Amputation of the ischemic limb: selection of the optimum site by thermography

Ocular Surface Temperature: Characterization in a Large Cohort of Healthy Human Eyes and Correlations to Systemic Cardiovascular Risk Factors

Purpose: To characterize ocular surface temperature (OST) in healthy eyes and its association with systemic risk factors of cardiovascular and ischemic heart disease. Methods: This prospective cross-sectional study included consenting subjects who were examined at the Institute for Medical Screening in Sheba Medical Center. A Therm-App™ thermal imaging camera (Opgal LTD, Israel) was used for OST acquisition, and the mean OST of the medial canthal, lateral canthal, and central cornea regions were measured. Room and body temperatures were also recorded. Past medical and ocular history as well as data from various clinical examinations performed at the same visit were obtained. Results: Thermographic images were obtained from 186 subjects, 150 of which were included in the final analysis. OST was significantly higher in the medial canthal, central cornea, and lateral canthal regions in people with a history of ischemic heart disease (p = 0.02, p = 0.02, and p = 0.03, respectively). There were no significant OST differences (ANOVA test) associated with the presence of hypertension, diabetes mellitus, or active smoking status. Conclusions: OST correlated positively with the presence of ischemic heart disease. This correlation, its pathophysiological base, and its clinical application warrants further investigation.

Ocular surface temperature differences in glaucoma

PURPOSE

Accumulating evidence suggests that neuroinflammation and immune response are part of the sequence of pathological events leading to optic nerve damage in glaucoma. Changes in tissue temperature due to inflammation can be measured by thermographic imaging. We investigated the ocular surface temperature (OST) profile of glaucomatous eyes to better understand the pathophysiology of these conditions.

METHODS

Subjects diagnosed with glaucoma (primary open angle glaucoma [POAG] or pseudo exfoliation glaucoma [PXFG]) treated at the Sam Rothberg Glaucoma Center (11/2019-11/2020.) were recruited. Healthy subjects with no ocular disease served as controls. The Therm-App thermal imaging camera was used for OST acquisition. Room and body temperatures were recorded, and the mean temperatures of the medial cantus, lateral cantus, and cornea were calculated with image processing software.

RESULTS

Thermographic images were obtained from 52 subjects (52 eyes: 25 POAG and 27 PXFG) and 66 controls (66 eyes). Eyes with glaucoma had a significantly higher OST compared to controls (mean 0.9 ± 0.3°C, p < 0.005). The difference between the two groups remained significant after adjustment for age, sex, intraocular pressure (IOP) and room and body temperatures. Lens status and topical IOP-lowering medication did not significantly affect OST. A subgroup analysis revealed that the OST was higher among eyes with POAG compared to eyes with PXFG, but not significantly.

CONCLUSIONS

Differences in the OST between glaucomatous and normal eyes strengthens current thinking that inflammation affects the pathophysiology of glaucoma. Longitudinal studies are warranted to establish the prognostic value of thermographic evaluations in these patients.

Optical Measurement of Tissue Oxygen Saturation

Advances in opto-electronic systems have meant that optical spectroscopy can now be used for noninvasive measurements in tissue in patients. A number of techniques have evolved over the last 15 years that make use of the characteristic differences in the absorption spectrum of deoxygenated and oxygenated hemoglobin to measure oxygen saturation. This article summarizes, in particular, those techniques that may prove to be applicable to measurements relating to lower extremity wounds. A short introduction is given about existing electrode methods before describing applications of near infrared and visible wavelength spectroscopy to measurements in tissue. The advantages and limitations of these methods are discussed. An example of an area where tissue spectroscopy is now in routine clinical use for tissue healing viability assessment is presented.

Thermographic patterns of the upper and lower limbs: baseline data

Objectives. To collect normative baseline data and identify any significant differences between hand and foot thermographic distribution patterns in a healthy adult population. Design. A single-centre, randomized, prospective study. Methods. Thermographic data was acquired using a FLIR camera for the data acquisition of both plantar and dorsal aspects of the feet, volar aspects of the hands, and anterior aspects of the lower limbs under controlled climate conditions. Results. There is general symmetry in skin temperature between the same regions in contralateral limbs, in terms of both magnitude and pattern. There was also minimal intersubject temperature variation with a consistent temperature pattern in toes and fingers. The thumb is the warmest digit with the temperature falling gradually between the 2nd and the 5th fingers. The big toe and the 5th toe are the warmest digits with the 2nd to the 4th toes being cooler. Conclusion. Measurement of skin temperature of the limbs using a thermal camera is feasible and reproducible. Temperature patterns in fingers and toes are consistent with similar temperatures in contralateral limbs in healthy subjects. This study provides the basis for further research to assess the clinical usefulness of thermography in the diagnosis of vascular insufficiency.

