- Email: [email protected]
Timing of the thermographic assessment of burns
Burn.5 Vol. 22, No. 1, pp. a-28. 19% Copyright (Q 1995 Elsevier Science Ltd for ISBI Printed in Great BritakAll rights reserved 0305-4179196 $15.00 + 0 00 ELSEVIER
0305-4179(95)00076-3
M. I. Liddington
and P. G. Shakespeare
Wessex Regional Bums Unit and Department UK
of Plastic and Maxillofacial
The fhermographic assessment of burns using infrared imaging has previously been shown to be a useful aid in the estimation of burn depth. In this study, fhermographic images of bums, obfained from 65 pafienfs over a d-year period, were reviewed. An infrared transparent, wafer-impermeable membrane wan used as a wound cover fo abolish evaporative cooling artefacfs. Single images were obtainedfrom patients wifh bums fo various parts of the body, excluding the hands. A significanf change in the temperature 01 deep burns was observed between days 2 and 3 after injury (chi-square, P < 0.01; Fisher exacf probabilify tesf between days2 and 3, P < 0.07). The results of this study suggest that thermography of burns, fo assessdepth, should be performed within 3 days following the injury.
Bums, Vol. 22, No. 1, 26-28,
1996
Introduction Thermographic imaging hasbeen widely used for medical conditions characterized, at least in part, by changes in localized skin blood flowI-‘. The thermographic camera detects the intensity of emitted infrared radiation from the surface of a radiating body. When used in the assessment of bums, detected infrared radiation is related to the cutaneous blood flow in the surface of the wound and indirectly gives information relating to burn depth. Thermography of bum wounds was first reported in 1966’ but, as with many of the early studies, was complicated by evaporative cooling artefacts. Hackett overcame this problem by allowing the burn to dry and showed that thermography was superior to clinical examination in estimating bum depth9. More recently, using a novel method to abolish evaporative cooling, Cole et al. showed that, in hand bums, a surface temperature of less than 31°C indicated a deep partial-thickness bum which required excision and skin grafting“‘. Admissions to a bums unit are unpredictable and the general condition of a patient may interfere with the accurate interpretation of a thermographic image. In some casesdressingsmay be applied before the opportunity for thermography arises.This, in conjunction with the policy of most burns
units to treat bums with
closed
dressings,
may mean that the earliest practical opportunity for thermography is 48 h following injury. Therefore, this initial study examined whether or not thermographic
Surgery, Salisbury General Hospital, Wiltshire,
information relating to bum depth was lost with time after injury, and determined whether or not thermography could have predicted those wounds which subsequently required surgery. Our results showed that deep wounds appeared cool for 3 days after injury, but after this time all thermographic information relating to bum depth was lost.
Methods Single thermographic images of bum wounds to 65 patients from a a-year period were reviewed. Clinical information relating to the depth of burn and subsequent treatment received, including bum excision and skin grafting, was collected from the patients’ records. The area and site of the bum and the need for resuscitation were also recorded. Using a water-impermeable, infrared transparent membrane to abolish evaporative cooling artefactsr’, thermography was performed in environment-controlled cubicles within the Wessex Bums Unit. Images were made using the Agema systemsAGA 782 scannercoupled to a digital image processing system (Agema Systems, Leighton Buzzard, UK). In addition to recording the bum wound temperature, a comparison was made between the temperature of the bum and that of the surrounding normal skin, In all cases,thermographic images were recorded before any excision and grafting had taken place, and no fully healed wounds were included. Hand bums were not included in this study. Statistical analysesof the relationship between thermographic characteristics and recorded clinical behaviour of the burn wound were made using chi-square and Fisher exact probability tests on data arranged -in contingency tables.
