Abstract

Introduction: Understanding the relationship between surface and water temperatures, length of exposure and depth of tissue injury is crucial. When providing expert opinion on potential non-accident injury cases, the duration of the injury and the temperature of any putative causative agent is always requested.

Methods: A systematic review was performed using the electronic databases Web of Science, PubMed, Ovid Medline, PsychInfo and Embase for papers published between 1945 to 2018. We looked exclusively at original papers investigating the relationship of time and temperature in the context of depth of burn injuries using Cochrane risk of bias tool to investigate methodology of each study design.

Results: A total of eight studies met the inclusion criteria. All studies were experimental models with only one comparative human-porcine model. Both contact and scald burns were investigated. There was overall agreement in all studies. The lowest temperature was 50°C that led to mid-dermal burns with a duration of exposure of ³10 minutes. The highest temperature was 100°C that led to deep-partial thickness burns in 10 seconds.

Conclusion: This review has emphasised several factors that affect the severity of contact and scald burn injuries. It should be noted that the time-temperature relationship and threshold are dependent on one another.

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Introduction

Burns affects people of all age groups and leads to scarring, disfigurement and even death [ 1]. It is a global health concern especially among young children, with the commonest burn injury being scalds [ 2]. To reduce the risk of burns, understanding the relationship between surface and water temperatures, length of exposure and depth of tissue injury is crucial. When providing expert opinion on potential non-accident injury cases, the duration of the injury and the temperature of any putative causative agent is always requested.

Having a standardized burn injury severity classification is highly important in clinical and research settings. However, clinical assessment to quantify burn depth through visual observation is challenging. Researchers have tried multiple ways to assess burn depth including MRI, ultrasonography, thermography, laser Doppler flowmetry, fluorescein fluorometry and vital dyes, with varying degrees of success [ 3, 4, 5, 6, 7, 8, 9, 10].

Burn depth is a key determinant of prognosis in terms of morbidity and mortality [ 1, 11]. Skin tissue thickness varies by body locations. The age of a person also affects skin thickness, with children having thinner skin than adults [ 12]. The exact site of the burn is important as the same temperature can have varying degrees of damage at different locations. Thicknesses of the epidermis, dermis, subcutaneous and muscle layers

were described to be at an average of 0.08mm, 2.00mm, 10.00mm and 30.00mm respectively [ 13, 14, 15]. A collection of

Table 1: Different tissue layers as described by the various studies
Authors Tissue Layers Body Location Reported thickness(mm)
Southwood [ 16] Epidermis Face 0.052
Back 0.065
Dermis Face 2.27
Back 2.36
Whitton & Everall [ 17] Epidermis Cheek 0.039
Upper arm 0.052
Forearm 0.061
Trunk 0.042
Sandby-Moller, Poulsen & Wulf [ 18] Epidermis Forearm 0.075
Shoulder 0.081
Buttock 0.097
Laurent et al. [ 19] Epidermal-Dermal Deltoid 2.09-2.13
Waist 1.9-2.01
Thigh 1.59-1.64
different studies [ 16, 17, 18, 19] reporting on the various thickness of the tissue layer is tabulated on Table 1.

Many studies used animal models for obvious reasons. The wound healing mechanism in human and porcine skins are similar, and thus porcine skin was often used in burn studies [ 20]. A number of studies have created numerical simulations and physically realistic models to enable computational predictions of burn depth using well-established calculation methods, with the most widely used being the Arrhenius equation. Moritz and Henriques demonstrated an inverse relationship between thermal exposure intensity and duration required to produce a burn [ 21].

