Tissue oxygenation and perfusion and the determination of glucose subcutaneously

Maintaining normoglycemia during intensive care admittance reduces mortality
and morbidity. Continuous subcutaneous glucose monitoring (CGM) is regarded as
a promising tool in the treatment of diabetes mellitus, even more now that the
first real time devices have become available, equipped with alarm function to
indicate hyper- and hypoglycemia. No intervention studies have been performed
using CGM measurements for clinical decision making in severely ill patients.
As CGM depends on the glucose concentration in the interstitial fluid, one
could expect the accuracy of CGM is compromised in severely ill patients,
because tissue oxygenation and perfusion is altered. There have been studies
correlating CGM values with plasma glucose values in the intensive care unit
(ICU). These studies report correlation coefficients of 0.74-0.95. No separate
analyses have been performed to analyze possible causes of low performance of
CGM devices in the ICU. Before CGSM can be implemented in the ICU for intensive
insulin therapy (IIT), the relation between tissue perfusion and oxygenation
and accuracy of CGM has to be investigated.

The main goal of this study is to investigate the performance of two CGM
devices, FreeStyle Navigator® CGM system and Guardian® RT in relation to the
subcutaneous microcirculatory perfusion (as measured by the orthogonal
polarization spectral imaging technique sublingually and near infrared
spectroscopy of the right thenar eminence), severity of disease (defined by
APACHE II and SOFA scores) and tissue oxygenation (as measured by pulse
oximetry).

The two CGM devices will be inserted and calibrated before surgery and will be
taken off 48 hours after surgery or earlier if patients are discharged from the
ICU within 48 hours. After surgery, every six hours OPS measurements will be
performed as well as the scoring of tissue oxygenation, mean arterial pressure,
heart rate, temperature and the use of vasoactive medication. Every hour,
glucose is measured with an arterial blood gas analyzer. Every day, SOFA and
APACHE II scores will be obtained and assessed whether the patient is septic.

The risk for participants is judged to be minor. The insertion and wearing of
the sensors is minimally invasive. Two extra venous blood samples of 10ml will
be obtained besides standard care samples. The patient may benefit from the
sensor measurements because due to the frequent glucose measurements the strict
bloodglucose regulation can be facilitated.