British Journal of Anaesthesia, Vol 84, Issue 1 28-32, Copyright © 2000 by Oxford University Press
AS Blake, GW Petley and CD Deakin
Extracorporeal circuits such as cardiopulmonary bypass (CPB) and renal
dialysis machines cause active and/or passive loss of body heat. Attempts
to quantify this heat loss are generally based on the Fick principle which
requires knowledge of the specific heat capacity (SHC) of blood. As changes
in packed cell volume are common, we investigated the effect of these
changes on the SHC of blood over a range of packed cell volumes (PCV) from
whole blood at 43.1% (3594 J kg-1 degrees C-1) to pure Hartmann's solution
(4153 J kg-1 degrees C-1). The SHC of other fluids used during CPB was also
measured and found to be 4139 J kg-1 degrees C-1 and 4082 J kg-1 degrees
C-1 for normal saline and Gelofusine, respectively. The maximum variability
in SHC over the range of PCV values encountered during CPB was calculated
to be small (5.5%). We conclude that use of a constant value of SHC for
calculation of thermal energy transfer is currently justified.
ARTICLES
Effects of changes in packed cell volume on the specific heat capacity of blood: implications for studies measuring heat exchange in extracorporeal circuits
Department of Medical Physics and Bioengineering, Southampton General Hospital, UK.
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