Top Ten Things You Need to Know About HBOT #6: How Infrared Spectroscopy Can Monitor Wound Oxygenation

In the fifth article in a series, this review article will discuss and give updates on top ten things we need to know about hyperbaric oxygen therapy (HBOT).

6

Did you know infrared spectroscopy might be a useful tool to monitor oxygenation within wound beds and surrounding tissue?

The healing of wounds is a complex task that is dependent on many factors. As we know, correcting underlying abnormalities is critical to healing.¹ An important factor to evaluate and address is wound hypoxia, as oxygen is one of the key elements of healing outcomes.² There are many tools available to clinicians to assist in the evaluation of limb perfusion including angiography, ankle-brachial index, and Doppler. However, they don’t necessarily evaluate wound bed oxygenation well.

For this, we must rely on other tools, such as TcPO₂, which we have described in detail in a previous installment of this series. TcPO₂ is able to measure periwound oxygenation but not oxygenation in the wound bed. TcPO₂ also cannot be done in plantar areas and it is a very technique specific requiring well-trained staff. Near-infrared spectroscopy (NIRS) is easy to use and can provide measurements of the wound bed, periwound area, plantar area and at the flap dehiscence site, which clearly will be beneficial.
 
NIRS is an up-and-coming technology that has been successfully used to evaluate functional tissue oxygen saturation in the management of wounds. NIRS is one of the newer options for the evaluation of oxygen delivery and usage in the microvasculature. This technology uses reflected light to calculate perfusion by taking advantage of subtle color changes that occur in hemoglobin when it is oxygenated. NIRS transmits very specific wavelengths of light: between 600 nm and 1000 nm. This allows for either a selective absorption or reflection of the light. The amount of light reflected can then be measured to determine the ratio of deoxygenated to oxygenated hemoglobin.²
 
In a pilot study by Serena, et al, a comparison between TCOM and NIRS in hard-to-heal wounds was performed.³ Results showed a strong correlation between both, with NIRS having a slight advantage by allowing measurement of oxygenation within the wound bed and a simplified approach to oxygenation measurement as compared to TCOM. Another group of researchers, Longobardi, et al, utilized NIRS to evaluate hyperbaric oxygen therapy (HBOT) in the treatment of venous leg ulcers.⁴ They found that NIRS was easy to use, had no contraindications, did not delay clinical care, and yielded valuable markers of healing. However, in another study by Bouyé, et al, both NIRS and TcPO₂ were used to predict the presence of arteriographically proven lesions. The results showed that NIRS had lower diagnostic accuracy than TcPO₂ for the prediction of arterial lesions.⁵  
 
There are many benefits of using NIRS technology. NIRS is a non-contact technology that comes with a reduced risk for cross-contamination. NIRS can also cover much larger surface areas than its counterparts (ie, TcPO₂) and can be taken before and after treatment, giving the clinician accurate and immediate guidance during a single clinical or surgical visit. There are no injectable dyes or contrast agents that need to be used, decreasing the potential for toxicity. The readings yielded by NIRS are very consistent between visits and the clinician is able to obtain readings from different points of view.⁶ Landsman, et al, published Table 1 to interpret wound bed and periwound oxygenation for further decision making.⁶ The sample size is small in the Landsman paper so it needs to be validated in a clinical trial setting with more patients. NIRS should be valuable in the setting of HBOT as it gives the clinician an accurate assessment of both the immediate and persisting effects of the treatment but needs validation with further clinical studies.   

In Summary

NIRS could be a valuable tool in the evaluation of wound hypoxia. It can be used in the setting of wound healing for diabetic foot ulcers, predicting flap failure, wound dehiscence, and skin graft incorporation. Other potential applications could include the evaluation of colorectal anastomosis. Could NIRS replace TcPO₂ in the near future? We have yet to see.
 
Denise Nemeth is a second-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 certified wound specialist with the American Board of Wound Management. Her interests include rural health, wound healing, colorectal 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. 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].
2. Landsman AS, Barnhart D, Sowa M. Near-infrared spectroscopy imaging for assessing skin and wound oxygen perfusion. Clin Podiatr Med Surg. 2018;35(3):343-355. doi: S0891-8422(18)30020-X [pii].
3. Serena TE, Yaakov R, Serena L, Mayhugh T, Harrell K. Comparing near infrared spectroscopy and transcutaneous oxygen measurement in hard-to-heal wounds: A pilot study. J Wound Care. 2020;29(Sup6):S4-S9. doi: 10.12968/jowc.2020.29.Sup6.S4 [doi].
4. Longobardi P, Hartwig V, Santarella L, et al. Potential markers of healing from near infrared spectroscopy imaging of venous leg ulcer. A randomized controlled clinical trial comparing conventional with hyperbaric oxygen treatment. Wound Repair Regen. 2020;28(6):856-866. doi: 10.1111/wrr.12853.
5. Bouyé P, Jacquinandi V, Picquet J, et al. Near-infrared spectroscopy and transcutaneous oxygen pressure during exercise to detect arterial ischemia at the buttock level: Comparison with arteriography. J Vasc Surg. 2005;41(6):994-999. doi: https://doi-org.uiwtx.idm.oclc.org/10.1016/j.jvs.2005.03.020.
6. Landsman A. Visualization of wound healing progression with near infrared spectroscopy: A retrospective study. Wounds. 2020;32(10):265-271.