StO2 Technology and the InSpectra™ StO2 System:
Interviews with Physicians
StO2 Clinical Usage in Iraq- An Interview with Dr. Greg Beilman (May 2006)
Dr. Greg Beilman, Director of Surgical Critical Care at the University of Minnesota and a trauma surgeon at North Memorial Hospital in Minneapolis, has long been interested in the potential utility of the tissue hemoglobin oxygen saturation (StO2) measurement in trauma care. He first conducted research involving StO2 measurements, derived from a Hutchinson Technology near infrared spectroscopy (NIRS) device, in 1994. In that study, a splenectomized porcine model of hemorrhagic shock, hind limb measurements of StO2, and oxygen delivery measurements taken from pulmonary arterial catheterization showed a linear relationship with a high degree of correlation. Subsequent animal studies further heightened his interest in clinical applications for tissue spectroscopy. In 2003, Dr. Beilman accepted an invitation from Hutchinson Technology to join our Trauma Advisory Board, a group of highly recognized trauma and critical care physicians who help guide our efforts in developing technology for clinical applications.
Dr. Beilman is also a Colonel in the U.S. Army Reserve, and served in Kosovo in 2000. In June, 2005, he was called to duty in Iraq to serve as the sole general surgeon in a combat support hospital near Tikrit. Before he left, he asked Hutchinson Technology to lend him an InSpectra™ Tissue Spectrometer, Model 325 to bring along, and we eagerly complied. Though it has FDA and CE clearance, the 325 was designed primarily for research use and has a limited clinical track record. We anticipated learning much from Dr. Beilman’s experiences and were not disappointed.
During his 93 days close to front-line combat in Iraq, Dr. Beilman treated nearly 300 patients of many nationalities and widely diverse levels of injury or illness. He used the InSpectra Tissue Spectrometer, Model 325 during treatment of about 10 percent of these patients. We asked him about his experiences.
Why did you bring an InSpectra Tissue Spectrometer to Iraq?
With the animal work I have done with the device in a hemorrhagic shock model, I felt pretty strongly that we were going to see the same type of changes in a patient that we saw in these studies. As a trauma surgeon who has had the opportunity to serve overseas, I felt this situation could provide the opportunity to assess quickly if the device is going to provide useful information in this setting.
Did the device fulfill your expectations?
When I evaluate a device, I am exploring whether it gives me information that correlates with a clinical condition of the patient and if I can use that information to make treatment decisions. Also, does it track with the appropriate treatment? I would say in my small experience— and I have to stress small experience —this device tracked the physiologic status of the patient very well during resuscitation. StO2 dropped when they were sick and returned towards normal with interventions.
How many patients did you monitor with the device?
About a dozen. There were about 30 more with a normal StO2. We did not feel we needed to use it to further evaluate these patients.
How did you decide which patients to monitor with the device?
Typically, in that setting patients did not come in one by one but three or four at a time. We had the device positioned in the bay that was going to receive the patients we felt would be the sickest. Once the nurses and I worked together to train everybody on it, we just put it on the patients that showed up in that trauma bay. The patients I was most interested in monitoring were the ones that came in with an obvious physiologic abnormality, so I could correlate the abnormality with the StO2 measurement.
What were your working conditions, and did they affect the performance of the device?
It was a modified field setting. We worked in climate-controlled buildings, air conditioned and some plumbing, that the army had taken over. They tried to seal the buildings from the dusty environment; however, I say tried, because nothing really seals out the dust. The device functioned pretty well for the three months. I simply had to clean the air filters on the back of the monitor every couple of weeks to remove the dust.
Did you measure StO2 on the thenar?
Yes, when it was not covered in blood or the patient had not lost his arms. If we could not measure thenar StO2, we measured on the deltoid or anterior thigh. My impression is that the deltoid or anterior thigh probably runs a little lower in terms of average StO2, and I think this has been shown in internal studies. I was also fortunate that most patients were skinny and physiologically healthy before their injury.
