Am. J. Respir. Crit. Care Med., Vol 149, No. 3, 03 1994, 751-758.
Feasibility of continuous oxygen delivery and cardiac output measurement by application of the Fick principle
PJ Feustel, RJ Perkins, JE Oppenlander, HH Stratton and IL Cohen
Department of Surgery, Albany Medical College, NY 12208.
Continuous mixed venous oxygen saturation (SVO2) measurements from
fiberoptic pulmonary artery catheters, arterial oxygen saturation (SaO2)
measurements from pulse oximetry, and minute-by-minute oxygen consumption
(VO2) measurements from indirect calorimetry can be used for
near-continuous estimation of cardiac output (Qt) and oxygen delivery (DO2)
by application of the Fick Principle. Assumptions required for calculation
of blood oxygen contents include constant hemoglobin concentration (Hgb)
and constant or negligible physically dissolved oxygen. First, the
influence of these assumptions on continuous Qt and DO2 determinations was
tested. Unmeasured changes in Hgb resulted in substantial error in
calculated Qt, whereas calculated DO2 was minimally affected. Both Qt and
DO2 were little altered by errors in PaO2 or PVO2. Second, the effects of
SVO2, SaO2, and VO2 measurement errors on Qt and DO2 calculations under
normal and extreme conditions were quantified. Relative errors in SVO2 were
increased by a factor of 4.2 in Qt estimations and by a factor of 3.2 in
DO2 measurements under normal conditions. These factors increased with
increasing SVO2, and thus, Qt and DO2 became increasingly unreliable as
oxygen extraction fell. Third, we compared continuous measurements of Qt
and DO2 with intermittent measurements made by thermodilution cardiac
output and blood sampling, and found correlation coefficients of 0.85 for
Qt and 0.89 for DO2. Fourth, common measurement errors in VO2 and DO2
calculated in this way were found to bias regressions between VO2 and DO2,
and this bias could be minimized only if the DO2 range were high and SVO2
were low.(ABSTRACT TRUNCATED AT 250 WORDS)
