Skin temperature can be a powerful indicator of the capability to heal, especially if noted under controlled conditions. Horwitz and Abramson reported in 1960 their results with their "vasodilatation test", the vasodilatation achieved by reflex heat and the oral administration of 25mg of tolazoline. Their patients were warmed with hot water bottles and covered with blankets with their toes bared in a 20 Centigrade constant temperature room. When their oral temperatures had leveled in the normal range, temperature probes were read on all ten toes. They claimed no impairment with a temperature > 30 degrees C, slight impairment in the 28-30, moderate 25-28 and severe 21-25 degrees centigrade. Some especially ischemic legs cooled below room temperature presumably due to evaporation. Amputation was rarely necessary with a reading over 26 degrees C (78.8o F). The test historically was helpful in gauging the degree of vascular impairment, estimating a prognosis for healing and documenting the benefit of treatment with the suction-pressure pneumatic boots (Landis) (Exemplary Circulator Boot Case).

 

Tips for the Elderly and Patients with PVD: _______________________________ Cold feet heal slowly as healing rates are temperature dependent. Application of direct heat is dangerous. How to stay warm in a cold house:

1)       A wool hat prevents heat loss from the head (Bald men take notice!)

2)       Long underwear and multiple layers of loose clothing

3)       A hot water bottle wrapped in a large towel may safely be placed under a sweater or under the blankets in the bed.

4)       Stay out of drafts

5)       Cover lesions with moist multi-electrolyte dressings changing as needed to keep free of collections of pus.

The test, unfortunately, was time-consuming as an hour or more might be required before the body core temperature leveled off in a normal range. Less rigorous preparation of the patient, however, may alter the results by environmental influences. Differences between even normal legs are common if only one is covered (a bandage, sock, or bootie on one foot and not the other) or if one foot is baking in the sunlight through a window, under a draft, or recently washed etc. The means of gauging the temperature is, of course, important. The hand of the nurse or doctor can be worthless. To the cold hand of the examiner in the winter, even the dead may feel warm.

Temperature, Age, Activity and Diet: Older and neuropathic diabetics may be insensitive both to heat and cold. When hypothermic, these patients may be expected to vasoconstrict their extremities producing cold extremities even in the absence of vascular disease. Muscular work and the ingestion of food and drink (especially protein and caffeine) help raise the body core temperature. A marginal diet and inactivity promote hypothermia.

Temperature, Diabetic Neuropathy and A-V Shunts: Temperature insensitivity is an important part of diabetic neuropathy. Vinik et al found that combination thermal and vibratory testing gave optimum sensitivity (92-95%) and specificity (77-86%) in its diagnosis. Indeed, they concluded that vibratory and thermal testing should be the primary screening tests for diabetic peripheral neuropathy. Temperature insensitivity is associated with small fiber nerve dysfunction which in turn is associated both with (a) a reduction in laser-Doppler-fluxmetry following stimulation with either acetycholine or thermal injury and (b) a significant reduction in transcutaneous oxygen tension (Pfutzner et al 2001). Likewise Gaylarde et al found the neuropathic patient to raise their transcutaneous oxygen tension less in the feet in response to the stress of heat (a 45 degree C sensing electrode). The combination of sensory unawareness and disturbed neurovascular dysfunction predisposes the neuropathic patient to foot ulcerations.

Diabetics, who have an autosympathectomy, shunt blood through A-V channels in the skin improving skin color, increasing heat loss and diverting oxygenated blood from the nutritive capillaries resulting in a decrease in transcutaneous oxygen tension (Davis and Greene 1959). As perfusion pressure decreases with the development of arteriosclerotic disease, it takes longer for the individual capillary to deliver enough oxygen to meet tissue needs and increasing numbers of capillaries remain open and rubor on dependency is seen. Similar rubor may be seen with necrotizing cellulitis. The latter may be suspected if a very low TcPO2 is found together with demonstrable waveforms on a photoelectricplethysmography apparatus. Such findings constitute a medical emergency as very low TcPO2 portend tissue necrosis which may be prevented with the local injection of antibiotics and their dissemination with boot therapy.

Wollersheim et al showed that closing the shunts with the administration of ephedrine increased capillary perfusion pressure and subcutaneous oxygen levels (1989).The use of ephedrine is not encouraged in these patients, however, because of its other detrimental effects (promoting hypertension and vasoconstriction, potentiating glaucoma and impeding insulin release). It is to be appreciated that a surgical sympathectomy likewise has significant undesirable effects.

