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Randomized controlled trial of the absorbency of four dressings and their effects on the evaporation of burn wounds

CHEN, Jiong; HAN, Chun-mao; SU, Guo-liang; TANG, Zhi-jian; SU, Shi-jie; LIN, Xiao-wei

Original article
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Background Wound dressings are divided into traditional and new types. The new dressings are thought to accelerate wound healing. The purpose of this study was to supplement the scanty data on the absorbency of the new dressings and their effects on evaporation from the burn surface.

Methods The water absorption rate of four dressings (carbon fiber dressing, hydrogel dressing, silver nanoparticle dressing, and vaseline gauze) were measured by the immersion-weight gain method. A total of 120 inpatients with 10% superficial partial-thickness burn wounds were randomly assigned to four groups, each with 30 participants. Carbon fiber dressing, hydrogel dressing, and silver nanoparticle dressing were used in groups A, B, and C as the primary dressing, and traditional vaseline gauze was used in group D as the control. Multi-spot evaporation from normal skin and naked wound, and from wounds covered with each of the four dressings was measured post-burn on days 1, 3, 5, and 7 by an EP-I evaporimeter under conditions of 21°C −22°C ambient temperature and 74%-78% humidity.

Results The absorption rates of the four dressings were 988% with carbon fiber dressing, 96% with silver nanoparticle, 41% with vaseline gauze, and 6% with hydrogel. Evaporation from the naked burn wounds was about 1/3 higher than from normal skin (P<0.01). Compared with wounds without applied dressing, evaporation from dressed wounds decreased and was time-dependent (P<0.01). The evaporation of wounds with carbon fiber dressing was the lowest ((13.40 ± 2.82) ml·h−1·m−2, P<0.01) on day 1 post-burn, compared with the other groups.

Conclusion All four dressings have water retention capacity while carbon fiber dressing has the highest absorption rate and shows the best containment and evaporation from the burn wound.

Department of Burn Surgery, Thrid Affiliated Hospital of Wenzhou Medical College, Wenzhou 325200, China (Chen J, Su GL, Tang ZJ, Su SJ and Lin XW)

Department of Burn Surgery, Second Affiliated Hospital, Medical College of Zhejiang University, Hangzhou 310006, China (Han CM) Correspondence to: Dr. HAN Chun-mao, Department of Burn Surgery, Second Affiliated Hospital, Medical College of Zhejiang University, Hangzhou 310006, China (Email: hanchunmao1@126.com)

(Received March 21, 2007) Edited by LUO Dan

Nowadays, around half of all dressings used in wound care worldwide are still traditional gauze dressings. It has been known for some years that new dressings, which are mainly wet dressings, can accelerate wound healing. Most new dressings have supporting scientific data on their water absorption rate, air permeability and water transmission rate in vitro under standard conditions of 37°C temperature and 20% humidity. However, in the clinical environment temperature and humidity will vary widely, and the microenvironment will obviously influence the effects of the dressing on wound healing, especially in locations with high humidity.

It is therefore necessary to know the water absorption rates of wound dressings and their effects on the evaporation of burn wounds under actual clinical conditions. In this study we measured the water absorption rates of four dressings and their effects on water evaporation from burn wounds through a highly sensitive EP-I evaporimeter and under conditions of 21°C −22°C ambient temperature and 74%-78% humidity, these being similar to the conditions found in air-conditioned wards in summer.

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METHODS

Design

This was a four-arm randomized controlled clinical trial. The trial was sponsored by the Second Hospital of the Medical College of Zhejiang University, and ethical approval and academic supervision were provided by the Third Hospital of Wenzhou Medical College.

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Materials

We used, firstly, a carbon fiber dressing (Shangansu dressing, provided by Beijing Aoerkang Scientific Developing Co. Ltd. [Registration No: {Jing Yao Guan Xie} 2002 No. 2640237]); secondly, hydrogel dressing (Baikangfuning, provided by Hangzhou Baikang Company [Registration No: {Zhe Yao Guan Xie} 2004 No. 2640155]); and thirdly, silver nanoparticle dressing (provided by Shenzhen Anson Nanometer Scientific Co. Ltd. [Registration No: {Yue Yao Guan Xie} 2000 No. 2640015, {Yue Wei Yong} No. 0680]). In the control group we used vaseline gauze (provided by Zhejiang Shaoxing Zhende Medical Dressing Co. Ltd. [Registration No. {Zhe Yao Guan Xie} 2003 No 2640076]).

