Topical negative pressure for partial thickness burns
Abstract
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
The objective of this review is to determine whether TNP promotes the healing of partial thickness burns in adults.
Background
Burn injury remains an important source of morbidity and mortality. Every year, approximately two million people are burned, up to 80,000 are hospitalised, and more than 6,500 die in the USA alone (Brigham 1996). A skin burn is damage to the skin caused by heat or other caustic materials like chemicals. The most immediate and obvious injury is one due to heat. Excessive heat causes rapid protein denaturation and cell damage, thereby making the initial event a complex and evolving injury, with both local and systemic consequences ‐ the latter manifesting once the burn area is greater than 20% of the body surface area (BSA) (Sheridan 2002).
Locally, the burn wound tends to extend in the acute phase of the injury secondary to microvascular changes, profound activation of white cells and platelets, and the development of oedema. Many small vessels are directly coagulated by the application of heat, while others will thrombose late and develop tissue dehydration (Boykin 1980). The systemic response to burning is characterised by interstitial oedema in distant organs, secondary to a combination of wound‐released mediators and hypoproteinaemia (Demling 1979; Youn 1992).
Burn wounds are often classified by depth: superficial (1st degree burn), partial thickness (2nd degree burn) or full thickness (3rd degree burn). Often, the depth of injury is diagnosed by the anatomic thickness of the skin involved (i.e. the epidermis [outer thin layer], stratum corneum ['outer most' layer] and the dermis [deepest layer]) and based on either clinical observation, objective assessment, or both. Clinical evaluation often relies on burn wound appearance; blanching, capillary return, presence and degree of fixed capillary staining and evaluation of retained light touch and pinprick sensation. Objective assessment tools such as laser doppler flowmetry, laser doppler imaging or indocyanine green video angiography, may be used to measure tissue perfusion and therefore, depth of burn injury (Demling 2005).
A first degree or superficial burn is confined exclusively to the epidermis or outer surface and is not generally a significant injury, as they heal rapidly and spontaneously. Partial thickness burns involve varying amounts of the dermis, may progress to become deeper, and heal with variable amounts of scarring, dependent in part on the depth of the burn.
Superficial partial thickness burns extend through the epidermis into the papillary, or superficial, layer of the dermis. These wounds become erythematous because the dermal tissue has become inflamed. When pressure is applied to the reddened area, the area will blanch and demonstrate a brisk or rapid capillary refill upon release of the pressure, a hallmark of the superficial partial thickness burn (Demling 2005; Johnson 2003). Thin‐walled, fluid‐filled blisters will develop within minutes of the injury. As these blisters break, the exposed nerve endings transmit the senses of superficial pain, light touch, and temperature, making these wounds extremely painful. The wound will be moist because the characteristic waterproofing of the epidermis has been lost, allowing body fluid to leak on the wound surface. Due to dermal vascular network involvement in this type of injury, moderate edema is usually present (Demling 2005; Johnson 2003).
Deep partial thickness burns extend downward into the reticular, or deeper, layer of the dermis and present as mixed red or waxy white. Areas of redness will continue to blanch when pressure is applied, but capillary refill may be absent or may be sluggish when pressure is released. Blisters are usually absent; however, the exposed surface of the wound is wet or moist, similar to superficial partial thickness burns. Oedema is marked and sensation is altered in areas of a deep partial thickness burn (Demling 2005; Johnson 2003)
Since the biology of wound healing has become better understood many strategies have been developed to try to manipulate this wound healing process (Banwell 1999), and minimize burn wound progression to involve deeper tissue in the acute phase. These range from a variety of dressings such as polyurethane films and hydrocolloids (Wasiak 2005), and skin substitutes to the use of more complex and experimental techniques such as hyperbaric oxygen therapy (Villanueva 2004), growth factors and cytokine biology (Atiyeh 2005).
One way of manipulating the wound environment with a view to promoting healing is to apply topical negative pressure (TNP) across the wound surface, via a dressing (Evans 2001). This negative pressure can induce an interstitial gradient shift which can cause a reduction in oedema, and secondary increase in dermal perfusion, thus aiding in the removal of blood or serous fluid (Banwell 2004). It is postulated that the ability of TNP to produce a mechanical stress or force that has a direct effect in cellular activity and, in particular, angiogenesis, may also contribute to a decrease in burn wound progression. The maintenance of a moist environment which provides optimal conditions for epithelialisation and the prevention of tissue desiccation (Banwell 1999; Banwell 2004) is also potentially advantageous (Pham 2003).