Time-temperature thresholds at which irreversible epidermal damage occurs is important to identify as it is used in the development of burn-prevention guidelines [ 22, 23]. For example, the results from the works by Moritz and Henriques have been adopted in setting international hot water safety standards. [ 21, 23]

The purpose of this paper is to present a systematic review of the evidence that relates surface temperature and duration of exposure and depth of burn injury. There is international importance of this area of research for societal benefits by improving public burn prevention guidelines, industrial standards and modifying devices to lessen the likelihood of getting burns [ 24, 25]. Burn care teams may also use this data to improve local therapeutic regimens. In clinical settings, a lack of adequate burn history context remains a perpetuating problem. If detailed information about the conditions of the event was available, predicted burn severity would be very useful in guiding management and treatment decisions, and when to refer patients to burn centres. Data on predicted burn injury would also help experts ascertain whether the injury is consistent with the history given, especially in cases of suspected abuse. This data would also aid clinicians in giving medicolegal advice in inflicted burn injury cases, as the duration of exposure causing the burn could be fundamental in deciding the prosecution.

Methods

A comprehensive review of published papers was performed using the electronic databases Web of Science, PubMed, Ovid Medline, PsychInfo and Embase. Articles that were included in the review were published between 1945 to 2018. We looked exclusively at original papers investigating the relationship of time and temperature in the context of depth of burn injuries. An attrition diagram is as depicted on Figure 1.

Figure 1. Attrition of studies

Keywords that were used were “temperature of water”, depth of burn*”, “scald* Injury*”, “duration of exposure”, “predictor of burn* severity”. Depth of injury was categorised as being superficial partial thickness (SPT) burns, mid-dermal burns, deep-dermal burns and full thickness burns. Epidermis only involvement was not included in this review.

Data extraction

Inclusion criteria for the review were all original studies, human studies, animal models, computational numerical models, comparative, non-comparative studies and English language articles. Studies were evaluated for mechanism of burns (contact and hot water scalded only), temperature at which burns was inflicted, duration of exposure and depth of burn injury involved.

Exclusion criteria for the review were duplicates papers, review papers, case reports, conference papers, abstracts only, non-English papers and papers that are not of relevance to the purpose of this review.

Author names, year of study, burn model and outcomes measured and reported in the articles were recorded ( Table 2).

Author Year of Study Burn model Outcomes measured (Yes/No)
Immersion injury Spill/splash burns injury Depth of Injury Time to re-epithelisation Cooling effect
Andrews et al. [ 31] 2017 Porcine Yes Yes Yes Yes No
Johnson et al. [ 13] 2011 Numerical Yes Yes Yes No Yes
Mortiz & Henrique [ 23] 1947 Porcine & Human Yes No Yes No No
Singer et al. [ 27] 2000 Porcine No ( Contact) No Yes No No
Abraham et al. [ 22] 2015 Numerical Yes No Yes No Yes
Medina et al. [ 28] 2018 Murine Yes No Yes No No
Cribbs, Luquette & Besner [ 29] 1998 Murine Yes No Yes Yes Yes
Singh et al. [ 30] 2016 Porcine No ( Contact) No Yes No Yes
Table 2. Outcomes measured by each study reviewed

Study designs, sample size and sample wounds were also included in the review ( Table 3).

Domains
Author Study design Burn model Sample size Sample wounds Clear inclusion criteria  Blinded outcome assessors  Attrition bias Funding bias  Ethical approval Risk of bias
Andrews et al. [ 31] Experimental Porcine 24 115 Yes Yes No No Yes Low
Johnson et al. [ 13] Experimental Numerical 16 16 Yes Unclear No Unclear Unclear High
Mortiz & Henriques [ 23] Comparative, Experimental Porcine and Human Pigs- 179, Human-33 Pigs- 179, Human 33 Yes Unclear No Unclear Unclear High
Singer et al. [ 27] Experimental Porcine 2 18 Yes Yes No No Unclear Low
Abraham et al. [ 22] Comparative, Experimental Computational unclear unclear Yes Unclear Unclear Unclear Unclear High
Medina et al. [ 28] Experimental Murine 8-15 mice unclear Yes No No No Yes Low
Cribbs, Luquette & Besner [ 29] Experimental Murine 47 47 Yes Yes No Yes Yes Low
Singh et al. [ 30] Experimental Porcine Unclear number of pigs 30 Yes Yes No No Yes Low
Table 3. Cochrane risk of bias tool assessment

Due to heterogeneity of each study design, extensive statistical analysis was not possible for this review. However, a curved line of best fit with associated power model equation and goodness of fit measure (R2) were calculated on the time and temperature scattered plot (Figure 2-5). A power model equation is a function with an equation in the form of y= xn, where n is a fraction greater than 0.

