William F. Dunn, MD, acknowledged that there are unanswered questions about the PA catheter, but he believes that restrictions on PA catheter use are unwise at present. He noted that there are many subgroups, such as patients with shock, who appear to benefit from PA catheter use.

These two experts addressed several key questions regarding the use of PA catheters in ARDS patients: Does the PA catheter help guide fluid management or oxygen delivery? Is it lack of staff training that has caused inconclusive--or poor--results to date? Can PA catheter-derived data really influence patient outcome?

One of the trends in treating ARDS is to minimize fluid accumulation in the lungs, and it has been theorized that the PA catheter may help guide fluid management. Indeed, a number of studies suggest that diuresis and fluid restriction improve pulmonary function in ARDS patients, said Dr. Buckley, a senior staff physician in the division of pulmonary and critical care medicine at Henry Ford Hospital in Detroit. For example, in a study by Humphrey et al,[1] all patients were given PA catheters, and diuresis was attempted to reduce wedge pressure. Sixteen of the 40 patients in this study experienced wedge pressure reductions of greater than 25%. Twelve (75%) of those 16 patients survived, compared with only seven (29%) of the other 24 patients.

Although these results may seem to support PA catheter use, they actually raise two questions, Dr. Buckley suggested. First, did "the reduction in wedge pressure cause the improved survival or simply predict those patients who are more likely to survive?" The fact that the patients who experienced reductions in wedge pressure were younger than the other patients supports the latter hypothesis, Dr. Buckley added.

Second, even if lowering the wedge pressure does increase survival, is it necessary to use a PA catheter to measure the pressure reduction? In other words, said Dr. Buckley, "If diuresis is so important, then why not use diuresis without a PA catheter?" He acknowledged that clinical estimates of fluid status and hemodynamics are often inaccurate, and "our accuracy falls even further with the severity of the disease." But, he added, knowing "that our clinical assessments are poor … does not tell us whether the PA catheter is the answer to this problem."

Another purported benefit of PA catheters is that they can be used to guide increases in oxygen delivery, said Dr. Buckley. However, a large study of more than 700 critically ill patients by Gattinoni et al[2] showed that PA catheter--guided therapy designed to improve hemodynamics (ie, achieve normal values for mixed venous oxygen saturation or supranormal levels for cardiac index) did not lower mortality or morbidity. This lack of difference in outcome was also found in a subgroup analysis of patients with respiratory failure. Thus, there is no proven reason to use PA catheters to augment oxygen delivery, Dr. Buckley believes.

Furthermore, he noted that the PA catheter is invasive and expensive, and its use requires a fair amount of time and work. He pointed to a large trial by Connors et al, in which right-heart catheterization was associated with a higher 30-day mortality (odds ratio, 1.24), a higher mean cost ($49,300 vs $35,700 without catheterization), and a longer length of stay in the intensive care unit (ICU; 14.8 days vs 13.0 days without catheterization).[3]

In describing the Connors study, Dr. Buckley said that it was "not a randomized clinical trial, but it's as close as you can get. It remains the most comprehensive large study evaluating the overall benefits and risks of PA catheter use in critically ill patients--including the subgroup with ARDS. So it's very difficult to ignore these results," he concluded.

A more positive view of PA catheter use was offered by Dr. Dunn, a member of the division of pulmonary and critical care medicine at the Mayo Clinic in Rochester, Minn. "Lack of proof does not equal lack of efficacy," he noted.

Dr. Dunn also commented on the Connors study but focused on the fact that the patients who underwent right-heart catheterization may have been sicker than the other patients in the study. "I think that Dr. Buckley and I would certainly agree with the statement made by Dr. Connors in the discussion section of the article, which says, 'as we found in this study, right-heart catheterization is more likely to be used in sicker patients, who are also more likely to die.'"

A possible flaw in the study by Connors et al is the method used to match the patients with PA catheters to controls. Because the study was not prospective, the matching was done retrospectively, using a scoring system that had not been previously validated. Thus, Dr. Dunn suggested that the two groups may not have been comparable.

