Edema in critically ill patients leads to overestimation of skeletal muscle mass measurements using Computed Tomography scans

Abstract Background Changes in muscle mass and quality are important targets for nutritional intervention in critical illness. Effects of such interventions may be assessed using sequential Computed Tomography(CT) scans. However, fluid and lipid infiltration potentially affects muscle area measurements. We aimed to study changes in muscle mass and quality in critical illness with special emphasis on the influence of edema on this assessment. Methods Changes in Skeletal Muscle area Index(SMI) and Radiation Attenuation(RA) at the level of vertebra L3 were analyzed using sequential CT scans of 77 patients with abdominal sepsis. Additionally, the relation between these changes and disease severity using the maximum Sequential Organ Failure Assessment(SOFA) score and change in edema were studied. Results Skeletal Muscle area Index(SMI) declined on average 0.35%(±1.22%) per day(p=0.013). However, in 41.6% of the study population SMI increased. Increasing edema formation was significantly associated with increased SMI and with a higher SOFA score. Muscle Radiation Attenuation decreased during critical illness, but was not significantly associated with changes in SMI or changes in edema. Conclusion In critically ill patients, edema affects skeletal muscle area measurements which leads to an overestimation of skeletal muscle area. A higher SOFA score was associated with edema formation. Since both edema and fat infiltration may affect muscle radiation attenuation, the separate effects of these on muscle quality are difficult to distinguish. When using abdominal CT scans to changes in muscle mass and quality in critically ill patients, researchers must be aware and careful with the interpretation of the results.