An Exciting Development in Continuous Cardiac Output
Acuity Care Technology: Hemodynamic monitoring is obviously an essential tool in the care of critically ill patients, but has something been missing with the technology?
Dr. McGee: From a perspective of the ICU there is always something lacking because for most patients we are doing a kind of very rudimentary monitoring of just vital signs and blood pressure, saturation and the intermittent sampling of blood gas and some other blood tests.
There are various stages of hemodynamic monitoring, but if it was very simple and didn't pose any risks or take any time or cost any money, I think you would like to have complete physiologic monitoring on every patient in the ICU. This would be some assessment of cardiac function, not only the flow and pressure, but also the efficiency of the [heart’s] pump — some combination of flow technology, like continuous cardiac output, with echo would be one of the ideal monitors that we could potentially have. You almost never get both because you could only get the echo intermittently, and you never really have that data continuously. So I think continuous monitoring of the two parameters is something that has been lacking.
In terms of the problems that we are most commonly confronted with — either hypotension or oliguria — I think traditional hemodynamic monitoring really has not been ideally suited to address them. It tells us a lot about the state of blood flow, about oxygen extraction and about various pressures, but it doesn't really give us great answers, at least some of the time, about what we should do when the patient's blood pressure is low or when there is not adequate urine output.
ACT: You’ve incorporated a relatively new hemodynamic monitoring system at your hospital — what are some of the ways that the minimally invasive continuous cardiac output monitoring through FloTrac has impacted patient care in your sphere of experience in the ICU?
DM: The beauty of this system is the simplicity — it has allowed me to expand more complex hemodynamic monitoring in a very simple fashion. That was one of the drawbacks with the older technology using a PA catheter: It took a significant amount of nursing and physician time and effort to place the catheter and then there was some risk to the patient in terms of doing a central line and threading a catheter through the right side of the heart. With FloTrac all we need to do is hook it up to an arterial catheter, which is a very common monitoring device in the ICU. It has really simplified the acquisition of physiologic data that was otherwise more complicated to obtain and posed at least some risk to the patient.
ACT: Has it solved some of the specific problems?
DM: It has, very specifically in the settings that I mentioned of hypotension and oliguria, which are problems that come up on a wide variety of patients in any ICU every day. But the thing I really like about this technology is that it gives us a parameter, specifically the stroke volume variation, which has been shown in multiple data sets to predict fluid responsiveness. It gives me a tool to know ahead of time whether or not patients will respond to fluids and obviously that is very important. It solves a question that existing technology really doesn't.
What’s exciting is the display of stroke volume variation, which, especially under conditions of mechanical ventilation, is where the data is the best — patients who are on positive pressure ventilation. This is a good predictor of fluid responsiveness, and because of the ease of obtaining this data with this monitor, this is something I would like to see a lot of doctors exploring in the OR and definitely in the ICU over the next five years.
ACT: Can you illustrate with any particular cases?
DM: Concerning the question of oliguria, the down side is that if you don't treat it correctly, the patient may develop renal failure, and we know that renal failure in an ICU population confers a very high mortality rate. The same applies to hypotension. If we don't treat that adequately and rapidly patients will develop organ failures, potentially increasing their risk of mortality.
There are a lot of individual cases where I am seeing I can optimize fluid management to avoid (in as much as you can in any patient with volume) either oliguria or hypotension, and it will give me a quick algorithm to know: No.1, if the patient is adequately fluid-resuscitated and No. 2, when that is no longer going to work and that I need to move to some other modality, either a vasopressor or an inotrope, or some other type of therapy to improve either their heart function and, secondarily, their kidney function.
ACT: Where in hemodynamic monitoring technology do you expect (or hope) the next advances and developments to occur?
DM: Those of us who are interested in physiology, we’d like to see the blood flow parameters, cardiac output, and information about oxygen extraction — so some type of continuous mixed venous oxygen sampling to give us that information.
Finally, I think in the instances that we have used echocardiography or transesophageal in echocardiography in conjunction with this technology, we really learn a lot about the patient's physiology.
There is a lot of opportunity to exploit stroke volume variability and then, simultaneously, if I can have a continuous picture of the heart as it is beating inside the chest — or have a continuous echo picture — that would give me at least all the data that I could possibly use to optimize cardiac physiology, and I think if you look in the operating room setting during some complex cardiac cases, for that brief time period, which may be up to several hours, they utilize all the technology simultaneously.
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