Could you provide us an example of the device in use?
A 19-year-old young man, caught in the middle of an altercation between coalition forces and Iraqi insurgents, was shot in the left hip. He came in severely hypotensive, and with a distended abdomen. Initial evaluation showed his systolic blood pressure was in the 60s, his heart rate was 150. The InSpectra device read 52 [87 ± 6% is considered normal]. Resuscitation with lactated ringers brought his heart rate down and blood pressure up. The StO2 tracked that as well and went up. We took him to the operating room to remove an injured segment of small bowel and debrided some tissue, and closed his abdomen.
In the ICU, his physiological parameters were normal at that point, and his StO2 was in the low 80s. Over the next two hours, he became hypotensive. His StO2 dropped into the low 60s, his heart rate went up to about 120 or 130, and his systolic blood pressure was in the high 80s or low 90s. I aggressively resuscitated him. He was mildly coagulopathic and anemic. So we administered two units of FFP, a unit of packed cells, and two liters of lactated ringers. This produced a good result, both in terms of his blood pressure and heart rate. His StO2 went back up into the low 80s.
Over the next six hours, he developed progressive signs of an abdominal compartment syndrome with mildly lower blood pressure, mildly increased heart rate but increased peak airway pressures and oliguria. With that, his StO2 dropped into the low 60s again. We took him back to the operating room, opened up his abdomen, packed him open and after that physiologic change, his pressures normalized, his physiologic parameters normalized, as did his StO2, which came up into the low 90s.
This is a good example of how the device works. One issue, however, is whether this device can serve as a canary” for somebody in shock that is subtle enough physiologically that we are not seeing it on our clinical exam. I cannot answer that question at this point with my small experience. But it certainly seems to be another parameter that could be used to look at patients who have acute hemorrhagic shock and track response to interventions during resuscitation.
Do you believe the device could prove useful in other clinical settings?
I believe it has potential uses, and I stress potential, because we really do
not have any strong clinical evidence in people yet. One potential use would be as a screening tool to help sort out people who are in shock in the field or in smaller hospitals, or for people who present initially in the emergency room. For example, someone who comes in with an injury or who potentially has a bad infection. If StO2 is normal, you would at least know that the oxygen delivered to the tissues is in a reasonable range which allows you some time to sort out what is going on and take care of some things. If it is abnormal, it may be prudent to consider an aggressive resuscitation protocol.
Do you plan to incorporate tissue spectroscopy into your clinical practice?
I hope to integrate it into our ER practice at North Memorial in the initial evaluation of trauma patients. I would also like to further study how it might be integrated into a hospital practice.
What modifications would you recommend for the InSpectra 325 device to make it more clinically useful?
I suggest an internal battery so we can unplug the device and make it portable without having to go through a new warm-up period. Also, make it small enough to flop on the bottom of the bed as you move the patient around, and finally, develop a patient interface that adheres to the skin more effectively.
Putting StO2 aside for the moment, what were some of the other lessons learned from your experiences in Iraq?
One clear lesson was that armor saves lives. I want to say that over and over again. Body armor and the armoring of trucks saved significant numbers of lives in this conflict compared to what we have seen in other conflicts. Tourniquets for battle field injuries save lives as well. That was something I was told in residency that we should never use. In my humble experience, however, tourniquets kept people alive long enough to make it to definitive care. Properly applied tourniquets with a reasonable transport time, less than a couple of hours, result in soldiers who make it to the hospital alive rather than dead.
Exploring StO2 in Hemorrhagic Shock - An Interview with Dr. Jacques Duranteau (May 2006)
Jacques Duranteau, MD, PhD, is professor in anesthesiology and intensive care at the Bicêtre Hospital at the University of Paris. Since graduating from medical school in 1986, he has published dozens of peer-reviewed articles on assessment of volume status, ischemia reperfusion, oxidative stress in critically ill patients, assessment of tissue oxygenation in critically ill patients, and microcirculation in shock. Given these interests, it makes sense that he would want to explore the utility of the StO2 measurement in trauma care. Last October, he began research using Hutchinson Technology’s InSpectra™ Tissue Spectrometer, Model 325. We asked him to update us on his research.
