Body cell mass evaluation in critically ill patients:
killing two birds with one stone
, Santo Morabito
, Aderville Cabassi
and Giuseppe Regolisti
See related research by Ismael et al., http://ccforum.com/content/18/2/R49
Body cell mass (BCM) is the metabolically active cell
mass involved in O
and energy expenditure. BCM measurement has been
suggested as a tool for the evaluation of nutritional
status. Since BCM is closely related to energy
expenditure, it could also represent a good reference
value for the calculation of nutrient needs. In a recent
issue of Critical Care, Ismael and colleagues used
bioelectrical impedance analysis parameters and
anthropometric variables to evaluate BCM in patients
with acute kidney injury, before and after a
hemodialysis session. The results of this study suggest
that BCM is relatively insensitive to major body fluid
shifts, a well known factor interfering with nutritional
evaluation/monitoring and energy need calculations
in the ICU. Thus, BCM seems to be a more 'stable'
nutritional variable, as it is apparently less influenced
by non-nutritional factors. The results of this paper
emphasize the need to identify biologically sound
parameters for nutritional status evaluation and
energy need calculation in critically ill patients; in this
regard, BCM could fulfill these expectations.
In a recent issue of Critical Care, Ismael and colleagues 
reported the results of a study on 31 hemodynamically
stable patients with acute kidney injury requiring
hemodialysis and able to tolerate ultrafiltration rates of
≥5% body weight per session (mean weight loss of 3.8 kg).
They derived intra- and extracellular water volumes from
low- and high-frequency resistances measured by multi-
frequency bioelectrical impedance analysis (BIA) of body
compartments, before and after hemodialysis. Moreover,
* Correspondence: firstname.lastname@example.org
Department of Clinical and Experimental Medicine, Acute and Chronic Renal
Failure Unit, Parma University, 43126 Parma, Italy
Full list of author information is available at the end of the article
they estimated body cell mass (BCM) from BIA parameters
and anthropometric variables, based on a recently devel-
oped regression equation specific for ICU patients .
The investigation aimed at evaluating the consistency and
clinical relevance of the current model for BCM calcula-
tion in case of massive changes in the external fluid
balance. The results of this promising study suggest that
estimated BCM is relatively insensitive to major body fluid
shifts, a frequent problem among critically ill patients,
and also a well known factor interfering with nutritional
evaluation and monitoring in this clinical setting. Thus,
BCM seems to be a more 'stable' nutritional variable, as it
appears less influenced by non-nutritional factors.
Many factors may significantly interfere with the meas-
urement and interpretation of the classical nutritional
variables in the ICU, especially when rapid changes of
fluid balance and/or renal function derangements are
At the same time, the precise definition of energy
needs, when the gold standard of indirect calorimetry is
not available, still relies on estimations obtained from
predictive formulas or on calculations using a fixed
amount of calories per kilogram of body weight , with
the latter being not always measured, and often heavily
affected by rapid modifications of fluid balance.
Critically ill patients may have wide variations in en-
ergy requirements [4,5], thus being at high risk for both
underfeeding and overfeeding. Therefore, the issue of
administering the right amount of calories at the right
time to these patients has gained major attention [6,7].
Indeed, recent data suggest that individual tailoring of
calorie supplementation in terms of both timing  and
intake [9,10] could impact significantly on the effects of
nutritional support on patients’prognosis.
BCM is the metabolically active component of fat-free
mass, and represents the cell mass actually involved in O
production and energy expenditure
. It is negatively affected in the course of critical illness,
and its measurement has been suggested as a tool for the
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Fiaccadori et al. Critical Care
evaluation of nutritional status in these patients [11,12].
Moreover, since it is closely related to energy expenditure,
BCM could also represent a good reference value for the
calculation of nutrient needs.
BCM can be directly measured by isotope dilution
methods (that is,
K), or estimated by predictive equa-
tions . However, the gold standard methods based on
radioactive tracer techniques are not amenable to rou-
tine use in the ICU. On the other hand, bedside estima-
tion of BCM, essentially using equations based on BIA
of body compartments, could represent a simple, non-
invasive and repeatable tool for nutritional status evalu-
ation in critically ill patients.
The results of the paper by Ismael and associates 
emphasize the need to identify biologically sound pa-
rameters for nutritional status evaluation and energy
need calculation in critically ill patients; in this regard,
BCM could fulfill these expectations.
Encouraging results have been obtained recently in
other clinical settings when interventions were tailored
based on BIA of body composition . A number of
open issues remain, however, and the overall impression
is that more data should be collected before this promising
approach can be applied routinely in ICU patients. Un-
doubtedly, by choosing short hemodialysis sessions, the au-
thors exploited a simple clinical model of rapid fluid
balance changes. However, the need to use high net ultra-
filtration rates inevitably selects a relatively more healthy
population of hemodynamically stable ICU patients. More-
over, a recent study that investigated the intrinsic error of
the BIA methods for estimating body fluid volume/com-
position in chronic dialysis patients demonstrated that
such estimates can be consistent at a population level, but
not always at the individual level due to wide limits of
agreement . Within this conceptual framework, it has
been also correctly observed that the prediction error of
methods based on BIA of body compartments is the sum
of many errors, namely the impedance measurement error,
the regression error, the intrinsic error of the reference
method, the electric volume model error, and the biological
variability among subjects .
In the selected population of ICU patients of their study,
the authors’approach seems to be physiologically sound
and effective. Thus, although their results cannot be im-
mediately translated to the complex and dynamically
changing clinical setting of the ICU, they are surely en-
couraging and should prompt further investigations on
this innovative approach that could possibly kill two
birds with one stone.
BCM: Body cell mass; BIA: Bioelectrical impedance analysis.
The authors declare that they have no competing interests.
Department of Clinical and Experimental Medicine, Acute and Chronic Renal
Failure Unit, Parma University, 43126 Parma, Italy.
Nephrology and Urology, Hemodialysis Unit, 'Sapienza' University, 00161
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Cite this article as: Fiaccadori et al.:Body cell mass evaluation in
critically ill patients: killing two birds with one stone. Critical Care
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01 May 2014