Thermal imaging today and its relevance to diabetes

From the historic and simple assessment of temperature by the clinical thermometer, modern infrared technology has opened up new perspectives, especially in the use of thermal imaging to map body surface temperature with a remote sensing camera. Since the 1960s, there is now a greater understanding of thermal physiology and the relationship between skin temperature and blood perfusion. Furthermore, the examination technique, and the advantages of computer-aided digital imaging has greatly improved the reliability of this technology in medicine. Studies in diabetology have shown the value of this new facility and its relevance to clinical assessment of peripheral perfusion and tissue viability.

When is a more proximal amputation needed?

Amputation may be the most appropriate therapy for an ischemic or infected limb, but the level at which to amputate is often difficult to determine. Selecting the appropriate level is crucial when performing an amputation. The goals of surgery are to maintain maximal limb length and ensure successful healing. When more of the foot and limb can be preserved, the chances for rehabilitation are improved. This article reviews how to determine the most appropriate level of amputation.

Laser Doppler velocimetry and platelet-derived growth factor as prognostic indicators for the healing of ulcers and ischaemic lesions of the lower limb

The prognostic potential of skin blood flow measured by laser Doppler and serum platelet-derived growth factor (PDGF) levels was evaluated in patients with ischaemic lesions or ulceration of the lower limb. The laser Doppler-derived skin blood flow and perfusion pressure were measured in 93 patients with ischaemic lesions or ulceration in 98 lower limbs. Of these lesions, 61% healed spontaneously or with conservative local therapy, while 39% required major surgery. The likelihood for healing was reduced by older age. Comparison of receiver operating curves demonstrated that the optimal sensitivity and specificity were obtained for a combination of skin blood flow and perfusion pressure measured at 44 degrees C rather than at room temperature. If the skin perfusion pressure and blood flow were greater than 15 mmHg and 100 U respectively at 44 degrees C, 91% lesions healed, while if they were less than these values none healed. This provided a sensitivity and specificity of 100% and 83% respectively. The serum PDGF concentration was measured by radioimmunoassay in 48 patients with ischaemic lesions or ulceration of the lower limb, and compared with that in 34 healthy controls and 15 patients who had undergone abdominal surgery 3-5 days previously. The median PDGF level in the control group (83 pmol/l) was significantly less than that in the post-laparotomy group (217 pmol/l). The median PDGF level in the 31 patients whose ulcers healed with conservative therapy (210 pmol/l) was significantly higher compared with that in the 17 patients with unhealed ulcers (70 pmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Transmetatarsal amputation in patients with peripheral vascular disease

Transmetatarsal amputation has the reputation of being an operation with a poor healing rate, and less than a 50% success rate had recently been reported. The outcome of this amputation in patients with peripheral vascular disease has been retrospectively studied in this paper by examining 34 transmetatarsal amputations performed over a 5-year period. Twelve patients had had previous toe amputations and 22 were diabetic with an overall healing rate of 68%. There was no significant difference in the success rate between diabetics and non-diabetics. One patient died in the postoperative period, giving an early post-operative mortality of 3%. Revision of failed transmetatarsal below-knee amputation resulted in healing in seven patients out of nine, suggesting that it does not compromise later amputation at a higher level. Healing did not appear to be influenced by factors such as sympathectomy, previous arterial reconstruction or peripheral pulses. Transmetatarsal amputation provides patients who have a short life expectancy with a durable functional stump which is prosthesis free.

