Bioimpedance can make it
Julius Grunow (Berlin, Germany)
BMI does not reflect body composition
Obesity paradox: Decreased mortality in overweight and obese patients contrary to decreased survival in general population (excluding the underweight and morbidly obese) – ? related to greater nutritional reserve
Low skeletal muscle mass is a risk factor for mortality in mechanically ventilated pts – as measured on CT (practical limitations for ICU pts)
Bioimpedance analysis (BIA) – bedside tool, radiation-free, reflects physician estimated hydrations levels quite well in prospective clinician-blinded study
Muscle mass at L3 level on a CT is highly reflective of whole body muscle mass. Assessing muscle mass from equations using BIA values vs. CT – Talluri and Janssen equations overestimate / Kyle equation underestimates
BIA cannot accurately / directly calculate muscle mass, however the values CORRELATE well – the consistency in this ‘relative inaccuracy’ may be useful
Phase angle (PhA) correlates well with muscle density = a good marker for muscle quality
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Bioimpedance should certainly not be used
Sandra Stapel (Amsterdam, The Netherlands)
Body composition analysis can identify pts with nutrition risk, limited physiological reserve and predict adverse outcome (in low muscle mass)
Estimation of different body compartments using Population-specific predictive equations (combination of electrical and anthropomorphic data)
- Not valid in critical illness
- Accuracy depends on two prerequisites
- accurate body weight (rarely available in ICU pts – often guess/estimate)
- normal fluid distribution (almost always abnormal in inflammation and after fluid resuscitation)
Potential applicability of BIA in ICU if
1) use weight / height-independent parameters e.g. PhA
2) measuring early in admission (PhA on Day 1 predictive of 28-d mortality in critical illness and several other pt groups; PhA on Day 5 no longer predictive, likely due to fluid resuscitation)
Low PhA associated with 90-d mortality
Further research should focus on methods to correct BIA equations for fluid imbalance and effects of nutrition / exercise on PhA.
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Phase angle to predict ICU outcome
Mette Berger (Lausanne, Switzerland)
Lean body mass determines outcome; fat – energy reserves, muscle – defence
Measuring LBM:
- DEXA – not practical
- CT – at L3 (well-validated) – not practical, radiation
- MRI – not feasible in ICU
- US thigh – operator variability, training required
- BIA – precise values, portable, quick and easy to perform
Main determinants of PhA
- In health: age, gender, BMI
- In disease states: malnutrition (Pre-albumin, subjective global assessment), inflammation (CRP, IL-6), fluid accumulation
Lower PhA in pts with advanced cancer undergoing palliative follow-up –> worse overall survival
Lower PhA on admission in pts who later died during ICU stay (PhA in combination with APACHE II / SAPS II scores provide multi-variable composite score for 28-d mortality)
PhA improves in pts receiving beta-hydroxy-beta-methylbutyrate (metabolite of leucine) vs placebo
Critical illness: Increased muscle catabolism and lung production of glutamine
- whole body production of essential and branched-chain amino acids almost doubles
- ICU pts low / high SOFA scores – increased glutamine production but decreased plasma [glutamine]
Pts with higher SOFA scores have significantly lower PhA
Currently ICU severity scores not specific for metabolic state
- PhA provides additional info reflecting cell viability and possibly protein metabolism (as seen in glutamine study)
- Pick pts who will benefit from nutritional support
