Patient management options are expanding with new technologies in critical care arena

BBI Newsletter, The,  July, 1996  

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Cardiac output monitoring attracts investment

A second major area of application for cardiorespiratory measurement technology in critical care patients is cardiac output monitoring. The thermodilution technique, introduced in 1977, has become the accepted clinical standard, but the original methodology employing saline that must be maintained at a fixed temperature is labor-intensive, costly, and associated with patient risk, and in addition errors of 15% to 20% have been reported even when meticulous care is exercised.

Innovations in that area include the introduction in 1990 of dual thermistor technology, as is available in the Dualtherm catheter manufactured by B. Braun Medical (Bethlehem, Pennsylvania), and continuous cardiac output systems from Baxter/Edwards Critical Care (Irvine, California) and Abbott Critical Care Systems (Mountain View, California). Use of dual thermistors, one placed upstream to measure the initial injectate temperature and a second downstream to measure the diluted injectate, eliminates one source of added labor and error, and simplifies operation. Continuous thermodilution cardiac output measurements employ a catheter with a heating filament that is feedback-controlled to deliver a fixed bolus of heat to the blood, and a distal thermistor to measure the temperature wash-out curve. Continuous cardiac output technology still has limitations, including errors in ventilated patients and patients with fever, and also exhibits a slow response (5 to 15 minutes) to rapid changes in cardiac output.

However, Baxter's introduction of continuous cardiac output technology combined in a single catheter with mixed venous oxygen saturation allowed Baxter to capture an estimated 19 share points from Abbott in the market for specialty catheters. That prompted Abbott's development of the Opti-Q catheter, offering similar capabilities. In addition, Opti-Q offers the advantage of a lack of dependence of oxygen saturation readings on hematocrit by virtue of the three-wavelength measurement technique employed (versus two wavelengths for the Baxter catheter).

In spite of those advances, there now is a clear trend toward reduced utilization of pulmonary artery catheters by critical care physicians. Table 3 shows historic trends in pulmonary artery wedge pressure monitoring procedures in the U.S., based on data from the National Center for Health Statistics indicating a clear decline, although estimation of trends from that data is complicated by changes in data collection and reporting methods. A key factor driving the decline in utilization is the realization that pulmonary artery catheters do not improve patient outcome, and in today's cost-conscious environment, it is increasingly difficult to justify the use of technology that does not provide measurable benefit.

Table 2

COPYRIGHT 1996 A Thomson Healthcare Company
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