Thermography, a Semi-quantitative Method: Thermography using a liquid crystal skin thermometer is a semi-quantitative method producing a multicolored picture of a wound and surrounding skin (normal skin about 95 degrees F). Strips are available over a range of 80-100 degrees F (26-38 degrees C). An increase over surrounding tissue is an indication of increased perfusion. The absence of an increase may be an indication of wound chronicity. The first three days after surgery, the incision and surrounding skin are about the same temperature. By day 4, the wound and adjacent skin cool. Zones of warmth narrow with the incision being warmer...heat in adjacent skin is not thought to be an inflammatory reaction but reactive hyperemia due to histamine and other vasodilators released by cellular damage at the time of wounding. Only a narrow area next to the incision has warmth due to inflammation. If the wound and adjacent skin do not cool by the 4th post-op day, the possibilities of tissue necrosis or infection should be entertained. Indeed, an increase in temperature of 4 degrees F over the contra lateral side may on occasion indicate a problem beneath the skin surface such as a deep abscess or pressure damage over a bony prominence. Nilsson (1975) found infrared thermography unsuccessful in detecting heat sources implanted subcutaneously in volunteers unless they had high power output or were implanted superficially; forced air convection was noted to markedly decrease contrasts in skin temperature.

Thermography and Wound Healing: Even in the absence of a constant temperature vascular laboratory, thermography has been reported to be useful in predicting wound healing. Wagner et al (1988) found both transcutaneous oxygen measurements and temperature helpful in predicting ability to heal a BKA as opposed to an AKA amputation; the average skin temperature and TcPO2 were higher in those who healed primarily versus those who required stump revision: 93.7 vs. 89.9 degrees F and midcalf TcPO2 36.6 vs. 16.4 mm Hg respectively. Other tests were less reliable predictors. In like fashion, Oishi et al found healing of BKA's associated with a cutaneous temperature of 31.9+/-1.5 degrees C (89.4+/-2.7 degrees F) vs. failed amputations with 30.5+/-2.2 degrees C (86.9+/-4.0 degrees F). Oishi et al also noted those healing their amputations also were able to raise their skin temperatures to a greater degree above the ambient temperature: 7.0+/-1.7 degrees C (12.6+/-3.1F) vs. 6.5+/-2.5 degrees C (11.7+/-4.5F). TcPO2, again was their best guide to healing, however, and regardless of its initial value, if after the inhalation of oxygen it raised 10 mm Hg or more, it predicted healing of the stump with a sensitivity of 98%. The temperature differences between the study of Wagner et al and Oishi et al likely represent differences in technique which likewise may affect screening studies. The prediction of future diabetic foot complications, while desirable, was not realized by Armstrong et al (2003) in their one-time screen with skin temperatures of 1588 patients.

External Heat Potentially Harmful: Skin Temperature is proportional to the perfusion of blood and falls between body core temperature and the environmental temperature. Healing processes are temperature-dependent slowing with cooling and speeding with heating unless the metabolic rate increases beyond the capacity of the arterial flow to supply oxygen and nutrients. Increasing blood flow to the skin supplies both heat and oxygen. While application of any form of external heat to the skin promotes local vasodilatation and increased blood flow in normal subjects, it may not do so in patients with significant peripheral vascular disease in whom it may lead to local hypoxia and tissue damage. Still, the application of heat may speed healing in those who can vasodilate and supply the needed oxygen tension.

The application of radiant heat to venous or pressure ulcers as opposed to ischemic or neuropathic ulcers may presumably increase local blood flow without the danger of producing local hypoxia. Bolton in culling the literature on pressure ulcers and radiant heat treatment made the following points: (a) gauze dressings may allow evaporation which allows significant cooling of a wound; (b) freshly cleansed wounds covered with occlusive dressings require 40 minutes to regain their original temperatures and three hours for normal mitotic and leukocyte activity; (c) the surface temperature of venous ulcers has been noted to rise 2.5 degrees C over 90 minutes after the application of a hydrocolloid dressing and then to remain stable over 24 hours; (d) similar temperature increases have been noted with a dressing in place after one hour of radiant heat treatment. She concluded that the use of a moisture-retentive dressing and less frequent dressing changes may achieve improved healing outcomes equal to that achieved by the local application of heat.