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Table 4 Methodologies for assessment of skeletal muscle in ICU [64,65,66]

From: Nutrition therapy in critical illness: a review of the literature for clinicians

MethodMeasurementDetailsBenefitsLimitations
CT image analysis at the abdominal (L3) area• Muscle CSA (cm2)
• Muscle quality (density) (Hounsfield units)
• Specialised software can be used to measure muscle area and density using a CT slice at L3
• Quantification of muscle CSA at L3 is highly correlated to whole body muscle (using scans performed for clinical purposes)
• Provides specific and precise results
• Published cut-off values to identify patients with lower than normal muscularity
• Limited for use in patients who have had a CT at L3 area
• Specialist training and time required for analysis
Bioimpedance analysis (multi-frequency or spectroscopy)• Fat-free mass (kg)
• Phase angle (50 kHz)
• Involves application of a weak current at differing frequencies, through electrodes placed on the hands and feet
• Total body water, percentage body fat, and fat-free mass are estimated via regression equations (with assumed constants for estimating intra- and extracellular water)
• Raw data such as phase angle (which is independent of weight and related to cellular health) may be a predictor of outcome in critically ill populations
• Easy and quick to use
• Safe (no radiation involved)
• Fat-free mass estimates are not likely to be reliable in critically ill patients who experience significant fluid shifts
• Positioning (separation in limbs) and electrode placement may be challenging in some ICU patients
Ultrasound• Muscle thickness (cm)
• Muscle CSA (cm2)
• Muscle quality (echogenicity)
• Muscle thickness and CSA can be measured at different sites (i.e. quadriceps, upper arm)
• Muscle quality can also be assessed using specialist software
• Readily available in most ICUs
• Easy, safe, and quick to use
• No consensus on the ideal sites to predict whole body muscle or to monitor changes over time
• Role of oedema on measurements is unclear
• No widely accepted cut-points to identify patients with low muscularity
  1. CSA cross-sectional area, CT computed tomography, ICU intensive care unit, L3 third lumbar