ICU Admission Muscle and Fat Mass, Survival, and Disability at Discharge: A Prospective Cohort Study

Abstract

Background: Skeletal muscle dysfunction occurring as a result of ICU admission associates with higher mortality. Although preadmission higher BMI correlates with better outcomes, the impact of baseline muscle and fat mass has not been defined. We therefore investigated the association of skeletal muscle and fat mass at ICU admission with survival and disability at hospital discharge.

Methods: This single-center, prospective, observational cohort study included medical ICU (MICU) patients from an academic institution in the Unites States. A total of 401 patients were evaluated with pectoralis muscle area (PMA) and subcutaneous adipose tissue (SAT) determinations conducted by CT scanning at the time of ICU admission, which were later correlated with clinical outcomes accounting for potential confounders.

Results: Larger admission PMA was associated with better outcomes, including higher 6-month survival (OR, 1.03; 95% CI, 1.01-1.04; P < .001), lower hospital mortality (OR, 0.96; 95% CI, 0.93-0.98; P < .001), and more ICU-free days (slope, 0.044 ± 0.019; P = .021). SAT was not significantly associated with any of the measured outcomes. In multivariable analyses, PMA association persisted with 6 months and hospital survival and ICU-free days, whereas SAT remained unassociated with survival or other outcomes. PMA was not associated with regaining of independence at the time of hospital discharge (OR, 0.99; 95% CI, 0.98-1.01; P = .56).

Conclusions: In this study cohort, ICU admission PMA was associated with survival during and following critical illness; it was unable to predict regaining an independent lifestyle following discharge. ICU admission SAT mass was not associated with survival or other measured outcomes.

Keywords: adipose tissue; critical illness; frailty; muscle wasting; pectoralis muscle area.

Figure 1

Sample CT scans used to determine muscle area in our cohort. A, Relatively nonwasted. B, Relatively wasted. Red indicates right pectoralis major muscle; green indicates left pectoralis major muscle; blue indicates right pectoralis minor muscle; and yellow indicates left pectoralis minor muscle.

Figure 2

Enrollment flowchart.

Figure 3

Kaplan-Meier survival at 6 months: Comparison of survival rate, expressed as percentage of patients alive over time, between patients with PMA below (red) and above (blue) the median value of 43.9 cm². At 6 months, 266 patients were alive, 127 had died, and eight could not be reached to determine status. P < .001, log-rank test. Pectoralis MA values for female patients were multiplied by 1.67 in this analysis. MA = muscle area.

Figure 4

Correlation between PMA and ICU-free days to day 28. Slope, 0.044 ± 0.019 days per cm² PMA; P = .021; r² = 0.013. PMA values for female patients were multiplied by 1.67 in this analysis. PMA = pectoralis muscle area.

Figure 5

Distribution of PMA stratified according to patient disposition at discharge. Comparison among three groups was done by ANOVA with Tukey test for multiplicity. The groups are different (ANOVA, P < .001), with died in hospital vs discharged independent (P < .001), died in hospital vs discharged not independent (P = .006), and discharged independent vs not independent (P = .56). (Definition of discharged independent and not independent are given in the Patients and Methods section.) PMA values for female patients were multiplied by 1.67 in this analysis. For box plots, center line is median, upper and lower lines are 75th and 25th percentiles, and whiskers are the nonoutlier range (< 1.5 interquartile range from box). See Figure 4 legend for expansion of abbreviation.