I recently referred a patient who has a chronic ulceration for a vascular consult. Non-invasive testing included ankle/brachial index (ABI), toe/brachial index (TBI), pulse volume recordings (PVR), skin perfusion pressure (SPP) and transcutaneous oxygen (TCOM or TcPO2). Macrocirculation in the lower extremity occurs through the posterior tibialis artery, anterior tibial artery and the peroneal arteries, the three main arteries that supply the limb. The ABI, TBI and PVR studies evaluate macrocirculation. The SPP and TcPO2 examine the microcirculation or skin capillaries within the skin layer.

All of these tests analyze for peripheral vascular disease. I wanted to take a closer look at measuring TcPO2 and how it can help determine the healing potential of a wound.

A transcutaneous oxygen measurement assesses the oxygen level of tissue beneath the skin. This an indirect measure of blood flow because the blood supply carries oxygen and the TcPO2 is a useful test for predicting wound healing and whether the patient would benefit from hyperbaric oxygen therapy (HBOT). We also know that hypoxic wounds will benefit from HBOT.

The TcPO2 test is painless and takes approximately 45 minutes with the patient in a supine position. Place electrodes on the affected limb and a control site. Ask the patient to breathe oxygen through a mask to see if there is an increase in the oxygen level around the wound. Electrodes in the sensors heat the area underneath the skin to dilate the capillaries so oxygen can flow freely to the skin.

The first step of the test measures the tissue oxygenation at room temperature. If the normal oxygen tension is greater than 30 mmHg in a patient without diabetes or greater than 40 mmHg in a patient with diabetes, then the wound should heal and the cause is due to some other factor such as poor nutrition, smoking, elevated blood sugar, suboptimal wound care, etc.

If the patient does not have normal oxygen tension, then one would measure the oxygenation of the tissues while the patient breathes 100 percent oxygen. An increase of tissue oxygenation indicates that the tissues are getting enough blood flow so HBOT should enhance wound healing. An inadequate response to oxygen usually indicates the patient has some form of arterial insufficiency and may benefit from a further vascular workup with intervention.

If this second stage of TcPO2 testing is inconclusive, one can have the patient try breathing 100 percent oxygen in an HBOT chamber. If there is an increase in tissue oxygenation, this will indicate that HBOT may be of benefit.

We cannot forget the importance of non-invasive testing, especially TcPO2, in patients who have chronic wounds in order to help evaluate the underlying peripheral vascular disease and the possible use of HBOT.

Suggested Reading
1. Available at http://www.perimed-instruments.com/applications/tests-and-methods/transc… .
2. Ratliff CR. TCOMs as a screening tool for hyperbaric oxygen therapy. Plast Surg Nurs.2000;20(1);15-7, quiz 18-9.

Original Posted on Podiatry Today.