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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 26  |  Issue : 1  |  Page : 72-76

Thermometry: A simple objective method for burn depth assessment


1 Department of Surgery, Plastic Surgery Unit, NSCB Government Medical College, Jabalpur, Madhya Pradesh, India
2 Department of Surgery, NSCB Government Medical College, Jabalpur, Madhya Pradesh, India
3 Department of Pathology, NSCB Government Medical College, Jabalpur, Madhya Pradesh, India

Date of Web Publication11-Mar-2019

Correspondence Address:
Prof. Pawan Agarwal
292/293, Napier Town, Jabalpur - 482 003, Madhya Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijb.ijb_19_18

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  Abstract 


Introduction: Accurate assessment of burn wound depth is important because it determines the choice of treatment and prognosis. Clinical evaluation remains the most commonly used modality with its accuracy varies from 50% to 70%. This study was conducted to assess the accuracy and feasibility of burn wound depth using noninvasive noncontact technique using infrared thermometry.
Materials and Methods: Fifteen patients' burn wounds depth was classified clinically into full-thickness, deep partial-thickness, or superficial partial-thickness burns. Thermometry was performed on 3rd day of burn injury using the handheld infrared thermometer. A punch biopsy was taken from all three areas (deep, deep-partial, and superficial-partial burns). A correlation between surface temperature and depth of burn by histopathology was done.
Results: 12/15 patients total burn surface area (TBSA < 65%) survived and three patients (TBSA > 65%) died. In 11/12survivors, thermometry correctly predicted final burn depth. One of 12 burns superficial burn was wrongly assessed clinically as full thickness but was correctly classified by thermometry and healed within 21 days without surgery. 3/12 burns on clinical assessment thought to be superficial were deep; two were correctly predicted by thermometry.
Conclusions: Handheld infrared thermometer can be used in conjunction with clinical examination to improve the efficacy of burn wound depth assessment.

Keywords: Burn depth, thermal burn, thermography, thermometry


How to cite this article:
Agarwal P, Sharma D, Wankhede S, Patel LK. Thermometry: A simple objective method for burn depth assessment. Indian J Burns 2018;26:72-6

How to cite this URL:
Agarwal P, Sharma D, Wankhede S, Patel LK. Thermometry: A simple objective method for burn depth assessment. Indian J Burns [serial online] 2018 [cited 2019 May 26];26:72-6. Available from: http://www.ijburns.com/text.asp?2018/26/1/72/253845




  Introduction Top


Early, rapid, and accurate assessment of burn wound depth is extremely important because it determines the choice of treatment and prognosis. Clinical evaluation remains the most commonly used modality for diagnosing the depth of burn; however, its accuracy varies from 50% to 70%.[1],[2] Many tools are available for improving the accuracy of depth of burn assessment. This study was conducted to assess the accuracy and feasibility of burn wound depth using noninvasive noncontact technique using infrared thermometry.


  Materials and Methods Top


This prospective study was conducted over 3 months from December 2017 to February 2018 in a tertiary referral center in Central India. Before commencing, the study local Ethics Committee Approval and written/informed consent from all patients were taken.

We evaluated 15 patients with thermal burn, and their burn wounds depth was classified clinically into full-thickness, deep partial-thickness, or superficial partial-thickness burns. Patients with electric, chemical, scalds, and 1st-degree thermal burn and who presented 3 days after the burn were excluded from the study. The burn wounds were assessed by two plastic surgeons, and detailed record of wounds was kept. Other demographic details, such as age, sex, extent, and site of the burn, were noted. The criteria for the diagnosis of full skin thickness burn included a dry blackish-brown parchment-like skin, loss of sensation, painless, loss of blanching on pressure, and thrombosed vein on the surface. The deep partial-thickness burn was clinically diagnosed by whitish-brown without capillary return, absent blisters, and painless. Burn was diagnosed with superficial partial thickness when it was pink-red with capillary return, blisters present, and painful.[3] All burn patients were treated with standard burn treatment protocol by initial resuscitation, antibiotics, wound care, and nutritional support according to the American Burn Association Practice Guidelines.[4] None of the patients underwent early excision and grafting, and their wounds were treated using conservative methods by daily dressing with silver sulfadiazine cream. Complete epithelialization or appearance of granulation on the wound was considered as the end point of the study.