He also noted that most of the excess risk presented by PA catheter use was found in postoperative patients. "There was not, in fact, an increased risk of death in what we traditionally identify as most of our medical ICU patients: patients with COPD exacerbations, congestive heart failure, cirrhosis, non--small-cell lung cancer, metastatic colon cancer, or nontraumatic coma," he said.

If there is an increased risk associated with PA catheter use, "The question is why?" Dr. Dunn added. "Is it a problem with catheter use per se? Or is it a problem with our system of training?"

A study by Iberti et al[4] supports the lack-of-training hypothesis. A 31-item questionnaire was administered to physicians using PA catheters at 13 institutions; when correct responses were tallied, the physicians had a mean score of only about 67%--about a D+, Dr. Dunn noted. Furthermore, there was an independent relationship between individual mean scores and the physician's level of training, the physician's frequency of catheter use, whether the physician was using the data derived from the catheters, and whether the physician worked in a primary medical school affiliate. "Incriminating evidence," acknowledged Dr. Dunn.

Dr. Dunn also believes that ICU staffing may affect outcome. For example, a study conducted by Reynolds et al[5] showed that once the management of an ICU was taken over by specialists trained in critical care there was a significant improvement in survival rates (from 26% to 43%) among septic shock patients despite an increase in the use of PA catheterization (from 48% to 68%).

Drs. Dunn and Buckley noted that the information from PA catheter-derived data can be used to alter therapy; both commented on a study by Mimoz et al,[6] in which PA catheter-derived data led to therapy changes in 65 (58%) of 112 patients. Overall, the study found no significant improvement in mortality with these changes in therapy.

However, subgroup analysis showed that mortality was markedly lower when the PA catheter was used to alter therapy in patients with shock unresponsive to standard therapy (mortality, 59% in these patients vs 100% in the patients with shock whose therapy was not changed).

Dr. Buckley viewed these findings as showing that PA catheter--prompted changes in therapy usually do not improve outcome. In contrast, Dr. Dunn felt that the improvements in the subgroup with shock were significant.

"Personally," concluded Dr. Dunn, "I believe that we need to reappraise how to utilize the PA catheter, how we train physicians, and how we staff our ICUs." However, he strongly urged physicians not to abandon the use of the PA catheter in ARDS patients.

Dr. Buckley countered that, currently, "the routine use of PA catheters in ARDS is not indicated." He added, "we need to either develop and assess alternative strategies or wait for a randomized clinical trial."

--Kristin Della Volpe

References
1. Humphrey H, Hall J, Sznajder I, et al. Improved survival in ARDS patients associated with a reduction in pulmonary capillary wedge pressure. Chest. 1990;97:1176-1180.
2. Gattinoni L, Brazzi L, Pelosi P, et al. A trial of goal-oriented hemodynamic therapy in critically ill patients. SvO2 Collaborative Group. N Engl J Med. 1995;333:1025-1032.
3. Connors AF Jr, Speroff T, Dawson NV, et al. The effectiveness of right heart catheterization in the initial care of critically ill patients. SUPPORT Investigators. JAMA. 1996;276:889-897.
4. Iberti TJ, Fischer EP, Leibowitz AB, et al. A multicenter study of physicians' knowledge of the pulmonary artery catheter. Pulmonary Artery Catheter Study Group. JAMA. 1990;264:2928-2932.
5. Reynolds HN, Haupt MT, Thill-Baharozian MC, Carlson RW. Impact of critical care physician staffing on patients with septic shock in a university hospital medical intensive care unit. JAMA. 1988;260:3446-3450.
6. Mimoz O, Rauss A, Rekik N, et al. Pulmonary artery catheterization in critically ill patients: a prospective analysis of outcome changes associated with catheter-prompted changes in therapy. Crit Care Med. 1994;22:573-579.

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