Title
Single injection thermodilution: A flow-corrected method
Author
Jansen, J.R.C.
Schreuder, J.J.
Settels, J.J.
Kornet, L.
Penn, O.C.K.M.
Mulder, P.G.H.
Versprille, A.
Wesseling, K.H.
TNO Biomedical Instrumentation
Publication year
1996
Abstract
Application of the Stewart-Hamilton equation in the thermodilution technique requires flow to be constant. In patients in whom ventilation of the lungs is controlled, flow modulations may occur leading to large errors in the estimation of mean cardiac output. Methods: To eliminate these errors, a modified equation was developed. The resulting flow-corrected equation needs an additional measure of the relative changes of blood flow during the period of the dilution curve. Relative flow was computed from the pulmonary artery pressure with use of the pulse contour method. Measurements were obtained in 16 patients undergoing elective coronary artery bypass surgery. In 11 patients (group A), pulmonary artery pressure was measured with a catheter tip transducer, in a partially overlapping group of 11 patients (group B), it was measured with a fluid-filled system. For reference cardiac output we used the proven method of four uncorrected thermodilution estimates equally spread over the ventilatory cycle. A total of 208 cardiac output estimates was obtained in group A, and 228 in group B. In group B, 48 estimates could not be corrected because of insufficient pulmonary artery pressure waveform quality from the fluid-filled system. Individual uncorrected Stewart-Hamilton estimates showed a large variability with respect to their mean. In group A, mean cardiac output was 5.01 l/min with a standard deviation of 0.53 l/min, or 10.6%. After flow correction, this scatter decreased to 5.0% (P < 0.0001). With no bias, the corresponding limits of agreement decreased from ± 1.06 to ± 0.5 l/min after flow correction. In group B, the scatter decreased similarly and the limits of agreement also became ± 0.5 l/min after flow correction. It was concluded that a single thermodilution cardiac output estimate using the flow-corrected equation is clinically feasible. This is obtained at the cost of a more complex computation and an extra pressure measurement, which often is already available. With this technique it is possible to reduce the fluid load to the patient considerably.
Subject
Instruments
Blood flow modulation
Pulse contour
Cardiac output
Artificial ventilation
Dilution curve
Cardiac Output
Thermodilution
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http://resolver.tudelft.nl/uuid:63f7dbbc-aa09-42c3-937a-1d33c5271eda
TNO identifier
280535
ISSN
0003-3022
Source
Anesthesiology, 85 (3), 481-490
Document type
article