Before thermometric assessment, the wounds were cleansed with a soap water solution to remove debris and antibiotic cream and allowed to dry spontaneously. All patients were kept at 23°C for 20 min to attain equilibrium with ambient temperature, and their wounds were covered with clingfilm (water-impermeable and infrared-transparent membranes) to avoid the cooling effect of evaporation of water from the surface of the wound. Thermometry was performed on 3rd day of burn injury using the handheld infrared thermometer (Kody Pharma Chennai, India). Burn wounds were imaged from a distance of 30 cm, measured by a sterile measuring tape, and oriented perpendicular to the skin. The temperature of the burn surface of full thickness, deep partial thickness, and superficial partial thickness was measured. The burn area was marked in 2.5-cm square; and the surface temperature of these squares was measured, and the mean temperature was calculated. In addition, the temperature of the surrounding normal skin was also recorded. At the time of recording of normal skin temperature, all the patients were afebrile. A punch biopsy was taken from all three areas (deep, deep partial, and superficial partial burns). A correlation between surface temperature and depth of burn by histopathology was done. In all survived patients, duration of wound healing, need for debridement, and skin grafting were assessed. Statistical analyses were performed using MedCalc for Windows, version 15.0 (MedCalc Software, Ostend, Belgium) and t-test was applied for comparison, and a critical level of <0.05 was taken as significant.


  Results Top


A total of 15 patients with thermal burns were included in the study. There were five males and 10 female patients. The average age was 29.93 years (range 14–45 years). Average total burn surface area (TBSA) was 64.86% (range 25%–98%). The mean surface temperature assessed using thermometry of superficial partial-thickness, deep partial-thickness, and full-thickness burns were 37.06°C, 35.64°C, and 33.01°C, respectively. The mean normal skin temperature was 37.12°C [Table 1].
Table 1: The mean surface temperature assessed by thermography of superficial partial-thickness, deep partial-thickness, and full-thickness burns and normal skin

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The mean temperature difference between superficial partial-thickness burn and normal skin was not statistically significant (0.06°C, P = 0.380259). However, the mean temperature difference between superficial partial and deep partial burns (1.42°C, P = 0.0001), between superficial partial-thickness and full-thickness burns (4.12°C, P < 00001), and between deep partial-thickness and full-thickness burns (2.7°C P < 0.00001) was statistically significant [Table 2].
Table 2: Mean temperature difference in centigrade between different depths of burn and normal skin

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There was a good correlation between depth of burn (assessed by clinically and histopathology) and surface temperature. With increasing depth of burn, the surface temperature decreases [Figure 1].
Figure 1: Correlation of depth of burn with surface temperature

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12/15 patients (TBSA <65%) survived and three patients (TBSA >65%) died. All 12 survived patients were followed up, and their wound healing pattern assessed. Superficial burn (mean temperature 37.06°C) healed within 3 weeks' time. All deep partial-thickness (mean temperature 35.64°C) and full-thickness areas (mean temperature - 33.01°C)granulated and required skin grafting.

Thermometry correctly predicted final burn depth in 11/12 survivors. One of 12 burns superficial burn was wrongly assessed clinically as full thickness but was correctly classified by thermometry and healed within 21 days without surgery. Three out of 12 burns on clinical assessment thought to be superficial were deep; two were correctly predicted by thermometry.

On histopathology, all superficial partial-thickness burn showed occluded vessels and denatured proteins; whereas full-thickness burn biopsies showed collagen denaturation [Figure 2], [Figure 3], [Figure 4].
Figure 2: Superficial partial-thickness burn showing occluded vessels and denatured proteins

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Figure 3: Deep partial-thickness burn showing collagen destruction in more than half thickness of skin with occluded vessels and denatured proteins

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Figure 4: Full-thickness burn showing collagen denaturation

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  Discussion Top


Clinical evaluation of burn depth remains the most commonly used and inexpensive method; however, its accuracy varies from 50% to 70% and is limited by poor interobserver reliability. This calls for an objective tool for the assessment of burn depth. In addition, assessing burn depth in the early days after burn is even more difficult. Estimation of burn depth may determine the prognosis, as the burns requiring excision and grafting if misdiagnosed, have the risk of developing hypertrophic scarring. This burn depth assessment gets complicated by the dynamic changes during the postburn period and infection which may result in the conversion of more superficial to deep burn wound.[5] Apart from determining the prognosis and choice of treatment methods, objective burn depth assessment is also used for the comparison of different wound dressings.[6]

