Dynamic indices of fluid responsiveness and tissue perfusion

A too low circulating volume (hypovolemia), and more specifically a too low
central blood volume may result in inadequate tissue perfusion with as
consequence ischemia and organ failure. In the anaesthesiology and intensive
care medicine, intra-venous volume is often administered aiming to improve
tissue perfusion and oxygenation. On the other hand, too much circulating
volume (hypervolemia) may evoke pulmonary and interstitial oedema, thereby
contributing to further tissue injury with development of organ dysfunction and
eventually death. During the last decade, much research concentrated on the
development of biomarkers which predict a subject*s volume responsiveness. In
mechanically ventilated subjects, arterial pressure variations have shown to be
good indices to predict whether a subject will or will not benefit from a fluid
challenge (intra-venous volume administration). In spontaneously breathing
subjects, a paced breathing frequency of 6 breaths per minute in combination
with a respiratory resistor improve the predictive value of arterial pressure
variations. The majority of studies limited the investigated end-point on a
fluid challenge to cardiac output or stroke volume. However, the ultimate goal
of a fluid challenge is an optimisation of tissue perfusion/oxygenation. The
present study is designed to investigate the effects of volume expansion
(simulated by tilt back) under circumstances of simulated central hypovolemia
at the level of the tissues.

The main objective of this study is to determine the relationship between
arterial pressure variability indices and tissue perfusion/oxygenation between
normo- and hypovolemia in healthy spontaneously breathing subjects .

Observational study.

In the laboratory for Cardiovascular Physiology, hemodynamic parameters (blood
pressure (BP), stroke volume (SV), heart rate (HR) and cardiac output (CO)),
respiratory parameters (tidal volume, airway pressure/flow) and parameters
reflecting tissue perfusion (cerebral blood flow (CBF), cerebral/muscle
oxygenation and arterial oxygen saturation) are evaluated under conditions of
simulated normovolemia (supine resting position) and hypovolemia (simulated by
30 and 70 degrees head-up tilt positions). The parameters will also be
evaluated when the subject is slowly rocking on the tilt table (oscillatory
tilting).

There are no foreseen risks with participating in this study. The burden for
the subject is minimal because all the measurements are non-invasive. The
measurements are done using patches placed on the abdomen and chest, a cuff
around the finger, breathing through a mouthpiece ans sensors which are
attached on the head using a headband and on a forearm muscle. The subject is
asked to breath in a breathing pattern of 6 breathes per minute and to breath
through a resistor. This can be experienced as uncomfortable, as for headband
or mounted fingercuff. However, this does happen for a short time and will
directly disappear at the end of the measurement.