Results A total of 65 thermographic images were reviewed in patients (37 men and 28 women), with- an average age of 22 years (range I-48 years). The average body surface area burned was 10.5 per cent (range 0.545 per cent), and the areasof the body studied are shown in TabZeI. Almost all of the partial-thickness wounds, which healed spontaneously, were found to be warmer than the surrounding skin (2~931) regardless of the time between injury and thermographic assessment (Figurelb). The deeper wounds, which subsequently required excision and
Liddington
and Shakespeare:
Timing
of the thermographic
assessment
skin grafting, were initially cooler than the surrounding skin (11112 wounds appeared cooler in the first 3 days: TableII). However, 3 days following injury these wounds underwent a significant change in their thermographic appearance(Figurela) and becameeither the sametemperature as the surrounding skin or warmer (IS/Z wounds appeared warmer after 3 days. Chi-square P< 0.01; Fisher exact probability test between days 2 and 3 P< 0.01: Table II). There was no absolute surfacetemperature which indicated those burns which subsequentlyrequired surgical treatment. Table1 Anatomical distribution thermography in the study
Position
of bum wounds
studied by
Patients 0-d
of burn
Trunk and groin Head and neck Arm Leg Feet
20 4 19 17 5
Total
65
$
a.)
of bums
27
Discussion Thermography was first demonstrated to be potentially useful in estimating depth of bum injury when fullthickness bums*were shown to be cooler than partialthicknessbums”. In these early studies,evaporation from a wound surfacedistorted the thermographic assessmentof bum depth, and both superficial and deep bums appeared proportionately cooler as a result1”813. Some investigators abrogated the effects of evaporation by spraying all wounds with water”. Hackett9 overcame this problem by allowing the bum to dry before recording the thermographic image. Using this technique he demonstrated that thermography was superior to clinical examination estimating bum depth9. The present trend of excising and grafting bums considered unlikely to heal well spontaneously demandsan accurate assessmentof bum depth soon after injury. The chief problem for thermographic assessmentof bums has, in the past, been the delay necessary to allow the bum to dry. It has recently been shown that evaporative cooling artefacts can be abolished by covering the wound with an infrared transparent, water-impermeable membrane(Clingfilm@,or a polythene bag)l.
Excised and skin-grafted
b.)
Spontaneously
healed
6 127 n
1 10 5 8 16 8 sf
4
1
-20
2
m -4 3 E
-6 I,
I I 0123456
I
1
I
-6
I
---r-r0123456
0
Days after injury
it
Figure I. Temperature
Days after injury
difference distribution
between bum wound and surrounding
unburned
skin.
Table11 Number of wounds and their thermographic appearance relative to the surrounding unburned skin (n= 65). A significant change in relative temperature occurred between days 2 and 3 in the group which required excision and grafting (&-square P< 0.01; Fisher exact probability test P< 0.01). There was no difference in the distribution of relative wound temperature in burns that healed spontaneously Days after injury
Excised and grafted Warmer Cooler Spontaneously healed Warmer Cooler
0
1
2
3
4
5
6+
0 4
1 3
0 4
5 0
4 2
1 0
8 2
8 2
5 0
10 1
1 0
2 0
1 0
1 0
28
The results of this study show that, if evaporative cooling artefacts are abolished, thermography is very useful in estimating bum depth within the first 3 days following injury. Initially, the wounds that required excision and grafting appeared cooler as a result of the destruction of dermal blood vessels, but after 3 days a significant change occurred and the wounds appeared warmer in comparison with surrounding unburned skin. This warming was possibly the result of vascular ingrowth in order to produce fibrous and granulation tissue, leading to the poorly healed, unsightly scarsfound with deeper bums. Almost all of the wounds which healed spontaneously were warmer than the surrounding skin on each day following burn injury, suggesting the presenceof an intact cutaneous circulation. However, in this preliminary study we have not examined any relationship between thermographic appearanceand the development of hypertrophic scarring in burn wounds. These findings do not contradict those of Hackettg, but simply reflect the different conditions under which observations were made. Deep bum wounds, not covered by polythene, appear cool by thermography after injury’. This reflects the continued evaporative cooling from the wound and then through the dried eschar. Conversely, similarly uncovered superficial bums appear cool on initial examination due to evaporative heat loss over a moist surface but then appear to warm aS the exudate dries and ‘seals’ the wound against evaporative cooling. In this study, by using a water-impermeable membrane we were able to show warming of deep partial-thickness bums after 3 days and that superficial bums appearedwarm at all times after injury. Whilst in the hand the absolute temperature of the burn appears to be a reliable guide to the prognosis of clinical outcome’O, this hasnot been establishedfor bums to other areasof the body. From our results we can conclude that the most accurate per&d for the thermographic assessment of bum depth is within the first 3 days following injury, often the most difficult time to assess bum depth clinically. It may be possible to predict within this period, by thermography, which bums will require excision and grafting. This information may enable the clinician to plan thermographic assessmentof bums after stabilization of the patient and in accordance with the bum-dressing regimen employed within the bums unit. Further studies will follow bum wounds prospectively in order to determine the thermographic appearance of bums considered likely to heal spontaneously, but which subsequently form hypertrophic scars.
