling supported a programme of increased breakdown (r=-0.83, p=0.005) and depressed synthesis (r=-.69, p=0.041). Conclusions: Early rapid skeletal muscle wasting occurs in critical illness, is greatest in those with multi-organ failure, and results from suppression of protein synthesis and increases in catabolism. These effects are independent of feeding and are commonly associated with myonecrosis.