Relationships between skin temperature and perfusion in the arm and leg

Relationships between skin temperature (Tsk) and perfusion have been studied to provide a basis for the use of Tsk in the non-invasive assessment of limb circulation in peripheral vascular disease. Raising the ambient temperature (Ta) from 20 to 30 degrees C increased the perfusion of the glabrous skin of the hands and feet without changing that of the skin of the forearm or calf. On a fractional basis the response in the hand and foot was the same. Tsk was higher in the arms than the legs and in the proximal than distal parts of the limbs. A fall in Tsk was often seen when Ta rose from 20 to 25 degrees C and was attributed to counter-current cooling. Subsequently Tsk rose even in regions where there was no increase in skin perfusion. Tsk can only be related to its perfusion in the fingers, palm and toes. Forearm Tsk was related to the perfusion of the digits. This relationship implies a link with the arterial inflow to the limb which determines the size of its thermal core. Heat conduction from the core seemed important for the skin of areas like the forearm and calf where the constant, low perfusion limited the amount of heat which could be transported to it directly by the blood. The importance of conduction was supported by studies, at Ta 20 degrees C, on subjects during calf muscle exercise and on patients with arterio-venous fistulae. Here an increase in the arterial inflow to the limb was associated with a rise in Tsk of the forearm/calf unrelated to the perfusion of its skin.

Primary survival and prosthetic fitting of lower limb amputees

During the period 1984-1985 amputation of the lower limb at a level potentially requiring a prosthesis was performed on 577 patients in 16 operative units. The mean age was 75.7 years for females and 68.1 for males. The most common site of the amputation was above the knee (49.9%). The majority of amputations (93.8%) were performed for vascular diseases and diabetes. Survival figures showed that 25.5% of amputees died within 2 months of amputation, 60.7% were alive after one year and 43.2% after two years. Out of a total of 577 patients, 26.9% were fitted with a prosthesis. Out of below-knee and above-knee amputees surviving over 2 months, 61.5% and 27.2% respectively were fitted with a prosthesis. There were markedly fewer prosthetic fittings in the over-60 age group. Diabetic patients of both sexes were fitted with a prosthesis more often than arterio-sclerotic patients. Among tumour patients 82.4% received a prosthesis. In the study area more emphasis must be put on the concept of preserving the knee joint and preoperative assessment of vascular patients for selection of amputation level. Every effort must be made to avoid delay in the postoperative mobilization and rehabilitation. Prosthetic fitting of amputees could be improved by better liaison between surgical unit and specialized rehabilitation unit and by closer team approach of amputee care.

The value of skin temperature measurements in forecasting the healing of a below-knee amputation for end-stage ischaemia of the leg in peripheral vascular disease

In order to forecast the healing of a Burgess type below-knee amputation the skin temperature of the leg has been studied before operation in 39 instances using infra-red thermography in a 26 degrees C environment. Healing bore no relation to the mean skin temperature of the calf or that of the skin at the site of the anterior incision. However, when the skin temperature at the site of the incision for the long posterior flap was greater than 30.4 degrees C or when the ratio of the temperatures at the posterior and anterior incision sites (P/A) was greater than 0.98 healing was significantly more likely to occur. It is proposed that the temperatures at these sites should be used to assess the prospect of such an amputation healing.

Amputation for peripheral vascular disease: the case for level selection

One hundred major lower limb amputations were performed for end stage peripheral vascular disease over a 15-month period. Selection of amputation level was made on the basis of laboratory criteria using skin blood flow and infrared thermography data. Eighty-one amputations were performed at the below-knee level with six failures. This resulted in a final below-knee: above-knee amputation ratio of 3:1. It is clear that there are still many centres in the UK where above-knee amputation is the accepted operation, despite the inherent drawbacks to this procedure. We recommend that more attention is given to achieving higher below-knee amputation rates to improve the chances of amputee mobility and therefore quality of life.

The effect of adjuvant oxygen therapy on transcutaneous pO2 and healing in the below-knee amputee