Cochrane Risk of Bias Assessment

The Cochrane risk of bias tool was used to investigate the methodology of each study design with direct reference to Higgins & Green (2011)’s Cochrane Handbook for Systematic Reviews of Interventions [ 26]. Study design methodology was examined for inclusion criteria, blinding of assessors, attrition biasness, funding bias, ethical biasness and overall risk of bias. The risk of bias of the study was then classified as ‘low’ or ‘high’ ( Table 3).

Results:

A total of eight studies [ 13, 22, 23, 27, 28, 29, 30, 31] met the inclusion criteria of this study. With adherence to predefined inclusion and exclusion criteria, 10 duplicated studies were removed during preliminary assessment of article titles. Eight other studies that were obtained through scanning of relevant articles were included initially and investigated further for relevance. Forty-four papers unrelated to topic of review, six review papers, three case reports, five conference papers, nine abstract only studies and three non-English papers were removed. Five further studies with no extractable full text were removed as well. According to the risk of bias assessment, five studies had a low risk of bias and three other studies had a high risk of bias. The temperatures as well as their associated durations of exposure were tabulated ( Table 4)

Author Average burn size Superficial-partial burns Mid-dermal burns Deep-partial burns Full thickness
Mechanism of Burn Temperature (℃) Duration of exposure Temperature (℃) Duration of exposure Temperature (℃) Duration of exposure Temperature (℃) Duration of exposure
Andrews et al. [ 31] Hot water scald 17.5 ± 0.7cm2 n/a n/a 50 ≥10 minutes 55 ≥ 5 minutes n/a n/a
55 2 minutes 60 1 minute
60 30 seconds 70 >15 seconds
85 5 seconds
90 5 seconds
Johnson et al. [ 13] Hot water scald n/a 60 7.5-20 seconds n/a n/a 70 20 seconds 60 110 seconds
70 7.5-10 seconds 80 10 seconds 70 110 seconds
80 7.5 seconds 90 7.5-10 seconds 80 20-110 seconds
90 20-100 seconds
Singer et al. [ 27] Contact with heated aluminium rod 2.5 cm x 2.5 cm x 7.5 cm 60 10-30 seconds 70 20 seconds 70 30 seconds 70 30 seconds
70 10 seconds 80 10-20 seconds 80 10-30seconds 90 30 seconds
90 10 seconds 90 20 seconds 100 10-30 seconds
100 10 seconds
Abraham et al. [ 22] Convection coefficient ( Cooling) n/a n/a n/a n/a n/a 63 38 seconds n/a n/a
66 29 seconds
68 23 seconds
71 19 seconds
77 14 seconds
82 11 seconds
88 8.8 seconds
91 7.8 seconds
93 7.2 seconds
Convection Coefficient ( No Cooling) n/a n/a n/a n/a n/a 63 31 seconds n/a n/a
66 23 seconds
68 17 seconds
71 14 seconds
77 10 seconds
82 7.6 seconds
88 5.9 seconds
91 5 seconds
93 4.6 seconds
Medina et al. [ 28] Hot water scald 2x3cm 54 18 seconds n/a n/a 54 20 seconds 54 22 seconds
Cribbs, Luquette & Besner [ 29] Hot water scald 2x3cm n/a n/a n/a n/a n/a n/a 60 45 seconds
Singh et al. [ 30] Contact with heated aluminium rod 7.065 cm2 100 15 seconds 100 20 seconds 100 30 seconds n/a n/a
Table 4. Reported temperature and duration of exposure leading to depth of burns injury according to published literatures

and discussed below. Time and temperature relationship scatter plots for SPT, mid-dermal, deep-dermal and full thickness burns were as depicted in Figures 2,3,4 and 5 respectively.

