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From the earliest days of critical care medicine, the importance of measuring cardiac output and hemodynamic monitoring were recognized in understanding the physiology of critically ill patients, especially those in shock. However, methods for measuring cardiac output were cumbersome or not widely available. Ashish K. Khanna, MD, FCCP, FCCM, is joined by Margaret M. Parker, MD, MCCM, to discuss the evolution of the pulmonary artery catheter in critically ill patients, as discussed in “The Story of the Pulmonary Artery Catheter: Five Decades in Critical Care Medicine,” published in the February issue of Critical Care Medicine (Parker M et al. Crit Care Med. 2023;51:159-163). Dr. Parker is professor emeritus of pediatrics at Stony Brook University School of Medicine in Stony Brook, New York, USA.
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Category: CCM Podcast
Dr. Khanna: Hello and welcome to the Society of Critical Care Medicine podcast. I’m your host, Ashish Khanna. Today is a very special episode of this podcast, and that’s because our very special guest today was herself at some stage a very active host for the same podcast. So yes, today, I’ll be speaking with Dr. Margaret Parker, MD, MCCM, and we will be talking about the article, “The Story of the Pulmonary Artery Catheter: Five Decades in Critical Care Medicine.” This article was published in the February 2023 issue of Critical Care Medicine. As Dr. Parker will tell us, this is for a special Critical Care Medicine 50th anniversary series. To access the full article, please visit ccmjournal.org. Dr. Parker is professor emeritus of pediatrics at Stony Brook University Renaissance School of Medicine in Stony Brook, New York. Welcome, Dr. Parker. How does it feel to be a guest on this podcast?
Dr. Parker: Well, it’s quite different from being the interviewer, but I appreciate the opportunity and thank you for the introduction.
Dr. Khanna: Before we start, do you have any disclosures to report to our audience?
Dr. Parker: No, I have nothing to disclose.
Dr. Khanna: All right. Let’s get right into it because this is a really interesting, well-thought-out piece, a really illustrious group of coauthors who I might mention, Michael Pinsky, Jukka Takala, and Jean-Louis Vincent; all of them come together with Dr. Parker herself and talk about the evolution of the pulmonary artery catheter in Critical Care Medicine. I’m going to ask you, Dr. Parker, how did you come to write this article? Where did all of this start?
Dr. Parker: Well, Tim Buchman, the editor-in-chief of Critical Care Medicine, charged the senior editors to come up with a series of papers to celebrate the 50th anniversary of the journal. One of the topics that we came up with was looking at how the use of the pulmonary artery catheter has changed as reflected by papers in the journal. Obviously, there are many, many papers in many, many journals about the pulmonary artery catheter, but we were specifically looking at what was published in Critical Care Medicine over the past five decades.
Dr. Khanna: There was a lot of work being done in the background as you’re telling us this story, so please go on.
Dr. Parker: In the inaugural issue of Critical Care Medicine, Peter Safar, who was president of SCCM at the time, wrote an editorial in which he described the purposes of the new journal. He described nine purposes, five of which are relevant to this discussion: to provide a vehicle for new information; to review and synthesize information; to provide peer review for original publications; to publish recommendations, guidelines, and standards; to report evaluations on new equipment and techniques; and most importantly, this is a sixth, to provide a forum for open discussion of controversial topics. As you well know, the pulmonary artery catheter has been highly controversial over the years. This paper, as I said, is not intended to discuss all of the extensive history on the use of the pulmonary artery catheter, but rather to focus on what is reflected in Critical Care Medicine in terms of particularly these five points.
Dr. Khanna: Excellent. You’ve already touched on this a little bit, but it looks like you and your coauthors did a lot of preplanning with this writeup. Can you give us more specifics around that?
Dr. Parker: Yes. We searched Critical Care Medicine for articles related to the pulmonary artery catheter. There are over 400 articles in Critical Care Medicine focusing on the use of the pulmonary artery catheter. If you look at articles that include data on using the pulmonary artery catheter, there are over 2000. We sorted through those 400 articles to try to weave the story of what has happened with the pulmonary artery catheter over the five decades of the journal.