There are a number of names to describe the treatment of a wound with TNP including sub‐atmospheric pressure, vacuum‐sealing technique, sealed surface wound suction vacuum assisted closure, vacuum assisted closure, negative pressure therapy or dressing, foam suction dressing, vacuum compression, vacuum pack technique, negative pressure dressing and foam suction dressing (Banwell 2004). For the purposes of this review this intervention will be referred to as TNP.
The use of TNP in burn wound management has been described by a number of clinicians (Kamolz 2004; Schrank 2004), and TNP is also used to treat donor sites and skin grafts (Moisidis 2004). Given its wide variety use and application in other wound conditions such as ulcers, we plan to summarise the evidence to determine whether TNP is safe, effective and beneficial to those patient with partial thickness burns.
Objectives
The objective of this review is to determine whether TNP promotes the healing of partial thickness burns in adults.
Methods
Criteria for considering studies for this review
Types of studies
All randomised or controlled clinical trials that evaluate the effectiveness of TNP for partial thickness burns.
Types of participants
Trials that include people of either sex, aged over 18 years of age and with a partial thickness burn determined by either clinical evaluation or objective assessment, or both. Clinical evaluation relies on burn wound appearance, blanching, capillary return, presence and degree of fixed capillary staining and evaluation of retained light touch and pinprick sensation. Objective assessment concerns the measurement of tissue perfusion using measuring modalities such as laser doppler flowmetry, laser doppler imaging or indocyanine green (ICG) video angiography.
Types of interventions
Studies will be included where TNP is compared with any alternative burn wound therapy. All modes of delivery of negative pressure including commercially available devices such as (VAC Pump KCI, Texas, USA), wall suction or surgical drainage bottles will be examined as will negative pressure cycles that vary in degree, application (including continuous and/or intermittent pressure cycles) and duration. Where regimens differ significantly between studies, we will state this clearly and discuss the implications.
Types of outcome measures
Primary outcome measures:
time to complete healing,
rate of change in wound area,
proportion of wounds completely healed within the trial period.
Secondary outcomes:
incidence of wound infection;
reported adverse events,
measures of satisfaction or patient preference and quality of life.
Search methods for identification of studies
We will search the following databases:
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Cochrane Central Register of Controlled Trials (CENTRAL, latest issue);
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Cochrane Wounds Group Specialised Register;
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Cochrane Injuries Group Specialised Register;
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MEDLINE (1966 to present);
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EMBASE (1980 to present);
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CINAHL (1982 to present)
The following search strategy will be used for CENTRAL and adapted for the other databases. No language restrictions will apply.
1. VACUUM explode all trees (MeSH)
2. ((negative pressure) near therap*)
3. ((negative pressure) near dressing*)
4. (subatmospheric near pressure) or (sub next atmospheric near pressure)
5. (subatmospheric near dressing*) or (sub atmospheric near dressing*)
6. (topical near negative near pressure)
7. (topical near negative near dressing*)
8. (vacuum near therap*)
9. (vacuum and dressing*)
10. (vacuum near seal*)
11. (vacuum near wound*)
12. (vacuum near closure)
13. (vacuum near pack*)
14. (sealed near surface)
15. vac
16. (wound* near suction*)
17. (suction near drainage*)
18. (vacuum near drainage*)
19. (dressing* near suction)
20. (foam near suction*)
21. (#1 or #2 or #3 or #4 or #5 or #6 or #7 or #8 or #9 or #10 or #11 or #12 or #13 or #14 or #15 or #16 or #17 or #18 or #19 or #20)
22. BURNS explode tree 1 (MeSH)
23. (burn or burns or burned) 2
24. (burn:au or burns:au or burned:au)
25. (#23 and (not #24))
26. (burn:ti or burn:ab or burns:ti or burns:ab or burned:ti or burned:ab)
27. (#24 and #26)
28. (#22 or #25 or #26 or #27)
29. (partial near thickness)
30. (thermal near injur*)
31. (mid next dermal) 2
32. (deep next dermal)
33. (#28 or #29 or #30 or #31 or #32)
34. (#21 and #33)
In addition, we will contact experts in the field of burns and TNP; contact authors of relevant studies to request details of unpublished or ongoing investigations, check relevant available conference proceedings and citations of retrieved studies for further trials.
