Identifying risks before surgery – with simple means

Risks during surgery, especially cardiological risks, are still very high in the Western world. However, conventional methods for measuring such risks before surgery are costly or even not always meaningful. And increasing economization in hospitals also makes it more difficult for staff to find time for a comprehensive pre-op analysis. 

Professor Eugenijus Kaniusas has long conducted research in the field of apnea at the Vienna University of Technology in cooperation with the Medical University of Vienna. In this MEDICA-tradefair.com interview, he explains how this research led him to a way to measure OR risks by simple means so that they can be lowered, what it takes to make these measurements, and how the newly developed device will ultimately work.

Professor Kaniusas, what applications is the device you are currently developing made for?

Eugenijus Kaniusas: It is designed to measure preoperative risk, that is, anesthesia fitness. We use it to determine how fit a patient is before the upcoming surgery. This works by means of a device that records physical regulatory fitness, i.e. how the body reacts to external influences and compensates for them. During surgery, nothing else happens but a big imbalance: the body has a lot of stress - we try to map this before the surgery. In doing so, we use stopped breathing as a destabilizing stimulus. How well the body handles this mild stress says a lot about the regulatory fitness in the body.

This then in turn tells the anesthesiologist how to prepare for surgery and what to pay special attention to. Ultimately, therefore, the surgeon or the anesthesiologist have indications of the dynamic functional fitness of the patient - instead of the classic static anatomical fitness.

How can we imagine the structure of the device?

Kaniusas: The device consists of measurement units that are classic and can already be found in a typical operating room. These are the classic pulse wave analysis, oximetry, the electrocardiogram (ECG) and blood pressure measurement. Some equipment is put on the patient - this is done in a few minutes before the operation. Then the patient willingly holds their breath for as long as possible, usually this is up to a minute. Within the next one or two minutes, the result is available.

What parameters does the device measure exactly?

Kaniusas: Essentially, five physical parameters are recorded. One of them, for example, is how long the patient has held their breath. If someone can hold their breath for more than 60 seconds, we assume that regulatory fitness is present - because the body can apparently cope well with apneas, i.e., internal imbalance. However, in most patients, this tends not to be the case. To measure this more accurately, we look at peripheral water constriction, the extent to which the vessels in the periphery were constricted during the apnea. If this constriction is strong enough, it means that the so-called diving reflex or regulatory fitness to compensate for the lack of oxygen to the central organs is present.

Furthermore, we measure the arterial oxygen saturation: If during apnea the oxygen level does not drop too much, fitness is also present. From the oxygen saturation we notice if the body can handle the situation.

Then there is the heart rate variation: when you hold your breath, bradycardia usually occurs, that is, the heart rate drops to reduce oxygen consumption in the heart; if this drop is prominent enough, that is another point for fitness.

Finally, we measure the change in blood pressure. From these four parameters plus the stopped air, we then calculate a kind of weighted index. This not only switches a traffic light indicator (green-yellow-red), but also gives a numerical value from zero to one hundred – according to which the anesthesiologist can determine whether the patient is at risk.

What risks are minimized by these findings?

Kaniusas: It's primarily about cardiovascular and pulmonary risks, because regulatory fitness relates to exactly that. If a patient loses blood during surgery, for example, the cardiovascular system naturally has to compensate for that loss by readjusting. We capture this ability to compensate before surgery by means of this mild stress of arrested breathing.

I like to compare this with a nuclear power plant: To test a nuclear power plant, you don't let it explode or stop, but you destabilize it very mildly. And then you see how well the power plant returns to normal. We do something similar here with humans by briefly throwing them off balance.

How accurate is the measurement?

Kaniusas: We have made some measurements on patients; the results are promising. At this point, however, I cannot give a value because we are planning a clinical study with the Medical University of Vienna that will primarily answer this question. In the process, we will probably compare ourselves with the ASA index - that's the American Society of Anesthesiology's index, which goes from one to four: one stands for healthy patients, two and three for those with mild and severe illnesses, and four for patients in a life-threatening condition. 

Why was it necessary to develop such a device?

Kaniusas: I was scientifically active in the field of involuntary sleep apnea for ten years, and then in the research areas that dealt with voluntary diving apnea. A subsequent collaboration with anesthesiologists then made me aware of the needs for increased preoperative safety. The numbers of cardiac and non-cardiac complications in surgery are massive. So, based on my previous research in apnea, it was obvious that regulatory mechanisms should not only be observed, but also used in terms of clinical assessment of preoperative fitness.