Temperature and Duration of exposure implicated in Superficial Partial-Thickness (SPT) burns

Based on the available literature on the thickness of the epidermal and dermal layer of various body parts, Johnson et al. [ 13] designed a numerical model to investigate the depth of injury of skin layers in relation to hot water temperature. It was considered that burn beyond 2mm was deemed as full thickness involvement and anything less than 1mm was recognised as superficial partial thickness. The experimental model of 16 burns reported that a water temperature of 60C with a duration of 7.5 seconds to 20 seconds led to the development of superficial partial thickness (SPT) burn injury. A similar depth of scald injury was seen at 70C and 80C with a duration of exposure of 7.5-10 seconds and 7.5 seconds respectively.

Singer et al.’s [ 27] article discussed a two-way experimental model using six different temperatures for three durations of exposures of 10, 20 and 30 seconds on two porcine models. The study utilised a preheated aluminium rod in water temperatures of 50C, 60C, 70C, 80C, 90C and 100C on areas with an average of 2.5 cm by 2.5 cm by 7.5 cm in size. It was reported that at 60C and a contact time of 10-30 seconds there was evidence of superficial partial thickness burns.

An experimental murine study carried out by Medina et al. [ 28] studied the bare area of the mouse that was directly in contact with the hot water without the presence of any air bubbles that may affect the set temperature of 54C. A scoring system was developed from score 1 to 4 with 1 being limited to the epidermis, 2 extending through the epidermis but not beyond the base of the hair follicle, score 3 extending beyond the hair follicle but not through the dermis and score 4 through the dermis into the hypodermis. It was noted that at 54C with a duration of 18 seconds, burn depth was categorised under score 2 which represented a superficial partial thickness burn.

Cribbs, Luquette & Besner’s [ 29] murine model investigated burns inflicted on 47 mice and 47 wounds with an average size of 2 x 3cm. The study utilised temperature of 60°C for 45 seconds followed by cooling in water with a temperature of 4°C for another 45 seconds. It was reported that based on histological evaluation, 69% of the mice had superficial partial thickness burns with the other 11% having mixed partial thickness burns.

Singh et al. [ 30] developed an experimental model using contact from a customized aluminium rod to inflict injury at 100C on the dorsum of pig skin. The article measured burn injury inflicted at different times from 5 seconds to 30 seconds using a constant force of 10 Newtons. It was noted that with a duration of exposure of 15 seconds, the depth of injury observed was at 1.21mm indicating superficial partial thickness burns.

Based on the SPT burn time-temperature scattered plot ( Figure 2), the curved line of best fit equation was noted to be y= 91.212x-0.128. The goodness of fit measure (R2) was equalled to 0.1075 which meant that our data explained 10.75% of the variability of the response data from the mean.

Temperature and Duration of exposure implicated in Mid-dermal burns

Andrews et al. [ 31] in his experimental study on using hot water scald injuries to porcine models reported that 50C, 55C and 60C of water with an exposure time of 10 minutes, two minutes and 30 seconds respectively can cause mid-dermal burns based on wound examinations at day 3 for immersion injury. It was also noted that spill/splash scalds injuries were evident at 75C for 5 seconds with a temperature of 90C being statistically significant (p<0.05) when compared to temperatures between 60-85C.

Under H&E staining, it was noted that dermal parameters were becoming more evident in Singer et al.’s [ 27] study of contact burns on porcine models at when exposed to longer periods. Temperatures of 70C, 80C and 90C, at durations of 20 seconds, 10-20 seconds and 10 seconds respectively recorded a depth of injury of between 1mm to 2mm when measured using an ocular micro-meter indicating mid-dermal involvement. Singh et al. [ 30] reported that the depth of injury was at 1.61mm when the porcine wound was inflicted with a contact burn of 100C with a duration of 20 seconds.

Based on the mid-dermal burn time-temperature scattered plot ( Figure 3), the curved line of best fit equation was noted to be y= 118.66x-0.145. The goodness of fit measure (R2) was equalled to 0.6851 which meant that our data explained 68.51% of the variability of the response data from the mean.

