Transcutaneous Oximetry That the Surgeon Wants to Use to Cancel an Amputation

The study is not interpretable as performed. Four problems, in order of importance:

1. Electrode siting. The electrode is on the sloughy ulcer bed. Slough is avascular and the reading reflects dead tissue, not the perfusion of the skin that must heal. The electrode belongs on intact periulcer skin 1–2 cm from the margin, or on a reference site such as the dorsum of the foot or first web space.
2. Stabilisation time. Five minutes at 44 °C is far too short; the electrode needs 10–15 minutes (often 20) to reach a plateau after heating, and the value must be stable over consecutive readings before it is recorded.
3. Smoking. Two cigarettes 25 minutes earlier produces cutaneous vasoconstriction and lowers both baseline and challenge values. He should abstain for at least 2 hours, ideally longer, and the time of the last cigarette must be documented.
4. Conditions not recorded. Temperature, blood pressure, oedema, whether he was on supplemental oxygen, and calibration status all affect the result and must be documented.

Which numbers can be used: none of them for a candidacy decision. The 205 mmHg in-chamber figure is falsely reassuring because it was measured over non-viable tissue, and the baseline values are uninterpretable given the smoking and the short stabilisation. The correct action is to repeat the study properly, not to base a surgical decision on this tracing. The ABPI of 0.68 and the absent pulses still require a vascular opinion regardless of oximetry.

Interpretation

• A periulcer baseline in the low 20s indicates severe regional hypoperfusion and predicts failure of healing without intervention. Values below about 30–40 mmHg are generally regarded as inadequate for healing.
• An in-chamber value of 190 mmHg shows that the microcirculation can respond to a hyperbaric oxygen challenge. Values above roughly 200 mmHg predict a good healing response; below about 100 mmHg predict failure; 100–200 is intermediate. This patient sits at the top of the intermediate band, which supports a trial of therapy rather than a guarantee.
• The in-chamber value is a provocation test: it answers "can this tissue be oxygenated if we give him oxygen under pressure?", not "will this particular wound heal".

Recommendations

• Hyperbaric oxygen is an adjunct, not an alternative to revascularisation. An ABPI of 0.68 with a tissue defect warrants angiography and assessment for distal bypass or angioplasty; "nothing to revascularise" should be confirmed by imaging, not by ABPI alone.
• If revascularisation is genuinely not possible, proceed with hyperbaric oxygen at 2.4 ATA, 90 minutes, once daily, 30 treatments initially, alongside debridement, offloading, infection control and glycaemic management. Reassess the wound at 20–30 treatments and stop if there is no objective improvement.
• If amputation remains necessary, schedule it within a few hours after a treatment so that the surgical site benefits from the session. Tell the anaesthetist and the ward about the chamber schedule, and avoid a long gap between the last treatment and surgery.
• Document that oximetry predicts, but does not determine, outcome; the decision belongs to the treating team.

Interpretation: an in-chamber value below about 100 mmHg indicates that even at 2.4 ATA the periulcer tissue cannot be oxygenated adequately. Hyperbaric oxygen is very unlikely to heal this wound, and a course of 30–40 treatments would expose him to chamber time, travel and cost for little chance of benefit.

Advice

• Do not recommend hyperbaric oxygen as a wound-healing adjunct on this result.
• Redirect the effort to what can still change the outcome: formal angiography and a distal bypass or endovascular opinion, aggressive debridement of infected bone, offloading, and glycaemic control. If neither revascularisation nor healing is achievable, a planned amputation at the most distal viable level, performed promptly, is better than a futile course of therapy and a delayed amputation through infected tissue.
• Consider a second opinion on the vascular imaging rather than repeating oximetry; the problem is inflow, not the test.

Communicating with the surgeon

• Give the number and its threshold explicitly: "periulcer transcutaneous oxygen at 2.4 ATA is 85 mmHg; below 100 mmHg predicts failure, so I do not support hyperbaric oxygen for this wound."
• State what the test does and does not prove, and that it does not by itself justify amputation - the vascular imaging does.
• Put the recommendation in writing with the measurement conditions, the electrode site and the reference values, so the decision is documented and cannot be attributed to the hypobaric service's silence while the director is away.