It’s 2 a.m. and you’re seven hours into a 12-hour overnight shift. Your pager announces that EMS is bringing in a 56-year-old woman from home for shortness of breath. Upon arrival the patient is hypotensive, tachycardic, hypoxic and febrile. Your nurses establish two peripheral IVs and a quick portable CXR confirms your suspicion that she has an extensive left-sided pneumonia. By the time your labs are back you’ve started broad-spectrum antibiotic coverage and the patient has had your sepsis protocol recommended 30 cc/kg of normal saline with minimal improvement in either her blood pressure or heart rate. So now you’re scratching your head. Does she need more volume? Does she need pressers? Does she just need to get the hell out of your ED and to an ICU?
Mounting sepsis literature (outlined very well by the American College of Emergency Physicians at acep.org/sepsis) indicates that appropriate early goal-directed therapy significantly improves morbidity and mortality and that the earlier it is applied the better. If your ICU is like mine you’ll hope there is still a bed available. If there is a bed you can count on at least an hour before the patient is transferred up and settled in, meaning it will be over an hour before the patient gets the same physician attention you’ve been giving her in the ED. So how can we monitor the vital hemodynamics critical to patient resuscitations? In the past, this often meant technically difficult and fairly invasive procedures, such as Swann-Ganz catheters. Thanks to the ever-increasing number of minimally invasive monitoring devices this is no longer the case.
As with many medical innovations, the bleeding edge of minimally invasive monitoring can be an intimidating place. There are many product choices even within minimally invasive cardiac monitoring, and each device is unique, from the formulas used to determine the readouts you see on the display to the method used to capture the data. This month we will look at the Vigileo monitoring system from Edwards Lifesciences.
The core of this system is the Vigileo Monitor, which is simply the hub of the system. As the brains of the system, the monitor accepts input from the various Edwards accessories and performs the mathematical heavy lifting. The monitor itself is about the same size and shape as a typical ED monitor. At this point in time the monitor does not interact with other monitors you might be using and therefore will be a second free-standing patient monitor that displays the output of the various Edwards devices.
The first device we will talk about is the PreSep Central Venous Oximetry Catheter. This is a triple-lumen catheter which acts in all respects like the central lines that we are all used to placing. There is one big difference, however: the PreSep catheter has an optical fiber that runs the length of the catheter. This optical fiber allows for continuous monitoring of Central Venous Oxygen Saturation (ScvO2). ScvO2 acts as a surrogate for Mixed Venous Oxygen Saturation (SvO2) obtained from the pulmonary artery via the much more technically difficult Swan-Ganz catheter. While this point is still under some debate, there is a growing body of literature that measurement of tissue oxygen consumption via ScvO2 helps guide patient resuscitations and therefore improves outcomes. The PreSep Central Venous Oximetry Catheter has some varieties to choose from including a pediatric version and a silver impregnated version for infection resistance. There are also variations in the way the product is packaged ranging from a catheter in a preformed plastic tray to a fully-draped setup with its own sterile field. While this may seem like a minor difference, you’ll quickly miss the pull-out sterile field if you order the kits without them.
Here are some notes regarding utilization of the kit. In order to appropriately measure ScvO2, the catheter tip must be placed above the superior vena cava. This limits it to use to sub-clavian or internal jugular lines only. Also, in order to utilize the ScvO2 monitoring, the kit must first be calibrated. This can be done one of two ways, prior to insertion in the patient or after completion of line placement. There are pros and cons to each. If you calibrate the catheter prior to insertion you must keep control of the dirty end of the catheter hooked to the monitor while placing your sterile line. This can often become obtrusive and awkward during the procedure. The alternative requires a new blood sample to be drawn from the patient in order to measure the Hgb for calibration. Depending on how aggressively you resuscitate your patient and/or how slow your lab is, these results may be invalid by the time you get them. From my experience the points you’ll gain from nurses for using the former method far outweigh the minimal interference you get from having the line attached to the monitor.