Thermometry assesses the burn wound temperature by measuring infrared radiation emitted from burn wounds as an indicator of their depths. It is based on the fact that deep wounds are colder than superficial ones because of higher degrees of microvascular coagulation/less vascular perfusion and correlates temperature inversely with depth. Thermometry assesses skin temperature down to gradients as small as 0.1°C.[7],[8],[9] The most accurate period for the thermometric assessment of burn depth is within the first 3 days following burn which is often the most difficult time to assess clinically. After this window of opportunity, thermometry information is lost due to vascular ingrowth.[10]

There are many studies reporting the accuracy of thermometry as high as 90% based on 1°–2° differences in temperature in superficial and deep burn wound or with surrounding normal skin.[9],[11] Thermometry is superior to clinical examination in estimating burn depth. However, ambient temperature, evaporation of water from the surface, sensitive timing, granulating wound, and variations in the depth of vasculature in different body locations can lead to inaccurate results.[10],[12] Evaporative cooling effect and ambient temperature fallacies can be corrected using water-impermeable, infrared-transparent membrane and by keeping the patient at 23°C for 20 min to attain equilibrium with environmental temperature.[13]

Punch biopsy of burn tissue with the histological analysis is considered as the “gold standard” of burn depth assessment and should be used to compare with other diagnostic modalities.[14] On histopathology, occluded vessels and denatured proteins indicating devitalized tissue suggest that a burn is partial thickness whereas collagen denaturation suggests that it is full thickness.[15],[16] However, biopsy has certain disadvantages as follows: sampling error, tissue shrinkage, and structural tissue damage may not necessarily correlate with functional loss because of progressive nature of burn wounds. In addition, it is an invasive procedure which causes additional scarring and increases the risk for infection and needs an experienced pathologist to interpret results.[17]

Digital photographic images can be used in conjunction with clinical examination which increases the accuracy to 90% and is a useful adjunct for remote consultation.[18],[19] However, even high-resolution digital images lack 3-dimensionality and preclude tactile examination.[20]

Various vital dyes, such as  Evans blue More Details, patent blue V, and bromophenol blue, have been used in burn depth assessment.[21] These dyes assess large area of burn quickly but need for injection, limited postinjection time window, inability to differentiate between partial-thickness and full-thickness burns, expensive, and sophisticated infrastructure limits their clinical use.[11],[14],[20] Indocyanine green video angiography and laser Doppler techniques are also used for burn depth detection by monitoring the cutaneous circulation with an accuracy of 99%. These are the less invasive, faster, and most widely used techniques with accuracy compared to wound biopsy.[22],[23] However, these are not available in most burn units as required expanse and technical sophistication restricts their usage to high-tech hospitals/research settings.

Many previous studies have used the digital thermographic camera to assess the depth of burn based on infrared radiation. These cameras produced different colored infrared images of wounds depending on the degree of burn depth. However, this technique requires sophisticated cameras and software which may not be available in resource-poor units.[24],[25] Others have measured the changes in heat transfer processes (thermal diffusivity and conductivity) after cold excitation (active dynamic thermography) and found them to be more accurate than static thermography.[26]

This is the first time a handheld infrared thermometer has been used to measure the surface temperature of burn wounds to assess the depth of burn. The surface temperature was compared with clinical assessment and burn wound biopsy, and it was found that burn wound depth assessment by thermometry correlated well with histopathology. Therefore, we recommend the use of handheld infrared thermometer to improve the efficacy of burn wound depth assessment in conjunction with clinical examination. It is accurate, reproducible, rapid, easy, cost-effective, noncontact, and objective way which can assess large burn area depth quickly. This can be used at primary health care centers and smaller hospital where burn specialists are not available and can also be used for remote consultation.

Limitations of the study are small number of cases, single-center study, and assessment of burn depth on 3rd day. This study should be considered preliminary, and the results will need to be validated in more patients.


  Conclusions Top


Handheld infrared thermometer can be used in conjunction with clinical examination to improve the efficacy of burn wound depth assessment.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2]



 

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