title: Skeletal muscle quality as assessed by CT-derived skeletal muscle density is associated with 6-month mortality in mechanically ventilated critically ill patients.
abstract: Muscle quantity at intensive care unit (ICU) admission has been independently associated with mortality. In addition to quantity, muscle quality may be important for survival. Muscle quality is influenced by fatty infiltration or myosteatosis, which can be assessed on computed tomography (CT) scans by analysing skeletal muscle density (SMD) and the amount of intermuscular adipose tissue (IMAT). We investigated whether CT-derived low skeletal muscle quality at ICU admission is independently associated with 6-month mortality and other clinical outcomes.
  
  
  
  This retrospective study included 491 mechanically ventilated critically ill adult patients with a CT scan of the abdomen made 1 day before to 4 days after ICU admission. Cox regression analysis was used to determine the association between SMD or IMAT and 6-month mortality, with adjustments for Acute Physiological, Age, and Chronic Health Evaluation (APACHE) II score, body mass index (BMI), and skeletal muscle area. Logistic and linear regression analyses were used for other clinical outcomes.
  
  
  
  Mean APACHE II score was 24 ± 8 and 6-month mortality was 35.6%. Non-survivors had a lower SMD (25.1 vs. 31.4 Hounsfield Units (HU); p < 0.001), and more IMAT (17.1 vs. 13.3 cm2; p = 0.004). Higher SMD was associated with a lower 6-month mortality (hazard ratio (HR) per 10 HU, 0.640; 95% confidence interval (CI), 0.552-0.742; p < 0.001), and also after correction for APACHE II score, BMI, and skeletal muscle area (HR, 0.774; 95% CI, 0.643-0.931; p = 0.006). Higher IMAT was not significantly associated with higher 6-month mortality after adjustment for confounders. A 10 HU increase in SMD was associated with a 14% shorter hospital length of stay.
  
  
  
  Low skeletal muscle quality at ICU admission, as assessed by CT-derived skeletal muscle density, is independently associated with higher 6-month mortality in mechanically ventilated patients. Thus, muscle quality as well as muscle quantity are prognostic factors in the ICU.
  
  
  
  Retrospectively registered (initial release on 06/23/2016) at ClinicalTrials.gov: NCT02817646 .
authors.affiliation: Department of Intensive Care Medicine, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands. w.looijaard@vumc.nl.|Institute for Cardiovascular Research, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands. w.looijaard@vumc.nl.|VU University Medical Center Amsterdam, Room ZH 7D174, P.O. Box 7057, 1007 MB, Amsterdam, The Netherlands. w.looijaard@vumc.nl.
authors.forename: Wilhelmus G P M
authors.identifier: 0000-0003-0572-6022
authors.initials: WG
authors.lastname: Looijaard
authors.affiliation: Department of Nutrition and Dietetics, Internal Medicine, VU University Medical Center Amsterdam, De Boelelaan 1117, 1081 HV, Amsterdam, The Netherlands.
authors.forename: Ingeborg M
authors.initials: IM
authors.lastname: Dekker
authors.affiliation: Department of Intensive Care Medicine, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.|Institute for Cardiovascular Research, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.
authors.forename: Sandra N
authors.initials: SN
authors.lastname: Stapel
authors.affiliation: Department of Intensive Care Medicine, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.|Institute for Cardiovascular Research, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.
authors.forename: Armand R J
authors.initials: AR
authors.lastname: Girbes
authors.affiliation: Department of Epidemiology and Biostatistics, VU University Medical Center Amsterdam, van der Boechorststraat 7, Amsterdam, The Netherlands.
authors.forename: Jos W R
authors.initials: JW
authors.lastname: Twisk
authors.affiliation: Department of Intensive Care Medicine, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.|Institute for Cardiovascular Research, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.
authors.forename: Heleen M
authors.initials: HM
authors.lastname: Oudemans-van Straaten
authors.affiliation: Department of Intensive Care Medicine, VU University Medical Center Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.|Department of Nutrition and Dietetics, Internal Medicine, VU University Medical Center Amsterdam, De Boelelaan 1117, 1081 HV, Amsterdam, The Netherlands.|Department of Nutrition and Dietetics, Amsterdam University of Applied Sciences, Dr. Meurerlaan 8, Amsterdam, The Netherlands.
authors.forename: Peter J M
authors.initials: PJ
authors.lastname: Weijs
mesh_terms: D018806:APACHE; D034861:Abdominal Wall / Q000503:physiopathology*; D000328:Adult; D000368:Aged; D016638:Critical Illness / Q000453:epidemiology / Q000401:mortality*; D006801:Humans; D007362:Intensive Care Units / Q000458:organization & administration / Q000706:statistics & numerical data; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D016016:Proportional Hazards Models; D012121:Respiration, Artificial / Q000401:mortality* / Q000706:statistics & numerical data; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed / Q000379:methods* / Q000706:statistics & numerical data
keywords: CT; Computed tomography; Intensive care unit; Intermuscular adipose tissue; Mortality; Muscle; Muscle quality; Myosteatosis; Outcome; Skeletal muscle density