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Measurement of absorbency

We determined the water absorption rate of the dressings by the immersing weight method in vitro.1 We put a 100 cm2 sample of the dressings in water (25°C) in a square plate for 5 minutes, then took the dressings out of the water for 1 minute, and weighed them in a balance with 0.2 g gradations (balance made by the Shanghai Balance Machine Factory, Shanghai Precision & Scientific Instrument Co. Ltd.). We repeated this 10 times and calculated the average values. We calculated absorption rates by the formula: Absorption rate (C%) = (Wb-Wa)/Wa × 100%, where Wa and Wb were the weight of the dressings before and after immersion in water.

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Inclusion criteria

The trial was conducted from May 2005 to November 2006 and eligible participants were all inpatients with burns who met the following criteria. Patient admitted to hospital within 24 hours after the burn, 18-65 years old, male or female, with partial thickness burn wounds (TBSA <10%) and with no electronic or chemical wounds, or wounds caused by some other reasons. All patients were to give signed informed consent.

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Withdrawals

During the trial, any participant was withdrawn who no longer met the inclusion criteria, who revoked informed consent, and asked to be withdrawn from the trial (or had a relative ask on their behalf), had poor clinical compliance, had obviously abnormal laboratory data switched to an alternative dressing because of adverse events, or developed a serious infection.

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Randomization method

One hundred and twenty patients were randomly assigned by a computer-generated random sequence to four equal-sized groups, each group having an assigned treatment code. Carbon fiber dressing was used in group A, hydrogel dressing in group B, silver nanoparticle dressing in group C, and vaseline gauze in group D.

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Clinical management

The burn wounds were covered with the assigned dressing after being routinely cleaned with saline. Twelve layers of gauzes were then applied over each dressing and the dressing was changed daily.

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Measurement of evaporation

A highly sensitive EP-I evaporimeter (Servomed Evaporimeter, Sweden) was used to measure multi-spot evaporation of normal skin and of burn wounds before and after being covered with dressing. Post-burn measurements were made on days 1, 3, 5, and 7. A high-precision manostat was used during the measurements, after allowing 15 minutes for the warming of the instrument and adjusting to zero. In accordance with the manufacturer's instructions, the ambient temperature during the measurements was maintained at 21°C −22°C and humidity was maintained at 74%-78%, the body temperature of the patients was normal and the patients were calm. In addition there were no marked flows of air in the measuring room.

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Statistical analysis

The quantitative data were recorded as mean ± standard deviation (SD) and were analyzed with the ANOVA or the Kruskal-Wallis test. Qualitative data were analyzed with chi-square test. SPSS 10.0 was used. We assumed statistical significance when P<0.05.

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RESULTS

Patient demographics

There were no statistically significant differences in the baseline characteristics of the four patient groups, as shown in Table 1.

Table 1

Table 1

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Absorption rates of the four dressings

The absorption rates (C%) by weight of dressing per 100 cm2 before and after immersion in water were calculated. As shown in Table 2, they were 988% (carbon fiber dressing), 96% (silver nanoparticle dressing), 41% (vaseline gauze) and 6% (hydrogel dressing).

Table 2

Table 2

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Evaporation of normal skin and post-burn wounds

Between the four groups there were no statistically significant differences by ANOVA testing in the multi-spots evaporation measurements of post-burn wounds on days 1, 3, 5, and 7 (P>0.05). However, compared to normal skin, the evaporation of partial thickness wounds was increased by 1/3. The evaporation of partial thickness wound with applied dressing on day 1 post-burn was less than 1/2 that of naked wound (P<0.01). Compared to groups B, C, and D on day 1, the evaporation of the wound in group A (carbon fiber dressing) was statistically significant lower (P<0.01). The temperatures were (21.42 ± 0.44)°C, (21.30 ± 0.39)°C, (21.27 ± 0.37)°C and (21.45 ± 0.40)°C and the humidities were (77.50 ± 0.86)%, (77.37 ± 1.07)%, (77.47 ± 0.97)% and (77.57 ± 0.37)% on days 1, 3, 5, and 7 respectively. There were no statistically significant differences among the four groups (P>0.05) (Table 3).

Table 3

Table 3

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DISCUSSION

Generally speaking, new dressings have a higher water-retention capacity than traditional gauze (dry gauze) dressings, and are better at preventing water evaporation from the wound. They provide an acidic and moist microenvironment for the wound through their sealing and water-retention properties, thus promoting the breakdown of necrotic tissue, fibroblast proliferation, growth of granulation tissue and re-epithelization so as to accelerate wound healing.2