Burns: Vol. 22, No. 1, 1996
References 1 Akerman S, Kopp S.Intra-articularand skin surfacetemperature of the tempera-mandibularjoint in patients with rheumatoid arthritis. Acts Odontol Stand 1988; 46: 4J-48. 2 Emery G, Jones J, Brown M. Clinical application of infrared thermography in the diagnosis of appendicitis. Am ; Emerg Med 1994;12:48-50. 3 Greenstein D, Brown TF, Kester RC. Assessment of chemical lumbar sympathecfomy in critical limb ischaemia using thermal imaging.lnt] Ch Monitor Compuf1994; 11: 3 J-34 4 McCollum PT, Spence VA, Walker WF. Amputation frt; peripheral vascular disease: the caseFor level selection.Br i Surg1988; 75:1193-1795. 5 Mordon S, Beacco C. Rotteleur G et ai. Relation between skin surface temperature and minimal blanching during argon, Nd-YAG 532, and CW dye 585 iaser therapy o’i port-wine stains. Lasers Surg Med 1993; 13: 124- 126. 6 Rosenblum JA, Cohen JM, Lee M. Hyperhidrosis - a case history. Angiology 1994; 45: 61.-64. 7 Sepey M, Hessler C, Bruchez M et al. Faclat thermography during nasal provocation tests with histamine and allergen. Allergy 1993;48:314-318. 8 Mladick R, Georgiade N, Thome F. A ciinical evaluation oi the use of thermography in determining the depth of bum injury. Plast Reconstr surg 1966; 38: 512..-518. 9 Hackett MEJ. The use of thermography in the assessment ni bum and blood supply of flaps, with preliminary reports or: its use in Dupuytrenscontractureandtreatment of varicose ulcers.Br ] Plast Surg 1974; 2 7: 3 I 1-3 i i. I@ Cole RP, Jones SG, Shakespeare PG. Thermographic assessment of hand bums. Bcrrns 1990; 16: 60-63. 11 Cole RP, Shakespeare PG, Chissell HG et al. Thermographlc assessment of burns using a non-permeable membrane as wound covering. Burns 1991: 17: 117-i22, 12 Watson ACH, Vasilescu C. Thermography in plastic surgery ]R Co11Surg Edinb 1972; 17: 247-252. 13 Anselmo VJ, Zawacki BE. Effect of evaporative surface cooling on thermographic assessment of bum depth. Radiology1977;123:331-332. 14 Newman P, Pollock M, Reid WH et al. A practical technique for the thermographic estimation of bum depth: a preliminary report. Bums 1981; 8: 59--63.
Paper accepted after revision 16 May 19%.
Acknowledgements We would like to thank the staff of the Wessex Bums Unit for their help and Mr L. F.A. Rossifor allowing us to study his patients.
