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What you need to know about
T-Stat® Tumor Monitoring

What is T-Stat?

T-Stat is an FDA approved Tissue Oximeter that is sensitive to angiogenesis and local tissue ischemia, without invasive sampling.

T-Stat measures the amount of available oxygen in the blood AFTER a tissue has extracted as much as it can absorb. It is a noninvasive measure of perfusion that does not require invasive catheters or blood sampling.

Because T-Stat measures blood in the tissues, it is different than a Pulse Oximeter, which measures blood in the arteries, as shown here (Figure 1):

Figure 1. Tissue Oximeters Detect and Monitor Low or Unstable Perfusion

What is the benefit of T-Stat?

In animals, T-Stat can be used as a monitor of anesthesia and sufficiency of oxygenation during procedures.

In tumor research models, T-Stat reports real-time capillary-venous oxygenation of tumors, using a noninvasive measure, as shown below:

This value is abnormal for many tumors, as shown below:

 The tissue saturation of hypoxic tumors responds in seconds to reductions in blood flow ischemia (Friedland, Maxim, et al. Stanford, 2004), as shown below:

Levels of pigmented compounds such as chemotherapy drugs can also be measured in real time, as shown:

What should I normally see?

For healthy patients, T-Stat normally reads 63-75% (neonates read slightly lower) (figure 2, at right).

T-Stat normals are very DIFFERENT than pulse oximeter normals. This is because the tissues of healthy patients normally remove enough oxygen from arterial blood to drop T-Stat levels to 25% to 35% below the pulse oximeter.

What is abnormal, and what do these readings mean?

There are 2 important ways to think about abnormal T-Stat readings at the bedside.

First, consider the T-Stat reading . T-Stat readings below 55% are rarely normal, and indicate an increased risk of inadequate oxygen delivery (figure 3, at right)

T-Stat values below 55% indicate ongoing tissue hypoxia.

If left untreated, T-Stat values below 30% may rapidly lead to tissue death.

Second, if a Pulse Oximeter measurement is available, consider the gap between T-Stat and the Pulse Oximeter . The gap between tissue and pulse oximeter readings grows with impaired oxygen delivery.

A difference of 38% or more between T-Stat and Pulse Oximeter suggests an impaired delivery of oxygen to tissue.

Low T-Stat readings and widened Pulse-Tissue gaps may be caused by:

_•    Decreased systemic blood flow (hypovolemia, shock, heart dysfunction)
_•    Vascular lesions and inadequate revascularization
_•    Anemia
_•    Increased metabolism (fever, stress, sepsis)
_•    Changes in drips, medications, or ventilator settings that worsen perfusion

How long does it take to place a T-Stat sensor?

A T-Stat endoscopic measurement is made in seconds. Placing the T-Stat sensor during endoscopy or surgery may require 1-3 minutes. Follow placement instructions, available online or in T-Stat packaging.

What care does a T-Stat sensor require?

If a T-Stat sensor is reading well, the monitor will display a green dot and "Monitoring" at the bottom of the screen. If T-Stat is NOT getting a good signal, the monitor will show a yellow or red dot with a warning message. Correcting the displayed problem often restores readings.

The illuminated sensor tip should never press against tissue. Pressure on the tissue by the sensor tip may disrupt local tissue blood flow and cause the saturation to fall.

T-Stat is sensitive to free blood under the probe, which oxygenates in room air and elevates the T-Stat reading. Probe removal and cleaning with an alcohol swab may be required.

What if I have more questions?

Read the T-Stat brochure or instructions, available online at www.spectros.com. If you have additional questions, you may call us at 1-877-TSTAT-303, or email your question to info@spectros.com.

(Tumor About rev 2007.11.22)