In 1963 Winter et al3 showed in Nature that epithelium cells migrate and proliferate faster in a moist environment. Twenty years later, new dressings that could keep the wound moist emerged on the overseas market, hydrogel dressing being one of the most important.4,5 Its main ingredient polyurethane, has good biological compatibility and can alleviate pain and promote wound healing without damaging or leaving fibers in the wound; in addition, hydrogel has good absorption and water-retention capacity.6 The antibiotic effect of silver has long been valued in dressings7 and has shown good results. When new silver dressings was used on burn patients, the residual silver in the blood and urine of the patients has been determined by graphite furnace atomic absorption spectrometry, and has been thought to be safe.8,9 When used in burn wounds, silver could hasten recovery.10 In pharmacoeconomic evaluations, silver dressings showed good pharmacoeconomic value on partial thickness burn wounds, in a cost-effectiveness analysis.11 Carbon fiber dressing is a newly developed macromolecular medical dressing that has been used clinically and has the advantages of high absorption capacity, and non-cytotoxicity; it is non-irritable, non-allergenic and can clean the wound. In addition, it has high absorption capacity and can suppress inflammation and promote recovery.12 Vaseline gauze has been used in the therapy of burn wounds for many years as a traditional dressing and has been the control gold standard in the evaluation of new dressings. The three new dressing studied in this trial have all shown some effect in clinical use, but no research has been reported on their absorption rates or on the effect of the dressings on evaporation from the wound and on the water-retention capacity of the wound. Although clinicians have made assumptions on the absorption and water-retention capacity of these new dressings, reliable evidence is needed.

This trial shows that evaporation from naked partial thickness wounds increased on day 1 post-burn in all four groups under conditions of temperature and humidity which showed no statistically significant difference. Guo and colleagues13 observed the evaporation of multi-areas and multi-depths on burn wounds in 50 patients. He showed that the evaporation on normal skin was 6.5-15.1 ml·h−1·m−2, that evaporation from the wound post-burn increased immediately, reaching 90.5-93.5 ml·h−1·m−2 on day 1. In this trial, under conditions of 21°C −22°C ambient temperature and 74%-78% humidity, the evaporation of partial thickness burn wounds was measured as 29.63-30.97 ml·h−1·m−2, and this difference may be explained by the relatively lower temperature and higher humidity and burn depth, all of which would potentially affect evaporation from the wound.14 Higher humidity would have the effect of decreasing evaporation, since evaporation is only 30-32 ml·h−1·m−2 when humidity in the laboratory is 74%. We conducted the trial under humidity conditions of 74%-78%, so a partial thickness wound evaporation was achieved, which means that water transmission is less here in our moist environment of Southern China and that escharosis is slower than in Northern China. It has been reported that15 evaporation of 1 ml of water would consume 2.42 J of energy. Covered with a dressing with good water-retention capacity, a wound can recover more quickly in this moist environment without drying out, and the lessened evaporation and lessened consumption of heat could assist the high metabolic reaction that occurs in situ.16

Among the four dressings tested in this trial, the absorption of carbon fiber dressing was higher than that of silver nanoparticle, vaseline gauze or hydrogel dressing. Evaporation of partial thickness wounds with applied dressing decreased in all cases by 1/2, compared with that of naked wounds, hence all four dressings can decrease evaporation from wounds. The evaporation in group A (carbon fiber dressing) on day 1 decreased most obviously, in our view because carbon fiber dressing is an active carbon macromolecule material and the strong absorption capacity of active carbon could serve to maintain the water inside the dressing, so as to create a moist environment and decrease evaporation. Group B (hydrogel dressing) is a reticular hydrophilic macromolecule which contains large amount of water. Although it allows higher evaporation than carbon fiber dressing, it absorbs less water and can maintain the water in wounds. It has a lower absorption rate than group C (silver nanoparticle) and group D (vaseline gauze), but the evaporation difference in these three groups is not statistically significant and they all still have a good water-retention capacity. Of the four dressings studied, silver nanoparticle dressing and vaseline gauze were only modestly effective in decreasing the evaporation of burn wounds and maintaining their water content, but the reasons for this are unclear. It may be that silver nanoparticles on the cotton fiber only partially inhibited evaporation from the wound. Compared to dry gauze, vaseline gauze could act as a more effective barrier over the wound surface, so as to create a relatively moist environment and decrease evaporation and direct water loss from wounds.

As wound recovery theory advances, the water-retention capacity of wound surface dressings has been taken more and more seriously.17 Active polynucleated macrophages have been found in the wound liquid collected from the dressings,18 and it is hypothesized that any factors that attract macrophages could promote wound healing.19 It is thought that the wound healing requires not only a moist environment, but also proper temperatures and an appropriate pH value and hypoxia tension.20 In addition, other factors such as cytokines and microcirculation will influence the wound healing. The water-retention capacity of dressings, as well as their other effects such as on cytokines, should be studied more rigorously in order to provide better underpinning evidence on the management of wounds, and also to assist in the discovery of new classes of dressing to promote healing.

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Keywords:

burns; dressing; absorption; evaporation

© 2007 Chinese Medical Association