The debate on the Swan Ganz catheter continues, this time spurred by a well done report documenting declining use of the catheter over the last decade, the results of an analysis of an administrative database (available at http://jama.ama-assn.org/cgi/content/short/298/4/423 ).
The arguments used in this debate continue to befuddle me with their obvious lack of logical consistency with many other things that are going on apparently unnoticed around us, and about which no fuss is being made. I will enumerate some of these here.
1.) An air of derision often accompanies denouncements of the Swan Ganz catheter because it is "invasive". This buzz word, however, carries little consequence in reality. That something is "invasive" does not necessarily mean that it is riskier than other things that are done that are "non-invasive". Administration of Cytoxan or other chemotherapeutic agents is not "invasive" by the common definition of the term, yet is clearly very risky. Other analogies abound. I am not convinced by hyperbolic statements of "invasiveness" that are not supported by actual negative consequences of the device that exceed other risks which we routinely take (and take for granted) in medicine.
2.) And what are the actual negative consequences? In the FACTT trial of ARDSnet, the only adverse consequence was transient arrythmias. I remain unconvinced.
3.) What OTHER "invasive" (their definition, not mine) things do we routinely do that have no proven mortality benefit? How about arterial lines, or many (most?) central lines? Why is not the critical care (especially the academic critical care) community rallying against those, if it is invasive devices of unproven [mortality] benefit that we are concerned with?
4.) Why must this device, unlike almost all other devices and diagnostic modalities, demonstrate a mortality benefit in order to qualify for our acceptance? Must the ECHOcardiogram (within the ICU or without) reduce mortality for its use to be justified? Not invasive, no risks, doesn't count you say. OK, how about CT angiogram? There are increasing data about the carcinogenecity of radiation from CT scans (Lee et al, 2004, Health Policy and Practice, "Diagnostic CT Scans..", available at: http://radiology.rsnajnls.org/cgi/reprint/231/2/393.pdf), and there is not insubstantial renal morbidity and risk of anaphylactoid reactions to the dye. Yet we evaluate the CT angiogram on the basis of its ability to identify pulmonary emboli (sensitivity and specificity and the like), not to reduce mortality (and meanwhile we largely ignore the risks or accept them as the costs of diagnosis). How many patients would be required to conduct such a study of mortality reduction with CT angiogram? Is there a study in existence of a diagnostic modality the use of which improves mortality? Is there precedent for such a thing? Should it surprise us that intervening more proximally (diagnosis rather than treatment) in a clinical pathway makes it harder (or impossible) to demonstrate a benefit further downstream?
5.) Let's extend the analogy. Suppose we were to design a study of routine use of CT angiogram in the ICU for this or that indication, let's say sudden unexplained hypoxemia. Suppose also that this study shows no benefit (mortality or otherwise) of routine use in this patient population. Does this mean that I should stop using CT angiogram on a selective basis, as those who call for a moratorium imply I should do with the Swan?
6.) If the arterial line analogy was not sufficient, because there was not a recent study demonstrating a lack of mortality benefit with this device, we have an alternative candidate: the Canadian Critical Care Trials Group study of ("invasive") BAL for the diagnosis of VAP published in the NEJM in December ( http://content.nejm.org/cgi/content/abstract/355/25/2619 ). No rallying cry, no proposed moratorium followed this extermely well conducted trial. No denouncement of BAL in the editorial (http://content.nejm.org/cgi/content/extract/355/25/2691). Quite the contrary - the exclusion of patients with staph and pseudomonas was construed as all but undermining the validity of the results for application to clinical practice. At my own institution, pre-existing staunch enthusiasm for BAL diagnosis of VAP has not wavered since publication of this trial.
I am no Swan Ganz apologist, and I rarely use the device. But the state of the debate and the arguments used to denounce the Swan do not stand the test of logic or consistency that I expect of the critical care community. And this leads me to believe that these arguments are the spawn of idealogy and sanctimoniousness, rather than logic and balanced consideration.
An afterthought - Perhaps the most obvious moratorium for the academic community to call for is a moratorium on clinical trials of the Swan. They continue to be performed long after it became clear, meta-analytically, that it will be impossible to show a convincing positive result. The prior probability is now prohibitively low for any reasonably-sized trial to move the posterior away from the prior or sway the results of a meta-analysis.
This is discussion forum for physicians, researchers, and other healthcare professionals interested in the epistemology of medical knowledge, the limitations of the evidence, how clinical trials evidence is generated, disseminated, and incorporated into clinical practice, how the evidence should optimally be incorporated into practice, and what the value of the evidence is to science, individual patients, and society.
Wednesday, July 25, 2007
The Swan Ganz graces the pages of JAMA yet again
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I agree completely and would add only the following. As you stated, the PA catheter is a diagnostic test. Further testing/trials of this device if done should focus (as they always should have) on figuring out whether or not the thing is actually a good diagnostic test, i.e. can data be obtained from this device which can reliably diagnose a condition? In all the years that the device has existed, this question has yet to be adequately answered.ReplyDelete