The addition of the TruWave Disposable Pressure Transducer to the PreSep Central Venous Oximetry Catheter or any other CVC catheter allows you to monitor Central Venous Pressure (CVP) from the bedside monitor. If the CVP is slaved to the Vigileo monitor via a cable from the bedside monitor, systemic vascular resistance (SVR) can be monitored continuously. As with ScvO2, the jury is debating the utility of CVP in patient resuscitations. While individual readings may not be the holy grail we thought they were a few years ago, most agree that, like blood pressure, frequent serial measurements are a useful tool in medical resuscitations. The TruWave transducer requires no calibration prior to use. You simply place the transducer at the level of the heart in the same way you would for an arterial line – zero to atmospheric air – and capture a measurement. Of note you will have to turn off your fluids going through the catheter prior to taking a measurement, but only if fluids are running through the same distal lumen pressure measurements are measured. You can also add the Venous Arterial blood Management Protection System (VAMP) to the TruWave. The VAMP system allows for needless blood draws from the catheter with a minimum of wasted blood and consistent sampling. As with the PreSep Central Cather the VAMP system also comes in a pediatric version. This setup allows for easy and frequent monitoring of your patient’s CVP as well as labs.
The final addition to the Vigileo monitor is the FloTrac Sensor. This is an instrument that is used as a surrogate for the measurement of Continuous Cardiac Output (CCO), Stroke Volume (SV), Stroke Volume Variation (SVV), and when used in conjunction with CVP Vigileo can display Systemic Vascular Variation (SVR) continuously. The FloTrac sensor hooks up to a standard arterial line with measurements taken by the device while the Vigileo does its behind-the-scenes voodoo to determine all of the above information. The FloTrac sensor is a continuous monitoring device which updates every 20 seconds. SVV, when used within its limitations, is a sensitive indicator of preload responsiveness. SVV is very helpful in managing your patients’ fluid resuscitation and keeping them on the flat part of the Starling curve.
In my institution (Washington University in St. Louis) the Edwards Vigileo is used mainly in the resuscitation and differentiation of potentially septic patients. To that end I personally find the combination of CVP and ScvO2 to be adequate for most situations. When you find that you need more information then these two devices can provide, the TruWave system gives you near ICU-caliber information from just a couple of easily-obtained sites. Edwards Lifescience’s web site, www.edwards.com, provides dozens of resources including educational cartoons and diagrams, case studies, and a thorough PDF on the science behind the measurements. There is even an extensive library of literature both on their products and critical care in general. Keep in mind that there is a learning curve with these tools both for nursing and physicians. Nurses will need in-servicing on setting up and running the monitors while physicians will need to update themselves on the Institute for Healthcare Improvement’s 2008 “Surviving Sepsis” Campaign (http://www.ihi.org). As I’ve already stated, when used in isolation or as single bits of information, some of the data points obtained by the Vigileo system are not the Holy Grail we thought they were a few years ago. However, when you use this data in a dynamic fashion – not only monitoring your patient’s current state but also their response to your treatments – we see the real power behind these minimally-invasive tools.
In the case of your septic patient with pneumonia, placement of a central venous sepsis catheter reveals a CVP of 10, showing that her tank is likely full and more fluid boluses will not help but may push her into pulmonary edema, greatly worsening her prognosis. Along with the CVP you note a ScvO2 of 60, indicating that she is suffering from tissue hypoxia likely due to increased demand. Based on her hemoglobin of 6 you move to PRBC in conjunction with Levophed for increased O2 carrying capacity as well as inotropy. While all of this costs you some extra time in the ED, it is one of the few things we do in the front end that improves patient outcomes in the end. Oh, and you can tell your bean-counters that it saves the hospital money as well. In the end your patient has a short ICU stay with a few extra days on the floor before being discharged home with no adverse outcomes. Thanks to your knowledge and little help from the tech gods, your patient survived her battle with sepsis.