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Critical Care  2002 

Why measure cardiac output?

DOI: 10.1186/cc1863

Keywords: clinical trial, circulatory shock, hemodynamic monitoring

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Cardiac output is a primary determinant of global oxygen transport from the heart to the body. Also, because the major function of the cardiovascular system is to supply sufficient amounts of oxygen to meet the metabolic demands of the tissues, it appears reasonable to measure cardiac output in the assessment of cardiovascular insufficiency. Regrettably, numerous studies have shown that neither absolute values for cardiac output nor its change in response to therapy reflect the adequacy of local blood flow or outcome from critical illness [1,2]. Clearly, one may have a cardiac output within the normal range (e.g. 2.5 l/min per m2) and still be in circulatory shock if metabolic demand is increased or blood flow distribution is deranged. Treating septic shock patients with the goal of augmenting cardiac output to high levels (i.e. >3.5 l/min per m2) does not improve survival rates [3,4,5] and may actually increase mortality [6]. Thus, why measure cardiac output?Clearly, a very low cardiac output is detrimental. Critically ill patients who are unable to sustain a cardiac index in excess of 2 l/min per m2, despite aggressive therapy, have a very high mortality rate [4]. In many of these patients the cause of the low cardiac output is inadequate cardiac filling, which is responsive to fluid resuscitation. However, in patients with combined cardiac and respiratory disease, it is often difficult to assess the adequacy of resuscitation without measurement of cardiac output. Furthermore, a recent single center study of septic patients treated in an emergency department [7] documented that rapid early resuscitation with a goal of re-establishing adequate oxygen delivery resulted in a markedly reduced mortality and duration of hospital stay. Thus, at least in some patients, measurement of cardiac output is indicated as an aid to prognosis and diagnosis, and to monitor the adequacy of therapy.If it is useful to measure cardiac output, then it is also important that its measurem


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