To the Editor.
—Right heart catheters are used to measure cardiac output, which is a global (as opposed to individual tissue) measure of whole-body delivery and to estimate left ventricular filling pressure. It is difficult to escape the conclusion that RHCs are often essential for diagnosing the cause of unexpected hypotension (oligemic, cardiogenic, distributive, obstructive).1 However, when it comes to decisions regarding long-term therapy, it is equally difficult to escape the conclusion that there is currently no consensus regarding "critical" or "optimal" RHC values.2 In fact, the concept of a "critical" whole-body delivery value may be flawed for the simple reason that cardiac output is too crude a measure of flow to an individual tissue. For example, flow distal to a critical arterial stenosis cannot be improved by increasing cardiac output, unless this increase is accompanied by an increase in blood pressure. Likewise, flow to ischemic viscera during sepsis may not
Schlichtig R. Effectiveness of Right Heart Catheterization: Time for a Randomized Trial. JAMA. 1997;277(2):112. doi:10.1001/jama.1997.03540260026024