Marino The ICU Book 4e, IE

148 Hemodynamic Monitoring

Tissue Oxygenation The hemodynamic patterns just described can identify a hemodynamic problem, but they provide no information about the impact of the prob- lem on tissue oxygenation. The addition of the oxygen uptake (VO 2 ) will correct this shortcoming, and can help identify a state of clinical shock. Clinical shock can be defined as a condition where tissue oxygenation is inadequate for the needs of aerobic metabolism. Since a VO 2 that is below normal can be used as indirect evidence of oxygen-limited aerobic metabolism, a subnormal VO 2 can be used as indirect evidence of clinical shock. The following example shows how the VO 2 can add to the evalu- ation of a patient with cardiac pump failure.

e

Table 8.3

Compensated Heart Failure vs. Cardiogenic Shock Cardiogenic Shock

Heart Failure

High CVP Low CI High SVRI Low VO 2

High CVP Low CI High SVRI Normal VO 2

Without the VO 2 measurement in Table 8.3, it is impossible to differenti- ate compensated heart failure from cardiogenic shock. This illustrates how oxygen transport monitoring can be used to determine the conse- quences of hemodynamic abnormalities on systemic oxygenation. Oxygen transport monitoring is described in more detail in Chapter 10. A FINALWORD Despite the wealth of physiologically relevant information provided by the PA catheter, the catheter has been vilified and almost abandoned in recent years because clinical studies have shown added risk with little or no survival benefit, associated with use of the catheter (2–4). The follow- ing points are made in support of the PA catheter. 1. First and foremost, t he PA catheter is a monitoring device, not a therapy . If a PA catheter is placed to evaluate a problem and it uncovers a dis- order that is untreatable (e.g., cardiogenic shock), the problem is not the catheter, but a lack of effective therapy. Clinical outcomes should be used to evaluate therapies, not measurements. 2. In addition, surveys indicate that physicians often don’t understand the measurements provided by PA catheters (19,20). Any tool can be a weapon in the wrong hands. 3. Finally, the incessant use of mortality rates to evaluate critical care interventions is problematic because the presumption that every inter- vention has to save lives to be of value is flawed. Interventions should (and