Dr. Khanna: I love the story of the pulmonary artery catheter. Tell us more, and specifically, how have you seen it grow through your long and illustrious career in critical care medicine?
Dr. Parker: Sure. In the very early days of critical care, it was recognized that it was important to understand physiology and shock, but it was very difficult to measure hemodynamics. The development of the pulmonary artery catheter allowed intensivists to routinely measure hemodynamic parameters. In the 1970s and early 1980s, most critically ill patients had pulmonary artery catheters placed. It was almost part of the ICU admitting physical to get a pulmonary artery catheter. It taught us a lot about physiology in patients who are critically ill and with shock. In the early years, it was routinely used, and our knowledge, our understanding of physiology greatly increased. As we understood physiology, we also started to look at the responses to our therapies and trying to modify that physiology.
Shoemaker did some very seminal work in using the pulmonary artery catheter and hemodynamics to develop therapeutic strategies for critically ill patients. One of his seminal papers was one in which he described goal-directed hemodynamic treatment in surgical patients; he managed patients either with specific hemodynamic goals for mixed venous oxygen saturation and cardiac output or according to routine surgical management. He reported that the patients who were treated with goal-directed therapy had improved outcomes.
Over the years, there’s been a lot of interest in looking at therapeutic responses. As it has evolved, it’s been a highly controversial matter. It was also recognized that clinicians were not particularly good at predicting hemodynamic parameters. As we got better at using the pulmonary artery catheter and it was used more widely, there were surveys done that asked clinicians before they put a PAC in, What do you think the patient’s cardiac output is going to be? What do you think their hemodynamic status is going to be? Clinicians weren’t particularly good at predicting it. Furthermore, once the PAC was placed, therapeutic changes were frequently made in response to what we had learned about the patient’s hemodynamic status.
Dr. Khanna: That’s a fascinating story. I’d like to know more, Dr. Parker, about how and why the use of the pulmonary artery catheter started changing. Was there a part of the story where you really felt that, here is the change period with the Swan-Ganz catheter?
Dr. Parker: As I said, over the initial 15 or so years of Critical Care Medicine and the rapidly growing critical care field, the pulmonary artery catheter was used in almost everybody. But there were those who raised the question, Are we really improving outcomes or are we potentially harming patients? Over the next decade and a half, from the mid-’80s to the late ‘90s perhaps, there were many papers discussing the potential value versus the potential harm associated with the use of the pulmonary artery catheter. There were studies on either side, some of which demonstrated improvement and some of which didn’t. Further studies using goal-directed therapy, following up on Shoemaker’s study, sometimes demonstrated that trying to reach supernormal hemodynamic goals was actually harmful to patients. And there were many studies that tried to establish whether or not the pulmonary artery catheter was of benefit.
There were a number of studies in Critical Care Medicine, one by Mimoz et al, that reported that patients in shock in whom a change in therapy was instituted based on the pulmonary artery catheter had an improved prognosis. If you put in a pulmonary artery catheter and you modified your treatment based on your findings, those patients tended to do better. Other studies reported there was no difference in mortality with the use of the pulmonary artery catheter. Even more recently, Ivanov reported a reduction in morbidity with pulmonary artery catheter-guided treatment in a National Trauma Data Bank study looking at the use of the PAC in severely injured patients. That study also reported a reduction in mortality.
So there are studies that show benefit, there are studies that show lack of benefit, and we don’t really know who are the best patients in whom the PAC should be used. So, either the information we get with the PAC does not result in significant changes in management and, as the Mimoz study showed, those patients are not likely to benefit, or perhaps the changes in management based on the findings from the pulmonary artery catheter do not improve outcomes. Remember, the PAC is a monitoring tool, it’s not a therapeutic tool by itself. It gives us information, we act on that information. First of all, the measurements have to be correct. Secondly, we have to make good decisions based on the information that we get.