What is the purpose of your research involving the InSpectra Tissue Spectrometer, Model 325?
We want to test whether the device could be useful for patients in hemorrhagic shock as it is not easy during the initial phase of hemorrhagic shock to monitor these patients. Usually, we have mean arterial pressure (MAP) and heart rate to conduct our resuscitation. I think that StO2, which is an oxygenation parameter, could be useful for adjusting resuscitation, adjusting fluid expansion, hemoglobin
concentration, or in the use of catecholamine. It is very important to have simple monitoring because hemorrhagic shock is a very unstable situation. The monitoring has to be accurate and continuous, since it is important to get a very quick idea of the evolution of hemorrhagic shock. The monitor has to be easy to use and easy to interpret. I think this device could be great for tissue oxygen saturation because it does indeed seem very easy to use and reliable. Again, I want to test this. It also makes sense to me to monitor on the thenar because this area should be one of the first areas in the body to sacrifice circulation during hemorrhagic shock. If you can correct this value, maybe you correct all the other oxygenation values in the body as well.
Are you using other oxygenation parameters now?
Yes, we use venous saturation from a central or femoral catheter. These are continuous readings now, with a monitor, but the problem of course is access. Or you can also test discontinuously with a blood gas analyzer. What is great with StO2 is that you can quickly get a value noninvasively. In our research, we are comparing venous saturation values by femoral catheter with tissue oxygen saturation. We are looking at any possible correlation of venous saturation with the StO2.
Can you describe the trial?
We want to capture patients in hemorrhagic shock. We perform the monitoring as quickly as possible when the patients arrive in the hospital. It is very important to get the StO2 value quickly, during the hemorrhagic shock, when the patient has a very low arterial pressure. This is the time when it would be important to have tissue saturation as an index of oxygenation. The idea is also to see the evolution of this parameter during resuscitation and if there is parallel recovery of mean arterial pressure. It is too early to tell if the correlation is good or not. The research will be concluded in about six months.
How might the device be used in the hospital?
If it proves useful, it could be used in the hospital phase, not only in hemorrhagic shock but also possibly during septic shock as an additional monitor for the physician. I think that during hemorrhagic shock it is a plus because it is very difficult to quickly get sophisticated monitoring. It might also prove useful in the pre-hospital phase.
Having worked in both the U.S.and France, could you describe the differences between their emergency medical systems?
The main difference is that in the U.S. you have only paramedics at the accident scene, while in France each unit has a physician and nurse as well as a driver. This unit makes the triage after the examination of the patient. We call it the S.A.M.U (Services D’aide Medicale Urgente). In France, the dispatching physicians of the S.A.M.U. direct patients to the appropriate facility according to the results of the on-scene assessment. Thus, many patients bypass emergency departments. The S.A.M.U. handles all pre-hospital triage of patients. Anyone can reach it through a dedicated phone number. There are 95 S.A.M.U. regions in France, each with one or two main hospitals able to take in trauma patients. There are five in Paris.
Please contrast the role of the anesthesiologist in France with the trauma surgeon in the U.S.
In France, the anesthesiologists are present in the operating room, as they are in the U.S. They are also in charge of surgical intensive care. Some are also in charge of the S.A.M.U. system. Therefore, they are deeply involved in intensive care as well as pre-hospital care. It is a big difference in comparison to the U.S. In France, there is an orthopedic surgeon, general surgeon, and specialty surgeon, but no trauma surgeon as you have in the U.S. The anesthesiologist assesses the patient, and takes charge of the patient during resuscitation, scanning, and hospitalization— everything up to the operating room, where the surgeon takes charge.
What changes are taking place in the way France conducts emergency medicine?
Over the last few years, we have seen the development of dedicated trauma centers. This is a clear trend.
