Is the measurement of cardiac output useful in clinical practice?

The derivation of the "cardiac output" in man is fraught with difficulties whatever principle of measurement is used. The theories underlying the principles involved are sound; the problem arises in their application to the measurement in man. Of equal moment are the immense practical difficulties in applying the techniques available. Together these difficulties frequently give rise to unacceptable errors in the derivation of the "cardiac output". There is no "gold standard" of measurement; all methods have inherent difficulties in their application to man. If intense attention is paid to the practice of any one of the techniques available, then it is possible to reduce the variability of the measurement to acceptable proportions, but the conditions necessary to obtain such narrow ranges of variability in the human subject rarely obtain in routine clinical practice. These realizations apply to the techniques available at present, and it is difficult to imagine that there will be further development of the invasive methods available which would negate these. In contrast, it is possible that refinement of some of the non-invasive techniques now being introduced will allow reasonably reliable measurement of the cardiac output with greater facility than is possible at present. Finally, this brings into question the whole objective of the utility of measurement of cardiac output in practice. Frequently it is measured without due deference to its usefulness. Doubtless there are situations in which the measurement of cardiac output may be of scientific, if not of individual clinical benefit, for example the influence of drugs in hypertension and heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)