Nontouch Infrared Skin Thermometry: An Underutilized Tool

Wound care clinicians and patients can identify surface skin temperature differences with noncontact infrared skin thermometers.1 These inflammatory changes can be important for the early identification of neuropathic complications (eg, repetitive trauma and Charcot foot) and deep/surrounding wound infection. This technology can replace the subjective and often inaccurate assessment of skin temperature differences using the back of the clinician’s hand.2 Role in Preventing Foot Ulcers Persons with diabetes and a high-risk neuropathic foot can use infrared thermometry at six sites on the foot to monitor plantar temperature changes: the first, third, and fifth metatarsal head, as well as the two midsides of the foot and the heel. If a temperature differential of 4 °F or higher is detected at any site, patients should restrict ambulation to reduce repetitive trauma and in turn reduce the likelihood of new foot ulcers.3 Three randomized controlled studies4–6 demonstrated that infrared thermometry prevented most new neuropathic ulcers in this patient population compared with both standard care and an education session for daily foot examinations, rendering this technology one of the few with strong clinical evidence.1,4–6 Charcot Joint A Charcot joint occurs from neuropathy and trauma, leading to microfractures of the bone (Charcot neuroarthropathy). It can occur in any joint, but this discussion is limited to the foot as the most common site. Acute swelling, often with deformity of a neuropathic foot, may be a sign of Charcot neuroarthropathy. The patient usually does not have a foot ulcer or loss of skin integrity, and there may be acute pain in an otherwise painless foot (Figure 1).Figure 1: BILATERAL CHARCOT FEET© WoundPediaClinicians and patients can use the infrared thermometer to assess the aforementioned six sites on each foot. The increased temperature is often 8 °F to 15 °F warmer than the mirror image on the opposite foot.7 With an acute Charcot joint, patients should not apply any direct weight on the foot and use a wheelchair, contact cast, or removable cast walker. Given a loss of proprioception, crutches may be associated with falls. With patient self-monitoring, and as the temperature normalizes, weight bearing can gradually be increased with custom orthopedic shoes, including the introduction of a CROW (Charcot Restraint Orthotic Walker). Infection Infrared thermometry was introduced into the Toronto Regional Dermatology and Wound Clinic in 1996 to detect early infection signs to prevent destruction of cellular and/or tissue-based products. This use of infrared thermometry contributed to the creation of the NERDS and STONEES mnemonics,8–10 which use clinical signs to differentiate superficial (NERDS) from deep and surrounding infection (STONEES; Figure 2). In reviewing the individual factor analysis of each of the STONEES criteria, an increase in skin temperature of 3 °F or higher versus a mirror-image measurement of noninfected comparator skin is more than 8 times more likely to be associated with deep and surrounding infection9 (although two or more other STONEES criteria are also required for definitive diagnosis).Figure 2: CLINICAL CRITERIA FOR INFECTION© WoundPediaPOINTS TO CONSIDER Inexpensive, commercially available noncontact infrared thermometers are useful instruments for wound care practitioners.1 The Fahrenheit scale is preferable to the Celsius scale because it allows detection of smaller intervals of temperature differences making it easier to interpret at the bedside. These thermometers (cost $25–100) are just as effective as scientific grade thermometers (eg, Exergen, at a cost of $615.07).11,12 Smart et al13 have similarly validated mini-infrared thermometers that can be carried in a nurse’s pocket to be equivalent to the scientific standard. Infrared thermometers should have a continuous mode with a maximum temperature reading and convert to Fahrenheit from Centigrade.14 Using the validated whole-wound zigzag method (Figure 3)14 when the thermometer is in activated continuous mode, practitioners can determine a maximum temperature more quickly than measuring four distinct areas to obtain the highest reading around the margin of an ulcer. Maliyar et al15 validated nontouch infrared thermometry had a 3 °F increased or higher temperature compared to the mirror image on the opposite leg but cautioned that temperatures on the front and back of the same extremity may be misleading because of transfer of heat from an active infection. The industrial nontouch infrared thermometers can be held 8 to 12 inches from the skin/wound and give an accurate measurement compared with the scientific standard thermometer (eg, Exergen) that must be held within 1 to 2 cm of the skin surface.2,12 The closer distance is more likely to result in accidental bacterial contamination from the wound surface or exudate. Interrater reliability has been validated with similar infrared thermometer results between two independent observers.11 Although arterial disease with ischemic changes can lower skin temperature, there are no validated studies on the use of nontouch surface infrared thermometry for this indication. Figure 3: ZIGZAG TECHNIQUE© WoundPedia

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