Correspondence should be addressed to: Dr P. G. Shakespeare,
WessexRegionalBumsUnit, SalisburyGeneralHospital,Salisbury, Wiltshire
SP2 8BJ, UK.
0305-4179(95)00076-3
M. I. Liddington
and P. G. Shakespeare
Wessex Regional Bums Unit and Department UK
of Plastic and Maxillofacial
The fhermographic assessment of burns using infrared imaging has previously been shown to be a useful aid in the estimation of burn depth. In this study, fhermographic images of bums, obfained from 65 pafienfs over a d-year period, were reviewed. An infrared transparent, wafer-impermeable membrane wan used as a wound cover fo abolish evaporative cooling artefacfs. Single images were obtainedfrom patients wifh bums fo various parts of the body, excluding the hands. A significanf change in the temperature 01 deep burns was observed between days 2 and 3 after injury (chi-square, P < 0.01; Fisher exacf probabilify tesf between days2 and 3, P < 0.07). The results of this study suggest that thermography of burns, fo assessdepth, should be performed within 3 days following the injury.
Bums, Vol. 22, No. 1, 26-28,
1996
Introduction Thermographic imaging hasbeen widely used for medical conditions characterized, at least in part, by changes in localized skin blood flowI-‘. The thermographic camera detects the intensity of emitted infrared radiation from the surface of a radiating body. When used in the assessment of bums, detected infrared radiation is related to the cutaneous blood flow in the surface of the wound and indirectly gives information relating to burn depth. Thermography of bum wounds was first reported in 1966’ but, as with many of the early studies, was complicated by evaporative cooling artefacts. Hackett overcame this problem by allowing the burn to dry and showed that thermography was superior to clinical examination in estimating bum depth9. More recently, using a novel method to abolish evaporative cooling, Cole et al. showed that, in hand bums, a surface temperature of less than 31°C indicated a deep partial-thickness bum which required excision and skin grafting“‘. Admissions to a bums unit are unpredictable and the general condition of a patient may interfere with the accurate interpretation of a thermographic image. In some casesdressingsmay be applied before the opportunity for thermography arises.This, in conjunction with the policy of most burns
units to treat bums with
closed
dressings,
may mean that the earliest practical opportunity for thermography is 48 h following injury. Therefore, this initial study examined whether or not thermographic
Surgery, Salisbury General Hospital, Wiltshire,
information relating to bum depth was lost with time after injury, and determined whether or not thermography could have predicted those wounds which subsequently required surgery. Our results showed that deep wounds appeared cool for 3 days after injury, but after this time all thermographic information relating to bum depth was lost.
Methods Single thermographic images of bum wounds to 65 patients from a a-year period were reviewed. Clinical information relating to the depth of burn and subsequent treatment received, including bum excision and skin grafting, was collected from the patients’ records. The area and site of the bum and the need for resuscitation were also recorded. Using a water-impermeable, infrared transparent membrane to abolish evaporative cooling artefactsr’, thermography was performed in environment-controlled cubicles within the Wessex Bums Unit. Images were made using the Agema systemsAGA 782 scannercoupled to a digital image processing system (Agema Systems, Leighton Buzzard, UK). In addition to recording the bum wound temperature, a comparison was made between the temperature of the bum and that of the surrounding normal skin, In all cases,thermographic images were recorded before any excision and grafting had taken place, and no fully healed wounds were included. Hand bums were not included in this study. Statistical analysesof the relationship between thermographic characteristics and recorded clinical behaviour of the burn wound were made using chi-square and Fisher exact probability tests on data arranged -in contingency tables.