Data collection and analysis
Trial identification
Titles retrieved by the initial search will be scanned by JW and HC to exclude obviously irrelevant studies. Two authors (JW and HC) will then identify trials that may meet the inclusion criteria. Full‐text articles will be retrieved and reviewed by the authors for the purpose of applying inclusion criteria independently. In all instances, differences of opinion will be resolved by discussion.
Data extraction
Data from the studies will be extracted independently by two authors using standardised forms developed for this review. The following data will be extracted: country of origin; care setting; study design, baseline characteristics of participants by treatment group, inclusion/exclusion criteria, details of intervention and comparison, outcome measures and results. Primary authors will be contacted to provide information if missing data are encountered or if necessary data, such as adverse events, are not clearly stated. All differences will be resolved by discussion among the authors.
Quality assessment
Study quality will be assessed by two authors (JW and HC) based on the method outlined in Schulz 1995. In all instances, differences of opinion will be resolved by discussion. Results from the study quality will be presented in a descriptive manner. The following characteristics will be assessed:
Adequacy of the randomisation process:
Trials will be awarded the following grades for adequacy of the randomisation process:
A = Adequate sequence generation is reported using random number tables, computer random number generator, coin tossing, or shuffling.
B = Did not specify one of the adequate reported methods in (A) but mentioned randomisation method.
C = Other methods of allocation that may not be random.
Adequacy of the allocation concealment process:
Trials will be awarded the following grades for allocation concealment:
A = Adequate: a randomization method described that would not allow an investigator/participant to know or influence an intervention group before an eligible participant entered the study, such as central randomisation; serially numbered, opaque, sealed envelopes.
B = Unclear: trial states that it is 'randomized', but no information on the method used is reported or a method is reported that was not clearly adequate.
C = Inadequate: inadequate method of randomization used, such as alternate medical record numbers or unsealed envelopes; or any information in the study that indicated that investigators or participants could influence the intervention group.
Minimal potential for selection bias after allocation:
A = Yes: Specifically reported by authors that ITT was undertaken and this was confirmed on study assessment, or not stated but evident from study assessment that ITT was undertaken
B = Unclear. Reported but unable to confirm on study assessment, or not reported and unable to confirm by study assessment.
C = No: Lack of ITT confirmed on study assessment (Patients who were randomised were not included in the analysis because they did not receive the study intervention, they withdrew from the study or were not included because of protocol violation) regardless of whether ITT reported or not
Completeness of follow‐up:
Percentage of participants for whom data was complete at defined study end‐point
Level of masking (treatment provider, patient, outcome assessor):
It is unlikely due to the nature of the intervention that trials will be able to blind the patient or treatment provider, therefore the level of masking for trials will be rated as follows:
A = Trials which report any blinding of either outcome assessor (most likely) or treatment provider or patient (less likely)
B = Unclear whether any blinding was undertaken
C = Blinding not undertaken
Data Analyses
We will assess statistical heterogeneity using the I2 statistic and give consideration to the appropriateness of pooling and meta‐analysis based on the amount of statistical and clinical heterogeneity. We will use a fixed effect model where there is no evidence of significant heterogeneity between studies (I2 less than 40%), and employ a random effects model when such heterogeneity is likely (DerSimonian 1986; Higgins 2003).
For proportions (dichotomous outcomes), we will present the relative risk (RR) and corresponding 95% confidence intervals (CI) for each study. For continuous outcomes we will present the mean difference and corresponding 95% CI for each study. Where appropriate, the pooled WMD will be calculated using the inverse variance method. Time‐to‐event data will be analysed using survival analysis with the treatment effect expressed as a hazard ratio.
Where appropriate, we will explore heterogeneity and perform subgroup analyses based on the type of burn injury i.e. superficial or deep partial thickness burn. Subgroup analysis will be done by calculation of relative risk (RR) or weighted mean difference (WMD) in each subgroup and examination of the 95% confidence intervals. We will take non‐overlap in intervals to indicate a statistically significant difference between subgroups. We will make all analyses on an intention‐to‐treat basis where possible, and where not possible we will state this clearly.
We will explore publication bias using funnel plots or other corrective analytical methods, depending on the number of clinical trials included in the systematic review.