Figure 2. Time-temperature relationship in mid-dermal burns according to published literaturesPower model equation

Temperature and Duration of exposure implicated in Deep partial-thickness (DPT) burns

Further to the experimental study by Andrews et al. [ 31], the article reported on the time and temperature recordings that led to a deeper dermal injury. It was reported that up to 88% of the depth of the dermis was damaged after immersion in 55C of hot water for 5 minutes. Three other immersion temperatures were tested in the report, 70C, 85C and 90C which reportedly cause deep-dermal scalded injuries at 15 seconds, 5 seconds and 5 seconds respectively.

Johnson et al.’s [ 13] numerical model also reported that hot water exposure of 70C, 80C and 90C for a duration of 20 seconds, 10 seconds as well as 7.5-10 seconds respectively produced deep-dermal scald injuries. At 70C, a 20 second exposure yielded a burn 1.2 mm deep which was considered as partial thickness while exposure to a temperature of 80C resulted in injury depth of between 1 mm to 2.3 mm. This was categorised as being deep-dermal.

Singer et al.’s [ 27] study further reported on a series of time and temperature leading to deep-dermal burns. It was reported that temperatures of 70C, 80C, 90C and 100C for a duration of 30 seconds, 10-30 seconds, 20 seconds and 10 seconds led to a significant dermal injury of depth of  2mm, indicating deep dermal involvement.

Abraham et al.’s [ 22] comparative experimental study used a numerical model which applied sophisticated convection coefficients to represent hot water scalding. It was noted that temperatures of 63C, 66C, 68C and 71C for a duration of 38 seconds, 29 seconds, 23 seconds and 19 seconds respectively with cooling led to deep-partial thickness burns. In addition to that, temperatures of 77C, 82C, 88C, 91C and 93C for a duration of 14 seconds, 11 seconds, 8.8 seconds, 7.8 seconds and 7.2 seconds respectively with cooling, also led to evidence of deep partial-thickness burns. Its counterpart study reported a temperature of 63C, 66C, 68C and 71C with a duration of exposure of 31 seconds, 23 seconds, 17 seconds and 14 seconds without cooling led resulted in deep-partial thickness injuries. Additional temperatures were 77C, 82C, 88C, 91C and 93C for a duration of 10 seconds, 7.6 seconds, 5.9 seconds, 5 seconds and 4.6 seconds respectively that led to deep partial-thickness burns. At a temperature of 100C and 30 seconds exposure, Singh et al. [30] article reported a burn depth of 1.91mm indicating deep-partial thickness contact burn.

Based on the DPT burn time-temperature scattered plot ( Figure 4), the line of best fit equation was noted to be y= 113.23x-0.142. The goodness of fit measure (R2) was equalled to 0.5206 which meant that our data explained 52.06% of the variability of the response data from the mean.

Figure 3. Time-temperature relationship in deep-partial burns according to published literatures; Power model equation

Temperature and Duration of exposure implicated in Full Thickness (FT) burn

Johnson et al.’s [ 13] experimental study found that water temperature of 60°C and an exposure duration of 110 seconds led to evidence of skin necrosis due to thermal injury beyond 2mm. In addition to that, water temperature of 70C with a duration of exposure of 110s reported a depth of injury of approximately 4mm and 80C, at 5.9mm which is far beyond the entire dermal layer. However, the relationship between temperature and depth of injury was evident as at 90C, both 20 and 110 seconds resulted in full thickness injuries in their numerical models.

A depth of injury of  2.5mm was noted in Singer et al.’s [ 27] article for contact burns at temperatures of 70C, 90C and 100C, at durations of 30 seconds, 30 seconds and 10-30 seconds respectively. Additionally, the murine study by Medina et al. [ 28] further reported that at 54C paired with a duration of 22 seconds of exposure led to full thickness burns in majority of the mice used in the study.

Based on the FT burn time-temperature scattered plot ( Figure 5), the line of best fit equation was noted to be y= 102.54x-0.077. The goodness of fit measure (R2) was equalled to 0.0923 which meant that our data explained 9.23% of the variability of the response data from the mean.

Figure 4. Time-temperature relationship in full thickness burns according to published literatures; Power model