Results A total of 65 thermographic images were reviewed in patients (37 men and 28 women), with- an average age of 22 years (range I-48 years). The average body surface area burned was 10.5 per cent (range 0.545 per cent), and the areasof the body studied are shown in TabZeI. Almost all of the partial-thickness wounds, which healed spontaneously, were found to be warmer than the surrounding skin (2~931) regardless of the time between injury and thermographic assessment (Figurelb). The deeper wounds, which subsequently required excision and
Liddington
and Shakespeare:
Timing
of the thermographic
assessment
skin grafting, were initially cooler than the surrounding skin (11112 wounds appeared cooler in the first 3 days: TableII). However, 3 days following injury these wounds underwent a significant change in their thermographic appearance(Figurela) and becameeither the sametemperature as the surrounding skin or warmer (IS/Z wounds appeared warmer after 3 days. Chi-square P< 0.01; Fisher exact probability test between days 2 and 3 P< 0.01: Table II). There was no absolute surfacetemperature which indicated those burns which subsequentlyrequired surgical treatment. Table1 Anatomical distribution thermography in the study
Position
of bum wounds
studied by
Patients 0-d
of burn
Trunk and groin Head and neck Arm Leg Feet
20 4 19 17 5
Total
65
$
a.)
of bums
27
Discussion Thermography was first demonstrated to be potentially useful in estimating depth of bum injury when fullthickness bums*were shown to be cooler than partialthicknessbums”. In these early studies,evaporation from a wound surfacedistorted the thermographic assessmentof bum depth, and both superficial and deep bums appeared proportionately cooler as a result1”813. Some investigators abrogated the effects of evaporation by spraying all wounds with water”. Hackett9 overcame this problem by allowing the bum to dry before recording the thermographic image. Using this technique he demonstrated that thermography was superior to clinical examination estimating bum depth9. The present trend of excising and grafting bums considered unlikely to heal well spontaneously demandsan accurate assessmentof bum depth soon after injury. The chief problem for thermographic assessmentof bums has, in the past, been the delay necessary to allow the bum to dry. It has recently been shown that evaporative cooling artefacts can be abolished by covering the wound with an infrared transparent, water-impermeable membrane(Clingfilm@,or a polythene bag)l.
Excised and skin-grafted
b.)
Spontaneously
healed
6 127 n
1 10 5 8 16 8 sf
4
1
-20
2
m -4 3 E
-6 I,
I I 0123456
I
1
I
-6
I
---r-r0123456
0
Days after injury
it
Figure I. Temperature
Days after injury
difference distribution
between bum wound and surrounding
unburned
skin.
Table11 Number of wounds and their thermographic appearance relative to the surrounding unburned skin (n= 65). A significant change in relative temperature occurred between days 2 and 3 in the group which required excision and grafting (&-square P< 0.01; Fisher exact probability test P< 0.01). There was no difference in the distribution of relative wound temperature in burns that healed spontaneously Days after injury
Excised and grafted Warmer Cooler Spontaneously healed Warmer Cooler
0
1
2
3
4
5
6+
0 4
1 3
0 4
5 0
4 2
1 0
8 2
8 2
5 0
10 1
1 0
2 0
1 0
1 0
28
The results of this study show that, if evaporative cooling artefacts are abolished, thermography is very useful in estimating bum depth within the first 3 days following injury. Initially, the wounds that required excision and grafting appeared cooler as a result of the destruction of dermal blood vessels, but after 3 days a significant change occurred and the wounds appeared warmer in comparison with surrounding unburned skin. This warming was possibly the result of vascular ingrowth in order to produce fibrous and granulation tissue, leading to the poorly healed, unsightly scarsfound with deeper bums. Almost all of the wounds which healed spontaneously were warmer than the surrounding skin on each day following burn injury, suggesting the presenceof an intact cutaneous circulation. However, in this preliminary study we have not examined any relationship between thermographic appearanceand the development of hypertrophic scarring in burn wounds. These findings do not contradict those of Hackettg, but simply reflect the different conditions under which observations were made. Deep bum wounds, not covered by polythene, appear cool by thermography after injury’. This reflects the continued evaporative cooling from the wound and then through the dried eschar. Conversely, similarly uncovered superficial bums appear cool on initial examination due to evaporative heat loss over a moist surface but then appear to warm aS the exudate dries and ‘seals’ the wound against evaporative cooling. In this study, by using a water-impermeable membrane we were able to show warming of deep partial-thickness bums after 3 days and that superficial bums appearedwarm at all times after injury. Whilst in the hand the absolute temperature of the burn appears to be a reliable guide to the prognosis of clinical outcome’O, this hasnot been establishedfor bums to other areasof the body. From our results we can conclude that the most accurate per&d for the thermographic assessment of bum depth is within the first 3 days following injury, often the most difficult time to assess bum depth clinically. It may be possible to predict within this period, by thermography, which bums will require excision and grafting. This information may enable the clinician to plan thermographic assessmentof bums after stabilization of the patient and in accordance with the bum-dressing regimen employed within the bums unit. Further studies will follow bum wounds prospectively in order to determine the thermographic appearance of bums considered likely to heal spontaneously, but which subsequently form hypertrophic scars.
