Straight Talk Tuesday

I’d like to set the record straight once and for all about transcutaneous oximetry in assessing patients with non-healing wounds. I am not sure why this is so hard. Let’s begin by agreeing that wound healing is a beautifully physiological designed process which proceeds without a hitch in most people. That means wounds don’t NOT heal for no reason. When a patient comes into a wound center, the way we approach them should begin with the following simple question, “Why has this wound failed to heal?” A common reason for healing failure is tissue hypoxia or ischemia (which are not the same thing). I start with transcutaneous oximetry (properly abbreviated TcPO2 but I’ll use TCOM). If the TCOM is low (say, 30 mmHg or less), then the next question is, “Is this value low due to arteriovascular disease or some other process?” So, I will do an oxygen challenge with 100% oxygen at a high rate of flow using a face mask. If the TCOM value increases to >100 mmHg, the baseline periwound hypoxia is NOT due to vascular disease. Most likely they have a diffusion barrier like edema. If the TCOM value stays the same or decreases while breathing oxygen, they are highly likely to end up with an amputation unless they get revascularized. The patient needs anatomical studies to see if they are a candidate for revascularization.

IT DOES NOT MATTER WHETHER THE ULCER IS DUE TO HITTING THEIR LEG ON THE COFFEE TABLE, SURGERY, OR DIABETIC NEUROPATHY. THE PRINCIPLE IS THE SAME. We must start by asking ourselves, “Why hasn’t this wound healed?” After the patient is revascularized, we recheck the TCOM while breathing air at sea level, and if it is now >30 mmHg, they will probably heal without HBOT. If it is still low, they likely need HBOT.

What I see happen instead of the above is that physicians use an increase in TCOM with sea level oxygen breathing (the “oxygen challenge”) as a way to select patients for HBOT. When you use an increase TCOM in response to sea level (normobaric oxygen breathing) as the way to select patients for HBOT all you are doing is picking the patients WITHOUT vascular disease to put in the chamber.

What is the point of that? That is like saying your “no child left behind” program is to take all the kids with high aptitude scores and put them advanced placement classes. Everyone knows that smart kids will do well in advanced classes. The point of a “no child left behind” program is to help the kids in trouble! For our patients the idea is to do LIMB SALVAGE. If you want to do that, then pick the patients with a BAD oxygen challenge and get them revascularized. They are the ones that need help. After revascularization, if their TCOMs on air are still poor, put THOSE patients in the chamber and check their TCOM during HBOT. If it the in-chamber TCOM is >200 mmHg then there is about an 85% chance that they will do well with HBOT. If the in-chamber TCOM is <50 mmHg then the odds of HBOT helping them are VERY low (but not zero).

That’s how you do limb salvage. A limb salvage program is not built in the concept of selecting all the patients WITHOUT VASCULAR DISEASE to provide with HBOT. Failing to understand that the role of HBOT is to correct tissue hypoxia that persists AFTER REVASCULARIATION HAS BEEN ATTEMPTED is one of the reasons that the Margolis and Thom study showed HBOT was “ineffective” in diabetic foot ulcers. We cannot show the value of HBOT if we use it on patients who 1) were going to get well anyway and didn’t need it or 2) were in such dire straits that they could not be helped.

Why is this so hard to grasp?