Lean Body Mass Assessment: Interpretations of Ultrasound

Christan Bury MS, RD, LD, CNSCClinical Dietitian – Intensive Care Unit

Cleveland Clinic Cleveland, OH

Learning ObjectivesUpon completion of this session, the learner will be able to:1. Describe the benefits and limitations of portable

ultrasound to measure body composition2. Summarize the principles of measurement for

ultrasound 3. Interpret ultrasound results

Ultrasound• Introduced as alternative

to skin calipers• Recent research has

suggested that US may be as accurate as MRI in ability to quantify tissue thickness

• Rectus femoris muscle thickness representative of overall muscle mass

Ultrasound

• Benefits: – Easily performed at bedside– Available in most ICUs– Low cost, painless– No risk to patients (no exposure to radiation)

• Limitations– Affected by edema– Prone to technical errors– Unable to be used in patients with lower extremity

injury or pre-existing skeletal deformity

Ultrasound

• High frequency sound waves passed from a transducer through skin

• Sound waves echo back at different frequencies - differentiation among tissues– Echoes converted into

signals for analysis

Ultrasound• Air < adipose tissue < muscle < bone– Difficulty differentiating between muscle-

bone and adipose-bone interfaces• The strength of each image is

represented by a dot, and the dot’s position represents the depth by which the echo was received– The dots are combined to form an image

Air

Muscle

Bone

Impedance

High

Medium

None

Ultrasound

• Probe Selection• Musculoskeletal

structures – Long, striated

and layered • High frequency,

linear array – 8.0 MHz and

higher provide the highest resolution

Ultrasound• Probe Selection• Musculoskeletal-

long, striated and layered

• High frequency, linear array - 8.0 MHz and provide the highest resolution

Ultrasound

• Quadriceps femoris – surrogate for lean body

mass• Difficult to assess

absolute values alone– no reference values

• Repeated measures- changes in lean body mass over time

Ultrasound• Procedure– lay supine with knee

extended and relaxed– Locate the top of the

patella and anterior superior iliac spine

– Measure the midpoint between the two areas of interest

Heyland et al. Top Up Trial Manual

Ultrasound• Generous amount of

water soluble transmission gel applied to prob

• Transducer pressed against skin surface at 900 angle (perpendicular to skin)

• Maximal compression applied once appropriate area visualized on screen

Ultrasound

• Start at maximum depth to easily identify femur, then focus in as much as possible

• Area of interest focused and frozen on screen, then measured using electronic calipers

UncompressedUltrasound

Resolution 2/2 edema

Mid-Thigh

Max Compression

Mid-Thigh

Calipers

Ultrasound: Summary

• Ultrasounds are readily available at the bedside and are of no additional risk to the patient

• Allow for identification of quadriceps muscle thickness

• May be useful in measuring changes in muscle thickness over time

Learning Assessment Question

1. Which of the following is true of bedside US:

a) Edema has no effect on the results of quadriceps muscle layer thickness

b) You should minimally compress the probe when assessing the quadriceps

c) The curved probe is preferred over the linear probe for the assessment of the quadriceps femoris

d) The quadriceps measurement is best used to assess a change in LBM over time