Burns: Vol. 22, No. 1, 1996
References 1 Akerman S, Kopp S.Intra-articularand skin surfacetemperature of the tempera-mandibularjoint in patients with rheumatoid arthritis. Acts Odontol Stand 1988; 46: 4J-48. 2 Emery G, Jones J, Brown M. Clinical application of infrared thermography in the diagnosis of appendicitis. Am ; Emerg Med 1994;12:48-50. 3 Greenstein D, Brown TF, Kester RC. Assessment of chemical lumbar sympathecfomy in critical limb ischaemia using thermal imaging.lnt] Ch Monitor Compuf1994; 11: 3 J-34 4 McCollum PT, Spence VA, Walker WF. Amputation frt; peripheral vascular disease: the caseFor level selection.Br i Surg1988; 75:1193-1795. 5 Mordon S, Beacco C. Rotteleur G et ai. Relation between skin surface temperature and minimal blanching during argon, Nd-YAG 532, and CW dye 585 iaser therapy o’i port-wine stains. Lasers Surg Med 1993; 13: 124- 126. 6 Rosenblum JA, Cohen JM, Lee M. Hyperhidrosis - a case history. Angiology 1994; 45: 61.-64. 7 Sepey M, Hessler C, Bruchez M et al. Faclat thermography during nasal provocation tests with histamine and allergen. Allergy 1993;48:314-318. 8 Mladick R, Georgiade N, Thome F. A ciinical evaluation oi the use of thermography in determining the depth of bum injury. Plast Reconstr surg 1966; 38: 512..-518. 9 Hackett MEJ. The use of thermography in the assessment ni bum and blood supply of flaps, with preliminary reports or: its use in Dupuytrenscontractureandtreatment of varicose ulcers.Br ] Plast Surg 1974; 2 7: 3 I 1-3 i i. I@ Cole RP, Jones SG, Shakespeare PG. Thermographic assessment of hand bums. Bcrrns 1990; 16: 60-63. 11 Cole RP, Shakespeare PG, Chissell HG et al. Thermographlc assessment of burns using a non-permeable membrane as wound covering. Burns 1991: 17: 117-i22, 12 Watson ACH, Vasilescu C. Thermography in plastic surgery ]R Co11Surg Edinb 1972; 17: 247-252. 13 Anselmo VJ, Zawacki BE. Effect of evaporative surface cooling on thermographic assessment of bum depth. Radiology1977;123:331-332. 14 Newman P, Pollock M, Reid WH et al. A practical technique for the thermographic estimation of bum depth: a preliminary report. Bums 1981; 8: 59--63.
Paper accepted after revision 16 May 19%.
Acknowledgements We would like to thank the staff of the Wessex Bums Unit for their help and Mr L. F.A. Rossifor allowing us to study his patients.
Correspondence should be addressed to: Dr P. G. Shakespeare,
WessexRegionalBumsUnit, SalisburyGeneralHospital,Salisbury, Wiltshire
SP2 8BJ, UK.