One of the issues that came up as the use of the pulmonary artery catheter changed was, it was recognized that clinicians—physicians, and nurses—didn’t always have adequate knowledge about how to make the measurements, what the measurements meant, and so forth. If you’re not getting accurate information from a pulmonary artery catheter, one would certainly not expect any benefit. In response to some of these studies that looked at suboptimal clinician knowledge on the part of both physicians and nurses, SCCM developed an online education program. But unfortunately, it was not widely implemented, so that has not continued.
Dr. Khanna: Wow. This gets more and more fascinating as I learn more about this. And very rightly said, there’s a tendency to believe that you put the catheter in and it’s going to magically fix the patient. But as you rightly say, it’s not a therapeutic tool, it’s just a monitoring device. Dr. Parker, there was a consensus conference of SCCM that talked about the pulmonary artery catheter. Can you tell us more about this meeting and some of the things they talked about and how that helped shape the history of the catheter?
Dr. Parker: Yes. In 1997, recognizing the controversy that had developed around the use of the PAC, SCCM sponsored a multidisciplinary consensus conference, and the literature was reviewed in depth. To make a long story short, there was very little objective information in the literature. There were no RCTs, for example. Most of the recommendations ended up being based on expert opinion because there was so little reliable data available. Interestingly, this consensus conference statement was highly criticized by some because they didn’t use a formal evidence-based medicine process, and expert opinion is potentially subject to bias. Rob Taylor, who led the consensus conference, noted that it was a rigorous process at the time used to grade the evidence, although it wasn’t the current way that we grade evidence now, but it was rigorously looked at.
Most of the recommendations for when to use it, as I said, did end up being expert opinion on whom to use the catheter. There was agreement that education of clinicians on how to: A) place the catheter, B) obtain accurate information, and C) use the information was important, and there was certainly broad agreement that additional study was necessary, although it isn’t clear that a randomized controlled trial is the best mechanism to increase understanding about when we should be using the pulmonary artery catheter.
Dr. Khanna: Where do you think research is necessary in this field? What are the ideal sorts of studies we should design?
Dr. Parker: I think it’s a very difficult area to study. I think there needs to be careful selection of a homogeneous patient population. Some of the pulmonary artery catheter studies have been all comers or different kinds of patients, so patient selection to get a single patient population is important, and the use of the pulmonary artery catheter has to be carefully supervised or evaluated to make sure the information is accurate. I think having clear therapeutic protocols has happened in a number of studies in more recent years, is a very helpful way to get information about whether or not the pulmonary artery catheter is leading us to improving outcomes. Although it still is not necessarily clear whether it’s the use of the catheter that doesn’t improve outcomes in some of these studies or whether we just have the wrong therapeutic protocol. So I think clear definitions of who we’re studying and what we’re looking at as we do so is important.
Dr. Khanna: Dr. Parker, as we look at these five decades of the pulmonary artery catheter, it looks like this last decade or so, especially the last few years, we’ve seen a little bit of a decline in the use of the PAC. Why do you think that’s happening?
Dr. Parker: There’s unquestionably been a decline in the use of the PAC. I have seen it within my career. I started in critical care in the early ‘80s when we put PACs in everybody. It has gradually declined to the point where the PAC is really used for some more specific purposes now rather than routinely. I think the lack of demonstrated benefit was one factor that led people to use it less often. The complications are really not related to the placement of the catheter. That’s the complications related to placement of central line for the most part, but defining the therapeutic protocols and goal-directed therapy has not been as clearly beneficial as we thought it was going to be. In addition, over the past few decades, there have been more noninvasive techniques developed, particularly echocardiography, but other alternative strategies for measuring cardiac output, systemic vascular resistance, and so forth, making an invasive strategy with the pulmonary artery catheter less essential.
