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Top Ten Things You Need to Know About HBOT #7: Role of Transcutaneous Oxygen in Predicting Wound Healing Failure
In the fourth article in a series, these authors discuss and give updates on the top ten things we need to know about HBO therapy (HBOT).
7
Did you know that transcutaneous oxygen pressure (TcPO2) is a better test than the ankle-brachial index (ABI) in predicting failure to heal?
As wound care professionals, our major goals include improving outcomes, increasing the quality of life of our patients, and contributing to wound healing and limb preservation. This is why it is of great importance that clinicians consider the prediction of wound healing, wound healing failure, and risk of major amputations in patients with DFUs and chronic nonhealing wounds. Doing so allows us not only to stratify risks but also to target interventions for limb salvage.1
It has been said it is easier to predict which wounds will not heal than those that will heal because hypoxia is often the final common denominator for wound failure. We say that predicting both good and bad outcomes of a wound is a far more complex task. Rates of healing and major amputations are very variable amongst patients with DFUs.1 Prediction of outcomes of any nature requires a multifactorial approach and a profound understanding of underlying pathophysiology, as well as a fine-tuned clinical judgment that allows us to tailor interventions to that pathophysiology.
Although several tests intended to identify significant wound hypoxia and underlying pathology have been used—including ankle-brachial index (ABI), skin perfusion pressure, infrared spectrography, and laser Doppler flowmetry—TcPO2 is the most useful for predicting the failure of a wound to heal. TcPO2 is a non-invasive assessment tool that measures local tissue oxygen tension in tissue fluids just below the skin.2 This tool measures the oxygen tension of the peri-wound, not the actual pressure of oxygen within the wound, as this is very difficult to assess.3 Transcutaneous oxygen pressure is also most effective at predicting other outcomes such as the healing of a planned amputation, response to HBOT, and success of revascularization interventions.2,4
A systematic review and meta-analysis by Wang et al suggests that ABI performs poorly in predicting the healing of foot ulcers and only modestly in predicting limb amputations and in fact, TcPO2 is a better test for predicting both outcomes.5
Some literature reports that a TcPO2 value of ≥30 mmHg is associated with higher chances of healing.1 Additionally, other authors report that wound complications tend to increase as TcPO2 levels decrease and fall below 40 mmHg.6 A consensus statement by Fife et al recommends and defines wound hypoxia as a TcPO2 value that is < 30 mmHg in patients without diabetes, < 40 mmHg in patients with diabetes, and < 50 mmHg in patients with both diabetes and renal failure.3 Furthermore, whileTcPO2 is a great predictor of revascularization success, we must keep in mind that to reach optimal levels of measurements with TcPO2 for wound healing after a vascular procedure, there may be a delay of 3–4 weeks.7
Additionally, TcPO2 testing also has two physiological challenges. The first is the normobaric oxygen challenge (100% oxygen challenge)—where measurements are made after the patient is given 100% oxygen for 10 minutes. Values of at least above 40 mmHg or double than the baseline are used to consider if patient may benefit from HBO therapy.8 A paradoxical decrease in oxygen values during the 100% oxygen challenge is associated with very poor prognosis.9 The second test is the leg elevation test, which is performed by lifting the patient’s leg by 30 degrees. A decrease in oxygen values is suggestive of macrovascular disease.
In-chamber transcutaneous oxygen measurement (TCOM) at 2 ATA remains the best predictor of benefit in diabetic foot ulcers.10 Among patients with an in-chamber TCOM >200 mmHg, Fife et al showed that 78.3% benefited from HBOT compared to those with an in-chamber TCOM < 100 mmHg.11 In the study, only 18% of those patients benefited.
The Society for Vascular Surgery (SVS) Lower Extremity Threatened Limb Classifcation System, also known as the “WIfI” (Wound, Ischemia, and foot Infection) is a widely used tool that helps clinicians stratify the risk of lower limb loss. The SVS WIfI classification system takes into account three major factors: the clinical description of the wound (W), the level of ischemia (I), and the clinical manifestations of infection (fI). When evaluating for ischemia, SVS WIfI considers TcPO2 measurements and classifies the degree of ischemia with a grading system from 0–3, based on these measurements.
