ICU admission body composition: skeletal muscle, bone, and fat effects on mortality and disability at hospital discharge-a prospective, cohort study

Abstract

Background: Reduced body weight at the time of intensive care unit (ICU) admission is associated with worse survival, and a paradoxical benefit of obesity has been suggested in critical illness. However, no research has addressed the survival effects of disaggregated body constituents of dry weight such as skeletal muscle, fat, and bone density.

Methods: Single-center, prospective observational cohort study of medical ICU (MICU) patients from an academic institution in the USA. Five hundred and seven patients requiring CT scanning of chest or abdomen within the first 24 h of ICU admission were evaluated with erector spinae muscle (ESM) and subcutaneous adipose tissue (SAT) areas and with bone density determinations at the time of ICU admission, which were correlated with clinical outcomes accounting for potential confounders.

Results: Larger admission ESM area was associated with decreased odds of 6-month mortality (OR per cm², 0.96; 95% CI, 0.94-0.97; p < 0.001) and disability at discharge (OR per cm², 0.98; 95% CI, 0.96-0.99; p = 0.012). Higher bone density was similarly associated with lower odds of mortality (OR per 100 HU, 0.69; 95% CI, 0.49-0.96; p = 0.027) and disability at discharge (OR per 100 HU, 0.52; 95% CI, 0.37-0.74; p < 0.001). SAT area was not significantly associated with these outcomes' measures. Multivariable modeling indicated that ESM area remained significantly associated with 6-month mortality and survival after adjusting for other covariates including preadmission comorbidities, albumin, functional independence before admission, severity scores, age, and exercise capacity.

Conclusion: In our cohort, ICU admission skeletal muscle mass measured with ESM area and bone density were associated with survival and disability at discharge, although muscle area was the only component that remained significantly associated with survival after multivariable adjustments. SAT had no association with the analyzed outcome measures.

Keywords: Adipose tissue; Bone density; Critical illness; Mortality; Skeletal muscle.

Fig. 1

Sample computed tomography (CT) scans used to determine muscle area in our cohort. a Erector spinae muscle cross-sectional area (ESMCSA) measured at the T12 level: blue indicate right muscle and red, left muscle. b Bone density measured in the region of interest (ROI) indicated with yellow circle, at the T12 level. c Subcutaneous adipose tissue (SAT) measured at the T7-8 level, highlighted in green

Fig. 2

Enrollment flowchart

Fig. 3

a Kaplan-Meier survival at 6 months based on ESCSA. Comparison of survival rate between patients with erector spinae muscle (ESM) cross-sectional area below divided in 4 quartiles. 1st quartile, red; 2nd quartile, black; 3rd quartile, blue; and 4th quartile, green (p < 0.001; log-rank test). At 6 months, 317 patients were alive, 168 had died, and 22 could not be reached to determine status. Female ESM was multiplied by 1.67 in this analysis (see supplement for details). b Distribution of erector spinae muscle CSA (in cm²) stratified by disposition at discharge. Comparison between groups was done with non-parametric Mann-Whitney test (p = 0.003). The groups are different with discharged independent (n = 231) greater than not independent (n = 150). See definition of discharged independent and not independent in the “Materials and methods” section. Female ESM area was multiplied by 1.67 in this analysis. For box plots, center line is median, upper and lower lines are 75th and 25th percentile, and whiskers are the non-outlier range (< 1.5 IQR from box)