The PAC is more commonly used in surgical units, it’s placed in the OR and the patients go to the surgical postop areas with the catheter in place. It’s useful in cardiogenic shock, cardiac surgery, and for pulmonary hypertension. There are likely other patients who potentially might benefit, but many times we can get the information we need using noninvasive techniques. And we still are left with the issue of what do we do with the information we get, how do our therapeutic protocols guide our therapy, which really is the most important point of all of our evaluations of hemodynamics.
Dr. Khanna: Right. The noninvasive technology and the evolution of the PAC and looking to the future. There are a few things that have happened. The PAC itself, there’s a lot of talk around making the PAC do more and get us more information, sort of the smarter version of the PAC. Then there’s also this concurrent development of minimally invasive or noninvasive technology that can at least get a cardiac output or a systemic vascular resistance. How do you see all of this shaping up in the next 10 to to 20 years? What does the future hold for us?
Dr. Parker: I think as our technology gets better and better, our ability to evaluate hemodynamic status noninvasively is going to increase. I don’t think the use of the pulmonary artery catheter is going to increase. If anything, it’s going to further decrease. I didn’t mention before, but one of the concerns as the use of a tool like the PAC decreases is that people have less experience with it and they’re not very good with it. The less experienced you are with something, the greater the risk of complications for the patient. So the noninvasive techniques for evaluating hemodynamics are increasingly important, as they should be, and I think that we will likely see some additional new techniques over the next decade or two, and I suspect that we will continue to use the pulmonary artery catheter in limited and less frequent circumstances.
Dr. Khanna: Wow. This is just looking at a crystal ball. I can clearly look at the ICU of the future and I hope that things get more portable, things get to a point where we can do a lot of the things that the PAC did for us with more miniature versions and noninvasive versions. I’ll hopefully be looking at this evolve in front of me as I practice clinically. Dr. Parker, thank you for your time today. I’m going to wind up this podcast by asking you to summarize the story of the PAC for our audience.
Dr. Parker: Okay. Well, it was an interesting story to put together as my coauthors and I worked on this, and I would like to thank them. You mentioned them at the beginning, so thank you for that. This story is really four parts. The initial story was the description of physiology and learning to use the tool to understand what was going on with the patient and guide our therapy. The second part of the story is learning the limitations of pulmonary artery catheter use, including appropriate knowledge and expertise in obtaining information, as well as learning which patients might benefit from management of the use of the pulmonary artery catheter. The third part is the story of the decline in the use of the pulmonary artery catheter, partly due to failure to interpret correctly and partly due to the development of noninvasive techniques and, as I mentioned, that’s likely to continue.
The fourth part is the development of the understanding that a large, randomized controlled trial might not be the right way to evaluate monitoring technology. It’s great for therapeutic interventions but, for a monitoring tool, the RCT is probably not the way to go. Looking at the use of the PAC in different populations and evaluating the outcome of the patients in that setting, but not randomized per se, is likely to give us better information. How we use it and how we look at the knowledge that we gain and how we gain new knowledge about the PAC are continuing to change.
I think, in summary, the story of the pulmonary artery catheter shows that the journal did meet the goals that Peter Safar laid out in that initial issue and demonstrates many of the purposes of the journal being fulfilled. I think he would be proud of the contributions to the journal.
Dr. Ashish Khanna: Thank you once more, Dr. Parker. It’s been wonderful having this conversation with you, and what a wonderful way to end this podcast by saluting Dr. Safar and his vision for the journal and his vision for critical care medicine. Thank you so much.
Dr. Parker: Thank you. It’s been a pleasure.
Dr. Khanna: This concludes another edition of the Society of Critical Care Medicine podcast for the Society of Critical Care Medicine podcast. I’m your host, Ashish Khanna.
Ashish K. Khanna, MD, FCCP, FCCM, is a staff intensivist and anesthesiologist, associate professor of anesthesiology and section head for research in the Department of Anesthesiology, Section on Critical Care Medicine, at Wake Forest University School of Medicine in Winston-Salem, North Carolina, USA.
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