Development of a bedside-applicable ultrasound protocol to estimate fat mass index derived from whole body dual-energy x-ray absorptiometry scans

Influence of Subcutaneous Adipose Tissue and Skeletal Muscle Thickness on Rectus Femoris Echo Intensity in Younger and Older Males and Females

OBJECTIVES

Ultrasound measurements of muscle echo intensity are commonly used surrogates of muscle composition (eg, intramuscular adipose tissue). However, given that soundwaves are increasingly attenuated with tissue depth, the interpretation of echo intensity may be confounded by adipose and skeletal muscle thickness. Our objectives are to compare the associations between adipose or muscle tissue thickness and rectus femoris echo intensity in younger and older males and females.

METHODS

Participants included in this analysis were derived from 3 previously published cohorts of younger (<45 years) and older (≥60 years) males and females. Ultrasound images of the rectus femoris were evaluated for muscle thickness, echo intensity, and subcutaneous adipose tissue thickness.

RESULTS

Older adults (n: 49 males, 19 females) had a higher body mass index (P = .001) compared with younger adults (n: 37 males, 49 females). Muscle thickness was negatively associated with echo intensity in older males (r = -0.59) and females (r = -0.53), whereas no associations were observed in younger males (r = 0.00) or females (r = -0.11). Subcutaneous adipose tissue thickness displayed no associations with echo intensity in any group.

CONCLUSIONS

Despite the known influence of subcutaneous adipose tissue thickness on beam attenuation, we observed no association with muscle echo intensity, indicating that adipose tissue correction may be required to better understand muscle echo intensity across differences in adiposity. The negative associations between muscle thickness and echo intensity in older, but not younger adults, suggests these associations may be related to the co-occurrence of skeletal muscle atrophy and intramuscular adipose tissue infiltration with advancing age.

Comparison between handheld ultrasound and regional and whole-body dual energy x-ray absorptiometry (DXA) for body fat assessment

OBJECTIVES

To determine the extent of agreement between a handheld ultrasound (US) attached to an android tablet and the reference method dual energy x-ray absorptiometry (DXA) for the measurement of adiposity.

METHODS

A whole-body DXA scan and abdominal adipose tissue thickness measurements using a handheld US were obtained from 104 adults (63 females, 41 males). Body fat percent (BF%), total fat mass (kg), and trunk fat mass (kg) were obtained from DXA. Subcutaneous adipose tissue (SAT), superficial subcutaneous adipose tissue (SSAT), and deep subcutaneous adipose tissue (DSAT) thickness were obtained from US. Sex-specific total fat mass, trunk fat mass, and BF% estimates by US were compared with DXA. Spearman's correlations and Bland-Altman plots were used to assess agreement between the methods.

RESULTS

US SAT correlated strongly with total fat mass for both females (r_s = 0.74) and males (r_s = 0.87) as did trunk fat mass (females, r_s = 0.81; males, r_s = 0.83); as did SSAT and DSAT (females: r_s = 0.65 and r_s = 0.66; males: r_s = 0.63 and r_s = 0.85, respectively, all p-values < 0.0001). Bland-Altman plots demonstrated strong agreement for total and trunk fat mass for both males and females. For BF%, acceptable limits of agreement were observed for males but not for females, substantial proportional bias as indicated by a negative slope was noted for BF% using SAT (r = -0.298, p = 0.0177).

CONCLUSION

The handheld US and technique to analyze abdominal adipose tissue thickness showed strong agreement with DXA results and generated highly comparable estimates for total and trunk fat mass for both sexes.

Thickness of rectus abdominis measured by ultrasound in critically ill patients after abdominal surgery: A retrospective cohort study

BACKGROUND

Early identification of patients at high risk of prolonged mechanical ventilation is important in critical care. Sarcopenia, the loss of muscle mass and function, has been reported to be associated with extended mechanical ventilation and prolonged ICU stay. Although ultrasound is noninvasive and widely used in critical care, there is no standard method of using it to assess sarcopenia.

OBJECTIVES

The study aims to investigate the relationship between outcomes of critically ill patients and the ratio of BMI to the thickness of rectus abdominis measured by a standardised ultrasound examination.

DESIGN

A retrospective cohort study.

SETTING

Surgical ICU of a tertiary referral hospital, from October 2017 to June 2018. The thickness of rectus abdominis (RA) was measured while performing extended focused assessment sonography for trauma. BMI was divided by the thickness of rectus abdominis over the upper abdomen to derive the BMI-RA thickness ratio.

PATIENTS

Sixteen male and 11 female patients admitted to ICU after major abdominal surgery.

MAIN OUTCOME MEASURES

The primary outcome was in-hospital mortality, and the secondary outcomes were durations of mechanical ventilation, ICU stay and hospital stay. The disease severity, serum albumin level and BMI-RA thickness ratio were also analysed.

RESULTS

Ultrasound measurement was easy to perform without adverse effects. The BMI-RA thickness ratio was significantly higher in nonsurvivors and was associated with ICU stay, hospital stay and duration of mechanical ventilation. Multivariable logistic regression showed that the BMI-RA thickness ratio was a predictor of in-hospital mortality.

CONCLUSION

The BMI-RA thickness ratio is related to the outcomes of patients transferred to ICU after major abdominal surgery. Measuring the thickness of rectus abdominis by ultrasound is well tolerated and easy to perform in surgical ICU. Larger prospective studies are required to confirm current findings.