In the same vein, values are assigned for a particular wound in the categories wound grades and infection grades.12
In Summary
TcPO2 is a great tool in predicting failure of wound healing, response to HBOT, predicting the best level of amputation, and for prognostic stratification of wounds for limb salvage. Recently, there has been an increasing interest with regards to the use of near infrared spectroscopy (NIRS) for evaluation of wound hypoxia. We will be working on reviewing the role NIRS in the evaluation of wounds in a subsequent article in this series.
Denise Nemeth is a first-year medical student at the University of the Incarnate Word School of Osteopathic Medicine in San Antonio, TX. Formerly a general and vascular surgery PA in a rural community, Ms. Nemeth aspires to become a general surgeon. She is a certified wound specialist with the American Board of Wound Management. Her interests include rural health, wound healing, colarectal surgery, and minimally invasive surgery.
Jayesh B. Shah is Immediate Past president of the American College of Hyperbaric Medicine and serves as medical director for two wound centers based in San Antonio, TX. In addition, he is president of South Texas Wound Associates, San Antonio. He is also the past president of both the American Association of Physicians of Indian Origin and the Bexar County Medical Society and Current of Board of Trustees of Texas Medical Association.
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References
1. Brownrigg JR, Hinchliffe RJ, Apelqvist J, et al. Performance of prognostic markers in the prediction of wound healing or amputation among patients with foot ulcers in diabetes: A systematic review. Diabetes Metab Res Rev. 2016;32 Suppl 1:128-135. doi: 10.1002/dmrr.2704 [doi].
2. Shah JB. Correction of hypoxia, a critical element for wound bed preparation guidelines: TIMEO2 principle of wound bed preparation. J Am Col Certif Wound Spec. 2011;3(2):26-32. doi: 10.1016/j.jcws.2011.09.001 [doi].
3. Fife CE, Smart DR, Sheffield PJ, Hopf HW, Hawkins G, Clarke D. Transcutaneous oximetry in clinical practice: Consensus statements from an expert panel based on evidence. Undersea Hyperb Med. 2009;36(1):43-53.
4. Grolman RE, Wilkerson DK, Taylor J, Allinson P, Zatina MA. Transcutaneous oxygen measurements predict a beneficial response to hyperbaric oxygen therapy in patients with nonhealing wounds and critical limb ischemia. Am Surg. 2001;67(11):1072-9; discussion 1080.
5. Wang Z, Hasan R, Firwana B, et al. A systematic review and meta-analysis of tests to predict wound healing in diabetic foot. J Vasc Surg. 2016;63(2 Suppl):29S-2. doi: S0741-5214(15)02026-1 [pii].
6. Conte MS, Bradbury AW, Kolh P, et al. Global vascular guidelines on the management of chronic limb-threatening ischemia. J Vasc Surg. 2019;69(6S):3S-125S.e40. doi: S0741-5214(19)30321-0 [pii].
7. Caselli A, Latini V, Lapenna A, et al. Transcutaneous oxygen tension monitoring after successful revascularization in diabetic patients with ischaemic foot ulcers. Diabet Med. 2005;22(4):460-465. doi: ME1446 [pii].
8. Sheffield PJ. Measuring tissue oxygen tension: A review. Undersea Hyperb Med. 1998;25(3):179-188.
9. Shah JB, Ram DM, Fredrick E, Otto GH, Sheffield PJ. Determination of ideal PtcO2 measurement time in evaluation of hypoxic wound patients. Undersea Hyperb Med. 2008;35(1):41-51.
10. Fife C. Straight talk Tuesday. 2019.
11. Fife CE, Buyukcakir C, Otto GH, et al. The predictive value of transcutaneous oxygen tension measurement in diabetic lower extremity ulcers treated with hyperbaric oxygen therapy: A retrospective analysis of 1,144 patients. Wound Repair Regen. 2002;10(4):198-207. doi: 10402 [pii].
12. Mills JL S, Conte MS, Armstrong DG, et al. The society for vascular surgery lower extremity threatened limb classification system: Risk stratification based on wound, ischemia, and foot infection (WIfI). J Vasc Surg. 2014;59(1):220-2. doi: S0741-5214(13)01515-2 [pii].