The effects on tissue oxygenation of postoperative adjuvant oxygen have been studied in a group of 20 patients undergoing below-knee (BK) amputation for vascular disease. Ten patients received no therapy, the remainder receiving 28% oxygen for 48 hours following surgery. The results showed that the transcutaneous pO2 in the amputation flaps fell significantly by some 20 mmHg (p less than 0.01) following surgery and that this fall was prevented by the use of adjuvant oxygen. The fall was not observed in the non-amputated limbs. TcpO2 took almost two weeks to reach its pre-operative levels in the amputated limbs. The effect on stump healing of adjuvant oxygen therapy was investigated in a randomized controlled trial in a series of 39 patients undergoing BK amputation. There were 22 patients in the control (untreated) group and 17 in the treated group (adjuvant oxygen for 48 hours). In the treated group 14 patients healed primarily and three amputations failed. In the untreated group 14 limbs healed primarily, one secondarily and there were 7 failures. The pre-operative transcutaneous values in the stumps which failed (26 mmHg +/- 14) was significantly lower (p less than 0.005) than in those which healed (40 mmHg +/- 9). The mean pre-operative TcpO2 in the patients in whom healing occurred in the treated group (35 mmHg +/- 10) was significantly lower (p less than 0.001) than the mean pressure observed in the untreated group (44 mmHg +/- 9).

A rationale for skew flaps in below-knee amputation surgery

The use of thermography in the assessment of amputation levels has demonstrated a medial to lateral thermal gradient in many cases. In order to see whether this reflected a true medial to lateral skin blood flow gradient, a prospective study was set up to measure blood flow medially and laterally below the knee. Twenty-one patients, presenting for amputation assessment with end-stage peripheral vascular disease, were studied. Skin blood flows were measured using an intradermal radioisotope clearance technique. Results showed a highly significant difference between medial and lateral skin blood flows (t = 4.79; p less than 0.001). In view of the significantly higher blood flow in the medial skin of the lower leg, it is suggested that a more medially based posterior below-knee amputation skin flap may be of more value in some patients.

Assessment of tissue viability in relation to the selection of amputation level

Assessment of the optimum level of amputation of an ischaemic limb can be exceptionally difficult. For this reason there has been an intensive effort, particularly in the past 20 years, to find suitable non-invasive ancillary methods to aid in the amputation level selection. This paper reviews three separate research and development areas which have evolved simultaneously in our laboratory: skin partial oxygen pressure, skin blood flow, and infrared thermography. The physiological basis for each of these measurements is discussed along with the merits and demerits of each.

Prediction of amputation wound healing: the role of transcutaneous pO2 assessment

With the recent trend towards more distal lower limb and below-knee amputation for peripheral vascular disease, failure of amputation healing remains a common clinical problem. There is an urgent need for more objective measures of selecting the most appropriate distal amputation level compatible with healing. Oxygen availability is the final arbiter of tissue viability and healing potential, and we have shown that the measurement of transcutaneous pO2 (TcpO2) accurately reflects the degree of ischaemia in the lower limb. In 59 patients having 62 amputations for peripheral vascular disease significantly lower TcpO2 levels were related to amputation failure. Below-knee amputations with a pre-operative below-knee TcpO2 of above 35 mmHg always healed, and failures had levels of 35 mmHg or less. Nine out of sixteen patients having above-knee amputations had pre-operative below-knee TcpO2 values well above 35 mmHg, suggesting that they may possibly have undergone successful below-knee amputation. No correlation between ankle systolic pressure and amputation healing was found. TcpO2 measurement is simple, non-invasive and reliable and offers an exciting research advance in the assessment of effective tissue perfusion.

The relationship between temperature isotherms and skin blood flow in the ischemic limb

This study was conducted in order to establish a relationship between thermographically defined levels of viability in the ischemic limb and a measurement of skin blood flow. Color thermograms (10 colors, 0.6 degree C apart) defined the temperature gradient and skin blood flow was measured, using the radioactive clearance method in three discrete isotherms set 1.8 degrees C apart. The differences in skin blood flow measured in the three separate isotherms were significant (P less than 0.001). The results of this study support previously unqualified assertions that thermographic temperature gradients along an ischemic limb are indicative of local microcirculatory status. The potential of the thermographic method for demarcating viable and nonviable skin flaps at the chosen site of amputation is confirmed.

The place of amputation in the management of the ischaemic lower limb in the dysvascular geriatric patient

Statistics show that today the majority of amputations of the leg are peripheral vascular disease in patients over the age of 60. The stages of management are discussed and in particular a plea made for taking a balanced view of vascular salvage procedure and amputation as alternative treatments. The advantages are stressed for these patients to be treated in a unit where the resources for appropriate investigation are available and the surgeon has the support of a multi-disciplinary team. The importance of the pre- and post-amputation rehabilitation programme is discussed.